Mixing heads for polyurethane foam - have rapid operation by spring-loaded needle valve for each liq. which only opens while liq. is sufficiently pressurised for injection

摘要

A liquid circulation block for mixing heads, and partic. those with parallel jets in polyurethane foam appts. has a circulation nozzle with needle which closes against a seating in a flow bore; this needle has an annular surface exposed to the pressure of the liquid to open the nozzle and is spring-loaded in the direction of closure. ADVANTAGE - The design eases the normal problems of severe pressure drop after each injection, corresp. need for renewed pressure build-up and hence long cycle time and low output rate. In partic. the pressure only drops to e.g. 30-40 bars.