Wear-resistant Protection Measures for Molds for Glass Fiber Reinforced Plastics

Glass fiber contained in reinforced plastics continuously scours mold cavities, runners and seal positions during high-speed filling of injection molding. It easily causes mold surface abrasion, fogging of polished surfaces and dimensional deviation, shortening mold service life. Wear-resistant protection of molds needs comprehensive implementation from steel selection, surface hardening treatment, mold structure optimization, injection process control and daily maintenance.

1. Matching selection of mold steel

The degree of glass fiber abrasion is related to glass fiber content. Pre-hardened wear-resistant steel can be selected for low glass fiber content, while high-temperature tempered steel with high hardness is preferred for high glass fiber materials. Improved steel hardness resists cutting wear from glass fiber. Cavity, gate, runner and other heavy scouring areas can adopt solid high-hardness steel or local insert scheme, avoiding using expensive steel for the whole mold and controlling processing cost. Steel shall undergo sufficient tempering to reduce residual internal stress and prevent deformation or cracking during subsequent surface treatment, ensuring long-term dimensional stability of molds.

2. Surface hardening and wear-resistant treatment of molds

Surface protection is applied for zones scoured by glass fiber. Different surface treatment methods vary in wear resistance. Nitriding treatment suits large-area cavities. It features high surface hardness, small deformation, good wear resistance and anti-seizure capacity, suitable for complex shell molds. PVD coating provides higher hardness and low friction coefficient, effectively reducing abrasion caused by glass fiber scraping. It is mostly used for high-speed scouring positions including gates, runners and rib grooves. Molds need polishing before coating to guarantee stable coating adhesion. TD treatment delivers stronger wear resistance, suitable for molds with long-term high-volume mass production to resist severe cutting wear of glass fiber. However, the treatment temperature is relatively high, so mold deformation risk shall be assessed in advance.

3. Mold structure optimization to reduce scouring wear

The gate is the primary scouring position where melt enters the cavity. High-speed glass fiber melt directly hitting the cavity wall will quickly erode the mold. Avoid the gate facing the straight cavity wall during design, add buffer structures to change the impact direction of melt flow and reduce local scouring intensity. Runner cross-sections are designed with smooth transitions, removing sharp corners and steps to prevent eddy current at corners which aggravates abrasion of mold surface. Rib grooves and narrow gaps are thin-wall positions with fast melt flow and higher wear speed. Replaceable inserts are adopted preferentially in these zones. Worn inserts can be directly replaced to reduce mold modification workload for the whole mold. Reduce large-area exposed scouring on parting line sealing surfaces, and design proper venting to prevent burnt material and carbon deposits that accelerate surface damage.

4. Injection process parameters to reduce wear load

Excessively high injection speed increases cutting effect of glass fiber on mold surface. On the premise of meeting filling requirements, properly lower injection rate to slow melt scouring strength. Do not set barrel temperature too high to prevent substrate degradation. Degraded materials bring corrosive properties, which together with glass fiber aggravate mold loss. Keep raw materials fully dried to reduce pores and accumulated materials caused by moisture. Long-term accumulated materials attached to cavity surface will damage wear-resistant coating. Control packing pressure. Excessively high packing pressure increases friction between molded parts and cavity wall, which may scratch mold surface during demolding. Clean the barrel regularly to prevent hard carbon particles mixing into melt. Hard carbon particles will scrape the cavity together with glass fiber.

5. Protection control during assembly and trial molding

Clean molds thoroughly during assembly to remove metal scraps and polishing dust. Inspect cavity surface before trial molding to prevent hard particles from pressing and damaging wear-resistant surface after mold closing. Use low-speed and low-pressure parameters at the initial stage of trial molding and adjust parameters gradually. Do not directly use limit mass production parameters to avoid damage of new hardened surface caused by instantaneous high-speed melt flow. Pay attention to areas such as gates and rib grooves during trial molding, check scratches on product surface caused by mold wear and predict wear trend in advance.

6. Daily maintenance in mass production

Clean cavities, runners and vent grooves to remove residual glass fiber powder and carbon deposits after each shutdown. Use soft copper tools for cleaning, and prohibit hard steel tools from scraping mold surface to avoid scratching wear-resistant protective layers. Inspect gates and narrow rib inserts regularly to monitor wear status. Repair or replace inserts timely when wear reaches the threshold. Clean and apply anti-rust agent before long-term shutdown. Although wear-resistant coatings have wear resistance, they do not support long-term anti-rust performance, so special mold anti-rust agent is required to protect the surface layer. Review mold dimensions periodically, monitor dimensional changes brought by wear and formulate maintenance plans in advance to guarantee stable product dimensions.