Common Maintenance Items for Plastic Molds
Plastic molds are core equipment in injection molding production. Operating under long-term high pressure, high temperature, and repeated opening and closing, molds are prone to failures caused by component wear, fatigue, material residue, and improper operation, which directly affect part quality and production efficiency. Mold maintenance targets key systems including molding, guiding, pouring, ejection, cooling, and venting, covering routine maintenance and emergency troubleshooting. The following are common maintenance items classified by core components.
Molding Component Maintenance
Molding components—including cavities, cores, and inserts—directly contact plastic melt and determine part shape and dimensional accuracy; they are also the most frequently maintained parts.
Surface Defect Repair: Scratches, pits, and rust often appear on cavity and core surfaces due to impurities, residual release agent, or humidity. Maintenance includes fine polishing with sandpaper and oilstone. Nitriding or chrome plating may be applied to improve hardness and smoothness and prevent sticking and rough surfaces.
Dimensional and Shape Correction: Deformation, sinking, and out-of-tolerance dimensions may occur due to excessive injection pressure or material fatigue. Professional measuring equipment is used to detect deviations; correction is done via grinding or wire cutting, and severely damaged parts are replaced.
Flash and Corner Repair: Poor fitting or worn molding surfaces cause flash. Matching surfaces are ground and corners repaired. Loose or displaced inserts are re-fixed to ensure tight fitting and prevent material leakage.
Guide and Positioning System Maintenance
The guiding and positioning system ensures accurate alignment and smooth motion during mold opening and closing. It mainly includes guide pillars, guide bushes, locating pins, and guide plates. Failures cause jamming, offset, and collision damage.
Worn guide pillars and bushes with excessive clearance are reground or replaced; coaxiality is corrected to eliminate shaking and noise.
Loose or deformed locating pins are tightened or replaced to ensure accurate parting surface matching.
Worn guide plates are reground and relubricated to maintain smooth sliding of slides and ejection mechanisms.
Gating System Maintenance
The gating system delivers molten plastic to the cavity, including sprue bushes, runners, gates, and hot runner components. Malfunctions cause poor flow, short shots, stringing, and cold slugs.
Conventional Gating: Worn sprue bushes are repaired or seals replaced. Runners are cleaned of cold slugs and polished to reduce flow resistance. Blocked or stringing gates are cleared and resized.
Hot Runner Maintenance: Clogged or leaking nozzles are cleaned or replaced. Failed heating coils and thermocouples are replaced to ensure accurate temperature control. Leaking hot runner manifolds are resealed and worn areas repaired.
Ejection System Maintenance
The ejection system removes molded parts from the cavity, including ejector pins, ejector sleeves, ejector plates, return springs, and hydraulic cylinders. It suffers repeated stress and frequent failures.
Bent ejector pins and sleeves are straightened; broken or severely worn parts are replaced. Matching clearances are reground for smooth movement to avoid white marks, streaks, and cracking.
Deformed ejector plates are corrected and ground for flatness. Fatigued return springs are replaced to ensure accurate reset.
Leaking or low-pressure hydraulic cylinders are repaired with new seals, and hydraulic oil is replenished.
Cooling and Venting System Maintenance
The cooling system controls mold temperature for rapid and uniform solidification. The venting system expels air to prevent burns, short shots, and trapped gas defects.
Cooling System: Blocked or scaled waterlines are unclogged with high-pressure water or chemical cleaning. Damaged fittings and aged seals are replaced. Local cooling imbalance is improved by optimizing circuit layout.
Venting System: Blocked vent grooves are cleaned. Vent depth is precisely adjusted—too shallow causes trapped gas, too deep causes flash. Worn vent areas are repaired.
Other Auxiliary Component Maintenance
Worn or warped parting surfaces are ground and flattened to eliminate flash.
Slides, angle pins, and core-pulling mechanisms are adjusted, re-lubricated, or replaced to ensure smooth movement and correct return.
Damaged clamping mechanisms and locating rings are repaired or replaced.
Rust is removed and surfaces refurbished as needed.
Loose or broken fasteners are tightened or replaced.
Aged or damaged O-rings and seals are replaced to prevent material and water leakage.
Conclusion
Plastic mold maintenance requires accurate fault diagnosis and targeted repairs. Combined with routine preventive maintenance, it reduces failures, extends service life, and ensures continuous and stable injection molding production.
