Single Guide Bar & Double Guide Bar Fabrics Jimmy K.C. Lam The Hong Kong Polytechnic University
Agenda n Factors that can affect the properties of warp knit fabrics n Single guide bar fabrics n Double guide bar fabrics n Part-set threading: eyelet fabrics
Factors affect warp knit fabric properties n Yarn type –This is exactly the same case as on weft knitted fabric. Yarn and fibre properties like pilling, felting, elasticity, electrostatics, handle and bulkiness will give great influence on warp knit fabric.. n Finishing –The history of yarn and finish of fabric such as washing, tentering and brushing will affect the fabric handle, density, appearance and dimensional stability. n Fabric Structure –This item included the lapping movement of guide bars, the number of guide bar used, the threading of each bar and weft insertion..
Characteristics Warp knit fabrics produced by one guide bar alone have the following drawback: n Poor Dimensional Stability –Like a loosely knitted single jersey in weft knitting. n Lower Patterning potential –One of the main fabric design elements on warp knit is the use of guide bars. –The modern raschel machines have expanded from 48 guide bars to 76 just for the purpose of increasing the pattern potential.
Characteristics (II) n Poor Cover –In knitting the regular structures, the number of yarns used to form a loop is directly proportional to the number of guide bar. For single bar fabrics, most loops are composed of one yarn only and consequently the cover is not as good as 2 or 3 guide bar. n Loop distortion –The loops of each course tend to deflect to the same direction as the guide bar overlap. This problem is not so serious in those two or more bar fabrics, simply because the guide bars usually move in a direction opposite to each other. n Edge curling –All single bar fabrics are made of unbalanced structures and fabrics will curl to one side.
Examples n Pillar Stitches n Pillar stitch is a chain of loops produced by a single needle. n For example, if a machine has 2000 needles, it will produce 2000 chains of loops instead of a unique piece of fabric. n However, pillar stitches are used as the ground structure for other multi bar structures.
Pillar stitches with weft insertion n The only possible way to make a fabric out of single guide bar pillar stitch is to add weft yarn to link up the chains. n Fabrics of this type are used for decoration purposes.
Half Tricot n Also known as 1 X 1 closed lap n The 1 X 1 lap is the basic formation of warp knit fabric. n The guide bar feeds yarn on a needle in the first course, and then it moves sideways to feed yarn on the neighbouring needle in the second course and repeat n All the warp knit fabrics are formed in the similar manner, except that there might be more guide bars used, more courses per repeat, or different underlaps and different direction of guide bar shogging.
Modification of Half Tricot The difference between these three fabrics is the amount of guide bar shogging for underlaps. Fabric weight: 3x1 > 2x1 > 1x1 Finished Width: 3x1 < 2x1 < 1x1
Single Atlas n A typical single guide bar fabric with horizontal stripe effect n The lapping movement of guide bar moves in one direction for a number of courses and then return; this changes the direction of inclination of loops.
Characteristics n Good Dimensional stability, reasonable cover –Most of two bar fabrics are tightly knitted with their underlaps in different directions, the fabrics have much lower elasticity compared with weft knitted n Better loop shape and ladder resistance –Each loop is composed by two individual loops stick together. In most cases, the loops are formed by overlap in opposite direction; therefore, the resultant loop is perfectly balanced and show no distortion
Characteristics (II) n Reasonable weight –The weight of two guide bar fabrics is not necessary equal to double the weight of the single guide bar fabric. »28 gauge single bar fabric, 150 deniers »28 gauge two bar fabric, 75 deniers »28 gauge three bar fabric, 50 deniers –The resultant count on each loop is similar, but the stitch density and underlaps will influence the fabric wieght.with weft knitted n Better pattern scope –Two guide bar machine can have the following pattern »vertical colour stripes;- colour check effects; »two different guide bars with individual overlap and underlap movements »two guide bars of different materials; »application of different warp tensions.
Examples : Full Tricot n This structure is actually knitting two “half tricot” together with two bars moving in opposite direction. n This is a balanced structure, the two set of warp yarns are doing their overlap in opposite direction. This result in perfect upright loops in the fabric surface.
Locknit n Most two guide bar structures are not balanced. n Although all structures have their overlap and underlaps in the opposite direction, but the underlap displacements of the two bars are different. n Locknit is one of the examples. n The FGB makes a longer undrlap than BGB, and the result is the fabric will give lower sideway elasticity than tricot.
Satin n Satin is a locknit base structure. It contains even longer underlap in the FGB. I.e 3 to 4 needles underlap and the BGB will remain 1x1 closed lap. n The excessive length of underlap at the back of the fabric will give very good light reflection when the FGB yarns are flat acetate. n E.g FGB= 1-0/3-4 and BGB=1-2/1-0
Reverse locknit and Sharkskin n They are very similar to locknit. The only difference is the swapping of the chain notations between FGB and BGB. –Reverse locknit: FGB=1-0/1-2; BGB=2-3/1-0 –Sharkskin : FGB=1-0/1-2; BGB=4-5/1-0 n The reverse locknit and locknit fabrics if knitted under the same condition show different appearance and properties. n The reverse locknit is more rigid fabric because the BGB long underlaps are trapped by the shorter FGB underlap.
Sharkskin The Sharkskin which has a longer underlap 4-5/1-0 on the BGB, will be even heavier in weight
Queen’s Cord n Queen’s cord is a very stable structure. n The pillar stitches act as warp yarns and the long underlaps act as weft yarns in the fabric. n Therefore, its dimensional stability should be near to the woven fabrics.
Double Atlas n Combination of two pieces of single atlas knitting together with opposite lapping direction. n The two guide bar (double atlas) will give a solid vertical wales and is more stable than single atlas. n Normally double atlas is knitted with colour patterns.
Marquisette Curtain Net n This is a two bar inlay fabric with FGB making the pillar stitch and the BGB making the inlay. n It is common to make on raschel machine because of coarser gauge and the underlaps can shog for longer distance. n The inlay yarns, which will never form into loops in the fabric, is usually thicker, and sometimes, fancy yarns are used. n In warp knitting, the FGB is always used for knitting ground structure, and the guide bars for inlay are always at the back. –For example: A 6 bar raschel will have to used the first 2 bars for the ground structure and the No. 3, 4, 5, and 6 guide bars for inlay yarn as pattern bars
Marquisette Curtain Net The 2 bar Marqiosette os a see through net fabric composed of square cells, is used for low cost curtain net. FGB:1-0/0-1 BGB:0-0/1-1/0-0/3-3/2-2/3-3
Raschel Lace Ground Structure n The modern raschel laces are knitted with up to 48 guide bar, and normally the first 2 or 3 bars are used for ground structure, and the rest are called the pattern bars. n The most popular ground structure for raschel is a two bar structure called TULLE n FGB: 2-0/0-2/2-0/2-4/4-4/2-4 n BGB:0-0/2-2/0-0/4-4/2-2/4-4
Two guide bar fabrics with part set threading n The term part set threading means that the guide bar is party threaded with warp yarn, and the pattern of threading could be: –1 in 1 out –2 in 1 out; –2 in 2 out; or any fancy setout
Eyelet formation n The formation of holes or eyelets on warp knit fabrics is purely a kind of miss connection between the wales on a particular spot for a certain courses.
Eyelet formation (II) n Fig A: both guide bars are fully threaded, a normal warp knit fabric can be produced n Fig B: both guide bars are half set ( 1 in 1 out) and the relative position of the bars are shown in the diagram. No fabric can be formed because of the lack of connection between wales. n Fig C: both guide bars are half set, but the relative position of the bars are off set. No fabric can be formed because the loops will press off at the “X” needles.