Valve arrangement for controlling the dosage of fluid additives into a plastic melt

摘要

Additives are fed from pressurized vessel (7) by piston (D1) to extruder (E1). The reciprocating motion of extruder screw (1) is linked (3) to the motion of piston (D1). Flow is controlled by two valves (K1, K2) timed to fill the dosing cylinder (DZ) on the backward stroke and directing the flow to feed line (14) on return stroke. The valves are driven by externally controlled pneumatic actuators. Independent claims are also included for the following: (1) process of timing the valves so that additive fills the dosing cylinder (DZ) during the backward stroke of the screw (1) and piston (D1) and then directing the flow to the feed line (14) on the forward stroke while preventing return flow to the additive vessel (7); (2) valve arrangement where the additive can recirculate between the vessel (7) and the valve (K1) in an additional circuit; and (3) process of returning excess additive to the vessel (7) during filling of the dosing cylinder (DZ).