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What Points Shall We Take an Note Regarding the Moulding of EVA Case Boxes?
The key to EVA case moulding lies in precisely matching the VA content to the required hardness, whilst strictly controlling the three factors of ‘temperature, pressure and time’ to prevent loss of elasticity caused by insufficient setting or excessive hardening.
Control of Key Process Parameters when EVA Case Shape
Temperature control: Cold pressing and baking typically require125°C–135°C, whilst hot-press moulding temperatures are usually within the160°C–200°C range; excessively high temperatures cause the product to become hard and lose elasticity, whilst excessively low temperatures result in poor plasticisation and inadequate setting.
Pressure setting: This must be adjusted according to wall thickness; generally, around50 kg/cm² is appropriate; excessive pressure inhibits foaming or causes over-densification, whilst insufficient pressure leads to dimensional instability, delamination or excessive flash.
Time Coordination: Following heating and softening, sufficient holding time is required to allow the material to fill the mould cavity and cure; for thick-walled parts, the holding time should be extended, followed by thorough cooling (usually by water cooling) before demoulding to prevent springback deformation.
Material selection: Select the VA content (typically 15%–28%) based on the load-bearing requirements of the product’s various sections; load-bearing areas require high hardness (e.g. Shore 60+), whilst non-load-bearing areas may have lower hardness; mismatches between hardness and structural requirements are strictly prohibited. Material and Mould Considerations
Raw Material Pre-treatment: EVA is highly hygroscopic and must be dried at 60°C–80°C for 2–4 hours prior to use to prevent moisture-induced bubbles, pitting or uneven foaming.
Mould Condition: Ensure the mould surface maintains a constant and uniform temperature and that the cooling channels are unobstructed; guide pins and bushings must be well-lubricated to avoid dimensional deviations in the product caused by deformation under stress or wear. Multi-layer lamination: Where a composite of fabric + EVA + lining is involved, the adhesive activation temperature and lamination pressure must be optimised simultaneously to prevent delamination or localised bubbling.
Avoiding Common Defects Failure to set shape: Manifested as sagging or springback; the main causes are low temperature, insufficient pressure or inadequate cooling.
Excessive Hardness and Brittle Cracking: Primarily caused by excessive temperature, excessive pressure or incorrect selection of VA content.
Surface Defects: Flow marks and air bubbles are often caused by raw materials not being fully cured, excessive injection or compression speeds, or uneven mould temperature. Before operation, it is essential to verify the stability of the equipment’s hydraulic system and safety devices; operation whilst the equipment is faulty is strictly prohibited. The first piece of each batch must undergo hardness, dimensional and impact resistance tests to verify the validity of the parameters.
