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Precautions for operation of plastic sheet machine:
(1) The temperature of each section on the barrel of the plastic sheet production equipment increases gradually from the feeding section to the joint of the barrel and the forming mold.
(2) The mold temperature is slightly higher than the barrel temperature. The higher temperature should be controlled at 5-10 ℃. The temperature at both ends of the mold is slightly higher than the temperature in the mold, and the temperature is controlled at 5-10 ℃.
(3) In the form of sheet feeding, the upper surface of the intermediate roll of the three rollers should be on a horizontal plane with the lower plane of the die lip; the end face of the lip should be parallel to the center line of the intermediate roll, with a distance of 50-100 mm.
(4) The die lip gap should be slightly less than or equal to the thickness of the plate, and the middle gap of the die lip should be slightly smaller than the end die lip gap at both sides.
(5) It should be noted that the roughness r of three roll working face should not be greater than 0.2pm. When cleaning the roll surface, it is not allowed to scratch the roll surface with a hard steel knife, but the copper knife should be used to clean the residual material on the roll surface.
(6) The roller surface should have some middle height; the gap between the three rollers should be equal to or slightly larger than the thickness of the plate.
(7) Mold temperature control should be stable. When the temperature is high, the flow speed of the melt in the mold becomes faster; when the temperature is low, the flow speed of the melt in the mold becomes slow. The unstable flow rate of molten material will cause the longitudinal thickness error of plate (sheet) products to be large.
(8) Pay attention to control the temperature of the working face of the three rollers. The temperature of the feeding roller is slightly higher than that of the discharging roller. If the roller surface temperature is too high, the slab is not easy to roll off, and the product surface is easy to produce cross grain; if the temperature is low, the product surface is not glossy. According to this phenomenon, the roller surface temperature control should be adjusted in time.
(9) The running speed of the three rollers is slightly higher than the extrusion speed of the slab from the die mouth, and the speed difference is generally less than 10%. The working speed of the three rollers should be controlled smoothly. Too fast or too slow running speed has great influence on the thickness error of the plate.
(10) When polyolefin plastics were extruded into plates (sheets), the screw structure was abrupt, the compression ratio was (3-4) 1, the melt flow rate was HDPE 0.3 ~ 2.0 g 10 min, LDPE 0.1 ~ 0.3 g 1 min, PP 0.5 ~ 1.5 g 10 min. The gradual change screw should be selected for the extrusion molding plate (sheet) of ABS and other amorphous polymer resin, and the compression ratio is (1.6-2.5) 1.
(11) For extrusion molding of plastic sheet (sheet), dehumidification treatment is not required for PVC, PE and PP resin in general, and other plastics (such as ABS, polyamide, etc.) should be dehumidified and dried before extrusion. Otherwise, exhaust type extruder should be used for extrusion molding.
