Braided base fabrics for shoe press belts

- 28036 Madrid

IS 2 216 166 T3

DESCRIPTION

Braided base fabrics for shoe press tapes.

Background of the invention

1. Field of the invention

The present invention relates to mechanisms for the removal of water from a web of material and, more particularly, from a fibrous web that is being treated to obtain a paper product in a paper machine. Specifically, the present invention is a waterproof tape designed for use in a long press pass press of a papermaking machine. The tape can also be used in other papermaking and paper handling applications, such as calendering.

two. Description of the prior art

In the course of the papermaking process, a fibrous web is formed on a forming wire by deposition of a fibrous slurry or pulp thereon. A large amount of water is drained from the pasta during this procedure, after which the newly formed web continues to a pressing section. The pressing section includes a series of pressing pressing steps, in which the fibrous web is subjected to compressive forces calculated to remove water from it. The web finally proceeds to a drying section, which includes heated drying drums around which the web is driven. Heated drying drums reduce the water content of the web to a desirable value through evaporation.

Increasing energy costs have made it increasingly desirable to remove as much water from the web as possible before it enters the drying section. Drying drums are often heated from within by steam, and the associated costs can be substantial, especially when a large amount of water needs to be removed from the web.

Traditionally, thought sections have included a series of clamping passages made up of pairs of adjacent cylindrical press rollers. In recent years, the use of long press tightening steps has been found to be advantageous over the use of tightening steps formed by pairs of adjacent press rollers. The longer a band can be subjected to pressure in the tightening step, the greater the amount of water that can be removed from it and, consequently, the less water will remain within the band to be evaporated off in the band. drying section.

The present invention relates to shoe type long squeeze pitch presses. In this variety of long squeeze pitch press, the squeeze pitch is formed between a cylindrical press roller and an arcuate pressure shoe. The latter has a cylindrical concave surface having a radius of curvature close to that of the cylindrical pressing roller. When the roller and shoe are brought into close physical proximity to each other, a clamping pitch is formed that can be five to ten times longer, depending on the machine direction, than that between two rollers. pressing. This increases the so-called residence time of the fibrous web in the long clamping step, while maintaining the same level of compression per square centimeter in pressure force as is used in a two-roll press. The result of this new long squeeze pitch technology has been a drastic increase in the removal of water from the fibrous web in the long squeeze step, compared to conventional paper machine squeezes.

A shoe-type long press pass-through press requires a special belt, such as that shown in US Patent No. 5,238,537. This belt has been designed to protect the press fabric that supports, transports and dries or drains the fibrous web, from accelerated wear that could occur as a result of direct sliding contact with the pressure shoe in static position. Said belt must be provided with a smooth and impermeable surface that slides or slides over the stationary shoe, on a lubricating film of oil. The belt travels through the clamping passage at approximately the same speed as the press fabric, thereby subjecting the press fabric to a minimal degree of rubbing with the surface of the belt.

The tapes of the variant shown in US Patent No. 5,238,537 are made by impregnating a woven base fabric, which takes the form of an endless loop, with a synthetic polymer resin. Preferably, the resin forms a coating of some predetermined thickness on at least the inner surface of the tape, such that the yarns from which the base fabric is woven can be protected from direct contact with the fabric component. Long squeeze pitch press arcuate press shoe. It is specifically this coating that must present a smooth and impermeable surface in order to slide easily over the lubricated shoe and prevent any quantity of the lubricating oil from penetrating into the belt structure and contaminating the press fabric, or fabrics, as well. like the fibrous band.

The tape base fabric illustrated in US Patent No. 5,238,537 can be woven from single filament yarns into a single or multilayer fabric, and is woven in such a way that it is open enough to allow the impregnation material to fully permeate the fabric. This eliminates the possibility of any empty or hollow space forming in the final tape. Such voids can allow the lubricant that is used between the belt and the shoe to pass through the belt and contaminate the press fabric (s) and fibrous belt.

Once the impregnation material has dried or hardened to a solid state, it is mainly bonded to the base fabric by means of mechanical interlocking, in which the dried impregnation material surrounds the threads of the fabric. base. In addition, there may be some kind of chemical bonding or adhesion between the dried impregnation material and the yarn material of the base fabric.

While the tapes illustrated in US Patent No. 5,238,537 have proven to be durable, reliable, and long-life in long press pitch presses, improvements are continually being made to both the structure of such tapes and the hardware. methods for their manufacture. Some of the improvements

ES 2 216 166 T3 are driven by the need to prevent the polymeric resin coating from peeling or peeling from the base fabric, and refer to means of improving mechanical, and possibly chemical, interlocking or coupling between the fabric of base and liner. Other improvements relate to the structure of the base fabrics themselves, and are designed to make the base fabrics stronger and more durable, or to conform to the exact dimensional specifications required for a given application. Still other improvements relate to the coating processes themselves, and are aimed at the complete impregnation of the base fabric and the provision of a uniformly thick coating of polymeric resin material on the inner surface of its endless configuration, of In this way, the step of inverting the tape (turning it inside out) during the manufacturing process is omitted.

The present invention relates to the base fabric of a long squeeze pitch pressure tape. More specifically, the present invention is a long press pitch press belt having a base fabric in the form of an endless braided structure. In addition to being useful as a long press pitch press belt, the present invention can also be used in other papermaking and paper handling applications such as calendering.

Summary of the invention

Therefore, the present invention consists of an endless belt impregnated with resin and intended for a press with a long squeeze pitch. The belt can also be used in a shoe-type calender, as well as in both a long-press pitch press and such a calender comprising a cylindrical press roller and an arcuate pressure shoe that together define a tightening step between them. The resin-impregnated endless belt passes through the pinch passage in direct sliding contact with the arcuate pressure shoe, and separates a fibrous web being treated at this location, and perhaps a press fabric or fabrics that support the fibrous web, of the arcuate pressure shoe, thereby protecting the fibrous web and press fabric or fabrics from damage caused by direct sliding contact with the arcuate pressure shoe, and from contamination with any amount of lubricant present in the bowed pressure pad.

The resin impregnated endless belt comprises a base fabric provided in the form of a braided structure having a plurality of layers of braided yarns. In each of the layers, at least one thread thereof extends until it penetrates a continuous layer, in order to form a mutual interlock between them. The layers are consequently stuck together, and are not able to detach from each other. The base fabric is provided in the form of an endless loop having an inner surface, an outer surface, a longitudinal direction, and a transverse direction, and is assembled in accordance with the teachings of commonly assigned U.S. Patent No. 5,501,133, in the name of Brookstein et al. This patent was disclosed on March 26, 1996 and is entitled "Apparatus for the manufacture of a braid structure."

At least the inner surface of the base fabric is coated with a polymeric resin material, such as polyurethane. The coating permeates the base fabric and makes it impervious to liquids such as oil and water, and is polished and burnished to provide a smooth surface and to give the tape a uniform thickness.

The present invention will now be described in a more exhaustive degree of detail, making frequent references to the figures, which are listed and identified as follows.

Brief description of the drawings

Figure 1 is a cross-sectional side view of a long press pitch press;

Figure 2 is a perspective view of a tape of the present invention;

Figure 3 is a perspective view of an alternative embodiment of the tape; and Figure 4 is a perspective view of another embodiment of the tape.

Detailed description of the preferred embodiments

In Figure 1 there is shown, in a cross-sectional side view, a long press pass press for removing water from a fibrous web being processed into a paper product on a paper machine. The press nip 10 is defined by a cylindrical press roll 12 and an arcuate pressure shoe 14. The arcuate pressure shoe 14 has approximately the same radius of curvature as the cylindrical press roll 12. The distance between the cylindrical press roller 12 and the arcuate press shoe 14 can be adjusted by hydraulic means operatively attached to the arcuate press shoe 14 in order to control the load of the clamping passage 10. The smooth cylindrical pressure roller 12 may consist of a roller controlled by a crown, which engages or engages with the arcuate pressure shoe 14 in order to obtain a level clamping pitch profile in the transverse direction to the machine.

The long squeeze pitch press belt 16 extends in a closed loop passing through a squeeze passage 10, thus separating the cylindrical press roll 12 from the arcuate pressure shoe 14. A wet press cloth 18, as well as a fibrous web 20, which are being processed to form a sheet or sheet of paper, pass one next to the other through the clamping passage 10, as indicated by the arrows in Figure 1 . The fibrous web 20 is supported by the wet press fabric 18 and comes into direct contact with the smooth cylindrical press roll 12 in the clamping step 10. The fibrous web 20 and the wet press cloth 18 proceed through the passage. torque 10, as indicated by the arrows. The long squeeze pitch press belt 16, which also travels through the squeeze pitch 10 as indicated by the arrows, that is, counterclockwise (counterclockwise), such and as illustrated in Figure 1, it protects the wet press fabric 18 from direct sliding contact against the arcuate pressure shoe 14, and glides over it on a lubricating film of oil. The long press pitch press belt 16 must therefore be impermeable to oil, such that neither the wet press cloth 18 nor the fibrous web 20 is contaminated with it.

In Figure 2 a perspective view of the press belt 16 of tightening step lar3 is provided.

ES 2 216 166 T3 go. The tape 16 has an inner surface 28 and an outer surface 30. On the outer surface 30 the base fabric of the tape 16 may be visible.

Figure 3 is a perspective view of an alternative embodiment of the tape 32. The tape 32 has an inner surface 34 and an outer surface 36. The outer surface 36 is provided with a plurality of grooves or grooves 38, arranged, for example , around the belt 32 and according to its longitudinal direction, in order to temporarily store the water extracted by pressing the fibrous belt 20 in the clamping step 10.

Alternatively, the outer surface of the tape may be provided with a plurality of blind holes arranged in a certain desired geometric configuration for temporary water storage. Figure 4 is a perspective view of such an alternative embodiment of tape 40. Tape 40 has an inner surface 42 and an outer surface 44. The outer surface 44 is provided with a plurality of knockouts 46, which are so named because they do not extend completely through the belt 40.

The long press pitch press belts 16, 32, 40 of the present invention include a base fabric consisting of a braided structure. The braided structure comprises a plurality of braided layers of yarns in which the layers are laid in a single pass of a braiding machine, such that at least one layer yarn extends into a contiguous layer to form an interlock or mutual blocking between the layers.

The braided structure of the base fabrics can be manufactured in accordance with the teachings of commonly assigned U.S. Patent No. 5,501,133 (the

Patent 5,501,133), in the name of Brookstein et al., And entitled "Apparatus for the manufacture of a braid structure". Patent 5,501,133 shows a multilayer braided structure in which the layers are braided with each other. The mutual braiding between the layers provides a bond between them that prevents the detachment of the multiple braided layers from one another.

The interlocking between the layers may consist of a direct interlocking in which the interlocking or interlocking yarn passes from a first layer to a second contiguous layer, and passes around at least one yarn of the second layer.

Alternatively, the interlocking between the layers can be an indirect interlocking in which an interlocking thread passes from the first layer through the second layer and into another, not necessarily contiguous, layer of the structure, and passes through a strand of the other layer so that it serves to join the first layer together with the other layer and, at the same time, to join the layers located between them.

In order to manufacture a base fabric for a long press pitch press belt, the braided structure may be of a hollow tubular shape. In view of the fact that long press pitch press belts, depending on the size requirements of the long press pitch presses in which they are installed, have lengths between approximately 3 and 12 meters (approximately 10 to 40 feet), measured lengthwise around their endless looping shapes, and widths between about 250 and 1. 125 centimeters (approximately 100 to 450 inches), measured crosswise across these shapes, production of the base fabric may require a cylindrical braiding mandrel that has a diameter between approximately 1 to 4 meters (approximately 3 to 12 feet ), and a length between approximately 250 and 1,125 centimeters (approximately 100 and 450 inches).

The multilayer braided structure of the base fabric is made by supplying a plurality of yarns from a first set of movable package carriers to a braiding zone to form a braid layer gap or passage in which each mobile package carrier traverses a first predetermined serpentine or spiral path, and supplying a plurality of yarns from a second set of movable package carriers to a braiding zone to form a gap or braiding layer passage in which each movable package carrier in the second set traverses a second predetermined serpentine run, and in it each of the serpentine paths has been arranged in such a way that at least one package carrier of each set is capable of carrying a thread from its respective layer to the bosom of the other layer, in order to intersect it with the another layer.

As mentioned above, the second layer can be contiguous with the first layer. Alternatively, the second layer can be separated from the first layer so that a number of intermediate layers are interposed between them. In such circumstances, a yarn associated with the package carrier is used that runs between the first and second layers so that it passes through all of the intermediate layers before forming a positive interlock with the second layer.

It is also possible to supply yarns from static bundle carriers to the braiding zone between two or more layers in such a way as to interlock with yarns from respective movable bundle carriers. The yarns supplied from the static package carriers maintain a longitudinal or axial orientation with respect to the cylindrical braiding mandrel. In this way, the base fabric can be provided with reinforcing yarns that extend in the cross belt direction, or cross machine direction. Such reinforcement is useful when the belt is of the "press sleeve" variety, which is held by clamping rings on the edges extending in the width direction of the press.

The cylindrical braiding mandrel may be located in the braiding zone, in order to form the required hollow braid structure. The first layer of the braid is then formed on the mandrel, and the second layer and subsequent layers are formed on top of the first layer. The mandrel can be moved through the braiding zone as braiding takes place, such that a hollow and continuous braided structure is built thereon. All layers of the multilayer braided structure are drawn or laid in a single mandrel pass through the braiding machine.

The plurality of package carriers and serpentine paths are arranged on the surface

ES 2 216 166 T3 of a tubular braiding machine, the inner surface having a plurality of serpentine paths formed therein. The moving package carriers traverse the serpentine paths; the static package carriers are fixed on the inner surface of the tubular braiding machine.

The braid-forming zone is preferably located on the longitudinal axis of the tubular braiding machine, and as the braided structure is formed, it, or more specifically, the cylindrical braiding mandrel, travels through the tubular braiding machine, along the longitudinal axis thereof.

In order to be used as a base fabric for a long press pitch press belt, the braided structure preferably consists of threads that form an angle of 85 ° or more with the longitudinal axis of the cylindrical braid mandrel. In other words, the threads of the base fabric will define helices twisted over one another to the left and to the right, each of which forms an angle of 5 ° or less with respect to the machine direction of the passing press belt. long tightening. This will make the long pinch press belt less likely to warp as a result of machine direction applied stress, and can be achieved by minimizing the number of movable package carriers that are used to make the braided structure. .

The base fabric can be made from any of the varieties of yarn used by those of ordinary skill in the art to produce fabrics or fabric for use in paper machines. Single-filament yarns are preferred, although single-filament doubled yarns, multi-filament yarns, and multi-filament doubled yarns can also be used. The yarns can be made of any of the polymeric resins from which yarns of the fabric intended for papermaking machines are usually extruded, such as polyamide, polyester, polyether-etherketone (PEEK - "polyetheretherketone") resins. , polyaramid and polyolefin.

The braided structure of the base fabric must have a sufficient opening or gap to guarantee its complete impregnation by the polymeric resin material with which it is to be coated. Complete impregnation eliminates the possibility of unwanted voids forming in the finished tape. Voids are particularly undesirable because they can allow the lubricating oil that is used between the belt and the bowed pressure shoe to pass through the belt and contaminate the press fabric 18, or press fabrics, as well as the fibrous web. wet 20 that is being treated to become paper.

Once the braiding of the base fabric is complete, it can be removed from the cylindrical braiding mandrel and coated with a polymeric resin material using techniques well known in the art. Alternatively, the coating can be carried out, at least in part, while the base fabric is still on the cylindrical braiding mandrel.

The polymeric resin material is applied to at least one of the surfaces of the base fabric, this surface being the one that will ultimately be the inner surface of the tape. As the inner surface slides through the arcuate and lubricated pressure pad 14, the coating of the polymeric resin material protects the base fabric from such sliding contact and from wear as a result of abrasion that would otherwise occur. would produce. The polymeric resin material also permeates the base fabric and makes the tape oil and water tight. The polymeric resin material can be polyurethane, and, in such a case, it is preferably a composition thereof made up of 100% solid components, in order to avoid the formation of bubbles during the curing or drying process that the resin undergoes. polymeric after being applied to the base fabric. After drying, the coating of polymeric resin material is polished and burnished in order to provide the tape with a smooth surface and a uniform thickness.

Alternatively, both surfaces of the base fabric can be coated with a polymeric resin material. After the polymeric resin material has dried, both the inner and outer surfaces of the tape can be polished and honed to provide the tape with smooth surfaces and uniform thickness. Finally, the external surface can be provided, by cutting, marking, engraving or drilling, with a plurality of grooves or grooves, for example, according to the longitudinal direction around the belt, or with blind holes for the temporary storage of the extracted water. by pressing the fibrous web 20 in the pressing tightening step 10.

It will be appreciated that various modifications of the foregoing will be obvious to one of ordinary skill in the art, without departing from the scope of the claims which follow.