How to clean the screw properly
1.Choose the right heating device
The most common and effective way to remove plastic from a screw is by burning or baking it, but acetylene flame should never be used to clean a screw. Acetylene flames can reach temperatures of up to 3000°C. Using acetylene flames to clean the screw will not only damage the metal properties of the screw, but will also significantly affect the mechanical tolerances of the screw.。
If the acetylene flame turns permanently blue when baking a part of the screw, it means that the metal structure of this part of the screw has changed, which will lead to a reduction in the wear resistance of this part and even to the peeling of the anti-wear layer from the base metal. In addition, partial heating with an acetylene flame can cause overheating on one side of the screw, which can lead to bending of the screw. Most screws are made of 4140.H.T. steel with very tight tolerances, generally within 0.03mm.
The straightness of the screw is mostly within 0.01mm. When the screw is baked and cooled by acetylene flame, it is usually difficult to return to the original straightness. The correct and effective way: use a blowtorch to clean the screw immediately after use. Because the screw carries the heat of the process at this time, the heat distribution of the screw is still uniform.
2.Choose the right cleaning agent
Today’s highly developed commodity economy, there is no shortage of all kinds of screw cleaners (screw cleaning material) on the market, most of them are expensive, the use of good and bad results. Whether to use commercial cleaners, depending on the different manufacturers and production; plastic processing enterprises can also be based on their own production, the use of different resins to do screw cleaning material, can save a lot of money for the unit.
3.Choose the right cleaning method
The first step in cleaning the screw is to turn off the charging insert, i.e. to close the lower port at the bottom of the hopper; then reduce the screw speed to 15-25r/min and maintain this speed until the melt flow stops at the front of the die head. The temperature of all heating zones of the barrel should be set at 200° C. As soon as the barrel reaches this temperature, start cleaning.
Depending on the extrusion process (it may be necessary to remove the die to reduce the risk of excessive pressure at the front end of the extruder), the cleaning must be done by one person: the operator observes the screw speed and torque from the control panel, while observing the extrusion pressure to ensure that the system pressure is not too high. The screw speed should be kept within 20r/min during the whole process. In low-pressure die applications, the die should not be removed for cleaning in the first place. Stop and remove the die head as soon as the extrudate is fully converted from process resin to clean resin, then restart the screw (within 10r/min) to allow residual clean resin to escape.
4.Choose the right cleaning tools
Proper and appropriate tools and cleaning materials should include: heat-resistant gloves, goggles, copper scrapers, copper brushes, copper wire mesh, stearic acid, electric drills, barrel rulers, and cotton cloth.
Once the clean resin has stopped being extruded, the screw can be withdrawn from the equipment. For screws with cooling systems, remove the hose lines and rotating connections before starting the screw extraction equipment (which may be attached to the gearbox). Use the screw extraction device to push the screw forward to expose 4-5 screw blocks for cleaning.
The cleaning resin on the screw can be cleaned with a copper scraper copper brush. After the cleaning resin on the exposed screw is cleaned, the screw extraction equipment is used to push forward 4-5 screw blocks and continue cleaning. This is repeated and eventually the majority of the screw is pushed out of the barrel.
Once most of the cleaning resin has been removed, some stearic acid is sprinkled on the screw; the remaining residue is then removed using a copper wire mesh, and after the entire screw has been polished with the mesh, a cotton cloth is used for the final wiping step. This is to ensure that the screw does not carry any contaminants in its next production run. After the screw has been completely cleaned, it can be set aside until the rest of the machine has been completely cleaned as well. If the screw is to be stored, a layer of grease should be applied to the surface to prevent rusting.
Steel tools such as steel screwdrivers, scrapers or pry bars should never be used to clean the screw to remove plastic stuck to the screw, as steel can damage the surface of the screw and barrel.
How to properly clean the barrel of the machine
Cleaning the barrel is much easier than cleaning the screw, but it is also very important.
1. the barrel temperature is also set at 200°C while preparing the barrel for cleaning.
2. screwing the round steel brush to the drill bar and electric drill to form the cleaning tool, and then wrapping the brush with copper wire mesh.
3. before inserting the cleaning tool into the barrel, sprinkle some stearic acid into the barrel or spread the stearic acid on the copper wire mesh of the cleaning tool.
4.as soon as the copper wire mesh is inserted into the barrel, start the electric drill to rotate it while artificially moving it back and forth until this back and forth movement becomes free of resistance.
5.After the copper wire mesh is removed from the barrel, a cotton cloth is wiped back and forth through the barrel to remove any cleaning resin or fatty acid residue; after several passes of this wipe, the barrel is now clean. The thoroughly cleaned screw and barrel are then ready for assembly for the next production run!