BASIC KNITTING ELEMENTS FOR A CIRCULAR KNITTING MACHINE
NEEDLES
The needles are the most important stitch forming elements. They are displaced vertically up and down and are mounted into the tricks or cuts of the knitting cylinder.
There are three types of needles namely:
1. Latch needle
2. Spring bearded needle 3. Compound needle.
We can divide a needle into three main parts:
A. the hook, which takes and retains the thread tube looped;
B. the hook opening and closing device, that allows the hook to alternatively take a new thread and release the previous one;
C. a system allowing the needle to move and form the loop.
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1=Butt,2=Butt height,3=Back shank,4=Stem,5=Crimp,6=Groove,7=Cheek,8=Hook,9=Hook width,10=Latch,11=Rivet Fig: Needle |
Sinker
The sinker is the second primary knitting element. It is a thin metal plate with an individual or a collective action operating approximately at right angles from the hook side of the needle bed, between adjacent needles.
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.
In the past it has not been possible to producing loop cloth of ideal quality since loops would twist or coil making it difficult to finish a loop fabric into satisfactory velor. Furthermore loops which were supposed to appear on the front of a fabric would sometimes appear on the other side. The back of loop cloth was therefore apt to have objectionable loose protruding loops and double tuck stitches.
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1=Butt,2=Butt breadth,3=Height of shank,4=Buldge,5=Neb,6=Length of neb,7=Throat angle,8=Sinker platform height,9=Breadth of lower shank,10=Clearance,11=Throat Fig: sinker. |
Sinkers Operation
1. 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.
2. The sinker remains at its forward position when the needle attains its clearing position.
3. 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.
4. Sinker remains in backward position and the needle descends to its lowest position drawing the new loop through the old one.
5. 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.
Jack
In circular knitting machines of the rotatable cylinder type a well know means for selectively actuating the knitting instrumentalist is that of a pattern controlled slider jack system. Engaged the known type of slider jack system it is common practice to transmit the dictates of the pattern controlled slider jack directly to a needle actuating jack. Circular knitting machines which utilize a slider jack system must have a cylinder of sufficient length to accommodate the circular series of needle, needle actuating jacks and slider jacks which are slid ably mounted in the slots formed on the periphery of said cylinder. The slider jack must be raised a sufficient distance so as to raise the needle actuating jack or intermediate jack to a level where its operating butt will be engaged by a cam member and raise said jack to knitting height which in turn will raise its respective needle to the required height to perform its intended function.
Dial
Dial is the upper steel needle bed used in double knit machines. Into the grooves of the dial, the needles are mounted horizontally and are allowed to move radially in and out by their dial cams. The number of grooves per unit space conforms to the cylinder gauge in most of the cases.
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Fig: dial |
CYLINDER
The cylinder is a steel circular bed having grooves/tricks/cuts on its outer periphery into which the needles are mounted. With reference to the tricks, the needles move vertically up and down by their butt being in contact with the cam track. The number of tricks per inch i.e., number of needles per inch decides the gauge of the machine. Machines are built as low as 4 NPI to as high
as 32 NPI. Based on the machine gauge, the fineness of the yarn to be knitted can be varied. The diameter of the cylinder also varied based on the type and width of the fabric and a maximum of 75 cm diameter machines are available. |
Fig: Cylinder |
CAMS
The knitting cams are hardened steels and they are the assembly of different cam plates so that a track for butt can be arranged. Each needle movement is obtained by means of cams acting on the needle butts.
The upward movement of the needle is obtained by the rising cams or clearing cams. The rising cam places the needle at a certain level as it approaches the yarn area. Cams controlling the downward movement of the needles are called stitch cams.
The stitch cam draws the needle down below the knitting level, thereby drawing a loop formed by the fed yarn through the loop already on the needle. The lowest point to which the needle is drawn by the stitch cam is called the "cast-off" position. They are screwed to the cylindrical cam ring and are adjustable in vertical direction. If the stitch cam is raised, then shorter loop is drawn below the sinker level and a tighter fabric will result. With lowering of stitch cam, a reverse result is obtained. Guard cams keep the needle butts in their race-way.
Running cams or the needle butts at a low level until they meet the next rising cam. |
FEEDERS/STRIPPERS
Feeders are the yarn guides placed close to the needles to the full circumference of the knitting zone. The feeders feed the yarn into the needle hooks and control the needle latches in their open position while the needle attain their clearing position. They consist of a yarn guiding hole and a bevel edge to guard the latches of the approaching needles. They are slightly curved to the corresponding curvature of the needle bed. Feeders may have two holes also for the purpose of plating.
Yarn feeders can be divided into “positive” or “negative” types depending on the possibility of controlling the yarn feeding speed and uniformity.
The feeder brackets can be adjusted to set their distance from the needle and to ensure yarn feed into needle hooks. Stripers are the feeders designed to deliver two or more yarns individually to the same feed. They can be considered as moving guide replacing the holes of fixed guides. In a two color stripe, two different colored yarns are supplied by two stripper fingers and their engagement is controlled by an endless control chain which governs the guide change at the appropriate feeds. At each revolution, a counter may select the movement of all the striper chains. The stripes are used on both single and double bed machines.
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Fig: Feeders/Stripers |
S&R
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