Knitting technology, Third Edition

20
Circular garment-length machines
20.1
Circular versus flat machines
On the basis of knitted stitches per minute against the capital cost of the machine,
circular garment-length machines are generally more productive than V-bed flat
machines for cut-and-sew knitwear. Prior to computer controls, the price/perfor-
mance ratio was 1 : 3 in favour of body-width circular machines. Against electronic
V-bed flat machines, however, circular machine builders had to move to less versa-
tile large-diameter machines (33–36 inches) in order to achieve a ratio of even 
1.2 : 1.There are large numbers of body-width RTR and SPJ mechanically-controlled
machines still in operation, as well as some that have been retro-fitted with elec-
tronic controls.
Circular garment-length machines are mainly of the rib cylinder and dial type
(Fig. 20.1) or of the double-cylinder purl type. Although more restricted in pat-
terning capabilities than flat machines, they may offer advantages in productivity
and fineness of gauge.
Many are of the revolving cam-box type whose cams, selection units and striper
units are altered when their externally positioned levers are contacted as they pass
by the control position on the periphery of the machine (Fig. 20.2).
The peg drum control unit for the garment-length programme is now tending to
be replaced by an endless film loop that is driven by a horizontal perforated roller.
The film is advanced by one row of holes for each feed or transfer section that passes
per cam-box revolution. When no changes are required, an economiser rack-wheel
operates.
On 
Bentley
machines, the 
Mechatape Pattern Control Unit
was introduced to
replace peg drums or trick-wheels and provide a virtually unlimited pattern depth,
faster running speeds, easier pattern preparation and more rapid pattern changes.
The control unit consists of a drum whose perforations correspond to the staggered
rows of punched hole positions on a plastic film loop. Each row operates through
the bank of horizontal levers onto the levers of a passing selection unit. The arrange-
ment in the selection unit is fixed for a complete circuit of the machine whilst it
selects onto the jack pressers arranged around the cylinder.

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Circular garment-length machines
245
The fabric take-down mechanism cannot be driven directly by the machine rota-
tion as the length of fabric knitted per machine revolution can vary in different parts
of the garment sequence. The slipping-belt system is an efficient arrangement that
accommodates itself to the varying rates of fabric production.
The take-down rollers and the belt pulley that drives them via worm gearing are