Industrial Flat-bed Knitting Machines
There are two major types of industrial knitting machines: the Circular and the Flat-bed. Circular knitting machines produce lightweight fabrics used in garments such as tee shirts and underwear. Flat-bed knitting machines, more versatile and much better developed, make sweaters and other outwear which often call for patterns, designs, and shapes.
Industrial knitting machines use latched needles to produce the interlocking stitches found in knitted fabrics. A latched needle is a hooked needle with a hinged latch that can swing one way to expose the hook or swing the other way to close over the hook.
On a flat-bed knitting machine, the latched needles are placed inside parallel grooves of a needle bed, which is a machined steel plate up to several feet in length. Symmetrical systems of cams, housed in a carriage, raise and then lower the needles in succession as the carriage traverses the length of the needle bed. When the cams come into contact with the needles, the needles are pushed upwards while the stitches that are already hanging on the needles slide downwards, pushing back the latches and then come to rest beyond the latches as the needles reach a plateau called the knit position. At the knit position, a yarn feeder that travels along with the carriage introduces a new strand of yarn onto the hooks of the needles. Then the needles are pushed downwards while the stitches formerly resting beyond the latches now slide upwards, closing the latches over the new strand of yarn, and then finally move off the needle altogether, forming a row of new stitches in the process. In essence, the new strand of yarn is inserted (knitted) into the original stitches to form new stitches, replacing the original stitches on the needles. This process is then repeated to produce a piece of knitted fabric. Tension adjustments regulate the downward travels of the needles and determine how tight or loose the fabric is, by varying the amount of yarn used in making the new stitches.
The number of needles a needle bed can accommodate within one inch of its length determines the weight of the fabric it produces, and that number is the gauge of the machine. The higher the gauge number is, the lighter the fabric becomes because of the finer yarn required. An outerwear sweater is typically 5-14 gauge, and a tee shirt is 22-32 gauge
A flat-bed knitting machine has two needle beds, forming an inverted vee with an inclusive angle of about 60-degree. The two needle beds are usually slightly offset horizontally so opposite needles would not interfere with one another. Knitting is done between the needle beds, and rollers then pull the knitted fabric downward. Although there are two needle beds in a flat-bed knitting machine, it is possible to utilize only one of them, resulting in a piece of single-knit fabric. Conversely, using both needle beds at the same time would produce a piece of double-knit fabric, which is comparatively heavier and more stable. Designs in color are technically difficult to produce on single-knit fabrics.
Before the advent of computerized control systems, functions of flat-bed knitting machines were controlled mechanically by punch cards. Needle selections, necessary to produce patterns, designs, and shapes, were achieved by using rolls of cumbersome steel 'jacquard' cards with corresponding "On" and "Off" holes for each needles on a needle bed. To set up such a machine for a new design is a labor intensive and time-consuming task.
The age of computerized knitting machines began in the 1960s; and by the 1990s, flat-bed knitting machines with full CAD-CAM functions have arrived. Machine control are now software driven, and needle selections are now done electro-magnetically by miniature solenoids. Machine set up is now as fast as data could be transferred from the design computer to the computers onboard the machines. Designers and technicians can now preview products in three dimensions, and can even simulate production runs to anticipate possible design flaw or technical problem.
Traditionally, sweaters are knitted in separated pieces, called panels, of fronts, backs, left sleeves, and right sleeves, and then the panels are joined together to form a sweater. Utility sweaters, including those for the military, are “cut and sewn” sweaters in which the panels are knitted in rectangles and then cut to sizes and shapes, and finally sewed together, using serging machines. Fashion sweaters are “full-fashioned” sweaters in which the panels are meticulously knitted to specific sizes and shapes and then precisely joined together by skilled operators, using linking machines which are basically small knitting machines that knit one stitch at a time.
Nowadays, using a new breed of flat-bed Knitting Machines called Whole Garment Machines, it is possible to produce complete sweaters all within the knitting process, bypassing the cutting table and the linking machines altogether. A whole-garment knitting machine knits three tubes, one as the body and the other two as the sleeves, on the same needle bed simultaneously, and then finally knit the three tubes together to form a sweater. These sweaters are full-fashioned and have no seam at all, offering a new level of fit and comfort. Perhaps you already own a seamless Whole Garment sweater from Banana Republic or from GAP?