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Warp Knitting. Warp knitting: In a warp knitted structure, each loop in the horizontal direction is made from a different thread and the number of threads used to produce such a fabric is at least equal to the number of loops in a horizontal row.
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Warp Knitting Warp knitting: • In a warp knitted structure, each loop in the horizontal direction is made from a different thread and the number of threads used to produce such a fabric is at least equal to the number of loops in a horizontal row. • In warp knitting, the thread runs thoroughly in a vertical direction Weft knitting: • In a weft knitted structure, a horizontal row of loops can be made by using one thread and thread runs in horizontal direction
Guide: • Warp guides are thin metal plates drilled with a hollow in their lower end through which a warp end may be threaded if required, they are held together at their upper end in a metal lead and are spaced in it to the cam gauge as the m/c • The leads in turn are attached to a guide bar so that the guides hang down from it with each one occupying a position at least midway between two adjacent needles in this position. The warp thread can not be received by the needles and it will merely produce a straight vertical float. • The needles only receive the warp thread in their hooks if the guide bar overlaps across their hook or across the side remote from their hooks when the guide bar underlaps.
Guide bar: • A bar running the full width of the m/s and equipped with guides through which threads are passed so that the lateral motions, imparted to the guide bars by the pattern control device, are transmitted to the threads. • The individual guides are usually cast in 1 units- which in turn are fitted on the guide bars. • The guides swing between and around the needles in order to wrap the yarn around them to form a new loop. They also shog side ways to connect the wales into a fabric. • The minimum no of guide bars and warp sheets for commercially acceptable structures is usually two.
Chain link: • The identity Y-shaped chain links are similar in appearance to a turning fork with the fork and leading. The tail of the preceding links fits into the fork of the succeeding link. The links are held together by pins that are pushed through holes in the sides of the fork and tail. The pins pass through all the tracks and chains, and the ends fit into grooves in the serrated flanges of the pattern drum so that as the drum turns, the chain links are advanced in unison in correct timing relationship. • The link is slightly arched to fit the surface of the pattern drum; the forkside is the leading part of the link when connecting a chain. Links are made to fit certain m/c gauge. To eliminate any confusion, the gauge is stamped onto the links together with the height of the link are ground to produce a slope. The angle and length of the ground edge must be very accurately set so that the shogging movement is correctly timed.
Pattern mechanism: • The shogging movement is initiated by varying the radius of the continuously turning pattern shaft either in the form of different heights of pattern links which poses over a pattern drum attached to the shaft or in the form of carefully shaped solid metal circular cams, termed pattern wheels, attached to it. An increase in height one link to the next produces a thrust against the end of the guide by shogging it positively into the m/c a decrease will produce a negative shog towards the pattern shaft as the result of the action of a return spring. A constant height will produce no shog if the guide bar will continued to swing through the same needle space. The periphery of the pattern wheel or chain track is scanned by a roller which is link by a flexible jointed push-rod to the end of the guide bar. The under side of the rod near the roller is supported on the side with moves freely or a metal surface as shogging occurs.
Lapping movement of the guide bar: • When needle bar observed in plain view from above, it can be see that the guides of a guide bar are required to execute a compound lapping movement composed of two separately derived motions- 1. A sewing motion 2 .A shogging motion • They act at right angles to each other in order for their threads to form overlap and underlap paths which are joined together around the needles. The movement of guide towards front side from backside of the m/c and from back towards the front side. Swinging motion: • The swing motion is an arc from the front of the m/c to the hook side and a later return swing. It occurs between adjacent needles and is a fixed, collective and automatic action for all the guide bars as they are pivoted on a common rocker shaft.
Shogging movements: • The sideways shogging movements which occurs parallel to the underlaps and overlaps. The occurrence, timing, direction and extent of each shog is separately controlled for each guide bet by each guide bar by its pattern chain links or pattern wheel. Attached to a horizontal pattern shaft driven from the main cam shaft but set at right angles to it at one end of the m/c.
Lapping diagram: Lapping diagram are drawn around horizontal rows of points that represent needles in plain view, usually assuming the pattern mechanism to be on the right. As the guides position themselves in the spaces between the needles the positions between vertical columns of points can be given chain link numbers commencing with the ‘O’ position which is to the right of the right hand column of points. Provided the direction and extent of the overlaps are correctly indicated in the lapping diagram and chain notation, the under laps will always be corrected position as each extends from the end of one overlap to the start of the next. Here, 0…3 → Chain link ‘-’ → Overlap ‘/’ → Under lap
Basic overlap/under lap variations:All guide bar lapping movements are composed of one or more of the following lapping variation • An overlap followed by an underlap in the opposite direction (closed lap) • An over lap followed by an underlap in the same direction (open lap) • Only overlaps and no underlaps (open laps) • Only underlaps and no overlaps (Laying-in) 5. Neitheir overlaps nor underlaps (Miss lapping) (1-0/1-2//) (0-1/2-1//) 01/1-2// Fig: Close lap Fig: Open lap Fig: Open laps
0-0/2-2/1-1/3-3// Fig: Miss-lapping Fig: laying-in Basic lapping movements: 1.Pillar/Chain stitch 2.Tricot stitch or 1 and 1 lapping movement 3.Cord stitch or 2 and 1 lapping movement 4.Longer reciprocating lapping movement 5.Atlas stitch or lapping movements 6.Two needle overlap
1-0/0-1 1-0/1-0 Fig: closed lap Open lap Pillar stitch: Tricot stitch: Cord stitch : Closed open 1-2/1-0 2-1/0-1 Open Closed 3-2/0-1// 2-3/1-0//
4-3/0-1// 3-4/1-///Open lap close lap Longer reciprocating lapping movements: Atlas stitch: Two course atlas 3-4/3-2/2-1/1-0/1-2/2-3// Three course Tricot atlas
Types of warp knitting m/c: Two major classes of warp knitting m/cs:- 1. Tricot warp knitting m/c 2. Raschel warp knitting m/c. Features Tricot warp knitting m/c: • In the past, tricot m/cs mainly employed bearded needles with a pressure bar • Tricot m/cs have a gauge expressed in needle per inch and chain link numbering 0, 1, 2, 3, 4 etc. generally with three links per course • Their sinkers, which are joined to each other at the front and back, never move clear of the needles as they combine the functions of holding down, knocking over and supporting the fabric • The fabric is drawn-away towards the batching roller almost at right angles to the needles bar.
The warp beams are accommodated in an inclined arc towards the back of the m/c with the top beam supplying the front guide bar and the bottom beam supplying the back guide bar • The warp sheets pass over the top of the guide bar rocker shaft to their tension rails situated at the front of the m/c • Mechanical attention to the knitting elements is carried out at the front of the m/c, as the beams prevent across to the back. • As all the warp sheets are drawn over the rocker shaft to the m/c, it is easier to thread up the guide bars commencing with the needle bar. • The guide bars are therefore numbered from the back towards the front of the m/c because of threading sequence.
Knitting elements of tricot m/c: The main knitting elements of a tricot warp knitting m/cs are- • Needle • Sinker • Guides and guide bar Needle: In the past, bearded needle used. But compound needle is used in the most of the modern tricot m/c. at present compound needle is widely used in tricot m/c. mainly two parts in compound needle Stem – The main part and formed with hook and butt stem placed in the trick of needle bed Sliding latch – Placed in the cut parts of stem which can move up and down. Sliding latch attached to ″ lead which
