Knitting Elements PDF

Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Knitting Elements  The basic elements of knitting machines are: o The Knitting Needles o The Sinker o The Jack o The Cams o The Needle Bed o The Yarn Fe...

Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Knitting Elements  The basic elements of knitting machines are: o The Knitting Needles o The Sinker o The Jack o The Cams o The Needle Bed o The Yarn Feeding  Knitting needle is the main element of any knitting machine which has been discussed earlier. The Sinker  The sinker is the second primary knitting element (the needle being the first).  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. Position of sinker and needle Parts of the Sinker  The main parts of sinkers are as follows: 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 Prepared By: Engr. Shakeel Ahmad Paracha Page 1 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Functions of the Sinker  Sinkers may perform one or more of the following functions; dependent upon the machine’s knitting action and consequent sinker shape and movement: o Loop formation o Holding-down o Knocking-over  Loop Formation: The main function of the sinker is to assist the needles in the loop formation by sinking or knitting newly laid yarns into loop as its forward edge or catch (C) advances between the two adjacent needles. This is only for bearded needle, whereas on latch needle weft knitting machines and warp knitting machines, loop formation is not a function of the sinkers.  Holding-down: The 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 that are being formed, and to prevent the old loops from being lifted as the needles rise to clear them from their hooks. The protruding nib or nose of sinker (N) is positioned over the sinker loop of the old loop (O), preventing it from rising with the needle.  Knocking-over: The third function of the sinker - as a knock-over surface - is illustrated in fig., where its upper surface or belly (B) supports the old loop (O) as the new loop (NL) is drawn through it. Action of the loop-forming sinker Action of the loop-holding sinker Action of the knock-over sinker The Jack  The jack is a secondary weft knitting element which may be used to provide versatility of latch needle selection and movement.  It is placed below and in the same trick as the needle and has its own operating butt and cam system. Prepared By: Engr. Shakeel Ahmad Paracha Page 2 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) The Cam  All needles have a reciprocating action. Cams are the devices which convert the rotary machine drive into a suitable reciprocating action for the needles and other elements.  The cams are carefully profiled to produce precisely-timed movement and dwell periods.  The movements may be represented in the form of a time-displacement graph. The Cam Types of the Cam  There are two types of the cams: o Engineering cams  It is circular cam.  Circular engineering cams control the motion of bars of elements which move as a single units in cottons patent to and warp knitting machine.  They are attached to a rotary drive shaft situated parallel to and below the needle bar.  In warp knitting machines, four types of cam drive have been worked:  Single acting cams  Cam & counter cams  Box cams  Contour cams o Knitting cams  The angular knitting cam acts directly on the butts of needles or other elements to produce individual or serial movement in the tricks of latch needle weft knitting machines as the butts pass through the stationary cam system or the cams pass across the stationary tricks.  There are three groups of knitting cams:  Knit cam  Tuck cam  Miss cam Prepared By: Engr. Shakeel Ahmad Paracha Page 3 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Knitting Cams  Knitting cams are solid steel plates and with the assembly of different cam plates a track for a butt can be arranged.  Each needle movement can be obtained by means of cams acting on the needle butt.  Knitting cams are attached, either individually or in unit form, to a cam-plate, and depending upon machine design, are fixed, exchangeable or adjustable. Cams and Latch needle moment Needle moment through cam tricks  The angular knitting cam acts directly onto the butts of needles or other elements to produce individual or serial movement in the tricks of a latch needle weft knitting machine.  Two arrangements exist: o Revolving cylinder machines  The needle butts pass through the stationary cam system and the fabric hanging from the needles revolves with them. o Rotating cam-box circular machines  The cams with the yarn feeds pass across the stationary needle bed.  In weft knitting, the yarn feed position is fixed in relation to the cam system.  The yarn feed moves with or remains stationary with the cam system, as do the yarn packages and tackle (except in the case of flat machines where the cam carriage only reciprocates away from and towards the stationary yarn packages and does not revolve). Circular knitting machine with angular / circular knitting cams Prepared By: Engr. Shakeel Ahmad Paracha Page 4 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Knitting cam design  Knitting cam consists of two cam systems: o Needle cam system o Sinker cam system  The needle cam system / race consists of: 1. Clearing / rising / raising cam 2. Stitch / lowering cam 3. Up-throw / counter / running cam  Which are vertically adjustable together for alteration of stitch length. 4. Guard cam 5. Return cam 6. Guard cam  The three sections of the sinker cam system / race are: 7. Race cam 8. Sinker withdrawing cam 9. Sinker-return cam  Which is adjustable in accordance with the stitch length. Needle and sinker cam system Prepared By: Engr. Shakeel Ahmad Paracha Page 5 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Needle Cam System 1. Clearing / rising cam / raising cam: The upward movement of the needle is obtained by the rising cam or clearing cam. The rising cam places the needle at a certain level as it approaches the yarn area. The raising cam causes the needles to be lifted to either tuck, clearing, loop transfer or needle transfer height, depending upon machine design. 2. Stitch / lowering cam: The stitch cam controls the downward movement of the needles thus controlling the amount of yarn drawn into the needle loop; it also functions simultaneously as a knock-over cam. 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 the cam, a reverse result is obtained. 3. Up-throw / counter / running cam: Running cam or up-through cam keeps the needle butts at a low level until they meet the next rising cam. The up-throw or counter cam takes the needles back to the rest position and allows the newly-formed loops to relax. The stitch cam is normally adjustable for different loop lengths and it may be attached to slide together with the up-throw cam, so that the two are adjusted in unison. 4. Guard cam: The guard cams are often placed on the opposite side of the cam-race to limit the movement of the butts and to prevent needles from falling out of track. Guard cam keeps the needle butts in their raceway. 5. Return cam: Sinkers are supposed to move backward and forward in relation to needles. A separate set of separate cams is contained in the sinker ring. Its time is synchronized to needle timing and is called as return cam. 6. Guard cam: The guard cams are often placed on the opposite side of the cam-race to limit the movement of the butts and to prevent needles from falling out of track. Guard cam keeps the needle butts in their raceway. Sinker Cam System 7. Race cam: This cam is used to bring the sinker into the knitting action. 8. Sinker withdrawing cam: This cam is used to withdraw the sinker out of the knitting action. 9. Sinker-return cam: This cam is used to push the sinker and get ready the sinker for the next knitting action.  Cam systems generate both the needle and the sinker displacements for sinker machines and cylinder and dial displacements for double jersey machines.  Fig. shows both the sinker cam track above and the needle cam track below.  The needle track shows the typical three stage needle displacement of (1 / 4) the raising or clearing cam, (2 / 3) the lowering or stitch cam and (5 / 6) the guard cam that returns the needle to its entry position for the next cam system.  The sinker track shows the engaged position (7) when the needle is clearing.  The sinker disengages in (8 & 9) so that knock-over can take place and re-engages into (7).  The displacement diagrams of the needles and sinkers are also shown. Prepared By: Engr. Shakeel Ahmad Paracha Page 6 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) The Needle Bed  Functions of the needle bed are as follows: o It is used to hold together the knitting needles and sinkers at exact defined distance and position. o It is used to guide the needles and sinkers during the stitch formation process.  Needle beds could be classified into various types depending upon the type of knitting process. The needle bed The Needle Bed Classification  There are two main types of the needle beds: o Circular needle bed  Single needle bed  Double needle bed o Flat needle bed  Single needle bed  Double needle bed Prepared By: Engr. Shakeel Ahmad Paracha Page 7 of 8  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Single needle bed (circular) Double needle bed (circular) Double needle bed (flat) Yarn Feeding  Basically two types of yarn feeding are there: o Moving the needles past the stationary yarn feed:  Most circular weft knitting machines have revolving needle cylinders and stationary cams, feeders and yarn packages.  In this case, the fabric tube must revolve with the needles, as must the fabric rollers and take-up mechanism. o Moving the yarn past the stationary needle bed:  As when the yarn moves past the needles, the fabric will be stationary because the loops hang from the needles.  This arrangement exists on all warp knitting machines, and on weft knitting machines with straight beds and circular machines with stationary cylinders and dial. Prepared By: Engr. Shakeel Ahmad Paracha Page 8 of 8