Thermoplastic foam injection moulding ejected rapidly - after local cooling to harden ejector thrust region of moulding

摘要

The mould (after completion of injection) is initially opened a distance of a few millimetres and the moulding is subjected to local blasts of coolant in the region of the ejectors only. This causes local hardening; the mould is then immediately opened to its full extent and the ejectors expel the moulding. Several coolant blasts may be applied in succession, causing the coolant to spread between the surface of the moulding and the mould. Pref. coolants are liquefied gas, water or steam. Water may be introduced after the first coolant, to glaze the surface of the moulding. Coolant, or an additional fluid may be used to eject the moulding. Used for foam mouldings which are porous throughout, with reduced porosity near the surface, or for those with a porous core and a closed surface. Local cooling provides quickly attained local strength, permitting ejection without waiting for more extensive cooling of the moulding or mould.