Retrofits Relieve Competitive Pressure

Just ask Davis-Standard LLC, a builder of blow-molding machinery in Somerville, N.J. Some of its customers had asked the builder to upgrade the 20-year-old, multimillion-dollar winders at the end of their blow-molding lines. These customers wanted to wind very thin films of Mylar and other difficult-to-wind materials onto rolls.|The problem was that the material would tend to fuse and buckle when too much pressure was applied during winding. The system’s frequency response to the feedback from the load cell measuring the pressure was simply too slow for handling these materials. To avoid waste, the winder had to either roll slower or run at lower pressure, which lowered the density of the final roll beyond acceptable limits.The control loop needed a faster response if it was going to coordinate the rolling action with the speed at which the molding line was feeding the blown material. Because the job would entail more than simply replacing the old analog controller with a newer digital one, the builder consulted with control experts at automation supplier Bosch Rexroth Corp., of Hoffman Estates, Ill. The Bosch engineers would need to compensate for the machine’s poor frequency response, add two pressure transducers, and update valves and other hydraulic components.The new Bosch HACD digital controller can accommodate both analog and digital signals, as well as serial synchronous interface inputs and a number of buses. “So the controller lends itself very easily to communicate with different machine controllers without the complexities of proprietary communications and handshaking that a lot of machine controllers used to use,” says Rick Garcia, applications engineer in the Plastics Group at Bosch Rexroth.The greater resolution generated by the upgrade allows the machine to maintain pressure on the roll within 0.1 pound per linear inch, which is an order of magnitude better than before. The blown-film manufacturers buying this retrofit package are getting as much as a third more material on a roll. So rather than ripping out their old winders and spending between $1 million and $3 million for each new one, they can bring their 20-year-old machines up to modern specifications for less than $30,000. To read the entire article, "Don't Rip Out Your Old Automation Just Yet", go to www.automationworld.com/feature-4347