Sprue with large mixing chamber for multicomponent plastics - has annular inlet slots for components and positive expulsion of mixt

摘要

A sprue unit for the injection, into a mould, of a plastics mixt. of liq. components, esp. cell-forming plastics, comprises a mixing chamber of annular cross-section with annular slot-shaped feed nozzles for the individual components leading into this annular chamber from its outer and inner annular surfaces. After the mixt. has reacted and filled the mould space, the remaining mixt. within the chamber is expelled into the mould. Pref., the chamber is a cylindrical space bounded by stationary outer and inner walls, and having an annular piston sliding axially in it; the piston, as it moves forward and expels the residual material into the mould, also obturates the annular nozzles for the components. The annular chamber may be a frustoconical space having its narrow end towards the mould, the outer face in this case being formed of a stationary component of the sprue unit and the inner face by an axially sliding piston which, in the closed posn., obturates the outlets of the component feed nozzles and, in the open posn., beings them into alignment opposite one another. The wide end of the frustoconical mixing chamber may be towards the mould. Large quantities of materials can be mixed intensively at high speedf the mixing chamber is completely emptied after the mould has been filled by the positive displacement action of the piston, so that no residual plug of material remains.