16 Flat knitting and socks knitting

S. Natarajan

1. Introduction

The basic principles of loop formation as well as the meaning of variousterms in flat bed machines are to that of circular knitting machines. However, we are going to discuss the path of yarn during knitting, the knitting camsystem and some special features related to flat bed knitting which not unique in this system.

Flat knitting machines, also referred to as “Flatbeds” or “V-beds,”. The interactions between the yarn and the knitting elements that create the fabric occur at the apex of the V and the fabric moves away downward between the two beds, drawn down by the takedown system.

2. Types of flat knitting machines

    The flat bed machines are available as single bed for producing plain or single jersey structures and double bed for producing rib and purl structures. Flat bed machine with interlock gating is not available on account of difficulty in knitting using two sets of needles in each bed by traversing of cam carriages. A double bed flat knitting machine can easily be converted to single jersey knitting machine by detaching one bed along with its cam carriage from the combined one and hence most of the commercial flat bed machines are supplied with two beds.

V-bed machines have two rib gated, diagonally approaching needle beds set at between 90 and 105 degrees to each other and have inverted V-shape appearance. Flat bed purls or links-links machines are mainly employed to knit some speciality fabrics using double hooked latch needles. The one set of needles are transferred to knit in either of two directly opposed needle beds by means of a set of sliders in each bed.

Power V-bed flat machines are used mainly for the production of knitwear for children, women and men. They range from simple machines through mechanical jacquard machines to fully electronic and computerized flat machines, even equipped with presser foot. The developments in the automation of fabric designing, pattern preparation, and electronic needle selection, as well as in the range of structures and effects which can be produced, have been tremendous. In fact, flat machines and their products are now regarded as extremely sophisticated. High quality garments can now be produced at competitive prices owing to revolutionary garment production systems feasible with presser foot. Two- and three-dimensional structures as well as complete garments without any seams or joins can be produced on the latest electronic flat knitting machines and the associated design systems.

3. Range of machine gauge and width

The common range of gauge is 5 to 12 npi, the machine may be coarse as 2.5 npi and may as fine as 18 npi. Further by removing or keeping idle alternate needles the gauge of the machine can be reduced to half.The width of flatbed machines also varies widely in the range of 6 to 96 inches (15 to 244 cm) but it has no relationship with gauge. The hand operated machines are available in the range of about 24 to 48 inches and the power driven machines are manufactured having width about 24 to 80 inches.

The cross-sectional view of simple V-bed Rib machine is shown in Fig. As observed, the two beds are in inverted ‘V’ position. The yarn package in the form of cone is placed on the cone holder (spindle), generally at the back of the machine.

Yarn is withdrawn and passes through guides, tensioner and yarn take up or compensating spring before entering the yarn carrier. The yarn carrier moves with the cam carriage on each bed. The fabric is made in the small gap between the two beds and taken downwards by the take down load.

The cam carriage is connected with a motor. As soon as the carriage reaches from one side to the other, a two way switch changes the direction of current in the motor and the carriage moves in opposite direction.

The needles used now-a-days in flat knitting is invariably of latch needle type.

A few of the other knitting elements found in flat knitting machines are as follows:

Jack: In most of the modern flat knitting machines there are additional knitting elements in the tricks which are involved in the formation of knitted loop. These are called jacks. The jacks which have different shapes according to the manufacturer are used to facilitate the needle selection required for patterning. The other names used to describe the different jacks are ‘intermediate jack’ and ‘selector’.

Knock over bits: The trick walls are replaced at the needle bed verges by fixed, polished and thin knock over bit edges. In rib machine, a knock over bit in one bed aligned opposite to a needle trick in the other bed. During knitting, the edges of the knock over bits restrain the sinker loops as they pass between the needles and thus assist in knocking over of the old loops and in the formation of the new loops. Flat machines generally employ holding down sinkers as the take down tension and the loops in the other bed help to hold the old loops down on the needle stems.

Cover plate: This is a thin metal blade located in a slot across the top of the needle bed tricks which prevents the stem of the needles from pivoting upward out of the tricks as a result of the take down tension drawing the needle hooks downwards, whilst allowing the needles to slidefreely in their tricks. The plate can be withdrawn sideways out of the needle bed to allow needles to be removed

Security spring: The tail of each needle is supported by a security spring which fits at the lower edge of the needle bed. The position of the needle in the trick can be changed with the help of this security spring for its selection during loop formation due to traverse of the cam carriage.

Latch brushes: The latch brushes are attached to the cam-plates of both needle beds to ensure the full opening of the latches. The support of the brushes are adjustable to ensure precise setting of the bristles relative to the needles.

Cam carriage: The cam carriage contains the knitting cams and many other important parts or attachments required for knitting. The carriage is fitted with a handle and some setting knobs on the top. The carriage is traversed manually by means of the handle for imparting required motions to the needles on the stationary needle bed for loop formation. In modern automatic machines the carriage is given to and fro motion by means of electrical motor. The cam carriage of computerized double flat bedknitting machine is shown in Fig. The tension dial fitted on the cam carriage basically regulates the stitch cam setting (say 1 to 8) and thus effects the tension on the yarn but it is not a tensioner.

Carriage guide rails: The cam carriage either slides or runs on ball bearings or wheels along guide rails, one of which is fixed over the lower end of each needle bed.

Yarn carrier: Yarn carrier is a small attachment through which each yarn used in knitting is fed to the needle hook for loop formation. Each yarn carrier is threaded separately and attached to a block which slides along a bar like carriage guide rail. It extends the full width of the machine. The yarn carriers are picked up and pulled along the needle bed or left behind by the carriage as per requirement of the design either manually or automatically. The construction as well as the function of yarn carriers is different in different machines particularly during plating and intarsia knitting.

4. Knitting Cam system

    xThe typical cam system, underside of a cam-carriage, forming the trackwhich guides the needle butts for knitting action in single jersey flat bedmachine is shown in Fig. The symmetrical camming arrangement istypical in many flat bed machines as it enables a similar knitting action tobe achieved in both directions of carriage traverse in the needle bed. Theneedle butts enter the cam system from the right during a left to rightcarriage traverse and from left during a right to left traverse. Thereforetwo raising/clearing cams and two stitch cams are required in each camsystem. Only one cam of each type does its function during a traverse andthe other acts as a guard cam by forming part of the cam-track for thebutts. So the roles of the two cams are reversed in the traverse of thecarriage in opposite direction.

Considering left to right traverse of the carriage, the needle butts enterthe cam system from right side. The idle positions of the needles aremaintained so long they are under the control of the auxiliary stitch cam{A.S. (L)} and stitch cam {S. (L)}. The needles start rising under the controlof the raising cam {R. (R)} and the upward motion of the needles is completedby the clearing cam {C. (R)}. The clearing cam has been made of two piecesraising cam and cardigan cam – in order to get tucking and normal loopformation facilities. When the needles move up under the control of theright side raising and clearing cam, the stitch cam acts as a guard cam. Afterreaching of the clearing or tucking height, the needles start descending underthe control of the stitch cam {S.(R)}. During this stage, the raising cam {R.(L)} acts as a guard cam. After loop formation, the needles moves up tosome extent to reach the idle position due to the take-down load and guardedby the auxiliary stitch cam {A.S. (R)}. However, during traverse of thecarriage in opposite direction, the stitch cam {S. (R)} becomes guard camand stitch cam {S. (L)} performs the function of stitch cam. Similarly, theraising cam {R. (L)} along  with cardigan cam {C. (L)} perform the clearingaction and the raising cam {R. (R)} becomes guard cam.

Yarn tensioner and storage feeder

Yarn tension variation is one of the major problems in flat knitting whichcan easily vary the size of the manufactured knit panels. To eliminate orminimize the yarn tension variation, now-a-days storage feeder are used in modern flat knitting machines along with auxiliaryyarn tensioner and automated tension controller in addition to the tensionersand guides used in ordinary machines. The auxiliary tensioner is requiredto monitor the yarn between storage feeder and yarn carrier.

Fabric take-down

The newly formed portion of the fabric in every knitting cycle must bewithdrawn (generally downward direction) from the knitting zone at aconstant rate and the motion used for the purpose is known as take-downmotion. In fact, in order to allow the formation of new row of knittedloops, the previous row of loops located in the hooks must be preventedfrom riding up with the ascending needles so that old loops are cleared ofthe hooks. The position of the old loops is maintained to a particular levelby applying the take-down tension. There are different techniques to applythe take-down tension. The simplest and oldest technique is to hold thefabric in place by pulling it downwards. Generally, dead weight is attachedwith the fabric in most of the flat bed machines for developing the take-down tension/load.

5. Sock manufacturing stages

The sock machine sector encompasses a wide range of different machines. Socks are produced on single and double-cylinder machines and also on single-cylinder machines with dial. In addition, transfer techniques on single-cylinder machines with dial offer wide scope for patterning. These machines are offered with commonly used diameters of 3.5 to 5 inches, and use needles ranging in thicknesses from 0.4 mm to 1.55 mm depending on the gauge. The machines are fitted with between 1 and 4 feeders depending on the patterning possibilities. In contrast to large-scale knitting machines, sock machines do not knit continuoustubular fabric but complete individual socks. The technical sophistication of these machines is evidenced bythe fact that they are able to automatically close the sock toeand so produce a finished article in a single work cycle. Typical fields of application include the manufacture of men‘s, women‘s and children‘s socks, sports and function socks as well as medical socks.

Contour or shape of the sock

The overall shape and appearance of socks can be viewed in Fig.The starting portion of the sock is the welt at the top. The length of thiszone is about 2 inches. The portion below the welt is called calf or leg.

The calf portion is much longer than the welt zone. The fancy design effectis mainly produced in this zone with the help of jacquard if required byusing yarns of different colours. In addition to the base yarn (s), spandexorlycra is also introduced in this zone for increased elasticity of the socks.Next to calf is the heel (heel pouch). The heel area is generally madedenser and thicker by using either coarser or additional yarns for achievinghigher abrasion resistance to withstand the constant frictional forces duringuse. The major portion of the socks which extend from the heel to the toeis called the foot zone. The extent of this zone depends on the foot sizeand ultimately the size of the socks. As soon as the foot portion is knitted,the toe is knitted with the same yarn or the yarn reserved for toe purpose

6.   Production of heel and toe

   Three-dimensional ‘turned’ heel and toe pouches as shown in fig. are knitted in plain sothat, in the case of double-cylinder machines, the heel section needles must be transferred down to knit from the bottom cylinder. A spring take-up holds the surplusyarn as the needles traverse towards the feed on the return oscillation, whilst apouch tension equaliser ensures that the pouch fabric is held down on the needlestems.

The pouch is preferably knitted in single feed so that the other feeds (if thereare any) are taken out of action, but an additional splicing yarn is striped in for reinforcement. The shape and extent of the spliced section may extend beyond thepouch. Reciprocation of the cylinder is produced by the drive at this point, beingtaken from the forward and backward oscillation of the quadrant. As thechangeover is mechanically complex, oscillatory knitting takes place at approximately two-thirds of the speed of circular knitting.

In socks with reciprocated heels and toes in single feed, over a third of the courseswill be in oscillatory knitting and may require over 60 per cent of the machine’soperating time, thus making this operation time-consuming and expensive.During the oscillatory knitting of the pouch, the remaining needles (approximately half) are raised into a high inactive cam-track by the introduction of a cam. This operates only on the long knitting butts allocated specifically to them,so that they retain their loops (for the instep) from the last course of circular knitting.

   During narrowing, the leading needle in each direction of oscillation is lifted upto join the other needles in the inactive track by the action of one of two side pickersthat are alternately in action according to the direction of oscillation. These pickersoperate throughout the oscillatory motion.

During widening, a down picker is introduced that lowers two needles at a time,thus cancelling the effect of the up picker and putting an extra needle into action.Each of the side pickers has an L-shaped recess and these are positioned facingoutwards at the approach into the cam system so that in either direction of oscillation, the knitting butt of the leading heel needle or slider is caught by the recess.The continued movement of the cylinder causes the picker to be moved backwardsand, as its movement is restricted, it pivots upwards in its holder to place the buttinto the high inactive track; the spring attached to the picker then pulls it downagain.

The down picker, when brought into action, moves down from the inactive trackbringing two needles down with it each time. It has a recess on each side of its undersurface so that two butts can be accommodated in each direction of oscillation.

Linkingis the conventional method of toe closing that occurs after knitting duringmaking-up. A slacker course of loops on the instep is joined loop-to-loop to a similarcourse in the toe pouch, by stitching on a linking machine. This is, however, an expensive, relatively slow and skilled operation. Many novel methods have been devised for closing toes during the knitting operation. Generally, they have been restricted to single-cylinder sock machines, incoarser gauges, and not double-cylinder sock machines or seamless stocking andtights machines. They have achieved only limited success against conventional toeclosing during post-knitting operations where automated seaming and handlingtechniques have considerably reduced labour content, time, and costs involved.

The main disadvantages of toe closing on the knitting machine have been one ormore of the following: the necessity for a complex adaptation of the knittingmachine and its knitting sequence with high capital costs; reduced productionspeeds; lower patterning potential; poor comfort; unsatisfactory wearing properties;and unconventional appearance. The following methods have been devised to overcome some of these disadvantages:

The true-linked toe. The appearance and comfort of a true-linked toe can now beachieved on a linking machine supplied directly from the knitting machine. Thelinking machine is either directly mounted on the knitting machine or it is supplied from a bank of machines. One sock is linked whilst the next is knitted.

The Sangiacomo Lin Toe: It can be fitted to cylinder and dial true ribmachines. The dial with its double loops is transferred to a Frullini patented, flange-mounted linking machine at the same time as the next sock is beingknitted.

The knitted closed toe. Knitted toe closure involves commencing at the toe and joining the instep needle loops to the toe loops. As the welt is knitted last, thereis a problem in obtaining a neat, secure finish.

The Matec Closed Toe. With this system, the closing line on the outside of thesock is practically invisible and the result is equal to that achieved by handlinking. The time taken to close the toe is 5–6 seconds. All yarn waste is eliminated. It is possible to retrofit this to all Matec single-cylinder machines.

REFERENCES and URLs

1. Sadhan C. Ray, “Fundamentals and Advances in Knitting Technology”, WPI Publishing, March, 2012
2. David J Spencer, “A comprehensive handbook and practical guide Knitting Technology”, WPI Publishing, 2001