What precautions should be taken when cleaning engineering plastics extrusion production lines?

Cleaning engineering plastics extrusion production lines is a very important and meticulous task. Improper cleaning can lead to material degradation, contamination of subsequent products, and even equipment damage. Understanding the precautions for cleaning engineering plastics extrusion production lines can ensure the stable operation of the machine.

1. Core Principles

Safety First: Before cleaning the engineering plastics extrusion production line, a "lock/tag" procedure must be performed, and the power and heat sources must be disconnected. All operators must wear high-temperature gloves, protective glasses, and long-sleeved work clothes to prevent burns and cuts.

Prevention is Key: Use a "material change" cleaning method as much as possible to reduce disassembly. During production breaks or material changes, perform planned light cleaning to avoid prolonged material accumulation and carbonization.

Suitable Temperature: Cleaning temperature is crucial. Excessive temperature will cause material degradation and carbonization, making cleaning more difficult; insufficient temperature will prevent the material from melting, and forced disassembly will damage the equipment. Generally, the cleaning temperature should be set between the melting temperatures of the material to be cleaned and the cleaning material (e.g., PP/PE), slightly above their melting points.

Efficiency and Cost Balance: Choose the most economical and effective cleaning method, balancing downtime, material costs, and cleaning results.

2. Cleaning Methods and Precautions

Based on the degree of contamination and material change type, select the following methods:

(1) Physical Disassembly Cleaning

This is the most thorough but also the most time-consuming and potentially most damaging method to the equipment. Use only in the following situations:
The material is severely degraded or carbonized, clogging the flow channels.
Changing from high-melting-point plastics (e.g., PEEK) to low-melting-point plastics (e.g., PE).
Color switching with extremely high requirements (e.g., changing from black to pure white).
The equipment requires major overhaul or long-term downtime.

Precautions: Cooling Operation: Disassembly must begin only after the equipment temperature has dropped to a safe range (usually below 100°C). High-temperature disassembly is strictly prohibited to prevent burns and component deformation. Use the correct tools: Use non-metallic or soft metal tools such as copper scrapers, copper brushes, and brass wire wheels to avoid scratching the hardened layer on the screw and barrel inner wall. Steel tools are strictly prohibited.
Disassemble in sequence: Follow the equipment manual and disassemble the die head, connector, screw, etc., in sequence.
Clean promptly: Clean the disassembled parts as soon as possible while they are still warm, as the residue is softer and easier to remove.
Professional polishing: After cleaning, the flow channels can be lightly polished with professional polishing paste or fine sandpaper to restore smoothness.

(2) Machine washing method (material exchange)

This is the most common and efficient method. A "cleaning material" with good thermal stability and flowability is used to push out the old material from the production line.

Common cleaning material selection:
Polypropylene (PP) or polyethylene (PE) resin: General-purpose cleaning material, low cost, suitable for switching between most engineering plastics (such as ABS, PC, PA). PE has better flowability. Screw cleaning feed: Commercially available specialized products, typically containing abrasive and chemical cleaning components, effective against stubborn carbonized layers.
Crushed feed: Using crushed feed from the new material to be produced for transitional cleaning is the most economical and pollution-free method.

Operating Procedures and Precautions:
Emptying the hopper: Stop the supply of old material and empty the remaining old material from the hopper.

Cooling/Heating:
Switching from high-temperature to low-temperature material: First, lower the temperature of each section to the production temperature range of the new material, then add the cleaning feed.

Switching from low-temperature to high-temperature material: Maintain or slightly increase the temperature to the processing temperature of the old material, add the cleaning feed, and after cleaning, raise the temperature to the temperature of the new material.

Adding in small amounts multiple times: When adding the cleaning feed, add it in small amounts multiple times, judging the cleaning progress by observing the color and purity of the extruded strip.

Utilizing recycled material: The extruded mixture can be marked as recycled material and used in proportion in subsequent products where color requirements are not high.

3. Special Cleaning of Key Components

(1) Screw and Barrel

During disassembly and cleaning, focus on the compression and metering sections of the screw, as well as the back of the screw threads, as these areas are prone to material accumulation.
When installing the screw, proceed with care to avoid scratching the inner wall of the barrel.

(2) Die Head (Orifice)

The die head has complex flow channels and is one of the most difficult parts to clean.
Offline Heating: Place the removed die head in a dedicated cleaning furnace and heat it using a programmed temperature control system to carbonize and burn off any remaining material. This is the most effective method.
Salt Bath: A traditional and effective method, but it is environmentally unfriendly and requires safety precautions.
Solvent Immersion: For some plastics (such as POM/PC), specific solvents (e.g., dichloromethane for PC) can be used for softening, but the toxicity, volatility, and corrosiveness of the solvent to metals must be considered.

(3) Filter Screen/Screen Changer

Regularly replacing the filter screen is crucial for maintaining stable production line pressure.
For manual screen changing, the contaminated screen should be removed immediately while still hot after shutdown. For automatic screen changers (such as plate type and mesh belt type), ensure smooth operation and good sealing to prevent material leakage.

(4) Auxiliary Equipment

Cooling water tank/traction machine: Regularly clean oil stains and precipitates from the water tank, and check and clean residues on the pressure rollers/traction belt to prevent scratching the product.
Pelletizer: Before stopping the machine, rinse it with pure PE or PP to clean the pelletizing chamber and blades of residual material. Regularly sharpen the moving and stationary blades to keep them sharp.

4. Safety and Environmental Precautions

Ventilation: Harmful fumes will be generated during the cleaning process, especially when heating and degrading materials. Good ventilation must be ensured in the work area.
Waste Disposal: Waste and degraded materials should be classified and disposed of according to environmental protection regulations. Severely degraded carbonized materials generally cannot be reused.
Fire Prevention: High-temperature components and polymer dust pose a fire risk. Fire extinguishers should be provided in the work area. Chemical protection: If using solvents or special cleaning agents, read the MSDS (Material Safety Data Sheet) and take personal protective measures (gas mask, rubber gloves).