GB2325881A

GB2325881A - Seam construction for papermaking fabric

Info

Publication number: GB2325881A
Application number: GB9711408A
Authority: GB
Inventors: Mark Hodson
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1997-06-04
Filing date: 1997-06-04
Publication date: 1998-12-09
Also published as: GB9711408D0

Abstract

A seam construction for joining abutting edges of a woven fabric comprises a pair of interdigitable helical loop spirals 13, 14 connected by a pintle wire 15, each loop being connected to the respective fabric edge by a respective cross machine yam 17, 18 which passes through the loops of the respective spiral and is secured to the fabric by selected machine direction terminal yams 16, 16a, 16b which pass about the said terminal yarns only.

Description

SEAM CONSTRUCTION FOR PAPERMAKING FABRIC This invention relates to a seam construction for a papermaking fabric, particularly, but not exclusively to a dryer fabric seam construction.

Woven dryer fabrics and similar fabrics for use in paper machines are manufactured in sheet form and their ends joined by seams to form endless belts. In some forms of seam, the junction of the fabric ends is achieved by passing a rod through interdigitated loops extending from each fabric end. Whatever its actual composition, this rod is usually referred to as a "pintle wire". The fabric is usually woven, with warp yarns extending in the intended machine direction, for example polyester yarns in the order of 0.50 mm diameter and weft yarns extending in the cross-machine direction for example polyester yarns in the order of 0.70 mm diameter.

In the following, the term 'MD yarn' refers to yarns extending in the direction of movement of the machine, i.e. along the fabric, whilst 'CMD yarn' refers to yarns extending laterally across the fabric at right angles to the MD yams.

A known type of seam is the SL seam. In this some of the MD yarns are extended beyond the final cross-machine yarn to form an empty loop, the yarn end then being back woven into the fabric, another yarn ending short to provide weave space for this woven-back end. Any MD yarn within the weave repeat may be extended in this way. An array of loops is formed along the edge of the fabric, which can be interdigitated with similar loops on the other edge, and a pintle wire can be passed through the interdigitated loops to secure the resulting seam.

A further known type of seam is the LS seam. In this version, two flattened helical coils usually of a suitable plastics material are provided each secured to one of the edges ofthe fabric by means of MD yarns looped around the adjacent portions of the coil loops. In some embodiments, two MD yarns are looped about each coil loop and woven back into the fabric, two other MD yarns being ended short to provide space for the back weaving.

The SL seam has been found in practice not to be strong enough for use on machines with a high running tension. In addition the LS seam is not as fine or level as the SL seam and may cause marking of a paper web as well as linear marking due to the increase of permeability created by the gaps present in the seam area or by a change of profile due to proudness or depression of the seam. The LS seam is however of sufficient strength for machines with a high running tension, but produces more embossing of the paper web processed on the fabric. Surface coverings such as fibrous or polymer layers, e.g flocked fibres, on the spiral coils and/or seam region has also been tried, yet this is an expensive and difficult technique which still does not guarantee no marking.

An object of the present invention is to provide an improved seam construction which combines the strength of the LS spiral seam with the fineness of the SL seam and lies substantially within the plane of the fabric, thereby reducing marking.

According to the invention, a seam for joining abutted edges of a woven fabric to form an endless belt comprises a pair of interdigitable helical loop spirals, each spiral being attached to a respective fabric edge, and the spirals being connected by a pintle wire or the like which passes through the loops of the spirals when said loops are interdigitated, characterised in that each loop is connected to the respective fabric edge by a respective ultimate cross-machine yarn of the fabric, which passes through the loops of the respective spiral, and is secured into the weave of the fabric by selected machine direction yarns which are passed around the said ultimate yarn and back woven into the fabric.

In a preferred embodiment, one machine direction yarn is passed about the said ultimate yarn for each loop of the respective spiral member. Two spiral loops may be provided in each repeat, with MD yarns being passed about the ultimate yarn alternately from opposite sides of the weave.

The ultimate yarn of each fabric end may be an oversized yarn of greater diameter than the remainder ofthe cross machine direction warp yarns.

The pintle wire and/or each of the said ultimate yarns may be sheathed in an expandable material which is expanded eg. by heat treatment on completion of the seam, to swell the effective diameter of said yarns and/or pintle wire to reduce the gaps occurring in the seam zone, and this further reduces the risk of paper marking by the seam further. This also hinders spiral rotation, thereby making seaming of the fabric on the paper machine easier.

In manufacture of the seam, the MD warp yarns may be either looped about the ultimate yarn which is kept in place, or the looping may be done about an extra thick yarn, which is then removed and replaced by a standard diameter yarn after forming the seam incorporating the spiral.

A preferred embodiment of seam construction according to the invention will now be further described by way of example with reference to the accompanying drawings wherein: Fig. 1 is a diagrammatic enlargement in plan view of the seam area of a fabric incorporating a seam construction according to the invention; Fig.2 is a diagrammatic cross-section ofthe seam area; and Fig.3 is an enlarged diagram showing details of the weave in one fabric end region of the seam.

Figs. 1 and 2 show in enlarged diagrammatic plan and sectional view, part of a seam region of a seam according to the invention. A fabric has a first end 10 and a second end 11 which are joined by the seam. The fabric is woven from eg. polyester cross-machine yarns 12 in the order of 0.7 mm diameter. The last three such yarns in each end region are shown. The seam is formed by a respective flattened helical spiral coil provided on each fabric end 10, coil 13 on first end 10 and coil 14 on second end 11. The coils are joined by a pintle wire 15, which passes through the interdigitated loops. The pintle wire may be similar in material and dimensions to the cross-machine yarns 12.

The fabric also includes machine-direction (MD) yarns 16, interwoven through the cross-machine yarns 12 in an alternating repeat pattern. Alternate MD yarns 16 are looped over respective end ones ("ultimate" yarns) ofthe weft yarns 12, respectively 17 in end region 10, and 18 in end region 11. Yarns 1 6a providing long loops over the end yarns alternate with yarns 16b, providing short loops over the end yams.

The end yarns 17,18 are respectively passed through the loops of respective coils 13,14. None ofthe MD yarns 16 are passed around any part of either coil. As best seen in fig.2 each coil 1.,14 is passed around the pintle wire 15 and the respective end yarn 17 or 18.

This construction provides a strong seam suitable for use in machines with high running tension and which provides a level seam area whilst enabling a fine seam to be obtained which will reduce embossing of paper sheets treated on the fabric.

The seam may be further improved by using end yarns and/or a pintle wire coated with an expandable sheath which is expanded after fabrication of the seam to fill up gaps in the seam so that properties of the seam area for example, density, permeability and contact are compatible with those of the rest of the fabric. To the same end, the gaps between end yarns 17,18 and pintle wire 15 may be filled by feeding finer gauge threads through the coil loops 13,14 parallel to the yarns 17,18 and pintle wire 15, across the machine direction.

The seam constructions according to the invention may be used forjoining fabrics for paper machine clothing for any suitable paper making stage, including dryer fabrics, forming wires, press felts etc. and may be covered with any one or more of a single or multilayer fibrous batt or woven material or formed of solid plastics sheet material, etc.

Claims

crarMs

1. A seam for joining abutted edges of a woven fabric to form an endless belt, comprising a pair of interdigitable helical loop spirals, each spiral being attached to a respective fabric edge and the spirals being connected by a pintle wire or the like which passes through the loops of the spirals when said loops are interdigitated; characterised in that each loop is connected to the respective fabric edge by a respective ultimate cross-machine yarn of the fabric, which passes through the loops of the respective spiral, and is secured into the weave of the fabric by selected machine direction yarns which are passed around said ultimate yarn and back woven into fabric.

2. A seam according to claim 1, wherein one respective machine direction yarn is passed about said ultimate yarn for each loop of the respective spiral member.

3. A seam according to claim 1 or 2 wherein two spiral loops are included in each machine direction yarn pattern repeat, with respective machine direction yarns being passed about the ultimate yarn alternating from opposite sides of the weave.

4. A seam according to any preceding claim, wherein the ultimate yarn of each fabric end is an oversized yarn of greater diameter than the remainder of the cross-machine direction yarns.

5. A seam according to any preceding claim, wherein in manufacture, the machine direction yarns are looped about said ultimate yarn.

6. A seam according to any one of claiis 1 to 5, wherein in manufacture, the machine direction yaras are looped about on extra thick yarn, which is then removed and replaced by a standard diameter yarn after incorporation of the spiral into the seam.