siegling transilon

conveyor and processing belts

Recommendations
for machine design
Contents2	Definitions and description
3

Drums

5

Take-up systems

6

Belt support

9Knife edges

10 Belt tracking
19 Cleaning devices

For further information, see our brochureno. 304 Calculation methods – conveyor belts.

Siegling – total belting solutions

Definitions and description

In standard conveyors for light materials handling, the conveyor belt runs
over two end drums (in this case end
and drive drums).
The best configuration, called a head
drive, is where the drive drum is at theend of the conveyor where the pro­ducts are discharged. In this case, theforces operating are being applied
more efficiently than they would bewith a tail drive (see calculations).
In long conveyors and with heavyloads, support rollers are often usedinstead of slider beds to reduce theeffective pull. The end drum should be
fitted so that its position is adjustable,
so it can function as a tension drum.
With centre distances greater than2000 mm, support rollers should also
be installed on the return side. This prevents excessive belt sag from the belt’s
own weight. ➁➀➁If the centre distance cannot or only
slightly be adjusted, e.g. because conveyors are positioned directly after one
another, take-up systems are put on
the return side. ➂➂In light materials handling, conveyors
with troughed belts are used for conveying bulk goods. In this case, two or
three-section sets of support rollers are
fitted to the upper side.
Alternatively the belt support can betroughed.
Please see page 8 for more informationon the transition area between the
drum and trough.

2

DrumsDrum diameter

Particularly in wide conveyors, drums
with diameters that are too small are
subject to inadmissibly significant
deflection, resulting in unwanted belt
creasing and mistracking.
Make a counter-check (see page 17).
Drum diameters should always be aslarge as possible. The minimum diameter permitted is determined by:– The effective pull to be transmitted(see method for calculating the drive
drum diameter).

Drive drum

The crown height values, stated in thetable below under lines II and III, aremaximum values and should in certain
exceptional cases be reduced to match
those in line I. In particular if lateralforces cause the belt to crease otherwise.
This also applies to centre drives, orwide belts where the distances
between the end and drive drum are
too small to compensate for the tension in the belt.
The drive drum can be cylindrical,
if tracking devices are used.

3– The flexural properties of the belt
used (see dmin in the product range).
– The flexural properties of the lateraland longitudinal profiles welded on(Technical Information 2, ref. no. 318).

We recommend the drive has a cylindrical centre section with tapered
edges. The length of the cylindricalsection of the drum should be b/2.
For further information, please see
page 11.
If the belt width is considerably lessthan the drum length, the belt width
determines the proportions of thedrive drum.

Guidelines for conicity h [mm]Drum diameter [mm]to 200> 200 to 500

> 500

I

Single-ply belts

0.5

0.8

1.0

II

Double-ply belts
NOVO, E10/M, E15/M, E20/M

0.7

1.3

1.5

III

3-ply belts

1.0

1.6

2.0

Drums

Lagged surface

As regards 0, U0, A0, E0, V1, U1, UH
coatings, drum lagging is often applied
to improve friction on the drive drum.
The lagging should be made of anabrasion-resistant material, like polyurethane or rubber.
Plastic laggings should have a hardnessof at least 85 Shore A at 20 °C in order
to avoid too much wear and tear.
Rubber laggings should have a hardness of more than 65 Shore A and be
made of an abrasion-resistant rubber.
Another method that customers canapply themselves is to wind friction
lagging, e.g. Siegling Transilon with U2
coating, in a spiral form around the
drum.

Bare surface

The faces of all drums should besmooth. Any pronounced grooves
caused by rotation of the drum will
have a detrimental effect on tracking.
Roughness RZ ≤ 25 (DIN EN ISO 4287)(Peak to valley height ≤ 25 µm)
Similarly to the wound drum lagging
method, we recommend that wide
drums with a bare surface should also
be lathed asymmetrically from eitherside to the centre.

4

To avoid any guidance problems, were­commend, particularly where broad
drums are concerned, winding the friction lagging symmetrically for bothsides towards the centre of the drum.
Any existing patterns or profiled drum
laggings (e.g. with rhomboid patterns)
must also be symmetrical to the centreof the drum.

Any rotational grooves left on the
drum will be symmetrical and therefore neutral in terms of tracking.

Take-up systems

Screw-operated take-up system

The contact pressure of the belt on thedrive drum, required to transmit theeffective pull, is produced by elongating the belt using a tensioning device.
The end drum can serve as a tensioning drum, if its position can be adjusted by screws (remaining parallel to thedrive drum).

Conveyors are often configured likethis when Siegling Transilon is used,because Siegling Transilon hardly
stretches at all (meaning a short takeup) and is virtually dimensionally stable(requiring no re-tensioning).
An inflexible tensioning device would
however not permit any compensation
for belts lengthening if they stretch
when the conveyor starts up, or due tounequal loads, or the impact of temperature.

Force-dependent take-up systems

On very long, heavily-loaded conveyors, this take-up system should belocated directly after the drive drum tocompensate immediately for elongations on the top face when the conveyor starts up.
Force-dependent tensioning can for
example be achieved with a weightsuspended from a rope or cord.
Alternatively, pneumatic, hydraulic or
spring-loaded take-up systems can be
used.

5

Force-dependent take-up systems arerecommended in high and fluctuating
temperatures.

A force-dependent take-up system is
not suitable for reversible drives.

Belt support

Slider bed

Slider beds have to be adjusted exactly,
because due to sliding friction they
have a strong impact on the belt. Theiredges must be chamfered off. Place
support areas about 2 to 3 mm lower
than the belt.
Generally sheet metal, hard plastics(Resopal, Duropal or similar) and bonded plywood are used as support material. Together with the smooth undersides of Siegling Transilon belts, thesematerials have excellent friction behaviour. Depending on the surface properties and conditions the belts are operated in, it may be necessary to makealterations.

Support rollers

6

Avoid slatted frames as supports if possible, as they often increase the wear
and tear on the belt and noise when
the belt is running.

It is important to clean the sliding supports before switching on the conveyor, as residues from protective paints orvarnishes, or other dirt can cause significant disturbances (e.g. tracking
problems, damage to the belt andincreased friction).

Support rollers are commonly associated with low levels of drag and smooth
tracking behaviour. For this reason they
are almost exclusively equipped withroller bearings and low friction sealing.
To keep their moment of inertia as low
as possible, the roller tube is usually
made of precision steel tubes or small
flue tubes (see DIN EN 10220).

Plastic support rollers are also used (theadvantage: they are corrosion resistantand very dirt resistant. Please note:electrostatic build-up is possible).
The support roller pitch is determinedaccording to the length of the edge ofthe unit good you want to convey. If
the support roller pitch is ≤ ½ edge
length, the weight of the goods will
always be borne by two rollers.

Support roller layout

Layouts and dimensions of support
rollers are laid down in DIN 22107/
ISO 1537. The purpose of the M form
(DIN term) is to support the belt whendriven in a flat state on the top andreturn side and the troughed belt on
the return side. On the top face,troughed belts are always supported
by support rollers in an N or P shape.

≥ 10 mm

Form M support roller

Form N2 2-piece offset≤ 10 mmTwo-piece sets of support rollers
should have a staggered layout andoverlap by approx. 10 mm.
In the case of a two-piece support roller layout where there is no overlap, thegap between the support rollers must
be kept as small as possible to avoid
creases.

Support roller pitch for unit goods

The distances between the support
rollers are determined according to thelength of the edge of the unit goods
you want to convey. If the support roller distance is ≤ ½ edge length, thegoods are always supported by tworollers.

Form P 3-piece offset

Form P 3-piece troughed angle 20 to 40°

Form N2 2-piece

The support roller pitch depends on
the belt pull and the masses. The following formula is used to calculate it:

l0

l0 =

yB . 800 . F
m'0 + m'B

F = ε % . k1% . b0

yB
[mm]
[N]

F
m'0 + m'B

If maximum sag of 1 % is permitted, inother words if yB = 0.01 l0 is used, then

l0 =

8.F
m'o + m'B

Recommendation:lu ≈ 2 – 3 l0 max

7

lu

[mm]

l0 max ≤ 2 b0

k1%

b0
ε%

= 	Support roller pitch on
upper side [mm]= 	Support roller pitch on the
return side [mm]= 	Maximum conveyor belt sag[mm]= 	Belt pull in the placeconcerned in N= 	Weight of goods conveyed
and belt in kg/m
= 	Relaxed tension/elongation
value in accordance withISO 21181 in N/mm width= Belt width in mm= 	Elongation at fittingBelt support

Snub rollers

Snub rollers are used when:– The conveyor belts’ arc of contact on
the drive drums is to be increased;

When using belts with a patterned
surface, we recommend lagging thedrums to reduce noise– The distance between the top andreturn side must be small for design
or construction reasons.

Minimum diameters for small
arcs of contact

If the arc of contact of snub rollers, support and guide rollers is small, the dia­meters of these rollers may equal 1/2
dmin, as long as the arc of contact does
not exceed 15° (for dmin see appropriate data sheets).

Transition lengths

The top edge of the end drum mustalign with the top edges of the centre
troughing rollers.
In the transition area of the troughedbelt from the drum to the belt support
point (and vice versa) the edges are
subjected to increased elongation.
As a result, the following guidelines
should be observed for the transition
length ls:

Is = belt width b0 · Factor c7[mm]

Please note:to ensure proper belt guidance, we
recommend the end drum should bea tapered/cylindrical design.

Troughing angle

15°

20°

30°

40°

c7

0.7

0.9

1.5

2

If the trough-shaped belt is supported by metal sheets, their edges towards theend rollers have to be well chamfered. In this case, we recommend you contact
Forbo Siegling application engineers.

8Knife edges

Fixed knife edges

The belt’s energy consumption increases when it rotates round a knife edge.
At the same time, because of the friction on the knife edge at high velocities, the belt can heat up significantly.
Where elongation at fitting is low(< 0.3 %) this friction can cause the belt
to shrink lengthways.
For this reason, the arc of contact
should be as small as possible (lowpower consumption and heat buildup, little pre-tensioning required).

Rolling knife edges

9

If the knife edge belt only runs in one
direction, instead of the usual screw
tension take-up, a force-dependent
tension roller can be installed after thedrive drum to ensure correct elongation in the belt. This moveable tension

Rolling knife edges are increasingly
being used because the friction on the
knife edge is reduced significantly.
Knife edge radii of 4 – 10 mm are normally used.

roller decreases the belt tension on the
knife edge and, in comparison with thefixed screw tension take-up, canreduce the frictional force on the knifeedge considerably.

Belt tracking

Fundamentals of straight conveyor
belt tracking

The conveyor must be as rigid as possible. Its shape must unaffected by forces exerted by the belt.
All drums on the conveyor, particularly
the drive drum, must be clean. Remove
rust inhibitor, oil, encrusted dirt fromslider beds or supports, drums and rollers. Exchange damaged or heavilyworn parts.

Another method is first to align thedrive drum so that it is at right angles
and then adjust the end drum till thecentre distances 1 are equal.

Goods should always be loaded onto
the centre of the belt and in the direction conveyed. Goods must not be
dropped from large heights.

Starting from the end drum, you canthen align each support roller or table/
slider bed section individually so thatthe axles are parallel.

Attention should be paid to the surface
quality of the drums.

< 90°

90°

Align knife edges, drive and end
drums, as well as support rollers so thatthey are parallel.
Align the end drums so that they areparallel to each other and at rightangles to the conveyor, by adjusting
the drums till each centre distance 1
and each diagonal 2 are equal.

Misaligned drums will cause belt
mistracking.

10

Drums are aligned at right angles:
the belt runs straight.

Effect of temperature

An uneven distribution of heat andload on the belt will lead to non-uniform changes in its inner tension state.
This creates control forces that may
cause the belt to mistrack. We recommend using an automatic belt tracking
device.

Effect of conicity and belt width

The drum is tapered/cylindrical.

A tapered/cylindrical drum centres aconveyor belt.
The higher the belt velocity and drum
diameter, the greater the centreing
effect.
For recommendations on conicity,refer to page 3.

Excessive conicity.
The belt does not hug drum and is not
guided. If the centre distance is small,select elongation at fitting so that the
belt edges always hug the drum.
Belt is too narrow.
Solution: Match drum proportions tobelt width.

Belt is wider than the drum.
Avoid at all costs because of unevencontrol, above all in laterally flexible
belt types.

11

Belt tracking

Effect of support rollers

Depending on the belt velocity,
troughed belt tracking can be
improved by rotating some of the siderollers up to approx. 3° in direction ofbelt travel.

You can often control non-troughed
belts adequately by installing some
support rollers, so that their horizontal
position can be adjusted. You can thenpivot them by about 2 – 4°.
We recommend this method for longbelts.

Effect of negatively-troughed rollers

A negatively-troughed set of rollers on
the return side centres the belt quite
well if placed near the tail drum.

12

ABelt control with tapered/cylindrical drums

B

Centre distance– Fit the belt and drums A + B sothat their axles are parallel until
the elongation at fitting you
require is reached.
– You can correct belt tracking bytensioning or slackening one endof the tension drum. The conveyor
belt will move towards the slacker
belt edge.
– You might need to use a belt
guidance system close to the end
drum (e.g. with short, wide belts).

Belt width

Adjustment

End drum

Drive drum

Tapered/cylindrical drums should be
adjustable in order to compensate for
production tolerances in the conveyor
and the belt.
If conveyors are ≥ 5 m long, both end
drums should be tapered/cylindrical.

In square conveyors (centre distance ~belt width) or where even poorer
length to width ratios occur, the belt
can no longer be adjusted withtapered/cylindrical drums. We recommend using an automatic belt control
system (page 15).

If tapered/cylindrical drums do not
guide the belt sufficiently, rollers
placed at an angle, or automatic belt
control devices can be used.

Using snub rollers

Adjustment

12–	All drums must be in their basic
setting so that their axles areparallel.
– Fit the belt and adjust tension
drum B (keeping the axle parallelto other drums) until the tension
required has been achieved.
–	Adjust belt tracking with drums C
and D. You might have to install abelt tracking system, by using
drum C or D as the control drum.

Very efficient tracking is achieved if you
use snub rollers C and D, above allwhen these come into contact withthe coated side of the conveyor belt
(because of a good friction coefficient).

The most efficient control is always
provided by the snub roller at the end
drum; by snub roller D running in
direction 1 and snub roller C running in
direction 2.

The snub rollers should be adjustable along the XY axis
(where the belt tracks upwards and downwards). As a result,the belt edges are hardly affected at all and major distortionof the fabric is prevented. By using snub rollers that can be
adjusted by motor, very effective automatic belt control canbe achieved (see page 15).
13

Belt tracking

Take-up system on the return side

Adjustment–	All drums must be in their basic
setting so that their axles areparallel.
– Fit the belt and adjust tension
drum E (keeping its axles parallelwith the other drums) until thetension required has beenachieved.
–	Adjust the belt tracking with snubroller C and if necessary with end
drums G and F or plate H. Youmight need a belt guidance system here.

End rollers G and F and tension drum E
can be adjusted in the direction thearrow is pointing in, whereby the tension drum E can also be used as adrive.

Please refer to the following and previous pages for more information on thelayout, design and control propertiesof drums A, B, C and D.

One simple solution is to mount drums
G, F and E on a plate H as a single unit
which is adjustable in the direction thearrow is pointing in.

Reversing conveyors

Adjustment–	All drums must be in their basic
setting so that their axles areparallel.
– Fit the belt and adjust tension
drum B (keeping its axles parallelwith the other drums) until thetension required has beenachieved.
– In reversing conveyors, belt tracking should be adjusted on thetapered/cylindrical drums, not thesnub rollers.

14

1

Important for perfect tracking inreverse operation is the precision withwhich the conveyor and belt havebeen manufactured.
Adjusting the belts for reverse operation takes some skill. A belt adjusted in
one direction, often mistracks in theother direction.

2

It takes some time until the drums
have been correctly adjusted. We recommend using a belt control systemfor both directions in very short andwide conveyors.

Knife edge conveyors

Adjustment­–	Adjust all drums and the knifeedge so that axles are parallel.
­– Fit the belt and adjust tension
drum C till its axles are parallelwith the other drums and the tension required has been achieved.
Keep the belt tension as low as
possible to avoid applying unnecessary stress and the build up ofheat (due to friction) on the knifeedge.
­–	Adjust belt tracking with drums B,
C, D and E or plate H. A belt guidance system might be advisable.

Shorter knife edge belts can be guided, as shown in the figure above. Drive
drum A should be tapered/cylindrical,
end drums B, D, E and tension drum C
cylindrical and adjustable in the direction the arrow is pointing in, so thatthe belt can be adjusted.

Automatic belt guidance systems are
generally used for long knife edge conveyors (e.g. in cooling tunnels). Belt
tracking is indicated by belt edge sensors.
As outlined on page 14, drums C, D
and E can be mounted onto an adjustable plate H.

Belt edge sensors

There are different kinds of belt edge
sensors, e.g. mechanical, hydraulic,electrical, optical and pneumatic. They
activate the control system when differences in the position of the beltedge occur.

Automatic belt control

15

Pneumatic device

Photoelectric cell

Belts are often controlled automaticallyby using swivel-mounted snub rollers.
They are usually adjusted with the aidof electrically-operated threaded spindles, or pneumatic cylinders after theactual values of the belt edges havebeen identified by the sensors.

SensorElectric eye

Purely mechanical solutions without
auxiliary power are also possible insmall conveyors.

Belt tracking

Using belts with longitudinal profiles

Transversal forces can be absorbed bylongitudinal profiles that have been
welded on. These profiles should be
supported by grooves in the slider bed
and not transmit any transversal forces
to the end drums. The grooves in theend drums must be at least 8 – 10 mm
wider than the profile.
This rule applies to center distances of>1.5 m. Where center distances are<1.5 m, lateral guidance can also be
provided via the grooves in the end
drums but, in this case, the slider bed
grooves must then be wider. We recommend that you consult Forbo
Siegling’s application engineers about
the design.
Please see Technical Information 2,
ref. no. 318 which gives details of minimum belt lengths, profile dimensions,types and minimum drum diameters.

In support rollers break the edgesof the groove

Groove in rollers or drums

End drum groove with 1 wedge profile(in centre)

1 longitudinal profile (in centre)
Table or support roller groove

2 wedge profiles at the sides of the beltz = approx. 5 – 10 mm

2 flat profiles on belt edgesz = approx. 5 – 10 mm

Loose concurrently-running plastic roller

Loose concurrently-running plastic roller

All types of enforced guidance systems
that could damage the belt edges,
such as for example check strips, roller
etc must be avoided.
If significant lateral forces occur, anautomatic control device should be
used.
The two halves of the table should
only be fixed in position, or the guide
strips attached, once the belt is running satisfactorily. Minimum play must
be retained to allow for tolerances.
Increase the groove depth h if the system is exposed to significant soiling. If
two longitudinal profiles are used, thedimension z must be big enough.

16

=	Active force [N](line load) resulting from belt pulland drums’ own weight.
FR= √ (2 . ε . k1% . bo)2 + (9.81 . mTr )2
I= Bearing centre distance [mm]d, da, di = Shaft diameter [mm]yTr
= Drum deflection [mm]mTr
= Drum weight [kg]k1%=	Relaxed belt pull [N/mm]
at 1 % elongation
FR

Bending of drums and rollers

Excessive drum deflection is often thecause of tracking problems in wide
belts.
Reasons for deflection:– Belt pull increasing proportionately
to the width of the belt
– Drum diameters are small due totechnical requirements.
Therefore, please ensure that thefollowing values are not exceeded:

ExampleA 2500 mm wide Siegling Transilon
belt, type E 12/2 U0/UH, rotates arounda steel drum, 150 mm in diameter and
10 mm thick at an arc of contact of180°. The belt runs horizontally.

– Tapered/cylindrical drum deflection
yTr ≤ 0.5 h,– in cylindrical drums greater deflectionof yTr ≤ h is permitted– See drive drums for h values.

E 12/2 approx. 0.2 to 0.3 % tensioned
Drum weight = 27 kg
E = modulus of elasticity N/mm2
E for steel = 2.1 · 105 N/mm2

I
da
di
k1%

FR = √(2 . 0.3 . 12 . 2500)2 + (9.81 . 27)2

Solid drum

= 18002 N
80 . 18002 . 26003
yTr =96 . 2.1 . 105 . (1504 – 1304) . π
yTr 1.81 > 0.35 mm = fzul

Reinforced by central braceyTr =80 . 9001 . 13003
96 . 2.1 . 105 . (1504 – 1304) . π

yTr = 0.23 mm < 0.35 mm

Seal strips

Where light bulk goods are concerned,
seal strips made of the conveyor beltmaterial can be a good low-friction
solution that seals at the same time.

17

=
=
=
=

Contact Forbo Siegling applicationengineers to help you choose suitablebelt types.

yTr =2600 mm
150 mm
130 mm12

80 · FR . I3
E . d4 . π . 96[mm]dTubular drumyTr =80 . FR . I3
E (da4 – di4) . π . 96

[mm]

di
da

Belt tracking

Sideskirts

Hopper walls or guide strips should
open in the direction of belt travel toprevent the products sticking between
the sideskirt (strip) and belt. They
should be as flush with the belt as necessary for the particular product in

Product discharge

Unit goods are frequently discharged
or transferred from the belt at thesides. In this case, ensure that the lateral forces acting on the belt are kept toa minimum. Swivel-mounted ploughsthat do not touch the belt are commonly used.
To avoid the belt mistracking whenit conveys the products upwards
or downwards, we recommend as
follows:

question. Sideskirts resting on the belt
increase the effective pull. Take thisincrease into account when sizing thebelt. Apply sideskirts at right angles tothe belt.

– Lag the support rollers in the feedzone with a friction lagging toincrease the friction coefficient
between the support rollers and thebelt (see above).
– Make changes in the design toincrease the areas of belt wrap in thefeed zone (see below).
Greater force is required in the case ofmultiple belt wraps due to counter
bending and where low temperatures
occur. By inserting a tapered/cylindricaldrum, belt tracking can be stabilised at
the sides too.
The belt cannot be guided via the beltedge in light conveyor belts.

Product feed

During loading operations, the conveyor belt is subjected to mechanicalstress vertically (from impact) and tangentially due to the relative velocity
between the goods conveyed and the
belt.

18

The designer’s task is to provide systems that enable the product to be fed
onto the belt gently and at a similar (orideally the same velocity) in the direction of belt travel. The products shouldbe placed on the middle of the belt, toavoid the belt mistracking (for example
using chutes, guide plates, funnels,
feed hoppers etc.).

Support rollers with abrasion-resistant,adhesive lagging

Cleaning devices

Scrapers

There are a number of methods
for re­moving product residues thathave stuck to the conveyor belt. How
effective these methods are does however depend on the conditions athand. In many instances, one or more
scrapers are sufficient: strips made ofplastic or rubber in a smooth or profile
steel frame, in a transverse position to
the direction of belt travel. It is important to select the scraper material carefully (do not use any old pieces of conveyor belt, as this will cause unnecessary wear and tear on the conveyor
belt).
The belt scraper (a) should be placed
as closely as possible to the belt or
touch it slightly. Since the scraper issubject to wear and tear, an adjustment method (slots etc) must be pro-

Brushes

To clean the belt, rotating brushes orbelt cleaning systems can be used. If
the pro­ducts conveyed are very sticky,
a water spray system or a water immersion system ensure the brushes do notclog up.

19

c

a

b

c

vided. Plough-type scrapers (b) areoften applied to the return side in frontof the end drum. The scrapers prevent
any products getting between the
drum and belt. There should only beslight contact with the belt.

When cleaning devices are used, allowances must be made when calculating
the power consumption:

Smooth drums without any lagging
can be kept clean with scrapers madeof steel (c). These scrapers can bemounted flush with the surface of thedrum and match the shape (e.g. trapezoidal) of the drum.

PR		

Please note:
If cleaning devices are improperly fitted, forces can occur at the sides thatcause the belt to mistrack.

FA= Contact force

FUR =	Effective pull of thecleaning device= 	Power consumption of
the cleaning device

FUR = 	 FA . µ
F .V
PR = UR1000

Siegling – total belting solutions
Committed staff, quality oriented organization and­production processes ensure the constantly high standardsof our products and services.

Forbo Siegling service – anytime, anywhere
The Forbo Siegling Group employs around 2,400 people.
Our products are manufactured in ten production facilities
across the world. You can find companies and agencies
with warehouses and workshops in over 80 countries.
Forbo Siegling service points are located in more than
300 places worldwide.

Forbo Siegling GmbH
Lilienthalstrasse 6/8, D-30179 HannoverPhone +49 511 6704 0
www.forbo-siegling.com, siegling@forbo.com

02/21 · UDH · Reproduction of text or parts thereof only with our approval. Subject to change.

Ref. no. 305-2

Forbo Movement Systems complies with total quality management principles. Our quality management system has
ISO 9001 certification at all production and fabrication sites.
What’s more, many sites have ISO 14001 environmental
management certifi­cation.