Liquid feeding control method

Abstract

Liquid reaction molding (LRM) shot size and ratio control is achieved using a programmable controller (microprocessor) to select on a first-come-first-served basis one mold from among several and to manipulate a plunger metering pump system by retracting each of a pair of pump plungers to the same position each time the system is reset and to decompress or reduce pressures after injection. Each and every shot is started from this uniform reset position. Later steps in the sequence are: taking the hydraulic slack out of each pump system by prepressurizing which is done by advancing each plunger from said position independently until each and all liquid systems reach a threshold pressure (which pressure may differ from one liquid system to the other), feeding the shot size or quantity of each liquid (i.e. injection) by advancing the plunger a predetermined amount (or stroke) from the place it arrives upon reaching the threshold pressure, and to decompress by reversing plunger movement after injection but before any valve manipulations occur. Ratio control is exercised by slaving one plunger to another plunger during injection. The position of the pump plungers where the threshold pressures are reached is called a 'floating zero.' A satellite LRM system has a single shot size control and feeding system (as above) furnishing reagents to one of several molds connected to it in response to a first-come-first-served selection program in the controller. The above uniform reset feature permits faster response to a request for a shot.