After the fabric is woven into the finished product, the fabric will be shaped in order to allow the fabric to have certain special uses. Because after the fabric is shaped, its physical and chemical properties are relatively stable, such as shrinkage, width, warp and weft density, etc., which are not easy to change, and the cloth surface is also relatively smooth. However, due to the high setting temperature, you should pay attention to the color changes before and after setting, especially some sensitive colors, such as gray, army green, light khaki, etc., so you should generally pay attention to the color after setting. At the same time, shaping can control the width, warp and weft density, shrinkage, etc. of the cloth, especially the control of shrinkage, which directly affects the processing cost, which also requires special attention.
01 Main process parameters and control
1. Formula
That is, the material liquid is added when setting, and the proportion of various chemicals used in the material liquid determines the feel, slippage, color, etc. of the cloth surface after setting.
2. Roller pressure
The pressure of the feeding roller during shaping determines the amount of material liquid carried by the cloth, which has an important impact on the feel and color of the cloth surface.
3. Baking temperature
The drying temperature during shaping is one of the main factors affecting the shaping quality. Especially in the resin finishing process, the shaping and drying temperature has a great impact on the dimensional stability and surface smoothness of the fabric. For soft finishing, drying temperature It is advisable to control the dryness of the cloth surface, and the baking temperature should not be too high, otherwise it will affect the feel of the fabric.
4. Overfeeding
The size of the overfeed directly affects the weft density of the fabric, thereby affecting the shrinkage performance of the fabric. At the same time, in order to take into account the tension during fabric production, wrinkles and weft skew must be appropriately prevented.
5. Stenter width
The setting width determines the width of the fabric after setting, so that the width of the fabric after setting can meet the process requirements, and the width of the fabric after preshrinking can meet the customer’s requirements.
02 Heat setting process conditions
Fabric heat setting is usually a process of maintaining a certain size of the fabric under certain temperature and humidity conditions, heating it for a certain period of time and then cooling it. Therefore, the main process conditions for heat setting are nothing more than temperature, time, tension and swelling agent.
1. Temperature
Temperature is the most important factor affecting the quality of heat setting. Because after the fabric is heat-set, the extent to which the original wrinkles are eliminated, the surface smoothness is improved, the dimensional thermal stability and other wearing properties of the fabric are closely related to the heat-set temperature.
2. Time
Setting time is another main process condition for heat setting. After the fabric enters the heating zone, the time required for heating and setting can be roughly divided into the following parts:
①After the fabric enters the heating zone, the time required to heat the fabric surface to the setting temperature is also called the heating time.
②After the fabric surface reaches the setting temperature, the heat penetration time required for the fibers inside and outside the fabric to have the same setting temperature is required.
③After the fabric reaches the setting temperature, the time required for the molecules in the fiber to adjust according to the setting conditions is also called the molecular adjustment time.
④The time required for the fabric to come out of the drying room and fix the size of the fabric for cooling, or called the cooling time.
The finalization time usually refers to the time required for the first three items, but does not include the fourth item. If the first item is regarded as a preheating effect, then the setting time only refers to the time required for the second and third items, that is, the time required for heat penetration and molecular adjustment. The time required for heating and heat penetration depends on the performance of the heat source, the weight of the fabric per unit area, the thermal conductivity of the fiber and the moisture content of the fabric.
3. Tension
The tension on the fabric during the heat setting process has a certain impact on the setting quality, including the dimensional thermal stability, strength and breaking elongation of the fabric. The thermal stability of the warp direction increases with the increase of the warp overfeed during shaping, while the thermal stability of the weft direction decreases with the increase of the width stretching degree.
The average single yarn strength of the fabric after shaping is slightly higher than that of the unshaped fabric, and the change in the weft direction is more obvious than that in the warp direction. The elongation at break of the fabric after setting decreases in the weft direction as the stretch degree increases, while in the warp direction it increases as the overfeed increases.
Therefore, in order to obtain good dimensional thermal stability of the fabric and improve the wearing performance of the fabric, the warp direction should be appropriately overfeeded during heat setting, and the weft stretch should not be too high. For this reason, it is required not to use large warp tension in pre-treatment to avoid excessive elongation in the weft direction and force a large shrinkage in the weft direction, so that a larger stretching is required in the end.
1. The number of refolding of molecular chains increases with the increase of heat treatment temperature:
2. Tension hinders the refolding of molecular chains;
3. At very high temperatures, the role of tension in hindering chain folding is greatly reduced.
Tension has a significant impact on fiber structure, and fiber structures are closely related. Therefore, it is important to pay attention to the control of tension during any shaping process.
4. Swelling agent
Moisture has a “loose” fiber structure, which enhances the fluid-like movement of macromolecular segments. The plasticizing effect of moisture during the heat setting process affects the supramolecular structure and physical properties of the fiber.
03Shaped curling
1. Stenter shaping
In the rolling groove of the setting machine, soft finishing can meet the customer’s requirements for the cloth and make it less likely to be scratched on the cloth guide wheel. Stenter setting makes the fabric surface flat and stable in size, which can eliminate the formation of the fabric during the dyeing and finishing process. wrinkles and creases. At the same time, the shaping process conditions need to be strictly controlled during shaping.
①The setting temperature should be determined according to the elastic shrinkage and thickness of the fabric. If the temperature is too high, the strength will decrease, the elasticity will decrease, and the fabric may change color. If the setting temperature is too low, the fabric will curl easily, the width will be unstable, and the shrinkage rate will be large;
②The speed of the setting machine mainly depends on the length of the setting area and the setting temperature. If the speed is too fast, the setting effect will be ineffective. Fine wrinkles are difficult to solve during the dyeing and finishing process. If the speed is slow, especially under high temperature conditions, the fabric will turn yellow and its elasticity will decrease.
③For stereotyped overfeeding, after determining the fabric width, select the appropriate overfeeding amount and tension, which affects the fabric’s weight, elasticity, and the production of wrinkles on the fabric surface. For example, if the fabric tension is small, the overfeeding is large, and the fabric surface If it is uneven, it is difficult to eliminate the fine wrinkles produced by the fabric during the dyeing process. The tension is large and the overfeed amount is small, which will cause curling during heat setting.
2. Finalizing conditions
When pre-styling cotton-spandex knitted fabrics, it should be taken into account that spandex yarns produced by different manufacturers are adapted to different setting temperatures. For example, spandex can withstand a setting temperature of 190°C, while spandex produced by some other manufacturers has a lower setting temperature of about 180°C. Generally, knitted fabrics with a spandex content of less than 5% and without serious hemming when cutting can be directly dyed in open width after pre-shaping. Knitted fabrics with a content of more than 5% and open edges that affect dyeing must be sewn after pre-shaping. Dyeing can only be done if the tube is made into a synthetic tube, otherwise the dyeing problem caused by curling cannot be overcome.
When dyeing knitted fabrics, choosing the appropriate cloth speed and nozzle pressure can achieve better dyeing results. The cycle time is preferably 2 to 3 minutes. The speed calculation formula is: cloth speed = cloth loop length/cloth cycle time.
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