Plate (sheet) material forming process
The plastics of the production board (sheet) are mainly soft polyvinyl chloride, hard polyvinyl chloride, polyethylene.
Alkene, polyamide, polymethyl, polycarbonate, cellulose acetate, etc., the first four varieties are more common.
Plastic sheets (sheets) are available in single and multi-layer, flat and corrugated sheets, foamed and non-foamed, and the width of single material and composite material is generally 1m-1.5m, up to 4m wide.
Plastic sheets (sheets) can be used to make containers, storage tanks, pipeline villages, electrical insulation materials, construction and decorative materials, packaging materials for the food and pharmaceutical industries, and the like.
(1) Process flow
The extrusion process of plastic sheet (sheet) extrusion is as follows (different raw materials are slightly different):
Ingredients--kneading--granulation--plasticizing extrusion--head molding--three-roll calendering--cooling conveying--traction--cutting--inspection--packaging
(2) Process control factors
1 extrusion temperature. Generally, the die temperature should be higher than the body temperature by about 5 °C -10 °C, the die temperature is too low, the plate is dull and easy to crack: the die temperature is too high, the material is easily discolored and decomposed, and the plate has bubbles. The temperature of the flat die is generally controlled to be low in the middle and high in both sides. The fluctuation of the temperature at each point in the die should be controlled at ±5 °C, which is the basic condition for ensuring the uniform thickness of the plate.
2 three-roll calender roll temperature. The roller temperature of the three-roll calender is related to the molding material, the thickness of the sheet, and the arrangement position of the rolls. In order to prevent the sheet from sticking to the roller and the surface of the board to produce lateral stripes, the temperature of the roller should not be too high. However, if the temperature of the roll is too low, the surface of the plate is not easy to adhere to the surface of the roll, and the surface of the plate is likely to be spotted and dull. In order to prevent the sheet from vibrating due to internal stress, the sheet should be slowly cooled. This requires that the three rolls be provided with heating means and temperature control can be performed. Generally speaking, amorphous plastics such as polyvinyl chloride and ABS, the temperature of the roller should not exceed 100 ° C, can be heated by steam or hot water; when molding crystalline plastics such as polyolefin, the temperature of the roller exceeds 100 ° C, using oil heating It is advisable; when the surface of the sheet needs embossing, the middle roller is an engraved roller, and the temperature thereof can be increased as appropriate. If the middle roll is replaced with a heat-resistant butyl rubber roll with a Brinell hardness of 85, the roll should be cooled by cooling water to avoid sticking.
3 plate thickness and lip gap. The thickness of the sheet is related to the lip gap and the three roll spacing. The lip gap is generally equal to or slightly less than the thickness required for the sheet. The sheet is expanded from the die and expanded to a specified thickness after drawing and calendering. The three-roll gap generally refers to the nip at the exit of the web, and in view of the cooling shrinkage, the three-roll gap is generally adjusted to be equal to or slightly larger than the specified thickness of the sheet.
In addition to the thickness control and uniformity of the sheet, the die resistance can be controlled by the die resistance block to adjust the flow resistance and the thickness of the sheet.
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