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Knitting

Knitting is the action of interlinking loops of yarn to form a fabric.  The first records of knitted fabrics came from the Coptic Egyptians in the 5th century AD. Knitting arrived in Europe in the 1400’s. Knitted garments were used to provide practical clothing for warmth, protection and ease of movement, starting with coverings for the extremities –head, feet and hands –and then for the body.  Henry the VIII was the first English monarch to wear knitted stockings.  As underclothing, it gave rise to ‘shirts’, underpants and ‘combinations’, and the ‘gansey’ or ‘jersey’ worn by fishermen.  Up until this point all knitted garments were produced by labour intensive hand knitting.  In 1589 Rev. William Lee invented the stocking frame in Nottingham, England.  This was the forerunner of modern knitting machines.  Although hand knitting is often thought of as a female pursuit both women and men patriotically knitted socks and comforts for solders during WW1 and WW2 (Fig 1)

Fig 1

Figure 1 Patriotic knitting

 

 

 

A knitted fabric consist of forming yarn(s) into loops, each of which is typically only released after a succeeding loop has been formed and intermeshed with it so that a secure ground loop structure is achieved.  There are two different types of knitting, Warp Knitting and Weft Knitting.   In Warp Knitting the yarn travels in a predominately vertical direction through the fabric (like the warp threads in a woven fabric) (Fig.2).  In Weft Knitting the yarn travels in a predominately horizontal direction across the fabric.    Weft knitted structure can also be produced using weft knitting machines or by hand knitting techniques, whereas warp knitted structures can only be produced using Warp knitting machines.  The structural properties of the fabrics produced by these two different techniques vary considerable, details of which are given in the following sections. 

Fig 2

Figure 2 - The structures of Woven fabric and the direction of travel of yarn in warp and weft knitted fabrics

 

General terms and principles of knitting technology

Knitted loop terminology

A `course’ of knit is a predominantly horizontal row of needle loops (in an upright fabric) produced by adjacent needles during the same knitting cycle (Fig. 3)

A `wale’ of knit is a predominantly vertical column of interlaced needle loops generally produced by the same needle at successive (not necessarily all) knitting cycles (Fig.3).

Fig 3

Figure 3 - Knitted loop terminology

Stitch density

Stitch density refers to the total number of loops in a measured area of fabric and not to the length of yarn in a loop (stitch length).  It is the total number of needle loops in a given area (such as ten square centimetres).  The figure is obtained by counting the number of courses in 10 cm and the number of wales in 10 cm, then multiplying the number of courses by the number of wales.

Technically upright

A knitted fabric is technically upright when its courses run horizontally and its wales run vertically, with the heads of the needle loops facing towards the top of the fabric Fig. 4).  The term technically up right is purely a technical description, and does not necessarily indicate the orientation from a designers view point.

Fig 4

Figure 4 - Plain knitted structure

Weft knitting machines

A knitting machine is an apparatus for applying mechanical movement in order to convert yarn into knitted loop structures.  These machines can either be powered by hand or by an external power source.

There is a great variety of weft knitting machines., including circular knitting machine like the example shown in Figure 5 and Flat bed machines (Fig.7).   The common features to all include a mechanism to feed yarn, under tension, to the needles which rise and fall on a cam track to create the stiches.

Fig 5

Figure 5 - Circular knitting machine

The circular knitting machine in Figure 5 only has a single bed of needles so is limited to producing plain knitted structures with no shaping.  They are often used to produce large pieces of fabric that can then be cut to shape and over-locked to prevent unravelling (an example of this is a T-shirt).

Needles

The hooked metal needle is the main element in a knitting machine.  There are different types of needle including the bearded needle and the latch needle (bearded needles only work on machines designed for bearded needles and vice versa for latch needles).  The features and action of a latch needle are described in figure 6 and video clip at: http://www.youtube.com/watch?v=ykkP6_N__Oc

Fig 6

Figure 6 - Action of a latch needle

Double bed knitting

To create more complex knitted fabrics on a weft knitting machine a double bed of needles is required.  The needles rise and fall as described above, however the second bed of needles is now opposite the first bed, so that as the needles rise they come into the space in between two adjacent needles on the opposite bed (Fig. 7).

Fig 7

Figure 7 - Double bed knitting

Plain knitted structures (single bed weft knit fabric)

Plain is the simplest and most economical weft knitted structure to produce, and has the maximum covering power.  It normally has 40% potential recovery after stretching.  

·         Plain knit will unravel from both ends (i.e. it will ladder)

·         It is a stable fabric (used for T-shirts etc.)

·         It is quick, cheap, easy to produce

·         If you pull it at the top and bottom it will curl to the front.  If you pull it at the sides it will curl to the back –which might be undesirable at the cuffs and hem of a garment.

·         `Plain’ does not refer to colour but fabric structure –a plain knit garment can be stripy! (Fig. 8)

·         The appearance of plain knit is different on the front and back (Fig. 9)

Fig 8

Figure 8 - Plain Knit (circled areas)

Fig 9

Figure 9 - Appearance of plan knit on front and back. Technical Front /Back’ relates to the machine direction (needles) not how the fabric is viewed for the end use

Rib structures (produced on double bed machine)

Ribbed structures are more durable than plain knit so it is often used at the cuffs of a plain knit garment (Fig,10). Additional points to note about plain knit rib are;

·         It does not curl

·         Thicker-so more expensive to produce than single bed structures

·         Good width extensibility and recovery

·         Unravels from the top only

·         The face loops move over the reverse loops to give the appearance of plain knit

Fig 10

Figure 10 - Ribbed areas on a garment (circled)

The simplest rib structure is 1x1 knit where all the needles on both needle beds are in action.  It is also possible to create other rib structures by using different needle set ups (this can be achieved by ‘knocking’ selected needles out of action so that they do not rise and take the yarn during the knitting process).  Two potential needle set ups and the rib structures they produce are illustrated in figure 11 and video link below.

Fig 11

Figure 11 - Two potential needle set up and the resulting rib structures

 

 

 

 

Tuck and miss stitch

Apart from the knitted loop stitch the two most commonly produced stitches are the tuck stitch and the miss stitch (float stitch).

Tuck

A tuck stich is composed of a held loop, one or more tuck loops and knitted loops.  It is produced when a needle holding its loop also receives the new loop.

The tuck loop assumes an inverted U-shaped configuration.

Tuck loops reduce fabric length and length-wise Elasticity? because the higher yarn tension on the tuck loop causes then to rob yarn from adjacent knitted loops, making them smaller and providing greater stability and shape retention (Fig 12). 

Fig 12

Figure 12 - Tuck stitch

Miss

A miss stitch or float stich is composed of a held loop, one of more float loops and knitted loops.  It is produced when a needle holding its old loop fails to receive the new yarn that passes, as a float loop to the back of the needle, and to the reverse side of the resultant stich.

A single float has the appearance of a U-shape on the reverse of the stitch.

Miss stitch (float stitch) fabrics are narrower than equivalent all-knit fabric because the wales are drawn closer together by the floats, and reducing width-wise Elasticity? and improving fabric stability.

A floating thread is useful for hiding unwanted coloured yarn when producing Jacquard designs (see 13 below).

Fig  13

Fig 13b

Figure 13 - Miss stitch

 

 

Colourwork

Colour plays a major role in fashion.  There are a variety of different ways to add different colours to weft knitted designs.

Horizontal stripes

This is the simplest way to add colour.  Horizontal striping provides the facility to select one from a choice of several coloured yarns at the machine feed position. 

Intarsia

Intarsia is a method of producing designs in knitted loops that form self-contained areas of pure colour. Brilliant colour definition is achieved, with the potential to use a large number of colours and no adverse effects on the physical properties of the structure such as reduction in Elasticity?.

Plating

Plating is another method of producing coloured work.  In plating two yarns are knitted simultaneously (normally contrasting colours) using a specially designed plating feeder.  Due to the needle setup sometimes one yarn will show on the face of the fabric while in other areas another yarn will show.  This can be used to create two colour plated motifs.  However the potential for the back yarn to ‘rob’ through and disrupt the motif pattern on the front has reduced the popularity of this technique.

Individual stitch selection

Individual stitch selection is the most versatile and widely employed method of knitting designs in colour.   This includes a variety of fabrics referred to as Jacquard fabrics.  Two different clourwork fabrics can be seen in Figure 14.  More information can be found here: 

http://www.k4i.org.uk/browse/knit_tech/knit_tech/V_bed_patterning/Jacquard_knitting.htm

Fig 14

Figure 14 - Two different methods of colourwork

 

 

Cad cam

Knitting will always be a mechanical action between the yarn and the knitting elements, but increasingly electronics are influencing the capabilities of modern knitting machines.  More information on the effect of  CAD CAM on the knitting industry can be found at: http://www.scribd.com/doc/44823540/CADCAM-in-Knitting

Integral garment machines

The opportunities that arise from CAD CAM and electronic knitting machines have meant that developments such as integral garment knitting have been possible.

Cutting knitted fabric into shapes and sewing the pieces together has been used to create garments since the eighteenth century.  In the 1970s knitwear companies began researching more efficient technologies that could produce a whole garment in one process (without the need for sewing).  This meant that garments could be knitted quickly and without the loss of fabric associated with cut-and-sew techniques.  'Wholegarment' technology was further developed in the 1990s by Shima Seiki of Japan.  http://www.shimaseiki.com/wholegarment/

'Other types of weft knitting machines'

Interlock

Interlock is a double bed weft knitted fabric.  It is knitted on machines which have an interlock gating.  This type of gating means that the needles in the two beds are directly opposite each other so that only one of the two can knit in a single pass of the yarn feeder.  This means that each pattern row requires two passes of a feeder, each with a separate yarn that knits on alternate needles, producing two half gauge 1x1 rib courses.

Interlock has the technical face of plan fabric on both sides, but its smooth surface cannot be stretched out to reveal the reversed mesh wale loops as the wales on each side are directly opposite each other. http://www.youtube.com/watch?v=9PedEe5ZtAg&feature=related

Purl machines

It is possible to produce double bed fabrics with purl stitches showing on both the technical face and back of the fabric using specially designed purl knitting machines with a double ended latch needle.  More information can be found at:

http://www.scribd.com/doc/49945049/PURL-KNITTED-STRUCTURES

Warp knitting

Warp knitting is the second and smaller section of machine knitting.  It was developed in 1769 but unlike weft knitting it was never a hand manipulated craft.   More on the history of warp knitting can be found at:

http://www.fibre2fashion.com/industry-article/technology-industry-article/emerging-technologies-in-warp-knitting/emerging-technologies-in-warp-knitting1.asp

In a warp knitting machine there is a simultaneous yarn-feeding and loop forming action occurring at every needle in the needle bar during the same knitting cycle.   Most patterning on a warp knitting machine is based on selective control over the guide bar lapping movements.  Warp knitting threads tend to have an approximate vertical path through the structure, which make the threads less likely to fray or unravel (Fig 2 and 15). The following link contains more information on the different types of warp knitting machines and the knitting action. 

http://www.scribd.com/doc/44821228/Compound-Needle-Warp-Knitting-Machine and http://www.warpknitting4u.com/2009/09/warp-knitting-elements.html

fig 15

Figure 15 - The warp knitting process

It is not possible to produce horizontal stripes with warp knitting (but you can make vertical stripes by feeding different coloured yarns to each needle).  Effects in open work can also be achieved without the use of special mechanisms.  These differences make it easy to visually distinguish between warp and weft knitted garments (Fig. 16).

Fig 16a

Fig 16b

Figure 16 - Warp knitted fabrics

 

Technical textiles (knitted)

Geotextiles

Geotextiles are fabrics used in the construction of road, drains, harbour works and many other civil engineering purposes.  There are a variety of advantages of using warp-knitted textiles instead of woven textiles.  More information can be found at: http://www.fibtex.lodz.pl/article616.html and http://www.indiantextilejournal.com/articles/FAdetails.asp?id=4192

Spacer fabrics

A spacer fabric is a double-faced fabric knitted on a double bar machine.  The distance between the two surfaces is retained after compression by the resilience of the pile yarn that passes between them (usually mono-Filament?) (Fig. 17).

Spacer fabrics are currently being used for the following applications

·         CYCLE HELMETS

·         BOOT SOLES

·         COMPOSITES

·         MEDICAL PRODUCTS

·         NEOPRENE REPLACEMENT

·         COMPRESSION BANDAGES

·         FIREMENS CLOTHING

·         BODY ARMOUR

·         SEATING

Fig 17

Figure 17 - Spacer fabric

More information on spacer fabrics can be found at

http://www.tx.ncsu.edu/jtatm/volume4issue4/Articles/Bruer/Bruer_full_149_05.pdf   and

http://www.baltex.co.uk/xd_spacer_fabrics.html

Knitted wire

Knitted wire is used in a wide range of products including;

·         Demister

·         Mist Eliminators

·         Anti-vandal Mesh

·         Grease Filters & Framed Filters

·         Anti Vibration Mounts

·         Heavy Duty Seals (Fig.18)

More information can be found at http://www.knitwire.com/

Fig 18

Figure 18 - Knitted wire mesh seals

Warp knitted nets

More information on the variety and uses of warp knitted nets can be found at

http://www.warpknitting4u.com/2009/08/warp-knitted-nets-in-fish-farming.html

http://www.indiantextilejournal.com/articles/FAdetails.asp?id=884

Composites

Knitted fabrics made from glass fibre, carbon, aramid and other similar material are used to form a wide range of composite materials. http://www.easycomposites.co.uk/Category/Fabric-and-reinforcement/kevlar-protective-textile-fabrics.aspx

Warp knitted multi-axial weft insertion

Multi-axial multi-ply fabrics are surface structures fixed by a stitch system consisting of one or several parallel and stretched yarn layers with different orientations. More information can be found at: http://www.karlmayer.com/internet/en/textilmaschinen/962.jsp

Stitch bonding or web knitting

Warp and weft knitting machines construct fabric from yarn, whereas stich bonding constructs fabric from fibrous webs etc.  See the link for more information http://www.karlmayer.com/internet/en/kmweltweit/3362.jsp

Circular warp knitting

Tubular, extensible, seamless nets have a variety of technical uses.  See the follow link for details. http://www.tritex.co.uk/index.html

V-bed technical fabrics

It is now possible to produce complex two and three dimensional fabrics on V-bed knitting machines.  These have a variety of uses including in the medical area

http://www.stoll.com/technical-textiles/4

http://www.stoll.com/technical-textiles/mecial-textiles/4_1

 

 

Technical textiles (knitted)

Geotextiles

Geotextiles are fabrics used in the construction of road, drains, harbour works and many other civil engineering purposes.  There are a variety of advantages of using warp-knitted textiles instead of woven textiles.  More information can be found at: http://www.fibtex.lodz.pl/article616.html and http://www.indiantextilejournal.com/articles/FAdetails.asp?id=4192

Spacer fabrics

A spacer fabric is a double-faced fabric knitted on a double bar machine.  The distance between the two surfaces is retained after compression by the resilience of the pile yarn that passes between them (usually mono-Filament?) (Fig. 17).

Spacer fabrics are currently being used for the following applications

·         CYCLE HELMETS

·         BOOT SOLES

·         COMPOSITES

·         MEDICAL PRODUCTS

·         NEOPRENE REPLACEMENT

·         COMPRESSION BANDAGES

·         FIREMENS CLOTHING

·         BODY ARMOUR

·         SEATING

Fig 17

Figure 17 - Spacer fabric

More information on spacer fabrics can be found at

http://www.tx.ncsu.edu/jtatm/volume4issue4/Articles/Bruer/Bruer_full_149_05.pdf   and

http://www.baltex.co.uk/xd_spacer_fabrics.html

Knitted wire

Knitted wire is used in a wide range of products including;

·         Demister

·         Mist Eliminators

·         Anti-vandal Mesh

·         Grease Filters & Framed Filters

·         Anti Vibration Mounts

·         Heavy Duty Seals (Fig.18)

More information can be found at http://www.knitwire.com/

Fig 18

Figure 18 - Knitted wire mesh seals

Warp knitted nets

More information on the variety and uses of warp knitted nets can be found at

http://www.warpknitting4u.com/2009/08/warp-knitted-nets-in-fish-farming.html

http://www.indiantextilejournal.com/articles/FAdetails.asp?id=884

Composites

Knitted fabrics made from glass fibre, carbon, aramid and other similar material are used to form a wide range of composite materials. http://www.easycomposites.co.uk/Category/Fabric-and-reinforcement/kevlar-protective-textile-fabrics.aspx

Warp knitted multi-axial weft insertion

Multi-axial multi-ply fabrics are surface structures fixed by a stitch system consisting of one or several parallel and stretched yarn layers with different orientations. More information can be found at: http://www.karlmayer.com/internet/en/textilmaschinen/962.jsp

Stitch bonding or web knitting

Warp and weft knitting machines construct fabric from yarn, whereas stich bonding constructs fabric from fibrous webs etc.  See the link for more information http://www.karlmayer.com/internet/en/kmweltweit/3362.jsp

Circular warp knitting

Tubular, extensible, seamless nets have a variety of technical uses.  See the follow link for details. http://www.tritex.co.uk/index.html

V-bed technical fabrics

It is now possible to produce complex two and three dimensional fabrics on V-bed knitting machines.  These have a variety of uses including in the medical area

http://www.stoll.com/technical-textiles/4

http://www.stoll.com/technical-textiles/mecial-textiles/4_1