Ms w Knitting

7/30/2019 Ms w Knitting

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Q. What is the principle of knitting?

Ans. In knitting, the yarns are initially formedinto loops, and then these loops are interconnectedin order to produce a textile structure. The terminterlooping is used to describe this technique of

forming fabrics. Based on this principle, a textilefabric is produced by using only one set of yarns.

Q. What are two distinct sectors of knitting industry ?

Ans. The knitting industry is divided into two distinct sectors, weft knitting and warpknitting.

Q. What are Courses :

Ans. Courses are rows of loops across the widthof the fabric produced by adjacement needlesduring the same knitting cycle, and are measuredin units of courses per centimeter. Figure K-1shows a simple plain-knitted structure, indicating acourse or row. The number of courses determinesthe length of the fabric.

Q. What are wales ?

Ans. Wales are the vertical columns of needle loops. The number of wales determines thewidth of the fabric and they are measured in units of wales per centimeter. (Refer figure K-1that indicates the wales and also the needle loop).

Q. What is stitch density ?

Ans. Stitch density is a term frequently used in knitting and represents the total number ofneedle loops in a given area. Stitch density is the product of the courses and wales per unitlength and is measured in units of loops per square centimeter.

Fig. : Interlooping of yarns

Fig.K-1 : Plain single jersey weftknitting


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Q. What is stitch length ?

Ans. The stitch length, measured in millimeters, is the length of yarn in the knitted loop.Stitch is one of the most important factors controlling the properties of knitted fabrics. It canbe determined by removing one course length (or part of a course length) from a fabric anddividing this length by the total number of needles knitting that length of yarn. Generally, the

larger the stitch length, the more open and lighter the fabric.

Q. What is the knitted loop ?

Ans. The unit of a knitted fabric is known as the loop (Refer figure K-1that illustrates howthe individual loops, both needle and sinker loops, are connected together to form the knittedstructure). A large number of loops, which are suitably connected together, will produce afabric in which the loops are arranged in horizontal and vertical rows. The loops in thehorizontal rows are courses and are made consecutively from one yarn package, with onethread of yarn feeding all the needles in the knitting unit. A vertical row of loops limited

together is called a wale. The loops in a wale are connected together by drawing each loopthrough the previous one.

Q. What is the principle of Weft knitting?

Ans. In weft knitting, the loops are formed across the width of the fabric, and each weftthread is fed, more or less, at right angles to the direction in which the fabric is produced. It ispossible to knit with only one thread or cone of yarn, though production demands haveresulted in circular weft knitting machines being manufactured with upto 192 threads (feeders)(Refer Fig. K-1).

Q. What is the principle of Warp knitting ?

Ans. Warp knitting is a method of producingfabric by using needles similar to those used inweft knitting, but with the knitted loops made fromeach warp thread being formed down the length ofthe fabric; the loops (courses) are formed verticallydown the length of the fabric from one thread asopposed to across the width of the fabric, as is thecase of weft knitting.

Fig. : Warp knitting


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Q. What is basic knitted structure?

Ans. Each stitch, knitted loop and yarn loopconsist of a top arc (head), two legsstitch is boundat the and two bottom half-arcs (feet). A upper andlower ends, i.e. at the head and at the feet. The

first loops (yarn loops) are bound only at the headwith loosely hanging feet. The knitted loops arebound only at the feet to the heads of the previousstitches.

At the place where the legs transform into feetthere are two points of contact with the previousstitch. These are defined as the binding points.Thus a stitch has four binding points, i.e. twobinding points at the head and two binding points atthe feet of each stitch. Two binding points,therefore, build a binding unit. Thus a stitch has atotal of eight contact points, four binding points andtwo binding units.

A knitted fabric is technically upright when its courses run horizontally and its wales runvertically with the heads of the knitted loops oriented towards the top and the first course atthe bottom of the fabric.

Q. What are technical face and technical back of stitch ?

Ans. For a stitch, depending on the position of the legs at the binding points, a technicalback and a technical front side is defined. If the feet of the stitches lie above the bindingpoints, and accordingly the legs below, then this is the technical back of the stitch, and it iscalled the back stitch, purl stitch, garter stitch or reverse stitch.

If on the other hand, the bottom half-arcs are below and the legs above, then this is thetechnical front of the stitch. This is called the face stitch or plain stitch, stocking stitch, jersey

stitch (USA) and flat stitch (USA). A face stitch is produced by intermeshing a yarn looptowards the technical face side of a fabric.

Fig. : Basic knitted structure

Fig. The technical front of a stitch and the technical back of a stitch


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of neighbouring wales (cross-over points) results in the wales of a rib knitted structure closingup. This gives rib structures better elastic properties widthwise than other basic knittedstructures. With rib structures in the lateral direction,extensions up to 140% can be achieved.Other construction of rib structures include 2 x 2 rib, where two wales of face stitchesalternate with two wales of reverse stitches. As the number of wales in each rib increases, theelasticity decreases as the number of changeovers from reverse to front reduces.

Q. What is purl knitted fabric?

Ans. If on the both sides of a relaxed weftknitted fabric only reverse stitches are visible,then this is defined as a purl knitted fabric.Generally, weft knitting machines are used toproduce these fabrics. Purl fabrics are producedby meshing the stitches in neighbouring coursesin opposite directions by using special latchneedles with two needle hooks. When the fabricis stretched lengthwise, then the face stitches arevisible. The fabric shrinks more in the direction ofwales, and once it is released, it relaxes to hide

the face stitches between the courses.The interlooping of the stitches of neighbouringcourses in opposite directions results in thecourses of a purl knitted structure closing up. The structure, therefore, has a large longitudinalextensibility which is largely elastic.

Q. What are interlock knitted fabrics ?

Ans. These could be considered as acombination of two rib knitted structures. Thereverse stitches of one rib knitted structure iscovered by the face stitches of the second ribknitted structure. On both sides of the fabric,

therefore, only face stitches are visible, and it isdifficult to detect the reverse stitches even when thefabric is stretched widthwise.

Q. What are tuck loops?

Ans. This is a loop that is integrated into a knittedstructure without actually connecting it with the

stitch immediately below it, though it is connectedwith a succeeding stitch. Tuck loops are formed bythe hook of the needle in question receiving a yarnloop in addition to the knitted loop. The knitted loopand the yarn loop are then meshed during the nextstitch forming process. A tuck loop is characterisedwith an upper binding unit and with a mis-sing lowerbinding unit, i.e. it is bound only at the head. Its legsare, therefore, not restricted at their feet by the headof a stitch so that the legs can open out towards the

Fig. Purl knitted fabric

Dial loops

Cylinder loopsFig. Interlock knitted fabric

Fig. Tuck Loops


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two neighbouring wales. When tucking occurs across two or more neighbouring wales, thehead of the tuck loop will float across the wales. Tuck loops reduce fabric length andlongitudinal elasticity because the higher yarn tension on the tuck and held loop(s) causesthem to rob yarn from the neighbouring stitches. The fabric width and lateral elasticity areincreased.

Tuck loops are employed in weft and warp knitting for patterning and/or to influence its elastic

behaviour and to vary the area density and the size of the fabric. In warp knitting, theequivalent of the tuck loop is the fall-plate or Henkel lap. Generally, the tuck loop in warpknitted fabrics has the appearance of diagonally running yarns in which the loops hang in thefeet of the stitches.

Q. What are floats ?

Ans. A float is a piece of yarn limited by stitcheswhich, in weft knitting, floats over wales. A float isgenerated when a stitch is missed out of a knittedstructure, and does not pass through the stitch belownor connect with the subsequent stitch. The length of

yarn that would have formed the stitch lies as a floatacross the wales. The extensibility of the fabric isreduced. Floats are created during jacquard knitting.

Q. What is knitted fabric geometry ?

Ans. There has been considerable research into the behaviour of single jersey structuresindifferent states of relaxation. These relaxation states include dry relaxed, wet relaxed andfully relaxed. On the machine the fabric is under stress. After a time off the machine the

fabric dry-relaxes. Wet relaxed fabric has been soaked in water and the fully relaxed state isachieved by agitation during drying, which should give a true relaxed state to all fabric types.The fundamental principle of this work was to enable plain single jersey fabric parameters tobe predicted prior to actual knitting.

Q. What is tightness factor ?

Ans. Tightness factor is the ratio of the area covered by the yarn in one loop to the areaoccupied by that loop.

The expression developed for the calculation of rightness factor (K) is given below :

TK =

l

Where, T = yarn liner density in tex

l = stitch length in millimeters

For more plain fabrics, the mean tightness factor is between 1.4 and 1.5, although they canrange between 1.2 and 1.6. Outside this range, fabrics are considered to be unsuitable forclothing applications.

Fig. Floats


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Q. What is fabric area density ?

Ans. The calculation of fabric are density is important in that it can be used as a guide toquality control procedures. In its simplest form, fabric area density for plain single jersey is asfollows :

s x l x T = gram per square metre100

Where, s = stitch density (loops per square cm)

l = stitch length in mmT = yarn linear density in tex

Calculations for 1 x 1 rib fabrics can be done in a similar way to the above, but it must beremembered that the face wales of the rib need to be doubled because these conceal thealternate wales knitted on the back of the fabric. In the case of plain interlock, only the face ofthe fabric is analysed and the results are doubled to arrive at the fabric area density (interlockis basically two 1 x 1 rib fabrics locked together). In practice, then, only one feeder isanalysed for interlock fabrics. It is normal practice to weigh a 10cm x 10cm piece of fabric

and multiply by 100 to arrive at the accrual area density in the correct units of grams persquare metre. This is then compared to the calculated area density, and the percentagedifference between the actual and calculated values should be less than three per cent. A re-check of the variables would be necessary if the difference was found to be greater.

Q. What is selvedge stitch ?

Ans. The selvedge of a weft knitted fabric is made by selvedge stitches. In these the yarncoming out of the last stitch of a course goes back through the same stitch and proceeds tothe next course. Thus the stitches at the end of a weft knitted fabric have three legs, and arecalled the selvedge stitches. A selvedge stitch has nine contact points.

Q. What are functions of knitting needles ?

Ans. In machine knitting needles are used to form stitches. Thus the primary function ofknitting needles is for interlooping yarns. They perform different functions depending on theknitting technique and the needle type.

Linking of new yarn loops with knitted loops and to carry the knitted loops during the earlystage of the stitch formation cycle are two important functions of a needle. This centralfunction of the knitting needle is independent of the knitting process and machine type, i.e.whether its a hand knitting machine or a high production warp knitting machine needles canalso be considered as the primary knitting elements as they are directly in contact with theyarn during the entire stitch formation cycle.

A knitting needle has a hook at one end to catch the yarn forwarded to the knitting zone, astem or a shaft to carry the knitted loop during the early stages of the stitch formationprocess, and a butt at the other end. The butt is used either to position the needle on a needlebar or to move the needle the stitch formation process. The regularity and finish of the knittingneedles influence directly the size and the shape of the stitches formed. On the other hand,they are subjected to intense mechanical forces during the stitch formation, and these wouldinfluence their performance. As such for manufacturing needles high quality steels are usedand they are hardened using special thermal treatments. During the early stages of theknitting cycle (a knitting cycle consists of all the knitting steps necessary to form a stitch), thehook of a needle is opened to release the retained knitted loop and to receive the new yarn


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loop which is then enclosed in the hook. Before the new yarn loop can be drawn through theknitted loop (linking up) the hook must be closed (bridge formation) for the knitted loop to slideover the closed hook. All needles must, therefore, have some method of closing and openingthe needle hook in order to retain the new yarn loop and exclude the knitted loop. Dependingon how the closing of the hook is achieved knitting needles are subdivided into the followingthree groups:

1) The bridge formation is achieved by applying an external force

2) The bridge formation is carried out due to the relative movement of the knitted loopand the knitting needle

3) The bridge formation is accomplished with an additional closing element

Q. What is bearded needle ?

Ans. Bearded needle or springneedle was invented by Rev. WilliamLee, in 1589. Therefore it is the firstknitting needle to be invented. It is also

the simplest and, therefore, thecheapest needle. Bearded needles aremade from steel wire (wire beardedneedle or round stem bearded needle)or from punched steel plate (flat stockbeaded needle). A bearded needle isshown in figure.

By applying an external force on to theneedle beard the needle hook is closed,and this is known as beard pressing. Inbearded needle knitting machines this isachieved by mounting all the needles onto a needle bar and then by either

moving a second metal bar, called thepresser bar towards the needle beardsor rotating the needle bar towards astationary presser bar. Such anarrangement limits the ability of pressingthe beards of individually, and thepatterning potential of bearded needlesis thus limited. This arrangement allowsthe needles to be reciprocatedcollectively. Knitting machinesemploying bearded needles are unableto compete in knitting the basicstructures and their simple derivatives toother knitting techniques employing

latch and compound needles, and theirapplications are reducing.

Fig. : Bearded needle


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Q. What is latch needle ?

Ans. Latch needle was invented byMatthew Townsends in 1849 and sincethen it has challenged the application ofbearded needles in machine knitting. The

latch needle is more expensive tomanufacture than the bearded needle andis more prone to making needle marks inknitting, but it has the advantage of beingself acting or loop controlled. For thisreason, it is the most widely used knittingneedle in weft knitting and is sometimestermed the automatic needle. Preciselymanufactured latch needles are todayknitting very high quality fabrics at veryhigh speeds.

A latch needle has the following importantparts:

1. the hook which draws and retainsthe new yarn loop;

2. the latch-blade;

3. the latch-spoon which is anextension of the latch-blade andbridges the gap between the hookand the stem covering the hookwhen closed;

4. the rivet or axle of the latchneedle;

5. the stem which carries the loop inthe clearing or rest position;

6. the butt which enables themovement of the needle by usingcams.

The knitted loop is cleared from the hookwhen the latch needle is lifted because theknitted loop slides down inside the hook and hits the latch. This causes it to pivot openallowing the knitted loop to slide off the latch down on to the stem. The hook is closedautomatically as the latch needle is lowered after a new yarn is supplied to it because theknitted loop which was on the stem slides upwards, contacting and pivoting the latch tightlyclosed.

As the latch needle continues with its downward motion the newly supplied yarn is drawn

through the knitted loop. Latch needles thus knit automatically. The opening and closing ofthe hook, i.e. the bridge formation, is carried out by the knitted loop without using additionalknitting elements. Such a phenomenon is very rare in processing machines. Except onRaschel machines (warp knitting), latch needles are arranged in the tricks or grooves of aneedle bed.

To produce purl knitted structures a special needle with a hook and a latch at each end of theneedle stem is used. Double-ended latch needles, also called purl needles, can slide throughthe knitted loop in order to knit from an opposite needle bed, and thus draw a loop from theopposite direction.

Fig. : Latch Needle


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The latch needles currently being used can be subdivided into the following three groups:

1. wire latch needle; the needle butt is made by bending the end of the needle stemopposite to the needle hook

2. punched latch needle; these are latch needles punched from steel plates

3. double ended latch needles; to produce purl knitted structures, double ended latchneedles, also called purl needles, slide through the knitted loops in order to knit fromthe opposite needle bed and thus draw a loop from the opposite direction.

The wire latch needles are employed in Hand Knitting Machines, in Hand Knitting Machineswith motor drive units and in some semi-automated power machines. In the automation ofknitting machines and in the development of high speed knitting machines, the wire latchneedles have lost their importance to punched steel latch needles. There are about 160different types of latch needles on offer from knitting needle manufacturers.

Punched steel latch needles can be subdivided into two different groups. These are:

1. normal latch needles;

2. loop transfer latch needles.

Loop transfer latch needles are employed in electronic flat bed knitting machines. A normallatch needle consists of three areas of different functions, which are shared by a loop transferlatch needle which also has a fourth area. These are:

1. needle hook area;

2. needle stem;

3. needle butt;

4. loop transfer area.

The needle hook area is of great importance, as its here all the relative motions between theneedle and yarn that are necessary for stitch formation to take place. The needle stem has a

connecting function, i.e. it establishes the connection between the hook and the butt. It alsohas a guidance function, i.e. to guide the needles in the tricks of the needle bed. The needlebutt has the function of reciprocating the latch needle between two dead centres in order toform stitches. The transfer area has the task of transferring the knitted loop to the oppositelatch needle. The form and the size of these four important areas will depend on theapplication of the latch needle.

It is a common practise in machine building to design certain parts with weak areas, so thatthey will break in the event of a malfunction of the machine, thus preventing major damage tomore expensive parts. The butt of a coarse gauge latch needle is designed with a weak areain the butt so that it will break if the knitting cam system jams, thus preventing seriousdamage to the tricks of the needle bed.

The latch plays a very important role in the stitch formation process. The latch is fixed to thecheeks or slot walls of the needle in such a way that the latch-spoon can be rotated between

two dead points. The cheeks are either punched or riveted to fulcrum the latch. Due to thisrotational movement the latch will open the hook in order to release the knitted loop. The latchrotational movement will also close the hook during the latter part of the knitting cycle so thata new loop could be drawn through the previous knitted loop. Although the latch is smallduring knitting it undergoes tremendous stresses. Modern knitting machines are highproduction machines, and in these machines the latch needles move in their tricks at veryhigh speeds. The strikingaction of the latch during the closing of the needle hook by the latchspoon depends on the working speed of the latch needle. It will be very high at higher workingspeeds. The stresses of the latch will result in very high reaction forces at the fulcrum.Therefore the bearing at the fulcrum is critical, and must satisfy the following conditions:


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a good movement of the latch;

a stable support of the latch.

he size of the rivet will depend on the size of the latch needle. With fine latch needles thefulcrum point is so small that it is almost invisible to the naked eye. The axle of the latch playsa major role in the function of the latch needle, and several interesting solutions have been

developed by needle manufacturers.

Q. Explain the knitting action with a latch needle.

Ans. To understand the different types of stitches, one has to look at how a simple knitstitch is formed. It would be easier to understand if one assume that a loop has already beenmade, which is held in the hook of the needle (Refer fig.).

When a stitch has been formed, the needle rises to take the new yarn to produce anotherstitch. While this is happening, the fabric must be held down to prevent its rising with theneedle. The loop (a) in the needle hook opens the latch of the needle as the needle rises.

When the needle has risen to its clearing height the old loop is below the latch on the needlestem. The needle is now in position to receive the new yarns (b) before starting to movedown. The needle begins to descend, causing old loop (a) to close the latch, so traping thenew yarn (b). When the needle reaches its lower position, the new loop (b) will have drawnthrough the old loop (a) known as knock-over-and the needle is now ready to rise so that thesequence can begin again.

Fig. Knitting action with a latch needle


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Q. Explain the knitting action of a latch needle and sinker machine ?

Ans. In this technique sinkers are employed to aid lop formation. Fig. shows the followingknitting actions of a latch needle and sinker machine :

In position (a) the sinker is in the forward position, with the throat of the sinker holding downthe fabric as the needle starts to rise.

At position (b) the sinker is still forward as the needle reaches the clearing height, but then at(c) it begins to move back and the needle descends to collect the new yarn, while at position(d), the old loop has closed the latch to trap the new thread and knockover is taking place.The sinker then moves forward (e) to hold down the fabric as the process start to repeat itself.The movement of sinkers is controlled by sinker cams.

Q. Show knitting action of a latch needle on a circular single jersey machine ?

Ans. Latch needles have an individual movement and slide-up and down in grooves whichare cut in a cylinder or needle bed. These groves are called tricks. The sliding movement, upor down of the needle is controlled by cams which form a track for the needle butt to follow.The stitch cam is adjustable, which means the stitch length or the length of the yarn in theknitted loop can be varied. Fig. shows a tyical cam system and a sequence of actions thatallow a loop to be formed by latch needle on a circular single jersey machine.

Fi . Knittin c cle of latch needle and sinker machine


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Q. What are compound needles ?

Ans. The first patent for a compound needle was awarded in 1856 to Jeacock of Leicester.The patent describes a knitting needle consisting of a needle part (the stem and the hook ofthe needle) and a tongue part (hook closing element). Both the two parts need to be

controlled independently, and thus the newneedle was named a compound needle. Thereare two types of compound needle in currentuse, the tubular pipe compound needle, wherethe tongue slides inside the tubular needle part,and the open stem pusher compound needle,where the tongue slides externally along agroove on the flat needle part. The pusher type ischeaper and simpler to manufacture and its twoparts are capable of separate replacement. Itsdimensions are narrower allowing tighter stitchesto be produced. Today, the open stem compoundneedles are finding most widespread use in warpknitting. The compound needle is expensive tomanufacture and each part requires separateand precise control from a drive shaft or camsystem. The compound needle has a short,smooth and simple action, without latch or beardinertia problems. The slim construction and shorthook makes it particularly suitable for theproduction of plain, fine warp knitted structures athigh manufacturing speeds. Feeding yarn into acompound needle is more critical than for thebearded or latch needle because the yarn has tobe laid precisely in the hook of the compound

Fig. Knitting cycle of latch needle circular machine

Fig. Compound need


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needle, in order to prevent fabric faults. By bearded or latch needle the yarn can be laidacross the beard or the open latch, and it will still be taken into the needle hook. On the otherhand the positively controlled two parts of the compound needle guarantees a opened hook atthe time of yarn in-lay during the knitting cycle.

Q. What are needle beds ?

Ans. Needle beds are employed in latch or compound needle weft knitting machines. Theirfunction is to hold particular knitting elements at exact defined distances and to guide themduring the stitch formation process. On an electronic flat bed knitting machine knittingelements such as latch needles or compound needles and needle selection elements areplaced in needle tricks. Modern electronic flat bed knitting machines are equipped withholding-down sinkers, and these are positioned at the top edge of the needle beds. As theneedle beds are subjected to tremendous stresses due to the movement of the knittingelements they are made from very high quality metals. On one surface of the needle bedgrooves (called tricks) of equal width and depth are preciously machined at equal distances.Lasers and numerically controlled cutting machines are used in their manufacture to ensure atolerance of +30 microns (30 micrometers). The needle manufacturers ensure a tolerance of -30 microns for their needles. The knitting elements are placed inside the tricks and are movedmechanically between two dead centres. The distance between two adjacent needle tricks is

called needle spacing (t). The needle tricks are wider at the top, where the needle hook isplaced, in order to accommodate the somewhat bigger knitted loop. This top edge also formsthe knocking over edge for the stitch formation.

Needle beds can be sub-divided into two main different forms:

1. Flat Form: a rectangular thick metal plate is used to manufacture the needle bed, e.g.the needle beds of flat bed knitting machines. In flat needle beds the needle tricks areparallel;

2. Circular Form : a metal cylinderor a metal disc is used to manufacture circular needlebeds, e.g. the needle bed(s) circular knitting machines. If the needle bed is madefrom a metal cylinder, then it is a cylindrical needle bed. If the needle bed is made outof a metal disc, then it is called the dial needle bed. In the metal cylinder the needletricks are machined parallel to the axis of the cylinder (axial needle tricks), whereas in

the dial the needle tricks are not parallel; they are all pointing towards the centre ofthe metal disc (radial needle tricks).

Industrial flat bed knitting machines are equipped with two flat needle beds arranged in theform of a roof, thus they are also called v-bed knitting machines. The important parts of a flatneedle bed are shown in the following figure:

Fig. Cross section of flat need bed


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Usually, all types of needle beds employ all the elements shown in the above diagram exceptthe needle security springs. The needle cover band maintains the knitting needles against thetrick base. It also has a braking effect on the knitting needles and prevent them from springingback. The knitting needles move axially between the lower edge of the cover band and thesecurity spring. By moving the security spring back the knitting needles can be brought out ofthe cam tracks, i.e. the knitting needles will be out of action.

The knock-over jack and its front edge with which the yarn comes in contact during knitting is

of a special shape. This edge is carefully polished in order to ensure the free sliding of theyarn during stitch formation without damaging the yarn. Also, in order to ensure freedownward movement of the knitted fabric between the two needle beds, the under sides ofthe top edges of the needle beds are machined to a special form.

The needle beds are characterised by the following two parameters:

1. the machine gauge; i.e.. the number of needle tricks in a reference length;

2. the maximum width of the fabric that can be knitted, this is known as the maximumknitting width

o in flat needle beds this is given by the distance between the first and the last

needle tricks of the needle bed;

o the diameter of the needle cylinder in the case of circular weft knitting

machines.

One inch is used as the reference length for the determination of the machine gauge of aneedle bed. As an example the correct designation of the machine gauge of a flat bed knittingmachine having seven needle tricks to an inch is E7. The capital letter E specifies that thereference length is an inch. Sometimes the gauge is also given as 7 npi (needles per inch).The distance between the centre lines of two neighbouring needle tricks is called the pitch (t),and it could be calculated by using the following mathematical relationship:

In the above equation the units of the needle bed pitch is in micrometers

The length of the portion of the needle bed, which is present with needle tricks is known asthe knitting width (maximum knitting width) of a flat needle bed. The knitting width will dependon the total number of needle tricks on the needle bed and the machine gauge. It could bedetermined using the following mathematical relationship:

In the above equation the units of knitting width is in centimeters.

Other important parameters of a needle bed are:

the width of the needle trick

the height of the needle trick

the base of the needle trick

the height of the needle bed

Q. Brief the types of knitting machine.

Ans. 1) Warp knitting machines

2) Weft knitting machines


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Q. Brief the types of warp knitting machines.

Ans. 1) Tricot warp knitting machine

2) Raschel machines

3) Straight bar knitting machines

4) Manual warp knitting machines

Q. Brief the types of weft knitting machines

Ans. 1) Flat weft knitting machines

2) Circular weft knitting machines (large diameter)

3) Circular weft knitting machine (small diameter)

4) Manual weft knitting machines

Q. Brief the specifications of Tricot warp knitting machine.

Ans.

Manufacturer Type Gauge Width

Karl Mayer KS 4 E 28 42

Karl Mayer KL 4 E 28 22

Liba Copcentra 2 E 28 42

Q. Brief the specifications of Raschel machines .

Ans.

Manufacturer Type Gauge Width Remark

Karl Mayer RJG 5/2 ER 28 75 Jacquard

Karl Mayer RJ 4 MSU ER 36 77 Magazineweft

Karl Mayer MRS 10 ER 36 50 Multibar

Karl Mayer RML 6F ER 36 50 Full plate

Karl Mayer DR 7 E-ST ER 36 25 Double face

Karl Mayer RML 4 ER 24 22 Pilot machine

Q. Brief the specifications of straight bar knitting machine.

Ans.


Scheller BS 32/4 21 gg 32


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Q. Brief the specifications of Manual warp knitting machine.

Ans.

Manufacturer Type Gauge Width Remark

Schlafhorst Pilot raschel ER 8 6 4 Guide bars

machine Single face

Schlafhorst Pilot raschel ER 8 6 4 Guide bars

machine Double face

Q. Brief the specifications of flat weft knitting machine.

Ans.


Stoll CMS 420 E 8 90

Stoll ANVH-BL E 8 90

Stoll IBOM/B E 10 71

Q. Brief the specifications of circular weft knitting machines (large diameters).

Ans.

Manufacturer Type Gauge Feeds RemarkMorat ST4 MK2 E 18 36 30 Electronicneedle control

Terrot UP 372 E 18 72 30 Mechanical3-way- Technology

Mayor & Cie Relanit 4 E 28 84 26 Single face,4-channel- Technology

Mayer & Cie FV 2.0 E 10 29 14

Mayer & Cie Ovja 3 E 16 24 33

Mayer & Cie Interlock E 20 12 18

Singer Supreme E 7 32 30 Pattrenwheel Needle Control

Q. Brief the specifications of circular weft knitting machines (small diameters).

Ans.

Manufacturer Type Gauge Feeds Krenzler RSK E 10 1 3.5

E 20 1 3.5

Lucas RR 2-4 s E 8 4 5.5


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Q. Brief the specifications of manual weft knitting machines.

Ans. Manufacturer Type Gauge Width RemarkStoll IBO E4 100cm Flat knitting mach.

Stoll IBO E5 100cm

Stoll IBO E6 100cm

Stoll IBO E6 120cm

Stoll IBO E7 120cm Stoll IBO E10 100cm

Stoll IBO E14 120cm

Stoll FAL E5 120cm Purl flat k.m.

C.F. Popp E1, 5 110cm Flat knitting mach.

Foster VA E6 4.75 Circular knitting mach.

Heumann Favorite E6 4.75 Circular knitting mach.

Q. Explain the knitting cycle of bearded needle Tricot warp knitting machine.

Ans. Position (a) in fig. shows that the needle bar has risen to the centre of its verticalpath. The fabric is held in the throat of the sinker to stop it rising with the needle and theguide bars will already have moved left or right one or more needle spaces for the firstmovement, which is known as the underlap.

At position (b) the guides have swung between the needles towards the back of the machineand stopped on the beard side. At this point the guides make a sideways movement of oneneedle space. This is called the overlap. These laps may be in the same or opposite

Fig. Knitting cycle of a bearded needle Tricot machine


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direction for each guide bar, depending on the structure being produced. The guides thenswing back to the front of the machine (c), with the overlap having wrapped a thread aroundthe needle. This overlap thread usually stops on the beard.

The second rise of the needle takes place, which is sufficient to allow the thread to fall off thebeard and onto the stem of the needle (d) before it descends (e) until the tip of the needle isjust underneath the top of the sinker. The presser then comes forward to close the beard.

At (f) the sinker moves backwards and, by its camming action, raises the old loop on theneedle stem, onto the closed beard. The presser then moves back and the needle descendstowards knock-over, which occurs at (g), when the old loop is thrown over the top of theneedle and the new loop is pulled through the old loop. Finally, the sinker moves forwards tohold the fabric down and the guide bars are repositioned ready for the next course (theunderlap).

Q. Explain the knitting cycle of a latch needle Raschel machine.

Ans. Figure shows the main elements involved in the loop formation of a Raschel warpknitting machine and illustrates thesequence of events in one machine

cycle. The guide bars are at thefront of the machine aftercompleting their underlap at (a),with the web holders being forwardto hold the fabric down as theneedle bar starts to rise from knock-over.

At (b) the needle bar has risen to itsfull height and the old loop hasslipped down the stem after openingthe latches, which are preventedfrom closing by the latch guard.The web holders can then start towithdraw and allow the guide barsto form the overlap.

The guide bars have swung to theback of the machine (c) and willthen move one needle spacesidways to form the overlap beforeswinging back to the front of themachine (d), so that the warpthreads can be laid into the needlehooks. The needle bar thendescends (e) and the old loopscontact and close the latches, sotrapping the new loops inside. Theweb holders start to move forwardsand, as the needle bar hascontinued its descent, its head haspassed below the surface of thetrick plate (f). This allows the newloops to be drawn through the oldloops, which are cost off and, as theweb holders advance over the trickplace, the underlap movementstarts again.

Fig. Knitting cycle of a latch needle Raschelmachine


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Q. Explain the knitting cycle of a compound needle Raschel machine.

Ans. Figure shows the various stages in loop formation for a compound needle warpknitting machine.

At (a) the needles are at the knock-over position after completion of the previous course, withthe web holders positioned between the needles to hold the fabric down.

The needles have risen to the full height at (b), with the closing element having risen to alesser extent, to allow the hook to open. The guide then swings between the needles towardsthe back of the machine for the start of the overlap (c), before making their sideways shogand swinging back to the front of the machine to complete the overlap (d). The web holdersthen begin to withdraw and the needle descends (e). This closes the element whichdescends at a slower rate to cose the hook and trap the newly wrapped yarn. The guidesthen shog sideways to reposition themselves in front of the needle space ready for the start ofthe next course, and the underlap is completed.

At (f) the needle has descended to the knock-over position and a new course of loops hasbeen produced.

Fig. Knitting cycle of a compound needleRaschel machine


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Q. Explain the knitting cycle of a flat bed purl machine.

Ans. Flat purl knitting uses two horizontal needle beds and double-ended latch needleswhich may, according to the selection and type of fabric being made, be transferred from onebed to the other, knitting first on the hook at one end and then on the hook at the other.

Figure shows the knitting cycle of a flat bed purl machine which has tricks in each of the

needle beds. They are in line with one another to enable the needles to transfer from onebed to the other. Sliders positioned in each trick control the double-ended latch needlemovement. Position (1) shows the needle kniting in the front bed under the control of theslider in that bed. In position (2), the needle has been moved to the centre, with both slidersengaging the needle hook. The sliders then start to move back, but the slider in the back bedis pressed down by a cam at point X, so that the front bed sliver is freed from the needle hookand the needle is transferred to the back bed.

In position (3), the slider in the back bed has control of the needle and it can be seen that theyarn is fed to the opposite end of the needle, when comapred to that of position (1). Position(4) shows that the slider in the back bed has moved the needle to the knock-over position tocomplete the formation of the purl stitch. It should be noted that a purl stitch is made when aloop is formed by one hook and then at the next course by the other hook of the same needle,so that one course is formed on the front bed and the next course is formed on the back bed

to create a 1 x 1 purl structure.

The flat bar machine is also capable of producing rib structures, dependent on the slider set-out. Structures such as 1x1, 2 x 2 and 3 x 1 ribs can be made by ensuring that the sameneedles knock-over in the same direction as each course is knitted. The machine isconsequently very versatile.

Fig. Knitting cycle of a compound needleRaschel machine


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Q. Explain the interlock knitting on a cylinder and dial circular weft knitting machine.

Ans. Figure shows the needle set-out on the machine, with long andshort needles alternating on thecylinder. In the dial, the needles areset out exactly opposite to those on

the cylinder. This means that, as aresult of the special arrangement ofthe cams only one set of needles willknit at each feeder. To make thispossible, there are two separte camtracks with one controlling the shortneedles and the other the long ones.At the first feeder only long needleswill knit, and at the second feeder onlyshort needles will knit so as toproduce one actual course of interlocktwo feeders are required. Figurereveals the interlock structure.

Q. What is machine gauge ?

Ans. The distance between two neighbouring needles, called pitch, determines the gaugeof the knitting machine. The number of knitting needles contained in a reference length isdefined as the machine gauge. Originally, knitting needles were cast in small metal blockstermed leads which were then fitted into the needle bar. In the weft knitting machines withbearded needles (straight bar weft knitting machine), the needles were cast two to a lead andgauged in the number of leads per 3 inches of the needle bar which is equivalent to a gaugeof the number of knitting needles in 1.5 inches. In bearded needle warp knitting machines(Tricot machines) the needles were cast three to a lead giving a gauge directly in needles perinch. In the Raschel warp knitting machine the latch needles were cast in 2 inch lead giving aRaschel gauge of needles per 2 inches. In latch needle weft knitting machines the gauge isnormally expressed in needle tricks per inch which in the USA is referred to as cut, beingshort for the phrase tricks per cut per inch.

Normally all primary knitting elements in the same machine are set to the same machinegauge. The pitch indicates the space available for the yarn. As the diameter of a yarn isproportional to its count, a relationship exists between the range of optimum counts of yarn

which may be knitted on a particular knitting machine and its machine gauge. Machine gaugethus influences the choice of yarns and their counts, and affects fabric properties such as theappearance and the fabric weight. For a given needle cylinder diameter or knitting width, finergauge machines tend to knit a wider fabric as more wales are involved. Coarse gauge knittingmachines have latch needles with larger dimensions requiring greater movements. Duringknitting the width of the knitting cams are correspondingly large so less cam systems can beaccommodated around a given needle cylinder diameter, so therefore coarser gauge knittingmachines often have fewer knitting systems.

There is a number of different machine gauge systems in current use. These are given in thetable.

Fig. Needle arrangement for interlock fabric


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Machine Gauge Reference Length Machine type

E (npi) 1.0 inch (2.5400 mm) Flat bed knitting machines,Circularknitting machinesTricot machines

gg 1.5 inches (38.1000 mm) Straight bar knitting machines

ER 2.0 inches Raschel machines

F 25.0000 mm Malimo Machines

Table : Machine gauge systems

Q. What are knitting cams ?

Ans. The movement of the latch or compound needles between two dead centres istechnically realised by means of inclined metal planes. These operate a defined distanceabove the needle bed and act on the butts of latch or compound needles. These inclinedplanes are called knitting cams and usually they are fixed on to a cam plate. The knitting

cams can be represented basically by three triangles.

A central cam raises the knitting needles. This cam is called the raising cam. The functions ofthe other two cams are to lower the raised knitting needles (lowering or stitch cam) and toprevent the raising needles from overshooting (guiding cam). The stitch cam on the left lowersthe knitting needles when the cam plate moves on the needle bed from left to right.Meanwhile the other lowering cam acts as the guiding cam. When the cam plate moves onthe needle bed from right to left the raised knitting needles are then lowered by the right stitchcam.

Fig.: The simplest representation of a knitting cam system of aflat bed knitting machine

The two elements, the raising cam and the sinking cams, are employed in all type of knittingmachines with latch or compound needles, whether they be circular weft knitting machines orflat bed weft knitting machines, hand or automatic.


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Q. What are characteristics of raising cams ?

Ans. During the stitch formation process depending on the knitted structure the needlesneed to be put into action and out of action. This can be easily achieved during knitting by notmoving a needle forward during the knitting cycle can not form a stitch, and this is realised bypreventing the butt of a needle coming into contact with the raising edge of the raising cam.Thus the raising cams are designed to facilitate this, and there are two popular constructions:

1. hinged or tongued type

The raising edge can be rotated away from the normal running position of the needlebutts;

2. sinkable type

The raising cam is attached to a mechanism that will allow the cam to be withdrawninto the cam plate, in order to change its position relative to the needle bed surface.When it is fully withdrawn into the cam plate, the raising cam passes above the buttsof the needles leaving them idle. Alternatively, in its lowered position the raising camis down on the needle bed and causes the butts of the knitting needles to ascend.Certain types of weft knitting machines employing high butt and low butt knittingneedles are equipped with raising cams that can be set to three different position:

o in all work position: Engages the butts of all the knitting needleso in half position: Engages the high butts only

o in out of step position : Leaves all the butts idle.

In flat bed knitting the sinkable raising cam is the most popular. Hinged type is more popularin circular knitting.

Tuck Cams

In order to form a tuck loop the following conditions need to be fulfilled:

1. Forward movement of a latch needle until the closed hook is opened (latch in hookopened position) by the knitted loop in the hook. The knitted loop must remain on the

opened latch;

2. A new yarn need to be laid across the needle hook.

The forward movement of the needle is influenced by the height of the raising cam, and,therefore, in order to form tuck loops the raising cam is split into two parts as shown in thefollowing figure:

Fig. : Modified raising cam


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Both parts, ie the knit cam and tuck cam, are mounted on to a cam plate with a cam withdrawmechanism. As such the two cams can be withdrawn independently, in order to form stitches,tuck loops and floats during knitting., and useful combinations are given in the table below:

Binding element required The cam to be withdrawn

Tuck loops Knit cam

Floats Tuck cam

Stitches None

Table : Cam positions for producing the binding elements during knitting

Q. How are characteristics of lowering cams ?

Ans. The primary requirement in the development of lowering cams is the angle ofdescension. This angle varies, generally, from 50 to 59 degrees, and influence the following:

1. The bouncing of knitting needle butts. This the rapid up and down movement of theneedle butts inside the cam track. This is very crucial and is more evident in high

speed circular knitting, as the knitting needle bouncing would cause excessivedamage to the needles.

2. The number of knitting needles drawing the same yarn simultaneously during thestitch formation.

If the knitting needles descend less rapidly, then the needle bouncing is reduced, but at thesame time the number of knitting needles being lowered simultaneously is increased causingthe tension in the knitting yarn to increase according to the loop sinking rule in knitting. Atpresent an angel between 45 to 55 degrees in flat bed knitting and 58 to 59 degrees incircular knitting are the standard values used by the knitting machine manufacturers.

In order to knit fabrics of different stitch lengths the lowering cams are designed with a limitedmobility, i.e. their vertical position can be altered. In effect, with a lowering cam placed in ahigh position, the knitting needles make a small descend, ie a shorter length of yarn will bepulled through the previous knitted loops by the needles, and thus smaller stitches will beformed. On the other hand, with a lowering cam placed in a low position, the knitting needlesdescend further back into the cam track, and form bigger stitches. That is the setting of thevertical position of the lowering cams determines the length of the stitches. For a givenmachine gauge, bigger stitches will form a slack fabric, where as smaller stitches will make atighter fabric. This is why, generally, the adjustment of the lowering cams is also known as thestitch length adjustment. How ever, this rule can not be applied in all cases. When positiveyarn feeding is used, the stitch length mainly depends on the amount of yarn supplied in tothe knitting needles, than on the position of the lowering cams. In this case, the position of thelowering cams will simply influence the yarn tension.

In order to ensure the readjustment of the lowering cams, each lowering cam is connected toa graduated scale. This way the position of the lowering cams can be fixed exactly. Knitting

machine manufacturers usually deliver a chart for adjusting lowering cams in relation to themachine type and for machine gauge. This table indicates the average position of thelowering cams for different kinds of fabrics which can be produced on the machine.

It is the flush jack position of the knitting needle that is used as the reference for establishingthe settings of the lowering cams. In this position the hook of the knitting needle is exactlyaligned, i.e. flushed, with the knocking-over-jack of the needle bed. For a stitch to be formed,the needle must descend lower than the flush jack position, which varies according to themachine gauge, the yarn count and finally the required stitch size. Following empiricalstandards are accepted when adjusting lowering cams:


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1. When knitting rib and rib based structures it is sufficient that the needles are loweredslightly beyond the flush jack position to form stitches.

2. When knitting plain or plain based structures it is necessary to lower the needles well

below the flush jack position.

3. The length of a tuck stitch is usually sufficient, when the knitting needle lowered to the

flush jack position.

Ms w Knitting

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