Sunday, 25 October 2009

Warp Knitting Power Net structure

One of the most popular nets on warp knitting is power net,power net produce by four bars Elastic Raschel machine with 1 in 1 out threaded for all guide bars (half threaded),usually produce in 28 gauge.The two front guide bars GB 1 and GB 2 knit the fish net structure and counter lap or shog opposite to each others.While the third  guide bar GB 3 and fourth guide bar GB 4,produce inlay shogging around the pillar stitches created by the two front guide bars.

The arrangement of threading in and the lapping movement of all guide bars illustrate in Fig .1,important is to note the way in which the four guide bars are threaded in relation to each others. The elastic yarn of the third guide bar are inlaid around the pillar stitch created by the the first guide bar,while the fourth guide bar inlays around pillar stitch of the second guide bar.

  Due the high tension of elastic yarn with relative high final stretch set on warping process, and les run-in on the knitting machine,the inlay pull straight and the net acquires its typical shapes as illustrated in Fig.2.
For medium-strong power net,usually used Nylon 70 denier on front guide bars GB 1- GB 2 and elastic yarn 280 denier for back guide bars GB 3 and GB 4.With run-in around 1000 mm/rack until 1100 mm/rack for GB 1 and GB 2.For  inlay bars GB 3 and GB 4 the run-in around 95 mm/rack to 120mm/rack with the density of the fabric between 26 to 30 courses /cm.

The Influence of Elastic-yarn on the Extensibility of the Power Net
By varying the tension of the elastic yarn while keeping the polyamide feed at a constant rate it is possible to produce a fabric with high or low length stretch.
If the elastic yarn thread is fed in with a particularly high tension, i.e. less elastic yarn is taken up per rack (unit of 480 courses), the stitch count of the greige goods increases.
The compacted fabric then provides a high longitudinal stretch while the width stretch of the net is low due to the increased tension of the elastic thread.
Furthermore, the greige width is only slightly narrower compared with the working width, though heavier in weight per m2.
The power net has low length stretch, if the elastic yarn is fed in with low thread tension, i.e. more elastic material is taken up per rack. In this case, the net structure is less compacted by the elastic yarn. Compared with a fabric containing elastic yarn with high run-in tension, the greige goods contract more in the width
and become lighter in weight per m2. With this setting, the length stretch is lower while the width stretch increases slightly.

The Influence of Polyamide on the Stretch Properties of Power Net
Another factor that has considerable influence on the stretch of a fabric is the amount of polyamide thread taken up per rack. A higher run-in leads to a more open net structure with the corresponding higher length and width stretch. The fabric width increases.
An article of corsetry produced with a considerably reduced polyamide feed has a tight loop structure that provides for little stretch in the length and width direction. The fabric width decreases.
In practice, keeping the above factors in mind, adjustments to elastic yarn and polyamide feed rates, as well as other machine settings are used to product the specific power net quality desired. The most important characteristics with regard to the fabric structure are the length and width stretch, the percentage of elastic yarn, uniformity of appearance, the fabric weight and width. It is the properties of the finished fabric that determines when and if production is taken up.