Dryer felt fabric

Abstract

 The disclosure is of a novel dryer felt or dryer felt fabric (10) for use in a paper making machine. Thefabric is characterized in part by a paper (24) contacting surface free of the load-bearing monofilament machine direction yarns (22). The fabric has an enhanced operating life as a dryer felt since the machine direction yarns are protected from direct contact with the paper sheet.

Description

[0001] The invention relates to paper machine clothing and more particularly relates to fabrics useful as dryer felts, and their use.

[0002] 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.

[0003] 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 shortened.

[0004] With the structured fabries of the present invention, employed as dryer felts, the cross-machine direction yarns support the paper sheet being dried. The monofilament machine direction yarns are thus protected from direct contact with degradative elements.

[0005] 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.

[0006] 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;

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.

[0007] 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.

[0008] Figure 1 is an enlarged, cross-sectional, side elevation of a portion of a fabric 10 embodying the invention. The fabric 10 comprises a first sinuous layer 12 of monofilament cross-machine direction yarns 14. The layer 12 forms a periphery of fabric 10 which in side profile shows peaks 16 and valley floors 18. A plurality of at least two peaks 16 in layer 12 are in a single plane forming an outer periphery of fabric 10. Preferably at least about 50 percent, most preferably all or substantially all of the peaks 16 are in the aforesaid plane. Valley floors 18 are in a separate plane inside of the plane formed by the peaks 16. ¹

[0009] 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'.

[0010] A plurality of monofilament machine direction yarns 22 are positioned between the outer fabric periphery formed by the outside planes, formed by the peaks 16 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 18 and peaks 16', valley floors 18'. Thus, as shown in Figure 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.

[0011] The sheet 24 is supported on the peaks 16 of the cross-machine direction yarn 14. 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 mechine 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.

[0012] In the embodiment fabric 10 the machine direction yarns 22 within layer 12 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.

[0013] The yarns 14, 14' and 22 may be monofilaments of 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, pblyolefin, 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.

[0014] 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 materials. In general, heat-setting may be carried out at temperatures of from about 150°F. to 375°F for from 15 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 eo made are readily employed as dryer felts in the dryer section 30 of a paper making machine as shown in Figure 2. As shown in Figure 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.

[0015] The following example sets forth the best mode contemplated by the inventors of making and using the invention but is not to be considered as limiting.

EXAMPLE 1

[0016] A fabric is prepared in a duplex weave of 0.020" diameter polyester monofilament (24 per inch) machine direction yarns and 0.020" diameter polyamide monofilament machine direction yarns (24 per inch) for a total of 48 machine direction yarns per inch interwoven with 0.020" diameter polyester monofilament (48 per inch; 24 top and 24 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. A representative portion of the fabric prepared is subjected to physical testing. The physical properties found are shown in Table I, below.

EXAMPLE 2

[0017] This is not an example of the invention, but is made for comparison purposes. A fabric is woven in a duplex weave (4 warps and 8 pick repeat) with machine and cross-machine direction yarns as follows:

machine direction - .020" diameter polyester monofilament at 24 per inch. .020" diameter polyamide monofilament at 24 per inch. "laid out in a two and two arrangement"

filling - .020" diameter polyester monofilament at 25 per inch. 12.5 top and 12.5 bottom.

[0018] After heat-setting, a fabric is obtained wherein the machine direction yarns are in the outer plane of the fabric where they knuckle over the cross-machine direction yarns.

[0019] A representative portion of the fabric is tested for its physical properties The test results are given in Table I, below.

[0020] 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;

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 cross-machine direction yarns at points between the outside and inside planes of each layer.

Drawing