Injection molded breathable steel properties
Injection molding breathable steel is a new mold material. Its unique porous structure and excellent breathability make it a key component in solving injection mold venting issues. It is widely used in the production of precision injection molding and complex plastic parts. Breathable steel, primarily composed of stainless steel, is manufactured through a specialized powder metallurgy process. Its interior is densely packed with interconnected micropores, typically ranging in diameter from 1 to 10 μm and boasting a porosity of 20% to 30%. These micropores form efficient venting channels. As the melt fills the mold cavity, trapped gas is rapidly expelled through the micropores, preventing defects such as burnt plastic surfaces, material shortages, and bubbles caused by trapped air. This reduces injection pressure and clamping force, extending mold life.
Injection molding breathable steel offers excellent air permeability and mechanical properties, meeting mold requirements. Its air permeability, measured as the gas transmission rate under a given pressure, typically reaches 0.5-5 L/(cm²・min) , significantly exceeding the efficiency of traditional venting slots. This makes it particularly suitable for molds with complex, deep cavities, thin walls, and other areas where venting slots are difficult to install. Furthermore, breathable steel boasts mechanical properties similar to those of ordinary mold steel, with a hardness of HRC30-45 and high compressive strength, enabling it to withstand the high pressure and impact of the injection molding process without deformation or damage. Furthermore, breathable steel exhibits excellent wear and corrosion resistance, and its surface can be polished to a high finish, ensuring the surface quality of the molded part. This makes it suitable for the production of high-precision, aesthetically pleasing parts, such as optical lenses and electronic connectors.
The processing properties of injection-molded breathable steel are unique, requiring specialized machining methods to ensure optimal performance. Due to the numerous micropores within breathable steel, traditional machining methods can clog the pores or damage the porous structure. Therefore, sharp cutting tools should be used, along with low cutting speeds and feed rates, to prevent excessive heat from clogging the pores. Specialized drill bits and taps should be used for drilling and tapping to ensure smooth hole walls and protect the surrounding microporous structure. Grinding should be performed using a fine-grained grinding wheel and adequately cooled wet grinding to prevent surface oxidation or pore clogging caused by grinding heat. After processing, the breathable steel must be cleaned to remove any residual debris and oil from the process. Ultrasonic cleaning is typically used to ensure unobstructed micropores and maintain breathability.
The use of breathable steel in injection molding molds requires rational design and installation to fully realize its venting effect. Breathable steel is typically used in gas-trapping areas of the mold cavity, such as the bottom of deep cavities, where ribs meet, and near the gate. Based on the cavity structure, the breathable steel is fabricated into inserts and embedded into the corresponding locations in the mold. The insert should fit tightly within the mold body to prevent melt from escaping through the gap. At the same time, an exhaust duct should be provided on the back of the breathable steel insert to direct the gas that has passed through the steel out of the mold. When designing the size of the breathable steel insert, its area and thickness should be determined based on the degree of air entrapment. Generally, the thickness should be kept to a minimum, preferably 5-10mm, to ensure smooth gas evacuation. Furthermore, the surface of the breathable steel insert should be flush with the cavity surface to avoid marks on the surface of the plastic part caused by steps, which could affect the product’s appearance.
Injection molding vent steel requires key considerations for use and maintenance to extend its service life and maintain its breathability. Before injection molding, the micropores of the vent steel inserts should be inspected for unobstructed flow. This can be done by purging with compressed air or vacuuming. Any blockage should be promptly cleaned. During production, avoid using plastics containing fillers such as glass fiber and minerals, as these can easily clog the pores of the vent steel, reducing its breathability. For used vent steel with clogged pores, chemical cleaning or high-temperature calcination can be used. Chemical cleaning involves soaking with a specialized cleaning agent to remove the blockage. High-temperature calcination involves heating the vent steel to 400-500°C to burn and decompose organic residues within the pores. Furthermore, vent steel should be protected from prolonged exposure to humidity to prevent rust from clogging the pores. It should be treated with rust-proofing during storage. With proper use and maintenance, injection molding vent steel can maintain excellent breathability over time, providing a stable exhaust solution for injection molding production.
