Plain structure

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Plain (the stocking stitch of hand knitting) is the base structure of ladies' hosiery, fully fashioned knitwear and single-jersey fabrics. Its use in ladies' suiting was popularised by Lily Langtry (1852-1929), known as the 'Jersey Lily' after her island birthplace. Other names for plain include stockinette, whilst in the USA the term 'shaker stitch' is applied to it when knitted in a coarse gauge of about 3- needles per inch (25 mm). The term 'plain knit may be used instead of just 'plain', particularly when the structure has a surface design.

Its technical face (Fig. 7.1) is smooth, with the side limbs of the needle loops having the appearance of columns of V's in the wales. These are useful as basic units of design when knitting with different coloured yarns.

On the technical back, the heads of the needle loops and the bases of the sinker loops form columns of interlocking semi-circles (Fig. 7.2), whose appearance is sometimes emphasised by knitting alternate courses in different coloured yarns.

Plain can be unroved from the course knitted last by pulling the needle loops through from the technical back, or from the course knitted first by pulling the sinker loops through from the technical face side. Loops can be prevented from unroving by binding-off.

If the yarn breaks, needle loops successively unmesh down a wale and sinker loops unmesh up a wale; this structural breakdown is termed laddering after 'Jacob's Ladder' [1].

Laddering is particularly prevalent in ladies' hosiery, where loops of fine smooth filaments are in a tensioned state; to reduce this tendency, certain ladder-resist structures have been devised. The tendency of the cut edges of plain fabric to unrove

Plain Structure
Fig. 7.1 The technical face of plain weft knitted fabric.
Weft Knitted Fabric
Fig. 7.2 The technical back of plain weft knitted fabric.
Structure Knitting
  1. 7.3 The three-dimensional structure of plain weft knitting [Milliken AGILON] magnified x130 by a stereoscan electron microscope. The arrows indicate the direction in which the fabric will tend to curl if it is cut. [By permission of Knitting Times, official publication of NKSA USA].
  2. 7.3 The three-dimensional structure of plain weft knitting [Milliken AGILON] magnified x130 by a stereoscan electron microscope. The arrows indicate the direction in which the fabric will tend to curl if it is cut. [By permission of Knitting Times, official publication of NKSA USA].

and fray when not in tubular or flat selvedged form can be overcome by securing them during seaming.

Knitted structures have a three-dimensional structure as shown in Fig. 7.3. At the point where the new needle loop is drawn through the old loop (I), the structure is composed of two yarn thicknesses (diameters) instead of one. The needle loop is therefore held down, both at its head (H) and its feet (F),by loops in the same wale, but its side limbs tend to curve upwards at (II).

When the fabric is cut, the loops are no longer held in this configuration so that the fabric curls towards the face at the top and bottom and towards the back at the sides. The same configuration causes face meshed wales of loops to be prominent in rib fabrics and the heads of loops and the sinker loops to be prominent in wales of purl stitches.

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

7.2.1 Production of single-jersey fabric on a circular latch needle machine

Most single-jersey fabric is produced on circular machines whose latch needle cylinder and sinker ring revolve through the stationary knitting cam systems that, together with their yarn feeders, are situated at regular intervals around the circumference of the cylinder. The yarn is supplied from cones, placed either on an integral overhead bobbin stand or on a free-standing creel, through tensioners, stop motions and guide eyes down to the yarn feeder guides.

The fabric, in tubular form, is drawn downwards from inside the needle cylinder by tension rollers and is wound onto the fabric-batching roller of the winding-down frame. The winding-down mechanism revolves in unison with the cylinder and fabric tube and is rack-lever operated via cam-followers running on the underside of a profiled cam ring. As the sinker cam-plate is mounted outside on the needle circle, the centre of the cylinder is open and the machine is referred to as an open top or sinker top machine.

Compared with a rib machine, a plain machine is simpler and more economical, with a potential for more feeders, higher running speeds and knitting a wider range of yarn counts. The most popular diameter is 26 inches (66 cm) giving an approximate finished fabric width of 60-70 inches (152-178 cm). An approximately suitable count may be obtained using the formula NeB = G2/18 or NeK = G2/15, where NeB = cotton spun count, NeK = worsted spun count, G = gauge in npi. For fine gauges, a heavier and stronger count may be necessary.

Examples of typical metric cotton counts for machine gauges are:

E 18 Nm1/24-1/32, E 20 Nm1/28-1/40, E 22 Nm1/32-1/44, E 24 Nm1/34-1/48, E 28 Nm1/50-1/70 The knitting head

Figure 7.4 shows a cross section of the knitting head all of whose stationary parts are shaded.

1 Yarn feeder guide, which is associated with its own set of knitting cams.

2 Latch needle.

3 Holding-down sinker - one between every needle space.

4 Needle cylinder (in this example, revolving clockwise).

5 Cylinder driving wheel.

Structure Needle Loom

6 Cylinder driving gear.

7 Sinker-operating cams, which form a raised track operating in the recess of the sinker.

8 Sinker cam-cap.

9 Sinker trick ring, which is simply and directly attached to the outside top of the needle cylinder thus causing the sinkers to revolve in unison with the needles.

10 Needle-retaining spring.

11 Needle-operating cams which, like the sinker cams, are stationary.

12 Cam-box.

13 Cam-plate.

14 Head plate.

15 Cylinder driving pinion attached to the main drive shaft. The knitting action

Figure 7.5(a-e) shows the knitting action of a latch needle and holding-down sinker during the production of a course of plain fabric.

  • a) Tucking in the hook or rest position. The sinker is forward, holding down the old loop whilst the needle rises from the rest position.
  • b) Clearing. The needle has been raised to its highest position clearing the old loop from its latch.
  • c) Yarn feeding. The sinker is partially withdrawn allowing the feeder to present its yarn to the descending needle hook and also freeing the old loop so that it can slide up the needle stem and under the open latch spoon.
  • d) Knock-over. The sinker is fully withdrawn whilst the needle descends to knockover its old loop on the sinker belly.
  • e) Holding-down. The sinker moves forward to hold down the new loop in its throat whilst the needle rises under the influence of the upthrow cam to the rest position where the head of the open hook just protrudes above the sinker belly.
Sinker Loop
Fig. 7.5 Knitting cycle of a single jersey latch needle machine. The cam system

Figure 7.6 shows the arrangement and relationship between the needle and sinker cams as the elements pass through in a left to right direction with the letters indicating the positions of the elements at the various points in the knitting cycle. The needle cam race consists of the following: the clearing cam (1) and its guard cam (4), the stitch cam (2) and upthrow cam (3) which are vertically adjustable together for alteration of stitch length, and the return cam (5) and its guard cam (6).

The three sections of the sinker cam race are the race cam (7), the sinker-withdrawing cam (8) and the sinker-return cam (9) which is adjustable in accordance with the stitch length. Sinker timing

The most forward position of the sinker during the knitting cycle is known as the push point and its relationship to the needles is known as the sinker timing. If the sinker cam-ring is adjusted so that the sinkers are advanced to the point where they rob yarn from the new stitches being formed, a lighter-weight fabric with oversized sinker loops and smaller needle loops is produced. If the ring is moved in the oppo

Cam Set Sinker Machine Circular
Sinker Cam

Needle cam system

Fig. 7.6 Sinker timing on a single jersey machine.

Needle cam system

Fig. 7.6 Sinker timing on a single jersey machine.

site direction, a tighter, heavier fabric is produced having smaller sinker loops and larger needle loops. The timing is normally set between the two extremes.

7.2.2 The 'contra' knitting technique

The 'contra', relative or shared loop knitting technique is used on some modern circular single-jersey fabric machines. The sinkers move vertically, to positively assist in holding-down and knocking-over the fabric loops so that they move in opposition to both the rise and the fall of the needles, as well as having the normal radial movement between the needles. The contra movement of the fabric loops considerably reduces the extent of the needle movement.

As on the old bearded needle sinker-wheel machines, one loop is almost fully formed before the next loop is commenced. There are thus less metal/yarn contact points (each of which doubles the tension of the previous point). Contra knitting therefore reduces the tendency to 'rob back', produces less knitting element stress, improves fabric quality, 'handles' yarns more gently, and enables weaker and lower quality yarns to be knitted. The smaller needle movement enables cam angles to be employed so that speeds up to 1.4m/sec can be achieved. (See also Section 13.10.)

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