Paper Technology Journal

Special Issue

Systemsfor Finishing

Contents

EDITORIAL
Foreword

1

SYSTEMS FOR FINISHING
A dream comes true

2

Voith Paper winders –for a better product profile

4

VariFlex™ two-drum slitter-winders –for perfect newsprint rolls at Rhein Papier, Hürth, Germany

8

Voith VariTop™ on PM 11 at SCA Graphic Paper Laakirchen –Top-notch winding
10
Twister™ Automatic –Fully automated roll wrapping with the Twister™

12

Janus™ Concept and Janus™ MK 2 –Milestones in calendering excellence

16

LWC paper calendering technology

23

SC paper calendering technology

28

Janus™ MK 2 –Engineering aspects of a modern online calender

33

Roll cover and coating effects
on calendering quality

37

Soft roll covers for Janus™ calenders

41

CeraCal™ – Optimized high-performance coating
for hard calender rolls

45

The Ecosoft™ calender family and its newest member,
the Ecosoft™ Delta

48

New concepts for coated mechanical papers

52

The DF coater – Coating technology of the new generation

56

Krieger completes the product range of Voith Paper –Infrared drying, integrated drying systems and meansfor contact free web-handling

62

Innovative Blue Solid treatment of wearing parts materials –not only for the paper industry
66
With the precision of a Swiss clock –VPT Walztechnik AG Zürich, a Voith Paper Group company,
converts a printing press at Burda/Offenburg
to Nipco™ Print Rolls

68

1

Dear reader,
this special “Finishing” edition of our Twogether Magazine is timed to coincide withthe long-awaited merger of Jagenberg Paper Technology with Voith Paper.
Having finally taken this step, we shall spare no effort to meet your high expectationsof our now even stronger organization.
The Voith Paper scope has now been ideally rounded off in the finishing sector. Thisparticularly applies for example to winders, coating and drying equipment.
Accordingly, the first few articles in this issue deal with the current state of winding
technology, optimally complemented with our Twister™ roll conveying and wrapping
technology. You will certainly hear a lot more about these concepts in the future.

Thomas Koller
Voith Paper
Krefeld

Also in calendering technology developments, Voith Paper has broken completely new
ground over the last few years – starting with the Janus™ concept and continuing into
online calendering, including some innovative roll cover and coating developments.
The limits of technological feasibility have been steadily widened and redefined,
thereby, at the same time, continuously improving cost-effectiveness.
Through trial and error we have come a long way. The overall result is neverthelessan unprecedented advance in calendering technology, which has made Voith Paper themarket leader in this field.
This issue, therefore, reviews in detail the state of the art in calendering technology
at the beginning of a new millennium.
Apart from calendering, roll slitting, winding and wrapping, coating and drying also
play a key role in the finishing process. Here again, the last decade has brought atransition from offline to online technology. Jagenberg technology ideally complements the Voith Paper and Voith IHI product portfolios in this segment.
As part of Voith Paper’s comprehensive partnership with the paper industry, we now
contribute even more decisively in the finishing sector to surface quality enhancement
over the entire product spectrum.
We sincerely hope this special Finishing edition of our Twogether Magazine will
provide you with and interesting as well as informative reading!

Thomas Koller
On behalf of the new Voith Paper Finishing Team2

A dream comes true
It was in 1999 that Michael Rogowski, then Chairman of
the Board of J. M. Voith AG, dreamed aloud of Jagenberg and Voith
joining forces – much to the displeasure of Rheinmetall Chairman of
the Board Hans U. Brauner. But the story goes back even further.

This is the full history of how Voith and Jagenberg came
together:Thomas Koller
Voith Paper
Krefeld, Germany

1993
Cooperation agreement with
Sulzer Escher Wyss (Ravensburg).
1994
Termination of agreement due to theVoith Sulzer joint venture.
1995/96
Cooperation agreement with Beloit.
November 1999
Divestiture to Sachsenring (Zwickau), an
automobile industry supplier; in parallel,
negotiations with Voith.
March 2000
Reversal of the Sachsenring transaction
in favour of sale to the investor group
Millennium Capital GmbH & Co. (Munich).

March 2000
Resignation of the Rheinmetall Chairmanof the Board, and reversal of theMillennium Capital transaction.
2000
Sales negotiations with Voith initiatedagain by the new Chairman of the Board
Klaus Eberhardt.
October 2001
Jagenberg AG Paper Technology Divisionsold to Voith.
June 2002
Folio sheeter business sold to Bielomatik.

3

To quote Voith Paper President and CEO
Hans Müller at a Zellcheming press conference in 1999: “The bride and bridegroom have finally found each other”.

After integration, the management organization of our expanded Finishing Division will be as follows:

But today, in autumn 2002, the honeymoon is over and building a marriage isthe order of the day. Among the farreaching decisions made during the firsthalf of this year were the following:Thomas Koller
Executive management spokesman withresponsibility for:● Production● Materials management, logistics, erection● Calenders● Nipco● Human resources● Closure of Jagenberg Maschinenbau
GmbH in order to trim production
capacities● Integration of Jagenberg PapiertechnikGmbH in to the Voith Paper Finishing
Division● Transfer of slitter-winder production
from Neuss to the Krefeld calender androll wrapping/transporting equipment.
The latter decision was taken in June thisyear. In December the Neuss team will already be moving to Krefeld, 39 km away.
And in future the coating technology division, also acquired from Jagenberg, will
be located in Heidenheim. About 35 former Jagenberg employees will remain in
Krefeld to look after the Jagenberg coating lines and rebuilds there.

Dr. Lothar Bopp
Member of the executive management
board (CFO) with responsibility for:● Law, patents, insurance● Information technology● Accounting, finance andcontrolling
Hans-Peter MarleauxMember of the executive management
board with responsibility for:● Sales of new and used machinery● Marketing● Trials for customers
Dr. Ing. Michael Schopen
Member of the executive management
board with responsibility for:● Slitter-winders● Paper roll wrapping and transportsystems● Service● Quality management

Apart from integration as rapidly as possible in Krefeld, our joint efforts toward
strengthening the Voith Paper Finishing
Division’s market positioning are mainly
focused on:● Slitter-winder product development● Further expansion of service activities● Ongoing optimization of slitter-winders
already delivered● Cost optimization.
After completing the integration process
in Krefeld, we shall be able to concentrate all the more again on our real mission – to serve our valuable customers!
The number of orders received
over the last few weeks is extremely encouraging – we areclearly on the upswing!

4

1

Voith Paper winders –for a better product profile

Printing paper rolls have become wider and bigger overthe last few years, and the trend shows every sign of continuing.
It goes without saying, that this has development consequences
for winders: new ways have to be found for the perfect windingof heavier rolls.
This article provides an overview of Voith’s wide range
Georg Müller
Voith Paper
Krefeld, Germanyof modern winders, and shows how tailored concepts ensuring
optimal winding quality, are put together by selecting the mostappropriate types according to application.

Four types of winders

This entire range is covered by four different types (Figs. 1, 2, 5 and 6):

Voith Paper has been supplying winders
for more than one hundred and twenty

VariSoft™, tissue winders

years. Always on the forefront of technol-

VariFlex™, the allrounderogy, they handle roll widths today from

VariPlus™, mainly for better and

70 mm to 4,600 mm and diameters up

especially coated papers

to 2,500 mm, weighing as much as

VariTop™, for the largest, heaviest

10 tonnes each.

and most demanding rolls.

52

Two different winding concepts

With the two-drum winder concept, nip

Fig. 1: VariPlus.

load between the drums and the paper

Fig. 2: VariSoft.

● The two-drum winder concept (Fig. 3)

rolls steadily increases with the winding● the single drum concept (Fig. 4).

diameter. With the single drum concept,
nip load can be adjusted as required,

On two-drum winders the entire roll set isFig. 3: Two-drum winder.
Fig. 4: Single drum winder.

because each roll is in a separate station.

wound supported on two drums, so that
there are two nips. These machines areThat is why for example VariTop™

user-friendly, very efficient, and can han-winders are technologically predestined

dle the narrowest rolls.

for the widest range of paper grades andproduct needs. However, the single drum

The VariFlex™ and VariSoft™ winders aretype of winder costs considerably moreboth of the two-drum type.

than the two-drum type. Therefore, there

3is always the question, based on producOn the single drum-winder, each papertion needs: until which point is the two-roll is wound in a separate station anddrum winder adequate, and when should

supported on a single drum, so that there

the single drum concept be used? Impor-

is only one nip per roll. Each station hastant in this context is, that with the devel-

its own axial drive to apply additional

opment of the MultiDrive™ and JagFlex™

torque to the respective roll. Single drum

drum covers (more details below), thewinders are very convenient to use, sinceapplication range of two-drum winders

each winding station is practically a sepa-

could decisively be extended.

rate machine.
Voith Paper offers single drum winders
under
brands.

the

VariPlus™

andThe new winder generation

VariTop™
To meet the ever-rising demands of higher speeds, wider machines, and better

4

6

5

Fig. 5: VariFlex.

winding quality, Voith Paper has devel-

The MultiDrive™ solid elastomer charac-

applications than MultiDrive™ covers.

oped a new generation of winders.

teristics are ideal for controlling winding

Rather than increasing the winding hard-

structure over a wide range, thus com-ness in the nip, the JagFlex™ covered

Under the brand name VariFlex™, for ex-

plying perfectly with product require-back drum in VariFlex™ winders only

ample, a two-drum concept is now avail-ments. For this reason the central drum

provides support. At the same time, theable for winding even the most sensitive,

in VariTop™ and VariPlus™ winders arecellular surface structure of this coverhigh-quality papers perfectly.

covered, as a standard, with MultiDrive™

material ensures non-slip torque trans-

elastomer.

mission to the roll.

single drum concepts have also been

In VariFlex™ two-drum winders, the front

JagFlex™ cover on the rider roll ensuresthoroughly modernized. At speeds up to

drum is covered with MultiDrive™. As agood contact with the paper over the

3,000 m/min, and with a much higher de-

result, this type of machine also pro-entire width, resulting in an excellent

gree of automation, they produce perfectduces a perfect winding structure thanks

winding process.

results with significantly wider and larger

to wide-ranging control. The MultiDrive™

rolls – wound cleanly, with perfect edge

cover ensures a stable web run of the slit

This makes the formerly “hard” drums

profiles and without any bursts, cracks

paper webs, thus resulting in perfectly

and rider rolls “soft”, thus greatly reduc-and/or wrinkles.

straight roll faces (no telescoping).

ing the stress on the paper in the contact

The well-proven VariTop™ and VariPlus™

area. Fig. 7 shows the kind of winding
One of the reasons for the perfect paper

Another important advantage is the excel-

errors which can be caused by hardroll quality attained by Voith Paper

lent compensation of CD thickness profile

drums. The corrugations shown in Fig. 7

winders is the soft-covered drums usedvariations, which verifiably prevents theare attributable to excessive stretching ofin these machines. Depending on specificnumerous winding errors unavoidable

the paper during winding on hard drums,

product requirements, covers are eitherwith conventional steel drums.

and are generally irreversible. The different winding dynamics of soft drumsof the MultiDrive™ or JagFlex™ type.
Both these materials consist of extremely

JagFlex™ cellular elastomer is much soft-

prevent this kind of fault, and a lot of

tough and abrasion-resistant elastomers

er than MultiDrive™ covers, and is also

others such as roll bursts, crepe wrin-(Fig. 6).

very compressible due to its cellularkles, cracks, dished rolls and telescoped

structure. It is used for quite different

rolls.

7

8

7

6

These new soft drum/roll systems can

R&D centre with pilot winder

aim thereby to enhance machine productivity such as by:easily be retrofitted to existing machines,
and numerous customers have alreadyVoith Paper has its own R&D center, withtaken advantage of this possibility.

a winder unit for universal applications(Fig. 9).

● increasing operating speed withoutrisk, above all for currently criticalgradesAutomation

This pilot machine can operate both inVoith Paper offers the following automa-

two-drum winder mode and single drum

tion options for winders:mode. All components, drive and control● optimizing automation for greatest
reliability and time savings.

units always comply with the latest state● Butt splicer for automated parent rollchangingof development. The extensive winding
tests conducted on this machine with● Automatic removal of empty spools

customers’ paper are preconditional for● High-precision machine stopping on

optimizing new installation layouts asreaching the defined paper length orwell as rebuilds.

Fig. 7: Corrugations.

roll diameter● Automated gluing of paper end tofinished roll after winding

Fig. 8: VariTop.

Prospects
Fig. 9: Pilot winder in R&D Center.

● Automated gluing of the web to thecores before winding● Web separation between start andfinish gluing● Feed and insertion of new cores in thecorrect sequence

In view of the time required for systemat- 9
ic new developments and improvements
to existing concepts, it goes without saying that Voith Paper is already working
on the next generation in this field.

● Feed of the new web over the entire
machine width.

Fig. 6: Elastomer-covered “soft” roll.

The principle governing all our development work is to uphold customer productquality during the winding process. We

81

VariFlex™ two-drum slitter-winders –for perfect newsprint rolls at Rhein Papier,Hürth, Germany
In the year 2000, Myllykoski – a global player and specialist incoated and uncoated graphic grades – decided on a completely new
central European newsprint production plant. After tender negotiations,the paper machine (PM 1) for this plant was ordered from Voith Paper
in March 2001. One month later an order was placed for two VariFlex L™
2-drum slitter-winders (working width 8,200 mm) and a VariFlex S™
Stefan Maierrewinder (working width 2,800 mm).

Voith Paper
Krefeld, Germany

The two slitter-winders are designed toNewsprint wound on conventional 2-drum

easily handle the entire output of PM 1,

slitter-winder with hard steel surfaces isi.e. 280,000 t.p.a. of newsprint with basisvery susceptible to folding. These hidden

weights from 36 to 48 g/m 2. At operating

faults, which usually remain undetected

speeds up to 2,500 m/min, finished paperin the paper mill, are bound to cause

rolls wound to a diameter of 1,350 mm

breaks in the printing press. As a result,are produced.

the entire newsprint roll is wasted. The
cause of folding is high radial nip loads

The results impressively proved again

between the steel drums and the paper

here, that VariFlex™ 2-drum slitter-winders

roll.

are the ideal solution for newsprint production. This article explains the reasons.

To avoid such high loads, paper roll

Systems for Finishing

9

Fig. 1: VariFlex™ two-drum slitter-winder at
Rhein Papier, Hürth, Germany.

weights had to be significantly restricted

With the VariFlex™ concept, the Multi-

Of course, the VariFlex™ concept is high-so far. The production output of conven-

Drive™ elastomer cover is compressedly automated. Apart from automaticallytional 2-drum slitter-winders, i.e. winders

by the weight of the roll. The reduction

splicing the old and new web ends during

equipped with steel drums, was therefore

in thickness of the cover leads to awinding, this also includes automatedlimited. With the VariFlex™ concept, thisdynamic deformation process within the

set-change with roll start and finish glu-

limitation is now a thing of the past

cover. I.e. the cover is accelerated in theing. As a result, production is practicallybecause the first drum is covered withnip area and its higher velocity is trans-

continuous and uninterrupted.

Multidrive™ elastomer. Winding dynam-

ferred to the roll. Since the resulting

ics on this special cover are quite differ-speed is higher than the web intake

Newsprint production today, generally

ent from those on hard steel drums. The

speed, the differential velocity exerts afrom 100% recovered paper and at highfollowing aspects are involved:

stretching force on the web which in-processing speeds, demands state-of-creases the winding hardness.

the-art slitter-winders for optimal results.
VariFlex™ two-drum slitter-winders en-

On the one hand, newsprint demands thegreatest possible winding hardness in theWith the MultiDrive™ technology it issure perfect winding quality at roll diam-ingoing nip in order to minimize folding

even possible to produce higher hard-eters up to 1,350 mm, thus proving thatproblems due to layer displacement

nesses – while simultaneously reducing

this is truly a future-oriented concept.

(J line). On the other hand, layer dis-

the web draw – than obtainable with steel

placement is caused by radial forces indrums of large diameters in combination

And true to the Voith philosophy, thethe ingoing nip, which must, therefore,

with high web draws.

customer shall have the last word:

Furthermore, flattening of the cover under“We at Rhein Papier”, said project leader

On machines with conventional steel

compression also reduces the radial nip

Bernhard

drums, winding hardness is increased byforces on the paper roll, thus eliminating

proud of our new production line. PM 1

the fact that the steel drums are deeply

layer displacement. As an additional ad-

broke all records for start-up speeds sopressed into the rolls – but this also in-vantage, the cover flexibility enables opti-

far, and our paper rolls were on the mar-creases the undesirable radial nip forces.

mal adaptation to the roll profile.

ket considerably earlier than originallybe minimized.
Schmidt,“arereallyplanned. The winding quality we now

With unequal cross-profiles, the result is
excessive overloading in some zones

Thanks to all these benefits, Voith Paper’s

achieve certainly confirms that we madeacross the roll width, which is bound to

new slitter-winder generation is alreadythe right choice with VariFlex™ slitter-cause winding defects.

known as “the soft revolution”. This sum-

winders. Currently the Voith team ismarizes very aptly one of the main rea-

working hand in hand with us on fine-Attempts have been made to combat thesons why this concept has attained suchtuning for even better results, and withlimitation of winding diameter by using

success so rapidly. More than 150 new

such excellent cooperation, we are mak-the largest possible drums and increas-machines and rebuilds (also of othering great progress. My complements anding the web tension – which however in-

makes) have so far been fitted with

thanks to all concerned!”creases break frequency – but without

Voith elastomer roll covers and operatingmuch success.

results are excellent in all cases.

10Voith VariTop™ on PM 11 at SCA
Graphic Paper Laakirchen, Austria –Top-notch winding
The SCA Group, a European leader in wood and pulp
processing, has concentrated its production of natural chlorine-freegraphic grades in Laakirchen, producing a total of about 485,000 t.p.a.
of SC-rotogravure and offset papers on PM 10 and 11 respectively.
These grades, such as Grapho Gravure, Grapho Set and Grapho
Grande, are notable for their high-volume uniformity with outstanding
opacity and print gloss, clean mottle-free surface, and excellent
Reinhard Hehner
Voith Paper
Krefeld, Germany

print density. Notable are also the strict ecological standards
maintained in Laakirchen, for which this plant has won a coveted
Austrian environment-protection award.

To

meet

all

these

demands,

SCA

was first launched. Its technical data are

Laakirchen decided on a state-of-the-art

as follows:

solution for their new PM 11. Based on● Working width 8,800 mm

the Voith Paper One Platform Concept,● Design width 12,000 mm

this production line incorporates all mod-● Operating speed 2,800 m/min

ules required for the highest quality SCA+

● Design speed 3,200 m/min

rotogravure and offset grades. It also in-● Winding diameter 1,500 mm

cludes a VariTop™ slitter-winder (Fig. 1),● Design winding diameter 1,650 mm

known as RSM 3, since it is the third one● Maximum paper roll weight 10 tons.

to be installed here – a sure sign of customer satisfaction!

From this data, the enormous reserves
incorporated in RSM 3 are clearly evi-

This RSM 3 belongs to the new genera-

dent. While paper rolls today are up totion of center drum winders, 150 of which

1,500 mm in diameter and 3,700 mm

have been supplied since the VariTop™

wide, a quantum leap is already apparent

11

Systems for Finishing

Fig. 1: VariTop™ slitter-winder on PM 11
at SCA Graphic Paper, Laakirchen.
Fig. 2: VariTop™ layout.

1

4

4

1
3

2

2

with respect to printing presses, whosebrated after sharpening. The glue applica-

rence, the probable cause and the recom-

working width will rise sooner or later totors are automatically swivelled into themended action.

4,300 mm. It is therefore very reassuring

operating position, and after applying

to know that this – and more – has al-glue to the paper they return to the park-

Dr. J. Hafellner, SCA Graphic Paper

ready been taken into account with theing position. Web tension is removed by

Laakirchen, was very impressed by the

new RSM 3 slitter-winder.

the web draw isolator roll installed be-

successful RSM 3 startup: “Installation

tween the unwind stand and the rewind

proceeded without a hitch in only six

Based on the VariTop™ layout shown instations. The rewind stations incorporate

weeks, largely thanks to complete work-

Fig. 2, here are some more details ofadditional center drives and rider rolls.

shop assembly beforehand. And I pay

this concept:

The stations are positioned in coordina-

tribute to the ingenious commissioning

Paper from the unwind (1) first runs

tion with the slitter knives. Thanks to theengineers: by first winding paper fromthrough the slitting station (2) and thecontrolled co-operation of web draw iso-the narrower PM 10 on to a new PM 11

glue application device, then enters thelator roll, center drives and rider rolls,

reel spool, they were able to test andnip between the web draw isolator roll

the winding structure of the finishedoptimize the RSM 3 VariTop™ prior to(web tension interruption roll) and thepaper rolls is optimized for subsequent

PM 11 startup. This enabled immediate

center drum (3), passes around the latterprocessing, with ideal geometric form

product processing afterwards, at thedrum and is finally taken up in the wind-(perfectly square ends; no telescoping).

same time stabilizing operating speeds at

ing stations (4). The slitter knives are au-

This is assisted by the MultiDrive™ cover

2,400 m/min. Optimization is currently intomatically positioned by a servo-drivenof the center drum. The RSM 3 slitter-progressbelt which moves the top and bottom

winder layout is largely decentralized,

speed to 2,800 m/min. The machine

knives. Since all elements are adjustedwith a busbar control system instead ofclearly has substantial potential, which

together, repositioning is also possible

parallel wiring. In addition to the masterwe and Voith shall soon be exploiting

with the sheet in the machine. The slittercomputer with graphic user interfaces instep by step.”

station is fitted with Blue Slit™ top

theknives, which last two to three times

monitors are also provided. Trouble-

Voith is very delighted about this positive

longer than conventional knives. And

shooting is assisted by a defect diagnosis

opinion, and pays tribute in turn to thethanks to the patented design of the bot-system which immediately indicates the

successful teamwork, which will certainly

tom knives, they do not have to be recali-

incident type, location and time of occur-

benefit the fine-tuning phase.

forraisingtheproduction

control room, local terminals with

12

1

Twister™ Automatic –Fully automated roll wrapping with theTwister™
This is a rare case of unanimous global opinion: the best
way of wrapping paper rolls is in packaging paper, with double
headers at each roll face. The carton or corrugated board innerheaders protect the vulnerable roll faces from damage duringtransport and storage. And together with the laminated wrapping
made of PE-coated kraft paper, the outer headers of the samematerial form a very sturdy and climatic-proof packaging.
Volker Schölzke
Voith Paper
Krefeld, Germany

Despite the cost involved, this kind of

one roll wrapping system using packag-

wrapping is used in practically every

ing paper. Such systems are well provenpaper mill worldwide. Hardly surprising,since decades, and they can be automat-

in view of the fact that packaging paper

ed to any degree according to require-

optimally meets all the legal and otherments.

requirements on paper roll wrappings. It
is much stronger and more durable thanDue to the wide variety of paper rolls,

plastic wrap, and it can be printed withhowever, conventional wrapping systems

all kinds of marketing information, warn-

can involve substantial costs. Headers

ings and classification codings. That isand packaging paper have to be stocked

why nearly every paper mill has at leastin sizes to suit different roll widths andSystems for Finishing13

diameters, and as far as possible, auto-

they installed a Twister™, less than half 2matic handling must be adjusted accord-

as many rolls are rejected by printers due

ingly.

to transport damage.

Voith Paper has opened up new horizons

The Twister™ offers so many benefits,

here by developing the Twister™ (Fig. 1).

apart from its great flexibility and compactness, that far more packaging instal-

It uses only one size of packaging paper,

lations of this type than any other were

500 mm wide, for the entire range ofrealized over the last four years. Since

paper roll widths and diameters. And

1996 Voith Paper has sold more than

thanks to the flexibility of this concept,

twenty Twister™ wrapping machines.

roll width changes in future are no problem. Another advantage of the Twister™

Encouraged by this success, Voith Paper

compared with conventional wrapping

saw no reason why the complex task ofmachines is that it eliminates multiple

fitting the inner and outer headers could

handling phases and complex feed andnot be simplified as well.
3

gluing systems. The lateral and angulardisplacement of the wrapping paper dis-

The fewer the parts, the fewer the prob-

penser is automatically done by a patent-

lems – so all previous components suched servo-drive system, so that the roll is

as transfer stations, clamps, elevators

spirally wrapped in a single operationand other devices have been replaced inwith the required number of layers. Ade-

this automatic header handling system byquate adhesive is applied in one or more

two 6-axis industrial robots.

tracks between the layers to fix themfirmly together.

In the Twister™ Automatic, a robot takes
each inner header directly from the pallet

The 500 mm wide wrapping paper used isstack by vacuum grippers, and holds it

also ideal for additional (optional) protec-

against the respective face of the rolltion of the roll edges, which are particu-

until it is firmly fixed by the automaticallylarly vulnerable to transport damage.

folded wrap overlap. The reach of theseFig. 1: Twister™ wrapping and folding station.
Fig. 2: Paper dispenser.

robots can be extended by mounting
The Twister™ greatly simplifies roll wrap-

them on an optional traverse, this addi-

ping without compromising efficiency intional axis being taken over by the robot

any way – on the contrary, the packed

control system. Even the widest variety ofrolls are sturdier and have a neater ap-

inner headers is easily handled by thepearance than with conventional wrap-

Twister™ Automatic without any transfer

ping. Our customers report that since

stations (Fig. 3).

Fig. 3: Inner header robot.

14

Fig. 4: Rolltronic™ user interface.

The double claw of the outer header ro-creases. Self-adhesive labels can also be

With the Twister™, each roll can be

bot automatically adapts to various diam-

used, the backing paper first being auto-

wrapped differently according to individ-

eters. Here again, the headers are taken

matically peeled off on the printer.

ual production and transport requirements. For example, a roll wrapped indirectly from the pallet stack, a special
separating device ensuring that even if

This roll wrapping system is rounded off

four layers for ocean shipping can follow

firmly linked together, they are removed

by a conveying system to deliver unpack-

immediately after a roll wrapped in only

individually. As soon as the header press

aged rolls to the Twister™ and transport

two layers with additional edge protec-

tilts into position, the robot places thewrapped rolls to the storage point.

tion.

Paper rolls are ejected from the winder

All this is possible thanks to the Roll-outer headers precisely on the pressure
plates, which can be as hot as 180° C.

on to a roller track with pneumatic stop.

tronic™ process control system specially

Roll labelling is taken over by a fourth ro-

This is segmented so that every second

developed for the Twister™ (Fig. 4).

bot. This picks up the two printed labels,

roll passes through on to the plate con-normally DIN A3 size, with its double

veyor, thus giving the winder operator

The Rolltronic™ process control system

gripper and passes the back of them overtime to inspect the roll faces and label

is linked online with the mill’s production

a hot glue applicator. It then presses one

each roll with a bar code. On their way toplanninglabel on the roll face and the other one on

the wrapping machine, the rolls are thencomputers. It also ensures that data suchthe roll body – neatly and without any

clearly identifiable by laser scanner.

as weight, width and diameter are always

andinventory

management

Systems for Finishing

15

Fig. 5: Layout of the Twister™ 2 Line Automatic.

assigned to the correct roll, thus elimi-

per hour. Although the modular Twister™

clearly arranged and functionally effi-

nating label printing errors.

concept enables numerous different lay-cient. The Twister™ Automatic eliminates

outs according to local conditions, theall peripheral elements and respective

Each element of the Voith Paper roll con-

Twister™ Line is the most popular ver-trouble sources, thus improving relia-

veyor system is specially designed tosion on the market.

bility and consequently long-term profitability.

avoid damage during handing. As always,
these components have been continuous-

Such a smoothly continuous wrapping

ly optimized over the years to ensure per-line, without any intermediate roll ejec-

The inherent risk with conventional wrap-

fect functionality.

tion or gripping, has long been the dreamping systems – of ever-increasing pro-of every paper production manager. It

duction outages due to ongoing wear andSince the plate conveyor runs on ball-

represents the ultimate in gentle roll han-tear – is substantially reduced with thebearings to minimize friction, low-pow-dling (Fig. 5).

Twister™ concept.

ered frequency-controlled AC-motors can
Together with roll transport elements

be used, despite today’s conveyor speeds
around 60 m/min and paper rolls weigh-Summary

optimized for the Twister™, Voith Paper
offers a comprehensive and cost-effective

ing up to ten tonnes each. Thanks to thenew plate conveyor generation, Twister™

Twister™ wrapping systems and theirpaper roll logistics concept ranging fromLine speeds can now be up to 120 rolls

conveying elements are uncomplicated,winder to roll storage.

16

Joachim Hinz
Voith Paper, Krefeld

Jost HefterVoith Paper, Krefeld

17

Systems for Finishing

The Janus™ Concept and Janus™ MK 2 –Milestones in calendering excellence
The history of papermaking is also the history of
calendering. When paper was still fashioned by hand, the surface
was made smooth enough to write on by rubbing with a stone, andlater on by water-driven hammers. It was the printers that got
things moving, and calendering really got underway with wooden
rollers turned by handles. This was actually the birth of modern
papermaking technology, for with the invention of the paper
machine around the turn of the eighteenth century, rolls wereused for continuous operation. Since then rolls have been the key
component of every paper machine and in particular, of every
calender.

Various problems arose in connection

there had hardly been made any improve-in supercalenders. Voith Paper pioneered

with rolls, however, and even machine

ment. The main reason for this long stag-

the implementation of this new roll covercalenders with chilled cast iron rolls were

nation in supercalender development wastechnology in 1995 with the innovative

not able to meet the rising demands on

its cotton rolls.

Janus™

paper quality. Although more advanced,
the supercalender was too slow for online

This situation changed dramatically when

To keep up with the production of a high-plastic-covered rolls were first installed30
25

Development of the soft calender around15
10

spread success, however, the soft calender likewise failed to meet all the quality

5

demands. In this respect the supercalen-1derremained

unchallenged,

althoughregard to the growing production of uncoated SC grades. Milestones in modern

Rebuilds

first online Janus™ calender in 1996, andcalendering technology were set by theabove all by the revolutionary Janus™

First Janus pilot calender

plastic-covered rolls. Despite its wide-

installations since then, particularly with

Uncoated grades
Coated grades

20
Numberbe used for the first time together withinreflected in the large number of Janus™
1speed paper machine, up to three super-

forward, because heated rolls could now

presented

The market need for this new approach is

expense of a separate calendering line.

1980 represented a considerable step

first

A quantum leap

operation and thus involved the additional

calenders were required.

calender,Krefeld, Germany.

1995 96

MK 2 in 1999, which is now state of theart in the paper industry.
This article, focusing mainly on SC
grades, shows the rapid progress madeby Voith Paper since launching this new97

98

99 2000 01 2002

calendering technology.

18

Fig. 1: Cumulative deliveries
of Janus™ calenders.
Fig. 2: Development of calendering speed.
Fig. 3: Productivity development.

1800

90
80
70
60

1400

On order/m AB

Calender speed [m/min]

1600

Paper machine speed
1200
1000
800
600
1980

1. Janus MK 2

1. Janus

2000

1. Janus2

1. Janus MK 2

Fig. 4: Port Hawkesbury installation.

SC-A+
~SC-B

50

SC-B

40
SC-A

30

SC-A+

20
~SC-A

1985

10
1990

1995

Development steps

0
1980

2000

1985

1990

1995

2000

for the first time, with significantly im-

in calendering technology. Compared

proved paper surface quality.

with the supercalender, it has multiplied

As shown in Fig. 2, offline Janus™ calen-

productivity several times.

dering technology increased calendering

Voith Paper engineers in Krefeld were en-

speeds for SC-A grades in only three orcouraged by this to develop a completely

four years to around 1,100 m/min, com-new concept: the Janus™ MK 2, whichpared with about 600 m/min for supercal-

took online calendering technology one

enders. Despite the accompanying speed

step further. The first online installation

Although this development took place inincrease of paper machines from aroundof this new Janus™ generation was ina relatively short period, it was technical-

1,200 to 1,600 m/min, only two offline

1999 at the same German mill in a Voithly very demanding and often plagued with

Janus™ calenders operating at 1,100 to

paper

SC-A

enormous difficulties. As shown by the

1,200 m/min, can handle, for example,

grades. The result was a further produc-

technical aspects explained below, somethe correspondingly higher production oftion increase at speeds up to 1,550 m/min.

drastic changes were necessary to makemachine,

this

time

for

an SC-A+ line in North America.

Interim review

up for the long stagnation in supercalenSince this new concept not only increas-

der development with a successful new

In 1996 the teamwork between a progres-es calendering speed significantly, butcalendering technology in only four tosive German papermaker and Voith Paper

also improves efficiency, the productivity

five years.

led to the world’s first online Janus™

of high-speed paper machines with online

calender installation for newsprint andJanus™

rotogravure printing grades.

Fig. 3 shows this in terms of tonnes per

calendersrises

dramatically.

Development findings

meter web width.

Plastic covers

new calendering era: online calendering

In only five years, the Janus™ concept

In the initial development phase, damage

speeds reached well over 1,350 m/min

has in fact brought about a quantum leap

frequently occurred to soft roll covers be-

This represented another milestone in the

3

19

4

cause the plastic was not strong enoughRoll surfaces

nisms affecting the rolls during operation. They are either applied thermally or

to stand up to long-term operation. The
self-heating and damping characteristics

The heated hard rolls with surface tem-galvanically, always taking account of op-of the roll cover material were therefore

peratures up to 170 °C play a decisive

timal doctoring. Both thermal and galvan-

optimized for better heat dissipation androle in calendering quality. At high calen-

ic surface coatings have been further op-

resistance to local pressure peaks.

dering temperatures, more stickies sepa-

timized over the last few years to combat

rate out of the paper and adhere to thethe faster abrasion and corrosion caused

This problem was also solved by continu-

rolls, and in some cases caused holes inby much higher operating speeds, tem-ous roll temperature control during oper-

the web and even breaks. This problem

peratures nearly twice as high, and above

ation, and by heating up the rolls to oper-

has now been solved by more efficientall, the significantly greater processating temperature before restarting. The

doctoring of all the calender rolls. One ofmoisture.

precise geometrical and thermal stability

the biggest challenges in this connection

thus attained not only helps to prevent

was plastic roll cover doctoring.

Barring

For that, special doctor bodies, blade

Roll humming and vibration due to bar-holders and blade materials were devel-ring is a well-known phenomenon, mainly

The result is considerably stronger plas-

oped for the new Janus™ MK 2 genera-in multi-roll calenders and in printing

tic roll covers, which now reach a service

tion. As shown in practice, the service

machines. In supercalenders, this hardly

life of around 1,000 hours. Since they arelife of hard rolls is too short unless they

ever occurred because of the short ser-currently limited to a maximum line load

are surface coated. They roughen too

vice life of filled rolls. With the muchof 400 to 450 N/mm, however, further

quickly, and become geometrically de-longer lasting roll covers used in Janus™

development work is still required to en-formed particularly at the web edges.

calenders, combined with higher operat-

able the higher line loads technologicallyVarious types of surface coating are used

ing speeds and line loads, the barring

possible.

today, depending on the wear mecha-

problem arose again.

roll cover damage, but also upholds uniform product quality.

20

Due to the elastic reaction of every roll

Threadingmization measures, the biggest improvements are the much more rigid stacksystem with paper, barring cannot be
eliminated even by the highest roll preci-

Critically important for integrating theframe and the significantly better acces-sion. However, soft roll covers have now

Janus™ calender in a paper machine issibility of nearly all components. The nat-been developed to the point where thethe threading procedure. Due to the highural frequency, which largely depends onnegative effects of barring – including

operating speed and the long zigzag web

the frame stiffness, is now five times

noisy running and paper surface defects

path through the calender, the paper tailhigher than with previous designs. In fu-– are largely avoided.

is subject to particularly high strain.

ture this will enable operating speeds ofSome types of cover materials were

After very intensive development work on

found to be less vulnerable to barring,

this aspect, almost exclusively on theand their optimization brought further im-

testbed, an optimal combination of Fibron

provements. In general, the best results

vacuum threading belts and transfer

so far have been obtained with Voithropes was found to minimize tail stress.

Web in-going moisture

well over 2,000 m/min without problem.

Modified process conditions

Paper Safir™ covers.
Numerous components of the Janus™

Due to the higher operating speeds, loads

Apart from other measures, online condi-

calender have been modified to free up

and temperatures, this new calenderingtion monitoring systems for the entire

the web run for the threading system.

concept requires different process condi-

roll stack are very effective. The Voith

Furthermore, paper tail quality is now im-tions. For example, ingoing web moisture

VMM and VTM systems provide very reli-proved by a double tail cutter which cuts

to the Janus™ MK 2 is significantly high-able early warning of developing barring

off the tail about 100 mm in from the web

er than before at 11 to 12%, in order toand roll surface wear.

end. This eliminates the edge section

attain the required paper gloss and final

with its extreme shrinkage stresses, edge

moisture content. Controlled moisturizing

damage and positional variations in thisprior to calendering, and steam boxes inzone.

the calender in combination with thick-

Quick opening

ness cross-profile control, are now state

Great attention was also paid to the
Structural rigidityof the art.

NipProtect™ system shuts off all nip line

Based on operating experience with all

Over-compensationloads simultaneously in less than 0.5

the first-generation Janus™ calenders,seconds. Although the bottom roll open-

this technology was systematically devel-

Paper quality not only depends on a per-ing distances are now more than threeoped into the new Janus™ MK 2 concept.

fectly uniform thickness cross-profile,times larger than in supercalenders, thisIts most outstanding feature is the 45°

but is also improved by a controlled in-

new hydraulic system – maintenance-freelayout, which differentiates the Janus™

crease in line load from nip to nip.

and self-adjusting – minimizes mechani-

MK 2 from all supercalender types.

Thanks to roll weight compensation, thequick-acting nip opening system necessary for roll protection. The innovative

Janus™ MK 2 incorporates an ideallycal shocks by opening the roll stacksmoothly under all circumstances.

Apart from the above mentioned opti-

increasing line load characteristic. Line

Systems for Finishing

21

Fig. 5: SC-grade calendering performanceby supercalenders and Janus™ calenders
as a function of operating speed.
Fig. 6: Supercalender / Janus™ calender
operating data for SC-A grades.
5

PPS-10s roughness [µm]1,0Working range
Supercalenders

Supercalender
750 m/min
340 N/mm
120°C heating
medium temperature

Janus Calender
1.100 m/min
370 N/mm
190°C heating
medium temperature

Janus Calender
1.100 m/min
370 N/mm
220°C heating
medium temperature

Janus Calender
1.100 m/min
370 N/mm
160°C heating
medium temperature

Gloss

52.3

57.9

59.3

53.8

PPS-10S roughness

0.98

0.9

0.87

0.95

Porosity

17

16

15

167

Blackening

55

56.1

57.5

53.9

Opacity

91.95

91.71

91.49

92.05

Brightness

68.43

67.55

66.24

68.41

Working range
Janus Calenders

1,2
1,4
Operating data

1,6
1,8
2,0

600

800 1000 1200 1400 1600 1800 2000
Calendering speed [m|min]load in the first nips is overcompensated,

modern paper machines, as far as thethe quality level is to be maintained ori.e. it is higher than in the uncompensat-

end of the dryer section, not only

improved at still higher speeds.

ed calender, and reduces again in thechanges web shrinkage in the calender,

lower nips. The Janus™ concept also

but also web run characteristics.

Fig. 6 compares other characteristics

ensures, however, that the paper is not

before and after rebuilding supercalen-

overpressed by excessive line loads inders to the Janus™ concept for SC-A

the top nips. The Janus™ MK 2 takes

Product qualityof an exactly controlled increase in line

Smoothness / roughness

incalendering

speed,

from

750 m/min to 1,100 m/min, hardly had
any effect on product quality. Similarload from nip to nip.
Web width

grades in a German paper mill. The steep
riseaccount of this with the creative method

Fig. 5 shows PPS roughness for SC

experiences are reported with other Voith

grades as a function of calendering speed

Paper installations of this type.

and type, based on test results which
It goes without saying that calenderingcorrespond well with the operating data

results depend very much on prior fac-also shown for some modern installa-

tors in the papermaking process, so thattions. Notably, maximum smoothness

Blackening is clearly also a function of

to optimize quality and output, the line

values have hardly been affected by theother process criteria, such as furnish.

conditions as a whole must be taken into

substantial rise in operating speeds soWith regard to the Janus™ calender it-

account.

far, and are rather increasing – as shown

self, it has been found that the right kindby the trend for SC-A+ grades.

of soft roll covers influence blackening

Blackening

results much more favourably than the

Apart from the kind of furnish and stock
preparation, process conditions in the

For unrestricted online production of SC-

paper machine are also very important.

A grades, however, further developments

The suppression of web shrinkage inin calendering technology are required if

filled cotton rolls used in supercalenders.

622

Coated papers
There are some aspects which apply, inin particular for roll offset grades, and re-

In less than five years, Voith Paper has

sults in general are more consistent thanupgraded calendering technology fromwith supercalenders.

the rather unsophisticated supercalender,

particular, to coated papers, where operating speeds and pressures are generally

restricted to intermittent offline operaLWC grades

lower than for SC grades, although intion, into the modern Janus™ concept
and now the Janus™ MK 2 generation,some cases with relatively high tempera-

Initial results with online Janus™ calen-

which meets the highest demands for on-tures.

dering show hardly any dust formationline operation. The optimal 45° layout ofwith these grades, and excellent printing

this calender – completely different frompress runnability. Print gloss is very highall its vertical predecessors – signals acompared with the paper surface gloss.

new era in calendering technology. For

Wood-free coated grades
Despite the higher operating speed of

the first time, online calendering is now

Janus™ calenders, outstanding gloss val-possible without the restrictions previ-

ues can be attained with these grades

Summary and conclusions

even at moderate line loads of 200-250
N/mm. Flatness is significantly improved,

ously applying. The trend has now been
set for the future – and it will certainly beThis quantum leap in calendering tech-followed up without delay.

nology not only demanded enormous
personnel effort and financial expense,
but is also the fruit of intensive teamwork

Prospects

with our customers, for whose patienceand understanding we give our sincere

Printing

paper–

increasingly

multi-

thanks.

coloured these days – is gaining groundas an advertising medium, even in competition with modern electronic media. To
uphold this trend, not only optimal productivity but also smoothness, gloss anduniformity are decisive. Since this applies
equally to coated and uncoated grades,
an increasingly important role will beplayed by the Janus™ concept in future.
Destined for stardom is the Janus™ MK 2
calender. Integrated online in the paper
machine, its possibilities are practicallyunlimited. Voith Paper's ongoing development effort will ensure that the Janus™
MK 2 stays abreast of all future demands.

Systems for Finishing

23

LWC paper calendering technology
LWC grades are used above all for printing multicoloured
magazines, brochures and catalogues. Surface quality demands onthese papers range from mat to high gloss, thus requiring a correspondingly wide spectrum of calendering technology.

Michael Ganasinski
Voith Paper
Krefeld, Germany

This review first examines the influenceof the base paper characteristics, coating
composition and pre-calendering on thecalendering results. Afterwards the mostsuitable Janus™ MK 2 layouts for thevarious LWC grades are presented, showing how the best calendering concept
for each particular application is arrived
at by selecting the correct option. An
actual installation – the PM 4 “Pioneer”
at Perlen Paper, Switzerland – is thendescribed, followed by a look at future
development prospects.

Influence of raw paper characteristics, coating formulationand pre-calendering
The greater penetration of coating material into highly porous papers negatively
affects gloss and smoothness due topoor surface coverage. To keep the coating on the surface, the structure of thebase paper must be dense enough. Thisis illustrated in Fig. 1, which compares
the gloss of LWC grades made from two

different kinds of base paper. Furthermore, with the increasing use of DIP(deinked pulp) for LWC production thesedays, there is a greater tendency to grey
mottling on the paper surface due toblackening.
The coating formulation also has a significant effect on gloss and smoothness. In
this connection, Fig. 2 shows the surface
gloss and smoothness potential of various coating components.
Considerable use is made in North America of plastic pigment additives, which
increase gloss and smoothness very effectively. Due to the high cost of thesepigments, however, calcium carbonate
and china clay are mainly used in Europe.
Irrespective of coating process (film,
blade or curtain coating) and formulation,
the base paper should be calibrated by
precalendering prior to coating (Fig. 3).
The advantages are twofold. On the one

Lehmann Tappi gloss 75° MD

Until just a few years ago, LWC grades
were calendered almost exclusively onsupercalenders. This changed dramatically when the Janus™ concept was introduced. Actually, LWC papers today can,to a great extent, be produced on-line.
The Voith Paper concepts are based on
the well-proven Janus™ calender.

52
50
45
40

39

35
30
Newsprint

LWC offset

Base paper quality1

24

Fig. 1: Effects of coated base paper quality
on gloss.
Fig. 2: Gloss and smoothness potentialof main coating components.
Fig. 3: Calender.
Fig. 4: Online Janus™ MK 2 calender,
1x10 rolls.
2Component

Gloss and smoothness

Comments

Plastic pigment+++

High costs

China clay++

Low brightness

Calcium carbonate+

High brightness

TalcumSlippage, reduces core bursting

StarchLow cost, increases stiffness

Latex

Influences air permeability
and printability

Fine ground+

Better coverage, high costs

High coat weight++

High costs

43

In these one-stack layouts, the two softcovered middle rolls form the reverse
nip. To correct two-sidedness in suchlayouts, different temperature settings are
required above and below the reverse nip.
In some cases, the base paper characteristics are particularly two-sided. Optimallayout conditions are then required forcorrecting this two-sidedness on a wellcontrolled basis.
For this purpose, Voith Paper offers forexample a 1x8, 2x3 or 2x5 Janus™ MK 2
layout.
hand the CD thickness profile is optimized, which significantly improves
runnability in the coating machine, andon the other hand moderate precalendering makes for more efficient calendering.

the paper are calendered in 2 and 4 hot
nips respectively.

Janus™ MK 2 layouts

Plastic-covered Nipco™ or Nipcorect™
top and bottom rolls are used, whereby a
Nipcorect™ roll is not normally required
if the web has been precalendered before
coating.

In the eight-roll version, the number of
hot nips per paper side is asymmetricallyarranged. The rougher paper side is calendered in four hot nips, and the smootherside in only two hot nips. Additionally,
different temperatures can be set on each
paper side to correct two-sidedness.

LWC offset grades can be calendered online in a 6-roll Janus™ MK 2, for example, or in a 10-roll Janus™ MK 2 (Fig. 4).
With these configurations, both sides of

The hot rolls are covered with abrasionresistant material and heated with oil.
Their surface temperature can reach
170 °C.

The 2x3 or 2x5-roll versions are particularly flexible, because they combine two
independent calendering stacks in a single frame.

Systems for Finishing

25

Fig. 5: Typical surface characteristics
of LWC papers.
Fig. 6: Product map for film coated LWC.
Fig. 7: Product map for blade coated LWC.

Selection of the optimal calendering concept depends on the one hand on surface
quality requirements, and on the other
hand on the required operating speed.
For it is these criteria which dictate theoperating conditions for Janus™ MK 2
technology to best meet customer needs.
Fig. 5 shows the typical surface quality
requirements for LWC grades.
As another aid to select the optimal calendering concept, Voith Paper has compiled “product maps” for a wide range of
paper grades. They are continuously extended and updated to take account not
only of ongoing research results at our
Krefeld test facility, but also of actual
field results in practice. These productmaps therefore give a detailed overview
of all the latest technological possibilities.
Figs. 6 and 7 show product map extracts for film coated and blade coated
LWC grades.
The main criterion here is attainable
gloss level as a function of paper machine speed and calendering concept.
For example, to produce film coated
LWC offset paper with ≤ 55% gloss at
1,400 m/min, Voith Paper would recommend an online Janus™ MK 2 layout with
1x6 or 2x3 rolls. For producing LWC ro-

Optimal calendering concepts for blade
coated LWC papers can similarly be determined as a function of PM speed andsurface quality requirements.

Online calendering experience
with LWC offset papers
The new online calendering generation
for LWC offset printing papers was pioneered by PM 4 at Perlen Papier AG,
Switzerland, commissioned in October2000 (Fig. 8).
Based on the Voith Paper “One Platform
Paper Machine Concept™”, this line includes the following components:● Duoformer TQv™ with ModuleJet
headbox;● Tandem-NipcoFlex™ press section,with double-felted first press and topfelted second press;● Well-proven TopDuoRun™ dryer
section;● Two-roll calender with 36-zone
Nipcorect™ roll for optimal CD profile
control;● SpeedFlow™ for simultaneous film
coating;● Airturn, infra-red drying, also used for
CD moisture profile control and hot air
float dryer;● 2x3-roll Janus™ MK 2 calender forexact compliance with surface quality
requirements;● Optimal wind-up of the extremelysmooth-surfaced grades produced

LWC grade

Gloss
Gardner [%]Roughness
PPS S 10 [µm]Offset satin–

1.8 - 2.8

Offset glossy

50 - 60

1.1 - 1.7

Rotogravure

55 - 70

0.75 - 1.2

5

6

70

Gloss Gardner [%]Selection of LWC calendering
concepts

togravure paper with gloss ≥ 65% Gardner on the same line, we recommend
two offline Janus™ MK 2 calenders with
1x10 rolls each.

65

Janus™
10-rolls

60

Janu s™
8-rolls

Janus™ 10-rolls
offline55

50

Janus™
6-rolls

451000 1200 1400 1600 1800 2000
PM operating speed [m/min]
7

70

65

Janus™
10-rolls

Janus™ 10-rolls
offlineJanu s™

Gloss Gardner [%]This means that apart from asymmetricaltemperature settings, each stack can be
operated at an individually variable line
force independent of the other stack.

60

8-rolls

55

Janus™
6-rolls50

45

Ecosoft™
2x2 rolls
350 N/mm

40

35

Ecosoft™
2x2 rolls
250 N/mm

301000 1200 1400 1600 1800 2000
PM operating speed [m/min]26

8

here, up to paper roll diameters of
3,200 mm and with minimal waste, isensured by a Sirius™ reel system atthe end of the line.
Operating at a web width of 5,360 mm
and a design speed of 1,500 m/min,
Perlen Paper’s Pioneer PM 4 breaks nosize or speed records (nor was it intended to), but it is certainly one of the mostinnovative lines to date.

coldset and heatset printing papers, mattand high-gloss LWC offset printing papers. This gives Perlen Paper the decisivecompetitive advantage of being able torespond very rapidly to market changes.
To attain this flexibility, the heated hardrolls are fixed mounted while the softrolls are self-loading Nipco™-F rolls. Not
only can the Nipco™ rolls close the nips
independently by controlling the shell
movement, but the individual line loads
can also be controlled precisely.

Perlen PM 4 Janus™ MK 2
The 2x3-roll Janus™ MK 2 calender, installed in Perlen Paper's Pioneer PM 4
(Fig. 8), offers further benefits on top of
the already mentioned design advantages. Thanks to its outstanding flexibility, the Janus™ MK 2 calender can handle
an exceptionally wide variety of grades
including standard newsprint, high gradeThis also has the advantage that there isno need to change the web run from 2x1nip to single nip operation, for example,
because it simply passes through theopen nips not required.
In the standard 2x2-nip operating mode,
high-gloss LWC offset printing papers
can be calendered at line loads from 300

N/mm to 400 N/mm and heating medium
temperatures from 180 °C to 230 °C.
This standard mode is also well provenfor calendering uncoated “Extra 70 Heatset” grades. In this case, the line loads
vary between 120 N/mm and 200 N/mm
in combination with heating medium temperatures around 80° C.
For producing matt LWC grades, theJanus™ MK 2 is currently operated in
2x1-nip mode, whereby each side of thepaper passes once over the heated rolls,
both of which with a heating medium
temperature of 80 °C. Line loads in thismode vary from 110 to 140 N/mm.
“Extra 70 Coldset” and standard newsprint grades can be calendered in singlenip mode (first nip in stack 2). In eachcase the line load is 50 N/mm and theheating medium temperature is 70 °C.

.

.

C
L

27

10

Fig. 8: Online Janus™ MK 2, Perlen PM 4.
Fig. 9: Quality characteristics of various
products on Perlen Paper’s pioneer PM 4.
Fig. 10 and 11: Online Janus™ MK 2,
Madison Paper, Alsip, USA.
9

LWC offset LWC matt Heat
60 g/m 2
60 g/m 2
Set
Gloss Lehmann
T480 [%]
measured inmachine direction

50

–

–

Gloss Gardner [%]measured inmachine direction 55 - 60

–

–

2.7

2.4

Roughness
PPS S20 [µm]–Brightness
T452 [%]

76

80

70

Opacity
DIN 5316 [%]

92

93

93

Thickness to DIN
EN 20534 [µm]

≈57

≈69

≈69

Bulk to DIN 53105[cm 3 /g]

≈0.95

≈1.15

≈1.3

Perlen Paper's Pioneer PM 4 produces up
to 550 tonnes per day of LWC gradeswith basis weights from 52 to 70 g/m 2,
and about 420 t.p.d. of improved
newsprint at 45 to 52 g/m 2.
The product quality characteristics so far
attained on this machine are tabulated inFig. 9.
Prospects, and other current
projects
Particularly for LWC offset and ULWC
production, there is a growing demandfor online machine concepts and online
calendering accordingly. Moreover withthe current trend toward lower basis
weights and higher DIP content, the riskof sheet breaks is increasing. This risk
can be counteracted very effectively byusing indirect coating processes in com-bination with Janus™ online calendering
technology.
Based on operating experience with PM 4
in Perlen, this trend will be followed up in
2002 and 2003 by commissioning two
more LWC production lines in the USA.
Each line will be equipped with an eightroll Janus™ MK 2 for online calenderingof high-quality LWC offset grades.
Fig. 10 shows the Janus™ MK 2 layout
in one of these two lines, at Madison
Paper, Alsip.
As previously explained, offline calendering is still in demand for high-quality
rotogravure printing papers. Instead ofthree supercalenders, for example, two
offline Janus™ MK 2 calenders can, however, be used for this purpose. Hereagain, there is a growing interest in online calendering concepts.

11

28

SC paper calendering
technology

1

A good twenty years ago, all SC grades were calendered
exclusively offline, usually with 12-roll supercalenders. The
development of softcalender technology enabled some SC grades –improved rotogravure newsprint as well as SC-B grades – to becalendered online, normally with only two nips.

Ulrich Rothfuss
Voith Paper
Krefeld, Germany

Due to its multiple nips with high coverage degree and rather low operating
speed of 500-700 m/min, the supercalender (Fig. 1) delivered the best quality
results. But as a typical offline system
and also using filled cotton rolls prone tomarking, it was not efficient enough. The
availability of supercalenders was very
low because of the frequent roll changes
required. And due to their restricted operating speed, up to three of them werenecessary to keep up with the output of ahigh-speed paper machine.
Unlike the supercalender, the Ecosoft™
calender (Fig. 2) can be integrated online
in the paper machine. This brings enormous advantages, not only with regard
to space and labour savings. Thanks to
its individually controllable nips, the Ecosoft™ calender guarantees the least two-sidedness and a perfect cross-profile. As
the Ecosoft™ uses polymer roll covers
not prone to marking, its availability ismuch higher than the availability of thesupercalender.
Because Ecosoft™ calenders generally
have only two nips, the calendering work
is less than in supercalenders, the moreso as they are run at paper machine
speeds, i.e. two or three times faster thansupercalenders.
The advent of Janus™ calendering technology in the middle of the nineties madeit possible, for the first time, to combine
the technological advantages of thesupercalender with the cost-effectivenessof the Ecosoft™ calender. High quality SC
grades could now be calendered online athigh speed with multiple nips.

Systems for Finishing

29

Fig. 1: Supercalender.
Fig. 2: Ecosoft™ calender.
Fig. 3: Janus™ MK 2 calender.
Fig. 4: SC paper grades.

2With further development of this technology, the Janus™ MK 2 calender generation was launched only a few years later(Fig. 3).
This concept with its 45° inclined layout
was the first one to meet the special demands of online calendering in full. Particularly notable about the Janus™ MK 2
are its high availability, fast roll changing, easy accessibility to all relevant
points of the calender, and anti-vibration
frame design to prevent barring.
Ecosoft™ calenders are mainly used today for standard newsprint and improved
SC-C grades.
For cold-set offset grades requiring
Bendtsen roughnesses around 130160 ml/min, a single soft-nip may sufficein some cases. Under certain conditions,these kinds of paper grades can also becalendered online with a single hard-nip.
For heat-set offset grades with Bendtsen
roughnesses around 80 ml/min, and for
improved SC-C grades, 2-nip softcalenders are always used.

3

Higher quality SC grades require morecalender nips. Depending on the furnish,product quality requirements and operating speed, Janus™ MK 2 calenders with
6, 8 or 10 rolls are used online for thispurpose. Offline, 10 or 12-roll calenders
are used.
Fig. 4 shows the respective calenderconfigurations, expressed as number of
hot nips, used for the various SC gradeswith their normal gloss and roughness
values.

Also shown here are the respective operating speed limits, which particularly inthe case of high quality SC-A grades, may
currently preclude online calendering.
Calendering results naturally depend verymuch on the furnish. Apart from traditional quality criteria such as gloss andsmoothness, optical characteristics are
increasingly important in this connection,
particularly with regard to blackening. Often an excessively high black calenderingindex limits calendering performance by

Grade

PPS roughness

Gardner gloss

Calender configuration

Operating speed

SC-C

2.5-3.5 m

15-25 %

2 hot nips

Unlimited

SC-B

1.6-2.5 m

25-35 %

2 hot nips

up to 1,500 m/min

4 hot nips

Unlimited

SC-B+

1.4-1.8 m

35-40 %

4 hot nips

up to 1,500 m/min

SC-B+

1.2-1.4 m

40-45 %

6 or 8 hot nips

up to 1,800 m/min

SC-A

1.05-1.2 m

40-50 %

8 hot nips

up to 1,500 m/min

SC-A+

0.95-1.15 m> 50 %

8 hot nips

up to 1,300 m/min

4

Janus™
10-rolls

1.3

PPS-10S roughness [m]

1,8
1,6
1,4

1.7

1.9

1,0

Janus™
6-rolls

2.1

2.3

1,2

Janu s™
8-rolls

1.5

Ecosoft™
2x2-rolls

40

45

50

55

60

65

70

Blackening index [%]preventing the use of higher line loads
and/or temperatures, which would otherwise improve gloss and smoothness.
The goal of low roughness combined withlowest possible black calendering canonly be reached, to a very limited extent,
by adjusting calendering conditions. Furnish quality and stock preparation have amuch greater effect here.
Numerous investigations have shown, forexample, that a high groundwood content
favourably affects the relation between
roughness and black calendering, while ahigh DIP content is rather unfavourable
in this respect.
Fig. 5 shows PPS-10 S roughness as afunction of the black calendering index.
This plot is based on the results of wideranging tests on SC papers from various
manufacturers, and takes account only offurnish influence.
Clearly visible at bottom left – the mostfavourable zone with low roughness andlow black calendering – is the predomi-

1.5

Janu s™

8-rolls
1.7

1.9
Janus™
6-rolls
2.1

Ecosoft™
2x2-rolls
2.51000 1200 1400 1600 1800 2000

PM operating speed [m/min]
5

Janus™
10-rolls

2.3

2.51000 1200 1400 1600 1800 2000
35

Janus™ 10-rolls offline

1.3

SC-B

PPS-10S roughness [m]Fig. 7: Product map for SC grades
TMP content > 80 %.

1.1

SC-A

Janus™ 10-rolls offline

SC-B

1.1
Fig. 6: Product map for SC grades
DIP content > 80 %.

PPS-10S roughness [m]Fig. 5: Furnish influence on calendering results.
GWD
TMP
DIP
Mix
SC production.

SC-A

30

PM operating speed [m/min]
6

nance of grades with high groundwood
content.
Grades with high TMP content are predominant in the zone of high roughness
and high black calendering, while DIPbased grades mainly appear in the unfavourable zone at top right, with highblack calendering and high roughness.
Calender design is fundamentally influenced by the paper machine concept,
above all the press section configuration,
since this is where the 2-sidedness androughness of the paper are determined.
Highly refined stock is more favourable
for calendering, in particular TMP stock.
Also the fillers type and content significantly affect calendering results. As a basic rule, the higher the fillers content, thebetter the calendering results. Calcium
carbonate and particularly PCC give significantly better optical qualities such aswith regard to opacity, brightness andblack calendering, however they result in
lower gloss and greater porosity than for
example flaky clay.

7

The question of optimal calender concept
is, therefore, investigated here not only
as a function of roughness and operating
speed, but also with respect to furnish.
Since stock influences vary so widely, weonly differentiate in the following between grades with a high DIP content andthose with a high TMP content.
Fig. 6 shows the effects for SC-B and
SC-A grades with a DIP content higher
than 80%. The zones covered by specificcalender concepts are defined as a function of operating speed and roughness.
For example, the high roughness and low
speed zone at bottom left is best suited
to Ecosoft™ calenders with only two nips.
Operating at 1,500 m/min, this kind of
calender can still attain a smoothness of
2.2 µm according to PPS-10 S. For a lower roughness such as 1.6 µm PPS-10 S, a
6-roll calender is required with two hot
nips per sheet side instead of 1.
For attaining a roughness of 1.15 µm
PPS-10 S at this speed of 1,500 m/min, a31Fig. 8: Janus calender, Port Hawkesbury,
Canada.

8

10-roll or 2x5-roll calender with four hot
nips per sheet side would be necessary.
The red line at the top delineates the
maximum limit for online calendering. If
for example a PPS roughness of 1.0 µm
is required at 1,500 m/min, operating
conditions are above this line and outside
the online calendering range. In this casetwo offline calenders are required, operating at about 1,000 m/min as against the
paper machine speed of 1,500 m/min.
Similarly, Fig. 7 shows the situation for
SC-B and SC-A grades with a TMP content higher than 80%. Clearly, gradeswith a high TMP content are more difficult to calender. The individual calenderconfiguration zones now start at higher
roughnesses and lower speeds.
Particularly, with regard to SC grades andonline calendering, Voith Paper’s integral
know-how – covering all process stages
from stock preparation and paper machinery to calendering and reeling – ensures optimal runnability and of course
printability.
The world’s biggest SC paper calenders
are the two offline 10-roll Janus™ machines at Stora Enso in Port Hawkesbury,
Canada (Fig. 8).
For the SC-A Plus grades produced here,
online calendering was precluded by
the high paper machine speed of over
1,600 m/min. With a web width of
9,600 mm and speeds of 1,150 m/min,
SC offset and SC rotogravure papers arecalendered here at line forces around
400 N/mm and roll surface temperatures
around 130°C.

Because these calenders operate at significantly higher temperatures than conventional supercalenders, on the one
hand an excellent finish is obtained atnearly twice supercalender speeds withhigh gloss and low blackening, but on theother hand web moisture loss is significantly higher.
To ensure a final moisture content
around 5%, for example, a web humidity
around 11% is required at the calenderintake for the aforesaid calendering conditions.
Together with the high steam quantities
applied to the paper surface by several
steam boxes to optimize calendering results, about 10 tonnes of water per hour
have to be removed from both calenders
by the building ventilation system. At thesame time, stringent demands are placedon the moisture cross-profile quality.
This installation has clearly shown thatoffline calendering of these grades raises
significantly more problems than online
calendering.

As a result, temperatures on the roll ends
not in contact with the web may rise to
the point of cover loss due to hot-spots.
At normal calendering speeds, webshrinkage is much less. The web thus remains wider than the length of the plasticroll covers, so that hot-spot problems do
not arise.
The non-calendered web edges are cut
off before winding.
Long-wave cross-profile variations arecontrolled in these calenders by the 10 to
12-zone Nipco™ rolls, and short-wave
variations by the multi-zone steam boxes.
This control strategy is now well proven.
The SC-A Plus grades produced in Port
Hawkesbury are now long-established on
the market, whereby the offset grades
represent the absolute benchmark in
North America. These grades are also
well-accepted in some areas of the LWC
market.

The main reason for these problems
is the intermittent offline calendering
process, with acceleration and deceleration phases during parent roll changes,
whereby the splice has to be made at
speeds of 20-40 m/min with opened nips.

Further offline Janus™ calenders for
SC-A Plus grades operate at Stora Enso,
Maxau, Germany, and Myllykoski, Finland, comprising two supercalender rebuilds in each case. Due to the high quality requirements for SC-A grades, there
are no online installations of this type as
yet.

Opening and closing the calender without
stopping the web always involves the riskof paper breaks. Furthermore, webshrinkage during the low-speed phases
shortly before and after splicing is so excessive that the web width may be lessthan the length of the plastic roll covers.

The new paper machine No. 11 at SCA
Graphic Paper Laakirchen, Austria, is also
fitted with a Janus™ MK 2 calender. Yet
this calender is installed offline. Initially,
this first offline calender will handle
an annual output of 240,000 tonnes at
reduced PM operating speed. When the

32
Fig. 9: Janus™ MK 2 calender,
Ettringen, Germany.

9

paper machine is run up to maximum
speed in the second expansion phase, asecond calender will have to be installed.
Since 1999 the first online calender ofthe new Janus™ MK 2 generation has
been in service on PM 5 at Lang/Ettringen, Germany, paper mill (Fig. 9). At
speeds of more than 1,500 m/min this8-roll calender, a good 8 m wide, now
finishes SC-B Plus grades with a highrecovered furnish content to a PPS
roughness of 1.5 µm at line loads around
300 N/mm and roll surface temperaturesof 130 °C.
Several test series on Ettringen PM 5
have shown that at high line forces andtemperatures, PPS-10 S roughnesses canbe reduced to 1.2 µm.
The extreme flexibility of this installation
enables not only Janus™ operation utilizing all nips, but also single-nip operation
for calendering standard newsprint.
In the latter mode, speeds exceeding
1,700 m/min have been attained.
In this case all the nips not used remain
open, so that roll changes can be prepared without interrupting production(e.g. cooling down the thermo-rolls). The
Janus™ MK 2 concept realized here, forthe first time, was an immediate successright from the beginning.
With good accessibility to all relevant
points of the calender, fast and easy rollchanging, extremely rigid anti-vibration
stand design and good runnability, this is
the optimal concept for trouble-free online calendering.

The multi-zone Nipcorect™ top and bottom rolls ensure an optimal thickness
cross-profile even in single-nip modefor standard-newsprint calendering. The
multi-zone steam boxes are not required
for these grades, and are only used in
Janus™ mode for correcting short-wave
cross-profile variations with SC grades.
The problem of excessive web moistureloss is even more critical in online than inoffline calendering, because for online
calendering, high web moisture content
with excellent humidity cross-profile atthe calender intake is absolutely indispensable.
In conventional offline calendering, the
web is dried in the paper machine toabout 2.5% moisture content and thenbrought to the required moisture levelwith suitable moistening spray nozzles.
Since calendering usually takes place
several hours after moistening, the paper
has time to soak up the water uniformly,
and problems such as drop marking never occur.
With online calendering, the web is notdried in the paper machine. Due to thehigh initial web humidity of about 15%,spray nozzles are used only for adjusting
the humidity cross-profile instead of forincreasing the humidity level.
To give the water drops enough time topenetrate the web thoroughly, thus avoiding drop marking and similar defects, thespray nozzles are installed at a point corresponding to about 1 second before the
web reaches the first calender nip. Normally there are 3 to 5 drying cylinders

between this moistening point and thecalender inlet.
By varying the number and positioning of
the steam boxes, the steam quantity andthe temperatures of the individual heatingrolls, gloss and smoothness on each sideof the web can be optimally adjusted
even with this kind of asymmetrical calender arrangement.
The world’s first multi-roll online Janus™
calender was commissioned in 1996 on
PM 4 at Lang Papier, Ettringen, Germany.
Further online Janus™ calenders are now
in service at Haindl Paper, Schongau,
Germany, and at Bowater in Donnacona,
Canada. These special online-calendered
SC-B Plus grades are now a well-established product in good demand on themarket.
In some cases these grades are already aviable alternative to supercalendered SCA products. For SC-B and SC-A grades,
and many others as well, there will be an
ongoing trend in future toward online calendering at ever increasing speeds.
With higher DIP content, lower basis
weights and steadily increasing fillers
content, the existing problems in thisconnection such as high blackening andhigher opacity losses will certainly not diminish – notwithstanding the advantagesof excellent printability and runnability.
As always, Voith Paper will meet thesechallenges in the interest of our customers with appropriate solutions andtechnologies. An important step in thisdirection is certainly the Janus™ MK 2
calender generation.

Systems for Finishing

33

Janus™ MK 2 –Engineering aspects of a modern
online calenderCompared with conventional multi-roll calenders, theJanus™ MK 2 with its 45° inclined layout offers significant
advantages for roll changing, accessibility, runnability, etc. Apartfrom these benefits, a good many details, decisively affecting
reliability and efficiency, are not so obvious at first sight.

Josef Schneid
Voith Paper
Krefeld, Germany

The NipProtect™ system

During opening, when the lowest intermediate roll has to move the greatest dis-

To start with, nip security has beentance, the compensation cylinder is al-

greatly improved with the NipProtect™

most fully extended and nearly all the oilsystem, which includes a number of cylin-

drainage holes are open.

ders centrally integrated in the levers of
the intermediate rolls (Fig. 1).

The cylinder stroke reduces from bottom
to top intermediate roll, and the number

Josef Kohnen
Voith Paper
Krefeld, Germany

The purpose of these cylinders is twofold.

of open drain holes is less accordingly.

During operation they balance out theDuring fast opening, the top intermediate

overhung masses and to some extent theroll therefore lowers more slowly thanmass of the intermediate roll. This results

the one below, etc. Due to the different

in higher line loads in the upper nips,

lowering speeds of the intermediate rolls,

thus increasing the calendering capacity

all nips open simultaneously in less thanfora given line load in the bottom nip.

0.5 seconds (Fig. 2). The further the

The degree of compensation depends onrolls lower, the more oil drainage holes

technological requirements, but is typically 85%.
Another patented function of these cylinders is fast roll nip-opening. When thebottom roll is lowered, all the intermediate rolls are lowered on the oil cushion of
the compensation cylinders.
Each cylinder incorporates a throttle piston with a row of oil drain holes, so thatthe oil drainage cross-section is automatically adjusted according to cylinder stroke.

1

34

Fig. 1: Compensation cylinder.
Fig. 2: Compensation cylinder arrangement/function principle NipProtect™ system.
Fig. 3: Fast opening – new system (NipProtect).
Fig. 4: Fast opening – old system.
Roll 2
Roll 4
Roll 7
Roll 11are closed, so that the lowering speed re-2
Opening nips
(light gap)

duces accordingly. Finally, all the rolls are

Automatic
speed reduction

Gentlelay down

gently laid down on a mechanical stop
0.4
Speed (m/s)(Fig. 2 and 3).
Fig. 4 shows conventional calender
opening by comparison. During rapid
opening, the intermediate rolls are laid

0.3
0.2
Bottom rolldown on mechanical stops one after the

0.1

other from top to bottom. The bottom

Top roll0calender nip is the last one to open, thusTime (s)leading to high structural loading.
Since June 2000 the first NipProtect™
system has been operating very success-3

Fast opening – new system (NipProtect)-20
0fully in a 9-m Janus™ calender. Meanwith NipProtect™, thus demonstrating theconfidence of our customers in this system.

40
Traverse (mm)while ten calenders have been equipped

Further advantages

80

All nips open
Breakdetected120

all rolls gently laid down on mechanical stops

160● Thanks to mechanical control of the oil

200
-0.2

drainage cross-section, the NipProtect™

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Time (s)system is extremely safe and reliable.
Even in the event of control element
failure, damping remains unaffected.
● At the end of the opening procedure,stops. This ensures complete safety
for the operating and maintenance per-

1. Nip open

40
Traverse (mm)all rolls are supported on mechanical

4

Fast opening – old system

-20
0

80

Break
detected120

sonnel.
Last nip open

160

● All pressures are controlled with mechanical valves. There are no proportional valves or electronic components.

200
-0.2

0

0.2

0.4

0.6
Time (s)

0.8

1.0

1.2

1.4

1.6

Systems for Finishing

35

Fig. 5: Roll stack.
Fig. 6: Eccentric offset adjustment.
Fig. 7: Roll offset arrangement.
5

SPS

Floating Stack● The Floating Stack system preventsmechanical damage, because there are

The Floating Stack system has thoroughly∆s∆s

optimized nip loading.
All the intermediate roll bearings aremounted in levers. The top and bottom

∆s
∆Pi

∆s

∆s
∆Pi

∆Pi

∆s

no fixed stops.
● All stack forces are automatically balanced.
● The system incorporates high overallrolls are self-loading Nipco™ rolls, eachdampingwith a shell stroke of 30 mm. As a result,behaviour, because it is suspended be-there is no fixed stop in the stack or for

tween two oil-cushioned Nipco™ rolls.

andoutstanding

dynamic

the top roll.

∆Pi
6

The roll stack positioning is monitored byIntermediate roll lever pivot

sensors on the Nipco™ rolls. During

offset – an effective measure

operation both the Nipco™ roll shells areagainst barring?

in the central position (Fig. 5).
One of the most controversial aspects ofDuring fast opening, pressure reduction

multi-roll calenders is roll cover life, par-in the top and bottom rolls has to be

ticularly in connection with roll barring.

equivalent to pressure reduction in the7
Thermo-roll

Top nip

Barring
n=7Soft rollπ

n=8bottom cylinders. If this is not precisely

Barring is a surface wear problem affect-

synchronized, conventional systems im-

ing both soft and hard rolls, caused bymediately react with excessive forces onnatural or externally excited vibrations of

the mechanical stops, possibly causing

the roll stack. Since every calender rolldamage. The Floating Stack eliminates

stack has its own natural frequencies,

this problem, because any difference inbarring is bound to occur sooner or later.

pressure reduction merely displaces thestack positioning slightly, without any

Barring can be prevented or delayed bynegative effects.

offsetting some of the intermediate rolls
perpendicular to the nip axis. This is

Other advantages of thedone by mounting the intermediate roll

Floating Stack systemlever pivot bolts eccentrically, thus enabling the pivot and roll position to be ad-

π/ 2
n=9

● The Floating Stack system is now welljusted by up to 20 mm (Fig. 6).

proven in about 100 online and offline

Thermo-roll

Bottom nip

installations, and is already operating

Barring frequencies can be detected bysuccessfully in three modern Janus™

installing a monitoring system. In prac-calenders.

tice, barring patterns exhibit integer mul-

36

8

Blade

Air hose
Central bar
Air hose
Cover plate

16˚

Doctorbody

New doctor blade system –This is a big advantage above all withfor optimal finish with therespect to the blade holder cover platehighest quality roll surfaces

and the doctor body.

Since paper surface quality reflects roll

The cross-machine stiffness of the coversurface finish, we developed for theplate has been reduced so that the blade

Janus™ MK 2 a doctor blade system

can follow the roll surface perfectly. In

doing full justice to the highest demands

web run direction, the cover plate is rigid(Fig. 8).

enough to prevent even widely fluctuating
loading forces from affecting the blade

The doctor blades have to keep the rollangle to any extent.

surfaces clean and prevent wrapping
Fig. 8: Doctor blade arrangement.

without causing any surface damage. The

Thanks to this compact design, 75 mm

efficiency with which they do this directly

wide blades can be used even for theaffects paper surface quality.

largest roll diameters and at an angle of16°, recommended for soft covers. Since

Uniform doctor blade loading at the low

they are much stiffer than 100 mm widelevel of 30 - 50 N/m is important for gen-blades, the blade angle varies less, andtiples of n = 25-60 wave peaks and val-

tle but effective roll scraping. Materials

the natural frequency of blade vibration isleys. Fig. 7 shows for example a barringand design were selected to avoid any

almost twice as high.

pattern with n = 8 wave peaks and valleys.

thermal deformation due to roll surface

Displacing the roll by e.g. π/2 changes

temperatures, which can be very high.

the peripheral distance from nip to nip,

Only the continuous central bar is madethus interfering with the vibrational feed-of steel, all other components over theback mechanism. The roll is decoupledentire blade holder and doctor body widthfrom the barring frequency, which helps

are made of carbon fibre laminate.

● Test measurements with a monitoring
system have already confirmed longer

Apart from these detailed examples ofour further development work on Janus™

to curtail barring from the outset.

State of technology

Prospects

Due to the low specific heat capacity and

MK 2 technology, we are of course work-

low thermal conductivity of this material,

ing on numerous other improvements.

the component surfaces get hot already

These are mainly concerned with the rollduring the warm-up phase, thus prevent-changing and drive systems.

ing condensation and drop formation
during production.

In parallel, the principles of Janus™ MK 2
technology have naturally been applied toservice life due to roll offset.
● Longer-term trials will show how roll

The extremely good strength to weight

other calendering sectors as well – see

offset can be optimally applied in orderratio of this material enables a strong andour “Ecosoft™ calender” article in thisto delay or prevent barring.

rigid design with compact dimensions.

issue.

Systems for Finishing

Fig. 1: Janus™ MK 2 calender.

Roll cover and coating effects
on calendering quality
To optimize printability, paper has to be calendered,for example, on the Janus™ MK 2 (Fig. 1) after leaving the paper
machine. Calenders are basically equipped with hard rolls and softrolls. The paper is calendered on the side contacting the heatedhard rolls, against which it is pressed with controlled force by thesoft rolls. To calender the paper on both sides, a reversing nip isrequired with two soft rolls in contact. The smoothness of the rollDr. Lothar
Zimmermann
Voith Paper
Krefeld, Germany

surfaces is critical for upholding a high surface gloss on the paper.
For this reason, development work has concentrated for years
on maintaining, above all, the heated roll surfaces within a certain
smoothness limit, even after long periods of operation.

37

38

Fig. 2: Hard cast roll surface.
Fig. 3: Doctored chromium roll surface.
Fig. 4: Spray coating microstructure,scale 1,000 : 1.
Fig. 5: HVOF coating: particle boundary
corrosion.
2

4

3

5

The steel or grey cast iron rolls used inas resistance to abrasion. The more thisFurther attempts were then made to

the first supercalenders wore out so

coating was used, the more it became

develop an optimal kind of roll coating.

rapidly that they soon had to be replaced

obvious that even this new coating tech-

In the meantime, technical advances inby chilled cast iron rolls. The impression

nology was not suitable for every applica-

galvanic chromium plating had increasedof such a roll surface in Fig. 2 clearlytion.

the attainable surface hardness fromshows the roughness due to the relatively
coarse iron carbide microstructure.

850 HV to 950 HV. This new kind of
producing

chromium surfacing is currently in ser-wood-free coated paper, was not satisfied

vice, with doctoring, at a mill producing

Surface quality was greatly improved

with the gloss attained using this kind of

SC-A+ grades. The customer is very sat-with chromium plated rolls, but their ex-

roll coating. And in another mill, produc-

isfied so far with product quality, but his

treme vulnerability to scratching preclud-ing SC grades, despite the long-term

heateded doctoring. Nevertheless, attempts wereabrasion difference between HVOF coatedgrooves due to doctoring. Although nostill made to doctor this type of roll.

rolls and chilled cast iron rolls (Figs. 2

roll coating with an optimally homoge-

and 4), there was no difference in paper

neous surface, also compatible with doc-

Fig. 3 shows a chromium roll surface

surface quality. In a third mill, also pro-toring, exists as yet, some very promis-

after about 38 days of operation. The

ducing SC papers, HVOF coating resulted

ing developments in spray coating tech-grooves in peripheral direction can stillin a significantly longer service life,

nology are underway at Voith Paper.

be seen. The overall surface roughness iswhich, however, was still far too short. It

0.15 Ra at that time and, therefore, stillturned out here that the surface had beenassures good operating conditions.

damaged by particle boundary corrosion

Soft roll cover and(Fig. 5).

surface characteristics

Oxygen Fuel) technology enabled ex-

The problem is that the spray coating

Due to the heavy loading on the inter-

tremely hard surface coatings (>1,100

particles impinging on the roll are me-mediate rolls of high-speed, high perfor-

HV) which could be ground to a smooth-chanically flattened on to the previous

mance Janus™ calenders, subsequent

ness of Ra < 0.08 µm. They were thenspray material without forming an inte-

development work concentrated on in-

used instead of chromium surfacing

gral bond. Under certain conditions thiscreasing the service life and reliability ofwherever doctoring was important as well

can lead to boundary corrosion.

their soft covers.

For

example,acustomerrollsalready

show

abrasion

The development of HVOF (High Velocity

Systems for Finishing

39

6
Roll:
Ra = 0.3 µm
Rz = 2.5 µm

Fig. 6: Effect of soft roll surface roughness
on calendering results.
v= 1,000 m/min, Q = 450 N/mm, T = 130°C
coated wood-free paper, calendered on bothsides, 100 g/m 2

Roll:
Ra = 0.5 µm
Rz = 4.5 µm

With the new cover materials now devel-

For coated papers, the most critical as-

ing, because they form a wide nip withoped, damage caused by internal flexural

pect is the surface smoothness of therelatively low compression.

overheating can be practically excluded.

soft rolls. Any hard filler particles pro-As the next stage of development, atten-

jecting from the roll covers easily pene-tion is now being focused on the covertrate the extremely fine-grained coating

Interaction between covers andproperties required for optimal calender-

surface, with negative effects on gloss.

coatings in the nip

ing results.

To prevent this, very smooth-surfaced

Gloss:
TS: 74%
BS: 82%Gloss:
TS: 82%
BS: 82%cover materials are used – at the expense

As explained above, one side of the paper

With soft rolls in particular, it is veryof abrasion resistance.

is calendered in the upper section of aimportant to differentiate between theSpecial requirements apply to roll covers

Janus™ calender, and the other side after

various paper grades. Some calendered

for technical grades such as silicon basethe reversing nip.

papers may require a high volume, forpaper. To make this kind of paper trans-

example, while in other cases gloss,

parent, the fibres have to be collapsed bySince the paper is calendered on the sidesmoothness and production speed takeextreme compression. Furthermore, thecontacting the heated roll, the soft rollpriority.

surface has to be extremely dense in or-

surfaces after the reversing nip have toder to prevent penetration of e.g. silicon

meet demanding requirements. This is

The main calendering requirements foroil during subsequent processing. The

impressively illustrated by a typical appli-

uncoated rotogravure printing papers areprimary demand on roll cover materials

cation for wood-free coated high-gloss

high gloss and above all smoothness,is, therefore, high compressive strength,

grades (Fig. 6).

with minimal blackening effects.

together with surface smoothness andThis demands high stress, high tempera-

extreme microhardness to compress the

Increasing roughness through wear of

fibres and make the paper transparent.

the heated roll surfaces has to be counteracted by increasing the line load.

tures, and possibly a good deal of steammoisturizing. Therefore the soft covers

Liner and board must retain a high vol-For a specified paper surface quality,

must not only stand up to high stressume after calendering. This requires very

the line load of e.g. 320 N/mm, required

levels, but also have the smoothest pos-

soft and smooth covers for only low

with freshly ground rolls, has to be in-sible surface and greatest possible abra-compression stress. Such covers tend tocreased during the service life to aroundsion resistance.

heat up due to considerable internal flex-

370 N/mm.

40

In this way, the required gloss androlls the production parameters can be

chromium plating plays an importantsmoothness values can still be attained

adjusted accordingly, for example byrole. Also recommended is CeraCal™

despite increased roughness of the heat-

reducing steam moistening and thus

spray coating. Initial trials with Cera-

ed roll surfaces (Ra >0.8). This is attrib-

reducing heated roll temperatures.

Cal™ show excellent results without
any particle boundary corrosion, also

utable to the more intensive contact
between web and heated rolls underWith these findings, the developmentwith steam moistening. Over an oper-

higher pressure, with better heat transfer

goals for roll covers and coatings areating period of 70 days so far, Cera-

as a result.

clear. Abrasion-resistant heated roll coat-

Cal™ coating surface roughness has

ings with a typical surface roughness ofremained within Ra = 0.1 µm.

Nevertheless, by maintaining heated rollRa < 0.1 µm are required, in combination● CeraCal™ spray coating is also recom-

surface roughness below approx. Ra 0.8,

with soft roll surface roughness below

mended for calendering SC-A, SC-B

paper quality requirements can be met

Ra = 0.15 µm.

and LWC grades.
● For SC-C and newsprint, uncoated rollswith lower line forces and less flexible

are adequate unless profile wear is adeformation of the soft covers.

problem.

Roll cover and coatingThis not only increases roll cover service

recommendations
Soft roll covers:

life, but also reduces drive power requirements and saves energy according-What are the best surfacing materials● For coated papers with high gloss re-ly. The overall benefit is even greater iftoday for optimal calendering of eachquirements, Rubin™ S covers are rec-soft roll surface quality can be improved

paper grade?

ommended.
● Recommended for less demanding

to match that of the heated rolls as far as
possible.
Furthermore, with particularly smooth

Hard roll coatings:

coated papers and LWC grades are● For wood-free coated grades demand-

Rubin™ covers. Due to the type and

ing

high

gloss

and

smoothness,quantity of fillers used, these are classified as medium quality covers.

Paper grade

Special characteristics

Roll coverRoll coating● Wherever high line loads and high production outputs are required, for ex-

Rubin™ S

CeraCal (chromium)

ample with SC-A and SC-B grades,

Wood-free coatedRubin™

CeraCal (chromium)

only Safir™ S covers can be recom-

LWC

Safir™ S (Rubin)

CeraCalmended. These are particularly tough

SC-A+

Safir™ S (Rubin)

CeraCaland abrasion-resistant.

SC-A

Safir™ S

CeraCalSC-B

Safir™ S

CeraCal (uncoated)

SC-C

Safir™ S (TopTec HC) UncoatedDecor (resin-impregnated) papers

Safir™ S

CeraCalTechnical papers

Safir™ S

CeraCal (uncoated)

TopTec HC

UncoatedWood-free coatedNewsprint

Very high gloss

Very high transparency

After addressing in this article roll coverand coating effects on calendering quality, the following articles in this issue report on the respective technical advancesand design developments.

Systems for Finishing

41

Soft roll covers for
Janus™ calenders
Voith Paper Service (formerly Scapa Kern) has been
producing soft calender roll covers for more than a decade.
A new cover generation has now been developed to take accountof the special demands on soft roll covers in multi-nip calenders.

Development history

Paper Service mainly comprise a fibre-of soft roll covers

glass-reinforced base layer and a surface
layer strengthened with aramide fibres.

The first two Janus™ calenders with softroll covers went into service in 1996, in-

The multi layered base construction iscluding the first Janus™ online calender.

built up by winding fibreglass textile withfillers and resin around a metal core. It

Modern calender roll covers are madeforms a dynamically strong composite,

Dr. Benno Baderof composite fibre materials, either withbonded both with the metal core and with

Voith Paper Service,Wimpassing, Austria

cast or fibre-reinforced surface layers.

the surface layer. To this purpose, thephysical characteristics of the base layer

The advantage of cast surface layers issuch as mechanical strength, Young’s

the high isotropy and the very smooth

modulus, deformation characteristics andand homogeneous surface. At the cost,bonding must comply on the inner side

however, of brittleness and a tendency towith the metal core material, and on theform cracks propagating in all directions

outside with the surface layer used for(Fig. 1).

calendering.

That is why Voith Paper only uses coverIn the first multi-nip calenders, hot-spot

materials with fibre-reinforced base andproblems increasingly arose due to thesurface layers (Fig. 2). The fracture char-high nip frequencies. They were caused

acteristics of the fibre-reinforced surface

by the thermal energy released during

layer are shown in Fig. 3.

repeated local overloading of the covermaterial.

Cover design principles
Due to the intrinsically low thermal conThe TopTec™, Rubin™ and Safir™ calen-

ductivity of polymer material, this heat

der roll covers manufactured by Voith

cannot be dissipated quickly enough, and42Fig. 1: Cracks extending over the entire
roll cover, mainly in the axial direction.
Fig. 2: Crack growth limitation byfiber reinforcement.

Fig. 5: Mechanical overload due to deposits.
Thickness of deposit 200 m
 100 m
 70 mFig. 3: Crack growth mechanism
a Fiber fractureb Fiber pull-out
c Crack bridging
d Matrix deformation.
Fig. 4: Roll damage due to deposits.

Fig. 6: Loss factor tan delta for various
calender roll covers.

1

3

2

4

b
a

c

d

the temperature rise causes cover expan-

By optimizing the material composition,

reason, Voith Paper roll covers have beension mainly in the radial direction. This

heat generation in the Rubin™ and Safir™

optimized in two directions.

process is repeated with every nip pass.

covers was nearly halved. As a result, theThe sum effect of periodic overloading anddamage caused by these effects has been

Rubin™ covers were optimized for use

thermal expansion is a self-energizing cy-

greatly reduced.

with coated papers (Fig. 7), where thecle, which even might continue after thesmoothest possible surface is required.

initial pulse due to roll deposits ceases.

This was attained by particularly fine

On high-speed calenders, this effect can

Surface quality

fillers distribution but with a reducedof polymer covers

fillers quantity.

The outstanding feature of cast covers

The resultant hardness is somewhat low-lead within minutes to hot-spot burningof polymer covers (Fig. 4).

is their extremely homogeneous ander, i.e. 90 Shore D, thus compromisingWith heavy deposits or edge overloading,smooth surface. To attain such quality

abrasion resistance and therefore service

even the latest cover materials cannot

with fibre-reinforced covers, enormous

life to a certain extent (Fig. 8).

stand up to this self-energizing effecttechnological and development effort is(Fig. 5). However, they are considerably

required. It was found that roll cover ser-

Rubin™ covers are ideal for calendering

more resistant to smaller nip fluctuations

vice life could only be optimized by com-

grades where the most important require-

such as in pressure or temperature. The

promising with surface quality. For thisment is high gloss.

amount of deformation energy converted

600

into heat during each nip pass depends

0,050
500

the polymer matrix and fillers or fibres.

5

Jalon Orange

JanuTec HC

TopTec 4

Jalon Sun

Jalon Orange D2

0,000

Jalon Yellow

0,010

100

Safir S

0,020

200

0

0,030

Rubin G

ture, as well as by interaction between

300

SuperTex“tan ” parameter, which can be influenced by an appropriate molecular struc-

0,040
400
tan 

Critical for this is the none-dimensional

Line load [kN/m]on the material properties (Fig. 6).

6

Systems for Finishing

43

Fig. 7: Coated paper surface.
Fig. 8: Fillers distribution in Rubin™ G cover.
Fig. 9: SC paper surface.
Fig. 10: Fillers distribution in Safir S cover.
78

9● Prestressing of the reference modelOn the other hand, for magazine papers

anism was not known in detail. To ana-

in particular (Fig. 9), roll covers withlyze the material stresses caused by suchhigh availability and service life are indis-

overloading, a finite-element simulation

pensable for cost-effective paper machinemodel was developed which reproduces

Despite these limitations, the simulation

operation.

the nip mechanisms very realistically

reproduces relatively well the physicalwithin certain limits.

processes taking place when a foreign

not taken into accountmaterial passes through the nip.

Safir™ covers are therefore optimized forbest possible resistance to abrasion,

On the hard steel roll of a nip with poly-

which makes them particularly proof

mer-covered counter-roll, a surface de-against barring. The very hard fillers used

posit was modelled (Fig. 11). In theto this purpose result in a cover surface

dynamic simulation model, this repre-

hardness of 92 Shore D (Fig. 10).

sents a foreign material accidentially In the first simulation a line load of

passing through the nip.

550 kN/m was assumed as roll loading.

Due

to

these

outstanding

Results

As the surface deposit passed throughqualities,

Safir™ roll covers are the most frequently

Simulation results revealed mechanicalthe nip, simulation showed that beyond aused in multi-nip calenders.

stresses and strains due to deformation

certain pressure due to the roll mass andcaused by the surface deposit. To get

inertia, the nip opened, and the resultant

Isolated cases of mechanical overloading

results quickly, simulation was subject

stresses in the cover corresponded ap-

often occur in practice. In contrast toto the following limitations as against

proximately to those which would occur

the continuous dynamic overloading de-reality:at ten times the line load. This is roughly
the same as the conditions occurring in

scribed above, which causes hot-spot
damage due to heat development, spo-

● Linear stress-strain characteristic as-

single-nip calenders or with the top andradic mechanical overloading can cause

sumed for the polymer cover material

bottom rolls in multi-nip calenders. The

damage which may take weeks to develop● Surface deposit material characteris-same behaviour has been observed on

due to high cover elasticity.

tics assumed the same as steel● Deformation of the steel roll not taken

Until recently, this kind of damage mech-

into accounttest calenders, where the intermediaterolls can evade due to their relatively low
mass.

10

44

Fig. 11: Finite element method (FEM)
simulation model design Line load.
Fig. 12: Compressive stress as a functionof deformation.
Line load

0,5-3 mmFig. 13: Shear stress in the tangential
direction with 3 mm deformation.

30 mm

13

11
12

1183

1200
Max. compressive stress [MPa]Fig. 14: Operating experience with calenderroll covers in a number of Janus™ calenders.
 Normal [%] Damage [%] Barring [%]1000

100% is165 grinding
cycles

Total

Safir

100% is82 grinding
cycles100% is100 grinding
cycles100% is52 grinding
cycles100% is32 grinding
cyclesSuperTex

JanuTec HC

50%

800

40%

636
600

30%
370

400

20%

200

10%

71
0

100% is422 grinding
cycles00,512
Plastic deformation of roll cover0%

Janus Yellow Janus Orange

In practice, however, the very heavy in- Since linear material parameters aredestroyed in the end. Since final destruc-termediate rolls of multi-nip calenders

assumed in the model, the resultant

tion may not occur until some weeks

cannot deflect so easily. The simulationstresses are, of course, a linear function

afterwards, troubleshooting can be a very

model was, therefore, adjusted by lock-of the surface deposit thickness. Theydifficult task.

ing-in the roll centres accordingly. Due toreach the equivalent of the stresses oc-

the resultant deformation, this revised

curring at about 50 times the line load

Ultrasonic inspection is a well-provenmodel(Fig. 12).

way of detecting damage due to mechani-

Already at relatively small deformations

cal deformation. It shows up any damageof only 0.5 mm, peak shear stresses ex-

at a relatively early stage, thus avoiding Surprisingly, the comparatively highceeding the material strength occur in thefurther damage due to cover bursting anddeformation rates when a foreign materi-cover cross-section (Fig. 13).

flying particles.

seemed to have relatively little effect. The

 Secondary peak shear stresses occur

Summary and conclusions

reason is that despite the high peripheral

tangentially in the transition zone be-

speed, the deformation rate is still well

tween the cover and the metal core.

All in all, there has been a significant

below the sonic velocity in the polymer

These secondary peak stresses are due toreduction of damage to soft roll covers

cover material, so that the shock waves,the different Young’s moduli of the cover(Fig. 14).

which can cause serious damage at unex-

and metal core materials, and can criti-

pected points, do not occur in the simu-

cally affect bonding of the cover to the

The type of damage has also changed.

lation model.

core. In practice, this is often where

Barring is the most frequent reason fordamage due to mechanical overload firstroll replacement, with mechanical dam-

The only identifiable effect in the dynamic

occurs. Such damage to the bonding lay-age in second place. Safir™ covers offer

simulation model is slightly asymmetricer is not immediately critical, but due tobetter running behaviour and longer

stresses in the nip as the surface deposit

dynamic loading during ongoing roll

grinding intervals than any other synthet-passes through.

operation it can spread until the cover is

ic cover currently on the market.

revealed

significantly

higherstresses than the previous one.

al passes through the nip at 1,500 m/min,

14

45

CeraCal™ –Optimized high-performance coating
for hard calender rolls
1

The ongoing trend toward faster calenders, increasingly
online, is bringing extreme demands on hot calender rolls. For highquality paper production, they have to ensure for months at timea high degree of smoothness without any appreciable contour
deviations. As mentioned in an other article there are efforts under
way to meet these requirements by perfecting electrolytic chromium
plating methods. Due to the vulnerability of chromium to scratching,Dr. Hasso Jungklaus
Voith Paper Service
Laakirchen, Austria

however, this approach is not very promising. That is why Voith Paper
Service is focusing instead on the development of suitable spraycoating.

Tailored thermal spray coatings

The hard carbide and boride materials

for hot rolls

used are embedded in various kinds ofmetallic matrix.

Thermal surface coating by plasma sprayhas been coming into greater use for

Depending on the materials used and thesome time now. Powdered composite

respective spray process, surface hard-materials are sprayed thereby onto thenesses of 1,500 HV or more can becomponent with high kinetic and thermal

attained. However, hardness is not nec-

energy, as shown in Fig. 1.

essarily a measure of wear resistance.

46

Fig. 1: CeraCal™ spray-coating application.
Fig. 2: Microsection through a CeraCal™
coating layer, scale 1,000 : 1.
Fig. 3: CeraCal™ carbide particles inthe µm range.
Fig. 4: Another type of coating, showing whiteoxidation seams around the carbide grains due
to overheating.
2

3

4More important for long service life is a

gen Fuel (HVOF) method, using an encap-

reduces the risk of chemical corrosion

coherent and well-bonded surface layer

sulated combustion chamber. This en-

separating out the carbide, which would

which is not too brittle.

ables pressures of 12 bar or more foralso lead to premature roughening. Thisadding the necessary kinetic energy com-well-flowing powder material is sprayed

The question has arisen as to whether

ponent to the thermal input. Moreover,by the HVOF nozzle on to the roll surface

multiphase surface coatings automatical-

by selecting an appropriate combustionin layers. The particles reach velocities ofly roughen faster than chromium plated

medium, overheating of the carbide sur-

700 m/s or more and form a coating withsurfaces due to lack of homogeneity,

facing material is prevented by keeping

a bond strength of more than 100 MPa

thus causing a faster decline in paper

the temperature below 500°C. Anotherand a hardness around 1,250 HV.

quality. As proved by the latest develop-

advantage by comparison with the deto-

ments in this field – for example thenation method is that the HVOF process

The roll surface can then be superfin-

CeraCal™ system – the opposite is true.

works continuously rather than intermit-

ished to Ra-roughness values of less thanThe main goal in developing this opti-

tently, thus building up an extremely ho-

0.03 µm, with negligible contour devia-

mized coating system for hard calendermogeneous surface layer (Fig. 2).

tions (< 8 µm over a working width of 9 m).

process combination perfectly matching

The spray coating powder comprises

The effectiveness of this method is shown

requirements.

spheroidal carbide pressed into a metallic

by electron scan microscope view com-carrier matrix. These spherical carbide

parisons of a CeraCal™ coating (Fig. 3)

rolls was to identify a materials andparticles ideally bond into the metal,

with another type of coating on the mar-

CeraCal™ –while at the same time the matrix metalket (Fig. 4). The carbide particles in thefor the toughest demands

component is reduced. Surface roughen-

CeraCal™ coating are firmly embedded ining due to breakaway or erosion of thethe matrix, while the much larger carbide

CeraCal™ hard-metal thermal spray coat-

hard coating material during operation isparticles of the other coating show white

ings are applied by the High Velocity Oxy-thus prevented. The low metallic content

seams. These white eta-phase seams areSystems for Finishing47

caused by peripheral carbon deficiency

endered SC-B grades measured an

As shown by these five examples, consid-

due to overheating. They weaken bonding

Ra-roughness of 0.12 µm on the Cera-

erable progress has now been made in

and resistance to chemical corrosion. The

Cal™ coating. Rolls in similar usage,

optimizing the surface coating of heated

CeraCal™ coating system avoids thisbut surfaced with another type of coat-rolls. Results are no longer limited by the

problem by limiting the heat input.

ing, had to be replaced after reaching

multiphasethe maximum roughness limit of Ra >spray coatings. If the respective parame-

0.3 µm in less than 2,000 hours.

ters are correctly adjusted, thermal spraycharacteristics

ofthermalcoatings not only meet all specific re-

Performance in practice● LWC paper causes step-wise wear onquirements for hard calender rolls, but

The CeraCal™ hard roll coating system ishard supercalender rolls due to highdeteriorate far less than chromium plated

suitable for all types of calender, bothpressure at the web edges. Based onrolls while producing quality results aswith hard-soft and hard-hard nips. Good

good experience with HVOF coatings,

least as good. Furthermore, the vulnera-

results have been obtained in hard-soft

this customer wanted to reduce sur-bility of chromium surfaces to doctoring

nips at line loads up to 550 kN/m and oilface wear to less than 40 µm in diame-

does not apply at all to CeraCal™ coat-feed temperatures up to 270 °C, with rollter per year. After two years of opera-

ings.

heating by steamboxes or external Cal-tion with CeraCal™ coating, annual

Coils. Doctor blades can be used withoutwear is less than 30 µm.

problem, but metal blades must be avoid-

Prospects

ed. We recommend doctor blades made● After installing a CeraCal™-surfacedof carbon fibre composite with heat re-thermo roll, a manufacturer of 50-

Further development work to optimize thesistant bonding resin.

70 g/m 2 coated paper for food packag-

variousparameters

influencing

this

ing has been able to reduce line load

process will also take into account theUsers report very positive results with

by 7% and roll temperature by 10%.

cost-benefit aspect. Field trials are cur-

CeraCal™ coatings, as shown by the fol-

Product smoothness is, nevertheless,rently underway with CeraCal™ coatings

lowing examples:

1.5 times higher, with a gloss increase

incorporating even finer carbide particles.

of 2 points.

If these trials with extremely demanding● A producer of coated grades with highapplications

confirm

thesignificantly

basis weights uses this type of coating● An SC-A producer coated his No. 3 wa-

longer service life expected, a favourable

in both calender stacks at 360 kN/m

ter-heated supercalender roll with Cera-

cost/benefit ratio will result despite theand 240 °C roll surface temperature.

Cal™ process, and after six months ofadditional costs involved.

After operating for 2.5 years, the first

undoctored operation found, that with

CeraCal™ coating still shows the origi-

unchanged surface roughness of Ra

nal surface roughness of Ra 0.04 µm.

0.12 µm, product quality was identicalto that with a chromium coating. He● After more than 4,500 operating hours

therefore decided to equip his new

at 390 kN/m and about 1,160 m/min

Janus MK 2 calender entirely withweb speed, the producer of online-cal-

CeraCal™-coated thermo rolls.

48

1

The Ecosoft™ calender family and its
newest member, the Ecosoft™ Delta
Online soft or hard calendering is a long-established procedure in papermaking. This article reports on the state of technology for both types of machine, as well as the new Ecosoft™ Delta
calender developed from the successful Janus™ MK 2 concept.

Nick Dodd

Ecosoft™ calenders cover almost all

1x2 or 2x2. The 1x3 and 2x3 versions are

Voith Paper
Manchester, Great Britain

requirements

also available but are not covered inforonlinecalendering,

including the following grades:

detail in this article.

● SC-BVoith● Newsprint

Ecosoft™ calenders for the entire range● Copying papersof applications – from lab calenders with● Coated papers

0.5 m web width to production calenders● Boardof 10.8 m width and with speeds of up to● Speciality grades.

2,200 m/min. Since such a wide range

supplies

custombuilt

clearly cannot be covered by a single

Guido Royla
Voith Paper
Krefeld, Germany

Paper

The nip in a soft (compact) calender ismachine concept, there are three types offormed between a soft-covered deflection

Ecosoft™ calenders:compensation roll (Econip™, Nipco™ or
Nipcorect™) and a Flexitherm™ roll.

● Ecosoft™ Modular

Depending on requirements, soft calen-● Ecosoft™ Delta

ders primarily have two different layouts:● Ecosoft™ U.

Systems for Finishing

49

Fig. 1: Shop assembly of an Ecosoft™ Modular
calender.
Fig. 2: Ecosoft™ calender applications.
Fig. 3: Ecosoft™ Modular layout.
Fig. 4: Ecosoft™ Modular design data.

3
2

2000
Ecosoft™ Uv [m/min]1500
Ecosoft™
Delta
1000
Ecosoft™
Modular
500
2

3,5

5

6,5

8

9,5

11

Web width [m]Calendersize

Web width range(mm)

Maximum
operating speed

Maximum
nip load

Maximum
operatingtemperature

ECO 1.1
ECO 1.2
ECO 2.1
ECO 2.2
ECO 3.1
ECO 3.2
ECO 4.1
ECO 4.2
ECO 5.1
ECO 5.2
ECO 6.1
ECO 6.2

1,350-2,150
1,600-2,400
1,750-2,750
2,000-3,000
2,250-3,250
2,500-3,500
2,750-3,750
3,000-4,000
3,250-4,250
3,500-4,500
3,800-4,800
4,100-5,100

800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
800 m/min
1,000 m/min
1,000 m/min

200 N/mm
235 N/mm
260 N/mm
260 N/mm
290 N/mm
300 N/mm
310 N/mm
325 N/mm
330 N/mm
350 N/mm
315 N/mm
335 N/mm

200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C
200 °C

Each calender type has a defined applica-

Milliani / Italytion range; however, there is a certain

2x2

amount of overlapping (Fig. 2).

Security papers

3,100 mmness with well-proven technology. This
100 m/min

modular system covers six calender sizes
for web widths from 1.35 to 5.1 m. It wasdeveloped for maximum operating speeds

Each Ecosoft™ calender version has its

Century Papers / Pakistan

up to 1,000 m/min, and particularly forown special features:

1x2

integration in paper machine rebuilds

2,000 mm

400 m/min

Coated board

Ecosoft™ Modular(Fig. 4).

Linan Jianjang / China

Ecosoft™ Modular calenders generally

2x2

use, as a standard, the proven Econip™-X

4,320 mm

800 m/min

Newsprint
Based

on

the

ongoing

successroll, which, in combination with the heated roll, forms an excellent nip with mini-of

Ecosoft™ calenders, with more than 200

Papier De Vizille / France

mal deviations in line force over thein service worldwide, the Ecosoft™ mod-2x2

entire web width.

ular concept was developed. Since thisWriting and printing papers

2,850 mm

600 m/min

Both the 2-roll and 2x2-roll versions canconcept was launched in the late nineties,
over 20 of these machines have been

Gloria / Peru

sold (Figs. 1 and 3). Most paper grades

1x2

benefit from this calender concept, cov-

Linerboard

sides.

The Ecosoft™ Modular concept uses

Pressure is applied by hydraulic cylinders

standard elements for all machine sizes.

underneath the bottom roll. All soft-calen-

Recent Ecosoft™ Modular calender instal-

Not only does this shorten delivery times,der functions are integrated in this mod-lations are as follows:

but it also ensures optimal cost-effective-

ular system, such as temperature mon-3,300 mmbe used throughout this modular system,
300 m/minthus enabling calendering on both sheet

ering the more economical line in Voith
Paper Finishing’s calendering technology.

4

50

5

595

595

1003

595

1003
1068

1003
1068

887-9101068

887-910595

887-910887-910595

887-910695

595

887-910

695

1068

695

1068

1068

595

595

595

595

695

595

887-910695

595

887-910

1068

1068
595

1003

6

695

887-910

1068
595

595

1003

7

1003

8

itoring and roll edge cooling by the Soft-

Dagang PM1+2 / China

the latest development in the Ecosoft™

rol™ system, threading with open nip, etc.

2x2

series comes into its own:

9,800 mm1,700 m/min

Copy paper
Additional components can also be incorporated in the machine concept, such as

Soporcel PM 2 / Portugal

steam moisturizers, external profiling

2x2

equipment, or sheet threading systems.

Copy paper

8,700 mm

Ecosoft™ Delta

1,500 m/min
Based on the successfully established
Janus™ MK 2 concept and well-tried

Despite the underlying idea of developinga standardized calender, this concept isRheinpapier Hürth PM1/

Ecosoft™ family, a new frame type has

also flexible enough to meet customized

Germany

been developed to round off this soft-cal-requirements.

1x2

8,200 mm2,200 m/min

ender range – the Delta frame.

Newsprint
This machine layout originated from theIn the future, Nipcorect™ rolls will also
be used in Ecosoft™ Modular calenders,

All these calenders are equipped with atJanus™ MK 2 concept, and transferring

thus providing the option of optimal

least one Nipcorect™ roll for calliper-pro-

the clearly proven advantages of this lay-cross profile correction.

filing. Their primary feature is a U-shaped

out to the Ecosoft™ calender was only aframe for symmetrical force transmission

matter of time.

Ecosoft™ U(Fig. 5).

Particularly for today's wide, high-speed

The Ecosoft™ U design enables con-single-nip operating mode in the bottom

installations, this type of machine is thevenient removal of the bottom roll on anip (Fig. 6).

ideal solution. Our references speak forretraction rail, without having to remove

themselves (the following are only a few

the top roll.

Several Janus™ MK 2 installations allow

By singling out this nip from the Janus
MK 2, the concept of the Delta frame ishighlights):
Although a good idea, the U-frame

now easy to understand (Fig. 7). In fact

Braviken PM 53 / Sweden

arrangement may not be possible in

the layout of a 2 x 2-roll Ecosoft™ calen-

2x2

some machine rooms due to the relatively

der is simply the mirror image of its rollwide aisle space required. This is where

pairing (Fig. 8).

8,950 mm

Newsprint

1,800 m/min

51

Fig. 5: Ecosoft™ U layout, 2 x 2 rolls.
Fig. 6: Janus™ layout, single nip bottom.
Fig. 7: Arrangement of Ecosoft™ Delta – 1 x 2.
Fig. 8: Arrangement of Ecosoft™ Delta – 2 x 2.
Fig. 9: Ecosoft™ Delta layout.
Fig. 10: Hard calender /machine calender layout.

30

9

10

The key feature of the Ecosoft™ Delta lay-

Hardnip calenders /open nip, and the nip is then closed atout is, therefore, the 45° arrangement ofmachine calenders

full web width.

(Fig. 9). Due to this layout, some of the

One of the many applications for machine

Both rolls are generally fitted with contin-

biggest advantages of the Janus™ havecalenders is the online caliper profiling of

uously operating doctors.

been integrated in the Ecosoft™ Delta

LWC base paper.

the calender rolls, as in the Janus™ MK 2

series:In the latest machine concepts, further● All components are well provenin practice● Vibration-free frame design

Fig. 10 shows the typical layout of acomponents can be added according tohardnip calender, with the following fea-

requirements such as:tures:● Steam moisturizers to control curl

(wide foundation, low center ofBased on a V-frame design, the nip isgravity of rolls)● Increased correction potential

formed by two hard rolls.

the highest operating speeds● Ionization systems to neutralize(deflection due to roll mass is notin the nip direction)● Tail transfer systems for threading at

The bottom roll is an Econip™, Nipco™ orelectrostatic charges after calendering.

● Easier roll change from the top

Nipcorect™ roll with deflection compen-● Maintenance-friendly accesssation, while at the top is a Flexitherm™

For optimal caliper profile, the heated roll

● Compact dimensions both in thechilled-cast iron heated roll. The Nipco™

in these calenders operates at the web

roll not only maintains a constant nip,

temperature, typically 60-120 °C, depend-

but also, to a certain extent, corrects

ing on application.

machine and cross-machine directions.
Customer recognition of these benefits inlong-wave

practice has already been demonstrated

caliper profiling is done by a Nipcorect™

caliper

deviations.

Finer
With the Ecosoft™ calender line, Voith

by the first sale of such a unit, with theroll.

Paper now covers all requirements forfollowing operating data:

soft calendering, including customized
Equipped in this way, the calender canmachines for special applications. In ourcontinued commitment for perfection, de-Web width:

6,490 mm

efficiently optimize caliper profile in the

Speed:

1,800 m/min

cross-machine direction. Each roll has atailed development work will of course

Newsprint.

separate drive. The tail is fed through thecontinue.

Paper grade:52

off-line

on-line(single side with blade or film coating)1

on-line(simultaneous film coating)

New concepts
for coated mechanical papers
Low paper prices and competition from improved supercalendered and coated woodfree paper are threatening the market
position of coated mechanical grades (lightweight coated paper).
Producers are under pressure to reduce their production costs while
Dr. Michael Trefz

maintaining or improving the paper quality. This situation is theVoith Paper
Heidenheim, Germany

background for the development of new on-line concepts that provide
maximum efficiency with greatly reduced costs for equipment.
These concepts and their potential will be discussed in this paper.
Lightweight coated papers are best characterized by their basis weight range andquality figures. In general, they are produced from stone groundwood or TMP
and include between 15% and 50% kraft
fiber. They are used for offset and rotogravure printing, and the different print
processes require certain differences inpaper-making and finishing. The following table gives a survey of the typical
product characteristics.

Machine concepts
Traditionally LWC papers are blade coated and supercalendered. Many of todays
major production lines were installed in
the 1980’s and include a paper machine,
an off-machine coater, re-reelers and twoor three supercalenders.
Later in the 1980’s, large machines withon-line coaters were built. It became at-Systems for Finishing

53

Fig. 1: Development of coater concepts.
Table 1: Typical properties of LWC paper.
Table 2: Comparison of machine concepts.
T1

Property

Unit

OffsetRoto

Basis weight g/m 2

48 - 70

48 - 70

Gloss 75°%

45 - 60

45 - 65

PPS-10Sm

1.1- 1.6

0.8 -1.2

Investment cost

100 %70 - 75 %60 - 64 %Bulk

cm 3/g0.8 -1.1

0.78 -1.0

Manpower req.

4

2

2

Brightness%

66 - 72

66 - 72

Quality aspects

Offset & Roto
No limitations

Offset only 10 g/m 2
max. coat weight

Opacity%

88 - 94

90 - 96

Offset & Roto
with blade
Offset only with film

tractive to save all the investment andspace for the re-reelers and the off-machine coater. As a trade-off, the overall
efficiency of such a machine with online
coaters was slightly reduced.
In the early 1990’s, improvements in theapplication of hot soft calendering madeit possible to develop the first LWC machines with both coating and calendering
on-line. Another reduction of investment(no supercalenders) and an even more
operational challenge came along. Machines like Port Alberni PM 5 andOrtviken PM 4 started in early 1996.
In the late 1990’s, another milestone incalendering technique made it possible toconsider multinip-calenders with polymer
covers on-line. An even better quality canbe produced with this new concept.
Fig. 1 and Table 2 show a generalcomparison of available machine concepts for coated mechanical grades.
Concept A is the conventional off-line
blade coater with a re-reeler between paper machine and coater. Concept B is theon-line coating section within the paper
machine. Concept C is also an on-line
coating section, but with only one coater

Concept A

Concept B

Concept C

Max. Speed(m/min)1,700 -1,800

1,600 -1,800

1,600 -1,800

Line Efficiency

75 - 85 %73 - 84 %75 - 85 %station for simultaneous coating of bothsides of the paper. The coating section
for concept A (off-line) requires rougly
double the space as concept B (on-line).
Most of the additional space is needed
for reel transport from the PM to the rereeler, the re-reeler itself and the unwind
for the off-line coater. The significant difference in price is mainly influenced by
the additional equipment such as threereels instead of one, continuous unwind
with flying splice, more reel spools, parent reel transportation carts.
The difference between concepts B and C
is the number of coating stations. In concept C, the coating is applied simultaneously to both sides of the sheet with apremetered film coater. Having only one
coater station instead of two provides another reduction of investment costs. The
efficiency is in the same range as withconcept B. However, there are certain
trade-offs coming with the film coating
technique as well as with the simultaneous application that will be discussed in
the next chapter. The comparison of theconcepts A to C is summarized in Table 2.
It is shown in Table 2, that the significant differences are the investment costs
and the number of operators needed.

Concept C with only one coater station
on-line is the most economical production line for coated mechanical grades aslong as only offset paper is produced. It
is still not possible to produce thesmooth surface needed for rotogravure
printing with the film coating technique.
The advantages and limitations of film
coating are discussed in the following
chapter.

Potential and limitationsof the new concept
A major breakthrough for coated mechanical paper was the rapid development of
the film coating technique in the early
1990’s. Advances in equipment and –more important in coating color formulations – made it possible to produce film
coated LWC paper for offset printing witha quality according to Table 1.
The driving force for this development
was the fact that film coating imposesmuch less stress on the paper during thecoating process. While the blade is a perfect digital hole detector – each holecauses a break – film coaters promise agreatly increased efficiency. The reduced
paper stress allows also to reduce the

T2

54

Fig. 2: Principle difference between film andblade coating.
Fig. 3: Max. possible speeds and coat weights
for film and blade coating.
Fig. 4: Gloss and roughness values for coatedmechanical gardes.
2

3
Premetered
Film

4
20

Applicator Roll

90

Film
Coating

Paper

Blade
Coating
Colour80
15

Gloss [%] (Hunter)ca.10 m

Coat weight [g/m2/side]

Film Splitting
Blade coated10
Film coated5

Fine paper
70
Offset
LWC

60
Rotogravure
LWC

50
40

MFC

30
Blade
Coating

Offset LWC(film coated)

0
Paper

amount of kraft fiber from a level between 40% to 50% down to somewherearound 20% and below. This fundamental
difference is also a major contribution to
any return-on-investment calculation.
The advantage, however, comes at a certain price. With maximum possible paper
machine speeds reaching 2,000 m/min,film coating requires careful optimizationof both the base paper properties and thecoating color formulation. The reason isshown in Fig. 2: While the blade more orless levels the surface topography of the
sheet, film coating applies a film of color
with a constant thickness of 10 to 15 microns onto the paper. It is obvious that arough base paper will be rough after
coating. Also the two-sidedness is much
more difficult to compensate with film
coating and should be avoided as muchas possible by carefully designing thewetend of the paper machine.
The major challenge for the quality is thefilm splitting effect. The elongational
forces at the nip opening cause a disturbance in the alignement of the mineral

0

1000
1500
Speed [m/min]2000

pigments on the sheet surface. This is
the reason why it is generally more difficult to reach similar gloss and smoothness levels as with blade coating. This
problem is solved by using very glossy
clay pigments and also some plastic pigment to enhance the final sheet quality.
Another aspect to be considered is themisting of color droplets created in theoutgoing side of the nip at high speeds
and high coat weights. These effects limit
the film coating technique today to theareas shown in Fig. 3. There should not
be a problem for coat weights of 8 g/m 2
and speeds up to 1,800 m/min. But beyond that, careful optimization and adaption of the coating color to the base paper is mandatory.
Finally, the use of film coating for lightweight coated paper was made possible
by new calendering techniques. Whileconventional blade coated paper produced with machines from the 1980’s isfinished with supercalenders, newer machines are equiped with hot soft calenders or multinip calenders with polymer

0.5

0.9
1.3
1.7
2.1
Roughness [m] (PPS-S10)

2.5

covers that allow high surface temperatures. The changes in the calendering
technique, which is primarily an increasein steel roll temperature, new polymer
covers, and the development of heat sensitive coating color components such as
plastic pigment made it much easier toreach satisfactory gloss levels.
A more detailed analysis of the quality
potential is shown in Fig. 4.
Film coated LWC can be produced withsurface roughness between 1.3 µm and2.0 µm PPS, depending on the base paper roughness and the calender configuration. As it is shown in Fig. 4, blade
coated and film coated LWC qualities
overlap in the area around 1.3 to 1.6 µm
PPS. Gloss levels are almost equal.
A medium quality blade coated paper is
as good as a premium film coated one.
This requires a coat weight of 10 g/m 2
per side. Although film coating has someof the above discussed limitations withregard to speed, coat weigths around
8 g/m 2 are possible at 1,800 m/min.

Systems for Finishing

Paper machine

Film Coater

Air flotation drying

Calender55

Wind-up system

5

Practical aspects
Film coated LWC with on-line calendering
is produced since 1996. The first two machines are using two separate film coating stations and hot soft calenders.
Main reasons to go for this concept was
the advantage of independent control ofcoat weight, coat weight profile and sheet
release with single-sided application.
The investment costs for the coating
section, however, is about 30% higher
compared with only one film coater for
simultaneous application. This was one
motivation to further develop the mosteconomic machine layout as it is shownin Fig. 5.
In this layout, the coating color is applied
simultaneously with a film coating station. As the sheet is coated with 8 to
10 g/m 2 per side, a contactless sheet run
into a drying section is required. The firstcontact of the sheet with a roll surface
should be at a point where the color isdryed beyond the immobilization point.
Otherwise color build-up on guide rolls
would damage the sheet surface. The
standard element for a contactless drying
section is an air turn to guide the sheet
into the required direction. The air turn istypically followed by an air flotation dryer

to evaporate the water. Since there is
only little danger of print mottle withlightweight coated grades (and coatweights below 10 g/m 2), the evaporation
rates can be chosen higher than in finepaper coating.

Fig. 5: Modern machine layout for light-weightcoated grades with simultaneous film coating andonline calender, design speed 1,800 m/min.

Other than in earlier installations, there
are no more hot soft calenders used.
They are being replaced by new developed multinip calenders with polymer
covers and steel roll temperatures between 120 ° and 140 °C.

The quality will fit into the typical range
for light weight coated offset papers. A
good example how development of newtechniques such as film coating and multinip calendering dramatically decreases
the investment costs while the quality is
maintained. The new concept is a suitable
upgrade for older newsprint or uncoatedmechanical machines.

The lower temperature is a major operational advantage over the hot soft calender, and technologically it is compensated by the number of nips that produce
the critical surface roughness. Spacewise
there is no significant difference between
both calender concepts.
By middle of 2000, the first machineswith this concept started up in Germany
and Switzerland. Compared to the conventional concept with the off-machinecoater and the supercalenders, the investment costs are dramatically reduced(about 36% to 40% less, according toTable 2).
On the other hand, a very high degree inautomation is required to keep the line
efficiency around the 80% value.

The new PM 4 at Perlen Papier in
Switzerland to a similar concept asshown in Fig. 5 is a perfect example forthat. The completely new machine that
replaces an old newsprint machine started up in the summer of 2000.

56

1

The DF coater –Coating technology of the new generation
This article introduces the DF (Direct Fountain) curtain
coater developed by Voith IHI Paper Technology. The DF coater isa relatively uncomplicated coating system with many advantages
such as user friendliness, high quality of coated surface and highproduction efficiency. Twenty DF coaters are already in service
worldwide, with widths up to 5 m and operating speeds up to
1,200 m/min, which corresponds to a maximum design speed ofHirofumi Morita
Voith IHI Paper Technology
Co., Ltd., Tokyo, Japan

1,500 m/min. The maximum design and production width currently
possible is 10 m. A maximum speed of 1,800 m/min was successfully attained with the pilot coater. Voith IHI is convinced that the
DF coater will be used much more for producing various coatedpaper grades in the near future.

Systems for Finishing

57

2

3
Distributor
Distributor
ColourCurtain
Web
CurtainColourpan

Web

4

Indirect Application

Fig. 1: Curtain coater.

Direct Application

Fig. 2: DF coating system.
Film coater

Blade coater

Curtain coater
Fig. 3: Cross-sectional view of the
DF coating process.
Fig. 4: Basic coating technology.

without filmsplitting

filmsplitting
contour coatleveling coatideal contour coatpressure penetrationpressure penetration

capillary suction

Curtain coating (Figs. 1 and 2) is a rel-dependability of the 20 DF coaters now in

out of the nozzle slot is accelerated due

atively new process with very high effi-

operation around the world.

to gravity. When it impinges on the web,ciency, good coating quality, easy opera-

the curtain film is further accelerated andtion, cleanliness, etc. So far, this type of

stretched. As a result, ideal coating quali-

coater was hardly used in paper produc-

The DF coating processtion, because of difficulties in controlling(Fig. 3)
With this coating method no metering el-

the air boundary layer on the web, coating color deaeration and curtain stability.

ty is attained.

The deaerated coating color, supplied toement is required after application, thus

the distributor (curtain head), flows

enabling a very even coating profile andVoith IHI has solved these issues andsmoothly downward to the nozzle, where

uniform coat weight and very stable coatmade curtain coating market-ready. This

it is evenly applied to the moving web.

weight adjustment.

is reflected by the excellent operation and

The velocity of the curtain film flowing

58

6
5000

20

4000
Width of curtain [mm]Coating weight [g/m 2]

5
25

C

15
10

A

B
E

5
D

3000
2000
1000

0

0
0

500

1000

1500

2000

2500

0

Coating speed [m/min]

400

800

1200

1600

Coating speed [m/min]With film coating, penetration is also

● Mechanical condition: optimal shape ofhigh due to the nip pressure applied by

distributor, stable color supply system,

Fig. 4 shows a comparison with the main

the rolls. In a comparison with otherefficient boundary air layer removal

coating methods currently used, i.e.

coating methods, curtain coating results

deviceblade coating and film coating.

in a more even thickness of coating film,● Coating color: spreadable coating

and much less color penetration sincecolor, no air bubbles, appropriate

Curtain coating and film coating are

only capillary action is involved. This isviscosity range.

premetering processes, where coating

why the curtain method results in ideal

color dosage is defined prior to applica-

contour coating.

Coating method comparisontion.

The operating windows (Fig. 5) of the DF
coater are significantly influenced by therheological characteristics of the coatingWith the blade coating method, the coat-

Operating requirements

color, however, the general limits are as

ing color is not metered until after appli-

and limits for theshown below:

cation.

Direct Fountain Coater● Window A: most suitable range

Since curtain coating is a pre-metering

For stable operation of the DF coater, themethod, a very even coated surface canfollowing conditions are required.

be achieved irrespective of web surface● Stable curtain film from the distributor

condition.

● Suitable coating color which spreads● Window D: potential range in case ofout evenly after impinging on the web.

relatively low solid content of coatingof coating color into the web is caused by

These requirements are met by appropri-● Window E: potential range requiring

blade load and the large amount of color

ate mechanical performance and rheolog-

mechanical improvement and coating

during dwell time.

ical characteristics of the coating color.

color enhancement.

● Window B: potential range depending

In the case of blade coating, penetration

on rheological characteristics● Window C: potential range withchanging coating parameterscolor.

Systems for Finishing

59

Fig. 5: Operating limits of the DF coater.
Fig. 6: DF coater references at the present
time. Maximum width currently: 5,000 mm.
Total units in service: 20.
Fig. 7: Double coating by single DF in tandem.
Fig. 8: Double coating by twin DF.
7
Distributor 1

Curtain 1

8
Twin Distributor

Distributor 2

Color A

Curtain 2

Web

Color BWeb

In the pilot trials, the possibility of coat-● No applicator roll change

design and production width currently

ing with the DF coater in window E was● Easy adjustment of coat weight.

possible is 10 m. A maximum coating
speed of 1,800 m/min was successfully

confirmed.
Low operation costs andattained with the pilot coater.

high productivity
Advantages of the DF coater
The many advantages of DF coaters com-

● Coating color savings

Future development● Compact coating color supply andof DF coaters

recirculation systempared with conventional coaters are set● No wear parts

The ongoing improvement of coating col-out below. These are mainly due to the● No down time needed for changing

ors for curtain coating will also enable

very simple coating mechanism and ideal
contour coating.

blades, rods, or rolls● Less down time due to web breaks.

pigment coatings with high solid content
for graphic papers in the future. Particularly in the case of woodcontaining LWC
paper with very low wet strength, the DF

High coating quality● Improved CD and MD profiles

DF coater references● No scratches, no streaks, no film

at the present time
Due to contamination and noise, it will

splitting● Good opacity and coveragecoater may be very effective.

Twenty DF coaters are now in service

become increasingly necessary in the fu-

worldwide (Fig. 6), including Japan, Asia,

ture to replace existing air knife coaters

Europe and the USA. The working widthwith DF coaters for board production. In

Easy operationof these curtain coaters is mostly 3 to 4

the near future double coating – wet on● No splashing, no mistingm, with coating speeds from 1,000 to

wet – will be possible using two DF● No metering element, no blade or rod

1,200 m/min. The maximum design speed

coaters in tandem, or a twin distributor

is currently 1,500 m/min. The maximum(Figs. 7 and 8).

(ideal contour coating).

change60

started operation with coating color on
Masahiro
Murakami

MichaelBoschert

October 16, 1998 and soon after started
commercial operation without any problems.

Director/Mill manager,
Nippon Paper Industries Co.,
Ltd., Nakoso MillWe already had experience with DF coating operations in the medium speed
range (700 m/min), but it was a first

We are pleasantly surprised by the excellent performance of Voith IHI’s DF Coater
Head installed on the No.4 Coater in our
Nakoso mill since 2001.
We trust that the DF Coater Head will
enhance our reputation and competitiveness to fully comply with our operationand quality requirement for customer
satisfaction.

Head of Division, Production
SD and Production Manager for
Thermal and Carbonless Copying Papers at August Koehler AG

challenge for us to handle a higher-speed

August Koehler AG, headquartered in(1,200 m/min) and wider machine (1.7 m

Oberkirch/Germany, was founded in 1807.

- 2.6 m). We therefore carefully investi-

The family-owned company is today one

gated the technical issues using the pilotof the world’s leading manufacturers ofcoater in Voith IHI several times and es-

specialty graphic papers. The Koehlertablished the most suitable air deflecting

Group manufactures not only decor

system and color preparation, which we

papers but mainly also coated papers likesucceeded in, starting up without any

carbonless copying and thermal paper.

problems.

Our company has long been associated,in a spirit of partnership, with Voith AG

We soon reached a normal commercial

as the process supplier for our systems.

operating speed of 1,200 m/min at an

In the field of coating we have again

early stage after start-up and, further-

implemented pioneering innovations to-more, we achieved a DF coating design

gether with Voith. Since the highest de-speed of 1,500 m/min. Now we are able

mands are made on the functional coat in

to produce carbonless capsule paper

terms of functionality and uniformity inwith one of the highest efficiencies in themachine and cross directions in the ther-world.

mal paper market segment, we decided
to place our full trust in the new develop-

ShinichiSuzuki

General Manager, Production
Dept., Mitsubishi Paper Mills
Ltd., Takasago MillThe DF Coater gives us higher perfor-

ment “Curtain Coating”. As a first step,

mance than other coaters both in terms

our CM1 was re-equipped for this methodof quality and productivity when produc-and simultaneously the new CM 2 de-ing information papers in our mill. And

signed with a DF Coater (Direct Fountain)

especially from the operational point ofand ordered from Voith.

view, we are sure that this method of DF

Following preliminary trials at Voith IHI

coating is much superior to other coatingin Japan, it soon became clear to us that

Takasago 12 CM (Mitsubishi Paper Mills)

methods because there is less noise, lessonly the DF Coater can meet our high de-

was designed as a high-speed coating

mist and the machine is therefore easiermands on thermal paper coating. Whatmachine for carbonless copying paper. It

to operate.

looked so simple on the pilot coating

Systems for Finishingmachine then had to be implemented in
the production systems.
DF Coaters are today in use on our two
coating machines and a new era has begun for us here at Koehler. In our opinion, the constancy of quality reached up
to now is not achievable with other coating technologies.
On all our coating units we have, in thepast, had to battle to obtain a constantcoating color. With the DF Coater, on theother hand, we have now achieved something that had previously been inconceivable to us. We start off with one coatingcolor formulation and no longer need tomake any corrections to this up to theend of production. Thanks to this constancy, we now have to ask ourselves:“Do we still need a quality test on thefinished paper?”As the DF Coater operates without contact, there are no longer any sheet breaksat the applicator. And because no wear
parts, such as blades or rods, are used
for Curtain Coating, these no longer haveto be replaced.
After over six months of use, we arehighly satisfied with this new and innovative coating technology and have decisively improved the quality of our papers.
I am sure that Curtain Coating has agreat future lying ahead of it. We at
Koehler have only made the decisive beginning with specialty papers. I can well
imagine that this technology could also
be used for mass-produced papers suchas LWC.

61

62

1

Krieger completes the
product range of Voith Paper –Infrared drying, integrated drying
systems and means for contact free
web-handlingWith the beginning of the year 2002, Krieger GmbH &Co. KG has become a member of the Voith Group of Companies.
Both companies have a long history of working successfully
together which makes the integration of Krieger equipment into
Voith Paper’s One Platform Concept a rather natural process.
Jan Eberhard
Krieger GmbH & Co. KG
Mönchengladbach, Germany

When it comes to finishing, drying thebe the method of choice for this purpose.

coating color in a fast, energy efficientWhilst Krieger has several installations

and quality preserving or rather quality

operational with its Infraelectric systemestablishing way, constitutes a challenge

in places where natural gas as well as liq-

which can only be met with the appropri-

uid petroleum gas are hard to get, gasate, state of the art equipment and a lot

fired infrared is favored in almost all cas-of experience. In almost all cases, in-es because of obvious economical advan-

frared drying (IR drying) has proven totages.

Systems for Finishing

63

2

Fig. 1: CB-Turn™ for non-contact web turnand IR emitter.
Fig. 2: Gas fired IR emitter principles usedin the paper industry.

Metal emitter

Ceramic emitter

Fibre emitter

Krieger is not only the expert with thesuitable for stepless (0%-100%) power

evident besides the higher specific ener-

most experience in this field but also thesetting for CD moisture profiling.

gy density, which can be important forsome applications in paper machines andonly manufacturer of gas fired infrared
emitters who can provide all different

The Ceramic emitter has a perfo-

types of design principles for such emit-

rated ceramic plate through which theters presently known (Fig. 1).

gas-air mixture flows before subsequent-In the Fibre emitter, the perforated

coating lines as well as for pilot coaters.

ly burning on its surface. Since the con-ceramic plate has been replaced by a

In all cases, the heat of combustion must

vective heat transfer to the ceramic plate

metallic fibre plate. Since the same mate-

be transferred to a solid body, since thetakes place at the root of the flame only,

rials as for the metal emitter are in use

flame itself emits virtually no IR radia-

this emitter principle has a marginally

here, though in the form of very thintion. In Krieger’s Metal emitter the

lower efficiency by comparison. To com-

fibres (~100 µm), the operating tempera-

gas-air mixture flows through an array ofpensate for this limitation, a metallic

ture is restricted to levels even below

nozzles at high speed and burns at thescreen is installed as a secondary emitter

those possible with the metal emitter.

exit of the nozzles. This design, based onin front of the ceramic plate. Neverthe-

the principles of impingement jet flow

less, since ceramic as a material permits

For the same reasons as on the ceramic

guarantees particularly good heat trans-

higher temperatures than metallic heating

emitter, the heat transfer in this case isfer. Besides, the emitter plates located inalloys, higher input power is possible

significantly poorer than with the metal

front of rather large nozzles makes thiswith this type of emitter than with metal

emitter. Moreover, the fibre material isemitter very resistant to both, contamina-

emitters.

even more critical in terms of its sensitivity to contamination and the risk of airtion from inside and outside and to air
Consequently, the radiated power on theflows causing dark spots than the ceram-

whole is somewhat higher. Given the low-

ic emitter. This explains why this type of

Likewise, this feature produces a relativeer thermal inertia (less metallic mass),

emitter is only used in cases where these

thermal inertia, making the metal emitter

faster heat-up and cool-down times are

criteria are of a certain importance.

flows.

64

Fig. 3: Typical integrated dryer™ installation
following a film press.
Fig. 4: CB-Turn™ for non-contact web turn.
Fig. 5: CB-Float™ nozzle in operation.
Fig. 6: Krieger Integrated Dryer™.
Fig. 7: InfraFloat™ concept – the air dryer isheated exclusively with exhaust heat from theIR dryers.

P

m bar

3

m bar

m bar

f

m bar

4

Apart from providing the right emitter forin the US) but also for cigarette paper

respect to the required drying energy,

each individual application, Krieger has(Feuerstein/Austria), coated fine paper

since the high efficiencies (72-75%) can

specialized in fitting complete drying/web(Arjo Wiggins Besse/F, Grycksbro/S) as

only be achieved if all IR emitter rows in-handling systems into very limited space.

well as for heavy board (FS-Karton/GER,

stalled are operational. If not, the burner

On the one hand, in these systems ener-

Iggesundshown in the functional diagram mustgy efficiency is increased by making use

GER).

Workington/GB,

Buchmann/of the energy contained in the exhaustalso run as a “backup burner”. Usually,
this burner chamber is only used for fastgases of the IR emitters by means of a

Besides the CB-Turn™, Krieger cancirculation air system and additional air-also provide a solution to replace guidehoods (Integrated Dryer™), on therolls for very small angles of wrap: The

The sophisticated system of dampers

other hand space limitations in existing

CB-Float™ nozzle (Fig. 5) comes inand pipes makes it possible to regulate

machines can frequently be dealt with byhandy whenever a slight polygonal sheet

the blowing air temperatures in the IR

using a CB-Turn™ for contact freerun is preferable to long, straight freedryer (max. 120 °C) independently of the

web turn in connection with an integrated

draws.

temperature in the hot-air dryer (max.

system (Figs. 1, 3, 6 and 7). This en-

system heat-up.

160 °C), in order to ensure maximum en-sures that the coating color is dried to

The InfraFloat™ concept (Fig. 7),

such an extent that coating deposits on

uniquely available from Krieger, achieves

the following drying cylinders and guidean even higher utilization of the heat con-

Despite its exceptionally high efficiency,

rolls are prevented.

tained in the exhaust gases applying an

the relatively large amount of space

optimized relation between the air-hoodrequired and higher investment costs ofergy efficiency as well as quality.

Krieger’s CB-Turn™ (Figs. 1 and 4)

length and the volume of exhaust heat

this system by comparison with the inte-

has proven its excellent runability notfrom the installed IR-hood(s). Neverthe-

grated dryer makes a careful expert

only for double sided coated LWC paper

less, this system depends upon a rela-analysis of possible applications neces-in installations following a filmpress (milltively undifferentiated product range withsary.

Systems for Finishing

65

6

5

The air-hood shown in Fig. 7 features
nozzles specially designed for the paper

7

industry and can, in connection with an
air heating device, be used as a standM

alone system (CB-Dryer) for LWC grades(3 recent installations in the US), highM

quality coated paper (Propal/Columbia)
as well as for virtually all other paperM

grades as has been proven many times in
the pilot coater of the PTS in Munich.
Taken all in all, through its flexibility andthe wide range of drying systems (IR andair), Krieger will prove to be a most valuable addition to the Voith family.

M

M

66

Innovative BLUE SOLID treatmentof wearing parts materials –not only for the paper industry

1

The BLUE SOLID Centre, formely belonging to Jagenberg
Papiertechnik GmbH, is meanwhile an integral part of Voith Paper.

In 1997 the former Jagenberg Papiertechnik launched a research project to investigate the effects of ion implantation
in metallic wearing surfaces in paper
machinery. The paper industry is particularly prone to wearing parts, whose
ongoing replacement or even failure
involves high costs or production losses
which can be critical in view of today’s
tough cost competition. By extending
component life, failures can be minimized
and production losses reduced accordingly.

Michael Hoffmann
Voith Paper
Krefeld, Germany

2

This project has been continued by asmall team of seven specialists, using theBLUE SOLID plasma process for ion implantation mainly on paper industry tools
and wearing parts which are successfully
marketed worldwide. In the meantime
several patents and proprietary brandnames have been registered.

The BLUE SOLID materials
treatment process
Material properties can be systematically
influenced by the BLUE SOLID process.
For example, relatively low grade materials can be imparted with characteristics
only found otherwise in expensive highgrade materials.
For wearing parts and cutting tools, themain properties positively influenced bythis process are as follows:● Resistance to wear and abrasion● Reverse bending fatigue strength● Emergency and dry running properties.
The following material characteristics arealso improved:● Tensile and compressive strength● Torsional fatigue strength● Resistance to corrosion and erosion.

Systems for Finishing

67

3

The BLUE SOLID process is most effective with the following materials:● Chromium steels, high-speed steels(HSS), sintered steels● Tool steels● Stainless steels● Chromium plating● Chromium alloy cast steels.
The principle of plasma ion implantation
is to impart component materials with theproperties of target materials such as
molybdenum, titanium, chromium, etc.
Ions from the target materials are implanted and anchored thereby in theworkpiece material. Thanks to the unusually low temperature level of this treatment, the microstructure can be systematically changed still maintaining material
strength. And since the dimensional precision of the workpiece remains unaffected, this process can be used as the final
finishing stage in component manufacturing. High-temperature treatment exceeding the annealing temperature of therespective material would cause uncontrollable and/or undesirable structuralchanges negatively affecting tenacity –not to speak of workpiece deformation.
For treatment by the BLUE SOLID process,workpieces are suspended in a vacuum
chamber. An electrostatic potential difference is generated between the workpieceand the chamber wall. In the presence ofreactive gases at constant vacuum, ionsseparate out of the target material andare accelerated between the poles. They
impact the workpiece equally distributed
over its surface, and become anchoredin the molecular structure. Since theions penetrate relatively deeply into themicrostructure due to the electrostatic

charge, this is not merely a superficial
coating process. The depth to which theions penetrate mainly depends on the
duration of treatment. By this means, themetal structure can be imparted with newproperties to improve the material characteristics.
Anchored to a depth of several tenths ofa millimeter in the microstructure, theimplanted ions remain effective on along-term basis. This process, therefore,
considerably extends the service life ofwearing parts such as cutting tools, doctor blades, refiner plates, screen baskets,
deflakers, etc.
Apart from extending service life, theBLUE SOLID process also offers several
other advantages:
By influencing surface tension and/or
smoothness, the reliability of a good
many papermaking process stages can be
improved.
Furthermore, costs can be optimized by
selecting less expensive component materials – which also opens up new design
possibilities.

A wide spectrum of services is offered by
the BLUE SOLID centre:● Plasma-treated wearing parts● BLUE SOLID treatment to customerorder● Practical and theoretical training
courses in cutting technology● Cutting system consulting service formodernization/optimization projects● Cutting system rebuilds● Cutting system optimization● Troubleshooting analysis of wearing
parts and cutting samples● CNC grinding service etc ...

Fig. 1: View inside a BLUE SOLID vacuum
chamber.
Fig. 2: Plasma-treated cutting tools, for example:
BLUE SLIT disc knife.
Fig. 3: Vacuum chamber.
Fig. 4: BLUE SOLID products.

Two different vacuum chamber sizes are
currently used for the BLUE SOLID
process: 11,000 x 400 x 400 mm, and3,150 x 650 x 750 mm. With such large
dimensions, even the biggest components can be treated.
The product offers range from BLUE SLIT
cutting tools for nearly all makes of paperroll slitter and guillotine to BLUE ROD
doctor blades for various coaters (Filmpress, Speedsizer, Speedcoater, Symziser
and Metering Blade Sizepress).

4

68

1

With the precision of a Swiss clock –VPT Walztechnik AG Zürich, a Voith Paper
Group company, converts a printing press
at Burda/Offenburg to Nipco™ Print Rolls
It is well known that Nipco™ Rolls are state-of-the-art in
the paper industry. Probably not so well known is the fact that they
are also very successfully used in other industrial sectors. In
rotogravure printing, for example, they play a decisive role, as thefollowing report confirms.

Eugen Schnyder
Voith Paper
Krefeld, Germany

Burda in Offenburg ranks among theleading companies in the European printing industry. It equipped two modern,
3,280-mm-wide Cerutti rotogravure units
with the Nipco™ Print System more thansix years ago. Because of the very goodexperience gained with the Nipco™
System, Burda placed an order with
VPT Walztechnik AG Zürich (VPWZ) last
autumn for the conversion of a 15-yearold, 2,450-mm-wide Cerutti rotogravure
printing press to the Nipco™ Print System. Every week, among other publications, parts of “Focus”, a magazine thatis impatiently awaited every Monday by abroad readership, are printed on this rotogravure printing press no. 14 in Offen-

burg. On time delivery of the printed
product is therefore an absolute “must”.
In other words: the rotogravure press
really must keep “rotating”; downtime isunacceptable. Taking all this into consideration, it becomes clear what it means
to convert a rotogravure printing press:
everything really has to “go like clockwork”.
This is the task that VPT Walztechnik AG,
Zürich faced recently. After a period of
only 6 months of application engineering,planning and manufacturing, rotogravure
press no. 14 had to be rebuilt. The scopeof supply included:

Systems for Finishing69

Fig. 1: Rotogravure printing press.
Fig. 2: Commissioning team.
Fig. 3: Mounting of Nipco™ print roll.

● 10 Nipco™ Print Rolls (two of which as
spares)● 1 complete new hydraulic system,
including controls● 8 hydraulic control blocks● Linking of the Nipco™ System controls
to the machine controls● Various mechanical adaptations andmodifications on the machine.
It was planned to stop the printing press
on April 15, 2002, a Monday morning, at
6.00 a.m. Official takeover was set for thefollowing Saturday morning. This date
had to be met – come what may.
The machine was stopped punctually, sothat the rebuild work could be started onschedule. VPWZ had prepared all of therebuild activities “with military precision”: every single dismantling/reinstallation step had been exactly determined inadvance in very small time intervals.
The pictures convey an impression of thesituation on site. At many points several
activities were done at the same time andvery close to each other. The color of thecommissioning engineers overalls showsin which printing press they were currently working. Besides the experts from
Zürich and Krefeld, there were 2 outside

3

teams assigned to mechanical tasks andthe laying of electrical lines and hydraulicpipes. Only very limited space was available in the machine, so the coordinationof activities was of prime importance.
Cooperation between all those involved
went off so smoothly, and the parts wereso precisely manufactured, pre-assembled and pre-tested, that the VPWZ’sproject manager, Marco Dell’Ava, report2
ed to the mill management in Offenburg
as early as Friday morning – that is a fullday earlier than planned! – that everything had been completed.
The highly satisfied reaction of the customer: “That went off like clockwork.”
But that was not all: the results of the rebuilt printing press met the expectations

that Burda had placed in the modernization right from the start. Properly reproducible setting values, a perfect web run,
optimal register and smooth press operation even at very high printing speeds
make a significant contribution to thegood performance and perfect print execution of the modernized printing press.
The readers, who purchased their “Focus”
on Monday, enjoyed its beautiful appearance. Of course they had not the faintest
idea of the stress and efforts behind thescene that were required to enable themto get “their” Focus in their hands as
usual. And that is a good thing.
It is sufficient for Burda to know: VPWZand Voith Paper are partners on whomthey can rely.

Paper Technology Journal
Newsmagazine for theinternational clientele,
partners and friends ofVoith Paper“twogether” is published twice annuallyin German and English. Contributions by
independent authors do not necessarilyreflect the opinion of the publisher.
Please address all correspondence andinquiries to the editor.

Editor:Dr. Wolfgang Möhle, Corporate Marketing,
Voith Paper Holding GmbH & Co. KG,
Tel. (++49) 73 21 37 64 05
Fax (++49) 73 21 37 70 08
P.O. Box 1970, D-89509 Heidenheim
wolfgang.moehle@voith.com
http://www.voithpaper.com
Editorial coordinator:
Manfred Schindler, D-73434 Aalen
Design, layout and typesetting:
MSW, P.O. Box 1243, D-73402 Aalen
Copyright 7/2002:
No part of this publication may be
reproduced or copied by any means
whatsoever without the express
permission of the editor.
Systems for Finishing, October 2002.

10/2002/21 MA Printed on chlorine-free bleached paper manufactured with Voith Paper Holding machinery.

Published by:Voith Paper Holding GmbH & Co. KG