Conductivity sensing ensures consistent rubber product quality while reducing costs.

The Foxboro Measurements & Instruments Division of Invensys has provided a solution for Calzin's sticky rubber situation. Calzin, an international supplier of coatings for the rubber industry, now offers Foxboro conductivity sensing technology as part of a measurement system that is said to help ensure that customers get consistent product quality, as well as reducing their labor and materials costs.

Without a properly mixed antitack additive, rubber production can indeed be a sticky situation. Too little calcium stearate powder, the main ingredient of the antitack liquid additive, and rubber sheets could adhere to each other, creating costly rework to bring them back into specification. Too much calcium stearate and sheets could slide off of pallets and end up in the scrap pile. Despite the fact that variations in the mixture have tremendous implications for labor and material costs, as well as product quality, rubber producers have relied on human judgement to develop antitack mixtures that work for their products.

Recently, however, Calzin has produced a measuring system that enables its customers to determine the exact proportions of calcium stearate concentrate and water for their application. Calzin ships the calcium stearate to customers as a concentrated dispersion, and they in turn dilute it with water for use as needed. Through what has largely been trial and error, customer technicians adjust the flow of water into the premix concentrate until they feel it has the right consistency.

"This is far from an exact science. There's a fine line between hitting or missing the proper ratio," according to Jeff Blanchard, vice president of Calzin. "For instance, if your target is a mixture of 3% solids, a 2% mixture will result in the rubber sticking to itself and may require rework. A 4% ratio can cause rubber sheets to slide off of pallets and possibly result in scrap. Worse yet, the excess can become airborne, resulting in severe dust problems that endanger workers," said Blanchard.

Seeking to help customers make more effective use of his product, Blanchard set out to develop an automated mixing system to remove the guess work and help his customers achieve consistent and repeatable release agent mixes. Figuring that determining the exact percent of solids ratio in the solution would provide a much more accurate and consistent solution, he hypothesized that conductivity sensing could deliver that information. His internet search for authorities on the subject led him to the Foxboro Measurements & Instruments Division of Invensys Process Systems. After preliminary discussions about his application, Blanchard met with Foxboro process measurement experts who demonstrated an electrodeless conductivity system with which he could measure and maintain percent solids ratios with high accuracy. "The Foxboro solution measures and maintains a predetermined percent solids ratio based on conductivity, which assures accurate batch composition every time," said Blanchard.

The Foxboro system consists of a conductivity analyzer with a tailored custom curve set, and an electrodeless conductivity sensor. The sensor measures the conductivity and sends a reading to the analyzer. From there, the software triggers alarms when conductivity setpoints are reached, which control a series of valves and pumps that supply the Calzin concentrate and water in proportion to maintain a predetermined target conductivity setting.

"The key was converting conductivity measurements into discemible information that technicians could understand. Through trial and error, a percent ratio chart was developed as a guide for determining percent solids at different temperatures," said Blanchard. "Conductivity is not the easiest thing to work with. It can be very temperamental. But Foxboro supplied a complete solution, including technical support that made it possible."

By automating the release agent mixing process, Calzin has improved the use of its additives, while assisting customers in reducing labor and material costs. "The most significant benefit for our customers is ease of use of our agents," said Blanchard.

The automated system also is said to reduce labor and material costs for customers. "In some cases, there have been as many as six people checking and adding to the release agent mixtures. Our system totally eliminates the 'too-many-cooks' problems through automation," he added.

J. Kevin Quackenbush

Invensys Process Systems