Q.
What is the principle of knitting?
Ans. In knitting, the yarns are initially formed into loops, and then these loops are interconnected in order to produce a textile structure. The term interlooping is used to describe this technique of forming fabrics. Based on this principle, a textile fabric is produced by using only one set of yarns.
Fig. : Interlooping of yarns
Q.
What are two distinct sectors of knitting industry ?
Ans. The knitting industry is divided into two distinct sectors, weft knitting and warp knitting.
Q.
What are Courses :
Ans. Courses are rows of loops across the width of the fabric produced by adjacement needles during the same knitting cycle, and are measured in units units of of courses courses per per centimeter. centimeter. Figure K-1 shows a simple plain-knitted structure, indicating a course or row. row. The number number of courses determines determines the length of the fabric.
Fig.K-1 : Plain single jersey weft knitting Q.
What are wales ?
Ans. Wales are the vertical columns columns of needle loops. The number of wales determines determines the width of the fabric and they are measured in units of wales per centimeter. (Refer figure K-1 that 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 of needle loops in a given area. Stitch density is the product of the courses and wales per unit length and is measured in units of loops per square centimeter.
Q.
What is stitch length ?
Ans. The stitch length, measured in millim millimeters, eters, is the length of yarn in the knitted loop. Stitch is one of the most most important factors controlling controlling the properties properties of knitted fabrics. It can be determined by removing one course length (or part of a course length) from a fabric and dividing this length length by the total number of needles knitting that 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 how the individual loops, loops, both needle and sinker loops, loops, are connected together to form the knitted structure). A large number of loops, loops, which are suitably connected connected together, will produce a fabric in which the loops loops are arranged in horizontal horizontal and vertical rows. rows. The loops in the horizontal rows are courses and are made consecutively from one yarn package, with one thread of yarn feeding all the needles needles in the knitting unit. unit. A vertical row of loops limited limited together is called a wale. wale. The loops in a wale are connected connected together by drawing each loop loop through 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 weft thread is fed, more or less, at right angles to the direction in which which the fabric is produced. It is possible to knit with only one thread or cone of yarn, though production demands have resulted in circular weft knitting machines being manufactured with upto 192 t hreads (feeders) (Refer Fig. K-1).
Q.
What is the principle of Warp knitting ?
Ans. Warp knitting is a method of producing fabric by using needles similar to those used in weft knitting, but with the knitted loops made from each warp thread being formed down the length of the fabric; the loops (courses) are formed vertically down the length of the fabric from one thread as opposed to across the width of the fabric, as is the case of weft knitting. knitting.
Fig. : Warp knitting
Q.
What is basic knitted structure?
Ans. Each stitch, knitted loop and yarn loop consist of a top arc (head ), two legsstitch is bound at the and two bottom half-arcs (feet ). A upper and lower ends, i.e. at the head and at the feet. The first loops (yarn loops) are bound only at the head with loosely hanging feet. The knitted loops are bound only at the feet to the heads of the previous stitches. At the place where the legs transform into feet there are two points of contact with the previous stitch. These are defined as the binding points. Thus a stitch has four binding points, i.e. two binding points at the head and t wo binding points at the feet of each stitch. Two binding points, therefore, build a binding unit. Thus a stitch has a total of eight contact points, four binding points and two binding units.
Fig. : Basic knitted structure
A knitted fabric is technically upright when its courses run horizontally and its wales run vertically with the heads of the knitted loops oriented towards the top and the first course at the 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 technical back and a technical front side is defined. If the feet of the stitches lie above the binding points, and accordingly the legs below, then this is the technical back of the stitch, and it is called 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 the technical 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 loop towards the technical face side of a fabric.
Fig. The technical front of a stitch and the technical back of a stitch
Q.
What are four basic knitted structures?
Ans. Depending on the geometrical arrangement of the face and reverse stitches in a knitted fabric, i.e. heads, legs and feet of stitches, the following four basic knitted structures are defined :
Q.
¾
plain knitted fabrics;
¾
rib knitted fabrics;
¾
purl (links-links) knitted fabrics;
¾
interlock knitted fabrics.
What is plain knitted fabric?
Ans. Plain single-jersey is the simplest weft knitted structure that is possible to produce on one set of needles. If a weft or warp knitted fabric has one side consisting only of face stitches, and the opposite side consisting of back stitches, then it is defined as a plain knitted fabric. It is also very frequently referred to as a single jersey fabric (single fabric). Plain knitted fabrics are produced by using one set of needles. As such all the stitches are meshed in one direction. These fabrics tend to roll at their edges. They roll from their technical back towards Fig. Plain knitted fabric the technical front at the top and lower edges. They also roll from their technical front towards the technical back at their selvedges. The structure is extensible in both lateral and longitudinal directions, but the lateral extension is twice that of the longitudinal extension. The yarn loop pulled in the longitudinal direction would extend by half its length, while when pulled in the lateral direction it could extend by the entire length. The degree of recovery from stretch depends on the fibres and the construction of the yarn.
Q.
What is rib knitted fabric?
Ans. The term rib is used to describe a knitted fabric with vertical row (wales) of loops meshed in the opposite direction to each other. If on both sides of a relaxed weft or warp knitted fabric only face stitches, i.e. the legs, are visible, then it is referred to as a rib knitted fabric and has been produced by meshing the stitches in neighbouring wales in opposite directions. This is achieved by knitting with two needle systems which are placed opposite to each other. As such these fabrics are also known as double jersey or double face fabrics. When the fabric is stretched widthwise, both sides of the fabric show alternately face and reverse stitches in each course. Once the fabric is released, it shrinks in its width, thus hiding the reverse st itches between the face stitches. These fabrics do not curl at their edges. The simplest rib structure is 1 x 1 rib. Fig. Rib knitted fabric
The longitudinal extensibility of the rib structure equals that of a plain knitted structure. The geometry of the yarn path influences the elastic behaviour of the knitted structures. The change of direction of the interlooping of the stitches
of neighbouring wales (cross-over points) results in the wales of a rib knitted structure closing up. This gives rib structures better elastic properties widthwise than other basic knitted structures. 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 stitches alternate with two wales of reverse stitches. As the number of wales in each rib increases, the elasticity 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 weft knitted fabric only reverse stitches are visible, then this is defined as a purl knitted fabric. Generally, weft knitting machines are used to produce these fabrics. Purl fabrics are produced by meshing the stitches in neighbouring courses in opposite directions by using special latch needles with two needle hooks. When the fabric is stretched lengthwise, then the face stitches are visible. The fabric shrinks more in the direction of wales, and once it is released, it relaxes to hide the face stitches between the courses. Fig. Purl knitted fabric The interlooping of the stitches of neighbouring courses in opposite directions results in the courses of a purl knitted structure closing up. The structure, t herefore, has a large longitudinal extensibility which is largely elastic.
Q.
What are interlock knitted fabrics ?
Ans. These could be considered as a combination of two rib knitted structures. The reverse stitches of one rib knitted structure is covered by the face stitches of the second rib knitted structure. On both sides of the fabric, therefore, only face stitches are visible, and it is difficult to detect the reverse stitches even when the fabric is stretched widthwise.
Dial loops
Cylinder loops Fig. Interlock knitted fabric Q.
What are tuck loops?
Ans. This is a loop that is integrated into a knitted structure without actually connecting it with the stitch immediately below it, though it is connected with a succeeding stitch. Tuck loops are formed by the hook of the needle in question receiving a yarn loop in addition to the knitted loop. The knitted loop and the yarn loop are then meshed during the next stitch forming process. A tuck loop is characterised with an upper binding unit and with a mis-sing lower binding unit, i.e. it is bound only at the head. Its legs are, therefore, not restricted at t heir feet by the head of a stitch so that the legs can open out towards the
Fig. Tuck Loops
two neighbouring wales. When tucking occurs across two or more neighbouring wales, the head of the tuck loop will float across the wales. Tuck loops reduce fabric length and longitudinal elasticity because the higher yarn tension on the tuck and held loop(s) causes them to rob yarn from the neighbouring stitches. The fabric width and lateral elasticity are increased. 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, the equivalent of the tuck loop is the fall-plate or Henkel lap. Generally, the tuck loop in warp knitted fabrics has the appearance of diagonally running yarns in which the loops hang in the feet of the stitches.
Q.
What are floats ?
Ans. A float is a piece of yarn limited by stitches which, in weft knitting, floats over wales. A float is generated when a stitch is missed out of a knitted structure, and does not pass through the stitch below nor connect with the subsequent stitch. The length of yarn that would have formed the stitch lies as a float across the wales. The extensibility of the fabric is reduced. Floats are created during jacquard knitting.
Fig. Floats Q.
What is knitted fabric geometry ?
Ans. There has been considerable research into the behaviour of single jersey structures indifferent states of relaxation. These relaxation states include dry relaxed, wet relaxed and fully 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 is achieved 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 to be 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 area occupied by that loop. The expression developed for the calculation of rightness factor (K) is given below : K
=
√T —— 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 can range between 1.2 and 1.6. Outside this range, fabrics are considered to be unsuitable for clothing applications.
Q.
What is fabric area density ?
Ans. The calculation of fabric are density is important in that it can be used as a guide to quality control procedures. In its simplest form, fabric area density for plain single jersey is as follows : sx lxT ————— = gram per square metre 100 Where, s = stitch density (loops per square cm) l = stitch length in mm T = 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 be remembered that the face wales of the rib need to be doubled because these conceal the alternate wales knitted on the back of the fabric. In the case of plain interlock, only the face of the fabric is analysed and the results are doubled to arrive at the fabric area density (interlock is basically two 1 x 1 rib fabrics locked together). In practice, then, only one feeder is analysed 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 per square metre. This is then compared to the calculated area density, and the percentage difference between the actual and calculated values should be less than three per cent. A recheck 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 yarn coming out of the last stitch of a course goes back through the same stitch and proceeds to the next course. Thus the stitches at the end of a weft knitted fabric have three legs, and are called 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 of knitting needles is for interlooping yarns. They perform different functions depending on the knitting technique and the needle type. Linking of new yarn loops with knitted loops and to carry the knitted loops during the early stage of the stitch formation cycle are two important functions of a needle. This central function 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 can also be considered as the primary knitting elements as they are directly in contact with the yarn during the entire stitch formation cycle. A knitting needle has a hook at one end to catch the yarn forwarded to the knitting zone, a stem or a shaft to carry the knitted loop during the early stages of the stitch formation process, and a butt at the other end. The butt is used either to position the needle on a needle bar or to move the needle the stitch formation process. The regularity and finish of the knitting needles 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 would influence their performance. As such for manufacturing needles high quality steels are used and they are hardened using special thermal treatments. During the early stages of the knitting cycle (a knitting cycle consists of all the knitting steps necessary to form a stitch), the hook of a needle is opened to release the retained knitted loop and to receive the new yarn
loop which is then enclosed in the hook. Before the new yarn loop can be drawn through the knitted loop (linking up) the hook must be closed (bridge formation) for the knitted loop to slide over the closed hook. All needles must, therefore, have some method of closing and opening the needle hook in order to retain the new yarn loop and exclude the knitted loop. Depending on how the closing of the hook is achieved knitting needles are subdivided into the following three 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 loop and the knitting needle
3)
The bridge formation is accomplished with an additional closing element
Q.
What is bearded needle ?
Ans. Bearded needle or spring needle was invented by Rev. William Lee, in 1589. Therefore it is the first knitting needle to be invented. It is also the simplest and, therefore, the cheapest needle. Bearded needles are made from steel wire (wire bearded needle or round stem bearded needle) or from punched steel plate (flat stock beaded needle). A bearded needle is shown in figure. By applying an external force on to the needle beard the needle hook is closed, and this is known as beard pressing. In bearded needle knitting machines this is achieved by mounting all the needles on to a needle bar and then by either moving a second metal bar, called the presser bar towards the needle beards or rotating the needle bar towards a stationary presser bar. Such an arrangement limits the ability of pressing the beards of individually, and the patterning potential of bearded needles is thus limited. This arrangement allows the needles to be reciprocated collectively. Knitting machines employing bearded needles are unable to compete in knitting the basic structures and their simple derivatives to other knitting techniques employing latch and compound needles, and their applications are reducing.
Fig. : Bearded needle
Q.
What is latch needle ?
Ans. Latch needle was invented by Matthew Townsend’s in 1849 and since then it has challenged the application of bearded needles in machine knitting. The latch needle is more expensive to manufacture than the bearded needle and is more prone to making needle marks in knitting, but it has the advantage of being self acting or loop controlled. For this reason, it is the most widely used knitting needle in weft knitting and is sometimes termed the automatic needle. Precisely manufactured latch needles are today knitting very high quality fabrics at very high speeds. A latch needle has the following important parts: 1.
the hook which draws and retains the new yarn loop;
2.
the latch-blade;
3.
the latch-spoon which is an extension of the latch-blade and bridges the gap between the hook and the stem covering the hook when closed;
4.
the rivet or axle of the latch needle;
5.
the stem which carries the loop in the clearing or rest position;
6.
the butt which enables the movement of the needle by using cams.
Fig. : Latch Needle The knitted loop is cleared from the hook when the latch needle is lifted because the knitted loop slides down inside the hook and hits the latch. This causes it to pivot open allowing the knitted loop to slide off the latch down on to the stem. The hook is closed automatically as the latch needle is lowered after a new yarn is supplied to it because the knitted loop which was on the stem slides upwards, contacting and pivoting the latch tightly closed. 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 of the hook, i.e. the bridge formation, is carried out by the knitted loop without using additional knitting elements. Such a phenomenon is very rare in processing machines. Except on Raschel machines (warp knitting), latch needles are arranged in the tricks or grooves of a needle bed. To produce purl knitted structures a special needle with a hook and a latch at each end of the needle stem is used. Double-ended latch needles, also called purl needles, can slide through the knitted loop in order to knit from an opposite needle bed, and thus draw a loop from the opposite direction.
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 stem opposite 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 latch needles, also called purl needles, slide through the knitted loops in order to knit from the 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 Machines with motor drive units and in some semi-automated power machines. In the automation of knitting machines and in the development of high speed knitting machines, the wire latch needles have lost their importance to punched steel latch needles. There are about 160 different 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 normal latch needle consists of three areas of different functions, which are shared by a loop transfer latch 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 the needle 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 also has a guidance function, i.e. to guide the needles in the tricks of the needle bed. The needle butt has the function of reciprocating the latch needle between two dead centres in order to form stitches. The transfer area has the task of transferring the knitted loop to the opposite latch needle. The form and the size of these four important areas will depend on the application of the latch needle. It is a common practise in machine building to design certain parts with weak areas, so that they will break in the event of a malfunction of the machine, thus preventing major damage to more expensive parts. The butt of a coarse gauge latch needle is designed with a weak area in the butt so that it will break if the knitting cam system jams, thus preventing serious damage to the tricks of the needle bed. The latch plays a very important role in the stitch formation process. The latch is fixed to the cheeks 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 this rotational movement the latch will open the hook in order to release the knitted loop. The latch rotational movement will also close the hook during the latter part of the knitting cycle so that a new loop could be drawn through the previous knitted loop. Although the latch is small during knitting it undergoes tremendous stresses. Modern knitting machines are high production machines, and in these machines the latch needles move in their tricks at very high speeds. The striking action of the latch during the closing of the needle hook by the latch spoon depends on the working speed of the latch needle. It will be very high at higher working speeds. 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 f ollowing conditions:
•
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 the fulcrum point is so small that it is almost invisible to the naked eye. The axle of the latch plays a 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 knit stitch is formed. It would be easier to understand if one assume that a loop has already been made, 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 another stitch. While this is happening, the fabric must be held down to prevent its rising with the needle. 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 needle stem. The needle is now in position to receive the new yarns (b) before starting to move down. The needle begins to descend, causing old loop (a) to close the latch, so traping the new yarn (b). When the needle reaches its lower position, the new loop (b) will have drawn through the old loop (a) known as knock-over-and the needle is now ready to rise so that the sequence can begin again.
Fig. Knitting action with a latch needle
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 following knitting 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 down the fabric as the needle starts to rise.
Fi . Knittin c cle of latch needle and sinker machine
At position (b) the sinker is still forward as t he 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 t he 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 which are cut in a cylinder or needle bed. These groves are called tricks. The sliding movement, up or 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 the knitted loop can be varied. Fig. shows a tyical cam system and a sequence of actions that allow a loop to be f ormed by latch needle on a circular single jersey machine.
Fig. Knitting cycle of latch needle circular machine
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 of the needle) and a tongue part (hook closing element). Both the two parts need to be controlled independently, and thus the new needle was named a compound needle. There are two types of compound needle in current use, the tubular pipe compound needle, where the tongue slides inside the tubular needle part, and the open stem pusher compound needle, where the tongue slides externally along a groove on the flat needle part. The pusher type is cheaper and simpler to manufacture and its two parts are capable of separate replacement. Its dimensions are narrower allowing tighter stitches to be produced. Today, the open stem compound needles are finding most widespread use in warp knitting. The compound needle is expensive to manufacture and each part requires separate and precise control from a drive shaft or cam system. The compound needle has a short, smooth and simple action, without latch or beard inertia problems. The slim construction and short hook makes it particularly suitable for the production of plain, fine warp knitted structures at high manufacturing speeds. Feeding yarn into a compound needle is more critical than for the bearded or latch needle because the yarn has to be laid precisely in the hook of the compound
Fig. Compound need
needle, in order to prevent fabric faults. By bearded or latch needle the yarn can be laid across the beard or the open latch, and it will still be taken into the needle hook. On the other hand the positively controlled two parts of the compound needle guarantees a opened hook at the 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. Their function is to hold particular knitting elements at exact defined distances and to guide them during the stitch formation process. On an electronic flat bed knitting machine knitting elements such as latch needles or compound needles and needle selection elements are placed in needle tricks. Modern electronic flat bed knitting machines are equipped with holding-down sinkers, and these are positioned at the top edge of the needle beds. As the needle beds are subjected to tremendous stresses due to the movement of the knitting elements they are made from very high quality metals. On one surface of the needle bed grooves (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 a tolerance 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 moved mechanically 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 is placed, in order to accommodate the somewhat bigger knitted loop. This top edge also forms the 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 are parallel;
2.
Circular Form : a metal cylinder or a metal disc is used to manufacture circular needle beds, e.g. the needle bed(s) circular knitting machines. If the needle bed is made from a metal cylinder, then it is a cylindrical needle bed. If the needle bed is made out of a metal disc, then it is called the dial needle bed. In the metal cylinder the needle tricks 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 of the metal disc (radial needle tricks).
Industrial flat bed knitting machines are equipped with two flat needle beds arranged in the form of a roof, thus they are also called v-bed knitting machines. The important parts of a flat needle bed are shown in the following figure:
Fig. Cross section of flat need bed
Usually, all types of needle beds employ all the elements shown in the above diagram except the needle security springs. The needle cover band maintains the knitting needles against the trick base. It also has a braking effect on the knitting needles and prevent them from springing back. The knitting needles move axially between the lower edge of the cover band and the security spring. By moving the security spring back the knitting needles can be brought out of the 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 the yarn during stitch formation without damaging the yarn. Also, in order to ensure free downward movement of the knitted fabric between the two needle beds, the under sides of the 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 maximum knitting width o
o
in flat needle beds this is given by the distance between the first and the last needle tricks of the needle bed; 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 a needle bed. As an example the correct designation of the machine gauge of a flat bed knitting machine having seven needle tricks to an inch is E7. The capital letter E specifies that the reference 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 as the knitting width (maximum knitting width) of a flat needle bed. The knitting width will depend on the total number of needle tricks on the needle bed and the machine gauge. It could be determined 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. Ans.
Brief the types of knitting machine. 1)
Warp knitting machines
2)
Weft knitting machines
Q. Ans.
Q. Ans.
Q.
Brief the types of warp knitting machines. 1)
Tricot warp knitting machine
2)
Raschel machines
3)
Straight bar knitting machines
4)
Manual warp knitting machines
Brief the types of weft knitting machines 1)
Flat weft knitting machines
2)
Circular weft knitting machines (large diameter)
3)
Circular weft knitting machine (small diameter)
4)
Manual weft knitting machines
Brief the specifications of Tricot warp knitting machine.
Ans.
Q.
Manufacturer
Type
Gauge
Width
Karl Mayer
KS 4
E 28
42”
Karl Mayer
KL 4
E 28
22”
Liba
Copcentra 2
E 28
42”
Brief the specifications of Raschel machines .
Ans.
Q.
Manufacturer
Type
Gauge
Width
Remark
Karl Mayer
RJG 5/2
ER 28
75”
Jacquard
Karl Mayer weft
RJ 4 MSU
ER 36
77”
Magazine
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
Brief the specifications of straight bar knitting machine.
Ans. Manufacturer
Type
Gauge
Width
Scheller
BS 32”/4
21 gg
32”
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 Schlafhorst
Pilot raschel
Single face ER 8
6”
4 Guide bars
machine
Q.
Double face
Brief the specifications of flat weft knitting machine.
Ans.
Q.
Manufacturer
Type
Gauge
Width
Stoll
CMS 420
E8
90”
Stoll
ANVH-BL
E8
90”
Stoll
IBOM/B
E 10
71”
Brief the specifications of circular weft knitting machines (large diameters).
Ans.
Q.
Manufacturer
Type
Gauge
Feeds
Remark
Morat needle control
ST4 MK2
E 18
36
30”
Electronic
Terrot 3-way-
UP 372
E 18
72
30”
Mechanical Technology”
Mayor & Cie 4-channel-
Relanit 4
E 28
84
26”
Single face, 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 wheel Needle
Supreme
E7
32
30”
Pattren Control
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”
E8
4
5.5”
Lucas
RR 2-4 s
Q. Ans.
Q.
Brief the specifications of manual weft knitting machines. Manufacturer
Type
Gauge
Width
Remark
Stoll
IBO
E4
100cm
Flat knitting mach.
Stoll
IBO
E5
100cm
“
Stoll
IBO
E6
100cm
“
Stoll
IBO
E6
120cm
“
Stoll Stoll Stoll Stoll C.F. Popp Foster
IBO IBO IBO FAL VA
E7 E10 E14 E5 E1, 5 E6
120cm 100cm 120cm 120cm 110cm ∅4.75”
“ “ “ Purl flat k.m. Flat knitting mach. Circular knitting mach.
Heumann
Favorite
E6
∅4.75”
Circular knitting mach.
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 vertical path. The fabric is held in the throat of the sinker to stop it rising with the needle and the guide bars will already have moved left or right one or more needle spaces for the first movement, which is known as the underlap.
Fig. Knitting cycle of a bearded needle Tricot machine
At position (b) the guides have swung between the needles towards t he back of the machine and stopped on the beard side. At this point the guides make a sideways movement of one needle space. This is called the overlap. These laps may be in the same or opposite
direction for each guide bar, depending on the structure being produced. The guides then swing back to the front of the machine (c), with the overlap having wrapped a thread around the 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 the beard and onto the stem of the needle (d) before it descends (e) until the tip of the needle is just 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 the needle stem, onto the closed beard. The presser then moves back and the needle descends towards knock-over, which occurs at (g), when the old loop is thrown over the top of the needle and the new loop is pulled through the old loop. Finally, the sinker moves forwards to hold the fabric down and the guide bars are repositioned ready for the next course (the underlap). 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 warp knitting machine and illustrates the sequence of events in one machine cycle. The guide bars are at the front of the machine after completing their underlap at (a), with the web holders being forward to hold the fabric down as the needle bar starts to rise from knockover. At (b) the needle bar has risen to its full height and the old loop has slipped down the stem after opening the latches, which are prevented from closing by the latch guard. The web holders can then start to withdraw and allow the guide bars to form the overlap. The guide bars have swung to the back of the machine (c) and will then move one needle space sidways to form the overlap before swinging back to the front of the machine (d), so that the warp threads can be laid into the needle hooks. The needle bar then descends (e) and the old loops contact and close the latches, so trapping the new loops inside. The web holders start to move forwards and, as the needle bar has continued its descent, its head has passed below the surface of the trick plate (f). This allows the new loops to be drawn through the old loops, which are cost off and, as the web holders advance over the trick place, the underlap movement starts again. Fig. Knitting cycle of a latch needle Raschel machine
Q.
Explain the knitting cycle of a compound needle Raschel machine.
Ans. Figure shows the various stages in loop formation for a compound needle warp knitting machine. At (a) the needles are at the knock-over position after completion of the previous course, with the 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 a lesser extent, to allow the hook to open. The guide then swings between the needles towards the back of the machine for the start of the overlap (c), before making their sideways shog and swinging back to the front of the machine to complete the overlap (d). The web holders then begin to withdraw and the needle descends (e). This closes the element which descends at a slower rate to cose the hook and trap the newly wrapped yarn. The guides then shog sideways to reposition themselves in front of t he needle space ready for the start of the next course, and the underlap is completed. At (f) the needle has descended to the knock-over position and a new course of loops has been produced.
Fig. Knitting cycle of a compound needle Raschel machine
Q.
Explain the knitting cycle of a flat bed purl machine.
Ans. Flat purl knitting uses two horizontal needle beds and double-ended latch needles which may, according to the selection and type of fabric being made, be transferred from one bed 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 one bed to the other. Sliders positioned in each trick control the double-ended latch needle movement. Position (1) shows the needle kniting in the front bed under the control of the slider in that bed. In position (2), the needle has been moved to the centre, with both sliders engaging the needle hook. The sliders then start to move back, but the slider in the back bed is pressed down by a cam at point X, so that the front bed sliver is freed from the needle hook and 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 the yarn 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 to complete the formation of the purl stitch. It should be noted that a purl stitch is made when a loop is formed by one hook and then at the next course by t he 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 setout. Structures such as 1x1, 2 x 2 and 3 x 1 ribs can be made by ensuring that the same needles knock-over in the same direction as each course is knitted. The machine is consequently very versatile.
Fig. Knitting cycle of a compound needle Raschel machine
Q.
Explain the interlock knitting on a cylinder and dial circular weft knitting machine.
Ans. Figure shows the needle setout on the machine, with long and short needles alternating on the cylinder. In the dial, the needles are set out exactly opposite to those on the cylinder. This means that, as a result of the special arrangement of the cams only one set of needles will knit at each feeder. To make this possible, there are two separte cam tracks with one controlling the short needles and the other the long ones. At the first feeder only long needles will knit, and at the second feeder only short needles will knit so as to produce one actual course of interlock two feeders are required. Figure reveals the interlock structure.
Fig. Needle arrangement for interlock fabric
Q.
What is machine gauge ?
Ans. The distance between two neighbouring needles, called pitch, determines the gauge of the knitting machine. The number of knitting needles contained in a reference length is defined as the machine gauge. Originally, knitting needles were cast in small metal blocks termed leads which were then fitted into the needle bar. In the weft knitting machines with bearded needles (straight bar weft knitting machine), the needles were cast two to a lead and gauged in the number of leads per 3 inches of the needle bar which is equivalent to a gauge of 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 per inch. In the Raschel warp knitting machine the latch needles were cast in 2 inch lead giving a Raschel gauge of needles per 2 inches. In latch needle weft knitting machines the gauge is normally expressed in needle tricks per inch which in the USA is referred to as “cut”, being short for the phrase “tricks per cut per inch”. Normally all primary knitting elements in the same machine are set to the same machine gauge. The pitch indicates the space available for the yarn. As the diameter of a yarn is proportional 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 gauge thus influences the choice of yarns and their counts, and affects fabric properties such as the appearance and the fabric weight. For a given needle cylinder diameter or knitting width, finer gauge machines tend to knit a wider fabric as more wales are involved. Coarse gauge knitting machines have latch needles with larger dimensions requiring greater movements. During knitting the width of the knitting cams are correspondingly large so less cam systems can be accommodated around a given needle cylinder diameter, so therefore coarser gauge knitting machines often have fewer knitting systems. There is a number of different machine gauge systems in current use. These are given in the table.
Machine Gauge
Reference Length
Machine type
E (npi)
1.0 inch (2.5400 mm)
Flat bed knitting machines,Circular knitting 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 is technically realised by means of inclined metal planes. These operate a defined distance above the needle bed and act on the butts of latch or compound needles. These inclined planes 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 of the other two cams are to lower the raised knitting needles (lowering or stitch cam) and to prevent the raising needles from overshooting (guiding cam). The stitch cam on the left lowers the 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 on the needle bed from right to left the raised knitting needles are then lowered by the right stitch cam.
Fig.: The simplest representation of a knitting cam system of a flat bed knitting machine The two elements, the raising cam and the sinking cams, are employed in all type of knitting machines with latch or compound needles, whether they be circular weft knitting machines or flat bed weft knitting machines, hand or automatic.
Q.
What are characteristics of raising cams ?
Ans. During the stitch formation process depending on the knitted structure the needles need to be put into action and out of action. This can be easily achieved during knitting by not moving a needle forward during the knitting cycle can not form a stitch, and this is realised by preventing 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 needle butts;
2.
sinkable type The raising cam is attached to a mechanism that will allow the cam to be withdrawn into 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 butts of the needles leaving them idle. Alternatively, in its lowered position the raising cam is 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 knitting needles are equipped with raising cams that can be set t o three different position: o
in all work position: Engages the butts of all the knitting needles
o
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 popular in circular knitting. Tuck Cams In order to form a tuck loop the f ollowing conditions need to be f ulfilled: 1.
Forward movement of a latch needle until the closed hook is opened (latch in hook opened 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 the following figure:
Fig. : Modified raising cam
Both parts, ie the knit cam and tuck cam, are mounted on to a cam plate with a cam withdraw mechanism. 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 of descension. 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 the needle 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 excessive damage to the needles.
2.
The number of knitting needles drawing the same yarn simultaneously during the stitch formation.
If the knitting needles descend less rapidly, then the needle bouncing is reduced, but at the same time the number of knitting needles being lowered simultaneously is increased causing the tension in the knitting yarn to increase according to the loop sinking rule in knitting. At present an angel between 45 to 55 degrees in flat bed knitting and 58 to 59 degrees in circular 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 limited mobility, i.e. their vertical position can be altered. In effect, with a lowering cam placed in a high position, the knitting needles make a small descend, ie a shorter length of yarn will be pulled through the previous knitted loops by the needles, and thus smaller stitches will be formed. On the other hand, with a lowering cam placed in a low position, the knitting needles descend further back into the cam track, and form bigger stitches. That is the setting of the vertical position of the lowering cams determines the length of the stitches. For a given machine gauge, bigger stitches will form a slack fabric, where as smaller stitches will make a tighter fabric. This is why, generally, the adjustment of the lowering cams is also known as the stitch length adjustment. How ever, this rule can not be applied in all cases. When positive yarn feeding is used, the stitch length mainly depends on the amount of yarn supplied in to the knitting needles, than on the position of the lowering cams. In this case, the position of the lowering cams will simply influence the yarn tension. In order to ensure the readjustment of the lowering cams, each lowering cam is connected to a 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 the machine type and for machine gauge. This table indicates the average position of the lowering 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 establishing the settings of the lowering cams. In this position the hook of the knitting needle is exactly aligned, 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 the machine gauge, the yarn count and finally the required stitch size. Following empirical standards are accepted when adjusting lowering cams:
1.
When knitting rib and rib based structures it is sufficient that the needles are lowered slightly 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.
