Chrome Plating Coating Selection Reference for Injection Molds Matching Different Raw Materials

Chrome plating coating is a common surface treatment technology for injection mold cavity. It can improve surface hardness, reduce friction, increase corrosion resistance and reduce material precipitation adhesion. Different plastic raw materials have different wear, corrosion and precipitation characteristics. Selecting whether to carry out chrome plating and formulate coating technical indicators according to raw material types can extend mold service life and stabilize product surface quality.

Basic Performance Characteristics of Mold Chrome Plating Coating

The hard chrome plating for mold has high surface hardness, low surface roughness after polishing, good anti-sticking performance. The coating can isolate the direct contact between plastic melt and mold steel substrate, reduce chemical corrosion caused by material decomposition. The coating thickness needs to be controlled reasonably. Excessively thick coating is easy to peel off under thermal cycling, while too thin coating cannot provide sufficient protection. Chrome plating can reduce the friction force during product demolding, which is helpful for soft materials such as TPU and TPE to solve sticking mold problem. However, chrome plating cannot resist strong abrasive wear of high fiber filled plastics for a long time.

Applicable Raw Material Types for Chrome Plating Coating

Chrome plating is highly recommended for non-filled soft elastomer materials, including TPU, TPE, PVC. These materials are easy to precipitate additives and stick to mold surface during molding. The smooth chrome plating surface reduces the adsorption of precipitates, reduces the frequency of mold cleaning, and improves the surface gloss of plastic parts. It is also suitable for ABS, HIPS, PP, PE non-filled general plastics. It can improve the corrosion resistance of mold surface when plastic decomposes and releases trace corrosive gas. For transparent plastics such as PMMA and PC, high-polished chrome plating can help obtain stable high-transparency surface and reduce surface defects.

Raw Materials Not Suitable or Restricted for Chrome Plating

For plastics filled with glass fiber, carbon fiber and mineral filler, hard filler will continuously scratch the chrome plating layer in mass production. The coating will wear quickly after long cycle, and local peeling may occur, so chrome plating is not the preferred scheme for high filling material molds. PEEK, PPS and other high-temperature engineering plastics are processed under ultra-high mold temperature. The thermal cycle stress is large, which increases the risk of coating peeling. For plastics that release strong corrosive gas during decomposition, such as some flame-retardant materials, the conventional chrome plating has limited anti-corrosion capacity and needs to cooperate with other surface treatment processes.

Mold Steel Base Matching Requirements Before Chrome Plating

Chrome plating is a surface coating, and the substrate steel quality determines the final coating stability. Before plating, check whether the mold surface has pores, cracks and scratches. Defects on the substrate will be amplified after plating. Pre-hardened steel and quenched tempered steel can be used as substrate. Stress relief treatment should be carried out before chrome plating to reduce internal stress of steel and prevent coating cracking under repeated heating and cooling. The matching clearance of sliding structures such as lifter and slider needs to reserve the thickness of chrome plating in advance during design, avoiding the change of fit clearance leading to movement jamming after plating.

Chrome Plating Process Parameter Selection and Thickness Control

Different application scenarios select different coating thickness. For molds focusing on anti-sticking and corrosion resistance with low wear, thin chrome plating with thickness 0.005~0.01mm is adopted, which has little influence on mold size. For molds requiring slight wear resistance, the thickness can be increased properly. After plating, fine polishing is required according to product appearance requirement. Mirror surface or matte texture can be processed on chrome layer. The processing of texture after chrome plating has certain limitations. If complex etching texture is required, texture processing shall be completed first and then chrome plating.

Daily Maintenance Notes for Chrome Plated Mold Surface

In production, avoid using hard grinding tools to scrape the coating surface. Hard tools will scratch the chrome layer and form peeling starting point. Use soft cleaning agent and soft cloth to remove precipitates and dirt regularly. During mold shutdown and storage, apply anti-rust oil compatible with chrome coating. Once local peeling of the coating is found during maintenance, stop using in time for repair, prevent melt from penetrating the peeling gap and corroding the steel substrate. Regularly check the coating status during mold overhaul, evaluate whether re-plating is needed according to wear degree.

Comprehensive Comparison with Other Surface Treatment Schemes

When selecting surface treatment, chrome plating shall be compared with nitriding, PVD coating and other schemes. Chrome plating has obvious advantages in anti-adhesion and surface polishing, with relatively low cost. Nitriding is more suitable for abrasive raw materials, improving substrate wear resistance. PVD coating has higher hardness and better wear resistance, but the cost is higher and the coating thickness is thinner. According to raw material type, product appearance requirement, production volume and budget, comprehensively select the surface treatment scheme to match the mold, avoid blindly using chrome plating for all mold projects.