In weaving machines, the triangular cross-section tunnel formed by dividing the warp threads into two layers before the weft is thrown is called the shed. Various systems have been developed to determine the warp threads that should be above or below the weft thread recorded through each opened shed. Each of these systems constitutes the shedding systems.
Shedding systems determine the tactile quality of the fabric and the degree of usability of the machine. In this respect, whether the weaving weave is simple or complex, the width and height of the knitting pattern primarily depend on the shedding system.
In weaving machines, the warps must be passed through the power wires in order to form a shed. The warps, whose power is passed through the wires, are moved up or down in groups before each insertion of the weft thread. The weft thread is thrown from this gap formed by this movement given to the warps and the fabric is formed. At least two frames are needed to form the mouthpiece.
The mouthpiece is named in two parts.
Front mouthpiece: It is the name given to the section from the comb to the woven fabric in the weaving machine. This section should be in such dimensions that the weft carrier can pass easily.
Rear nozzle: It is the name given to the part from the power to the reed in the weaving machine.
ACCORDING TO THE MOTION WARP YARNS MOVE :
is divided into three:
1-Upper mouthpiece: In dobby looms, if some warp threads are lifted up from the horizontal stop point and the remaining warp threads are left at the level of the horizontal stopping point, this opening is called the upper shed.
2-Lower nozzle: The shed form, which is formed by lowering some of the warp threads from the horizontal stance point and leaving the remaining warp threads at the horizontal stance point, is called the lower shed.
3-Full mouthpiece: The shed shape created by raising some of the warp threads above the horizontal stance and lowering the remaining warp threads below the horizontal stance is called full shed.
NOZZLE OPENING TYPES ACCORDING TO THE WAY THE MACHINE GETS NOZZLE:
is divided into three:
1-Open mouthpiece: It is the system in which only the frames that will move in the weaving machines move. That is, the frames that move up or down in the first weft will stay in place if they will do the same movement in the second weft. In this case, when the tambourine tightens the weft, the mouthpiece remains open. It is preferred to weave fabrics with low weft density in this type of shedding machines.
2-Semi-open mouthpiece: Two types of applications are carried out in this system. One is systems where the lower frames remain stationary, while the others, including the upper muzzle frames, move. It is a more common application in top shedding systems. Another method is the application where the frames forming the upper shed wait before they go all the way down, that is, to the zero point, and the other frames move normally.
3-Closed mouthpiece: It is the application in the machine where all warp threads are aligned after weft insertion. In other words, after the weft is completed when the drum is at its back point, the frames return to their normal stopping point (zero point) and the shed is closed. The weft thread stuck between the lower and upper warps is compressed by the stencil pushing the weft towards the fabric. Cloths with high weft density are woven in closed shed weaving looms.
HEIGHT OF HEIGHT AND CREATING SMOOTH WEAVING ON WEAVING MACHINES
Proper opening of the sheds during the weaving process is extremely important for weaving productivity. A properly opened shed will not allow breaks caused by the weft carrier element by attaching to the warp threads. In addition, excessive stretching of the warp threads will be prevented.
The ideal frame setting for muzzle formation is to give more movement to the first frame. If we adjust all the frames equally at the opening of the mouthpiece, we cannot obtain a good mouthpiece shape. Because the up and down threads move equally up and down, they will not be aligned in the nozzle. If the yarns in the opened shed are not aligned, it will make it difficult for the weft carrier to pass and warp breaks will occur due to friction. This type of mouthpiece is shown below.
As in the figure, by removing the small numbered frames more from the first frame, a smooth nozzle is formed through which the shuttle will pass. As can be seen, the threads that make up the upper and lower shed stand as a single thread on the front shed. In this case, warp breaks are prevented. Because the warp threads have gained integrity, there are no irregularities that will cause sets.
The direction of movement to be given to the frames is important for the fabric to be produced in the machines working with the eccentric and dobby shedding system. Especially in terms of replacing the old frames, the movement given to the frames is in two ways.
>>>> POSITIVE FRAME MOTION
Mouth formation occurs by applying force to the frames. Most of the energy used in weaving machines is used to move the frames to create the shed. In systems that form mouthpieces with positive frame movement, movement is given from the mouthpiece forming device not only for forming the frames but also for closing them. In these systems, although the energy consumption increases, the continuity and speed of the movement is in harmony with the cycle of the machine. The position of the frames in the muzzle formed by the positive shed opening system in the figure; Frame a is pulled up and frame b is pulled down by the shedding device. The shed is formed by the rise of some warp threads and the descending of others. As all warp threads are moving, breaks may occur due to friction.
>>>> NEGATIVE FRAME MOTION
In such systems, the movement of the frames is usually applied in one direction. In systems with negative frame movement, the preferred application is for the shedding device to move the frames upwards. The return of the upper shed frames is by means of springs or weights attached to the frames. The shedding system does not consume energy for the backward movement of the frames. It is a preferred system in modern weaving looms as it is suitable for use at high speeds. The figure shows the system in which the return springs are placed horizontally.
In the figure, the negative frame movement with the levers is shown schematically. In both devices, the retraction function is performed by mechanisms that are tensioned by opening the mouthpiece.
In the figure, the position of the forces created by the negative shedding system, (a) frame lifted up, (b) frame remained fixed. Jacquard shedding assemblies open the negative shedding. The weights suspended below the forces allow the forces to return to their original position when released. The negative shedding system is particularly well suited for high speed weaving machines. In modern weaving machines, negative shed movement is used by oscillating with an eccentric or dobby in weaving light and medium weight flat fabrics. The friction in the warp threads is minimal. Therefore, it allows it to reach high speeds.
Eccentric Shed Opening Systems:
Eccentric is the name given to parts that are not the same distance from the center and have different offsets. Also called cam.
Eccentric shedding systems are divided into two according to their mounting positions on weaving machines. In eccentric weaving machines, the eccentrics to control the frames are prepared according to the dobby plan of the knitting. It is conveniently placed on the camshaft. Eccentric Shed Openers;
- INTERNAL ECCENTRIC
- EXTERNAL EXCENTRIC
is divided into two. They are metal plates that are mounted on a rotating shaft in mechanical weaving machines and transmit the movement to the frames when opening the shed.
Eccentrics, which are usually placed on a rotating shaft (cabinet shaft), are used to move the frames. The frames are in contact with the eccentric. When the off-center nose of the eccentric comes into contact with the frame legs, the mouthpiece is opened by applying a pushing force.
Eccentrics can be disassembled and assembled as a group according to the braids to be used. There is a separate eccentric group for each knitting. This means; When it is desired to change the weave to be applied in the machine, the eccentric group must be changed. Eccentric groups can be run in the opposite direction to find the right shed in accordance with the knitting pattern according to the movement of the machine to the warps.
Internal Eccentric Shed Opening Systems:
In this type of weaving machines, eccentrics are placed between the two side walls of the weaving machine. It takes up less space. It is easier to transmit motion to frames. The number of frames is less than machines with external eccentric.
The lengths of the eccentrics in these machines are different from each other. The eccentric that moves the 1st frame is larger than the eccentric that moves the 2nd frame. The eccentrics are fixed to the knock camshaft, which is located below the crankshaft, while the knitted rag. Although it works up to 6 to 8 frames on these machines, it usually does not exceed 6 frames. It is the small diameter of the eccentric that lifts the frame in internal eccentric benches. What brings the frame down is the large diameter of the eccentric. When we want to change the fabric weave, the cam pack is usually changed. However, in some cases, it is possible to change the angular position of the cams relative to each other, thus changing the weave. While the weaving process takes place in the machines with internal eccentric, the pulley system is used to bring the frames to their initial positions in the negative system.
External Eccentric Shed Opening Systems
In this type of weaving machines, the eccentrics are located outside the side walls of the weaving machine frame. It occupies more space than internal eccentric shedding systems. Although external eccentric weaving machines take up more space, they are more preferred because they allow more frame and weft repeat lengths, and are easy to change and maintain the eccentric.
In order to increase the number of frames, the way of operating the eccentrics outside the machine is considered in opening the eccentric shedding. Although there is a possibility to run more frames this way than with internal camshaft machines, this is also limited. In other words, it can be removed up to 8-12 feet.
The camshaft positively controls the power to the frames with double-sided camshafts. The movements of the eccentrics are transmitted to the power frames by means of roller arms, transmitting arms and feet. Camshafts have a muzzle lift. With this, the roller arms are kept separate from the eccentrics and all the power frames are brought to the same height.