What is Sinker in Knitting?
Sinker is the second important knitting element in a knitting machine after the needle. It is a thin metal plate with an individual or collective action approximately at right angles from the hook side between adjoining needles. Sinker contains four important parts: nose, catch, butt and belly. Individual sinkers are kept between two needles, and separate cams give them forward and backward motion during knitting (Figure 1). The movement of the sinkers is controlled by the sinker cam segment which is fixed to a stationary sinker cam ring.
Figure 1: Structure and parts of a sinker
In the production of plain knitted fabric on a circular type single jersey knitting machine or straight-bar type flat knitting machine, sinkers are used to hold the fabric in position while the needle rises. This means that the fabric is tighter and the appearance and knitting speed can be improved.
Sinkers play two fundamental roles: they hold the already formed fabric down when the needles rise to knit the new course and support the fabric when the previous course is knocked over. The sinker, which has a particular shape, has two main parts: the nose (upper section) and the breast (lower section) which can move forward and backward horizontally driven by special cams.
The sinkers generally move to and fro in horizontal, i.e. at 90° to the direction of movement of needles and maintain a fixed height. The old loops or the cloth falls rest on the sinkers. The construction as well as the function of the sinker varies from machine to machine. Sinker is used in both weft and warp knitting in combination with latch needle as well bearded needle. Sinkers may be unnecessary when knitting (circular weft) with two needle beds as the second bed restrain the fabric loops whilst the other set needles move.
Sinkers capable of producing loop fabric are well known in the knitting industry. In such machines the sinkers generally include a blade having an upper edge which defines a lower knitting level and a nib having an upper edge which is at an upper knitting level. Long loops are formed at the upper knitting level of the sinkers with a loop yarn and a base yarn is knitted over the blade. The sinkers may be formed and their movement controlled to cause either the loop yarn to appear on one side of a fabric and the base yarn on the other or the loop yarn to appear on both sides.
Proper functioning of sinkers is crucial for the quality of the knitted fabric. If sinkers are not working correctly, it can lead to issues such as dropped stitches, uneven fabric, or poor loop formation.
Types and Functions of Sinker in Knitting Machine: Sinker may perform one or more of the following functions dependent upon the machines knitting action and consequent sinker shape and movement:
Loop formation,
Holding down and
Knocking over.
According to these functions the sinkers are also divided into three groups, such as loop forming sinker, holding-down sinker and knocking-over sinker.
Figure 2: Functions of sinker
a) The first function of the sinker is loop formation. On bearded needle weft knitting machines of the straight bar frame and sinker wheel type the main purpose of a sinker is to sink or kink the newly laid yarn into a loop as its forward edge or catch advances between the two adjoining needles. On the bearded needle loop wheel frame, the blades of burr wheels perform this function whereas on latch needle weft knitting machines and warp knitting machines, loop formation is not a function of the sinkers.
b) A second and more common function of sinkers on modern machines is to hold down the old loops at a lower level on the needle stems than the new loops which are being formed and prevent the old loops from being lifted as the needles rise to clear them from their hooks. The protruding nib or nose of the sinker is positioned over the sinker loops of the old loops preventing them from rising with the needles.
On tricot warp knitting machines and single bed weft knitting machines, a slot or throat is cut to hold and control the old loop. The sole function of the sinker may be as a web holder or stitch comb as on the Raschel warp knitting machine in which case only the underside of the nose performs the function.
On latch needle weft knitting machines the holding-down sinkers have a rectangular gap cut on their upper surface remote from the nose into which the sinker cam race fits to positively control the sinker’s movement.
Holding-down sinkers enable tighter structures with improved appearance to be obtained, the minimum draw-off tension is reduced, higher knitting speeds are possible and knitting can be commenced on empty needles.
Holding-down sinkers may be unnecessary when knitting with two needle beds as the second bed restrains the fabric loops whilst the other set of needles move.
c) The third function of the sinker– as a knock-over surface – where its upper surface or belly supports the old loop as the new loop is drawn through it.
On tricot warp knitting machines the sinker belly is specially shaped to assist with landing as well as knock-over.
On latch needle machines the verge or upper surface of the trick – plate serves as the knock- over surface.
Sinker Operation in Knitting Machine:
The held loop is positioned in the throat of the sinker when the sinker moves forward and the needle moves upward for clearing. The held loop is held by the throat and hence its movement along the needle is restricted.
Figure 3: Sinker operation in knitting machine
The sinker remains at its forward position when the needle attains its clearing position.
The sinker retracts when the needle comes down after feeding. At this stage, due to sinkers retraction, fabric or held loop is eased out. Also the sinker belly supported the fabric or held loop and hence its movements along the needle is prevented.
Sinker remains in backward position and the needle descends to its lowest position drawing the new loop through the old one.
Before the needle ascends, the sinker moves forward to push the knitted fabric a little and to hold the old loop away from the head of the needle and to be in a position to control the fabric.
Further the holding down sinkers enable tighter construction with improved appearance to be obtained, the minimum draw-off tension is reduced, higher knitting speeds are possible and knitting can be commenced on empty needles.
In some modern weft knitting machines, the sinkers also move in vertical direction in addition to its horizontal movement in order to get higher knitting speed which is technically known as CONTRA or RELANIT system.
Conclusion:
Sinker is an important part of knitting machine that helps in the formation of knitted fabric by holding the loops of yarn in place during the knitting process. It directly impacts on the quality of the final knitted fabric.
References:
Fundamentals and Advances in Knitting Technology by Sadhan C. Ray
Understanding Textiles for a Merchandiser By Shah Alimujjaman Belal
Knitting Technology, 3rd Edition by David J Spencer
Reference Book for Knitting by Carmine Mazza and Paola Zonda
Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
Textile Handbook By The Hong Kong Cotton Spinners Association
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
