How to clean polyurethane high pressure foam injection machine？

Cleaning a polyurethane high-pressure foaming injection machine is an extremely demanding task, not only affecting the lifespan of the equipment and product quality, but also directly impacting operator safety. Polyurethane raw materials (isocyanate and polyether) are chemically toxic and difficult to remove after curing. Understanding detailed cleaning procedures, methods, and key considerations will ensure stable equipment operation.

1. Cleaning Steps for a Polyurethane High-Pressure Foaming Injection Machine

Step 1: Safety Preparation
Personal protective equipment must be fully worn:
Safety glasses or full-face shield: to prevent chemical splashes from entering the eyes.
Chemical-resistant gloves (such as butyl rubber gloves): to prevent skin contact with raw materials.
Anti-static work clothes or aprons: to prevent raw materials from contaminating clothing and adhering to skin.
Safety shoes: to prevent injuries from heavy objects or chemical leaks.
Ensure the work area is well ventilated, preferably in an area with exhaust ventilation.

Prepare the appropriate cleaning agent:
Preferably, a cleaning agent recommended by the equipment manufacturer. Commonly used solvents include: dichloromethane, DMF (dimethylformamide), acetone, or high-purity solvent naphtha. Note: Most of these solvents are flammable and toxic and must be used with caution.
Environmentally friendly alternatives: Some specialized, environmentally friendly polyurethane cleaning fluids are available.
Tools: A wrench, a lint-free cloth, a soft scraper (plastic or wooden to avoid scratching metal surfaces), and a container for collecting waste liquid.

Step 2: Shutdown and Draining the Raw Materials
Normal Shutdown: Shut down the equipment according to operating procedures.
Draining the Raw Materials Drum: If the equipment will not be used for an extended period, remove the raw materials drum from the material bin and seal it securely.
Flushing the Material Bin with Detergent: Add a small amount of specialized detergent to the bin and circulate it briefly with a circulating pump before draining. This step provides initial dilution and removes any residual raw materials from the inner walls of the bin.

Step 3: Circulation Cleaning (Core Step)
This is the most common and effective daily cleaning method, used to remove residual material from the mixing head and piping.
Using the Detergent Circulation Method:
Insert the equipment's two suction hoses into containers of detergent. Start the "Purge" program on the machine control panel, or manually, and circulate the cleaning agent through the A and B material systems. This process dissolves any residual polyurethane in the pipes and mixhead.
The cycle time is typically 1-3 minutes, or as directed in the machine manual.

Step 4: Disassembly and Manual Cleaning of the Mixhead
For extended use, regular maintenance, or when changing raw material formulations, the mixhead must be thoroughly cleaned manually.
Pressure Relief: Ensure that the entire system is completely depressurized.
Disassembly of the Mixhead: Using specialized tools, carefully disassemble the mixhead according to the manufacturer's exploded view diagram. This typically involves removing the mixing chamber, piston, nozzle, and other parts.

Soaking and Scrubbing: Immediately soak the disassembled parts in a container of cleaning agent to prevent any solidified residue.
Use a soft-bristled brush (such as a copper or nylon brush) to carefully scrub each part. Avoid using hard brushes such as steel brushes to avoid scratching the precision-fitting surfaces.

For cured polyurethane, a longer soak or stronger cleaning agent may be necessary.

Drying and Inspection:
Dry all parts with a lint-free cloth.
Carefully inspect all parts, especially seals (O-rings). Replace any signs of wear, deterioration, or deformation.
Inspect the piston and mixing chamber for scratches or wear.

2. Key Precautions and Dos and Don'ts

Safety First: Wear personal protective equipment at all times and stay away from sources of ignition to prevent solvent poisoning and fire.
No Mixing: Absolutely never mix ISO-based cleaning agents into poly-based systems, or vice versa. This will cause them to react and solidify rapidly within the pipes, causing serious blockages.
Prompt Cleaning: Clean immediately after work. Once fully cured, polyurethane material is extremely difficult to remove and may cause permanent damage to the equipment.
Seal Replacement: Regular seal replacement is key to preventing leaks and ensuring accurate mixing ratios. Do not reuse old seals to save money.
Waste Disposal: Used cleaning agents and waste from cleaning are considered hazardous waste and should be disposed of professionally in accordance with local environmental regulations. Do not dump them carelessly.