METHOD AND DEVICE FOR WEIGHING AND MIXING MULTICOMPONENT PLASTIC, PARTICULARLY, POLYURETHANE

摘要

A method and apparatus for metering and mixing multi-component plastics, in particular polyurethane, in which two or more hydraulic piston and cylinder units (A1 and A2) for each component, operate periodically by a balanced procedure. The pressure for the second piston and cylinder unit which takes over metering is equilibrated, before the beginning of the metering procedure, with the pressure of the first piston and cylinder unit which is in the process of metering. Switching from one piston and cylinder unit to the other (e.g. from A1 to A2) takes place in such a way that metering is taken over by the second piston and cylinder units at the same time as the first piston and cylinder unit is switched off. This is achieved by providing a pilot valve which has zero overlap and inevitably releases the component stream from the first piston and cylinder unit at the same time as the other piston and cylinder unit is switched off. Pressurization and pressure equilibration are effected by a hydraulic control apparatus which is incorporated in the hydraulic loop of the volume stream and automatically equilibrates the initial pressure with the metering pressure. This permits pressurization and pressure equilibration without additional parts in the component system.