Transcript Warp Knit Fabric

Warp Knit
Basic Structure
Jimmy K.C. Lam
The Hong Kong Polytechnic University
Agenda
Characteristics of Warp Knit Fabric
 Advantages of Warp Knit Fabric
 Disadvantages of Warp Knit Fabric
 Formation of Warp Knit Fabric
 Pattern notation and Guide Bar Movement
 Lapping movement

–
–
–
–
Overlap only
Underlap only
overlap and underlap
neither overlap nor underlap
Advantages of Warp Knit Fabric

Dimensional Stability
– 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 as woven fabric.

Fabric Tightness
– The warp knitted fabrics are thinner than double knitted fabrics
and the loops are smaller than double knitted fabric.

Fabric appearance
– Most regular warp knitted fabrics give a nice, clean and
balanced loops on surface. Normally the technical face and
back for warp knitted are different.
Advantages (II)

Yarn unroving
– Yarn cannot be unroved from
a warp knit fabric from any
edges; this is the clear
difference between weft knit
fabrics.

Low Knitting cost
– The knitting cost is inversely
proportional to the machine
production speed
M ach in e
type
2 bar tricot
F abric W idth M ach in e
speed
O ver 400 cm 2000 cpm
C ircu lar
plain
A ir jet loom
U nder 200cm 1400 cpm
600 cm
600 ppm
S h u ttle loom 130 cm
150 ppm
Disadvantages


The warp knit is not suitable for apparel textile
because of the following drawback:
Raw Material
– Not 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 count
– Only 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.
Disadvantages (II)

Machine Stoppage
– Warp knitting machines must be stopped for changing warp
beams and piecing the broken threads. These are normally
take hours to complete

Pattern preparation
– 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 electronic raschel machine.

Fabric Faults
– One 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.
Disadvantages (III)

Small orders
– The warp knitted machines are built for mass production and
is not suitable for small orders and frequently changes
pattern.


DISCUSSION
Please explain why warp knitted fabrics are seldom
used on apparel and fashion market.
Formation 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.

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 Unit

The development of a pattern on warp knitting
machine is a combination of
– colour yarn pattern on warp beams;
– warp thread setting on guide bars; and
– lapping movement of the guide bars

For a simple single guide bar, single colour
fabric, the structure is based on the lapping
movement of the guide bar.
Guide Bar Shogging Mechanism
The control of the
lapping movement of
guide bar is from the
chain links on the
pattern
wheel
Chain Links
Different Height of
Links control the lapping
movement
The guide bar movements

There are three types of movements on the
guide bar, namely
– forward and backward swing;
– lateral movement for overlaps; and
– lateral movement for underlaps

The first one is controlled by the cam shaft, the
next two are controlled by the chain links
Example
Lapping movement of Half Tricot: 1-2/1-0
“1-2” indicates the guide bar is doing overlap from needle
position “1” to “2” ie. From right to left for one needle
“1-0” indicates the yarn is fed to the needles from the left to
right for one needle space.
The last example only shows one warp thread on one guide bar
for a repeat structure. When thousands of warp threads are on the same
guide bar, and all the warp threads are doing the same movement, a
knitted fabric is formed
Basic combination of overlap and
underlaps
All warp knit fabric structures are
composed of both overlap and underlap
1) Overlap Only




In 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 stitch
A pillar stitch is not a
fabric, but is commonly
used with other lapping
movements to form a
fabric.
2) Underlaps Only


Underlap 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.
3) Overlap with underlap

When overlap and underlap are worked
together, two type of fabrics can be formed
– The 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
1 X 1 Open Lap Fabric
1 X 1 Closed Lap Fabric
4) 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.
5) Double Needle Overlaps


Unlike the underlaps,
which can go across many
needles spaces; overlaps
can be in form of one or
two needles only
However, double needle
overlaps are not common
because of the difficulty in
the control of the warp
tension and let off.
Discussion

Write down the
lapping movements,
chain notations for the
given loop diagrams