Shedding mechanism shed formation and clarity
1. Shed formation
When opening, the warp yarns are divided into upper and lower layers as the heald frame relaxes, forming a diamond-shaped space, which is the shed. As shown in Figure 3-14(a), H is the maximum lifting stroke of the warp yarn, which is called the shed height; the horizontal distance from the cloth fell B to the back beam roller D is the shed length or shed depth, which can be divided into are the length l 1 of the front part of the shed and the length l 2 of the rear part; the entire shed is divided into two parts, the front and rear parts, by the heald frame. The front heald frame is the working part, and the weft yarn passes through here. When the shed is fully open, the angle formed by the upper and lower warp yarns at the cloth fell B is called the shed front angle, and the angle formed at the back beam roller D is called the shed back angle.
For water-jet looms, the theoretical warp position line is usually set as a horizontal line, that is, the line connecting point A to point D is a horizontal line, and a symmetrical shed is adopted, that is, h1 and h2 have the same height dimensions.
The horizontal line drawn through points A and D is also the standard for measuring the height of the rear beam D, see Figure 3-14(b). When the back beam is higher than the meridian, that is, when d>0, it is called a high back beam; when the back beam is lower than the meridian, that is, when d<0, it is called a low back beam. The warp position line has a significant impact on the warp breakage, tension, elongation and fabric appearance quality during the weaving process, and should be adjusted and controlled. The adjustment of the warp position line in weaving production generally refers to the change of the position of the back beam, and once the positions of other points are determined, they generally do not change.
2. Shed clarity
The degree to which the upper and lower warp yarns in the front of the shed are on the same plane is called the clarity of the shed. If the upper and lower warp yarns in the front of the shed are on the same plane, it is called a clear shed, which is conducive to the passage of weft yarns. However, in this opening method, the warp yarns are easily entangled, and the rear heald frame has a large movement, which can easily cause warp yarn breakage. If the upper and lower warp yarns in the front of the shed are not in the same plane, it is called an unclear shed. If the upper warp yarns in the front shed are not in the same plane and the lower warp yarns are in one plane, it is called a semi-clear shed. In this case In this case, the difference in the movement of the heald frame is small, and the movement of the back heald is smaller than the clear shed, which is advantageous, but it is necessary to prevent misweaving and warp breakage caused by the weft yarn penetrating into the non-clear warp layer.
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