Introduction: Knitting machine can produce continuous fabric like weaving or can make garment with proper shaping. On the basis of the product, machines may be classified as fabric length machine or garment length machine. Garment length machines are more complicated and less productive. There is another type of knitting machine according to shape of the needle bed equipped with bearded needles called straight bar frame.
Plain straight bar frame is a special type of weft knitting machine. In this article I will explain knitting and fashioning action of the plain straight bar frame machine.
Knitting Action of the Plain Straight Bar Frame: The following figures show the movement of the knitting elements to produce one course of loops:
Figure 1: Knitting action of a Plain Straight bar Frame
a) Thread laying: The carrier moves across the knitting head laying the yarn on the noses of the sinkers and dividers and the beard side of the needles.
b) Sinking: The slurcock (one for each knitting head) travelling behind the carrier, contacts the jacks and is shaped so that each jack in turn pushes its sinker forwards to kink a loop around every two adjacent needles.
c) Dividing: The catch bar moves the dividers forwards collectively, whilst the needle bar tips slightly out wards to allow the double loops to be divided into equal sized needle loops around every needle.
d) Pressing & e) Landing: The needle bar descends placing the new loops inside the hooks of the beards. The catch bar is now lowered so that the sinkers as well as the dividers are collectively controlled by it for the rest of the knitting cycle. They now start to with draw. The needle bar moves towards the sinker verge causing the beards to be pressed. A further downward movement of the needle bar ‘lands’ the previous course of loops, resting on the knocking-over bits, on to the closed beards.
Drop-Off: As the needle bar moves away from the pressing-edge, the sinkers and dividers withdraw so that the newly-formed course of loops drops off their noses onto the knocking-over bits.
f) Completion of knock-over: The needle bar descends to its lowest position. As the heads descend below the belly of the knocking-over bits, the old course of loops is collectively knocked-over.
Holding down: As the sinkers and dividers move collectively forward to hold down the fabric, the needle bar rises to the thread-laying position. The catch bar is slightly raised to release the sinkers for individual movement at the start of the next course.
On coarser gauge machines it is possible to accommodate sinkers with reinforced butts between every needle space thus eliminating dividers and their action. Some machines have selvedge dividers with a lower forward ledge so that when the yarn carrier stops over one divider the next divider inwards from it will be the last to take that traverse of yarn which will slide into its specially-shaped lower throat and form a tight selvedge.
Fashioning action of the Straight bar frame: The fashioning action or loop transfer for either narrowing or widening is performed in following steps:
Figure 2: Fashioning action of the Straight bar frame
a) The fashioning points or transfer needles descend and the needle bar tips backwards to clear them.
b) The needle bar moves towards the points causing the beards of needles engaged with points to be pressed and boxed or located in the grooves of the points.
c) The sinkers and dividers, which are collectively controlled by the catch bar, retire, and the needles and points descend together below the knocking-over bits so that the loops are cast-off onto the points.
d) The needles and points now rise and move clear of each other so that the points can make the sideways ‘fashion rack’ at the selvedge either by one needle for widening or by one, two or four needles for narrowing.
e) The needles and points now descend and the needles box with the points again so they receive the transferred loops. As the needles and points descend below the sinkers, the sinkers and dividers move forwards to hold down the loops.
f) Once the needles have slid up into the grooves of the points to receive the loops, the points rise to their high inoperative position. The needle bar rises causing the transferred loops to slip down onto the stems and the cam shaft is shagged back to the left again so that knitting can restart.
References:
Knitting Technology, 3rd Edition by David J Spencer
Understanding Textiles for a Merchandiser by Shah Alimujjaman Belal
Fundamentals and Advances in Knitting Technology by Sadhan C. Ray
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
