There are three principal methods of manipulating fibers or yarns into textile fabrics:
1) Interweaving – two sets of straight threads intersecting at right angles.
2) Intertwining – threads intertwined with each other at any angle.
3) Interlooping – yarns formed into loops and loops intermeshed into a structure.
The first, we commonly call weaving.
The second, we associate with twisting and braiding. It is the third method that describes knitting.
The knitted stitch usually consists of three or more intermeshed needle
loops (Fig. 1). The center loop is drawn through the head of the lower, previously formed loop and is, in turn, intermeshed through its head by the loop above it. Thus, in contrast to woven fabrics, where warp and weft threads are interlaced at a 90° angle, knitted fabrics comprise consecutive rows of interlocking loops.
This intermeshed loop structure makes knits highly elastic, especially along the vertical axis. Thus, they are more flexible and resilient than other textile structures. This makes them amenable to bending or curving around a surface without distorting. Woven fabrics, by comparison, are more constrained, and thus more rigid, typically only able to stretch on the bias. There are, however, techniques available to reduce the elongation of a knitted material where necessary in applications where stretch must be controlled or reduced.
Knitting is faster than braiding, but slower than weaving or twisting. Unlike weaving, braiding and twisting, knitting does not require the use of special yarn packages. This eliminates the requirement that the yarn be respooled, and thus reduces total production time.
Knitting also is no longer restricted to certain fiber types. Today, all types of fibers and materials have been knit into textile structures, including glass fiber, Kevlar and wire up to 0.38-mm diameter. Some machines can knit wire up to 20-30 mm/s. There are two types of knitting: warp and weft (see “Knitting Glossary,” below). Historically, warp knitting has been favored in technical textile applications, but that is beginning to change with new advances in weft and flat knitting technology.
Warp knitting, Fig. (a) is a method of forming a fabric in which the loops are made vertically along the length of the fabric from each warp yarn and intermeshing of loops take place in a flat form of lengthwise basis.
Weft knitting, Fig. (b) is a method of forming a fabric in which the loops are made in a horizontal way from a single yarn and intermeshing of loops takes place in a circular or flat form on a cross-wise basis.
A course is the series of loops that are connected horizontally or the horizontal row of loops made by adjacent knitting needles in the same cycle. A wale is the series of loops intermeshed vertically or the vertical column of loops made from the same needle in successive knitting cycles.