Pneumatic demoulding for soft plastic injection molding
Pneumatic demolding for injection molding soft rubber is a highly efficient demolding method developed for soft plastic products (such as silicone, TPU, and EVA). It utilizes compressed air pressure to eject the soft rubber product from the mold cavity, avoiding the damage that traditional mechanical demolding can cause. Soft rubber products typically exhibit high elasticity and flexibility, making mechanical demolding prone to deformation and tearing. However, pneumatic demolding protects the integrity of the product through the uniform application of air pressure. For example, in the production of silicone sealing rings, pneumatic demolding can prevent scratches from mechanical ejectors, ensuring optimal sealing performance. After adopting this technology, one sealing manufacturer saw its product qualification rate increase from 85% to 99%.
The pneumatic demolding system for soft plastic injection molding primarily consists of an air source, an air pressure regulating valve, an air pipe, an air valve, and air ducts on the mold. The air source provides compressed air, the air pressure regulating valve controls the air pressure for demolding, and the air valve controls the flow of compressed air. The air ducts on the mold direct the compressed air between the mold cavity and the part, creating a pressure differential and enabling demolding. When designing the air ducts, it is important to ensure uniform distribution of the air ducts so that the air pressure is evenly applied to the part surface, avoiding deformation caused by excessive local pressure. For example, when producing large soft plastic toys, multiple air ducts are required on the mold to ensure consistent air pressure in every area. One toy factory has optimized its air duct design to keep the deformation of the toy within 0.5mm after demolding.
Air pressure is a key parameter influencing the effectiveness of pneumatic demolding for soft plastic injection molding. Too little pressure cannot overcome the friction between the product and the mold cavity, making demolding difficult. Too much pressure can cause the product to over-expand, resulting in deformation or bubbles. Different soft plastic materials and product structures require different demolding pressures. For example, silicone products typically require a demolding pressure of 0.3-0.5 MPa, while TPU products require a higher pressure of 0.5-0.8 MPa due to their greater adhesion to the mold cavity. An electronics factory initially used an air pressure of 0.4 MPa when producing TPU phone cases, which resulted in demolding difficulties. After adjusting the pressure to 0.6 MPa, demolding became smooth and the product remained deformed.
Controlling the timing of demolding is also crucial for pneumatic demolding of soft plastic injection molding. Demolding too early prevents the product from fully cooling and setting, making it susceptible to deformation under the action of air pressure. Demolding too late increases adhesion between the product and the mold cavity, making demolding more difficult. Excessive cooling can also cause shrinkage, affecting dimensional accuracy. Typically, demolding should be performed when the product has cooled to a certain strength while still retaining good elasticity. For example, when producing EVA insoles, pneumatic demolding is performed when the mold temperature drops to 60-70°C. This ensures smooth demolding of the insole while preventing deformation. After multiple trials, a shoe material factory determined the optimal demolding timing, which resulted in a 25% improvement in the dimensional pass rate of insoles.
Maintenance of pneumatic demolding systems for soft plastic injection molding is also crucial. Regular inspection of the air source’s cleanliness is crucial to prevent moisture and impurities in the compressed air from entering the airway, potentially blocking it or corroding the mold. The air pressure regulating valve and air valve must also be regularly checked to ensure they are accurately controlling air pressure and opening and closing. Furthermore, the mold’s airway requires regular cleaning to prevent soft plastic debris from clogging it and affecting demolding. A medical device manufacturer implemented a maintenance system that includes weekly airway cleaning and monthly inspections of pneumatic components, reducing the failure rate of the pneumatic demolding system by 40% and ensuring continuous production.
