Knitting Doc

32
1 KNITTING The term knitting describes the technique of constructing textile structure by forming a continuous length of yarn into columns of vertically intermeshed loops. It is the interloping of yarns, which are interlaced in a variety of ways to form a fabric. It is a process of manufacturing a fabric by the intermeshing of loops of yarns. When one loop is drawn through another loop, a stitch is formed. Types of knitting 1. Weft knitting 2. Warp knitting Comparison between weft and warp knitting:- WEFT KNITTING WARP KNITTING The loops are formed across the width of fabric. The loops are formed vertically down the length of fabric. It is possible to knit with one thread. Warp beam is used. Staple as well as filament yarns can be worked successfully. Filament yarn can be worked successfully. Latch needles are used. Latch, beard, or compound needles are used. Less versatile machines. More versatile machines. Speed reduces with design change in cams. Change in pattern does not affect the speed of machines. Fabric quality is not consistent. Fabric quality is consistent. Loops are not uniform. Loops are uniform. Stretch in both direction. Stretch in widthwise direction. Less dimensional More dimensional

Transcript of Knitting Doc

Page 1: Knitting Doc

1

KNITTING

The term knitting describes the technique of constructing textile structure by forming a continuous length of yarn into columns of vertically intermeshed loops.

It is the interloping of yarns, which are interlaced in a variety of ways to form a fabric. It is a process of manufacturing a fabric by the intermeshing of loops of yarns. When one loop is drawn through another loop, a stitch is formed.

Types of knitting

1. Weft knitting 2. Warp knitting

Comparison between weft and warp knitting:-

WEFT KNITTING WARP KNITTING The loops are formed across

the width of fabric. The loops are formed vertically

down the length of fabric. It is possible to knit with one

thread. Warp beam is used.

Staple as well as filament yarns can be worked successfully.

Filament yarn can be worked successfully.

Latch needles are used. Latch, beard, or compound needles are used.

Less versatile machines. More versatile machines. Speed reduces with design

change in cams. Change in pattern does not

affect the speed of machines. Fabric quality is not consistent. Fabric quality is consistent. Loops are not uniform. Loops are uniform. Stretch in both direction. Stretch in widthwise direction. Less dimensional stability. More dimensional stability. Cheaper to produce. Costlier to produce. E.g. circular knitting machine. E.g. tricot & raschel machine.

1. Weft knitting

Page 2: Knitting Doc

1

The loops are made in a horizontal way from a single yarn and intermeshing of loops in a circular or flat form on a course-wise basis. In this method, one or more yarns are being fed (called ‘Feeds’) one at a time, to a multiplicity of knitting needles, placed in either lateral or circular fashion (Tubular). Each weft thread is fed, more or less, at right angles to the direction in which the fabric produced.

Course Wales

It is possible to knit with only one thread or cone of yarn, through production demands have resulted in circular weft knitting machines being manufactured with upto 192 threads (feeders).

Course – horizontal row of successive loops.Wale – vertical column of loops produced by the individual needles.Gauge – it express the number of needles/inch.Stitch length – length of yarns required to form a single loop.

Types of weft knitting

1. Single jersey2. Rib3. Interlock4. Purl

1. Single jersey

Page 3: Knitting Doc

1

This structure is produced by using one set of needles placed in the needle bed. It is done by drawing all the loops towards the technical face side.

Back side

Properties:-

• Simplest form of knitted structure.• V shaped loop on face side–Semi circular loops at backside.• Widthwise extensibility.• Non reversible.• If the single loop gets breaks, they tend to run or ladder.• Production rate is high because of stitch simplicity and its cost is low

because of machine simplicity.

Page 4: Knitting Doc

1

• If the yarn breaks, needle loops successively unmesh down a wale and sinker loops unmesh up a wale.

• Stitch length can be varied with cam setting.• Rigidity, air permeability, weight per unit area, bursting strength

changes with the stitch length.• The fabric may appear thick of flimsy if the stitch length is reduced or

increased.• The fabric can be unroved from either end and if a stitch is broken, the

wale will be disintegrate causing the stitches in that line to undo or ladder.

• Fabric tends to curl as the ends and side unless it has been heat set during the finishing.

The knitting action

Tucking in the hook for rest position :-

Page 5: Knitting Doc

1

The sinker is forward, holding down the old loop whilst the needle rises from the rest position.

Clearing :-

The needle has been raised to its highest position clearing the old loop from its latch.

Yarn feeding :-

The sinker is partially withdrawn allowing the feeder to present its yarn to the descending needle hook and also freeing the old loop so that it can slide up the needle stem and under the open latch spoon.

Knock-over :-

The sinker is fully withdrawn whilst the needle descends to knock-over its old loop on the sinker belly.

Page 6: Knitting Doc

1

Holding-down :-

The sinker moves forward to hold down the new loop in its throat whilst the needle rises under the influence of the upthrow cam to the reset position where the head of the open hook just protrudes above the sinker belly.

Cam

Page 7: Knitting Doc

1

Plain knitting

Rib

Page 8: Knitting Doc

1

• This structure is produced by using two set of needles (arrangement of needles side by side).

– Cylinder needle

– Dial needle

• It is done by drawing the loops towards the technical face side and backside alternatively.

Page 9: Knitting Doc

1

1x1 Rib

Page 10: Knitting Doc

1

Rib knits properties

• Face & back side having the same appearance (reversible).

• Used for collar, cuff and neck line.

• More elastic than the single jersey.

• Looks alternate vertical cords and thin ridges (1x1 Rib,2x2 Rib).

• Fabric generally produced on V-bed or circular machines.

• It is heavier and thicker structure than plain knit structure with similar gauge used. The rib machine also requires finer yarn than a similar gauge plain machine.

• It is more expensive fabric to produce than plain.

• The fabric does not curl at the edges due to its balanced nature.

• It can be unroved from the end knitted last by drawing the free loop heads through the back of each stitch.

• Rib fabrics are extensively used in the production of outwear garments.

Knitting action

Page 11: Knitting Doc

1

Clearing :-The cylinder and dial needle move out to clear the plain and rib loops formed in the previous cycle.

Yarn feeding :-

Page 12: Knitting Doc

1

The needles are withdrawn into their tricks so that the old loops are covered by the open latches and the new yarn is fed into the open hooks.

The dial needle has retracted before the cylinder needle and is in

the process of knocking-over the old loop.

Knocking-over :-

The needles are withdrawn into their tricks so that the old loops are cast off and the new loops are drawn through them.

Page 13: Knitting Doc

1

Cam

Needle timing

It is the relationship between the loop forming positions of the dial and cylinder needles measured as the distance in needles between the two stitch cam knock-over points.

Collective time adjustment is achieved by moving the dial cam-plate clockwise or anti-clockwise relative to the cylinder; individual adjustment at particular feeders (as required) is obtained by moving or changing the stitch cam profile.

Synchronized timing

If both the cylinder and dial needles knock over together, to produce loops of equal size, it is known as synchronized timing.

Page 14: Knitting Doc

1

Delayed timing

The dial knock-over occurs after about four cylinder needles have drawn loops and are rising slightly to relieve the strain.

The dial loops are thus larger than the cylinder loops and the fabric is tighter and has better rigidity; it is also heavier and wider, and less strain is produced on the yarn.

Interlock

Page 15: Knitting Doc

1

• This structure is produced by using Two set of needles placed opposite to each other.

– Cylinder needle

– Dial needle

• It is done by drawing the loops towards the technical face side at front and backside.

Properties

Page 16: Knitting Doc

1

• It looks with the V shaped structure at both front and back.

• It is called double jersey.

• Thicker, stronger fabric and similar smooth appearance on each side.

• Having less elongation than single jersey than & rib.

• Consequently, finer yarns are usually used to reduced the area density of the fabric.

• It unroves from the course knitted the last.

• The fabric becomes costlier due to thickness and less production.

• It is used for outwear fabrics (dress wear and skirts), often using wool, acrylic and polyester yarns, while cotton and polyester/cotton blends are used for the production of under garment.

Knitting action

The needle set out on the machine, with long and short needles alternating on the cylinder.

1 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 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.

Long needle cams were arranged for knitting at the first feeder and short needle cams at the second feeder.

At the first feeder, long needles in cylinder and dial knit, at the second feeder short needles knit together; needles not knitting at a feeder follow a run-through track.

Cam

Page 17: Knitting Doc

1

Notation

Purl

Page 18: Knitting Doc

1

Purl fabric has loops knitted to the front and back on alternate courses, in the contrast to a 1x1 rib fabric which is knitted to the front and back on alternative wales. If on both sides of a relaxed weft knitted fabric only reverse stitches are visible, then this is defined as a purl knitted fabric.

Purl was originally spelt ‘pearl’ and was so named because of its similar appearance to pearl droplets.

Properties

Purl fabric does not curl. Both sides are similar appearance. It extends easily in the lengthwise direction. It can be unroved from either end. The fabric is commonly used for children’s wear.

Knitting 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.

Page 19: Knitting Doc

1

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 fabric

Page 20: Knitting Doc

1

Comparision

PLAIN RIB PURL

Page 21: Knitting Doc

1

Definite face and back.

May be reversible. May be reversible.

Stretches equally in length and width.

Greater stretch in width.

Greater stretch in width.

Knit stitch on face, purl stitch on back.

Knit and purl stitches on face and back.

Knit and purl stitches on face and back.

Highest machine productivity.

Next highest machine productivity.

Lowest machine productivity

Uses – T-shirt, sweaters, full fashion.

Uses – Collars, cuffs, and trim.

Uses – kids wear, fancy garment parts.

Page 22: Knitting Doc

1

Machines used for weft knitting

Weft knitting

Single jersey Double jersey

Or or

Single bed knit Double bed knit

Single jersey (circular or flatbed machines)

Basic machines Auto striper Mini jacquard Fully jacquard Wrapper

Double jersey (circular or flatbed machines)

Basic machines Auto striper Mini jacquard Fully jacquard

Different types of double jersey:-

1. Rib 2. Interlock 3. Foma4. Thermal or Neva5. French rib6. Sheaker rib

Page 23: Knitting Doc

1

SINGLE KNITS:

Single Jersey, Pique, Auto stripper, Feeder strippers, Textures, Fleece, Velour, French Terry, Popcorn, Mini Jacquards, Computerized Jacquards, and Wrappers etc.

DOUBLE KNITS :

Interlocks, Drop Needle, Textures, Ribs, Flat back Ribs, Varigated Ribs, Feeder strippers, Auto strippers, Jacquards, Weffle, Mesh, etc.

In Nahar, we can observe only Weft knitting being  practiced . Nahar has World class production facility to knit 30 Tones fabric per

day on Circular Knitting Machines of both Dyed and Greige yarn using counts from 10’s to 2/80’s on different gauge machines ranging from 14gg to 28gg.

Page 24: Knitting Doc

1

Single jersey

It has the least possible structure that consists of only one loop. Visible side of loops on face surface looks like ‘V’. Laps on the reverse side looks like ‘O’ with a shifted bottom. Camber of yarns at longitudinal and cross section which causes

swinging welts of knitted fabrics with respect to elastic component of yarn deformation.

The transverse welt swings towards the face side and the longitudinal welt swings towards the face side and longitudinal welt swings towards the reverse.

Knitted fabric has a higher transversal strength than the longitudinal one.

At transverse deformation, a relaxed loop is reformed and a major length of the yarn lies down in the transversal direction (in the course direction, two sides of loops are moving).

At longitudinal deformation, there are two yarns remaining alongside, and relative elongation of knitted fabric will be approximately two- times lower.

Colour design possibilities comprise transverse strips. They are able to change material of the courses (e.g. their colours) with no change of structure.

More complicated patterns are produced by using locally coloured yarns. So it is called connected structure consist of a connection of knitted fabric strips of reversibly lapped yarns with required colours.

The advantage of this method is that we can save the yarn that is not lapped through the surface of other colours as it is with patterns of the next structure group.

Vertical coloured interfaces can be connected e.g. via crossing of reversible laps, which is a yarn connection of high quality.

Oblique interfaces are to be connected with common loops of neighbouring colour yarns, but only in several wales.

Page 25: Knitting Doc

1

Double jersey

The face and reverse wales are alternating in a way often being designed as 1:1 in the plain double-jersey weft structure, i.e. one face wale and one reverse wale.

The plain weft double-jersey structure does not turn as a whole. Nevertheless, that turning tendency will manifest just via distortion of courses.

It looks the same way from both sides and similar to the face of the weft single-jersey structure.

There are sides of loops on the surface from both sides (they look like a surface filled-up with the letters ‘V’).

Distortion of courses generates increased transverse elongation, which is approximately doubles contrary to the plain weft single-jersey structure.

Even transverse elongation is longer than the longitudinal one, that disproportion is bigger with weft double-jersey.

The distance of the face wales corresponds to the distance of the weft single-jersey structure wales, so that the reverse side is added extra without enlarging the textile surface.

Page 26: Knitting Doc

1

Machines Number of machinesBasic 34Auto-stripper 16Basic interlock 17Auto interlock 10Fully jacquard 6Wrapper 4

Total Number of Machines = 87

Machines: - Fukuhara, Terrot, Keum Yong, Mayer, Wellknit

Page 27: Knitting Doc

1

Machine Specifications :

Wellknit Machinery Co Ltd (Basic Machine)Needle : 1920TSpecs : 34” * 18G * 60F

Terrot (Interlock Machine)Needle : 3408 TSpecs : 34” * 16G

Fukuhara (Auto-stepper)Needle : 2640 TSpecs : 42” * 20G * 252F

Fukuhara (Auto-stepper 6 Colours )Needle : 2568Gauge : 24RPM : 20Diameter : 34”

Knitting Defects

Hole Needle Line Drop stitches Sinker Line Press off Oil Line Knots

FABRIC INSPECTION

There are 6 fabric inspection machines in the department.

They follow 4 point system for fabric inspection.