As a mainstay machine in the blending field, the twin-screw extruder's superior performance and customizability are its key advantages. It can combine different additives and fillers to achieve different particle shapes and properties with varying characteristics.
While it can process a wide variety of additives and fillers for extrusion, certain methods of obtaining these products can also lead to contamination problems, resulting in low flow rates or low pressures in many areas throughout the barrel.
In continuous processes like extrusion, contamination has adverse effects. Purging during extrusion is often more challenging than in other processes, and twin-screw extruders face even greater challenges due to the system's greater complexity compared to single-screw extruders.
Let's look at some cleaning methods for twin-screw extruders.
Resin Cleaning Method
Using polyester or epoxy resin for cleaning is generally used for cleaning new equipment or after the extruder has been used for a period of time. This method can be used when some material residue on the screw or barrel gels, slowing down the extrusion speed and causing significant color differences in different color varieties. In today's highly developed commodity economy, the market is flooded with various screw cleaners (screw cleaning materials), most of which are expensive and their effectiveness varies.
Whether to use commercially available cleaners depends on the manufacturer and production conditions. Plastic processing companies can also use different resins to make screw cleaners based on their own production needs, saving a considerable amount of money.
The first step in cleaning the screw is to close the feed plate, that is, close the feed port at the bottom of the hopper; then reduce the screw speed to 15-25 rpm and maintain this speed until the melt flow at the die tip stops. The temperature of all heating zones in the barrel should be set to 200°C. Once the barrel reaches this temperature, begin cleaning immediately.
Depending on the extrusion process (which may require removing the die to reduce the risk of excessive pressure at the extruder tip), cleaning must be performed by one person: the operator observes the screw speed and torque from the control panel, while also monitoring the extrusion pressure to ensure that the system pressure does not become too high. Throughout the process, the screw speed should be maintained below 20 rpm. In low-pressure die applications, do not remove the die for cleaning initially. Immediately stop the machine and remove the die as soon as the extrudate is completely converted from the processing resin to the cleaning resin. Then restart the screw (at a speed of 10 rpm) to allow any remaining cleaning resin to drain.
Disassembly Guide
Manually add washing material through the feed inlet until the extruded strip matches the color of the washing material granules. Stop feeding, empty the material, and stop the twin-screw extruder screw.
Open the screw extruder die to begin cleaning.
Rotate the twin-screw extruder screw and remove the orifice plate to drain any remaining washing material from the barrel. Clean the orifice plate.
Stop the extruder and pull out the screw to check if it is clean. Manually remove any residue from the screw. Reinstall the screw; add fresh material to flush out any remaining washing material from the barrel, and stop the screw.
Reinstall the twin-screw extruder orifice plate and die to complete the twin-screw extruder cleaning operation.
