During the high-temperature, high-pressure foaming process, how can the shoe mold surface resist material penetration and chemical corrosion to avoid "mold burn"?
Publish Time: 2025-09-16
In the manufacturing of athletic shoes, casual shoes, and functional shoe soles, foaming is a critical step in determining product performance and appearance. Polymer materials such as EVA, PU, or TPU are injected into a sealed shoe mold under high temperature and pressure, undergoing complex physical and chemical changes including melting, cross-linking, foaming, and cooling to set the mold. During this process, the shoe mold surface is subjected to extreme thermal stress, mechanical compression, and chemical attack. In particular, fine textured areas such as "popcorn" patterns, with their dense bumps and tiny gaps, are highly susceptible to material penetration and residue. If the shoe mold surface is not adequately protected, mold burn can occur—polymer decomposition products, additive residues, or carbonized materials adhere to the mold cavity, gradually accumulating to form stubborn dirt. This can lead to mold release difficulties, blurred textures, surface defects, and even scratches on the finished product. Therefore, maintaining a clean and stable shoe mold surface in this harsh environment is a key issue for ensuring production efficiency and consistent quality.The root cause of mold fuzziness lies in the long-term interaction between the material and the metal. Foaming raw materials often contain additives such as blowing agents, crosslinkers, lubricants, and antioxidants. At high temperatures, some components may decompose or migrate, chemically reacting with the shoe mold surface. Certain low-molecular-weight components, under high pressure, penetrate metal pores or scratches, solidifying after cooling and becoming difficult to remove. Furthermore, frequent thermal cycling causes shoe mold steel to undergo repeated expansion and contraction, gradually fatigue the surface microstructure, forming microcracks and further exacerbating material embedment. Once initial residue forms, it continuously absorbs new material during subsequent production, creating a vicious cycle that ultimately affects heat transfer efficiency and mold release performance.To address this challenge, the material selection and treatment of the shoe mold surface are crucial. High-quality shoe mold steel inherently possesses high density and purity, reducing internal porosity and impurities, thereby mitigating the risk of penetration at the source. Furthermore, heat treatment enhances the steel's overall hardness and wear resistance, ensuring it maintains shape stability under long-term friction and compression. More importantly, the application of surface enhancement technology creates a robust protective barrier.Coating technology is a common protective measure. Hard chrome plating is widely used for shoe mold surface treatment due to its high hardness, low friction coefficient, and excellent corrosion resistance. It not only seals the steel's micropores but also provides a smooth, non-stick surface, making it difficult for foaming materials to adhere. Modern processes are also increasingly employing more advanced coatings such as PVD (physical vapor deposition) or DLC (diamond-like carbon). Their nano-scale, dense structure further enhances resistance to penetration and chemical attack while maintaining excellent mold release properties.In addition to passive protection, shoe mold design itself also contributes to preventing mold sticking. A well-designed exhaust system is crucial. During the foaming process, trapped air and volatile gases in the mold cavity, if not promptly exhausted, can create localized high-temperature and high-pressure zones, accelerating material decomposition. Micro-venting slots or breathable steel areas at strategic locations ensure smooth gas escape and reduce the risk of carbonization. Furthermore, optimized shoe mold cooling water channel design ensures uniform and stable mold temperature, preventing localized overheating that can cause material charring.Daily maintenance is also essential. A well-defined cleaning cycle and appropriate cleaning agents can promptly remove initial residue and prevent accumulation. Some automated production lines are equipped with online mold cleaning systems that utilize microparticle spraying or chemical atomization to clean the gap between mold openings, maintaining a long-term clean mold surface.Ultimately, combating mold burnout isn't a single technological achievement; it's a systematic process encompassing materials, processes, design, and maintenance. This requires shoe molds to be not only molding tools but also precision supports capable of withstanding both chemical and thermodynamic challenges. When each pair of soles emerges flawlessly from the shoe mold, with crisp textures and a smooth surface, it's this invisible protective system that silently safeguards, ensuring every mold is as precise as the first.
