Range hood panel is a key appearance part of household kitchen appliances, mostly made of ABS, PC/ABS and modified engineering plastics, requiring high gloss, matte texture, fingerprint resistance, corrosion resistance and wear resistance. Mold surface treatment directly determines the appearance texture, surface finish and service life of the panel. Common processes include high-gloss mirror polishing, texture etching, chrome plating, electroless nickel plating, nitriding and PVD coating. Reasonable process matching can optimize product appearance quality and mold comprehensive performance.
High-Gloss Mirror PolishingHigh-gloss mirror polishing is the mainstream process for bright range hood panels, aiming to achieve ultra-smooth cavity surface with roughness Ra≤0.02-0.2μm, ensuring the plastic part has high gloss, high transparency, no orange peel and scratch defects. The process flow includes pretreatment, rough polishing, fine polishing and mirror finishing. In the pretreatment stage, grind the cavity with sandpaper from 600# to 2000# to remove CNC and EDM tool marks. Rough polishing adopts oil stone and abrasive paste to reduce roughness below 0.8μm. Fine polishing uses wool wheel and diamond paste with particle size gradually reduced from 3μm to 0.5μm to reach Ra≤0.05μm. The final mirror polishing uses non-woven fabric and nano abrasive paste to eliminate fog and pinholes.
Suitable mold steels include NAK80, S136 and 718H pre-hardened steel with hardness HRC 32-38, featuring easy polishing and small deformation. Ordinary P20 and 45# steel are not suitable for high-gloss polishing due to easy rust and poor finish. After polishing, ultrasonic cleaning and anti-rust treatment must be carried out to avoid black spots on plastic parts caused by residual polishing powder.
Texture Etching ProcessTexture etching, also known as graining, is applied to matte and imitation metal brushed range hood panels. It forms uniform grain, sand grain and brushed texture on the mold surface to achieve matte anti-fingerprint effect, cover welding lines and improve hand feeling. The process steps are surface pretreatment, anti-acid protection, corrosion treatment and post-processing. Polish the mold surface to Ra 0.8-1.6μm and degrease with ultrasonic cleaning. Paste anti-acid glue on non-texture areas and coat UV curing acid-resistant ink on the texture surface. Soak the mold in mixed acid solution at 25-40℃ for 5-20 minutes to control texture depth at 0.02-0.15mm. Finally, clean, neutralize and dry to ensure uniform texture depth.
Common texture types include VDI standard sand grain, MT leather grain and imitation brushed grain. Fine sand grain is suitable for dark matte panels with delicate texture and fingerprint resistance. Brushed grain is used for silver gray panels to simulate metal texture, and leather grain is matched with high-end models to improve grade.
Chrome Plating and Electroless Nickel Plating
Flame retardant and corrosive raw materials will produce acidic gas at high temperature, causing mold cavity rust and surface peeling. Electroplating hard chrome and electroless nickel plating can effectively improve corrosion resistance, wear resistance and demoulding performance. Hard chrome plating has a coating thickness of 0.01-0.03mm and hardness HV 800-1000, suitable for mass production molds over 500,000 shots and corrosive plastic forming. The coating is uniform and dense, improving scratch resistance of the cavity.
Electroless nickel plating adopts nickel-phosphorus alloy coating with thickness 5-10μm, which can evenly cover sharp corners and deep cavity positions with self-lubricating property. It is suitable for complex cavity molds and transparent PC/PMMA panels, reducing demoulding adhesion and surface scratch defects. The plating temperature is controlled at 85-95℃ to avoid mold deformation.
Nitriding Treatment ProcessNitriding is suitable for long-term mass production range hood molds filled with glass fiber. It improves surface hardness to HV 800-1200μm, enhances wear resistance and high-temperature fatigue resistance, and doubles mold service life. Gas nitriding is carried out at 500-550℃ for 20-30 hours with nitriding layer thickness 0.03-0.05mm. Ion nitriding has lower treatment temperature and smaller deformation, more suitable for precision cavity molds.
Suitable steels are quenched and tempered SKD61 and H13 with surface hardness up to HV 1000+ after nitriding, while the core maintains good toughness to resist impact and wear caused by glass fiber raw materials. Nitriding treatment can also improve high-temperature corrosion resistance and adapt to long-term continuous injection molding production.
PVD Coating Technology
PVD coating is a high-end strengthening process with coating thickness 2-5μm, including TiN, CrN and TiCN series. The hardness reaches above HV 2000 with low friction coefficient, having excellent wear resistance, corrosion resistance and anti-adhesion performance. The low-temperature deposition temperature of 200-500℃ will not cause mold deformation and dimensional deviation, suitable for high-end range hood appearance molds. The coating has strong bonding force and high-temperature resistance, and can be directly coated on high-gloss surface without secondary polishing. It is mostly matched with S136, NAK80 and SKD61 molds to optimize demoulding effect and reduce cavity wear.
Process Selection and Common Defect CountermeasuresSelect targeted processes according to panel appearance requirements: high-gloss panels adopt NAK80/S136 matching mirror polishing; matte anti-fingerprint panels use 718H/S136 with fine sand grain etching; flame retardant corrosive material molds are combined with chrome plating and nitriding. Common defects such as scratches and foggy surface are caused by insufficient polishing and residual impurities, which can be solved by re-polishing and ultrasonic cleaning. Uneven texture is adjusted by controlling corrosion temperature and time. Cavity rust needs timely anti-rust maintenance and supplementary coating treatment. Reasonable combination of surface treatment processes can balance appearance quality, production efficiency and mold service life.
