Fabric Club Of BD: Selvedge

Selvedge

Labels: Weaving Manufacturing Technology | at 10/25/2010 03:03:00 AM

Selvedges provide strength to fabric for safe handling of the fabric. Selvedge should not curl. In shuttle looms, there is no need for special selvedges; since the yarn is not cut after each filling insertion, the edges of the fabric are smooth and strong.

Fig: Normal Selvedge by Shuttle Loom

In shuttle-less weaving, since the pick yarn is cut after every insertion, there is fringe selvedge on both sides of the fabric. In this case, special selvedges are needed to prevent slipping of outside warp yarns out of the fabric. There are several types of selvedge designs that are used for this purpose with shuttle-less looms.

The weaving machines need mechanisms which through the formation of sufficiently strong selvedges bind the wefts together, thus imparting to the fabric a proper appearance and solidity and preventing the breaking up of the threads on the fabric edges during the subsequent operations.

Three kinds of selvedges can be formed:

· Tucked-in selvedges

· Leno selvedges

· Fused selvedges

Tucked-in selvedges:

A special hooked needle driven by a cam produces, after cutting, the insertion of the protruding thread end into the subsequent shed, thus forming a stronger edge.

Tucked-in selvedge can be formed by two different methods. With most common method the projecting weft tail is tucked in the form of a hairpin to a predetermined length (10-15 mm) into the next weave shed. This gives a firm & neat selvedge. A 2/1 or 3/1 rib with two ends per heald & 2 fold yarns with about 20% finer than the body yarn number give excellent results. Sulzer Bros. were the pioneer to introduce this type of tucked – in selvedge on their projectile machines but now-a-days it is also used on rapier & air-jet weaving machines.

Fig: Tucked-in Selvedge &Tucking process

This system is generally used for light to middle weight fabrics, when weave and fabric density permit. There are also available tuck-in selvedge motions which are entirely controlled by pneumatic or mixed pneumatic and mechanical devices.

Picture: Tucking Needle (Tsudakoma Air-Jet Loom)

Leno selvedges:

These selvedges are obtained by binding the wefts with strong additional threads working in gauze weave and by eliminating through cutting the protruding weft ends.

Fig: Leno Selvedge

The leno gauze system is optimally suited for heavy fabrics, blankets, wall coverings. Fig. A illustrates the operation scheme of the device proposed by a manufacturer, in which device two complete leno gauze mechanisms work in combination. A leno device produces the fabric selvedge, while the other device forms the auxiliary selvedge.

Fig. A : Leno creates the fabric selvedge.

Picture: Leno (Picanol Air-Jet Loom)

Chain stitch edges:

Chain Stitch edge are produce mostly on shuttle-less narrow fabric weaving machine weaving machine in which the pick is inserted by means of a needle. These machines run at a very high speed & the mechanism for forming chain does not affect high production operation. The chain stitch has not yet been used on wide weaving machines.

Fused selvedges:

These are obtained by pressing a hot mechanical element on the fabric edge; this method can be applied on fabrics in man-made fibres. Sometimes used to split wider fabrics in to narrow width fabrics.

Melt Selvedge:

This type of selvedge is also known as fused selvedge. The formation of this selvedge requires outermost ends of thermoplastic filament yarns e.g. polyester, polyamide polyolefin etc; with this method the edge ends are plasticized by means of an incandescent pin or ultrasonic & stuck together to produce a firm neat edge which does not curl up. This type of selvedge can be used with all types of weaving machines. This also requires dummy selvedge, so the wastages are high up to 2-4% depending upon the number of ends & width of fabrics.