On the deceleration principle of twin screw extruder

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with nearly 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

In most extruders, the change of screw speed is realized by adjusting the motor speed. The driving motor usually rotates at full speed of about 1750 rpm, which is too fast for an extruder screw. If it rotates at such a fast speed, too much friction heat will be generated, and the uniform and well stirred melt cannot be prepared due to the short residence time of the plastic. The typical reduction ratio should be between 10:1 and 20:1. In the first stage, both gears and pulley blocks can be used, but in the second stage, it is best to use gears and position the screw in the center of the last big gear. For some slow-moving machines (such as twin-screw for UPVC), there may be three deceleration stages, and the maximum speed may be as low as 30 rpm or less (ratio up to 60:1). On the other hand, some very long twin screws for stirring can run at 600 rpm or faster, so a very low deceleration rate and more deep cooling are required.

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