Injection Mold Vent Groove Blockage Cleaning Method

Vent grooves in injection molds are critical channels for releasing air, volatile gases, and decomposed gases from the cavity. Poor venting directly causes defects such as burning, short shots, bubbles, and flow marks. Industry data shows that nearly 30% of injection molding defects are related to blocked vents. Severe blockage can also scratch the cavity surface, damage parting lines, and increase maintenance costs. A standardized cleaning and maintenance process is therefore essential for stable production.

Common Blockage Causes

Carbon deposits and plastic residues are the main causes of blockages, accounting for more than 60% of failures. During high-temperature molding, plastic decomposes and forms carbon particles, fiber dust, and pigment clusters that easily accumulate in micro grooves only 0.02–0.04 mm deep. Flash and burrs often occur when vent depth is excessive, clamping force is insufficient, or mold surfaces are worn, allowing molten plastic to enter and solidify in vents. Lubricating oil, rust preventive, and excessive mold release agent can also mix with dust to form sludge that adheres inside vents. In addition, dirt from inserts and slides may be squeezed into vent channels during mold clamping.

Preparation Before Cleaning

All cleaning operations must be performed after the machine is stopped, power is cut off, and the mold has cooled below 45°C to ensure safety. Commonly used tools include copper pins, copper scrapers, fine oilstones, mold cleaner, cotton swabs, and air guns. Steel tools are prohibited to avoid damaging the mold surface. Before cleaning, use an air gun to remove surface dust and plastic debris from the cavity, parting lines, and insert gaps.

Cleaning Steps for Blocked Vents

First, spray mold cleaner on the vent area and wait 10–15 seconds to dissolve oil and sludge, then wipe with a clean cloth. Use a copper pin to gently remove carbon deposits and residues along the vent direction without changing the original groove size. For flash on the parting surface, use a copper sheet to slowly remove cured plastic. After cleaning, use a fine oilstone to lightly polish the vent entrance to eliminate burrs. Finally, blow through the entire vent path with high-pressure air to confirm smooth airflow.

Inspection After Cleaning

Visually inspect the vents to ensure they are clean, undamaged, and free of deformation. The depth should remain within the standard range of 0.02–0.04 mm. Conduct a low-pressure and low-speed test to verify that no burning, trapped air, or short shots appear on the molded parts. Check the parting line, inserts, and sliding components for scratches or abnormal gaps.

Preventive Measures

Regular maintenance is the most effective way to avoid vent blockage. Vents should be inspected and cleaned every 8 hours during continuous production, and deep cleaning should be performed every 50,000 cycles. Molding parameters such as temperature, injection speed, and holding pressure should be properly controlled to reduce plastic decomposition. The use of lubricants and release agents should be minimized to prevent contamination. Adequate clamping pressure helps reduce flash and blockage.

Conclusion

Vent grooves play a vital role in injection molding quality. Timely and proper cleaning reduces defects, extends mold life, and improves production stability. Combining daily cleaning with regular preventive maintenance can greatly reduce downtime and reject rates, ensuring efficient and reliable production.