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Author: Baina Date: Aug 19, 2022

How to Clean the Screw Part of Plastic Extrusion Equipment?

The cleaning of the screw of plastic extrusion equipment is more complicated, so how to clean it? Methods as below:

1. Select the correct heating device:

Using fire or roasting to remove the plastic fixed on the screw is a common method in plastic processing units, but correspondingly, acetylene flame cannot be used to clean the screw. The temperature of the acetylene flame can reach 3000 ℃. Using acetylene flame to clean the screw will not only destroy the metal characteristics of the screw but also significantly affect the mechanical tolerance of the screw.

If the acetylene flame turns blue for a long time when baking a certain part of the screw, it means that the metal structure of this part of the screw has changed, which will reduce the damage to this part, and even cause the anti-wear layer to peel off from the base metal.  In addition, the local heating of the acetylene flame will also cause overheating of one side of the screw, which will cause the screw to bend. Most screws use 4140. H.T. Made of steel, the tolerance is tight, generally within 0.03mm.

The straightness of the screw is mostly within 0.01mm. When the screw is baked and cooled by the acetylene flame, it is usually difficult to return to the original straightness. Correct method: use a blowtorch to clean the screw immediately after use. Because the screw has heat during processing at this time, the heat distribution of the screw is still uniform.

2. Choose the correct cleaning agent:

Now that the commodity economy is highly developed, there are many kinds of screw cleaners (screw cleaning materials) on the market, most of which are expensive, and the results are good or bad. Whether to use commercial cleaning agents depends on different manufacturers and production conditions; plastic processing enterprises can also use different resins as screw cleaning materials according to their own production conditions, which can save a lot of money for the unit.

3. Choose the correct cleaning method:

The first step in cleaning the screw is to close the feeding insert, that is, close the feeding port at the bottom of the hopper; then reduce the screw speed to 15-25r/min, and maintain this speed until the melt flow at the front of the die stops flowing. The temperature of all heated zones of the barrel should be set at 200°C. Cleaning begins as soon as the barrel reaches this temperature.

Depending on the extrusion process (the die may need to be removed to reduce the risk of excessive pressure at the front end of the extruder), cleaning needs to be done by one person: the operator observes the screw speed and torque from the control panel while observing the extrusion out pressure so that the system pressure will not be too high. During the whole process, the screw speed should be kept within 20r/min. In low-pressure die applications, do not remove the die for cleaning at first. Immediately stop the extrudate and remove the die head when the extrudate is completely converted from process resin to clean resin, and then restart the screw (within 10 r/min) so that the residual clean resin flows out.

4. Choose the correct cleaning tools:

Correct and appropriate tools and cleaning materials should include heat-resistant gloves, goggles, copper scrapers, copper brushes, copper wire mesh, stearic acid, electric drill, barrel ruler, and cotton cloth.

Once the clean resin has stopped extruding, the screw can be withdrawn from the apparatus. For screws with cooling systems, remove the hose lines and swivel connections before starting the screw extraction device (which may be attached to the gearbox). Use the screw extraction device to advance the screw to expose 4-5 screw blocks for cleaning.

The cleaning resin on the screw can be cleaned with a copper scraper and copper brush. After the cleaning resin on the exposed screw has been cleaned, use the screw extraction device to advance 4-5 screw blocks and continue cleaning. Repeatedly, most of the screws were pushed out of the barrel in the later period. Once most of the cleaning resin has been removed, sprinkle some stearic acid on the screw; then use a copper wire mesh to remove the remaining residue, and after the entire screw is polished with the copper wire mesh, use a cotton cloth for the next step. This is to ensure that the next production of the screw will not carry any contamination. After the screw has been completely cleaned, it can be set aside until the other implements have also been cleaned. If the screw needs to be stored, it should be coated with a layer of grease to prevent rust. Cleaning the screw Correspondingly, do not use steel tools, such as steel screwdrivers, scrapers or pry bars to remove plastic stuck to the screw, because steel will damage the surface of the screw and barrel.

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