Papermaker's Forming Fabric

The invention relates to a papermaker's fabric and more particularly to such a fabric free of edge curl while providing an excellent machine surface and an improved forming surface.

While the improved papermaker's fabric of the present invention could be advantageously used in the forming, transfer, press or drying sections of a papermaking machine, for purposes of an exemplary showing the fabric will be described in its application as a forming fabric.

Several well known types of papermaking machines utilize a forming fabric comprising a fabric of interwoven warp and filling yarns formed into an endless belt. A layer of wet pulp is deposited on the forming side of the papermaker's fabric and water is withdrawn from the pulp through the fabric by vacuum means or the like located on the machine side of the fabric.

Such papermaker's fabrics can be manufactured in two basic ways. First, they can be flat woven by a flat weaving process with their ends joined by any one of a number of well known methods to form an endless belt. Alternatively, they can be woven directly in the form of a continuous belt by means of an endless weaving process. Both methods are well known in the art. In a flat woven papermaker's fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction. In a papermaker's fabric having been woven in an endless fashion, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. As used herein the terms "machine direction" and "cross machine direction" refer respectively to a direction equivalent to the direction of travel of the papermaker's fabric on the papermaking machine and a direction transverse this direction of travel.

In the usual practice, papermaker's fabrics are manufactured utilizing weave patterns such as the 1/2 twill, 2/1 twill, 2/3 twill, 3/2 twill, 1/4 twill, 4/1 twill, 1/5 twill, 5/1 twill and variations thereof such as the sateens. These most commonly used weave patterns have one characteristic in common. They are all unbalanced weaves yielding two sided fabrics; one side being warp faced and the other side being filling faced. This characteristic leads to an imbalance of forces within the fabric structure. This imbalance of forces within the fabric structure, together with the different conditions which obtain at the edges of the papermaker's fabric when used on a papermaking machine (such difference including less lubrication by water, less vacuum being applied, etc.) result in a tendency of the papermaker's fabric to curl at its longitudinal edges. This tendency to curl results both in running problems and wear problems.

The present invention is based upon the discovery that if in a common unbalanced weave pattern (such as the 1/2 twill, 2/1 twill, 1/4 twill, 4/1 twill, 2/3 twill, 3/2 twill, 1/5 twill, 5/1 twill, 1/4 sateen and 4/1 sateen) selected parts of the weave are inverted, a more balanced weave is achieved and the forces within the resulting fabric are more nearly balanced. This, in turn, results in a flat fabric substantially free of edge curl and the problems attendant therewith.

Prior art workers have heretofore believed that a truly bicrimped fabric offered best sheet support and that the thinner the fabric the better its hydraulic action. Surprisingly, the weave patterns of the present invention eliminate pairing and yield a more bicrimped-like fabric. The forming side of the fabric displays improved sheet support and better sheet release. Sheet support is obtained from both yarn systems. The better sheet support is achieved through structural design rather than by providing a truly bicrimped fabric.

The fabric of the present invention has the same number of knuckles on both side and therefor is balanced. It is also thicker with greater internal volume, and yet it runs cleaner and displays better drainage. At the same time, the machine side of the fabric is characterized by substantially no reduction in wear quality.

The improved uniform surface support and the greater internal volume of the fabric of the present invention would also be advantageous when used in the transfer, press or dryer sections of a papermaking machine.

In accordance with the invention there is provided an improved papermaker's fabric substantially free of the tendency to curl at its longitudinal edges and providing an improved forming surface. The fabric comprises warp and filling yarns woven in a preselected conventional unbalanced weave pattern modified such that every other warp yarn occupies a position with respect to the filling yarns opposite to that which it would normally occupy according to the above mentioned preselected conventional unbalanced weave pattern.

The teachings of the present invention are applicable to any one of the following conventional unbalanced weave patterns: a 1/2 twill, a 2/1 twill, a 2/3 twill, a 3/2 twill, a 1/4 twill, a 4/1 twill, a 1/5 twill, a 5/1 twill, a 1/4 sateen and a 4/1 sateen.

The resulting fabric is flat, more bicrimped in nature and is characterized by a greater service life.

FIG. 1 is a weave diagram of a conventional 1/2 twill weave pattern on six harnesses.

FIG. 2 is a weave diagram illustrating the underside of the pattern of FIG. 1.

FIG. 3 is a weave diagram similar to FIG. 1 and illustrating the 1/2 twill pattern on six harnesses modified in accordance with the teachings of the present invention.

FIG. 4 is a fragmentary plan view of a fabric in accordance with the weave diagram of FIG. 3.

FIG. 5 is a diagrammatic representation of the six warp yarns or ends of FIG. 1 and their relationship to the three filling yarns or picks thereof.

FIG. 6 is a diagrammatic representation, similar to FIG. 5, and illustrates the six warp yarns or ends of FIG. 3 and their relationship to the three filling yarns or picks thereof.

FIG. 7 is a weave diagram of a conventional 1/4 twill weave pattern on 10 harnesses.

FIG. 8 is a weave diagram illustrating the underside of the weave pattern of FIG. 7.

FIG. 9 is a weave diagram illustrating the 1/4 twill weave pattern on 10 harnesses modified in accordance with the teachings of the present invention.

FIG. 10 is a fragmentary plan view of a fabric incorporating the weave pattern of FIG. 9.

FIG. 11 is a diagrammatic representation of the 10 warp yarns or ends of FIG. 7 and their relationship to the five filling yarns or picks thereof.

FIG. 12 is a diagrammatic representation of the 10 warp yarns or ends of FIG. 9 and their relationship to the five filling yarns or picks thereof.

FIG. 13 is a weave diagram equivalent to that of FIG. 3 turned 90.degree. so as to illustrate the modified 1/2 twill on 3 harnesses.

FIG. 14 is a fragmentary cross sectional representation of the modified fabric of FIGS. 3 and 4 woven on 3 harnesses.

Reference is first made to FIG. 1. This Figure is a weave diagram illustrating a conventional 1/2 twill weave pattern on six harnesses. The six vertical rows numbered 1 through 6 represent the six warp yarns of the diagram. The "X" marks on the diagram represent those points at which warp yarns or ends 1 through 6 appear at the surface of the fabric.

In the diagram of FIG. 1, the horizontal rows represent the three filling yarns or picks of the diagram, numbered 7 through 9. The "-" marks in the diagram illustrate those points at which the filling yarns are at the surface of the fabric.

FIG. 2 is a weave diagram similar to FIG. 1 and illustrates the underside of the weave pattern of FIG. 1. In FIG. 2, the positions of the "X" marks and "-" marks are simply interchanged with respect to their positions in FIG. 1.

FIGS. 1 and 2 illustrate clearly what was meant above by the statement that the conventional papermaker's unbalanced weave patterns are all characterized by the fact that they are two sided fabrics. The upper side of the fabric, as shown in FIG. 1, is filling faced. As can be clearly seen, the filling yarns 7, 8 and 9, represented by the "-" marks, appear far more frequently than the warp yarns, represented by the "X" marks. The opposite is true of the underside of the fabric as is shown in FIG. 2. As a result, the underside of the fabric is conventionally termed warp faced.

When a papermaker's fabric of the type shown in FIGS. 1 and 2 is utilized as a forming fabric with its upper surface (represented by FIG. 1) serving as the forming surface and its lower surface (represented by FIG. 2) serving as the machine surface, better wear characteristics are obtained for the forming fabric, but the fabric is at the same time characterized by a poorer forming surface. This is true because there are fewer knuckles (i.e. "X" marks) to support the pulp fibers deposited thereon. Sheet release is also impaired. In such use of the fabric, the edges thereof tend to curl downwardly.

Papermaker's have heretofore utilized a forming fabric of the type being discussed in an inverted condition so that its underside constitutes the forming surface of the fabric. This takes advantage of the greater number of knuckles (as is evident from FIG. 2) improving not only the surface of the sheet being made but also sheet release. Nevertheless, the fabric demonstrates poorer wear characteristics and service life. Furthermore, under these circumstances the edge curl, characteristic of such fabric, is an upward edge curl which further increases the problems attendant therewith.

FIG. 5 is a diagrammatic representation of the six warp yarns 1 through 6 and their relative positions with respect to the three filling yarns 7, 8 and 9. It will be evident from FIG. 5 that for each of the filling yarns 7, 8 and 9 only two of the warp yarns 1 through 6 pass thereover, while four of the warp yarns 1 through 6 pass thereunder. This situation creates the above noted imbalance of forces within the fabric which, in turn, produces the tendency for edge curl.

Reference is now made to FIG. 3. FIG. 3 is a weave diagram for a weave pattern or fabric in accordance with the teachings of the present invention. A comparison of FIGS. 1 and 3 will make it apparent that the weave pattern of FIG. 3 differs from that of FIG. 1 only in that every other warp yarn has been inverted so as to occupy a position with respect to the filling yarns 7, 8 and 9 opposite to that which it occupied in the weave pattern of FIG. 1. These inverted warp yarns are indicated at 1a, 3a and 5a. A further comparison of FIGS. 1 and 3 will make it immediately evident that the weave pattern of FIG. 3 is more balanced. The number of knuckles or "X" marks is equal to the number of warp yarn positions. The same is true of the reverse side of this weave pattern. FIG. 4 is a fragmentary plan view of a piece of fabric woven in accordance with the weave pattern of FIG. 3. FIG. 4 differs from FIG. 3 in that three additional filling yarns 10, 11 and 12 have been included so that the fabric may be more clearly represented.

Reference is now made to FIG. 6. FIG. 6 is a diagrammatic representation (similar to FIG. 5) illustrating the warp yarns 1a, 2, 3a, 4, 5a and 6 and their relative positions with respect to filling yarns 7, 8 and 9. It will be evident from FIG. 6 that each of the filling yarns 7, 8 and 9 have an equal number of warp yarns passing thereover and thereunder, unlike the situation which obtains in the weave pattern of FIGS. 1 and 5. It has been found that in a fabric of the type illustrated in FIGS. 3, 4 and 6 edge curl is no longer a problem. In addition, however, it has been found that pairing is eliminated with the result that the fabric is more bicrimped. This, together with the fact that the knuckles or "X" marks are more evenly distributed on both of the fabric surfaces results in better support for the sheet being formed on the forming surface with better sheet release and sheet surface characteristics while the wear characteristics of the papermaker's fabric are not impaired. The resulting papermaker's fabric is further characterized by less drag load on the paper machine, greater internal volume and better drainage.

FIGS. 7 through 12 illustrate another exemplary application of the teachings of the present invention to a conventional papermaker's unbalanced weave pattern. FIG. 7 illustrates a conventional 1/4 twill on 10 harnesses. FIG. 9 is similar to FIG. 7 illustrating the reverse side of the weave pattern of FIG. 7. In both FIGS. 7 and 8 the 10 warp yarns or ends are indicated at 13 through 22 while the five filling yarns or picks are illustrated at 23 through 27. Again it will be readily evident from FIGS. 7 and 8 that the unbalanced 1/4 twill weave shown therein is two sided, the upper side shown in FIG. 7 being filling faced while the underside shown in FIG. 8 is warped faced. The weave pattern of FIGS. 7 and 8 possess the same undesirable characteristics described with respect to the weave pattern of FIGS. 1 and 2. FIG. 11 is a diagrammatic representation (similar to FIG. 5) illustrating the 10 warp yarns or ends 13 through 22 and their relative positions with respect to the five filling yarns or picks 23 through 27. Again it will be evident from FIG. 11 that each of the filling yarns or picks 23 through 27 has 8 of the 10 warp yarns or ends passing thereunder and only 2 warp yarns or ends passing thereover. This results in the same unbalanced condition within the fabric as was described with respect to FIG. 5 above, resulting in edge curl and the like.

FIG. 9 illustrates a 1/4 twill on 10 harnesses of the type shown in FIGS. 7 and 8 modified in accordance with the present invention with every other warp yarn or end inverted so as to occupy a position with respect to the filling yarns opposite to that which it occupies in FIG. 7. The inverted warp yarns are indicated at 13a, 15a, 17a, 19a and 21a. This again results in a much more even distribution of knuckles or "X" marks on both sides of the fabric. FIG. 12 is a diagrammatic representation of the warp yarns or ends 13a, 14, 15a, 16, 17a, 18, 19a, 20, 21a, and 22 and their relative positions with respect to filling yarns or picks 23 through 27. Unlike the situation found in the diagrammatic representation of FIG. 11, each of the filling yarns or picks 23 through 27 has five warp yarns or ends passing thereover and five passing thereunder so that the forces within the fabric and more nearly balanced. FIG. 10 is a fragmentary plan view of a fabric woven in accordance with the weave pattern of FIG. 9 and the diagrammatic representation of FIG. 12. The fabric of FIG. 11 differs from the weave pattern of FIG. 9 only in that additional filling yarns or picks 28 through 32 are shown to better illustrate the fabric. The fabric of FIG. 10 is free of edge curl and is possessed of the same improved characteristics described with respect to the fabric of FIG. 4.

FIGS. 3 and 4 illustrate the 1/2 twill on six harnesses of FIG. 1 modified in accordance with the teachings of the present invention. The fabric of FIGS. 3 and 4 could be woven on three harnesses, rather than six. To represent such a fabric, it is only necessary to rotate the weave pattern of FIG. 3 90.degree. in a clockwise direction. Such a weave pattern is shown in FIG. 13.

In FIG. 13 the warp or ends of this modified 1/2 twill on three harnesses are indicated at 33, 34 and 35. The filling or picks are shown at 36 through 41. When the modified 1/2 twill is woven on three harnesses, the resulting fabric is a duplex fabric. This fabric is illustrated in cross section in FIG. 14. In this Figure the filling yarns or picks 36 through 41 are shown together with warp or ends 33 through 35.

The modified 1/4 twill fabric of FIGS. 9 and 10, woven on 10 harnesses, can similarly be woven on five harnesses. When this is done, the resulting fabric is similarly a duplex fabric.

These duplex fabrics are possessed of the same advantages described with respect to the fabric of FIGS. 3 and 4 and FIGS. 9 and 10.

Modifications may be made in the invention without departing from the spirit of it.