Reaction mixt. esp. for polyurethane - produced in chamber with cleaning piston, executes several strokes at specific intervals before next cycle starts

摘要

A method of producing a reaction mixt. from two or more flowable reaction components, for use in the prodn. of either solid or foamed prods., is carried out as follows. The components are continuously introduced for a predetermined period into a mixing chamber of a mixing head and are mixed together here; the reaction mixt. is discharged from the mixing chamber and the residue of material is expelled from the chamber by a piston which sweeps through it to clean the walls. After a predetermined interval, the piston executes one or more repeated cleaning strokes. Pref. a number of strokes may be carried out in succession; or a no. of strokes carried out at predetermined intervals; or immediately successive strokes amy alternate with strokes at predetermined intervals. Esp. used for the prodn. of polyurethane. The additional stroke or strokes of the piston remove the film which has partly formed after the first stroke of the piston was executed. It is this film which can cause great trouble during the next cycle by initiating a reaction and consequently blocking the discharge duct. The interval is predetermined to suit the reaction time of the film and should be such that the film has not completely hardened.