Advanced Process Technology, Inc. (Middlesex, NJ) is a leading designer and manufacturer of high-performance metering, mixing and dispensing equipment for casting urethane, nylon, polyester, and other polymers and resins. For more than 30 years, APT machines have successfully met the most stringent requirements from customers in the sporting goods, automotive, and electronic industries. APT's SRD-6000 Series Continuous Rotary Gear Pump Systems provide customers with the flexibility to define all process variables involved in mixing polymers as recipes, plus the precise control of those variables to create consistent, part-to-part quality. Control Technology Corporation's automation controllers dynamically control the high-performance metering, mixing and dispensing on the SRD-6000 to prevent scrap urethane before it's made. CTC is APT's controller of choice because "they have good support," said John Phillips, Director of Technical Service at APT. "They're fast to respond." How fast? One Wednesday afternoon, APT discovered that they needed several parts from CTC to fulfill an order that had to ship out that Friday to the customer. "I called [CTC Customer Service Coordinator] Jan Swaine late that afternoon. She got the order together, overnighted it, and we were able to assemble, test and ship the machine by Friday. It was really a great turnaround."

Finding the Right Mix
During resin formation, liquid resin and hardener are dispensed from separate vacuum/pressure tanks, through separate metering pumps and into a mixing chamber. Inside the chamber, the two ingredients are agitated on-the-fly to form a homogenous stream of mixed material. A chemical reaction begins as the formulation is dispensed into molds, where it hardens into the finished product. The filled molds may be replaced manually or automatically.

To make resin that comes out right all the time, many process variables must be tightly controlled, including ratio of resin to hardener, vacuum, temperature, and output rate to the molds. Of these variables, one of the most critical is the resin-to-hardener ratio. Because resin production is a continuous-flow process, the only thing that pushes finished product from the mixer into the molds is the introduction of new ingredients from the ingredient pipelines to the mixer. Therefore, if the ratio of resin to hardener is not strictly maintained throughout the process, a lot of scrap may result. The SRD-6000 addresses this with a servo-based, ratio-controlled system for dispensing these two ingredients into the mixing chamber. In this system, two servo-powered pumps, a master pump for resin and a slave pump for hardener, are tightly coupled by the CTC controller. The CTC controller adjusts the slave pump's output to compensate for deviations in the master pump's output, so that while total output of the two pumps may vary slightly, the ratio between the two outputs remains constant. The customer has the option of adjusting the slave pump rate after each shot is completed, or on an automatic, continuous basis. The CTC controller can make up to hundreds of adjustments per second to the pump speed.

The CTC controller also maintains consistent product quality by maintaining temperature. Temperature control is a major factor in ensuring that the density, and therefore, the weight, of the ingredients flowing into the mixer are within specification. Temperature is also critical to maintaining a product viscosity that is conducive to mixing and molding the product. CTC also maintains vacuum, which, along with temperature, is an important step for eliminating bubbles and other defects in the finished product. For specialized applications where vacuum is essential during molding as well as mixing, molds may be placed in a vacuum chamber connected to the mixer, and pour nozzles with xyz mobility can locate the molds and dispense the resin into the molds.

Cooking by the Book
The CTC controller on the SRD-6000 lets customers define process variables from the CTC touchscreen panel and download them as recipes to the data table in the controller. Recipes may be selected by name or by the number for the part they create. Alternatively, process variables may be configured in a spreadsheet and downloaded directly to the data table from the spreadsheet. APT designed the user interface for the recipe builder with Quickstep™, Control Technology's programming language. "Quickstep is something I really like," said John. "We get more of our people to program with Quickstep than with other languages. And CTC's tech support group was a big help in making the transition from ladder logic." It's essential to APT's business to have a control program that many people within the company can understand and modify, because a lot of their business comes from customers who want to add new features to off-the-shelf equipment. With Quickstep, modifications to the core program installed on the product are fast to build and debug.

Using CTC software and hardware, the SRD-6000 enables APT customers to maximize quality and minimize scrap, with an easy-to-use touchscreen interface. Control Technology Corporation and Advanced Process Technology have molded a successful operation in the SRD-6000.