Dishwasher spray arms are common household appliance functional plastic parts, which work in long-term hot water and detergent erosion environment, requiring uniform wall thickness, smooth internal water channels, good hydrolysis resistance and stable structural strength. The supporting injection moulds need to adapt to mass production demand, match PP and modified PP common raw materials, and achieve long service life and stable forming effect through reasonable steel selection, standardized heat treatment and precise mechanical processing.
Product Forming Features and Mould Application RequirementsMost spray arms are hollow tubular structures with dense water outlet holes and assembly buckle positions. The mainstream forming material is food-grade PP material, which has good fluidity but large forming shrinkage rate, and is prone to shrinkage depression at thick-wall positions and insufficient filling at thin-wall positions. Since the products are soaked in hot water for a long time, the internal forming stress must be controlled strictly to avoid later cracking. Therefore, the mould is required to have uniform cooling performance, smooth exhaust structure, high cavity finish and good corrosion and wear resistance, so as to adapt to continuous high-efficiency production and reduce daily failure rate.
Core Mold Steel Selection Standard
For ordinary household spray arms with medium and small batch output, pre-hardened P20 mould steel is preferred, with stable hardness, moderate cost and simple processing technology, which can meet the forming demand of pure PP materials. For large-scale automatic production, 718H mould steel with higher purity and better polishing performance is selected, which is not easy to deform after long-term opening and closing and suitable for long-term stable operation of injection machines. When forming glass fiber modified materials with strong wear resistance, S136 stainless anti-corrosion mould steel shall be used. After vacuum quenching and tempering, it has excellent wear resistance and acid-base corrosion resistance, which can effectively avoid cavity surface abrasion and rust. High-end export precision products can choose NAK80 mirror surface mould steel to reduce product internal stress and improve dimensional stability.
Mould bases adopt qualified S50C carbon steel with strong bearing capacity. Slender core pins of water holes and ejection parts are made of SKD61 heat-resistant steel to reduce bending and fracture failure. All quenched mould parts need deep cryogenic stress relief treatment after heat treatment to stabilize steel property and prevent later deformation affecting product assembly accuracy.
Auxiliary Accessories Matching and Processing Key PointsCooling water channels adopt stainless steel pipelines to avoid pipeline rust and blockage, and high-temperature resistant sealing parts are used for waterway connection to ensure stable mould temperature circulation. Guide pillars and guide sleeves adopt high wear-resistant matching parts to keep mould closing precision and ensure consistent aperture concentricity of finished products. In the actual processing process, finish machining is carried out according to product 3D drawings, reasonable machining allowance is reserved, and deep hole drilling and wire cutting technology are adopted to complete the processing of internal water channels and slender hole positions, ensuring smooth inner wall without processing traces.
Cavity surface polishing shall be carried out in strict accordance with product appearance standards, and the polishing direction is consistent with the demoulding direction to prevent scratch marks on products during demoulding. Standard exhaust grooves are processed at material filling terminals and hole positions to effectively discharge cavity air and solve filling shortage and material burning problems. After all mechanical processing is completed, the overall assembly and trial mould debugging are carried out, and local mould modification is made aiming at shrinkage, deformation and unsmooth water outlet to compensate forming shrinkage and optimize product overall dimension.
Later Debugging and Daily MaintenanceAfter the trial mould is qualified, lubrication and overall anti-rust treatment shall be done for all moving parts before formal production. In daily production, timely clean plastic residues inside the cavity and waterway accumulated water to do a good job in anti-rust protection. Regularly check the deformation degree of slender core pins and the wear state of sealing positions, and replace vulnerable accessories in time to extend the overall service life of the mould. Select matched mould steel and formulate targeted maintenance schemes according to different forming raw materials, so as to keep the long-term stable forming state of the mould.
SummaryThe core of spray arm injection mould material selection is to select economical pre-hardened steel for conventional production and select anti-wear and anti-corrosion special steel for high-wear and high-standard working conditions. Combined with product use environment and production output, the steel type is reasonably selected, and heat treatment and precision mechanical processing are strictly implemented. By optimizing cooling layout, exhaust structure and assembly precision, the produced spray arm plastic parts have smooth water flow channels, stable high temperature resistance and qualified appearance, which can effectively reduce mould maintenance cost and fully meet the standardized production demand of household appliance industry.
