A twin screw extruder is a commonly used equipment for plastic modification manufacturers. Today, we will introduce some small details that can improve the performance of the twin screw extruder. The tips outlined in this article include equipment modification, equipment maintenance, and operational specifications.
The feeding section of the barrel mostly uses water cooling, and is locked together with the second section barrel (heated) using flanges. Heat can be continuously conducted from the high-temperature section barrel to the cold section barrel, causing the second section barrel to fail to maintain a sufficient temperature. Usually, operators set the temperature of the second section barrel to 180℃, but due to heat loss in the feeding section, the actual stable temperature usually does not exceed 135℃.
A simple solution is to add 1-2 heat-insulating gaskets between the feeding section and the flange of the second section barrel, and replace the heat-insulating gaskets every few years, as these gaskets tend to degrade and wrinkle over time.
As we all know, turbulent flow in a water pump can cause more heat exchange on the pipe wall than laminar flow. Turbulent flow in high-pressure transmission has a high momentum exchange, which breaks the boundary layer. As a result, the vigorous fluid motion causes much more heat exchange between the pipe wall and the fluid. The cooling cycle system of the extruder generally has a pressure of 20-60psi.
To achieve turbulent flow, a pressure of 120PSI is required. Almost all the cooling system components (hoses and valves) of the extruder need to be upgraded to 150PSI to meet the safety factor of 120PSI. After the modification is completed, the cooling system can quickly discharge a large amount of heat during processing.
Sideways feeding is usually used to feed fillers into the twin screw extruder. Many processors need to achieve a high filling ratio with fillers that often have a low bulk density. The final filling ratio is limited by the following factors:
The volumetric feeding capacity of the side feeding and the volumetric feeding capacity of the main screw of the extruder. The volumetric feeding capacity depends on the free volume of the side feeding machine and the main screw, as well as the speeds of these two screws.
If a material can flow into the storage drum without being hindered by the main screw during testing, then the feeding speed of this material can be good. If the side feeding machine is directly connected to the main screw, then the amount of material that the main screw can accept will be limited.
Therefore, the main screw has threaded components with a long pitch, extending downstream of the side feeding port for 2D-4D lengths. This will allow the melt to pass quickly through the side feeding port, allowing the filler to be maximally fed into the main screw. If the design of the main screw causes any accumulation of material fed from the side, it will severely limit the feeding capacity of the filler.
The exhaust capacity that allows gas to be discharged from the twin screw extruder. The purpose of exhaust is to allow air to easily escape while protecting the filler from overflowing the exhaust port. The configuration is to open an upward exhaust port upstream of the side feeding port. Sometimes a small semi-slot exhaust is opened at the top of the side feeding machine.
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