In the dyeing and finishing of textiles, the warp direction is subjected to a large pulling force, resulting in elongation and narrowing of the length. In order to overcome this unstable state and ensure the dimensional stability of the textile, the speed of feeding into the cloth is adjusted during stentering or setting, which is super-feeding. The speed of feeding into the cloth is higher than the speed of the Hot Air Stenter machine called positive super-feeding (or over-feeding, shrink-code).
The positive overfeeding causes the warp yarn to retract, the weft density rises, the gram weight increases and the warp direction shrinks.
If the speed of the cloth is less than the speed of the Hot Air Stenter setting machine, it is called anti-overfeed (or negative overfeed, pull code). The anti-overfeeding causes the warp yarn to elongate, the weft density decreases, the gram weight decreases, and the warp direction shrinks. There are many dyeing factories in China that are willing to make some violations of the principle in order to pursue their own profits.
Stretching is a finishing work after dyeing, and it is also a very important process. In the process of stentering, some dyeing factories have worked harder than the amount of grey cloth input in order to process the fabric. They are very objective in thinking that most customers do not understand the reasons for this, letting them do whatever they want.
Now I have compiled some knowledge of overfeeding during tenter setting, for reference only.
In the dyeing and finishing process, the warp direction is subjected to a large pulling force, which tends to cause a narrowing of the warp direction, which is an unstable state, and the fabric undergoes warp shrinkage in water.
In order to reduce the warp shrinkage rate of the fabric and make the fabric size stable, in the tentering or setting, overfeeding is required, and the speed of feeding is greater than the speed of the Hot Air Stenter machine, so that the warp yarns are all retracted and the weft is pulled to specify the width of the door.
Overfeed: It is an action process that provides a specific proportion of the required amount according to the requirements of the next step.
Specific ratio: There are positive, negative or zero, that is, positive overfeed, negative overfeed or zero overfeed.
Requisite Amount: which is expressed as speed, flow, quantity, quality, etc.
The requirements for the next step: depends on the purpose of the treatment to be achieved.
The amount of overfeeding: it is by the super-feeding mechanism through the data relationship between the front and back of the mechanism.
Measurement and Control Instrument: It is the necessary matcher.
1. The Hot Air Stenter setting machine needs more fabrics to be fixed on the needle board in advance in order to eliminate the longitudinal stretching amount of the fabric before the dyeing process and meet the requirements of customers.
For example, the feeding mechanism runs 120M per minute, and the needle plate of the fixed fabric travels 100M per minute so that the 100M position is squeezed into the 120M fabric (plus overfeed +20%), and then the high temperature is set, and the fabric is 100M after the lower machine. The amount of longitudinal stretching is eliminated. At the same time, increasing the needle plate distance will control the fabric width, eliminating the lateral shrinkage of the fabric pre-dye bleaching process. Conversely, if the only 95M fabric is fed, it will be stretched to 100M (negative overfeed - 5%). This is also the way sellers make money, so the buyer stipulates the vertical and horizontal shrinkage and the average weight (knit) to distribute the amount of money.
2, Spinning and winding and even weaving, will involve or adjust the amount of overfeeding, such as the spun yarn, the spinning should be over-feeding; the roving yarn process is negative overfeeding (feeding a few 100m cotton wool spun into tens of meters of yarn); (precision) winder (lower and constant winding density of the super-feeding control); weaving machine weft feeder (control yarn In particular, the tension of the elastic yarn ensures non-negative overfeeding).
3, Much continuous processing equipment (other industries) also often have such a mechanism, such as the tensioner of the dyeing machine is to coordinate the front and rear speed, to control the negative overfeed of the fabric transported by the front mechanism, the fabric will not be excessively stretched.
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