Passive Sensor System for Detecting of Wear Problems in Paper Machine Clothing

Abstract

A stratified press fabric for the press section of a paper machine having a passive sensor system for detecting wear in the press fabric. The lower (non-surface) layer(s) of the stratified press fabric are produced using colored staple fiber batt material. As the surface of the fabric is worn away through use, the colored batt material is exposed to provide a visual indication of the wear. This visual indication allows the customer to readily determine the appropriate time to replace the press fabric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the stratified press fabric of the present invention;

FIG. 2 is a like view of an alternate embodiment thereof; and

FIG. 3 is a cross-sectional view taken as indicated by line 3-3 in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to these figures, FIG. 1 is a schematic perspective view of the press fabric 10 of the present invention. Press fabric 10 is of the on-machine-seamable variety and takes the form of an endless loop once its two ends 12,14 have been joined to one another at seam 16.

In an alternate embodiment, as shown in schematic perspective view in FIG. 2, press fabric 20 has no seam and is in the form of an endless loop.

FIG. 3 is a cross-sectional view taken as indicated by line 3-3 in FIG. 1. Press fabric 10 includes a base fabric 30. In general, the base fabric 30 may be a woven, nonwoven, nonwoven arrays of MD or CD oriented yarns, knitted or braided structure of yarns of the varieties used in the production of paper machine clothing, such as monofilament, plied monofilament and/or multifilament yarns extruded from polymeric resin materials. Resins from the families of polyamide, polyester, polyurethane, polyaramid and polyolefin resins may be used for this purpose.

The base fabric 30 may alternatively be composed of mesh fabrics, such as those shown in commonly assigned U.S. Pat. No. 4,427,734 to Johnson, the teachings of which are incorporated herein by reference. Further, the base fabric 30 may be produced by spirally winding a strip of woven, nonwoven, knitted, braided or mesh material according to the methods shown in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the teachings of which are incorporated herein by reference. The base fabric 30 may accordingly comprise a spirally wound strip, wherein each spiral turn is joined to the next by a continuous seam making the base fabric 30 endless in a longitudinal direction.

The base fabric 30 may be endless, or, as shown in FIG. 3, on-machine-seamable. As shown, base fabric 30 is woven from monofilament yams in a two-layer, or duplex, weave. Machine-direction yarns 32, which are the weft yarns in the on-machine-seamable base fabric 30, form seaming loops 34 which are interdigitated to create a passage through which a pintle 36 is directed to join the base fabric 30 into endless form. Cross-machine direction yams 38, which are the warp yarns during the weaving of the base fabric 30, are, like the machine-direction yarns 32, shown to be monofilament yarns for the purposes of illustration.

One or more layers of staple fiber batt material 40 are applied to the outside of base fabric 30, and optionally to the inside as well, and constituent fibers thereof are driven into base fabric 30 by needling. The attachment is effected so as to leave a layer of staple fiber batt material 40 on the outside, and optionally on the inside, of the base fabric 30.

A fine fabric 44 is then disposed on the staple fiber batt material 40 on the outside of the base fabric 30. The fine fabric 44 may be woven or nonwoven, and may be endless, flat-woven or spiraled onto the staple fiber batt material 40. As depicted in FIG. 3, the fine fabric 44 is of a single layer weave, such as the plain weave shown, of machine-direction yarns 46 and cross-machine-direction yarns 48, both of which may be monofilament yarns. However, yarns other than monofilament yarns may be used in the weaving of the fine fabric 44. Both the yarns 46,48 and the mesh formed by the woven structure of fine fabric 44 are finer than those of base fabric 30.

More generally, fine fabric 44, like base fabric 30, may be a woven, nonwoven, nonwoven arrays of MD or CD oriented yarns, knitted or braided structure of yarns of the varieties used in the production of paper machine clothing, such as monofilament, plied monofilament and/or multifilament yarns extruded from polymeric resin materials. Resins from the families of polyamide, polyester, polyurethane, polyaramid and polyolefin resins may be used for this purpose.

Fine fabric 44 may alternatively be composed of mesh fabrics, such as those shown in commonly assigned U.S. Pat. No. 4,427,734 to Johnson, the teachings of which are incorporated herein by reference. Further, the fine fabric 44 may be produced by spirally winding a strip of woven, nonwoven, knitted, braided or mesh material according to the methods shown in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the teachings of which are incorporated herein by reference. The fine fabric 44 may accordingly comprise a spirally wound strip, wherein each spiral turn is joined to the next by a continuous seam making the fine fabric 44 endless in a longitudinal direction.

If fine fabric 44 is endless, it may be disposed on staple fiber batt material 40 in the manner of a sleeve or sock. Moreover, where fine fabric 44 is endless, or spiraled onto staple fiber batt material 40 in accordance with the teachings of U.S. Pat. No. 5,360,656, and base fabric 30 is on-machine-seamable as depicted in FIG. 3, it will ultimately be necessary to cut fine fabric 44 transversely in the vicinity of the seam formed by seaming loop 34 and pintle 36 to enable the press fabric 10 to be installed on a paper machine, as is well known to those of ordinary skill in the art.

In any event, fine fabric 44 is so called because its component yarns and/or mesh material are finer (smaller size or diameter, thinner or of smaller denier) that those of base fabric 30, and its mesh is finer than that of base fabric 30. As an example, the fine fabric 44 may have openings no larger than 0.50 mm in any dimension.

Finally, one or more layers of staple fiber batt material 50 are applied to the outside of fine fabric 44, and constituent fibers thereof are driven into and entangled within fine fabric 44 by needling. The attachment is effected so as to leave a layer of staple fiber batt material 50 on the outside of the fine fabric 44.

Staple fiber batt material 40 and staple fiber batt material 50 may comprise staple fibers of any polymeric resin used in the production of paper machine clothing, but are preferably of a polyamide resin. The staple fibers making up staple fiber batt material 50 may have a smaller cross-sectional size or diameter or denier than those of staple fiber batt material 40. For example, the staple fibers of stable fiber batt material 50 may be of 6 denier, while staple fibers of staple fiber batt material 40 may be of 24 denier.

In contrast to the stratified press fabrics of the prior art, the fine fibers of staple fiber batt material 50 are separated from the relatively coarser fibers of staple fiber batt material 40 by fine fabric 44. The fine fabric 44 limits the amount by which the fine fibers of staple fiber batt material 50 penetrate into staple fiber batt material 40 and base fabric 30 during the needling of staple fiber batt material 50.

Moreover, when the backside of the press fabric 10 is needled, following the attachment of staple fiber batt material 50 to the face side, the fine mesh of fine fabric 44 prevents the transport of the relatively coarser staple fibers of staple fiber batt material 40 into the staple fiber batt material 50.

In the stratified press fabrics of the prior art, the fine fiber portion may be as great as 75% fine fiber after needling, while the coarse fiber portion may be as great as 75% coarse fibers, with the remaining 25% of the fibers in each portion being fibers of the opposite kind, driven thereinto by the needling. There is also an intermediate region at the interface between the fine and coarse fiber portions where the fine and coarse fibers are mixed. The present invention may eliminate or substantially reduce this mixing. As a result, there may be little or no coarse fibers of staple fiber batt material 40 on the face side of the press fabric 10.

In addition, fine fabric 44 provides press fabric 10 with added compaction resistance while minimally impeding water flow.

Among the advantages of the present stratified press fabric 10 are its superior smoothness characteristics, which result from its homogeneous layer of face side batt. This surface layer imparts a smoother surface to the wet paper web it contacts within a press nip.

The present stratified press fabric 10 minimizes rewet because the homogeneous layer of fine face side batt permits less water to return to the paper web following exit from a press nip compared to the press fabrics of the prior art. The same uniformity of the pressing surface maximizes the dryness of the paper sheet following exit from the nip. Moreover, the fine, homogeneous, smooth face side batt makes the press fabric 10 less prone to sheet blowing upon approach to a press nip, and reduces sheet marking because of its lack of needle tracks.

Of course, the fine fabric 44 is desirably “fine” enough not to mark a paper web through the staple fiber batt material 50 needled thereover, and to prevent relatively coarse staple fiber batt material 40 from mixing with the relatively fine staple fiber batt material 50 during the needling process. Furthermore, the fine fabric 44 may be “fine” enough to inhibit the transport of fibers 50 therethrough and have enough structural integrity to withstand the needling process.

Additionally, fine fabric 44 may be woven or knitted structures produced using yams (warp and weft) having diameters in the range from 0.04 mm to 0.50 mm. Such yams may have the same or different diameters or deniers. Further, the yarns may be extruded from polyamide, polyurethane, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyolefin and other polymeric resins commonly used for this purpose by those of ordinary skill in the art.

As an example, the fine fabric 44 may be woven from 0.25 mm polyamide warp yams and 0.25 mm polyamide weft yams, and have eighteen (18) of each per centimeter. Such fabric may have openings, which are approximately 0.30 mm by 0.30 mm, and which are sufficiently small to prevent the needling of coarse batt fibers therethrough from the inner side of the base fabric.

In another example, the fine fabric 44 may be woven from 0.19 mm polyethylene monofilament warp yarns and 0.25 mm polyethylene monofilament weft yams, at a density of 21.4 warp yarns per centimeter and 18 weft yams per centimeter. Such fabric may have openings which are approximately 0.28 mm by 0.30 mm.

Fine fabric 44 may alternatively be extruded of molded films, and may be perforated or unperforated. In the latter case, perforations will be made during the needling process. Nonwovens or spun-bonded materials may also be used.

Furthermore, this stratified/layered approach can be used to provide a passive sensor system for detecting wear in the press fabric. Namely, the lower (non-surface) layers of the stratified fabric can be produced using colored batt material. As the surface of the fabric is worn away by use, the colored batt material is exposed to provide a visual indication of the wear. For example, the stratified press fabric shown in FIG. 3 may comprise a white colored base fabric 30, a blue colored coarse staple fiber batt layer 40, a red colored fine fabric 44, and a white colored staple fiber batt material 50 forming the surface layer. During use, the white surface layer 50 will begin to wear away, thereby exposing the underlying red fine fabric 44 and/or blue coarse batt layer 40. This visual indication allows the customer to readily determine the appropriate time to replace the press fabric. This visual indication may be any color (e.g. a dark blue or red batt layer with a white surface layer). Alternatively, UV visible coloring may be used so that the fabric appears to be white, but black light can be used to detect for wear.

Modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the scope of the appended claims.

Claims

1. A stratified press fabric for the press section of a paper machine, comprising: a base fabric in the form of an endless loop having an outer side and an inner side;a first batt layer attached to the outer side of said base fabric;a fine fabric covering said first batt layer; anda second batt layer attached to said fine fabric;wherein said first batt layer has staple fiber batt material that is coarser and of a first color different than said second batt layer; said first color indicating wear when said second batt layer is worn such that the first batt layer is exposed.

2. The stratified press fabric according to claim 1, wherein said fine fabric is a second color different than said second batt layer; said second color indicating wear when said second batt layer is worn such that the fine fabric is exposed.

3. The stratified press fabric according to claim 1, further comprising a plurality of batt layers between said base fabric and said fine fabric; said plurality of batt layers having at least one layer of said first color for indicating wear.

4. The stratified press fabric according to claim 1, wherein said first color is only visible in ultraviolet light.

5. The stratified press fabric according to claim 1, wherein said fine fabric limits transfer of staple fiber batt material between said first and second batt layers.

6. A stratified press fabric for the press section of a paper machine, said press fabric comprising: a base support structure, said base support structure being in the form of an endless loop and having an outer side and an inner side;a first staple fiber batt material attached to said outer side of said base support structure, said first staple fiber batt material comprising a plurality of first staple fibers of a first color;a fine fabric, said fine fabric covering said first staple fiber batt material on said outer side of said base support structure; anda second staple fiber batt material attached to said fine fabric, said second staple fiber batt material comprising a plurality of second staple fibers of a second color different than said first color, said second staple fibers being finer than said first staple fibers;wherein said first color indicates wear when said second staple fiber batt material is worn such that the first staple fiber batt material is exposed;wherein said fine fabric limits transfer of said first staple fibers and said second staple fibers therethrough and intermingling of said first staple fibers and said second staple fibers.

7. A stratified press fabric as claimed in claim 6 wherein said base support structure is a fabric selected from the group consisting of woven, nonwoven, nonwoven arrays of MD or CD oriented yarns, knitted and braided fabrics.

8. A stratified press fabric as claimed in claim 7 wherein said base support structure is an extruded mesh fabric.

9. A stratified press fabric as claimed in claim 6, wherein said base support structure is a strip of material spirally wound in a plurality of turns, each turn being joined to those adjacent thereto by a continuous seam, said base support structure being endless in a longitudinal direction, said strip material being selected from the group consisting of woven fabrics, nonwoven fabrics, knitted fabrics, braided fabrics and extruded mesh fabrics.

10. A stratified press fabric as claimed in claim 6, wherein said base support structure is an on-machine-seamable fabric.

11. A stratified press fabric as claimed in claim 6, wherein said fine fabric is a fabric selected from the group consisting of woven, nonwoven, knitted and braided fabrics.

12. A stratified press fabric as claimed in claim 11, wherein said fine fabric is an extruded mesh fabric.

13. A stratified press fabric as claimed in claim 6, wherein said fine fabric is a strip material spirally wound in a plurality of turns, each turn being joined to those adjacent thereto by a continuous seam, said fine fabric being endless in a longitudinal direction, said strip material being selected from the group consisting of woven fabrics, nonwoven fabrics, knitted fabrics, braided fabrics and extruded mesh fabrics.

14. A stratified press fabric as claimed in claim 6, wherein said fine fabric is an endless fabric.

15. A stratified press fabric as claimed in claim 6, wherein said first staple fibers have a first diameter and said second staple fibers have a second diameter which is smaller than said first diameter.

16. A stratified press fabric as claimed in claim 6, wherein said first staple fibers have a first cross-sectional size and said second staple fibers have a second cross-sectional size which is smaller than said first cross-sectional size.

17. A stratified press fabric as claimed in claim 6, wherein said fine fabric has openings no larger than 0.50 mm in any dimension, so that said first staple fibers are not driven therethrough when said stratified press fabric is needled from said inner side of said base support structure.

18. A stratified press fabric as claimed in claim 6, wherein said support structure is comprised of two or more bases selected from the group consisting of woven, nonwoven, nonwoven arrays of MD or CD yarns, knitted, braided, extruded meshes of film structures.