Three elements of stenter shaping: temperature, time, tension
Definition of shaping
Styling is the main process of finishing. Through the mechanical action of the setting machine and the anti-shrinkage, softening, and hardening effects of chemical reagents, knitted fabrics can achieve a certain shrinkage, density, and feel, and can achieve the appearance of uniform width, smooth lines, and clear textures. .
Three elements of tenter shaping
1. Temperature
Temperature is the main factor affecting the quality of heat setting.
Because after the fabric is heat-set, the original wrinkles are eliminated, the surface smoothness is improved, the dimensional thermal stability of the fabric and other wearing properties , are closely related to the heat setting 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:
Heating time: After the fabric enters the heating zone, the surface of the fabric is heated The time required to reach the setting temperature.
Heat penetration time: After 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.
Molecular adjustment time: After the fabric reaches the setting temperature, the time required for the molecules in the fiber to adjust according to the setting conditions.
Cooling time: The time required for the fabric to come out of the drying room and fix the size of the fabric for cooling.
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.
About the time required for heating and heat penetration, it 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 significant impact on the setting quality. Including the dimensional thermal stability, strength and breaking elongation of the fabric all have a certain impact.
The warp dimensional thermal stability increases as the warp overfeed increases during shaping, while the weft dimensional thermal stability increases as the door width is stretched. decreases with increasing 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 breaking elongation of the fabric after setting, the weft direction decreases with the increase in stretch, while the warp direction changes with the increase in overfeed. big.
How to express yarn thickness
Indicates the thickness of yarn, including British count and Metric number.
① Commonly used imperial count (Ne), indicating how many 840 yards are contained in each pound of yarn. For example, 8S/1 means that each pound of yarn contains eight 840 yards.
② Metric count (Nm) refers to the length of yarn in meters per gram of weight. It can be seen from the definition that the smaller the yarn count value, the thicker the yarn. The units that indicate yarn thickness include denier and special number.
③ Denier (D) refers to the grams of yarn per 9,000 meters; Tex (Tex) refers to the grams of yarn per 1,000 meters. It can be seen from the definition that the larger the denier (special number) value, the thicker the yarn. The British system count and the metric system count are called fixed-weight units, and the denier and special numbers are called fixed-length units.
The meaning of some knitting process parameters
① CPI: the longitudinal density of the fabric, that is, along the loop The number of coil courses (modulus) within 1 inch in the longitudinal direction;
② WPI: The transverse density of the fabric, that isThe number of coil columns (number of needles) within 1 inch along the transverse direction of the coil;
③ Gram weight: the mass of the fabric per unit area (GM/M2);
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④ Yarn length: Generally expressed as 50C, which is the length of 50 coils. Measured in MM.
Main physical indicators that need to be controlled for shaping
1. Door width
Door width can be adjusted directly on the shaping machine during production. The adjustable door width on the shaping machine is in centimeters, but the company’s order requirements generally require door widths in inches. Therefore, during the production process, inches must be converted into centimeters before adjustment can be made. Conversion formula: 1 inch = 2.54 centimeters.
2. Gram weight
Generally, the gram weight is determined by adjusting overfeeding controlled. Under the condition that the other tensions remain unchanged, within a certain range, the greater the overfeed, the heavier the gram weight, and the smaller the overfeed, the lighter the gram weight. In addition, changes in door width and other tensions will also cause changes in the weight, but generally these methods are not used to adjust the weight. (Overfeeding compensation has certain limitations)
3. Cycle
Cycle is related to gram weight Closely related, refers to the repeating dimensions of the pattern from the starting point to the end point. Its control method is the same as that of gram weight. Typically, cycling is controlled by adjusting overfeed. When the remaining tension remains unchanged, within a certain range, the larger the overfeed is, the shorter the cycle will be, and the smaller the overfeed will be, the longer the cycle will be. In addition, changes in door width and other tensions will also cause changes in circulation, but generally these methods are not used to adjust circulation.
4. Shrinkage
Shrinkage is one of the main physical indicators that need to be controlled during shaping. The shrinkage must be even and reasonable to be OK. Generally speaking, the average shrinkage refers to the deviation of the shrinkage in the warp and weft directions not exceeding 3%. For fabrics with a particularly loose structure, the shrinkage deviation in the warp and weft directions can be as high as 7%, but it must be confirmed by SALES before mass production.
The so-called shrinkage is reasonable, for new fabric types, it refers to the shrinkage test results based on theThe set standard must reflect GEK’s production level. For old fabrics, it means that the shrinkage test results of the finished product must be within the deviation range allowed by the customer’s standards. There are many factors that affect shrinkage. Raw materials, knitting process, dyeing and washing process, styling process, mercerizing process, scratching/grinding/brushing process and the operation of each process may all affect shrinkage.
For shaping, shrinkage is mainly controlled through resin or pre-shaping.
For pure cotton fabrics, resin is generally used to control shrinkage. When the resin can fully react, the greater the amount of resin, the better the shrinkage, but the problem that arises is that the strength decreases more. Therefore, the amount of resin used is subject to certain restrictions.
For fabrics containing stretch frames and chemical fibers, pre-styling methods are generally used to control shrinkage, and when necessary, resin methods are used to assist.
For this type of fabric, the pre-shaping step is equivalent to the resin-passing step for pure cotton fabrics, which determines the quality of the finished product to a large extent, and its importance It goes without saying that it must be taken seriously. In addition, shrinkage is also related to width and weight. Within a certain range, the wider the door width, the greater the shrinkage in the weft direction, and vice versa, the smaller it is, the heavier the weight, the smaller the shrinkage in the meridional direction, and vice versa, so the shrinkage can be improved to a certain extent by adjusting the overfeed and door width. . The warp and weft shrinkage of the fabric itself is also relevant. Under ideal circumstances, the sum of the warp and weft shrinkage of a fabric in a certain state is a constant value. Therefore, as long as no external tension is added, when the shrinkage in one direction becomes smaller, the shrinkage in the other direction will become larger. This is the guiding principle of averaging shrinkage. Of course, in the actual production process, it is impossible not to add external tension to the fabric. Therefore, measures must be taken in advance to improve it. Such as backwash water, resin, etc. What specific measures should be taken require a certain amount of production experience to be accurately judged.
5. Distortion
Due to the twisting of the yarn, after the yarn is woven into a fabric There is a certain tendency to twist back and form distortions. The tendency for twisting is more pronounced in single-sided fabrics. The size of the distortion is related to the twist of the yarn itself, the fabric structure and the knitting process. Twist is generally controlled by oblique shaping or step-by-step shaping. In many cases, a combination of the two methods is also used. However, for resin fabrics, the only way to improve distortion is through diagonal shaping; for resin-coated fabrics, step-by-step styling can be used to improve distortion. When the amount of resin cannot be too large due to strong reasons or the slanting of the fabric itself is too large and exceeds the adjustable range of the setting machine, step-by-step setting cannot achieve the desired results.When seeking distortion, the method of combining oblique shaping and step-by-step shaping can be used to improve the distortion.
6. PILLING
PILLING is related to the quality of raw materials, fabric structure, resin reaction degree and related to the pre-treatment process. There are three main methods currently used to improve PILLING:
1) Enzyme washing;
2), pass through resin;
3), add appropriate amount of hard slurry to the materials.
7. Strength
Strength is a physical index that cannot be repaired, so it must be used in the production process Be careful to control. The strength is related to the quality of raw materials, cloth structure, knitting process, degree of resin reaction and pre-treatment process. For shaping, the damage to strong force should be minimized while ensuring physical indicators such as shrinkage, pilling, and distortion. When these indicators cannot be taken into consideration at the same time, priority should be given to maintaining strength.
8. Formaldehyde content
Generally speaking, high formaldehyde content is due to resin reaction Not entirely caused. Generally, the formaldehyde content requirement for adult clothing is <75ppm. For some orders that make children's clothing and underwear, the formaldehyde content is required to be <20ppm. As long as the resin reaction is sufficient, the formaldehyde content of adult clothing will generally meet the requirements. For demanding children's clothing and underwear items, try to avoid resin finishing. If it is necessary to pass the resin in order to achieve other physical indicators, you can only arrange to backwash the formaldehyde after passing the resin, and then wet-set it.
9. PH value
The customer requires that the PH value of the cloth surface be weakly acidic or medium. Generally, the pH value of finished products cannot exceed 8. NIKE, TOMMY and most domestic customers have strict requirements on PH value: light white PH range: 4.5-6.5. Therefore, all fabrics produced by these customers must pay attention to strict control of PH value.
The relationship between various physical indicators and raw materials and processes
1. The quality of raw materials and eachRelationship between physical indicators
The quality of raw materials affects the weight, width, strength, PILLING, and distortion of the finished product. Under the same conditions, the coarser the raw material, the heavier the weight, the wider the door width and the better the strength of the finished product. The better the cohesion of the raw materials, the smoother the surface, and the better the PILLING of the finished product. This is even more obvious on floral gray yarn fabrics. The higher the twist of the raw material, the greater the twist in the finished product.
2. The relationship between knitting technology and various physical indicators
When other conditions are the same Within a certain range, the denser the yarn length, the heavier the weight (except stretch fabric), the narrower the door width, the better the strength and the smaller the distortion. On the contrary, the sparser the yarn length, the lighter the weight (except stretch fabric), the wider the door width, the weaker the strength, and the greater the distortion.
3. The influence of dyeing and washing methods on various physical indicators
Generally speaking, other Under the same conditions, the fabrics dyed and washed with the PD method will have a narrower width and heavier weight than the fabrics dyed and washed with the YD or HD methods.
4. The influence of dyeing and washing machine models on various physical indicators
Under other conditions being the same In the case of cloth produced in high-temperature cylinders, the finished products are usually narrower in width and heavier in weight than those produced in normal-temperature cylinders (fabric types that have a greater impact: 1X1, 2X2 RIB, WAFFLE, needle cloth, loose-structured fabric…).
5. The relationship between finishing methods and various physical indicators
Mercerizing, scratching/grinding/ Finishing methods such as brushing, enzyme washing, and pre-styling all affect physical indicators to a certain extent.
Mercerization has a great impact on the finished product. The quality of the finished product is incomparable between mercerized and non-mercerized fabrics from the same vat. After mercerization, in addition to obtaining better cloth surface gloss, the structure of the cloth is much more stable than before, and the strength is also improved to a certain extent. Scratching/grinding/brushing and enzyme washing will damage the strength of the cloth to a certain extent, and the weight may also decrease. The pre-shaping of fabrics containing stretch frames and chemical fibers determines the quality of the finished product to a large extent. Pre-shaping is one of the important control links for this type of fabric. Temperature, speed, machine texture, weight, circulation, etc. must all be strictly controlled, otherwise the finished product may not meet customer requirements.
Determination of final width and overfeeding
For old fabric types, no pre-setting is required For shrinkable fabrics, just convert the required width of the order into centimeters and set it directly. For fabrics that need to be pre-shrunk, widen them by 2-3 inches. Overfeeding is mainly determined based on the tightness of the cloth and past production experience. The overfeeding of different fabric types varies greatly. When the set overfeeding is used for production and the machine weight and cycle do not meet the order requirements, adjustments must be made in a timely manner.
The overfeed of fabrics with mercerization requirements is generally smaller than that of fabrics without mercerization; the test methods are LINE DRY, HANG DRY, and FLAT DRY. The overfeed is generally smaller than the overfeed of cloth with TUMBLE DRY test method. Cloths that have nap before shaping are generally produced with larger overfeeds.
Responsibilities of each position in the setting machine
Front car:
1. Before starting the machine, sew the cloth according to the relevant requirements, place the materials, and check whether the rolling car is closed and whether the rolling car pressure meets the requirements.
2. Operate according to regulations, control the front vehicle’s cloth feeding situation, and do not move or press the cloth.
3. Keep the cloth feeding tight and tight, avoid being too tight or too loose, and keep it stable. Keep the cloth in the middle position and avoid swinging left and right or twisting together. The cloth cannot be folded before entering the rolling car.
4. During production, the material in the trough must be kept fully immersed in the pressure roller.
5. Before producing cloth that cannot handle resin or cloth with special finishing, thoroughly clean the trough, material tube, and rollers and pressure rollers that are in contact with the cloth surface. .
6. Check the condition of the cloth surface to see if there is oil stains, S-BOWING, etc. If any problems are found, notify the class and team leader as soon as possible.
7. It is strictly forbidden to mix materials with different formulas. The material list must be clearly read when pumping and discharging materials. When the materials are not enough, the craftsman must be notified to add materials. It is strictly prohibited. Add water and add ingredients.
CRRC:
1. Before starting the machine, strictly adjust each process parameter according to the process set in the checklist, paying special attention to the remarks on the checklist. Ensure that each process requirement can be implemented.
2. During the production process, the process parameters should be adjusted promptly according to the instructions of the subsequent vehicle. Without the instructions of the subsequent vehicle, the process parameters cannot be adjusted at will.
3. During the production process, the machine must be ensured to be normal and stable.
4. The edges should be controlled reasonably, and the fabric that has fallen off should be hung up in time.
5. When changing materials, changing cylinders, and raising and lowering temperatures, move quickly without artificially delaying time, so as to maximize the utilization rate of the machine. However, you must ensure that the work is done properly and cannot be hasty.
6. Supervise and guide the work of the front car, and cooperate with the rear car to ensure normal and smooth production.
7. When making specially finished cloth, the machine must be cleaned strictly according to relevant regulations.
8. Record the exact process parameters truthfully.
Rear car:
<p style="line-height: 1 , clean the air net as soon as possible after finishing the work and taking over the work.
2. Connect the cloth in time after turning on the machine, and try to avoid jammed cloth and stop the machine. Once the cloth is jammed, the response should be quick to avoid the cloth being left in the oven for a long time and becoming yellow or having air holes on the cloth surface.
3. The tension of the cloth should be kept moderate and stable, not too tight or too loose.
4. Check the quality of the first piece of cloth as soon as it comes off the machine:
Touch: Touch the cloth surface to see if it is not dry or too dry ;
Look: Check whether the slanting basically meets the requirements, whether there is any skew or bow weft, whether the cloth surface has scratches, indentations, oil stains, soft oil marks, off-edges, etc. (If the order requires that fluorescence cannot be stained, you need to turn on the fluorescent lamp to check whether there is fluorescence.);
Quantity: Whether the measurement cycle, door width, weight, bursting, slanting, etc. can meet the requirements;
Check: Check the physical test data of the produced tank and the data before the tank is finalized to determine the control points of the tank;
Tune: If repeat is found , slanting or gram weight, etc. are inconsistent with the process requirements, adjust the process parameters in a timely manner, such as adding or subtracting overfeeding, etc. If the cloth texture does not meet the requirements, CRRC must be notified in time for adjustment.
5. When producing large strips of fabric, the team and team leaders must be notified of the medium-volume cycle for timely adjustment.
6. If the following machine finds that the strength is abnormal, the cloth texture cannot be adjusted properly, or the weight, cycle, etc. cannot meet the requirements after adjusting the process parameters, etc., it cannot be handled by oneself. If any problem arises, notify the class and team leader as soon as possible to handle it.
7. After the process is stable, record the machine data truthfully and notify IN LINE QC for sample cutting. .
8. The produced cloth must be covered with a cloth cover and sent to the next process strictly according to the process. The samples are classified and stored according to relevant regulations.
9. When a cylinder of cloth starts to be produced and completed, the loading and unloading records must be entered in the system in a timely manner.
10. The rear car is a key position in controlling the quality of finished products. It must be coordinated with the middle car and the front car to ensure normal production.
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