In the metals industry, converting lines change the size and shape of metal alloys strips, including copper. As the product moves through machines, speed must be carefully controlled. Depending on the process, product velocity on one end of the roll of metal can vary considerably from the other end.
One recent machine retrofit of machine and motion controls increased productivity 40% since project completion, according to the plant maintenance manager, with an increase in quality and less scrap and a return on investment in six months.
Challenge: Repairs, speed
An aging metal converting line was experiencing an unacceptable amount of downtime. An existing 20-year-old control system was obsolete and procuring replacement parts was becoming very difficult. The customer needed better reliability, less scrap metal waste, and higher productivity from the traverse winding equipment. The line’s traverse winding and slitting application used six controllers that had been retrofitted with programmable logic controllers (PLCs) in an earlier project. Before the upgrade, workers had no way to accurately control tension and motor speeds.
Tighter motion controls
The customer had a three-week time frame to complete the winding and slitting upgrade project.
The system integrator worked closely with the customer to coordinate the project installation, so inventory could be built up, and they could shut down the line with confidence. To take advantage of the advances in motion control technology, the new PLCs and previously retrofit sidewinders’ PLCs were reprogrammed.
Hydraulic cylinders were converted to ball screw linear actuators capable of accommodating heavy loads. Changing from a hydraulic system to electric actuators with a servo drive and motor allowed tighter control over traverse position requirements, accuracy, and repeatability beyond that of the older hydraulics, without risk of oil leaks or related regular hydraulic maintenance. The hydraulic power unit was continually on and using energy; in the new design, servos use power only when needed for traversing, for less energy consumption.
To house the new equipment, a custom mechanical design was created to pull out the hydraulic cylinders and put in the electric actuators. The linear actuator performed as required, providing thousands of pounds of thrust when interfaced with the EDC-installed traverse winder PLCs while maintaining the ability to produce repeatable, programmable motion.
The outdated control system was upgraded to another vendor’s PLC. For the operator interface, a touchscreen human-machine interface was installed. Variable speed drives were replaced with new drives. Eight vector drives were used to uncoil, slit, and recoil; six servo drives were used for traversing; new contactors and circuit breakers were installed for all controls.
Installation included electrical contracting to run the cables and wires, retrofitting of the hydraulic cylinders, and replacement of all panels within the enclosures.
Better controls: More output
The customer said results have been excellent with nearly double the output since the upgrade. Previously, higher running speeds were impossible because the operators were unable to adequately control the tension enough. With the new control system optimized, tensions were constant, making for a higher quality edge, energy savings, and reduced wear.
The average running speed prior to the upgrade was 350 feet per minute (fpm). After the upgrade, the customer regularly runs at 600 fpm, and the machine is can run up to 850 fpm on a 1-in. strip, an impressive response for a traverse winder.
Machine upgrade: Before and after
Before the upgrade, the operator had to ramp up the machine speed slowly and watch the tension carefully. The machine ran at lower speeds to avoid having the operator lose control and produce scrap instead of good product.
After the upgrade, the operator pushes a button and the machine automatically ramps up speed to 600 fpm while maintaining proper tension on all the dancers. Good slit quality is produced with consistent tension through the slitting section. When the roll needs to be changed, the machine stops precisely within a couple of wraps of the end of the reel, so waste is further reduced.
The more robust control system gives added benefits such as monitoring and diagnostics for easier troubleshooting. After six months, the metal company realized return on its investment
The project was completed in less than three weeks so the customer did not risk running out of inventory; the line restarted in two weeks, despite controls from three major vendors. The project included a documentation update.
By Chuck Dillard
Article originally appeared on Control Engineering Magazine