Tips for Improving the Performance of Twin-screw Extruder

The twin-screw extruder is a commonly used equipment for modified plastics manufacturers. Here are some tips that can improve the performance of the twin-screw extruder: 


1. Add heat insulation gaskets between the feeding section and the flange of the second section


The feeding section of the extruder barrel is generally water-cooled, and is locked with the second section of the barrel (heating) by a flange, so that heat can be continuously conducted from the high-temperature barrel to the cold barrel. As a result, the second section of the barrel cannot maintain a sufficiently high temperature. Generally, the operator sets a temperature of 180°C in the second section of the barrel, but due to the heat loss in the feeding section, the actual temperature is usually  no more than 135°C.


The simplest solution is to add one to two heat insulation gaskets that are 1 mm thick between the feeding section and the flange of the second section of the barrel, and replace the gaskets every few years because they are prone to aging degradation and shrinkage.


2. Replace the extruder cooling system with a high-pressure cooling system


Turbulent current in a pump can lead to more heat exchange on the tube wall than laminar current. Turbulence in high-pressure transmission has a high degree of lateral momentum exchange because it breaks the boundary layer. As a result, the violent fluid movement causes massive heat exchange between the tube wall and the fluid.


The cooling circulation system of the extruder generally provides a pressure of 20 to 60 PSI. In order to achieve turbulent flow, it is best to reach a pressure of 120 PSI. Almost all cooling system components (hoses and valves) of the extruder should be upgraded to 150PSI to meet the safety factor of 120PSI. After the transformation is completed, the cooling system can discharge a large amount of heat in time during processing.


3. Use appropriate modifications to increase feeding capacity


Side feeding is usually used to feed the fillers into the twin-screw extruder. Many processors need to make fillers with high filling capacity, which are often of a quite low bulk density. The final filling volume is restricted by the following factors:


(1) The volumetric feeding capacity of side feeding and the volumetric loading capacity of the main screw of the extruder. The volumetric feeding capacity depends on the free volume of the side feed screw and the main screw and the speed of these two screws.


If a type of material can flow into the storage drum without the resistance of the main screw during the test, the feeding speed of this material can reach a very good level. If the side feeder is connected directly next to the main screw, the amount of material that the main screw can accept will be limited. Therefore, the screw of the main engine should preferably have a threaded element with a long pitch, extending 2D to 4D downstream of the side feed port. This will allow the melt to pass through the side feed port quickly, so that the filler can be eaten by the main screw to the maximum extent. If the screw design of the main engine causes any accumulation of side-feeding materials, it will severely limit the amount of filler fed.


(2) Exhaust capacity that allows gas to be discharged from the extruder. The purpose of exhaust is to make the air escape easily, and at the same time to protect the fillers from significant escape from the air vent. The best configuration would be opening an upward air vent upstream of the side feeding port. Sometimes, opening a small half-slit exhaust in the upper part of the side feeder is also feasible.

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