Presentation on theme: "Warp Knit Basic Structure"— Presentation transcript:
1Warp Knit Basic Structure Jimmy K.C. LamThe Hong Kong Polytechnic University
2Agenda Characteristics of Warp Knit Fabric Advantages of Warp Knit FabricDisadvantages of Warp Knit FabricFormation of Warp Knit FabricPattern notation and Guide Bar MovementLapping movementOverlap onlyUnderlap onlyoverlap and underlapneither overlap nor underlap
3Advantages of Warp Knit Fabric Dimensional StabilityIn general, warp knitted fabric are more stable than weft knitted fabric. By modifying its structure (by weft insertion), the warp knitted can be as good as woven fabric.Fabric TightnessThe warp knitted fabrics are thinner than double knitted fabrics and the loops are smaller than double knitted fabric.Fabric appearanceMost regular warp knitted fabrics give a nice, clean and balanced loops on surface. Normally the technical face and back for warp knitted are different.
4Advantages (II) Yarn unroving Low Knitting cost Yarn cannot be unroved from a warp knit fabric from any edges; this is the clear difference between weft knit fabrics.Low Knitting costThe knitting cost is inversely proportional to the machine production speed
5DisadvantagesThe warp knit is not suitable for apparel textile because of the following drawback:Raw MaterialNot all materials are suitable for warp knitting, especially those yarns with low yarn strength and irregular surface. Normally filament yarns are for warp knitting.Yarn countOnly a fine yarn count (50-70 deniers for 2 guide bar) is used for warp knitting. The spun yarns are seldom made to these fine counts.
6Disadvantages (II) Machine Stoppage Pattern preparation Fabric Faults Warp knitting machines must be stopped for changing warp beams and piecing the broken threads. These are normally take hours to completePattern preparationFor a fancy structures using multi-bar, large amount of time and chain links have to prepare. For jacquard selection, it is only possible on electronic raschel machine.Fabric FaultsOne special feature on warp knitting machine is no stop motions is equipped. The modern machines today are installed with optical scanner to scan the fabric and stop the machine in case the faults occurred.
7Disadvantages (III) Small orders DISCUSSION The warp knitted machines are built for mass production and is not suitable for small orders and frequently changes pattern.DISCUSSIONPlease explain why warp knitted fabrics are seldom used on apparel and fashion market.
8Formation of warp knit fabrics Unlike the weft knitted fabrics which can be produced by even one single end of yarn for any number of courses and wales, the warp knitted fabrics required one warp yarn for a wale.The warp knitted fabric is formed by knitting the warp yarns on the adjacent needles course by course and intermesh the loops with the neighbouring yarns to form fabric.
9From the diagrams below, it is clear that if a warp knit fabric required 1000 wales, then there must be 1000 warp yarns on thebeam and slightly more than 1000 needles on machine
10Pattern Control UnitThe development of a pattern on warp knitting machine is a combination ofcolour yarn pattern on warp beams;warp thread setting on guide bars; andlapping movement of the guide barsFor a simple single guide bar, single colour fabric, the structure is based on the lapping movement of the guide bar.
11Guide Bar Shogging Mechanism The control of thelapping movement ofguide bar is from thechain links on the patternwheel
12Chain LinksDifferent Height ofLinks control the lappingmovement
13The guide bar movements There are three types of movements on the guide bar, namelyforward and backward swing;lateral movement for overlaps; andlateral movement for underlapsThe first one is controlled by the cam shaft, the next two are controlled by the chain links
14Example Lapping movement of Half Tricot: 1-2/1-0 “1-2” indicates the guide bar is doing overlap from needleposition “1” to “2” ie. From right to left for one needle“1-0” indicates the yarn is fed to the needles from the left toright for one needle space.
15The last example only shows one warp thread on one guide bar for a repeat structure. When thousands of warp threads are on the sameguide bar, and all the warp threads are doing the same movement, aknitted fabric is formed
16Basic combination of overlap and underlaps All warp knit fabric structures are composed of both overlap and underlap
171) Overlap OnlyIn this group, the guide bar only feed yarn to the same needle all the time.The result is that each needle knits a chain of stitches.Example: 1-0/01, known as pillar stitchA pillar stitch is not a fabric, but is commonly used with other lapping movements to form a fabric.
182) Underlaps OnlyUnderlap alone cannot form into a fabric and is commonly used with other lapping movements.If a guide bar only made underlaps in a multi-guide structure, this guide bar is called inlay bar and the warp are called inlay yarn, which never form into loops but only “tie-in” at the back of the fabric.
193) Overlap with underlap When overlap and underlap are worked together, two type of fabrics can be formedThe first one, when overlap and underlap are moving the same direction, a open lap fabric will be formed.The second one, when overlap and underlap are moving in opposite direction, closed lap will be produced
214) Neither Overlap Nor Underlap This seems to be warp float in the fabric.The guide bars give no lateral movements for a few courses in the repeat, laying the warps straight in the fabric.For a multi guide bar fabric, it is used to hide colour warps at the back for a colour pattern.
225) Double Needle Overlaps Unlike the underlaps, which can go across many needles spaces; overlaps can be in form of one or two needles onlyHowever, double needle overlaps are not common because of the difficulty in the control of the warp tension and let off.
23DiscussionWrite down the lapping movements, chain notations for the given loop diagrams