Sheet shrinkage during processing of ABS sheet for refrigerator
DATE：2019/11/16 8:56:35 / READ： / SOURCE：This station
Sheet shrinkage during processing of ABS sheet for refrigerator
The most effective way to reduce the shrinkage of the sheet and reduce the difference between the vertical and horizontal shrinkage of the sheet is: 1 try to keep the extrusion speed consistent with the three-roll calendering speed; 2 strictly control the speed ratio of the three rolls, and minimize the speed difference of the three rolls. However, in actual operation, since the above two conditions are difficult to achieve due to the consideration of the thickness of the sheet, such as smoothness and smoothness, it is also necessary to adjust the temperature, the gap, etc., so as to minimize the shrinkage rate of the sheet.
Under the premise that the extrusion speed (screw rotation speed) is relatively stable and the three-roll gap is fixed, the speed at the time of about 1 cm between the lower and middle rolls and the pencil-like pile is the ideal three-roll speed, followed by two rolls. The pulling speed is equal to or slightly greater than the upper roller speed of the three rolls. It has been determined that the sheet produced in this state has the smallest shrinkage (generally not more than 3%) and the sheet surface is flat. At this point, it can be assumed that the extrusion speed is basically the same as the three-roller speed. If the pile between the lower and middle rolls is too large, it indicates that the extrusion speed is higher than the speed of the three rolls, the extruded material will collapse and affect the smoothness of the surface; the pile is too small or even no pile, indicating that the extrusion speed is less than three rolls. The speed will increase the tendency of the material to stretch, thereby increasing the shrinkage of the sheet and making the thickness of the sheet thin. The amount of stock between the lower and middle rolls is mainly determined by the speed of the middle roll. When the thickness of the sheet is appropriate, minimizing the speed ratio of the three rolls will significantly reduce the sheet shrinkage. Under the premise of convenient operation, the distance between the die (mould lip) and the three rolls should be minimized. Because the distance is too large, it is equivalent to the time that the extruded material is subjected to traction in hot air, and the extrusion material is extended under a certain external force (ie, three-roll traction force) and temperature (around hot air and its own material temperature). The longer the elongation, the greater the shrinkage during thermoforming, so the distance between the die lip and the three rolls is generally no more than 100 mm.
The temperature distribution of the three rolls is greatly affected by the shrinkage rate, and the temperatures of the lower roll, the middle roll, and the upper roll are respectively indicated by t, t, and t. Practice has proved that the best distribution from low to high, that is, t is less than t, t is less than t, the sheet shrinks small, and the board surface is flat. This is because the material extruded from the die first reaches the lower temperature lower roll, which gives faster cooling and lowers the elongation;
The middle roll and the upper roll cause the molecules frozen on the surface of the material to be heat treated, so that the crimped molecules gain energy. The former is advantageous for reducing the shrinkage rate, and the latter is advantageous for leveling.
The most effective way to reduce the shrinkage of the sheet and reduce the difference between the vertical and horizontal shrinkage of the sheet is: 1 try to keep the extrusion speed consistent with the three-roll calendering speed; 2 strictly control the speed ratio of the three rolls, and minimize the speed difference of the three rolls. However, in actual operation, since the above two conditions are difficult to achieve due to the consideration of the thickness of the sheet, such as smoothness and smoothness, it is also necessary to adjust the temperature, the gap, etc., so as to minimize the shrinkage rate of the sheet.
Under the premise that the extrusion speed (screw rotation speed) is relatively stable and the three-roll gap is fixed, the speed at the time of about 1 cm between the lower and middle rolls and the pencil-like pile is the ideal three-roll speed, followed by two rolls. The pulling speed is equal to or slightly greater than the upper roller speed of the three rolls. It has been determined that the sheet produced in this state has the smallest shrinkage (generally not more than 3%) and the sheet surface is flat. At this point, it can be assumed that the extrusion speed is basically the same as the three-roller speed. If the pile between the lower and middle rolls is too large, it indicates that the extrusion speed is higher than the speed of the three rolls, the extruded material will collapse and affect the smoothness of the surface; the pile is too small or even no pile, indicating that the extrusion speed is less than three rolls. The speed will increase the tendency of the material to stretch, thereby increasing the shrinkage of the sheet and making the thickness of the sheet thin. The amount of stock between the lower and middle rolls is mainly determined by the speed of the middle roll. When the thickness of the sheet is appropriate, minimizing the speed ratio of the three rolls will significantly reduce the sheet shrinkage. Under the premise of convenient operation, the distance between the die (mould lip) and the three rolls should be minimized. Because the distance is too large, it is equivalent to the time that the extruded material is subjected to traction in hot air, and the extrusion material is extended under a certain external force (ie, three-roll traction force) and temperature (around hot air and its own material temperature). The longer the elongation, the greater the shrinkage during thermoforming, so the distance between the die lip and the three rolls is generally no more than 100 mm.
The temperature distribution of the three rolls is greatly affected by the shrinkage rate, and the temperatures of the lower roll, the middle roll, and the upper roll are respectively indicated by t, t, and t. Practice has proved that the best distribution from low to high, that is, t is less than t, t is less than t, the sheet shrinks small, and the board surface is flat. This is because the material extruded from the die first reaches the lower temperature lower roll, which gives faster cooling and lowers the elongation;
The middle roll and the upper roll cause the molecules frozen on the surface of the material to be heat treated, so that the crimped molecules gain energy. The former is advantageous for reducing the shrinkage rate, and the latter is advantageous for leveling.
Author：admin