Solutions to Technological Challenges of Dual screw Extruder

What are the technical difficulties of dual screw extruder?

Increasing screw speed is beneficial to bubble formation, growth and rupture, and can reduce the filling length of material in the groove, enhance the updating effect of material quality transmission surface, and improve the stripping efficiency. However, excessively high speed reduces the residence time of material in the stripping section, and the stripping efficiency decreases instead.
The main factors influencing the stripping process in dual screw extruder are main screw speed, feed rate, and barrel set temperature. The change of these factors will affect the material temperature, groove filling degree, residence time and effective filling length, thus affecting the stripping process in many aspects. For a specific process, there is a working point that can achieve the highest stripping efficiency under stable conditions.
Properly reducing the feeding rate can reduce the filling rate of the exhaust section and improve stripping efficiency. However, too low feeding rate not only reduces the extrusion volume and produces fluctuation, but also reduces the foaming stripping efficiency due to the low filling rate. Therefore, the feeding rate must be moderate.
A twin screw extruder manufacturer can increase stripping efficiency by extending the material's residence time in the stripping section and lengthening the stripping section. Therefore, it is possible to consider increasing the length of the exhaust section and using multi-stage exhaust in the screw structure design of the dual screw extruder.

There are mainly two ways to deal with dual screw extruder in emergency stop situations: normal stop and emergency stop

The main steps are as follows

Normal stop

When the extruder stops without failure, it can be stopped in the following order: close the feeder outlet gate; set the feeding machine to zero and press the stop button; close the vacuum system, gradually reduce the screw speed (if a new material needs to be replaced, try to empty the remaining material in the barrel before the material is basically emptied), press the main motor stop button after adjusting the main motor speed to zero; cut off the main control cabinet's multi-power switch and the input power switch; close each water inlet valve; and cleaning the extruder cylinder are also essential steps. Adhering to this order ensures the safety of workers and machine components and can help prevent potential damage or issues that may arise through improper shutdown procedures.

Emergency stop

If an emergency occurs during the operation of dual screw extruder, the emergency stop button should be pressed immediately (or when the stop button of the fault section is pressed, the main machine will generally stop); after the emergency stop, remember to immediately set the speed knobs of the main motor and feeding motor to zero, and shut down other auxiliary systems. After processing the fault, restart the machine in the normal order.

The disassembly steps of the dual screw extruder

They are the same as those of a single-screw extruder. If the machine stops after extruding heat-sensitive materials such as PVC or POM, it is usually necessary to extrude the material in the barrel with polyolefin plastics to prevent the material from overheating and decomposing due to too long heating time before the next start-up. Disassembly and cleaning are required if necessary. When disassembling the machine, the flange of the head should be loosened while hot, and the filter plate and filter screen should be removed. Then, the screw should be operated to extrude the remaining material in the extruder, and the screw should be pulled out while hot. Finally, use copper rods or shovels to quickly clean the head, screw and residual material in the barrel. The cleaned components should be placed back in time, and if stored, a little rust preventive oil should be applied. The screw should be hung when placed.