To improve the service life of wood plastic composite material molds, it is necessary to establish a full chain technical system that runs through material foundation, process control, surface engineering, and operation and maintenance management. Especially in Linyi, Shandong, a WPC industry intensive area, practical experience has formed a replicable optimization path.
Collaborative strengthening of material matrix and heat treatment process
Using H13 hot work die steel as the substrate is a prerequisite for ensuring structural stability in high-temperature environments. The composite process of vacuum quenching and cryogenic treatment can significantly optimize the microstructure of materials: the vacuum environment avoids oxidation and decarburization, ensuring uniform distribution of hardness; Cryogenic treatment (-196 ℃ liquid nitrogen insulation for 2-4 hours) promotes the transformation of residual austenite into martensite, improving material toughness and thermal fatigue resistance. The mold treated in this way can extend its first service life by more than 30%, effectively suppressing early cracking caused by thermal cycling and laying a solid foundation for subsequent surface treatment.
Surface Strengthening: Differentiated Applications of Nitriding and Chromium Plating
Surface treatment is the core means to extend the service life of molds, and the appropriate solution should be selected according to the product characteristics:
Gas nitriding is suitable for extrusion molds of high fiber content (≥ 60%) WPC. Insulate in an ammonia atmosphere at 500-550 ℃ for 8-20 hours to form a 10-25 μ m nitride layer with a surface hardness of HV900-1100, significantly enhancing scratch resistance and anti sticking performance, reducing mechanical damage from wood powder to the mold cavity, and extending maintenance cycles by 2-3 times.
Electroplated hard chrome is more suitable for complex textured products, such as injection or compression molds that mimic wood grain or stone grain. After depositing a hard chromium layer of 15-30 μ m, the surface hardness exceeds HV800, with high wear resistance, low friction, and mirror finish, effectively preventing high-temperature adhesion between resin and fibers, making demolding smoother, and increasing the lifespan by 3-4 times, especially in PVC based systems.
Structural design: precise control of cooling and exhaust
The lifespan of the mold is affected by both thermal stress and gas retention, and the structural design must be refined
The conformal cooling water channel should penetrate the key area of the mold cavity, ensuring that the temperature gradient is controlled within 5 ℃/mm and the flow rate is maintained at 1.5-2.5m/s to avoid local overheating and thermal fatigue. The recommended diameter for the waterway is ≥ 8mm to prevent the accumulation of scale from affecting heat dissipation efficiency.
The micro exhaust groove should be set at the end of the melt, with a depth of 0.02-0.05mm, and equipped with a vacuum assisted exhaust system to completely eliminate trapped gases, prevent burning, bubbles, and internal stress concentration, and improve product consistency and mold durability.
Systematic execution of operational standards and maintenance management
70% of the mold life depends on the level of use and maintenance, and Linyi's high humidity climate requires strengthened anti rust management:
After each production is completed, oil-free compressed air must be used to thoroughly blow the flow channel, mold cavity, and cooling water circuit, remove residual wood powder and plastic debris, and prevent acidic degradation products from corroding the steel.
Immediately spray volatile anti rust oil (VCI type) after cleaning, with a focus on covering moving parts such as guide posts, sliders, and top pins; When the machine is shut down for a long time, it should be wrapped with anti rust film and stored in a dry environment with a humidity of ≤ 50%.
Perform endoscopic inspection every 50000 cycles, and use laser welding and precision polishing to repair micro cracks or minor strains in the mold cavity. It is strictly prohibited to use arc welding to avoid chain fracture caused by embrittlement in the heat affected zone.
Localization exploration and practice of cutting-edge technologies
Some leading enterprises in Linyi are introducing higher-level technologies to break through the bottleneck of lifespan:
PVD nano coating: Coatings such as chromium nitride (CrN) and diamond-like carbon (DLC) have a hardness of over HV2500 and a friction coefficient of less than 0.1. They have been piloted in high-end export markets, extending the lifespan of molds by 5-10 times and becoming a technical endorsement for EU green building projects.
UV curing surface coating: Jiangsu Zhongxin Home has achieved patented application, coating UV paint on the surface of finished products, indirectly reducing mold pollution frequency, reducing mold cleaning times, and extending effective working time.
Digital life tracking system: Chendong and other enterprises deploy sensor networks to real-time collect the number of cycles, temperature curves, and fault records of each mold, achieve predictive maintenance, reduce unplanned downtime, and promote the transformation of manufacturing towards intelligence.
Suggestions for selecting technical paths
In the local industrial context of Linyi, "nitriding treatment+standardized maintenance" is the most cost-effective combination solution, suitable for the vast majority of conventional products; If targeting the high-end market of the European Union or customized high-end projects, it is recommended to add PVD nano coating to achieve a qualitative leap from "durable" to "ultra durable", and build technical barriers and brand premiums.