The simplest rib fabric is 1 x 1 rib. The first rib frame was invented by Jedediah Strutt of Derby in 1755, who used a second set of needles to pick up and knit the sinker loops of the first set. It is now normally knitted with two sets of latch needles (Figures 7.7,7.8).
Rib has a vertical cord appearance because the face loop wales tend to move over and in front of the reverse loop wales. As the face loops show a reverse loop intermeshing on the other side, 1 x 1 rib has the appearance of the technical face of plain fabric on both sides until stretched to reveal the reverse loop wales in between.
1 x 1 rib is production of by two sets of needles being alternately set or gated between each other. Relaxed 1 x 1 rib is theoretically twice the thickness and half the width of an equivalent plain fabric, but it has twice as much width-wise recoverable stretch. In practice, 1 x 1 rib normally relaxes by approximately 30 per cent compared with its knitting width.
1 x 1 rib is balanced by alternate wales of face loops on each side; it therefore lies flat without curl when cut. It is a more expensive fabric to produce than plain and is a heavier structure; the rib machine also requires finer yarn than a similar gauge plain machine. Like all weft-knitted fabrics, it can be unroved from the end knitted last by drawing the free loop heads through to the back of each stitch. It can be distinguished from plain by the fact that the loops of certain wales are withdrawn in one direction and the others in the opposite direction, whereas the loops of plain are always withdrawn in the same direction, from the technical face to the technical back.
Mock Rib is plain fabric knitted on one set of needles, with an elastic yarn inlaid by tucking and missing so that the fabric concertinas and has the appearance of 1 x 1 rib. It is knitted at the tops of plain knit socks and gloves.
Rib cannot be unroved from the end knitted first because the sinker loops are securely anchored by the cross-meshing between face and reverse loop wales. This characteristic, together with its elasticity, makes rib particularly suitable for the extremities of articles such as tops of socks, cuffs of sleeves, rib borders of garments, and stolling and strapping for cardigans. Rib structures are elastic, form-fitting, and retain warmth better than plain structures.
There is a range of rib set-outs apart from 1 x 1 rib. The first figure in the designation indicates the number of adjacent plain wales and the second figure, the number of adjacent rib wales. Single or simple ribs have more than one plain wale but only one rib wale, such as 2/1, 3/1, etc. Broad ribs have a number of adjacent rib as well as plain wales, for example, 6/3 Derby Rib (Fig. 7.9). Adjacent wales of the same type are produced by adjacent needles in the same bed, without needles from the other bed knitting in between them at that point.
The standard procedure for rib set-outs is to take out of action in one bed, one less needle than the number of adjacent needles required to be working in the other bed (Fig. 7.9).
In the case of purl machines, the needles knit either in one bed or the other, so there are theoretically the same number of needles out of action in the opposite bed as are knitting in the first. In the case of 2/2 rib, Swiss rib (Fig. 7.9), this is produced on a rib machine by taking one needle out of action opposite the two needles knitting.
Swiss rib is sometimes confusingly termed 2/3 rib because 2 out of 3 needles in each bed are knitting. It is not possible to commence knitting on empty needles with the normal 2 x 2 arrangement because the two needles in each bed will not form individual loops - they will make one loop across the two hooks. One needle bed must be racked by one needle space so that the 2 x 2 needle set-out is arranged for 1 x 1 rib; this is termed 'skeleton 1 x 1'; after knitting the set-up course, the bed is racked back so that 2 x 2 rib knitting can commence.
represents needle out of action
Represents needle in action x x x x x x
6X3 Derby rib represents needle out of action
Represents needle in action x x x x x x
6X3 Derby rib
Skeleton IXI rib
English rib is produced on a purl machine (or rib machine) with two empty tricks opposite to the two needles knitting; this type of rib is less elastic than Swiss rib.
In garment-length knitting, a direct change of knitting from 2 x 2 to 1 x 1 rib brings every third needle into action. At the first course, the limbs of the loops knitted on these formerly empty needles open out, producing apertures between every two wales that spoil the appearance of the structure. This problem is overcome by knitting a tubular cover course of plain on all needles in one bed, then on all needles in the other bed. On each side, the sinker loops draw the wales together and prevent the loops on the newly-introduced needles from forcing the wales apart.
7.3.2 The knitting action of the circular rib machine
In a gauge range from 5 to 20npi, an approximately suitable count may be obtained using the formula NeB = G2/8.4, where NeB = cotton count and G = gauge in npi.
For underwear fabric, a popular gauge is E 14 with a count of 1/30's.
7.3.3 Needle timing
Needle timing (Fig. 7.11) is the relationship between the loop-forming positions of the dial and cylinder needles measured as the distance in needles between the two stitch cam knock-over points. Collective timing adjustment is achieved by moving the dial cam-plate clockwise or anti-clockwise relative to the cylinder; individual adjustment at particular feeders (as required) is obtained by moving or changing the stitch cam profile.
Synchronized timing (Fig. 7.12), also known as point, jacquard and 2 x 2 timing, is the term used when the two positions coincide with the yarn being pulled in an alternating manner in two directions by the needles, thus creating a high tension during loop formation.
With delayed timing, also called rib or interlock timing (Fig. 7.13) the dial knockover occurs after about four cylinder needles have drawn loops and are rising
Synchronized timing cams Delayed timing cams
Fig. 7.11 Needle cam timing for a circular rib machine.
slightly to relieve the strain. The dial loops are therefore composed of the extended loops drawn over the dial needle stems during cylinder knock-over, plus a little yarn robbed from the cylinder loops. The dial loops are thus larger than the cylinder loops and the fabric is tighter and has better rigidity; it is also heavier and wider, and less strain is produced on the yarn.
Rib jacquard or broad ribs cannot be produced in delayed timing because there will not always be cylinder needles knitting either side of the dial needles from which to draw yarn. Although the dial knock-over is delayed, it is actually achieved by advancing the timing of the cylinder knock-over (Fig. 7.11).
Advanced timing is the reverse of delayed timing. The cylinder loops rob from the dial, producing tighter dial loops; advancement can only be about one needle. This type of timing is sometimes used in the production of figured ripple doublejersey fabrics, where selected cylinder needles can rob from the all knitting dial needles .
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