METHOD FOR ADJUSTING LOOP COVERAGE OF WARP LOOP SEAM IN PAPER MACHINE FABRIC, AND PAPER MACHINE FABRIC SEAM

Abstract: A method for adjusting the loop coverage of a warp loop seam in a paper machine fabric and a seam in the paper machine fabric, where a longitudinal (L) adjustment thread (7) of the loop coverage is woven between loops (3) carrying the longitudinal (L) load of the warp loop seam, the diameter of the adjustment thread (7) in the lateral (W) direction is substantially greater than the diameter of the warp threads (1) forming the load carrying loops (3).

Description: METHOD FOR ADJUSTING LOOP COVERAGE OF WARP LOOP SEA IN PAPER MACHINE FABRIC, AND PAPER MACHINE FABRIC SEAM [0001] The invention relates to a method for adjusting the loop cov- erage of a three-parted paper machine fabric seam, where load carrying loops are formed of warp threads running in the longitudinal direction of the fabric at the ends of the fabric, and a longitudinal adjustment thread of the loop coverage is woven between the warp threads forming the loops. [0002] The invention also relates to a seam in a three-parted paper machine fabric comprising warp threads running substantially in the longitudinal direction of the fabric and weft threads in the lateral direction of the fabric, said threads being bound together, and load carrying loops are formed of the warp threads at the ends of the fabric, a longitudinal adjustment thread of the loop coverage is woven between the warp threads forming the loops, and the ends of the fabric are joined together using a warp loop seam. [0003] Paper machine fabrics, such as wires and felts, are used in different machines producing a web-like product from pulp, such as paper machines, board machines or the like, which will be hereafter referred to as 'paper machines'. A paper machine fabric is typically made of different threads of possibly varying cross-sections and materials in order to provide desired properties. Thread materials employed include polyester, polyphenylenesulphide, polyamide and other monofilament and multifilament threads as well as various compound threads. The manufacture of the fabrics employs different binding structures and combinations thereof, which should provide the fabric with desired properties suitable for the intended use. [0004] Joining the ends of paper machine fabrics together requires, as is known in the art, a particular seam structure that enables to achieve a reliable and durable joint. Such a seam is typically formed using warp threads running in the longitudinal direction of the fabric by bending said threads to form loops and by weaving the ends back so as to provide seam loops at the end of the fabric that allow to join the ends together in various known ways to form a warp loop seam. Other binding methods are also known in the art, but the warp loop seam provides such an advantage that the seam preferably has the same thickness as the fabric, and therefore the marking caused thereby and the wear of the seam caused by abrasion are insignificant. Even though the term marking is obvious to those skilled in the art, it should be mentioned that the term refers to the marks on the web produced by the fabric structure in the fabric. [0005] Certain paper machine fabrics - hereafter referred to as the fabric - aim to provide a large contact surface, in which case a high warp cov- erage is required. In some applications the high warp coverage provides the fabric with desired properties, such as a large contact surface against the web, great longitudinal strength and stability and low permeability. Thus, the problem the warp loop seam faces, is often an excessive loop density, wherefore the joining of the ends of the fabric together becomes difficult and time- consuming. This is a significant drawback since the joining must generally be carried out in poor lighting conditions and in a hot environment. A slowly occurring joining obviously increases the down time of the paper machine in question, and thus creates costs. A too high loop coverage is particularly a problem of a three-shed fabric structure, or the multiples thereof such as a six- shed, nine-shed etc. fabric structure. Here the term three-parted fabric structure refers to all the fabric structures mentioned. Finnish patent application 945430 discloses a solution in which the loops of the warp threads are twisted to resemble an s or z spiral for alleviating the joining, but this does not necessarily provide proper seaming if the loop coverage is wide. [0006] The idea of the invention is to provide a method for adjusting the loop coverage of a three-parted paper machine fabric and a seam in a three-parted paper machine fabric, in which the drawbacks mentioned above are avoided. [0007] The method of the invention is characterized in that the di- ameter of the adjustment thread in the lateral direction is substantially greater than the diameter of the warp threads forming the load carrying loops in said lateral direction. [0008] The seam in the paper machine fabric of the invention is characterized in that the diameter of the adjustment thread of the loop cover- age in the lateral direction is substantially greater than the diameter of the warp threads forming the load carrying loops in said direction [0009] An essential idea of the invention is that a longitudinal adjustment thread of the loop coverage to be woven between the threads carrying the longitudinal load of the fabric and forming adjacent loops to the warp loop seam provides a desired clearance between the loops and is substantially broader in the lateral direction of the fabric than the threads forming the loops of the loop seam. A further idea with a preferred embodiment is that the height of the adjustment threads in the perpendicular direction in relation to the lateral direction is such that the web-side surface of the seam is substantially smooth. [0010] The advantage of the invention is that the clearance of the loops in the warp loop seam of the three-parted fabric structures provided with high warp coverage is arranged to be such that the combination of the installation properties, permeability properties and strength properties of the seam can be optimized as desired so that the seam can be rapidly joined, the permeability thereof substantially equals that of the rest of the fabric and the loads placed upon the loops in the seam are relatively low. The rapid joining of the seam shortens the down time of a paper machine and reduces the costs created when the fabric is changed. When the permeability properties of the seam and the rest of the fabric are substantially equal, a continuous consistent drying effect is placed upon the web. The structure of the seam is simple and the manufacturing costs thereof are low. In addition the smooth web-side surface of the seam reduces the marking of the web. [0011] In the following the invention will be explained in greater detail in the accompanying drawings, in which Figure 1 schematically shows the loops on one side of a prior art warp loop seam from the web-side of the fabric, and Figure 2 schematically shows a part of an embodiment of the warp loop seam of the invention from the web-side of the fabric. [0012] Figure 1 schematically shows the loops on one side of a prior art warp loop seam from the web-side of the fabric. The fabric has a three-shed structure, meaning that the warp threads 1 in the longitudinal direction of the fabric form three threads, that is sets comprising a first, second and third thread 1a, 1b and 1c, which are repeated in similar form throughout the entire width of the fabric. The first 1a and the second 1b warp thread in the fabric sets form what is known as a load carrying loop 3 and the third 1c warp thread is bound at the edge of the fabric. The load carrying loops 3 receive the longitudinal L load of the fabric. The ends of the fabric are joined together in such a manner that the load carrying loops 3 at the opposite ends of the fabric are arranged between one another and a binding yarn or a pintle wire is threaded through a channel formed by said loops, thus forming a warp loop seam. As is known in the art, the cross sections of the warp and weft threads 1 and 2 to be used in the fabrics may be round, or shaped as a rectangle, oval or the like. [0013] In certain applications the three-shed structure provides advantages, such as a large contact surface and a plurality of contact points, which make the drying of the web more efficient, as well as great strength and stability. However, in a three-shed or similar fabric the loop coverage of the warp loop seam easily becomes too wide, as is shown in the fabric in Figure 1. The loops 3 at the opposite ends cannot be positioned between one another without bending. In such a case, a warp loop seam is difficult to mount, as the channel formed of the loops 3 at the opposite ends of the fabric and to which the binding yarn or pintle wire should be threaded becomes narrow and obscure in shape. The joining is time-consuming and therefore increases the down time of the paper machine in question and therefore increases the costs. [0014] Figure 2 schematically shows a part of an embodiment of the warp loop seam of the invention from the web-side of the fabric. The fabric has a three-shed structure like the one shown in Figure 1. Instead of the third warp thread 1c, an adjustment thread 7 of the loop coverage is woven which has a lateral W diameter that substantially exceeds that of the threads 1a, 1b of the load carrying loops 3. The binding of the adjustment thread 7 in relation to the basic binding is different than that of the warp 1 : the adjustment thread 7 repeatedly runs over three weft threads 2 and below one weft thread 2. The adjustment thread 7 does not form a loop around the last weft thread, instead it is cut to end at the edge of the fabric. The first and second warp thread 1a, 1b of the binding set in the warp 1 form a load carrying loop. By means of the ad- justment thread 7 the clearance of the loops 3 carrying load becomes so wide that the loops 3 can without any problems be positioned between the loops at the opposite end, and thus the seam can easily and rapidly be joined. When the lateral W diameter of the adjustment thread 7 is appropriately selected, the permeability properties of the seam can be set substantially at the same level as those of the rest of the fabric, in which case the seam dries the web substantially in the same extent as the rest of the fabric. This reduces the marking of the web caused by the seam. The adjustment thread 7 may naturally also be bound in the same way as the warp threads forming the load carrying loops 3. The adjustment threads of each fabric do not necessarily have to run in the same way; for example, a six-shed structure may apply two differently running adjustment threads 7 that alternate in the fabric. [0015] The fabric illustrated in Figure 2 deviates from the fabric shown in Figure 1 also in that the adjustment thread 7 has a longer weaving bend than the replaced third warp thread 1c and in that the bindings of the warp threads 1 forming the load carrying loop 3 are mirror images of one an- other. This is a principle known to those skilled in the art, and is therefore not discussed in more detail in this application. [0016] The drawings and the description associated therewith are merely intended to illustrate the inventive idea. The details of the invention may vary within the scope of the claims. Consequently the adjustment thread 7 can also be applied to other three-parted fabrics, such as six-shed and nine- shed fabrics. Depending on the application the properties of the seam can be emphasized in various ways, for example when producing webs requiring a particularly high-quality surface the width of the adjustment thread 7 is arranged so that the seam produces as few marks as possible on the web; in less marking applications the joining properties of the seam may be emphasized. The invention can be applied to single-layer or multi-layer paper machine fabrics. Adjustment threads 7 having a different profile and/or diameter can be used as a combination in the same seam.

Claims: CLAIMS 1. A method for adjusting the loop coverage of a three-parted paper machine fabric seam, where load carrying loops (3) are formed of warp threads (1) running in the longitudinal direction of the fabric at the ends of the fabric, and a longitudinal (L) adjustment thread (7) of the loop coverage is woven between the warp threads (1) forming the loops (3), characterized in that the diameter of the adjustment thread (7) in the lateral (W) direction is substantially greater than the diameter of the warp threads (1) forming the load carrying loops (3) in said lateral (W) direction. 2. A method as claimed in claim 1, characterized in that the height of the adjustment threads (7) in the perpendicular direction in relation to the lateral (W) direction is such that the web-side surface of the seam becomes substantially smooth. 3. A method as claimed in claim 1 or 2, characterized in that the cross sections of the adjustment threads (7) are identical with one another. 4. A method as claimed in any one of claims 1 to 2, character i z e d in that the cross sections of the adjustment threads (7) may have two or more different forms. 5. A method as claimed in any one of the preceding claims, characterized in that all the adjustment threads (7) are woven using a similar binding. 6. A method as claimed in claim 5, characterized in that the adjustment threads (7) run in the same way as the warp threads (1) forming the load carrying loops (3). 7. A method as claimed in any one of claims 1 to 4, characterized in that the adjustment threads (7) are woven using at least two different bindings. 8. A method as claimed in claim 7, characterized in that some of the adjustment threads (7) run in the same way as the warp threads (1) forming the load carrying loops (3). 9. A seam in a three-parted paper machine fabric comprising warp threads (1) running substantially in the longitudinal (L) direction of the fabric and weft threads (2) in the lateral (W) direction of the fabric, said threads being bound together, and load carrying loops (3) are formed of the warp threads (1) at the ends of the fabric, a longitudinal (L) adjustment thread (7) of the loop coverage is woven between the warp threads (1) forming the loops (3), and the ends of the fabric are joined together using a warp loop seam, characterized in that the diameter of the adjustment thread (7) of the loop cover- age in the lateral (W) direction is substantially greater than the diameter of the warp threads (1) forming the load carrying loops (3) in said direction (W). 10. A seam as claimed in claim 9, characterized in that the height of the adjustment threads (7) in the perpendicular direction in relation to the lateral (W) direction is arranged to be such that the web-side surface of the seam becomes substantially smooth. 11. A seam as claimed in any one of claims 9 to 10, character i z e d in that the cross sections of the adjustment threads (7) are identical with one another. 12. A seam as claimed in any one of claims 9 to 10, charac- terized in that the cross sections of the adjustment threads (7) may have two or more different forms. 13. A seam as claimed in any one of claims 9 to 12, characterized in that all the adjustment threads (7) are woven using a similar binding. 14. A seam as claimed in claim 13, characterized in that the adjustment threads (7) are arranged to run in the same way as the warp threads (1) forming the load carrying loops (3). 15. A seam as claimed in any one of claims ,9 to 12, characterized in that the adjustment threads (7) are woven using at least two different bindings. 16. A seam as claimed in claim 15, characterized in that some of the adjustment threads (7) are arranged to run in the same way as the warp threads (1) forming the load carrying loops (3).

Inventors: ENQVIST RAUNO, ENQVIST, RAUNO
Applicants: ENQVIST RAUNO, TAMFELT OYJ ABP, ENQVIST, RAUNO
Application year: 2001
Main classification: D21F1
IPC codes: D21F1