CA1319000C

CA1319000C - Extended nip (shoe) press belt and its manufacture

Info

Publication number: CA1319000C
Application number: CA000595198A
Authority: CA
Inventors: William H. Dutt
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1988-04-29
Filing date: 1989-03-30
Publication date: 1993-06-15
Anticipated expiration: 2010-06-15
Also published as: FI891143A0; JPH054479B2; IT1231252B; FR2630679A1; GB8909159D0; SE467057B; DE3913110A1; DE3913110C2; FI89615B; FI891143A; FI89615C; GB2218940B; FR2630679B1; JPH0261191A; BR8901964A; IT8947892A0; SE8901033D0; SE8901033L; GB2218940A

Abstract

ABSTRACT OF THE DISCLOSURE
A special belt, intended for use in an extended nip (shoe) press in a paper-making machine, is disclosed. The belt is produced from an endless fabric base which is coated and impregnated with polymer sheet by applied heat and pressure. The purpose of the belt is to provide a surface which moves along with the felt as it passes through the nip in an extended nip press, thereby lowering the rate at which the felt will wear due to friction. The impermeability of the belt insures that the lubricant between the belt and the surface of the shoe will not contaminate the felt and fibrous web. A method of manufacturing such a belt with a platen press and special insert plate is also disclosed.

Description

I1 13:L90~10 JCS/JFG:~n 2437-29 `

EXTENDED NIP (SHOE) PRESS BELT
I A ITS MANUFACTURE

I BACKGROUND OF THE INVENTION

Field of the Invention This inv~ntion relates to a method of more efficient water removal from a wet sheet of ~ibrous material in the press section of a papermaking machine. More specifically, it relatas to the production of a special belt for use in an extended nip (shoe) press and of a method for the manufacture of such a belt.

Description of the Prior Art jThe efficient removal of water from the wet sheet of ¦ fibrous material in the press section of a modern papermaking 1, machine is an important factor in toward the economical I production of paper. Various approaches toward improved water removal have been taken in the past and have involved ll different press designs and improvements in the press I clothing or felt used to absorb water from the wet sheet.

The goal of such approaches has always been to remove as much water as possible from the sheet before it reaches the dryer section of the papermaking machine. In that section, heat is applied to the sheet to drive of~ the remaining water. The I more water removed in the press section, therefore, the less will remain to be heated out or evaporated in the dryer section. Costs associated with such heating will then be reduced, and the plant will be operated and paper produced more economically.
The press section of a papermaking machine has historically consisted of a series of double rolls through ~4~

13190d(~

which passes the wet fibrous sheet either supported on top of an absorbent felt or sandwiched between two such felts. The ¦ region between the two rolls, referred to as the nip, is where the felt and wet fibrous sheet are compressed together, 1 and where water, squeezed from the sheet, is absorbed by the I felt.
Because the nip is of limited spatial extent, the dwell ¦ time, or time spent there by a given incremental length of felt and wet fibrous sheet, is brief. As a consequence, the press section of many papermaking machines commonly consists of a series of press rolls, so that sufficient water can be , removed from the sheet before it reaches the dryer section.
¦1 Further, as a way to improve water removal, the surfaces of the press rolls can be drilled with holes or I grooved, in order to provide ways for water to pass from the j falt. This will reduce rewetting of the sheet upon exit from the nip. As another refinement, suction can be applied from within a drilled press roll in order to draw additional quantities of water from the felt and away from the sheet.
ll Such a device is referred to as a suction press.
¦ Other approaches toward the removal of increased ¦¦ quantities of water in the press section involve attempts to lengthen the dwell time in the press nip. This can be accomplished by covering the press roll with an elastic, compressible material, so that the nip will be slightly broadened when the press rolls are brought together. Dwell time will be extended because it will take a given incremental length of wet sheet longer to cover this slightly greater distance.
I The greatest increase in dwell time, however, can be realized through the use of the extended nip (shoe) press.

Here, one of the two rolls in a conventional press is ~ 3~0~

replaced with a pressure shoe. The shoe is typically as wide as the press roll in the cross-machine direction. The side of the shoe facing the press roll is cylindrically concave, and of approximately the same radius as the roll. When the shoe is brought up to a position close to the roll, a narrow gap is cxeated between the surface of the spinning roll and the concave, stationary surface of the shoe. With a shoe of appropriate size, the length of this gap will be much l greater than that of the nip in a conventional two-roll press. Therefore, by passing the felts and wet fibrous sheet 1~ through such a gap, a greater dwell time is obtained and more ! 1I water is removed from the sheet.
¦ A potential problem arises, however, with the use of such a press. As the surface of the shoe is not itself in motion, friction between the felt and that surface will cause the felt to wear. To alleviate this problem, and to make it less likely that the felt will be damaged by friction, a 1 special belt is run between the surface of the shoe and the ¦ felt. Lubricated on the side in contact with the shoe, such a belt provides a surface moving in the same direction as the felt. Less frictional wear on the felt will occur because it j moves with the belt through the nip and does not itself slide over the shoe.
.,, SUMMARY OF THE INVENTION
This invention consists of a special belt for use in an extended nip (shoe) press and a method by which it can be manufactured. The object of the invention is to provide a means of producing these special belts in an economical way which requires fewer manufacturing steps than previously were necessary, and which ailows the use, as impregnates into a fabric base, of polymeric materials that could not Q ~

previously ba used. The fabric base is so impregnated in order to prevent the lubricating fluid on the side of the belt actually in contact with the surface of the shoe from passing through and contarninating the wet sheet and felt.
The invention envisions the use of a large heated platen press composed of two opposed platens and a special insert plate. The base fabric for the belt is provided in endless form, and is placed around the insert plate in a sleeve-like fashion.
Sheets of polymer are then placed in the platen press with the base fabric sleeve and the insert plate.
Pressure and heat are then applied, by closing the platen press which will cause the base fabric to become impregnated with the polymer. If required, the polymer can also be cured in this manner.
After a suitable time, the platen press is opened, and the base fabric sleeve is advanced on the insert plate until areas not yet impregnated with polymer are above and below the insert plate. Sheets of uncured polymer are inserted as before, and the above process is repeated until the entire inner surface of the base fabric sleeve has been so treated.
Modifications to this procedure may be suggested by the nature of one's inlmediate application. For example, if a higher degree of quality control is desired, only one side of the insert plate need be used at any given time. In such a case, heat and pressure will be applied with only one of the two platens, and the other will be unheated. Alternatively, one could apply the polymer sheet to both sides of the base fabric rather than to the inside alone.
B

Both the belt and its method of production have ! numerous advantages to commend themselves to future users.
Through the use of a platen press and insert plate to produce the special belts, one obtains a final product which did not 111 have to be turned inside out during manufacture. In addition, the current need to apply the polym~r to the surface of the base fabric as a coating, which would later I require curing and grinding, is eliminated. As a result, I equipment costs can be saved, processing time shortened, and a belt superior to those currently available produced. The I thickness uniformity of the resulting belt can easily be ! I controlled by maintaining a constant spacing between the ~1 insert plate and the upper and lower platens. Finally, '~ through the use of an insert plate and/or platens whose surfaces are not smooth a belt, whose surfaces have ridges, grooves, or other surface characteristics, rather than being j smooth, can be produced.

BRIEF DESÇRIPTION OF THE DRAWING
! ¦ In Figura 1 is depicted a scheme by which the special belt for the extended nip (shoe~ press can be manufactured according to this invention. Shown there is one mode in which this invention can be practiced, whereby polymer sheet is placed only between the base fabric and the insert plate.
Figures 2a, 2b, and 2c are plan views of the surface of an insert plate or platen which is smooth, grooved, or which has round protrusions, respectively, in order to impar~
corresponding surface characteristics, as desired, to the extended nip press belt.
Figures 3a, 3b, and 3c are section views of the insert plate or platen shown in Figures 2a, 2b, and 2c, respect ively .

13190~0 ~i ~ETAILED DESCRIPTION OF THE P~EFERRED EMBODIMENT
As shown in Figure 1, the method envisioned for ¦ prod~acing the special belts of this invention requires the use of a heated platen press having upper 1 and lower 2 platens. A special insert plate 3 fits into the space ~ between the upper 1 and lower 2 platens. In this~preferred j~ embodiment of the invention, the surfaces of these platens have identical linear dimensions and areas. The upper and ¦1 lower surfaces of the insert plate 3 facing the platens have these same size parameters. In addition, the platens 1, 2 and insert plate 3 should have at least the same width as that of the belts they will be used to produce.
! The base fabric 4 for the belt, supplied in endless form, is arranged around the insert plate 3 in a sleeve-¦ like fashion in the spaces between said plate and the upper 1 and lower 2 platens. This base fabric 4 can be either ~ single - or multi-layered and woven from polyester ! monofilament in a weave pattern that is sufficiently open to permit it to be completely impregnated and coated. This will eliminate the production of voids which would allow the lubricating fluid used between the belt and the shoe to pass through the belt and contaminate the felt and fibrous web.
i The base fabric 4, finally, can be supplied in any length as ¦¦ the method of this invention does not require the use of a mandrel.
Rolls 5, dxiven by an appropriate means, are used to keep the base fabric 4 taut, by being adjustable as indicated by the arrows 6, and to advance it section-by-section as it il is being treated in the manner taught by this disclosure.
Sheets of an uncured polymer 7, such as polyurethane, are placed between both sides of the insert plate 3 and the portions of the base fabric 4 above and below the insert . I

l3~sa~0 plate 3. The platen press is then closed by bringiny the upper 1 and lower 2 platens toward each other, compressiny the base fabric 4, polymer sheets 7, and insert plate 3 together. Pressure and heat from the platen press melt the polymer sheets 7 and force this liquified material into and around the woven structure of the base fabric 4. This procedure can also cure the polymer.
At the end of the time interval required for the above, the platen press i5 opened, by moving the upper 1 and lower 2 platens apart. The base fabric 4 is then advanced, by using the rolls 5, to the point where areas of the base fabric 4 into which no polymer sheet 7 has yet been forced are located above and below the insert plate 3. New polymer sheets 7 are then inserted between both sides of the insert plate 3 and the portions of the base fabric 4 above and below it. This time, however, the sheets are properly and tightly butted against the just previously pressed-in sheet, and the pressing-in process describecl above is repeated.
The steps of this procedure are repeated until the inside of the base fabric 4 has been completely treated in this manner, thus producing the special belt of this invention.
As noted above, it may often be of interest to produce an extended nip press belt whose surfaces are not absolutely smooth but rather have grooves, indentations, or other surface characteristics. This can be accomplished by using insert plates and/or platens having surface characteristics which will impart corresponding ones to the belt during production. Figure 2a shows a plan view of a smooth insert plate or platen, and Figure 3a is a section view of the same, for use in making a smooth belt. A grooved belt can be manufactured by using a grooved insert plate and/or platen 13~900J
having grooves 8, shown in the plan view of Figure 2b and in the ~ect.ion view of Figure 3b. Lastly, a belt haviny indentations can be produced by using an insert plate and/or '1 platen having protrusions 9, as shown in Figures 2c and 3c.

I¦ An infinit~ number of other possible surface patterns can be ¦ obtained through the use of appropriate insert plates and/or platens during he manufacture of the belt.
Modifications to the belt and this manufacturing process j would be obvious to one s]cilled in the art without departing I from the scope of the invention as defined in the appended claims.

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Claims

1. A method for manufacturing a belt, for use in extended nip (shoe) presses of a papermaking machine, which comprises the steps of:
(a) placing a fabric base and an insert plate in the space between the upper and lower platens of a platen press, said fabric base being supplied in endless form and being placed in sleeve-like fashion around said insert plate, said insert plate, and said upper and lower platens having substantially plane surfaces parallel to one another, said substantially plane surfaces being smooth;
(b) inserting polymer sheet in the platen press with the insert plate and fabric base;
(c) closing the platen press upon the insert plate, polymer sheet, and fabric base by moving said upper and lower platens toward one another until said insert plate is separated from said upper and lower platens by a predetermined spacing;
(d) heating at least one of said upper and lower platens;
(e) opening the platen press after a time sufficient to melt the polymer and force it, in liquid form, into the structure of the fabric base, and to cure said polymer;
(f) advancing the fabric base in the platen press just to a point where fabric, as yet untreated with polymer, is adjacent to the insert plate;
(g) inserting polymer sheet into the platen press, closely butting said polymer sheet to the polymer sheet previously pressed-in; and g (h) repeating steps (c) through (g) until the entire length of the fabric base has been so coated and impregnated with polymer, said polymer also being cured, so that said belt is coated, impregnated, cured, given a substantially plane, smooth surface and a uniform thickness in one manufacturing operation.

2. The method of claim 1, wherein said fabric base is maintained on a taut condition around said insert plate by a first roll and a second roll on opposite sides of said platen press.

3. The method of claim 2, wherein said first roll and said second roll advance said fabric base during the manufacture of said belt.

4. The method of claim 1, wherein said polymer sheet is inserted between the upper and lower surfaces of said insert plate and said fabric base.

5. The method of claim 1, wherein said polymer sheet is inserted in said platen press on both sides of said fabric base.

6. The method of claim 1, wherein said base fabric is woven from polyester monofilament in an open weave pattern.

7. The method of claim 6, wherein said base fabric is a single-layered weave.

8. The method of claim 6, wherein said base fabric is a multi-layered weave.

9. The method of claim 1, wherein said polymer is polyurethane.

10. The method of claim l, wherein said substantially plane surface of said insert plate is a completely smooth, plane surface.

11. The method of claim l, wherein said substantially plane surfaces of said upper and lower platens are completely smooth, plane surfaces.

12. The method of claim 1, wherein said substantially plane surface of said insert plate has a pattern to be impressed on a surface of said belt.

13. The method of claim l, wherein said substantially plane surfaces of said upper and lower platens have patterns to be impressed on a surface of said belt.