How to properly clean a plastic extruder?
Part One: How to Properly Clean the Screw
1. Do Not Use an Acetylene Flame
Using fire or flame to remove plastic fixed on the screw is a common method in plastic processing units, but using an
acetylene flame is absolutely unacceptable. The temperature of an acetylene flame can reach 3000°C.
Cleaning with an acetylene flame will not only destroy the metal characteristics of the screw but also significantly
affect its mechanical tolerances.
If the flame becomes permanently blue when baking a part of the screw, the metal structure of the screw has changed.
This will result in reduced wear resistance and may even cause the wear-resistant layer to peel off from the base
metal.
In addition, local heating with an acetylene flame can cause overheating on one side of the screw, leading to
bending.
Most screws are made of 4140 HT steel with tight tolerances, typically within 0.03 mm. Screw straightness is mostly
within 0.01 mm. When the screw is baked and cooled by an acetylene flame, it is usually difficult to return to its
original flatness.
The correct and effective method is to use a blower to clean the screw immediately after use. Since the screw retains
heat during processing, the heat distribution remains uniform.
2. Choosing the Right Cleaning Agent
Today, the commodity economy is highly developed. There are many types of screw cleaners on the market, most of which
are expensive and vary in effectiveness.
Whether to use commercial detergents depends on the manufacturer and production conditions. Plastic processing
companies can also use different resins to make their own screw cleaning materials according to their production
conditions, which can save significant costs.
3. Choosing the Correct Cleaning Method
The cleaning procedure for the screw is as follows: close the feeding insert (i.e., close the lower opening of the
hopper). Then reduce the screw speed to 15–25 r/min and maintain this speed until the melt flow at the front end of
the die stops.
The temperature of all heating zones of the barrel should be set to 200°C. Once the barrel reaches this temperature,
begin cleaning immediately.
Depending on the extrusion process (the die may need to be removed to reduce the risk of excessive pressure on the
front of the extruder), cleaning must be done by one person. The operator monitors screw speed and torque from the
control panel while observing extrusion pressure to ensure the system pressure does not become too high.
The screw speed should be kept within 20 r/min throughout the process. For low-pressure die applications, do not
remove the die for cleaning.
Immediately when the extrudate is completely converted from the processing resin to the cleaning resin, remove the
die and restart the screw (within 10 r/min) to allow residual cleaning resin to flow out.
4. Choosing the Right Cleaning Tools and Materials
The correct and appropriate tools and cleaning materials include:
- Heat-resistant gloves
- Goggles
- Copper scraper
- Copper brush
- Copper wire mesh
- Stearic acid
- Electric drill
- Barrel ruler
- Cotton cloth
5. Step-by-Step Screw Cleaning Process
Once the cleaning resin stops extruding, the screw can be withdrawn from the device. For screws with a cooling
system, remove the hose and swivel connection before starting the screw extraction device.
Use the screw extraction device to push the screw forward, exposing 4–5 inches of the screw for cleaning. Clean the
cleaning resin from the screw using a copper scraper or copper brush.
After cleaning the exposed section, advance the extraction device another 4–5 inches and continue cleaning. Repeat
this process until most of the screw is pushed out of the barrel.
Once most of the cleaning resin has been removed, sprinkle stearic acid onto the screw, then use copper wire mesh to
remove any remaining residue.
After polishing the entire screw with copper wire, wipe it one more time with a cotton cloth. This ensures the screw
will not carry any contaminants into the next production run.
After the screw has been completely cleaned, it can be set aside until other implements are cleaned. If the screw
needs to be stored, apply a layer of grease to the surface to prevent rust.
6. Important Warning
When cleaning the screw, never use steel tools such as steel screwdrivers, scrapers, or masts to remove plastic stuck
to the screw, as steel can damage the surface of both the screw and the barrel.
Part Two: How to Properly Clean the Barrel
Cleaning the barrel is much easier than cleaning the screw, but it is still very important.
Step-by-Step Barrel Cleaning Process
1. When preparing to clean the barrel, set the barrel temperature to 200°C.
2. Attach a round steel brush to a drill pipe and an electric drill as 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 onto the copper
wire of the cleaning tool.
4. When the copper mesh enters the barrel, start the electric drill to rotate, and move it back and forth manually
until the movement becomes resistance-free.
5. After removing the copper wire mesh from the barrel, use a bundle of cotton cloth to wipe back and forth in the
barrel to remove any cleaning resin or stearic acid residue.
After several such back-and-forth cleanings, the barrel cleaning is complete. The thoroughly cleaned screw and barrel
can be assembled at any time for the next production run.
Part Three: Cleaning for Color Changes, Screw and Mold Precautions
With increasing product diversity and richer colors, conversion between different materials and colors results in
long changeover times and more waste, causing confusion in production management and operation. Below are several
suggestions for your reference.
1. Clean the Outside of the Equipment First
After converting between different materials and colors, clean the original raw materials without leaving any dead
ends, especially areas that are difficult to wipe. Do not leave any residue.
The residual material in the screw and barrel must be extruded and emptied. For complex equipment and molds, remove
and clean them if necessary.
2. Using Cleaning Agents
If using a cleaning agent, after cleaning, heat the new material to be extruded and begin extrusion. Examine the
appearance of the extruded product. If the color is correct, normal production can begin. If not, repeat the above
process.
3. Small Tips for Reference
A. If different materials and colors are frequently changed, use the same mold for multiple runs.
Molds are difficult to clean, so this saves time and materials.
B. For different colors of the same material, color masterbatch can be added at the feed port for
production. Avoid using toner, as this can reduce the impact of different steps on color consistency.
C. Co-extrusion can be used to change the appearance color of the product, which can also reduce
changeover trouble.
D. For material conversion, if conditions permit, use products and equipment from the same material
family. For example, PP pipe equipment should be used to make other PP material products as much as possible, rather
than making PE products. Otherwise, if not cleaned properly, product performance may be affected.
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