Warp KnitWarp KnitBasic StructureBasic Structure

Jimmy K.C. LamJimmy K.C. Lam

The Hong Kong Polytechnic UniversityThe Hong Kong Polytechnic University

AgendaAgenda Characteristics of Warp Knit FabricCharacteristics of Warp Knit Fabric Advantages of Warp Knit FabricAdvantages of Warp Knit Fabric Disadvantages of Warp Knit FabricDisadvantages of Warp Knit Fabric Formation of Warp Knit FabricFormation of Warp Knit Fabric Pattern notation and Guide Bar MovementPattern notation and Guide Bar Movement Lapping movementLapping movement

– Overlap onlyOverlap only– Underlap onlyUnderlap only– overlap and underlapoverlap and underlap– neither overlap nor underlapneither overlap nor underlap

Advantages of Warp Knit FabricAdvantages of Warp Knit Fabric Dimensional StabilityDimensional Stability

– In general, warp knitted fabric are more stable than weft knitted fabric. By In 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 modifying its structure (by weft insertion), the warp knitted can be as good as woven fabric.as woven fabric.

Fabric TightnessFabric Tightness– The warp knitted fabrics are thinner than double knitted fabrics and the The warp knitted fabrics are thinner than double knitted fabrics and the

loops are smaller than double knitted fabric. loops are smaller than double knitted fabric.

Fabric appearanceFabric appearance– Most regular warp knitted fabrics give a nice, clean and balanced loops on Most regular warp knitted fabrics give a nice, clean and balanced loops on

surface. Normally the technical face and back for warp knitted are surface. Normally the technical face and back for warp knitted are different.different.

Advantages (II)Advantages (II) Yarn unrovingYarn unroving

– Yarn cannot be unroved from Yarn cannot be unroved from a warp knit fabric from any a warp knit fabric from any edges; this is the clear edges; this is the clear difference between weft knit difference between weft knit fabrics.fabrics.

Low Knitting costLow Knitting cost– The knitting cost is inversely The knitting cost is inversely

proportional to the machine proportional to the machine production speedproduction speed

Machinetype

Fabric Width Machinespeed

2 bar tricot Over 400 cm 2000 cpm

Circularplain

Under 200cm 1400 cpm

Air jet loom 600 cm 600 ppm

Shuttle loom 130 cm 150 ppm

DisadvantagesDisadvantages

The warp knit is not suitable for apparel textile The warp knit is not suitable for apparel textile because of the following drawback:because of the following drawback:

Raw MaterialRaw Material– Not all materials are suitable for warp knitting, especially Not all materials are suitable for warp knitting, especially

those yarns with low yarn strength and irregular surface. those yarns with low yarn strength and irregular surface. Normally filament yarns are for warp knitting.Normally filament yarns are for warp knitting.

Yarn countYarn count– Only a fine yarn count (50-70 deniers for 2 guide bar) is Only a fine yarn count (50-70 deniers for 2 guide bar) is

used for warp knitting. The spun yarns are seldom made to used for warp knitting. The spun yarns are seldom made to these fine counts.these fine counts.

Disadvantages (II)Disadvantages (II) Machine StoppageMachine Stoppage

– Warp knitting machines must be stopped for changing warp beams and Warp knitting machines must be stopped for changing warp beams and piecing the broken threads. These are normally take hours to completepiecing the broken threads. These are normally take hours to complete

Pattern preparationPattern preparation– For a fancy structures using multi-bar, large amount of time and chain For a fancy structures using multi-bar, large amount of time and chain

links have to prepare. For jacquard selection, it is only possible on links have to prepare. For jacquard selection, it is only possible on electronic raschel machine.electronic raschel machine.

Fabric FaultsFabric Faults– One special feature on warp knitting machine is no stop motions is One special feature on warp knitting machine is no stop motions is

equipped. The modern machines today are installed with optical scanner equipped. The modern machines today are installed with optical scanner to scan the fabric and stop the machine in case the faults occurred.to scan the fabric and stop the machine in case the faults occurred.

Disadvantages (III)Disadvantages (III)

Small ordersSmall orders– The warp knitted machines are built for mass production and The warp knitted machines are built for mass production and

is not suitable for small orders and frequently changes is not suitable for small orders and frequently changes pattern.pattern.

DISCUSSIONDISCUSSION Please explain why warp knitted fabrics are seldom Please explain why warp knitted fabrics are seldom

used on apparel and fashion market.used on apparel and fashion market.

Formation of warp knit fabricsFormation of warp knit fabrics

Unlike the weft knitted fabrics which can be Unlike the weft knitted fabrics which can be produced by even one single end of yarn for any produced by even one single end of yarn for any number of courses and wales, the warp knitted number of courses and wales, the warp knitted fabrics required one warp yarn for a wale.fabrics required one warp yarn for a wale.

The warp knitted fabric is formed by knitting The warp knitted fabric is formed by knitting the warp yarns on the adjacent needles course the warp yarns on the adjacent needles course by course and intermesh the loops with the by course and intermesh the loops with the neighbouring yarns to form fabric.neighbouring yarns to form fabric.

From the diagrams below, it is clear that if a warp knit fabric required 1000 wales, then there must be 1000 warp yarns on the beam and slightly more than 1000 needles on machine

Pattern Control UnitPattern Control Unit

The development of a pattern on warp knitting The development of a pattern on warp knitting machine is a combination ofmachine is a combination of– colour yarn pattern on warp beams;colour yarn pattern on warp beams;– warp thread setting on guide bars; andwarp thread setting on guide bars; and– lapping movement of the guide barslapping movement of the guide bars

For a simple single guide bar, single colour For a simple single guide bar, single colour fabric, the structure is based on the lapping fabric, the structure is based on the lapping movement of the guide bar.movement of the guide bar.

Guide Bar Shogging MechanismGuide Bar Shogging Mechanism

The control of thelapping movement ofguide bar is from thechain links on the pattern wheel

Chain LinksChain Links

Different Height ofLinks control the lappingmovement

The guide bar movementsThe guide bar movements

There are three types of movements on the There are three types of movements on the guide bar, namelyguide bar, namely– forward and backward swing;forward and backward swing;– lateral movement for overlaps; andlateral movement for overlaps; and– lateral movement for underlapslateral movement for underlaps

The first one is controlled by the cam shaft, the The first one is controlled by the cam shaft, the next two are controlled by the chain linksnext two are controlled by the chain links

ExampleExampleLapping 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.

The last example only shows one warp thread on one guide barfor a repeat structure. When thousands of warp threads are on the same

guide bar, and all the warp threads are doing the same movement, aknitted fabric is formed

Basic combination of overlap and Basic combination of overlap and underlapsunderlaps

All warp knit fabric structures are All warp knit fabric structures are composed of both overlap and underlapcomposed of both overlap and underlap

1) Overlap Only1) Overlap Only In this group, the guide In this group, the guide

bar only feed yarn to the bar only feed yarn to the same needle all the time.same needle all the time.

The result is that each The result is that each needle knits a chain of needle knits a chain of stitches.stitches.

Example: 1-0/01, known Example: 1-0/01, known as pillar stitchas pillar stitch

A pillar stitch is not a A pillar stitch is not a fabric, but is commonly fabric, but is commonly used with other lapping used with other lapping movements to form a movements to form a fabric.fabric.

2) Underlaps Only2) Underlaps Only Underlap alone cannot Underlap alone cannot

form into a fabric and is form into a fabric and is commonly used with other commonly used with other lapping movements.lapping movements.

If a guide bar only made If a guide bar only made underlaps in a multi-guide underlaps in a multi-guide structure, this guide bar is structure, this guide bar is called inlay bar and the called inlay bar and the warp are called inlay yarn, warp are called inlay yarn, which never form into loops which never form into loops but only “tie-in” at the back but only “tie-in” at the back of the fabric.of the fabric.

3) Overlap with underlap3) Overlap with underlap

When overlap and underlap are worked When overlap and underlap are worked together, two type of fabrics can be formedtogether, two type of fabrics can be formed– The first one, when overlap and underlap are The first one, when overlap and underlap are

moving the same direction, a open lap fabric will be moving the same direction, a open lap fabric will be formed.formed.

– The second one, when overlap and underlap are The second one, when overlap and underlap are moving in opposite direction, closed lap will be moving in opposite direction, closed lap will be producedproduced

1 X 1 Open Lap Fabric

1 X 1 Closed Lap Fabric

4) Neither Overlap Nor Underlap4) Neither Overlap Nor Underlap This seems to be warp This seems to be warp

float in the fabric.float in the fabric. The guide bars give no The guide bars give no

lateral movements for a lateral movements for a few courses in the repeat, few courses in the repeat, laying the warps straight laying the warps straight in the fabric.in the fabric.

For a multi guide bar For a multi guide bar fabric, it is used to hide fabric, it is used to hide colour warps at the back colour warps at the back for a colour pattern.for a colour pattern.

5) Double Needle Overlaps5) Double Needle Overlaps

Unlike the underlaps, Unlike the underlaps, which can go across many which can go across many needles spaces; overlaps needles spaces; overlaps can be in form of one or can be in form of one or two needles onlytwo needles only

However, double needle However, double needle overlaps are not common overlaps are not common because of the difficulty in because of the difficulty in the control of the warp the control of the warp tension and let off.tension and let off.

DiscussionDiscussion

Write down the Write down the lapping movements, lapping movements, chain notations for the chain notations for the given loop diagramsgiven loop diagrams