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Opening mechanism The shedding mechanism is one of the five major mechanisms of the loom and is an important mechanism necessary for forming fabrics. Its task is to divide the warp…

Opening mechanism

The shedding mechanism is one of the five major mechanisms of the loom and is an important mechanism necessary for forming fabrics. Its task is to divide the warp threads that penetrate the heald frames of each page into upper and lower layers in order to form a shed according to the requirements of the fabric structure. After the weft yarn is introduced, the shed is closed so that the warp and weft yarns form a staggered shape. The shedding mechanisms of air-jet looms include: crank connecting rod shedding, cam shedding, dobby shedding and jacquard shedding. The crank connecting rod shedding mechanism can only be used to weave plain fabrics, usually 4-page heald frames, and is currently rarely used on air-jet looms. The cam shedding mechanism can be equipped with 8-page heald frames at most. Depending on the type of cam configuration, it can weave plain weave, twill weave, satin weave, corduroy and other fabrics. The dobby shedding mechanism can be equipped with 16-page heald frames, and can weave small jacquard fabrics, and there are many suitable fabric varieties. The jacquard shedding mechanism has 1344 needles and 2688 needles, and can reach more than 20,000 needles. It can weave large jacquard fabrics and is increasingly used in air-jet looms. The cam opening mechanism is a conventional configuration of air-jet looms. The remaining forms are selected by users according to their needs.
The crank opening device is composed of two independent opening shafts A and B. The speed ratio between the main shaft of the loom and the open shaft is 1:2, and the phase difference between the left open crank and the right open crank of the open shaft is 180°. The rotation of the open crank reaches the open shafts A and B through the connecting rod and rocker, and drives the swing arm to drive the heald frame to move up and down. The size of the opening can be adjusted by adjusting the position of the connecting rod on the rocker. The number of heald frame pages can be selected from the following two options depending on the fabric thickness: 4 pages or 6 pages. There are three types of heald lengths: 280mm, 330mm, and 331mm. The right open shaft drives the 2nd and 4th page heald frames. The left open shaft drives the 1st and 3rd page heald frames. Figure 2-14 shows the recovery pattern of the heald frame of the crank opening mechanism.
Crank opening leisure has the characteristics of similar simple harmonic leisure, so it is more suitable for high speed. When the heald frame is in the upper or lower position, the lifting speed is low; when the heald frame is in the flat position, the lifting speed is high. For short fiber plain weave fabrics, the standard heddle leveling time is generally set at 310°, and for filament plain weave fabrics, the standard heddle leveling time is generally set at 330°. Generally speaking, it is helpful to reduce the friction of warp yarns, but it is not conducive to tightening the weft yarns and the fabric structure is not full. 2. Cam opening Cam opening can be divided into two types: negative type and positive type according to the nature of the heald frame driving mechanism. The negative cam opening mechanism consists of three parts: an opening cam box, a wire rope and a guide wheel, and a return heald box. It is controlled by the return heald spring in the return heald box to reset the heald frame. The positive open cam mechanism uses a conjugate cam to drive the heald frame up and down, and does not require a heald return device. European air jet looms are often equipped with positive cam shedding mechanisms and 8-page heald frames. Japanese models are mostly equipped with negative cam openings. (1) Negative cam opening mechanism: Since the cam profile shape can be designed according to the opening process, the casual nature of the cam opening mechanism can make up for the shortcomings of the casual nature of the link opening mechanism that is difficult to change, and expands the adaptability of the fabric. It can not only weave plain weave, twill weave and satin weave, but also weave corduroy and some fabrics that fit the tissue. Therefore, it is an opening type widely adopted by users (Figure 2-15). In Figure 2-15, when the cam changes from a small radius to a large radius, the wire rope connected to the heald frame is pulled to the right through the rotor and the opening arm to make the heald frame relax from the high point to the low point; at the same time, the return heald spring is stressed Force elongation saves energy. When the opening cam continues to rotate from a large radius to a small radius, the entire return heald system relies on the energy stored in the return heald spring to return the heald frame to its original position, that is, from low to high. This kind of opening mechanism is large, and the up and down relaxation pattern of the heald frame depends on the design of the outer contour shape of the opening cam; the recovery of the heald depends on the release of spring energy. Therefore, the design and arrangement of the cam outer contour directly affects the shedding performance, and the spring quality directly affects the stability of the heald frame. The laying of the heald frame must meet the following requirements: clear opening; suitable for high-speed operation; the laying of the heald frame must be stable; there should be a certain rest time when the opening is large. When weaving fabrics of the same organization, different types of cams need to be selected according to the weaving process parameters and fabric style requirements, as well as the loom speed and reed width.
For example: ZA series has four plain weave cams of P, G, Q or V shape to choose from based on known different requirements such as reed width, rotation speed, fabric density, style, etc. Twill, satin and corduroy can also be divided into Q shape or V shape. (2) Positive cam shedding mechanism: In order to make shedding more stable and precise, especially when weaving wide and heavy fabrics, the air-jet loom adopts a conjugate cam shedding mechanism, that is, a positive cam shedding mechanism, as shown in Figure 2 -16 shown. In Figure 2-16, when the main cam 7 changes from a small radius to a large radius, it passes through the rotor swing rod 6, connecting rod 5, swing rod 9, push-pull rod 11, angle rods 1 and 10, and vertical rods 2 and 4, so that the heald frame rises within its vertical rails. The main and auxiliary cams are one piece, with the same steering direction and the same speed. When the small radius of the auxiliary cam 8 turns to the large radius, on the contrary, the heald frame descends. Since the entire system relies on the conjugate accuracy of the two cams to ensure good constraint conditions, the heald frame has better accuracy and stability. The height position of the right end of the connecting rod 5 on the rotor swing rod 6 can adjust the stroke of the heald frame. The energy consumption of positive opening is lower than that of passive opening, and the vibration of the machine is small.
3. Multi-arm opening Dobby openings include upper and lower openingsAnd negative, positive and mechanical, electronic. When the air-jet loom weaves more complex fabrics (such as small patterns), a multi-arm shedding mechanism is required. The number of heald frames of the dobby equipped with the air-jet loom is mostly 16. The power of the dobby opening mechanism comes from the main engine, which transmits power to the input shaft of the dobby through the synchronous pulley and synchronous belt that are coaxial with the large pulley. The heald frame is driven up and down by the transmission mechanism. The mechanical dobby machine forms the expected fabric structure through the regular arrangement of pattern plates and pattern nails. The electronic dobby woven fabric data is input into the control system through the function keyboard to obtain the expected fabric. Therefore, the electronic dobby machine has the characteristics of fast change of fabric structure, large number of weft cycles, and easy operation. 4. Jacquard shedding The air-jet loom can be equipped with a jacquard shedding mechanism, which is suitable for weaving fabrics with large patterns, meeting the independent station lifting rules required for each warp yarn, and meeting the requirements of various designs and varieties.


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Author: clsrich