GB2080842A

GB2080842A - Woven papermakers' felt

Info

Publication number: GB2080842A
Application number: GB8121064A
Authority: GB
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1980-07-10
Filing date: 1981-07-08
Publication date: 1982-02-10
Also published as: JPS5742995A; BE889574A; DE3127359A1; FR2486549A1; CA1148003A; NL8103275A; AU7270281A; NZ197686A; AR228609A1; IT8148864A0; BR8104388A; GB2080842B; ZA814577B

Abstract

A papermakers' dryer felt comprises a first surface ply 12 of machine direction monofilament yarns 22, which are beneath the paper contacting face provided entirely by the cross-machine direction yarns 14, whose peaks 16 contact from 20% to 50% of the surface area of the paper, and a second ply 20 of cross-machine direction yarns 16' bound to the first ply 12 by the machine direction monofils 22. The cross-machine yarns may be mono or multifils and the peaks 16 may be abraded to provide the required paper contacting area. <IMAGE>

Description

SPECIFICATION Dryer felt fabric The invention relates to paper machine clothing and more particularly relates to fabrics useful as dryer felts, and their use.

The art is replete with descriptions of dryer felts and dryer felt fabrics. In spite of the wide variety of materials available, the ideal dryer fabric is yet to be found.

In recent years, dryer fabrics have been developed which are constructed partially or entirely from monofilaments. However, such fabrics have not been entirely satisfactory when employed to fashion dryer felts. The monofilaments are subject to abrasion and moist heat hydrolysis. In the prior art constructions the load bearing machine direction monofilament yarns may be rapidly degraded under some conditions of use so that the life of the dryer felt is shortered.

With the structured fabrics of the present invention, employed as dryer felts, the crossmachine direction yarns support the paper sheet being dried. The monofilament machine direction yarns are thus protected from direct contact with degradative elements. The overall operating life of the dryer felt is significantly increased over felts where the monofilament machine direction yarns are in contact with the paper sheet being dried.

Representative of the state of the art in regard to dryer fabrics are those described in U. S.

Patents 3,573,164 and 3,905,863.

The invention comprises a fabric for use as a paper machine dryer felt, which comprises; a first sinuous layer of cross-machine direction yarns, providing a fabric first periphery of peaks and valleys wherein a plurality of peaks are in a first outside plane and the valley floors are in a first inside plane, said peaks being of a character which provides about 20 to 50 percent of the surface area of the first periphery and 100 percent of the area which will come in contact with the paper sheet to be supported by the felt on a paper machine; a second sinuous layer of cross-machine direction yarns, providing a fabric second periphery of peaks and valleys wherein a plurality of peaks are in a second outside plane and the valley floors are in a second inside plane;; a plurality of monofilament machine direction yarns positioned between the first and second outside planes and interweaving the cross-machine direction yarns of the first and second layers at points between the outside and inside planes of at least one of said first and second layers and at points within the periphery of the other of said first and second layers.

By way of example, an illustrative embodiment of the invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a cross-sectional, side elevation of a portion of a preferred embodiment fabric of the invention.

Figure 2 is a schematic view of a portion of a drying section in a paper making machine.

Figure 3 is a top view of a portion of the fabric of Fig. 1.

Fig. 1 is an enlarged, cross-sectional, side elevation of a portion of a fabric 10 of the invention. The fabric 10 comprises a first sinuous layer 1 2 of monofilament cross-machine direction yarns 1 4. The layer 1 2 forms a periphery of fabric 10 which in side profile shows peaks 1 6 and valley floor 1 8. A plurality of at least two peaks 1 6 in layer 1 2 are in a single plane forming an outer periphery of fabric 1 0. Preferably at least about 50 percent, most preferably all or substantially all of the peaks 1 6 are in the aforesaid plane.Valley floors 1 8 are in a separate plane inside of the plane formed by the peaks 1 6.

A second sinuous layer 20 of monofilament cross-machine direction yarns 14' forms another periphery of the fabric 10 which also appears, in side profile, as peaks 16' and valley floors 18'. A plurality of at least two of the peaks 16' are in a single plane forming the outer periphery (preferably at least about 50 percent, most preferably all of the peaks 16' are in the periphery).

Valley floors 18' are in a separate, single plane inside of the plane formed by peaks 16'.

A plurality of monofilament machine direction yarns 22 are positioned between the outer fabric periphery formed by the outside planes, formed by the peaks 1 6 and the peaks 16' and interweave with the cross-machine direction yarns 14, 14' at points between the respective planes of peaks 16, valley floors 1 8 and peaks 16', valley floors 18'. Thus, as shown in Fig. 1, the knuckles of load bearing machine direction yarns 22 are below the peaks 16, 16' at the point where they interweave with the cross-machine direction yarns 14, 14' and do not come into direct contact with the sheet 24 of paper carried on fabric 10, when fabric 10 is employed as a dryer fabric on a paper making machine.The sheet 24 is supported on the peaks 1 6 of the cross-machine direction yarn 1 4. On the side of fabric 10 facing away from the carried sheet, the machine direction yarns 22 are also protected by the outwardly projecting peaks 16' from contact with elements of the paper making machine which might hasten abrasion or other degradation of the important load bearing machine direction yarns. However, it will be appreciated that the greatest degradation of yarns in a dryer fabric occurs in those monofilament yarns in contact with sheet 24. Thus, it is not critical that yarns 22 be protected by peaks 16' on the side of the fabric facing away from the carried sheet 24 although such is obviously preferred.Within the scope of the invention are fabrics where the yarns 22 are on the outer periphery of layer 20 where they pass through layer 20.

In the embodiment fabric 10 the machine direction yarns 22 within layer 1 2 are paired with the yarns 22 within layer 20 and the yarns within the pairs are slightly offset from each other in regard to vertical alignment, as they knuckle over the cross-machine direction yarns 14, 14'.

There are, in the weaving pattern, 4 sets of machine direction yarn 22 pairs. One pair interweaves with every fourth of cross-machine direction yarns 14, 14' and then the pattern repeats. Preferably, the machine direction yarns pass over at least one cross-machine direction yarn, under at least one following cross-machine direction yarn and over at least one further following cross-machine direction yarn of the upper cross-machine direction layer before running down to interconnect the lower cross-machine direction layer with the upper cross-machine direction layer, the machine yarns and cross-machine direction yarns being thus interconnected in a repeat pattern.Of course the weave will be such that the relationship of the machine direction yarns and the upper layer of cross-machine direction yarns will be such that the plane of the upper surfaces of the portions of the cross-machine direction yarns of the upper layer over which the machine direction yarns pass is relatively elevated in a direction away from the plane of the upper surface of the fabric; and the plane of the exposed upper surfaces of the portions of the machine direction yarns in the upper layer under which the cross-machine direction yarns pass is relatively depressed in the opposite direction, whereby the differences in elevation between the exposed upper surface portions of the machine direction yarns are protected from contact with paper sheet which contacts the surface of the cross-machine direction yarns in the upper layer.

The yarns 14, 14' and 22 may be monofilaments on any synthetic polymeric resin. The yarns 14 and 14' may also be multifilament yarns. Representative of such multi- and monofilaments are yarns of polyester, polyamide, polyolefin, polyaramid, polyimide and the like. Generally such yarns having diameters of from 10 to 40 mils are advantageously employed in the fabrics of the invention.

Following the weaving of the fabrics of the invention, they are heat set to stabilize the fabric and to draw the yarns into their desired relative positions. The machine direction yarns 22 are drawn inwardly of the outer surfaces of the fabric 10 and this pressure "crimps" the yarns 18, 18' so that the peaks 16, 16' are displaced to the outside plane of the fabric as previously described. The degree of heat-setting required to achieve the desired structure of the fabric 10 will of course vary depending on the nature of the yarns 14, 14' and 22. However, optimum times, temperatures and tensions placed on the fabric during heat-setting can be determined by those skilled in the art, employing trial and error technique for the different yarn material.In general, heat-setting may be carried out at temperatures of from about 1 50"F. to 375e F. for from 1 5 to 60 minutes. The fabrics of the invention may be woven flat and the ends joined by conventional seaming methods, known to those skilled in the art. The seamed belts so made are readily employed as dryer felts in the dryer section 30 of a paper making machine as shown in Fig. 2. As shown in Fig. 2, the paper sheet 24 is held against the steam cylinders 32 by the endless belt 34 of fabric 10 during passage of sheet 24 through dryer section 30.

As shown in Fig. 1 and in Fig. 3, a top view of the embodiment fabric of Fig. 1, the outermost portion or "knuckle" of peaks 1 6 have been partially abraded away to increase the surface area of the fabric 10 which functions as the support area for the paper sheet 24. The technique of abrading away portions of knuckles on fabrics is well known; see for example U. S.

Patents 3,573,164 and 3,905,863.

Advantageously, sufficient of the peaks 1 6 are abraded away to provide peaks 1 6 with a surface area comprising from about 20 to about 50 percent of the total surface area of the dryer fabric, in the outer periphery of layer 1 2. Most advantageously, the abraded peaks 1 6 comprise from 10 to 30 percent of the total surface area. When the peaks 1 6 provide the specified surface area of the dryer fabric, the dryer fabric 10 exhibits an improved drying efficiency in operation on a paper making machine. The increased area of contact between the peaks 1 6 and the paper sheet 24 being dried promotes a faster drying rate and, in many instances, enhances the sheet tensile strengths of the product paper dried thereon.

It is important that the machine direction yarns in the fabric of the invention are not abraded and remain substantially intact, since they are the load-bearing yarns of the fabric 10.

The following examples sets forth the best mode contemplated by the inventors of making and using the invention but are not to be considered as limiting.

1 EXAMPLE 1 A fabric is prepared in a duplex weave of 0.016" diameter polyester monofilament (100 per inch) machine direction yarns interwoven with 0.016" diameter polyester monofilament (44 per inch; 22 top and 22 bottom) filling or cross-machine direction yarns. After heat setting, a fabric is obtained having only cross-machine direction yarns in the outer plane of the fabric. The upper surface of the fabric is subjected to abrasion to remove up to 0.0051 inches of the crossmachine direction knuckles. This leaves the abraded knuckles providing 29.3% of the surface area of the fabric. The percentage of surface area making contact at varying degrees of knuckle abrasion up to 0.0051 inches is shown in the Table 1, below.

TABLE 1 Inches Removed by Sanding Percent Surface Contact O (not sanded) 4.3% 0.0010 7.8 0.0019 13.6 0.0034 14.3 0.0051 29.3 Both sanded and unsanded fabrics are used to make endless dryer belts and each is tested on a papermakers machine in the dryer section. It is observed that the runs with the sanded fabric of Example 1 improve the drying rate by 2-5 percent over the drying rate achieved using the unsanded fabric.

Those skilled in the art will appreciate that many modifications of the preferred embodiments described above may be made without departing from the spirit and the scope of the invention.

For example, the fabric of the invention may be woven to include various stuffer picks, to obtain fabrics of different permeabilities as will be appreciated by those skilled in the art.

Claims

1. A fabric for use as a paper machine dryer felt, which comprises; a first sinuous layer of cross-machine direction yarns, providing a fabric first periphery of peaks and valleys wherein a plurality of peaks are in a first outside plane and the valley floors are in a first inside plane, said peaks being of a character which provide about 20 to 50 percent of the surface area of the first periphery and 100 percent of the area which will come in contact with the paper sheet to be supported by the felt on a paper machine; a second sinuous layer of cross-machine direction yarns, providing a fabric second periphery of peaks and valleys wherein a plurality of peaks are in a second outside plane and the valley floors are in a second inside plane;; a plurality of monofilament machine direction yarns positioned between the first and second outside planes and interweaving the cross-machine direction yarns of the first and second outside planes and interweaving the cross-machine direction yarns of the first and second layers at points between the outside and inside planes of at least one of said first and second layers and at points within the periphery of the other of said first and second layers.

2. A dryer felt made up from the fabric of claim 1.

3. The fabric of claim 1 wherein the cross-machine direction yarns are monofilaments.

4. The fabric of claim 1 wherein the cross-machine direction yarns are multifilament yarns.

5. The fabric of claim 1 wherein the machine direction yarns interweave with the crossmachine direction yarns at points between the outside and inside planes of each layer.

6. The fabric of claim 1 wherein said percent is within the range of from about 10 to 30 percent.

7. A fabric for use as a paper machine dryer felt, the fabric being substantially as herein described with reference to and as illustrated by the accompanying drawing.