Spiers produced a successful machine of this type in 1930, termed the Spensa Purl machine. It has a revolving cylinder and internal sinkers and is capable of knitting garment-lengths with a tubular welt and rib border. In 1956, Wildt (Mellor Bromley) replaced it with the model SPJ, which has an anti-clockwise revolving cam-box, no dividing cams or internal sinkers, and sliders with pointed noses for opening the latches of needles knitting in the opposite cylinder. As well as being mechanically more reliable for purl knitting, the patterning potential of this model was improved over the years.
The main gauges are 6-12npi with 2/16's (NeK) worsted being an average count for 10-gauge. Machine diameters are 16-20 inches (40-50cm approx.) with six feeds; 22 inch (56 cm) (which replaced the 11 inch diameter for infantswear) with eight feeds; and a 33-inch (84cm) model with twelve feeds.
The machine produces knitwear garments for adults, children and infants with a separating course, welt, 1 x 1 or 2 x 2 rib border, and a body or sleeve panel sequence. Stitch patterning may include any of the following in plain colour or striped-in colours: plain and purl, tuck rib, tuck purl, float stitch jacquard, and rib jacquard.
The machine has the standard knitting-element arrangement for a purl machine of one set of double-ended needles that can be controlled for knitting or transferring by either of two sets of sliders that operate from opposing tricks of the top and bottom cylinders. The tricks of the top cylinder are held in alignment with the bottom cylinder by a dogless head, whilst the cam-boxes for the two cylinders are rotated in unison by means of a vertical cam-shaft and two pinions.
Figure 20.3 illustrates the basic arrangement of the elements and cams, subject to the machine builder's modification. Each set of sliders has a single operating butt position and is controlled from a knitting cam-box. The butts are alternately arranged long and short, with long butts in one cylinder opposite to short butts in the other for obtaining a 1 x 1 needle arrangement.
Controlled by a cam-box below the bottom knitting cam-box is a set of jacks having single operating butts. Each intermediate jack is supported at its base by the ledge of a spring-tailed jack, placed behind and below it in the same trick, which has a tail butt controlled by raising cams when not selected (the indirect selection principle was described in Section 11.9). The intermediate jacks thus translate the selection into a movement causing the bottom sliders to be lifted for knitting or transferring their needles.
The presser selectors have 79 butt positions, corresponding to the pattern units (or presser brackets) that have batteries of 79 slides. Of these, 75 are available for patterning. Of the bottom four, which are used for isolation purposes, three are controlled by the Cardomatic film with set-outs of 1-out-1-in, 2-out-2-in and cancelling out the knitting selection, whilst the other line of all-in butts can be selected from the Mechatape for cancelling all transferring.
Two full-size pattern units may be provided for double selection on the bottom cylinder at each feeder. At selection I, needles are selected to remain at miss height whilst the remainder are raised to clearing (knit) height. At selection II, of those needles taken to clearing height, some are selected to remain at that height whilst the others are raised to be transferred to the sliders in the top cylinder.
Thus at selection I, the tail butts of non-selected jacks pass over the raising cam K to lift their intermediate jacks onto cam k. As the intermediate jacks pass over k
they lift their bottom sliders onto the clearing cams KS putting them into the knitting track. The butts of non-lifted sliders will pass through in the welt (miss) track below the KS cams. S are the stitch cams for the knitting sliders, which can be automatically changed to any one of four pre-settings of 'quality' during the garment cycle.
Prior to selection II, the non-selected intermediate jacks are lowered by cam LJ and their spring-tailed jacks by cam LI. These jacks therefore have their bottom butt aligned with raising cam TR. If non-selected by selection II, they are raised over cam TR and lift their intermediate jacks over cam tr, raising their bottom sliders to transfer their needles to the top cylinder. At this moment, the tails of sliders that are transferring needles pass across the spring-loaded cam which presses down on them, causing the front of the slider to pivot upwards and unhook itself from the transferred needle. Needles of jacks non-selected at I but selected at II will pass through the upper cam track at knit height. Cam LII lowers the spring-tailed jacks ready for the next double-selection sequence.
In the knitting cam-boxes, certain cams are bolt cams of the plunge type, which are introduced or withdrawn out of the track as required for any cam-box revolu-
tion. When fully in action, they deflect all sliders passing through, when half in action they only deflect long butt sliders, and when out of action the cam-track is clear.
Cams W are the welt bolt cams, which guard the entrance to the welt tracks and, when fully in action, cause all sliders with needles to knit. Cam W is in for knitting or the transferring of all needles in the bottom cylinder, but is out of action for selected knit miss or knit tuck stitches. In the top cylinder there is no selection so therefore those bolt cams are used during pattern selection. Cam W is employed when knitting, transferring down or receiving transferred up needles in the top cylinder. Half in action, it is employed for knitting or transferring on a 1 x 1 arrangement, and when fully out of action, needles in the top cylinder will miss. Cam tb is the bolt cam for transferring needles down from the top cylinder and works in conjunction with spring loaded cam x.
In the bottom cylinder, the bolt cam TC can be introduced to cause needles controlled by sliders in the welt track to be lifted to tuck. When employed in conjunction with cam L0, the needles are immediately lowered to miss but their latches are opened.
Figure 20.4 shows part of a purl garment knitting sequence.
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