GB2295833A - Papermaking fabric with yarns having a multi-lobed cross-section - Google Patents

Description

PAPERXAKING FABRIC FORMED WITH YARNS RAVING A MULTI-LOBED CROSS-SECTION

2295833 This invention relates to a fabric construc- tion, and more particularly to a yarn construction for use in the manufacture of paper machine clothing such as forming fabrics, press felts or dryer fabrics.

Paper machine clothing is used in a papermaking machine or the like to dewater a fibrous web. In a very simple form, a papermaking fabric or other paper machine clothing may consist of a woven or non-woven base layer with a batt layer secured thereto, typically via a needling operation. The batt layer contacts the web, and water flows through the batt layer and the base layer under pressure from the press section, to dewater the web. To effectively remove water from the web, it is advantageous to maximize the flow- through capacity of the fabric. One way to accomplish this by increasing the void volume of the fabric base layer.

The base layer of paper machine clothing is often a woven layer consisting of a series of interwoven synthetic yarns. The yarns may be monofilaments, but more often are twistd or cabled yarns woven together. That is, each individual yarn may consist of a series of twisted or cabled strands, which in turn are woven together with other yarns consisting of twisted or cabled strands to form the base layer. For example, three individual strands may be twisted together to form a yarn or two single strands may be first twisted together, and two such twisted strands are in turn twisted together to yield a single yarn with a "two by two" construction. Yarns of this type are typically known as either threeply or four-ply constructions. These twisted or cabled yarn constructions are advantageous over monofilamenttype yarns, in that such constructions increase the void volume of the base layer and provide a more flexible base layer.

It is an object of the present invention to provide an alternative to, and improvement on, the stateof-the-art in paper machine clothing base layer yarn constructions. Specifically, it is an object of the invention to provide such a yarn which has similar properties to twisted or cabled yarns, yet which can be constructed without a twisting or cabling operation, thus reducing the number of steps involved in the manufacturing process. A further object of the invention is to provide a relatively simple yarn construction which can easily be incorporated into existing manufacturing operations, and which increases the void volume of the base layer and enhances the ability of the base layer to lock the fibers of the batt layer in place during the needling operation.

In accordance with the invention, a fabric, such as for use as the base layer in a papermaking fabric or the like, is formed of a series of yarns, with at least some of the yarns defining an integral multi-lobed cross-section. The multi-lobed cross-section is defined by a plurality of adjoined elongated strands, which cooperate to define an internal longitudinal passage extending throughout the length of the yarn. The adjoined strands are capable of being locally separated from each other at joints between adjacent strands. A fibrous batt layer is secured to the base layer, preferably via a needling operation. In the needling operation, the needles function to provide local separation of the strands to penetrate a portion of the batt layer therethrough. The portions of the strands adjacent the local separation engage the fibers of the penetrated portion of the batt layer, to grip the batt layer fibers to improve the locking of the batt layer to the base layer. Each strand defines an inner surface bordering the longitudi- nal passage and an outwardly facing outer surface, with joints between adjacent strands separating the strand inner and outer surfaces. The outer surface of each 1 strand is preferably smooth and continuously arcuate, and equidistant from a center defined by the longitudinal axis of the strand.

The invention further contemplates a method of making a fabric, particularly a papermaking fabric, substantially in accordance with the foregoing summary.

Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.

The drawings illustrate the best mode presently contemplated of carrying out the invention.

In the drawings:

Fig. 1 is a partial side elevation view showing the press section of a papermaking machine or the like; Fig. 2 is a partial side elevation view of a papermaking fabric used in the papermaking machine press section of Fig. 1; Fig. 3 is a view similar to Fig. 2, showing an alternative embodiment for the papermaking fabric; Fig. 4 is a cross-sectional view of a yarn used to construct the base layer of the papermaking fabrics of Figs. 2 and 3; Fig. 5 is a view similar to Fig. 4, showing a fibrous batt layer overlying the base layer constructed using yarns as shown in Fig. 4; and Fig. 6 is a view similar to Fig. 4, showing an alternative construction of the yarns used to form the papermaking fabric base layer.

Referring to Fig. 1, the press section of a papermaking machine or the like includes a pair of rolls 10, 12. A papermaking fabric 14 is trained about roll 12, and supports a web 16 which is engaged by roll 10.

In a manner as is known, rolls 10, 12 exert pressure on fabric 14 and web 16 to extract water from web 16.

Figs. 1 and 2 illustrate a papermaking press felt 14 in its simplest form, consisting of a base layer 18 and a batt layer 20. In an alternative construction of Fig. 3, a papermaking fabric 141 includes base layer 18 and top batt layer 20 and, in addition, a bottom batt layer 22. The constructions of papermaking fabric 14 as illustrated in Figs. 1, 2 and 3 are representative of numerous different papermaking fabric constructions which can be used in the press section of a papermaking machine, as the prior art is replete with various details in construction of papermaking fabrics of this type.

Fig. 4 illustrates a yarn 24 which is used to construct base layer 18 of papermaking fabric 14, 141, or the base layer of any other similarly constructed paper- making fabric used in the press section of a papermaking machine, or in any other location of a papermaking machine such as the forming or dryer sections. In a manner to be explained, incorporating yarns 24 into base layer 18 increases the void volume of papermaking fabric 14 to increase the water retention and flow-through capacity of fabric 14.

Base layer 18 may be a woven construction in which longitudinal machine direction yarns extend lengthwise throughout fabric 14 and are interwoven with perpendicularly, transverse cross-direction yarns. Alternatively, base layer 18 may be a non-woven construction using individual fibers or filaments formed into a sheetlike structure in accordance with conventional non-woven technology. The woven or non-woven base layer 18 is preferably formed using yarns or filaments such as 24 in its entirety. Alternatively, yarns or filaments such as 24 may only be used to partially form base layer 18, with the remainder being formed using conventional monofilament or twisted or cabled strand constructions.

Referring to Fig. 4, yarn 24 is a multi-lobed filamental construction consisting of adjoined strands 26a, 26b and 26c. Yarn 24 is formed in an extruding operation or the like, in which strands 26a, 26b and 26c are immediately joined together after forming while still in a semi-solid state, so that joints are formed at the contacting portions of strands 26a, 26b and 26c. A yarn such as 24 is available from Shakespeare of Columbia, SC under its designation NCR.

Strands 26a, 26b and 26c are substantially circular in cross-section individually and, when formed into yarn 24, provide an integral three-lobed cross section to yarn 24. Strands 26a, 26b and 26c define inner surfaces 28a, 28b and 28c, respectively, and outer surfaces 30a, 30b and 30c, respectively. Surfaces 28a and 30a of strand 26a are equidistant from a center of strand 26a defined by its longitudinal axis, and likewise for strands 26b and 26c. Strand inner surfaces 28a, 28b and 28c cooperate to define a longitudinal passage 32, which extends along the longitudinal axis of yarn 24.

With the above-described construction, yarn 24 defines an outer surface having three equally radially spaced indentations 34a, 34b and 34c terminating in respective nadirs 36a, 36b and 36c. An apex of the substantially triangular passage 32 is oriented toward each of nadirs 36a, 36b and 36c, with the joints between strands 26a, 26b and 26c lying therebetween.

As noted above, base layer 18 is formed in a woven or non-woven construction incorporating yarns 24.

Batt layer 20 is then secured to base layer 18, prefera bly using a conventional needling operation which, as is known, utilizes a large number of individual needles to insert the fibers of batt layer 20 into engagement with the yarns of base layer 18.

Fig. 5 illustrates a section of batt layer 20 as secured to one of the yarns 24 of base layer 18 as a result of the needling operation. As shown, a portion of batt layer 20 penetrates through yarn 24, being forced through yarn 24 by one of the needles during downward movement of the needling head. The needle functions to separate one of the strands, such as strand 26b, from the remaining strands during downward movement of the needle to locally separate strand 26b from strands 26a and 26c.

As can be appreciated, the rounded surfaces of strand 26a leading to nadir 36a guides the needle toward nadir 36d, and the needle then separates strand 24b at the joint between strands 26a and 26b. The needle then passes through passage 32 and toward indentation 34b, to sepa rate strand 26b from strand 26c. The arcuate nature of inner surfaces 28a, 28b and 28c function to guide the needles toward the apices of passage 32, to facilitate strand separation at the joints between adjacent strands.

The local separation of strand 26a from strands 26b and 26c provides an opening through which the pene trating portion of batt layer 20, shown at 38, extends.

Upon withdrawal of the needle, the portions of strands 24a, 24b and 24c adjacent the local separation function to engage the fibers of penetrating portion 38, to se curely lock batt layer 20 to base layer 18. As can be appreciated, the local separation as illustrated in Fig.

occurs throughout the surface area of base layer 18, wherever a needle penetrates one of yarns 24. If yarns 24 are used throughout the surface area of base layer 18, the batt locking capability of base layer 18 is signifi cantly increased over prior art constructions, which are unable to provide the same fiber gripping properties as are provided by the locally separated strands 24a, 24b and 24c.

Fig. 6 illustrates a four-lobed yarn 40 which can be used in place of yarn 24. Yarn 40 is formed by four adjoining strands 42a, 42b, 42C and 42d, in the same manner as described previously with respect to yarn 24, and is used as a substitute for a conventional two-by-two twisted or cabled yarn construction. Again, yarn 40 provides the same batt locking advantages as yarn 24 described above. However, in most situations the pene trating portion of the batt will extend through a local separation of two of strands 42a-42d from the other two strands. This effectively doubles the locking force exerted on the penetrating batt portion to increase the batt locking capability of the base fabric still further.

Yarns 24 and 40, which include the indentations such as 34a, 34b and 34c about their circumference, increase the void volume of base layer IS over that which would be accomplished by using a monofilament yarn. In addition, yarns 24 and 40 increase the flexibility and bendability of the resultant papermaking fabric 14 over that which could be accomplished using monofilament yarns, to render the papermaking fabric easier to install and to increase the useful life of the fabric.

It should be understood that yarns such as 24 can be used to form the base layer of any type of paper machine clothing, such as forming fabrics and dryer fabrics, and are not limited to press felts used in the press section.

It can thus be appreciated that use of a yarn such as 24 will result in an overall lower cost of manu facture for paper machine clothing by eliminating the twisting or cabling operation necessitated in prior art yarn constructions. Further, a three-lobe design such as yarn 24 could be used to replace a prior art two-by-two yarn construction. A fabric constructed in this manner would have an overall lesser weight of yarn than when a two-by-two yarn issued, resulting in lower cost of manu facture, while increasing the void volume of the fabric base layer. In addition, the welds or joints between the individual strands eliminate fabric damage and looping of the individual strands out of the base layer from the needling process.

Various alternatives and embodiments are con templated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.

8

Claims (1)

1. A papermaking fabric, comprising:

a base layer formed of a series of yarns, wherein at least some of the yarns have an integral lobed cross-section defining an internal longitudinal passage.

2. The fabric of claim 1, wherein the yarns of lobed cross-section are each defined by a plurality of adjoined elongate strands surrounding and defining the longitudinal passage.

3. The fabric of claim 2, wherein the adjoined strands are separable at the joints between adjacent strands, and further comprising a batt layer secured to the base layer.

4. The f abric of claim 3, wherein the batt layer is secured to the base layer by means of portions of the batt layer penetrating the base layer strands, locally separating the strands, and wherein portions of the strands adjacent the penetrating portions of the batt layer function to grip the penetrating portions of the batt layer to retain the batt layer securely on the base layer.

5. The fabric of claim 3 or claim 4, wherein each strand defines an inner surface bordering the internal longitudinal passage, an outwardly facing outer surface, and wherein the joints between adjacent strands separate the strand inner and outer surfaces.

6. The fabric of any of claims 3 to 5, wherein the outer surface of each strand is substantially smoothly and continuously arcuate and equidistant from a centre defined by the longitudinal axis of the strand.

9 7. A fabric according to claim 1, substantially as described with reference to Figures 1 to 5 or Figures 1 to 3 & 6 of the accompanying drawings.

8. A method of making a papermaking fabric, comprising the steps of:

forming a base layer from a series of yarns, wherein at least some of the yarns have a multi-lobed integral cross-section defining a longitudinal passage; and securing a batt layer to the base layer.

is 9. A method according to claim 8, wherein the multi-lobed yarns of the base layer are formed from a series of adjoined integral strands which are locally separable from each other; and the batt layer is secured to the base layer by means of portions of the batt layer penetrating the base layer strands, locally separating the strands, portions of the strands adjacent the penetrating portions of the batt layer functioning to grip the penetrating portions of the batt layer to retain the batt layer securely on the base layer.

10. A method according to claim 9, wherein the batt layer is secured to the base layer by a needling operation which locally separates the strands to insert portions of the batt layer therethrough.

11. A method according to claim 8, substantially as described with reference to Figures 1 to 5 or Figures 1 to 3 & 6 of the accompanying drawings.