EVA Injection Machine for High-Performance Molding | Zhenli

An EVA (Ethylene Vinyl Acetate) injection machine is specifically configured to process this unique copolymer known for its high flexibility, excellent clarity, and strong adhesive properties. The key challenge in processing EVA is its high vinyl acetate (VA) content, which can range from 5% to 40%, making it very soft, prone to sticking, and susceptible to thermal degradation at standard processing temperatures. Therefore, the machine requires a screw with a deep cut, low compression ratio (typically around 2:1) to gently plasticize the material without generating excessive shear heat. The barrel temperature profile is carefully managed, usually staying in a lower range of 130°C to 200°C, depending on the VA content, to prevent scorching and the release of acetic acid, which can be corrosive. A free flow nozzle is often used to prevent material hang up and drool. Given EVA's stickiness, mold release can be an issue, necessitating the use of specialized mold coatings and sometimes external release agents. The clamping unit must be sufficiently powerful to handle potential flash due to the material's low viscosity. EVA injection machines are crucial for producing a wide array of products, including sports shoe midsoles, foam sandals, toy parts, and medical padding. For these applications, the machine might be integrated with a chemical foaming agent (CFA) or physical foaming agent (PFA) system to create microcellular structures, requiring precise control over injection speed and pressure to achieve uniform cell size and density. When selecting an EVA injection machine, considerations include the material's specific melt flow index (MFI), the need for corrosion resistant materials in the barrel and screw for certain grades, and the machine's capability to maintain stable, low temperature processing conditions to ensure the final product's elastic and tactile properties.