In the dyeing and finishing process, the warp direction of textiles is pulled heavily, which leads to the elongation of the length and the narrowing of the width. In order to overcome this unstable state and ensure the size stability of textiles, the speed of fabric feeding is adjusted during stretching or setting, which is called overfeeding.
Feeding speed greater than the speed of the stenter or setting machine is called positive overfeeding (or overfeeding, shrinking code). Positive overfeeding causes warp to shrink, weft density to rise, gram weight to increase and warp shrinkage to decrease.
If the speed of cloth feeding is less than that of the stenter or setting machine, it is called reverse overfeeding (or negative overfeeding, stretching code). Reverse overfeeding makes warp stretch, weft density decrease, weight decrease and warp shrinkage increase. In order to pursue their own profits, many dye factories in China are willing to do something against the principle.
Stretch setting is the finishing work after dyeing, and it is also a very important process. In the process of stenting and setting, some dyeing factories have to work hard to process more fabric than grey fabric. They are very objective to think that most customers do not understand the reasons in this and let themselves do whatever they want.
Now, some overfeeding knowledge of the stenting and setting is sorted out for reference only.
In the dyeing and finishing process, the warp direction is subject to a large tension, which is easy to produce the situation of warp extension and weft narrowing, which is an unstable state. This kind of fabric will shrink in the water.
In order to reduce the warp shrinkage of the fabric and make the size of the fabric stable, overfeeding shall be carried out during stretching or setting. The feeding speed shall be faster than that of the stretching machine or setting machine, so that all warp yarns can be retracted and the weft direction can be pulled to the specified door width.
In general, the cloth with lighter weight is fed when it is set. In order to make the weight meet the requirements of the guests, overfeeding will make the cloth surface wavy, and the clothing factory is unable to cut the cloth, so it needs to be set again.... in the fabric setting process, there is the saying of overfeeding "" anti overfeeding ". Generally speaking, after the weft door width is determined, the radial tension will be applied. It is reflected in the machine that the speed of the fabric entering the machine is higher than that of the setting machine (chain speed), which is "positive overfeeding", resulting in the increase of the weft density of the finished fabric, that is, the increase of the weight per gram. So "anti overfeeding" is just the idea. However, it should be noted that the fabric will shrink to a certain extent if it is hit with "positive super weft". But "positive overfeeding" should be reduced in warp direction. The meridional shrinkage will be larger and the shrinkage will be smaller.
Analysis of some important proper nouns:
Overfeeding: it is an action process that provides a specific proportion of the required quantity according to the requirements of the next process.
Specific proportion: positive, negative or one, i.e. positive, negative overfeeding or zero overfeeding.
Demand: speed, flow, quantity, quality, etc.
Requirements for the next process: it is determined according to the processing purpose to be achieved.
Overfeeding: it is completed by the overfeeding mechanism through the above data relationship between the front and rear mechanisms.
Processing purpose: it is the main functional mechanism.
Overfeeding: auxiliary mechanism.
Measurement and control instrument: it is a necessary matcher.
Practical operation example:
1: in order to eliminate the longitudinal stretch of the bleaching and dyeing process before setting, and meet the size requirements of customers and design structure, more fabrics need to be fixed on the needle plate in advance. For example, the feeding mechanism feeds 120m per minute, and the needle plate of the fixed fabric moves 100m per minute, so the 100m position is squeezed into 120m fabric (positive overfeeding + 20%), and then the high-temperature setting is carried out. The fabric is 100m after the machine is off, eliminating the longitudinal stretch. At the same time, the distance between the needle plate and the general assembly can control the width of the fabric and eliminate the horizontal shrinkage of the bleaching and dyeing process before fixing the fabric. On the contrary, if only 95m fabric is fed, it will be stretched to 100m (negative overfeeding - 5%). It's also a way for sellers to make money, so buyers set vertical and horizontal shrinkage and square meter weight (knitting) to distribute the wealth.
2: spinning, winding and even weaving involve or adjust the overfeeding quantity. For example, the spinning of blended fancy yarn needs positive overfeeding to make one strand loop; the spinning process of roving is negative overfeeding (feeding hundreds of meters of cotton wool into tens of millions of meters of yarn); (precision) winding of winding machine (positive overfeeding controls the lower and constant winding density of winding); weft feeder of loom (controls the yarn, especially the elastic yarn) Tension, ensure non negative overfeeding).
3: many continuous processing equipment (other industries) often have this mechanism. For example, the tensioner of the dyeing machine is the mechanism to coordinate the speed before and after, control the negative overfeeding of the fabric transported by the front mechanism, so that the fabric will not be overstretched.
