​Control of three-roll calender

日期:2019/6/3 9:09:15 / 阅读: / 来源:本站

Control of three-roll calender
The three-roll calendering device is the key equipment for cooling, calendering and thickness of extruded sheet. The process conditions directly affect the thickness, smoothness, smoothness and shrinkage of the sheet.
Rate and other quality.
The extruded material is fed into the middle and middle rolls, and is transferred to the upper and middle rolls by the hoop roll, and then the three rolls are taken out. Practice has shown that the gap between the lower and middle rolls of the incoming material is strictly controlled to be slightly greater than or equal to the thickness of the product.
A value of not more than 3% is preferred. In order to avoid excessive expansion of the hot melt material, the sheet shrinkage rate is increased. The middle and upper roll gaps of the material are controlled to be slightly less than or equal to the product thickness not exceeding 3%.
When the temperature of the three rolls is constant, if it is greater than or more than 3%, not only will the thickness of the sheet be thicker, but also the pressure between the rolls will be too small to cause fogging on the surface of the sheet; if it is less than 3%, the thickness of the sheet will also be affected. The sheet is made thinner, and the pressure between the rolls is too large, causing ripples on the surface of the sheet.
Since the material temperature of the extrusion die is relatively high (about 180 ° C), in order to prevent the material from sticking to the roller, the temperature of the three rolls is generally controlled at 80 ° C - 110 ° C, and the maximum is not more than 120 ° C. At a reasonably set three-roller speed, if the temperature is lower than 80 °C or higher than 120 °C, the thickness of the sheet will be affected. The former is thickened due to the increase of material viscosity, and the flatness is affected; the latter is reduced due to the viscosity of the material. Thinning the sheet and affecting shrinkage.
The thickness of the sheet is constant in the gap between the die and the three rolls. When the temperature at the extrusion, die, and three rolls is relatively stable, it is mainly achieved by the speed of the three rolls. If the speed is fast, the thickness is thin, and when the speed is slow, the thickness is thick. Since the material is stretched during the three-roll calendering process, it is easy to orient the longitudinal molecules, affecting the shrinkage rate of the sheet and expanding the difference in the longitudinal and transverse properties. Therefore, pay attention to the speed ratio of the three rolls (stretching).
The three-roller speed is set as small as possible.
(3) Sheet shrinkage. 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 quality of the above-mentioned two conditions is difficult to achieve due to the consideration of the thickness of the sheet, such as smoothness and smoothness, adjustment of temperature, gap, etc. is required 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 between the lower and middle rolls is about 1 cm and is the pencil-like pile, which 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.

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