A safety tube (or disk) is installed at the discharge end of the barrel. If the pressure inside the barrel increases to an unsafe limit, the safety tube will break. A fracture pressure of about 50,000 kPa, which is 75% of the design limit, is typically used. A pressure sensor with an indicator is also provided to indicate the actual pressure condition of the screw discharge port. An adjustable shutdown and alarm switch is sometimes provided as an added safety device.
The barrel of the plastic extruder must be heated at startup to re-melt the polymer remaining in the machine during shutdown and maintain the temperature of the inner surface of the barrel at a level to maintain or actually heat the resin during operation. Due to the external heating provided by the barrel heating device, the efficiency is low, and it is better to use the screw shear heat provided by the driving power to increase as much heat as possible.
From the feed zone to the discharge, if the screw is performing the required adiabatic operation, the required barrel temperature profile is a configuration that gradually increases the set point so that each point along the screw is at the desired resin temperature. . It is therefore preferred to divide the heating zone into several heating zones. For 30:1 (L/D), the extruder is generally divided into six zones.
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