When planning to upgrade the control functions on its popular polyurethane resin dispensing equipment, Automatic Process Control (APC), based in Union, NJ, sought to increase the dispenser's functionality and precision, simplify operator interaction, and improve reliability and safety. The new controllers also had to integrate seamlessly into a machine already widely used and trusted in the polyurethane industry, with no inconsistencies in system behavior between newer-generation products and the company's sizable installed base. Market competition precluded any attempt to raise prices significantly.

To help execute this upgrade, APC turned to Bob Smith at Faber Motion Control, who selected Parker Hannifin controllers and associated automation.

The four-axis dispensing machine targeted by APC for the redesign provides metering, mixing, and dispensing of polyurethane resin. It can process reagent materials that are filled or unfilled, granular or chopped fiber, as well as hot melts and materials of high and low viscosity. The machine can handle up to four components and two color systems or two components and up to six color systems.

Several chemical streams are mixed in the dispensing machine, including a pre-polymer and a curative in the mix head, to create the final composition of the polyurethane for specific application. By adjusting weight ratios of the chemical streams, users can produce polymers that exhibit particular physical properties. APC chief engineer, Shawn Alexander, likens the process to creating a conventional two-part epoxy resin, although producing the polymer can involve four or five parts.

A typical APC manufacturing customer might use the dispenser system to make tires for forklifts or rollers for assembly lines. The manufacturer would load raw chemicals into pressurized tanks and use the APC dispensing equipment to meter the streams into the mix head before sending the resulting stream into a mold.

According to APC, the system's superior performance depends on close-tolerance component assemblies, a stable metering system, and an accurate temperature control system. Combined with flexible controls and a range of permitted material ratios, the dispenser can be used for long, continuous pour applications and small shots.

The upgrade project first examined the line of programmable linear controllers that APC used on the system. The controllers featured a gear-drive system and a drive shaft. Changing chemical stream concentrations to alter a plastic's hardness or color meant changing gears in pumps with internal stream temperatures of 120 °C. In such an environment, changeovers often took more than an hour.

Bottom line goals for APC's redesign of the dispensing system were to increase the machine's functionality and precision, simplify operator interaction, and improve reliability and safety. The upgrade also had to separate operators from the hot pump streams and reduce time required for changeovers.

When committing to this redesign, APC sought one vendor to supply a system—interface, controller modules with I/O connections, and servo motors—at a cost that would enable APC to work within marketplace constraints.

APC incorporated individual servo motors to drive precision metering pumps, replacing the common dc motor and drive shaft with an automated change-gear system. Individual motors allow infinite adjustment of pump-output ratios and increased dispensing accuracy. The new configuration includes a Parker 6K4 controller, SLVD servo drives, BE servo motors, and a PX10 workstation running Microsoft Windows-based InteractX human-machine interface software. APC's design for the new system houses the 6K4 controller servo drives, I/O connections, and machine-operator panel in a central unit.

According to APC, the biggest improvement in system performance is the reduction in time to change chemical compositions—from more than an hour to about 10 seconds. Operators can oversee and control everything from a touch-sensitive screen in a central location away from the pumps, increasing safety. Pump operation is automatic.

In addition to performing fine chemical-composition adjustments at the touch of a screen, the redesigned system can store all chemical recipes for specific plastics applications for easy retrieval, instead of requiring the manufacturer to record them manually. Large manufacturers may employ 50 to 100 recipes to accommodate all products. In the previous version of the system, each recipe required a separate gear combination and manual changeover. Tracking alternatives became a major headache for customers. The new, automated system inventories material consumption.

Changing reagents to begin producing a different polymer requires cleaning the reservoir that leads into the mix head. The old design demanded that an operator step in and physically flush the reservoir. Now a computer command initiates the purge, calling for injection of an appropriate solvent into the mix head. The operator can specify how long to maintain the purge to ensure a complete cleaning.