Burning or flame‑treating to remove plastic adhered to the screw is a common and effective method in plastic processing facilities. However, an acetylene flame should not be used for cleaning the screw, as its temperature can reach 3,000°C. Using an acetylene flame to clean the screw will degrade the metal’s properties and significantly compromise its performance.

I. How to Properly Clean a Screw Rod

1. Select the appropriate heating device.

Burning or flaming off the plastic adhering to the screw is a common and effective method used in plastic processing facilities; however, acetylene flames should not be employed for cleaning the screw. Acetylene flames can reach temperatures as high as 3,000°C, and using them to clean the screw will degrade the metal’s properties while also significantly compromising the screw’s dimensional tolerances.

If, during flame hardening of a particular section of the screw, the flame turns a persistent blue, it indicates that the metallurgical structure of that section has been altered. This can reduce the wear resistance of the area and may even lead to delamination between the wear‑resistant layer and the substrate metal. Furthermore, localized heating with an acetylene flame can cause overheating on one side of the screw, resulting in warping. Most screws are manufactured from 4140 H.T. steel, with very tight dimensional tolerances—typically within 0.03 mm.

The straightness of the screw is typically within 0.01 mm; however, after being heated with an acetylene flame and then cooled, it is usually very difficult to restore its original straightness. The correct and effective approach is to clean the screw with a blowtorch after use. Since the screw still retains heat from the machining process at this stage, its temperature distribution remains uniform.

2. Use the correct cleaning agent.

In today’s highly developed commodity economy, the market is replete with screw‑cleaning agents—often at a considerable price—and their performance varies widely. Whether to use commercially available cleaning agents depends on the specific manufacturer and production conditions; alternatively, plastic‑processing companies can formulate their own screw‑cleaning compounds using different resins, which can help reduce costs significantly.

3. Use the correct cleaning method

The first step in cleaning the screw is to close the feed gate, which shuts off the discharge opening 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 head comes to a complete stop. Set the temperature in all heating zones of the barrel to 200°C. Once the barrel has reached this temperature, begin the cleaning process.

Depending on the extrusion process—where it may be necessary to remove the die head to mitigate the risk of excessive pressure at the extruder’s feed end—the cleaning should be performed by a single operator. The operator monitors screw speed and torque from the control panel while also keeping an eye on extrusion pressure to ensure it does not exceed safe limits. Throughout the procedure, the screw speed should be maintained below 20 r/min. For low-pressure die applications, do not remove the die head for cleaning. Stop the machine and remove the die head only when the extrudate has fully transitioned from the processed resin to clean resin, then restart the screw at a speed between 10 and 20 r/min to allow any residual clean resin to discharge.

4. Use the correct cleaning tools

The appropriate tools and cleaning materials should include:

Heat-resistant gloves; safety goggles; copper scraper; copper brush; copper wire mesh; stearic acid; electric drill; cylinder gauge; cotton cloth.

Once the cleaning resin has ceased to extrude, the screw can be withdrawn from the equipment. For screws equipped with a cooling system, before activating the screw‑removal device— which may be integrated with the gearbox—first disconnect the hose lines and rotary unions. Use the screw‑removal device to advance the screw until 4–5 flight segments are exposed, facilitating cleaning.

The resin buildup on the screw can be removed using a copper scraper or a copper brush. Once the resin on the exposed portion of the screw has been thoroughly cleaned, employ the screw‑pulling device to advance the screw forward by 4–5 flight segments and continue cleaning. Repeat this process until most of the screw has been extracted from the barrel.

Once most of the cleaning resin has been removed, sprinkle some stearic acid onto the screw. Then, use a copper wire mesh to eliminate any remaining residues; once the entire screw has been thoroughly cleaned by the mesh, proceed with a final wipe using a cotton cloth. This ensures that the screw will be free of contaminants during the next production run. After the screw has been completely cleaned, set it aside until the other equipment has also been fully sanitized. If the screw is to be stored, apply a thin layer of grease to its surface to prevent rusting.

Do not use steel tools, such as steel screwdrivers, scrapers, or pry bars, to remove plastic adhering to the screw, as steel can damage the surfaces of both the screw and the barrel.

II. How to Properly Clean the Barrel

Cleaning the barrel is much easier and more convenient than cleaning the screw, but it’s still very important.

1. When preparing to clean the barrel, the barrel temperature is also set to 200°C.

2. Attach the round steel brush to the drill rod and the electric drill in the correct orientation to form a cleaning tool, then wrap the steel brush with copper wire mesh.

3. Before inserting the cleaning tool into the barrel, sprinkle some stearic acid into the barrel, or apply stearic acid to the copper wire mesh of the cleaning tool.

4. Once the copper wire mesh enters the barrel, start the electric drill to rotate it while manually moving it back and forth until this reciprocating motion encounters no resistance.

5. After removing the copper wire mesh from the barrel, use a cotton cloth to wipe back and forth inside the barrel to remove any residual cleaning resin or fatty acid residues; after several such passes, the barrel is thoroughly cleaned. The cleaned screw and barrel can then be reassembled for the next production run!