Web Exclusive - Intelligent hydraulics simplifies and smartens ...
Davis-Standard worked with Airline Hydraulics, who recommended the Rexroth intelligent system — specifically, four Rexroth HACD digital controllers, each one commanding a Rexroth CST4 hydraulic cylinder with a 3. The controllers also supply command signals to Rexroth 4WRPEH servo solenoid proportional valves that ensure smooth control of the up and down roll motion. Producing plastics for these applications requires precise control of the distance between rollers to control thickness, which is exactly what Davis-Standard wanted to provide: precise gap settings that can be changed in a matter of seconds. Hands-free gap control has substantial advantages over mechanical gap control found on traditional rollstack machines. The key to the XP Express hands-free system is electronic control of the hydraulic cylinders that actuate the chill rollers, including digital position feedback to monitor cylinder positioning at any time. To help users become more flexible in their manufacturing, Davis-Standard addressed these challenges on its XP Express roll stand system using Rexroth industrial hydraulics components to provide the intelligent control that allows users hands-free... Airline and Rexroth provided an alternate system solution to replace Davis-Standard’s existing hydraulic “hands-free” gap control system for the plastics extrusion industry. Rexroth servo valves and pressure transducers come fully assembled on the hydraulic cylinders and require no assembly time. Traditional gap setting and control methods are based on mechanical devices such as lever arms and pancake cylinders which are nudged to the desired position according to the given product on the production line. In plastics production, a rollstack machine draws raw polymer material between heavy rollers, which cools the material and gives the plastic sheet its desired surface finish and thickness. The rails are 35 to 45 mm wide and range in length from 396 to 575 mm. Airline recommended Rexroth linear motion components because they were the ideal choice for translating electronic precision into accurate mechanical motion. bore and a stroke between 5 and 12 in. There are two hydraulic cylinders per roller (one at each end) with each cylinder controlled independently. “We recognized that we could design a machine that would let electronic signals and transducers, not mechanical parts, control the gap settings and force. “The gap setting is the key to producing the finish customers want for their plastics products,” said Larry Mellow, project manager at Davis-Standard. Once set, the gap can also be difficult to monitor using traditional feedback methods because machine frames can flex under heavy loads, causing slight discrepancies in positioning. Airline Hydraulics also specified Rexroth mechanical components in the form of linear guide rails for carrying the bearing blocks associated with the rollers. , Bensalem, Pa. , Davis-Standard now provides advanced precise gap control technology. , builds equipment for the plastics industry and has a long history of producing quality machines for foam, flexible, and rigid sheet plastics extrusion. The HACD controllers communicate digitally to a third-party PLC via DeviceNet or Profibus and receive signals from both digital SSI linear position feedback and analog pressure transducers. 008 to more than 1 in. , depending on the application, which often include pharmaceutical containers, consumer products packaging, arts and crafts products, film, and much more....