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Precautions for Plastic Sheet Extruders

Time：

2017-05-17

1. On the barrel of plastic sheet‑producing equipment, the temperature gradually increases from the feeding section to the point where the barrel connects with the forming die. 2. The temperature of the forming die is slightly higher than that of the barrel, with the excess maintained within 5–10°C. At both ends of the die, the temperature is also slightly higher than in the die’s central region, with this elevated temperature kept within 5–10°C. 3. Regarding the sheet‑feeding configuration, the upper surface of the middle roller in the three‑roller system should be aligned horizontally with the lower plane of the die lip; furthermore, the end face of the die lip must be parallel to the centerline of the middle roller and positioned 50–100 mm away from it. 4. The gap at the die lip should be slightly smaller than or equal to the thickness of the finished sheet, while the central gap between the die lips should be slightly narrower than the gaps at the two side edges. 5. Note:

1. In plastic sheet production equipment, the temperature along the barrel increases progressively from the feeding section to the point where the barrel connects with the forming die.

2. The mold temperature should be slightly higher than the barrel temperature, with the excess maintained at 5–10°C. The temperatures at both ends of the mold should be slightly higher than the central temperature, also controlled within a range of 5–10°C.

3. In terms of the entry configuration, the upper surface of the middle roll in the three-roll system shall be flush with the lower plane of the die lip; the end face of the die lip shall be parallel to the centerline of the middle roll and spaced 50–100 mm away.

4. The gap at the die lip should be slightly less than or equal to the thickness of the molded part, and the central gap between the die lips should be slightly smaller than the gaps at the two end die lips.

5. Note that the surface roughness of the three-roll working surfaces shall not exceed 0.2 µm. When cleaning the roll surfaces, do not use hard steel blades to scrape or scratch them; instead, use copper‑based tools to remove residual material.

6. The roller surfaces should have a certain degree of camber; the gap between the three rollers should be equal to or slightly greater than the width of the sheet.

7. The temperature of the molding die must be kept stable. At higher temperatures, the molten material flows more rapidly within the mold; at lower temperatures, its flow rate slows down. Unstable flow rates can lead to significant variations in the longitudinal thickness of sheet‑molded products.

8. Pay attention to controlling the surface temperatures of the three rollers: the inlet roller should be slightly warmer, while the outlet roller should be slightly cooler. If the roller surfaces are too hot, the sheet material will have difficulty releasing from the rollers, and transverse streaks may appear on the product’s surface; if the temperature is too low, the product’s surface will lack gloss. Based on these observations, adjust the roller surface temperatures promptly as needed.

9. The operating speed of the three-roll system should be slightly higher than the extrusion speed of the sheet as it exits the die; typically, the speed difference should not exceed 10%. The three rolls must run at a stable speed, as excessively fast or slow operation can significantly affect the thickness tolerance of the sheet.