Machine for manufacturing paper such as tissue paper

A machine for manufacturing paper, such as tissue paper, includes a twin-wire former made up of a rotary forming roll and a pair of endless fabrics, each of which may be a wire or felt, lapped around the rotary forming roll to provide twin-wire web formation therewith. At the location where these endless fabrics travel beyond the forming roll they diverge from each other to define between themselves a diverging space where one of the endless fabrics has an upwardly directed surface on which the web is carried beyond the forming roll. This latter endless fabric carries the web to a press section where this latter endless fabric travels with the web through a first press nip of the press section defined between an inner press roll situated within the loop of the latter endless fabric and an outer press roll situated outside of the latter loop. This outer press roll is lapped by an additional endless fabric structure so that the web is situated at the first press nip between the latter additional fabric structure and the endless fabric which carries the web away from the forming roll. The web travels with the additional fabric structure around the outer press roll, to become detached from the endless fabric which carries the web away from the forming roll, and this outer press roll cooperates with a drying cylinder of a drying section of the paper machine to define therewith at least a second press nip.

BACKGROUND OF THE INVENTION 
The present invention relates to paper-manufacturing machines. 
In particular, the present invention relates to paper manufacturing 
machines designed to manufacture tissue paper. 
The machine to which the present invention relates includes a twin-wire 
forming section preceded by a single-wire forming section which serves to 
decrease the amount of dewatering which is required at the twin-wire 
forming section. Thus, a pair of endless fabrics, each of which may take 
the form either of a wire or felt, are lapped around a rotary forming roll 
to form a twin-wire former therewith, and one of these endless fabrics 
provides in advance of the forming roll a single-wire former with which, 
preferably, a dewatering structure such as a forming board cooperates. A 
headbox, which is preferably a hydraulic headbox, cooperates with that one 
of the endless fabrics where the single-wire web formation takes place to 
supply pulp stock thereto. 
In the manufacture of tissue paper it is well known to form the web on a 
relatively short wire section resembling a standard planar wire to which 
the headbox supplies the pulp stock at the region of a breast roll which 
is often formed with openings at its surface or which is provided with an 
internal vacuum, the web forming formation being carried by the wire past 
conventional dewatering members such as table rolls, deflectors, foil 
laths, suction boxes, and a suction roll, each of which removes water from 
the web. At the end of this wire section the partially dried web is 
transferred onto a pick-up felt, to be supported thereby while proceeding 
further towards the press and drying sections where additional drying 
takes place. In certain known constructions the above planar wire section 
has been entirely omitted. In this case the formation of the web is 
initially carried out entirely on a wire-covered suction breast roll from 
which the web is directly transferred onto the pick-up felt. 
Conventional constructions of the above type have a drawback in that, for 
example, the upper speed limit of the paper machine will be about 1500 
meters per minute. This relatively low maximum speed is necessitated 
because a relatively high draining pressure is essential, and this high 
draining pressure in turn causes an excessively great adherence of the web 
to the wire with resulting difficulties being encountered in connection 
with the detachment of the web from the wire. 
A further drawback of convention structures of the above type resides in 
the fact that the use of a separate pick-up means results in losses of 
energy as well as of fibers, and increases the first cost of the machine. 
Furthermore, conventional machines of the above type have certain 
limitations with respect to the use of inferior quality raw materials such 
as ground wood, deciduous wood, and waste paper pulp, owing to poor 
initial wet strength and also to poor ultimate strength. This drawback is 
primarily due to the well-known pick-up difficulties (occurrence of holes, 
web transfer, etc.) as well as to difficulties encountered in the reeling 
of the paper and its further conversion. 
Several types of twin-wire formers intended for the manufacture of tissue 
paper are well known. Most of these known twin-wire formers are so-called 
full throat formers, but these structures generally have the drawback that 
as a result of the throat forming process there is a poor formation of the 
web, and the web becomes excessively adherent to the wire, this latter 
undesirable result being caused by the extremely high dewatering rate at 
the initial web-forming stage. Moreover, with such structure difficulties 
are encountered at the web-transfer steps. 
With respect to the prior art reference may be made to U.S. Pat. Nos. 
3,378,435 and 3,537,954, the first of these patents disclosing a 
construction generally known as as a "Crescent" former. 
Also, reference may be made to U.S. Pat. No. 3,997,390 which discloses 
single-wire formation as an initial procedure with the possibility of 
controlling various process variables already used by practicing paper 
makers on Fourdrineer paper machines. In this connection the most 
essential process variables are the pulp stock discharge velocity with 
respect to the wire, the angle of incidence of the stock jet on the wire, 
and the rate at which water is drained from the suspension which is 
deposited on the wire. 
SUMMARY OF THE INVENTION 
In general it is an object of the present invention to provide improvements 
in known paper machines, particularly in paper machines designed to 
manufacture tissue paper. 
More specifically, it is a primary object of the invention to provide a 
former section wherein it is possible to use lower draining pressures that 
has heretofore been required at the initial stage of the forming process, 
while providing the possibility for increasing the draining pressure 
toward the end of the forming process, so that in this way detachment of 
the web from one wire of a twin-wire former section in such a way that it 
continues to be carried by the other wire thereof is facilitated. 
One of the most important objects of the present invention is to combine 
with procedures of the above type closed web conduction, which is to say 
web travel without any open draw, so that pick-up difficulties are 
eliminated. 
It is a further object of the present invention to influence the structural 
properties of the paper particularly by way of embossing the same, so as 
to increase the absorptivity and strength of the paper. 
Several other objects of the present invention include achieving a former 
wherein the dry matter content of the web is higher than has heretofore 
been possible prior to drying for example at a Yankee cylinder, providing 
a machine of simple and inexpensive construction primarily as a result of 
minimizing the number of expensive suction rolls which are required as 
well as the number of additional members which are subject to wear, and 
providing for the paper machine of the invention the advantages of 
perfusion drying by applying a pattern embosser which is inexpensive and 
results in lower operating costs. 
According to the invention, the web that is formed at a twin-wire former 
section of the machine is transferred on the top surface of an endless 
fabric means from the twin-wire former, without any open draw, to the 
press section of the machine and in particular to the first press nip 
defined by a pair of press rolls, in such a way that at the first press 
nip the web is interposed between the fabric which carries it from the 
twin-wire former and an endless fabric means forming part of the press 
means, the web being detached at the first press nip from the web which 
carries it to the press nip from the twin-wire former and continuing with 
the endless fabric means of the press means to a drying means where a 
second press nip is formed, for example between a Yankee cylinder and a 
press roll, while a specific pattern may be embossed on the web for 
example at the first press nip. 
Thus, the paper-manufacturing machine of the invention includes a twin-wire 
former means which includes a rotary forming roll means and inner and 
outer endless fabric means lapped around this forming roll means with the 
inner endless fabric means being situated at the forming roll means 
between the latter and the outer endless fabric means for carrying out 
twin-wire web formation between the inner and outer fabric means where 
they are lapped around the forming roll means. Each of these endless 
fabric means has an inner surface defining a closed loop and an outer 
surface directed away from the closed loop with twin-wire web formation 
taking place between the outer surfaces of the above inner and outer 
endless fabric means where they are lapped around the forming roll means. 
The inner and outer endless fabric means define between their outer 
surfaces where the inner and outer fabric means approach the forming roll 
means a converging space leading toward a starting end of a common path of 
travel of the inner and outer endless fabric means around the forming roll 
means where twin-wire web formation is initiated. One of the endless 
fabric means has at this converging space an upwardly directed outer 
surface, and a headbox means deposits pulp stock onto the latter upwardly 
directed outer surface for providing for single-wire web formation on the 
latter upwardly directed outer surface prior to twin-wire web formation, 
so that an initial dewatering action takes place during the single-wire 
web formation prior to further dewatering during the twin-wire web 
formation. The outer surfaces of the above inner and outer endless fabric 
means also define between themselves a diverging space where the inner and 
outer endless fabric means travel away from the forming roll means from a 
location where the inner and outer endless fabric means travel apart from 
each other at the end of the twin-wire formation at the location where the 
end of the lapping of the forming roll means by the inner and outer 
endless fabric means is situated. One of the endless fabric means has at 
the above diverging space an upwardly directed outer surface on which the 
web formed during twin-wire web formation rests while travelling beyond 
the forming roll means. A press section includes an inner press roll 
situated within the loop of that one of the above endless fabric means 
which carries the web beyond the forming roll means, the latter endless 
fabric means engaging the inner press roll of the press section. This 
press section includes also an outer press roll situated at the outside of 
the latter loop and cooperating with the inner press roll to define 
therewith the first nip of the press section. An additional endless fabric 
means is lapped around the outer press roll to provide for the web at te 
first press nip a path of travel between this additional endless fabric 
means and the endless fabric means which engages the inner press roll. The 
web travels beyond the first nip with the additional endless fabric means 
around the outer press roll to become detached from the endless fabric 
means which carries the web beyond the forming roll means. A drying 
section includes at least one rotary drying cylinder which cooperates with 
the outer press roll to define with the latter at least a second press nip 
where the web is detached from the above additional endless fabric means 
to travel around the drying cylinder in the drying section.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The particular machine illustrated is a tissue paper machine. 
The former part of the illustrated paper machine includes a hydraulic 
headbox 10 and a twin-wire former which includes the smooth-surfaced 
forming roll means 13 which is rotated about its axis in any suitable way. 
The forming roll means 13 rotates in a clockwise direction, as viewed in 
the drawing. The twin-wire forming means includes in addition to the 
forming roll means 13 an inner endless fabric means 11 and an outer 
endless fabric means 12. Each of the latter endless fabric means may be in 
the form of a wire or felt. During twin-wire web formation the inner 
endless fabric means 11 is situated directly next to the forming roll 
means 13 while the web W is compressed between the inner endless fabric 
means 11 and the outer endless fabric means 12, the fabric means 11 being 
situated between the forming roll means 13 and the fabric means 12 at the 
location where the pair of endless fabric means 11 and 12 are lapped 
around the forming roll means 13 to provide the twin-wire web formation. 
The inner surface of the outer endless fabric means 12 defines a closed 
loop in which are situated guide rolls 14 for the endless fabric means 12. 
The inner endless fabric means 11 also has an inner surface defining a 
closed loop, and within this closed loop there are a number of guiding 
rolls 15 for the endless fabric means 11, although there are also some 
guiding rolls 15 situated outside of the closed loop of the endless fabric 
means 11, in engagement with the outer surface thereof. In the event that 
the inner and outer endless fabric means 11 and 12 take the form of felts, 
there will be provided a conditioning apparatus for these felts, but such 
a conditioning apparatus has not been illustrated. 
The outer surfaces of the inner and outer endless fabric means 11 and 12 
define between themselves a converging space where the inner and outer 
endless fabric means travel toward the forming roll means 13 to start 
their common path of travel where the twin-wire web formation starts. It 
will be noted that in the particular example illustrated at this 
converging space the outer surface of the outer endless fabric means 12 is 
directed upwardly, and the hydraulic headbox means 10 deposits the pulp 
stock initially on this outer surface of the outer endless fabric means 12 
where the latter outer surface is directed upwardly so as to provide in 
this way a single-wire web formation before the twin-wire web formation 
takes place. In this way it is possible to provide a longer draining 
region for the web particularly during the initial stage of formation 
thereof. Thus it will be seen that the illustrated structure includes a 
single-wire web-forming portion 11a where draining of the deposited pulp 
stock is initiated, this single-wire web formation starting from the point 
O at the breast roll 14a and continuing up to the point C where twin-wire 
web formation starts, the web W having its initial stage of formation at 
this region 11a. 
After this initial part 11a of the draining region where single-wire web 
formation takes place there is within the loop of the wire 12 a dewatering 
means 21 which in the illustrated example takes the form of a forming 
board to promote dewatering action in a well-known manner by foil action 
and/or suction. Thus, at the location B the deposited pulp stock will 
undergo an effective dewatering action. An adjusting means 20 has been 
schematically illustrated as operatively connected with the hydraulic 
headbox means 10 so as to be capable of adjusting the size of the lip 
slice through which the pulp stock issues onto the outer surface of the 
endless fabric means 12 to initiate the single-wire web formation. By way 
of the adjusting means 20 it is possible not only to control the size of 
the lip slice but also to control the direction of the issuing jet of pulp 
stock with respect to the wire. 
From the location C where twin-wire web formation starts up to the location 
E where the twin-wire web formation ends, the pair of endless fabric means 
11 and 12 lap the forming roll means 13 through the sector .alpha. so that 
twin-wire web formation takes place at the region D where the inner and 
outer endless fabric means 11 and 12 lap the forming roll means 13. At 
this location the web is under compression between the inner fabric means 
11 and the outer endless fabric means 12, with dewatering taking place 
primarily by the action of a drainage pressure generated by centrifugal 
force (kinetic energy). The order of magnitude of the angle .alpha. by 
which the forming roll means 13 is lapped by the pair of endless fabric 
means 11 and 12 is appropriately 180.degree.. 
Of the several guide rolls for the outer endless fabric means 12, at least 
the roll 14b is supported so as to have its location capable of being 
adjusted, the adjusting means being indicated by the double-headed curved 
arrow passing through the roll 14b, so that in this way the degree of 
vacuum at the upper tangential point between the outer endless fabric 
means 12 and the forming roll means 13 (the location E) can be adjusted. 
By controlling this vacuum it is possible to influence the detachment of 
the web W from the outer endless fabric means 12 so as to assure that the 
web W follows the endless fabric means 11 when travelling beyond the 
location E. Thus it will be seen that at the region F the inner and outer 
endless fabric means 11 and 12 diverge from each other to define between 
themselves a diverging space where the outer surface of the endless fabric 
means 11 is directed upwardly, and the web W now is carried beyond the 
forming roll means 13 while resting on the upper outer surface of the 
endless fabric means 11. This reliable web transfer without any additional 
suction means can only be achieved by gradually increasing the draining 
pressure, and in this way a greater dry-matter content of the web W is 
achieved than in the case of previously known full throat formers. 
The web W that has thus been formed is transferred in accordance with the 
invention while adhering to the upper outer surface of the endless fabric 
means 11, away from the region where twin-wire web formation takes place, 
and it will be seen that the web W at this time is fully supported, 
without any open draw, on the outer surface of the endless fabric means 11 
while travelling substantially horizontally along a substantially straight 
path, without any intermediate steps or without any pick-up means or 
dewatering means additional to the fabric means being required. 
In this way the web W is transferred to the press section of the 
illustrated paper machine. This press section includes an inner press roll 
21 which defines with an outer press roll 22 of the press section the 
first press nip N.sub.1. The inner press roll 21 of course engages the 
inner endless fabric means 11 at its inner surface within the loop 
thereof. Thus, with the above-described machine of the invention the web, 
in accordance with an important feature of the invention, is delivered 
without any intermediate steps directly to the first press nip of the 
press section after being formed in the manner described above. 
With respect to the press section, the inner or lower press roll 21 is an 
efficiently dewatering roll inasmuch as it has a surface formed with 
spaces or recesses. Thus, for example, the dewatering press roll 21 can be 
formed at its outer surface with grooves or may have a number of blind 
bores extending partly through the thickness of the shell of the roll 21 
inwardly from the outer surface thereof. However it is also possible for 
the roll 21 to take the form of a wire-coated roll, or any roll having 
water-receiving spaces at its outer surface. 
The upper or outer press roll 22 at the first press nip N.sub.1 is a 
suction roll having a suction zone 22 .alpha.. Thus, at this first press 
nip N.sub.1 there is a substantially symmetrical dewatering in both 
directions. 
An endless fabric means 28 laps around the upper press roll 22 so that the 
web W at the first press nip is situated between the endless fabric means 
11 and the endless fabric means 28. The endless fabric means 28 may take 
the form, for example, of a suitable felt. This endless fabric means 28 is 
guided as schematically illustrated by guide rolls 27. Thus, as set forth 
above, dewatering at the first press nip N.sub.1 is symetrical, inasmuch 
as it takes place simultaneously in opposite directions, and the first 
suction zone 22 .alpha. provided at the upper or outer press roll 22 also 
contributes to the assurance that the web W is reliably detached from the 
endless fabric means 11 when travelling beyond the first press nip 
N.sub.1. Thus beyond the first press nip N.sub.1 the web W travels with 
the endless fabric means 28 while being at all times fully supported, 
which is to say while travelling in closed conduction without any open 
draw, and in this way the web reaches the second press nip N.sub.2 where 
the press roll 22 has a further suction zone 22 .beta.. 
As illustrated in the drawing, the second press nip N.sub.2 is defined by 
the outer press roll 22 and a rotary drying cylinder 45 of the drying 
section of the machine. This rotary cylinder 45 is a Yankee cylinder, the 
hood 47 which cooperates with the Yankee cylinder 45 being schematically 
illustrated. In some cases it is possible also to provide a third press 
nip at the Yankee cylinder 45, but such a third press nip is not required 
and is not illustrated. 
Thus, at the Yankee cylinder 45 the web W is detached from the fabric means 
28 and travels with the Yankee cylinder 45 which rotates in a clockwise 
direction, as viewed in the drawing. When the web travels on the cylinder 
45 beyond the hood 47, it is detached from the cylinder 45 by a doctor 
blade 46 which, as is well known, provides a creping action, the 
illustrated structure being particularly suitable for manufacturing tissue 
paper, as pointed out above. The web W removed by the doctor blade 46 is 
of course further guided as schematically illustrated at the right of the 
drawing beyond the cylinder 45 to suitable rolls where further treatment 
takes place in a well known manner. 
In the particular example illustrated in the drawing, the outer press roll 
22 is lapped by an additional endless fabric means which includes not only 
the endless fabric means 28 but also the endless fabric means 30 which is 
shown by way of a dot-dash line illustration. This endless fabric means 30 
is in the form of a wire suitable for pattern embossing, the wire 30 
lapping the roll 22 together with the felt 28 which is situated between 
the roll 22 and the wire 30. By means of this wire 30 it is possible to 
enhance properties which are important particularly in tissue paper, so 
that it is possible to provide the tissue paper with superior bulk, 
strength, and absorptivity. This wire 30 has a relatively open mesh and it 
produces impressions in the paper at the press nips N.sub.1 and N.sub.2. 
At the locations where the web W has thus been pressed, there will be an 
increased strength of the paper, while those areas of the paper which have 
not been contacted by the wire 30 will remain prominent, thus increasing 
the bulk and absorptivity of the paper. By way of this construction, which 
also is an important part of the invention, a structurally compact and 
inexpensive design is achieved. The wire 30 is guided by the illustrated 
rolls 31, the drawing also illustrating schematically a conditioning 
apparatus 32 for the wire 30. 
Thus, at the first press nip N.sub.1, the web W will travel between the 
endless fabric means 11 and the additional fabric means formed by the 
endless fabrics 28 and 30, with embossing taking place by way of the wire 
30 as set forth above. At the second press nip N.sub.2, the web travels 
between the drying cylinder 45 and the additional endless fabric means 28, 
30 with the embossing pressure also being provided by the wire 30 at this 
second press nip N.sub.2. 
Of course, the invention is not to be confined to the specific details 
presented above merely by way of example. The invention of course may vary 
within the scope of the inventive concept defined by the claims which 
follow.