Repair Methods for Worn Mold Parting Surface

The parting surface is the sealing joint between moving mold and fixed mold. Long-term mold opening and closing, high clamping force, melt erosion and foreign body extrusion will cause scratch, dent, enlarged gap and wear on parting surfaces, resulting in product flash, material overflow, dimensional out-of-tolerance and venting failure. Severe wear will lead to mold impact and incomplete mold closing. The repair work shall follow the procedure of cleaning & inspection, classified repair, fitting verification and anti-wear optimization according to wear degree.

Pre-inspection and Wear ClassificationDisassemble the mold thoroughly and clean oil, carbon deposition, plastic debris and rust on parting surfaces. Detect flatness, fitting gap and wear depth with straight edges, feeler gauges and dial indicators.Minor wear: fine scratches and slight surface pulling with gap ≤ 0.02 mm, only sporadic small flash occurs without obvious depression.Moderate wear: strip scratches and shallow dents with gap of 0.02~0.05 mm, large-area flash and deformed original venting grooves.Severe wear and mold impact: deep grooves, local collapse and hard indentation with gap ＞ 0.05 mm, accompanied by plate deformation, insert misalignment, abnormal noise during mold closing and large-area material overflow.

Targeted Repair for Different Wear DegreesMinor Scratches and Shallow Pulling (Depth ＜ 0.03 mm)Repair by grinding and polishing without welding. Polish raised burrs and scratch peaks along the surface with fine oil stones to keep the overall flatness. Use abrasive papers with different particle sizes for sequential fine grinding, and finish with mirror or matte treatment to unify surface roughness. Apply red lead powder for repeated mold opening and closing after grinding to check fitting status. Ensure the fitting rate of parting surfaces reaches over 90%, then clean dust and conduct trial molding.

Moderate Dents and Strip Scratches (Depth 0.03~0.10 mm)Adopt precision cold welding or argon arc welding with welding wire of the same material as the mold base to reduce internal stress and hardness deviation. Polish worn areas thoroughly before welding to remove fatigue layer and oxide layer. Precision cold welders are used for small damaged areas with tiny heat-affected zone to avoid plate deformation and material annealing. Argon arc welding is applied for large areas with layered surfacing and controlled current to prevent local overheating.

Rough level the welded area with grinding wheels and oil stones after welding, then conduct fine grinding to restore original surface height. Reserve allowance for fitting during repair. Repeatedly match and trim the surface with red lead powder, and restore the original size of venting grooves to prevent poor ventilation.

Severe Collapse and Mold Impact (Depth ＞ 0.10 mm)This type of wear is usually accompanied by plate deformation and loose inserts. For plates with slight deformation, perform overall surface grinding or milling on parting surfaces to remove the worn layer uniformly. Add backing plates and adjust ejection stroke if the mold closed height changes, and revise the height of runners and cavities to keep all matching dimensions unchanged.

For local concentrated damage and insert-type parting surfaces, replace damaged inserts directly for higher efficiency and precision. For integral cavity plates with large-area damage, conduct full surfacing welding followed by machining, and perform stress relief tempering after welding to prevent cracking and secondary deformation. Recheck the matching precision of positioning pins and stops after repair to avoid reoccurrence of misalignment and impact.

Repair of Worn Venting GroovesDeformed, deepened or chipped venting grooves cause both flash and burning defects. Level the entire parting surface first, then re-machine venting grooves strictly according to drawing dimensions. Keep the groove edge sharp without fillet to prevent material overflow. Unify the specification of all venting grooves on multi-cavity molds.

Fitting, Trial Molding and Precision VerificationFitting is the key to ensure sealing effect after repair. Evenly coat red lead detection agent on parting surfaces, and trim high points according to coloring marks after low-speed mold closing. Repeat the operation until uniform coloring is obtained without virtual gaps and hard points.

Preventive Measures to Delay Re-wearProduction Environment ControlFully dry raw materials to prevent agglomeration. Install magnetic separators on hoppers and barrels to remove iron debris and avoid scratch on parting surfaces. Clean the mold regularly to prevent accumulation of carbon and plastic dirt.

Mold Structural OptimizationEmbed wear-resistant strips or spray wear-resistant coatings such as nitriding and tungsten carbide coating on vulnerable areas of parting surfaces to improve surface hardness and wear resistance. Add stops and tapered positioning surfaces to share clamping pressure on flat parting surfaces.

Standardization of Process ParametersProhibit operation under excessive rated clamping force. Match appropriate injection pressure and speed to reduce melt erosion on parting surfaces. Regularly check the clearance of guide pins, guide bushes and positioning pins, and replace worn parts timely to prevent mold misalignment and impact.

Daily MaintenanceEstablish regular inspection rules. Clean parting surfaces and apply special mold anti-rust oil during production breaks. Conduct comprehensive anti-rust treatment before long-term shutdown to avoid surface peeling caused by rust.