Weft knitting structure

Plain structure is formed on single bed machine whereas the other three are made on double bed machines. But the arrangements of needles in the two beds are different for obtaining rib, interlock and purl structures.Most of the weft knitting is of tubular form.weft knitting machine four basic structure.

weft knitted structure:

Plain
Rib
Interlock
Purl

Plain structure:

Plain is produced by the needles knitting as a one set, drawing the loops far away from the technical back and towards the technical face side of the fabric. Plain is that the simplest and most economical weft knitted structure to supply and has the utmost covering power. It usually has a 40% potential recovery in width after expansion. It typically features a potential recovery of 40% width after stretching.

Plain Structure

Plain knitting machine, process and structure

Single jersey weft knitting machine has only one bed which may be flat or circular.
Machine has only one bed which may be flat or circular.
There is only one set of needles and one cam system in the machine.
Minimum one yarn is needed to produce a fabric.
Single-faced structure, i.e. only one type of loops – Face or Back – are visible on the surface
Fabric thickness is approximately two times the diameter of the yarn used.
Properties like rigidity, air permeability, bursting strength, etc. Courses per inch and Wales per inch in the fabric inversely vary with loop length.
Fabric shrinks in width/circumference and the extent of shrinkage is about in the range of 25–40%.
Stitch length can be varied with stitch cam setting.
Because of stitch simplicity, production rate is high and machine is simple and cheap.
Yarn /course can be unproved from starting and ending end of knitting.
Fabric has good extensibility in both length and width direction but width-wise extensibility is generally much higher than length-wise extensibility.
Fabric shortens in width if the same is extended in length by tension and vice-versa.
Knitted loops tend to distort easily under tension which help to give form fitting and comfort.
Because of side limbs of the loops on the face side, it feels smoother on face side than back side.
Loops are V-shaped on technical face and semi-circular on technical back of the fabric.

Rib Structure:

1 x 1 ribs is production of by two sets of needles being alternately set or gated between each other. Relaxed 1 x1 rib is theoretically twice the thickness and half the width of an equivalent plain fabric, but it has twice the maximum amount width-wise recoverable stretch.

In practice, 1 x 1 rib normally relaxes by approximately 30 per cent compared with its knitting width. It is a more expensive fabric than plain.

Rib Structure

The knitting action of a circular rib machine

The cylinder and dial needles move out to clear the plain and rib loops formed within previous cycle.
Yarn Feeding. The needles are withdrawn into their tricks order that the old loops are covered by the open latches and therefore new yarn is fed into the open hooks.
Knocking-over. The needles are withdrawn into their tricks in order that the old loops are cast off and the new loops are drawn through.

Rib knitting machine, process and structure :

Machine has two beds – may be flat or circular.
There are two sets of needles – one in each bed.
There are two cam systems – one in each bed
Fabric surface is vertically corrugated or ribbed
Rib fabrics are double-faced structures as well as balanced structures
Each course is made of face loop and back loop in alternative order, the order may be 1×1, 2×2, 3×3, 6×3, etc.
Face loops are made by the needles in front or bottom bed and back loops are made by needles in the back or top bed
Fabric surface is rough or harsh in feel
Rib machine requires finer yarn and results in comparatively costly fabric.
Minimum one yarn is needed to produce a fabric

Interlock Structure:

Interlock has the technical face of plain fabric on both sides, but its smooth surface cannot be stretched out to reveal the reverse meshed loop wales because the wales on each side are exactly opposite to each other and are locked together. The interlock structure is the only weft knitted base not normally used for individual needle selection designs.

Interlock Structure

An interlock machine must have the following:

Interlock gating, the needles in two beds being exactly opposite each other so that only one of the two can knit at any feeder.
Two separate cam systems in each bed, each controlling half the needles in an alternate sequence, one cam system controlling knitting at one feeder, and the other at the next feeder.
Needles set out alternately, one controlled from one cam system, the next from the other; diagonal and not opposite needles in each bed knit together.

Interlock knitting machine, process and structure

Interlock Weft knitting Machine has two beds. Machines may be flat or circular, but generally circular.
There are two sub sets of needles in each bed, the sub sets are known as short needles and long needles, respectively.
Short needles and long needles don’t make loop simultaneously but with a time gap.
Two sets of cam system, cam path in each bed accommodate short and long needles of the corresponding beds.
Loops made by one set of needles are locked by the loops made by the other set of needles.
Short needles in one bed make loops in conjunction with short needles in the other bed, similarly long needles in one bed make loops in conjunction with long needles in the other bed.
Separate yarns are to be supplied to the short needles and long needles for loop formation through separate feeders.
Each interlock course is composed of two rib courses
Minimum two yarns are needed to produce a fabric.
Fabric has double faced as well as very stable structure.
Fabric surface is smooth.
Fabric is equally thicker to rib but much more compact.
Fabric neither curls nor ladder.
Machine is complicated and costly.
Fabrics are dimensional stable, heavy and costly.

Purl Structure:

Purl structures have one or more wales which contain both face and reverse loops. This can be achieved with double-ended latch needles or by rib loop transfer from one bed to the other, combined with needle bed racking. The tricks of the two needle beds in purl machines are exactly opposite to each other and in the same plane. As the needle moves across between the two needle beds, the old loop slides off the latch of the hook that produced it and moves along the needle towards the other hook.

Purl structure

Purl needle transfer action

Engagement of the head of the receiving slider with the needle hook that was originally knitting from the opposing bed.
Cam action causing the head of the delivering slider to pivot outwards from the trick and thus disengage itself from the other hook of the needle.
Sufficient free space to allow the heads of the sliders to pivot outwards from their tricks during engagement and disengagement of the needles.
A positive action which maintains the engagement of the head of a slider with a needle hook throughout its knitting cycle by ensuring that it is pressed down into the trick.

Purl knitting machine, process and structure

Purl weft knitting Machine has two beds. Machines may be flat or circular.
There is only one set of needles which change the bed in alternative knitting cycle.
Needles are shifted from one bed to another bed with the help of sliders. Two sliders are needed for each needle
Same needle makes face loop in one bed and back loop in other bed.
Fabric has horizontal corrugation or rib appearance on the surfaces, opposite to rib fabric.
Fabric is reversible in appearance and has soft handle.
Fabric has very high extensibility in length direction, making it suitable for kids wear.
Fabric does not curl at the edges because of alternate face and back loop courses.
Machines are very rare.