Does the plastic compounding and modification system need to be cleaned?

Regular and thorough cleaning of the plastic compounding and modification system is a crucial task, just as important as the production operation itself. It's not an optional task, but a core maintenance step to ensure product quality, production efficiency, and equipment safety.

1. Why is cleaning necessary? (The Importance of Cleaning)

Preventing product contamination and cross-contamination (Primary Reason)
Color Switching: When switching from a dark material (such as black) to a light-colored material (such as white or transparent), trace amounts of residual pigment can cause the entire batch of product to be scrapped due to color discrepancies.
Material Switching: When switching from one plastic (such as PP) to an incompatible plastic (such as PC or PA), residual old material can cause "fish eyes," gels, or weak spots, severely degrading the performance of the new product.
Additive Switching: Different formulations contain different additives (such as flame retardants or toughening agents). Residue can disrupt the chemical balance of the new formulation, causing product failure.

Ensuring Product Quality Stability
Material accumulated in equipment dead zones can degrade under prolonged high temperatures, turning yellow and charring, forming a black "carbonized material." These charred particles periodically break off and mix into new products, causing black spots and crystals on the product surface or degrading mechanical properties.

Maintaining Equipment Efficiency and Performance
Degradation products accumulated in the screw, barrel, and die head, acting like scale, can affect heat transfer efficiency and increase screw rotational resistance, leading to increased energy consumption.
Clogged filters and die heads can lead to abnormally high backpressure and unstable discharge, impacting production and quality.

Ensuring Production Safety
Degradation of certain plastics (such as PVC) at high temperatures releases corrosive gases (such as HCl), accelerating equipment corrosion.
Degradation products accumulated near hot runners and heater coils can pose a fire hazard.

Facilitating Repair and Maintenance
Regular cleaning helps detect wear on the screw and barrel, allowing for proactive repair planning and avoiding costly unexpected failures.

2. Cleaning Timing

Batch cleaning: After completing a production batch or order, before switching colors, materials, or formulas.
Planned cleaning: Preventive cleaning performed after a certain period of continuous operation (such as a week or a month) based on production experience.

Mandatory cleaning:
 When the following situations occur:
Black spots and impurities continue to appear in the product.
The die head pressure increases abnormally.
The equipment operating current fluctuates abnormally.
The physical properties of the product are unstable.

3. Cleaning methods and steps

Cleaning work needs to follow the principle of "from top to bottom, from outside to inside", and is usually divided into the following stages:

(1). Shutdown and cooling

Stop feeding and let the system run idle to drain the remaining material.
Gradually reduce the temperature of each section to a safe range (such as 150-200°C) to avoid high temperature burns and rapid carbonization of the material.

(2). Physical cleaning

Disassembly cleaning: This is the most thorough method.
Disassemble the machine head, die head, and filter screen.
Use non-metallic tools such as copper scrapers, copper brushes, and bamboo scrapers (to prevent scratching the hardened steel surface) to clean the residual melt in the screw, the inner wall of the barrel, and the die flow channel.
Note: You must wait until the temperature drops to a safe range before operating, and wear high-temperature gloves.
Screw extraction cleaning: Regularly extract the entire screw from the barrel for comprehensive inspection and cleaning.

(3). Chemical cleaning

This is the most commonly used method in the case of non-stop operation or minor disassembly.
General cleaning material: Use special PE/PP-based cleaning materials, which have good compatibility and flushing ability and can "push" residues out of the system.
High-efficiency cleaning material: Special materials containing abrasives or chemical cleaning ingredients can strongly peel off carbonized layers and stubborn deposits.

"Material replacement" method:
Principle: Use a high amount of new or recycled materials to flush out the old materials.
Technique: Follow the compatibility principle. For example, when cleaning a PC system, you can first use PE to clean it, and then use PC to push away PE. Because PC and PE are incompatible, they are easy to separate.
Economic method: Add crushed return material (sprue material) for flushing, which is low cost.

(4). High-temperature combustion method

For some thermosetting plastics or extremely stubborn degradants, it may be necessary to raise the equipment temperature above the ignition point of the degradant, let air in to burn it into ash, and then use tools to clean it. Warning: This method is high-risk and requires professional personnel, with strict fire prevention measures.

4. Best Practices and Precautions

Production Sequencing Optimization: Arrange production sequences appropriately, following the principle of "from shallow to deep, from common to specific" to reduce the frequency and difficulty of cleaning.
Proper Protection: Wear high-temperature gloves, safety glasses, and a hard hat throughout the cleaning process to prevent burns and mechanical injuries.
Standardized Operations: Ensure energy isolation (tag out and lock out) of equipment before cleaning to prevent accidental startup.
Records and Tracking: Establish cleaning and maintenance records to track cleaning results and equipment status, and optimize cleaning cycles.