Mold Surface Rust (Damage)

In the rotational molding production process, the product exhibits the quality defect of 「Mold Surface Rust (Damage)」. The specific manifestation is that mold surface rust or damage affects the product appearance. This defect is relatively common when processing powder materials such as LLDPE, HDPE, PVC, and PA, and its occurrence conditions are usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness. When the Mold Surface Rust (Damage) situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, and mechanical properties, which not only reduces the product's use functionality and safety, but also directly increases the scrap rate and production cost. Therefore, this problem needs to be systematically diagnosed and optimized from multiple dimensions such as material selection, the rotational molding machine, the heating oven, the rotating arm, the cooling station status, and heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness.

1. Mold material not corrosion-resistant. The mold is the core tool that gives the product its shape and surface quality. Unreasonable mold design, such as improper runner/gate dimensions, insufficient venting, and insufficient demolding draft angle, will directly lead to molding defects. The machining accuracy, surface treatment quality, and daily maintenance status of the mold also directly affect product quality. 2. Wear from long-term use. Mechanical wear and loosening during long-term equipment operation will lead to gap changes, accuracy reduction, and unstable operation, thereby causing various process and quality problems. Establishing a regular detection and preventive maintenance system for equipment operating status, and timely repairing or replacing worn parts, is a necessary measure to maintain equipment accuracy and process stability. 3. Humid storage environment. Moisture is one of the variables that need to be controlled with emphasis in plastic processing. Moisture in hygroscopic resin evaporates rapidly during high-temperature melting to produce bubbles and silver streaks, and can also trigger hydrolysis reactions leading to molecular weight reduction. Adequate drying treatment and strict moisture-regain prevention management are the basic prerequisites for ensuring melt quality. In terms of equipment maintenance, the regular overhaul and accuracy confirmation of the rotational molding machine, heating oven, rotating arm, and cooling station are not in place, causing the actual operating parameters of the equipment to deviate from process requirements, which will also become a potential inducement of the Mold Surface Rust (Damage) problem.

1. Use stainless steel or nickel-plated molds. Before introducing new tools, new materials, or new methods, adequate applicability evaluation and small-batch verification should be carried out. It is recommended to first conduct offline tests or simulation analysis outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety. Make good change management records to facilitate subsequent traceability and experience accumulation. 2. Regular maintenance and polishing. Polishing operations should proceed step by step from coarse to fine, and the grinding direction should be changed each time a finer abrasive is used to eliminate the texture marks from the previous pass. The final surface roughness should be tested with a roughness meter to confirm it meets the standard. After polishing, thoroughly clean to remove abrasive and grinding agent residues to prevent them from entering the melt and contaminating the product. 3. Improve storage conditions. Optimization work needs to be based on accurate diagnosis of the root cause of the problem, and blind attempts should be avoided. It is recommended to first determine the key influencing factors and their interactions through process DOE test methods or historical production data analysis, and then carry out targeted parameter optimization and structural improvement to achieve twice the result with half the effort. In terms of material management, incoming inspection of raw materials and in-process inspection of work-in-progress products should be strengthened, and the key performance indicators of powder materials such as LLDPE, HDPE, PVC, and PA should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the 「Mold Surface Rust (Damage)」 problem can be attributed to the combined effects of multiple factors such as mold material not being corrosion-resistant and wear from long-term use. To solve this problem, it is necessary to start from aspects such as using stainless steel or nickel-plated molds and regular maintenance and polishing and take systematic treatment measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, and achieve stable production and continuous improvement through powder melting uniformity and product wall thickness control.