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(11) | EP 0 027 033 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Papermaking apparatus and method |
| (57) The disclosure is of an improved dryer fabric (felt) (10) for use in a paper making
machine to improve the drying of paper (24). The improvement resides in part, in employing
a monofilament dryer fabric characterized in part by an exceptionally smooth surface
to support the paper moving through the dryer section. The smooth surface is obtained
by constructing the fabric so that substantially all of the monofilament warp (22)
and weft yarns (14) at the surface peak in a single plane. |
[0001] The invention relates to paper machine clothing and more particularly relates to improved dryer felt components of paper machine apparatus.
[0002] Papermaking machines are well known in the art. The modern papermaking machine is in essence a device for removing water from the paper furnish. The water is removed sequentially in three stages or sections of the machine. In the first or forming section, the furnish is deposited on a moving forming wire and water drained through the wire to leave a paper sheet of web having a solids content of circa 18 to 25 percent by weight. The formed web is carried into a wet press felt section and passed through one or more nip presses on a moving press felt to remove sufficient water to form a sheet having a solids content of 36 to 44 percent by weight. This sheet is transferred to the dryer section of the papermaking machine where dryer felts press the paper sheet to hot steam heated cylinders to obtain a 92 to 96 percent solids content.
[0003] The clothing employed on the paper making machine must perform a widely diverse range of functions, according to the position on the machine, i.e., forming, press or dryer section. In view of the diversity of functions, the clothing for use in each section of the machine must be manufactured to meet specific design requirements essential to the particular section. In the absence of meeting the specific felt design requirements demanded in each section of the machine, the overall operation of the machine will be unsatisfactory. Optimum operating lives of the felts will not be achieved, product quality may be adversely affected, machine speeds may be lowered or drying efficiency may be impeded.
[0004] In the dryer section of the paper making machine, one or more dryer felts are employed as endless belts to support the paper sheet or web in its final drying. The felt aids in drying, controls shrinkage of the web and prevents cockles. The felt fabric must possess strength, dimensional stability, resistance to chemical and thermal degradation, resistance to abrasion and have a functional permeability. In recent years all monofilament structured fabrics have been developed to meet the above-described needs of a dryer felt. However, dryer felts fabricated from all monofilament fabrics, have heretofore not been entirely satisfactory. The previously used fabrics have relatively rough surfaces, which are broughtin contact with the paper sheet to be dried. This rough surface can mark the paper sheet. This of course may be highly undesirable, resulting in a high percentage of unsatisfactory paper product.
[0005] In our invention, the dryer felt employed in the dryer section of a conventional paper making machine is fabricated from an all monofilament fabric of a particular weave which provides an exceptionally smooth surface to contact the paper sheet. As a result, relatively mark free paper product is obtained, while all of the desired advantages of an all monofilament dryer felt are retained. Unexpectedly, the paper drying rate is substantially increased by the invention.
[0006] The invention comprises, in the dryer section of a paper making machine which includes an endless dryer felt, the improvement which comprises; a dryer felt fabricated from a woven fabric which comprises;
a plurality of sinuous, monofilament yarns forming an upper layer of the fabric, the outer surface of said layer being the paper contacting surface of the fabric;
a plurality of sinuous, monofilament yarns forming a lower layer of the fabric;
a plurality of sinuous monofilament warp (machine direction) yarns interweaving with the weft (cross machine direction) yarns in the upper layer and with the weft yarns in the lower layer, the upper surface of the warp yarns where they pass over the weft yarns in the upper layer forming part of the paper contacting surface of the fabric.
[0007] By way of example, certain illustrative embodiments of the invention will now be described with reference to the accompanying drawings, of which:
Figure 1 is an enlarged, cross-sectional, side elevation of a portion of a preferred embodiment fabric employed in a dryer felt embodying the invention.
Figure 2 is a schematic view of a portion of a drying section in a paper making machine.
Figure 3 is a "fingerprint" of the paper sheet contacting surface of the fabric shown in Figure 1.
Figure 4 is a view like Figure 1 but of an alternate embodiment fabric embodying the invention.
[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 weft yarns 14. The layer 12 forms a periphery of fabric 10 which in side profile shows peaks 16 and valley floors 18. At least two peaks 16 in layer 12 are in a single plane and at least two of the valley floors 18 are in a separate, single plane inside of the plane formed by peaks 16.
[0009] A second sinuous layer 20 of monofilament weft yarns 14' forms another periphery of the fabric 10 which also appears, in side profile, as peaks 16' and valley floors 18'. At least two of the peaks 16' are in a single plane and at least 2 of the valley floors 18' are in a separate, single plane inside of the plane formed by peaks 16'.
[0010] A plurality of monofilament warp yarns 22 are positioned between the outside planes formed by the peaks 16 and the peaks 16' and interweave with the weft 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 warp yarns 22 have peaks 23 which are in the same plane as the peaks 16 and 16'. The peaks 16 and 23 are in a single plane which is the surface plane of fabric 10 which will support the paper sheet 24 when the fabric 10 is fashioned into a dryer felt and employed in accordance with the present invention. Thus, the upper peripheral surface of the fabric 10 which supports paper 24 is tangent to the plane within which the peaks 16 of weft yarns 14 and the peaks 23 of warp yarns 22 lie as the paper 24 supporting elements.
[0011] In the embodiment fabric 10 the warp yarns 22 within layer 20 and the yarns within the pairs are offset from each other in regard to vertical alignment as they knuckle over the weft yarns 14, 14'. There are, in the weaving pattern, 4 sets of warp yarn 22 pairs. One pair interweaves with every fourth of the weft yarns 14, 14' and the pattern repeats.
[0012] The monofilament yarns 14, 14' and 22 may be monofilaments of any synthetic polymeric resin. Representative of such monofilaments are monofilaments of polyester, polyamide, polyolefin, polyaramid, polyimide and the like.
[0013] Generally such monofilaments having diameters of from 8 to 40 mils are advantageously employed in the fabrics of the invention.
[0014] The fabrics embodying the invention are heat-set to stabilize the fabric and to set the yarns in their positions relative to each other. It will be appreciated by those skilled in the art that the degree of heat-setting required to obtain the desired structure will vary depending on the type of materials used in the yarns 14, 14' and 22. The optimum temperatures, times and tensions employed in heat-setting may be determined by trial and error techniques for each type of yarns employed in the fabrics embodying the invention. In general, heat-setting may be carried out at a temperature within the range of from about 150oF to 375°F for from 15 to 60 minutes.
[0015] The fabrics embodying the invention may be woven endless or they may be woven flat and the ends joined by conventional seaming methods, known to those skilled in the art. The endless belts so 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 cylinder 32 by the endless belt 34 of fabric 10 during passage of sheet 24 through dryer section 30.
[0016] The following examples set forth the best mode contemplated by the inventors of making and using the invention but are not to be considered as limiting.
EXAMPLE 1
[0017] A fabric embodying the invention was woven with machine direction yarns (warps) of 0.16" diameter polyester monofilaments in a density of 80 yarns to the inch and cross-machine direction yarns (weft) of the same monofilaments in a density of 48 yarns to the incho The resulting fabric was heat-set until all yarns in the outer surface (warps and weft) had their outer peaks in a single plane, i.e., as shown by a fingerprint resembling that in Figure 3 of the accompanying drawings.
[0018] A representative portion of the fabric prepared was subjected to physical testing. The physical properties found are shown in Table I, below.
[0019] The fabric is made endless with a pin seam and installed as a dryer felt on a paper making machine. Any other conventional means of seaming the fabric may also be employed. Paper products are unmarked by the contact with the dryer felt.
[0020] Figure 3 is an "enlarged fingerprint", i.e.; a diagram of the paper sheet contacting surface of the fabric prepared in Example lo From the Figure 3, it will be seen that although the peaks 16 (knuckles of weft yarns 14) provide most of the surface area supporting the paper sheet 24, the peaks 23 (knuckles) of the warp yarns 22) also provide substantial support for the sheet 24 and the result is an extremely smooth, non-marking surface for the fabric and a dryer belt prepared therefrom. The smooth surface has more sheet contact points per square inch for a more even pressure distribution to the paper sheet 24 as compared to conventional monofilament dryer felts. This enhances heat transfer to the paper sheet 24 from the hot dryer can in the dryer section of the paper making machine.
EXAMPLE 2
[0021] Four endless dryer felts are made up from fabric prepared in accordance with the above Example 1. The dryer felts are installed in both top and bottom positions of a two-dryer section papermaking machine, and two papermaking runs are made. The ambient conditions under which the runs were made, paper sheet speed, steam pressures and average can and paper sheet temperatures are given in Table 2, below with measurements of the sheet moisture on entering and leaving the dryer sections. The TAPPI drying rate is calculated and shown also.
[0022] The Table 2 shows in comparison to runs with a dryer felt of similar construction but wherein only the warp yarns make substantial contact with the wet sheet, the following improvements:
number of dryer cans in the section.
[0023] Those skilled in the art will appreciate that many modifications can be made to the above-described preferred embodiments of the invention without departing from the spirit and the scope of the invention. For example, although the layer 12 must have a smooth surface for contact with the paper sheet 24, the lower layer 20 need not have the same smooth outer surface. Thus, the peaks 16' of yarns 14' need not be in a plane tangent to the peaks 23 of warp yarns 22 where they knuckle over the weft yarns 14'. Either of the peaks 23 or 16' can form the outer periphery of the lower layer 20. This embodiment fabric is shown in Figure 4, where component yarns and layers are numbered to correspond to the same parts shown in Fig. 1 for the fabric 100 As also shown in Fig. 4, the number of interlacings of peaks 23 over weft 14' can be increased. This will prevent weft 14' from being as sinuously curved in plane 20 without altering the smooth surface of the face plane 120 Also, the fabric of the invention may be woven to include various stuffer picks, to obtain fabrics of different permeabilities and any multilayer weaves known in the art may be used to weave the fabric used in the invention.
1. In the dryer section of a paper making machine which includes an endless dryer
felt, the improvement which comprises; a dryer felt fabricated from a woven fabric
which comprises:
a plurality of sinuous, monofilament weft yarns forming an upper layer of the fabric, the outer surface of said layer being the paper contacting surface of the fabric;
a plurality of sinuous, monofilament weft yarns forming a lower layer of the fabric;
a plurality of sinuous, monofilament warp yarns interweaving with the weft yarns in the upper layer and with the weft yarns in the lower layer, the upper surface of the warp yarns where they pass over the weft yarns in the upper layer forming part of the paper contacting surface of the fabric.
2 The improvement of claim 1 wherein the monofilaments are polyester.
3. An improved method of drying paper sheets in the dryer section of a paper making
machine which includes an endless dryer felt, said improvement comprising employing
as the dryer felt one fabricated from a fabric, which comprises;
a first sinuous layer of monofilament weft yarns, forming an upper layer of the fabric, the outer surface of said layer being the paper contacting surface of the fabric;
a plurality of sinuous, filament weft yarns forming a lower layer of the fabric;
a plurality of sinuous, monofilament warp yarns interweaving with the weft yarns in the upper layer and with the weft yarns in the lower layer, the upper surface of the warp yarns where they pass over the weft yarns in the upper layer forming part of the paper contacting surface of the fabric.