Automatic process control for vacuum dispensing equipment

The electric equipment and electronics industries have been increasingly utilizing casting resins as substitutes for traditional insulating materials for years. The excellent insulating properties of vacuum-processed resins permits the manufacture of compact, light weight and maintenance-free products. Casting resins are used for potting, encapsulating, molding and for scaling of various types of components. The major types of curable casting resins include: epoxy, polyurethane, silicone and polyester. These materials generate no by-products and cure free of voids. Resin and hardener are prepared by stirring in separate vessels under vacuum and thermal influence. Materials are then pumped under vacuum in the desired mix ratio and filling volumes by internal metering pumps, through the static mixer directly into the molds which are positioned inside the vacuum casting chamber. During the process it is necessary to control process parameters such as pressures and temperatures. With synchronously driven and electronically controlled metering pumps, it is possible to have on-line control of the ratio between resin and hardener for each stroke of the metering pumps. This is accomplished by a comparison of pressures and times. In case of any deviation, the microprocessor gives an alarm and indicates the disturbances on the monitor with a written problem description. Therefore the system is not allowed to operate under wrong process conditions