Improving Energy Efficiency and ROI for Forge Presses
Creating 7 million lb of pressure to bear on heated metal billets is noisy and hot. For the customer, powerful hydraulic pressure comes with high electrical energy cost and wear and tear on expensive hydraulic pumps and other moving parts.
ERIE Press Systems, incorporated in 1895, became a leading forging hammer manufacturer. ERIE continued to expand as it introduced mechanical presses in the early 1900s for the burgeoning automotive and other heavy manufacturing industries. Growth was further complemented with the development of hydraulic presses and machinery for other forging and forming applications for ferrous and nonferrous metals, as well as composites. For more than 100 years, ERIE Press has been a leading supplier of custom-engineered presses and machinery, designing and building rugged, user-friendly, highly efficient, safe, reliable, and long-lasting machines.
Energy-Use Challenge
In 2012, McInnes Rolled Rings decided to expand their ring rolling capacity and invest in a new forge press: a 3,500-ton Ring Preform press. The company's seamless rolled rings range from 4 to 144 in. in diameter, using carbon, alloy, and stainless steel. The rings commonly are used as bearings or gears in large industrial machines, like drills, cranes, turbines and mining equipment, or as flanges and seals in pipelines and other high-pressure vessels.
McInnes Rolled Rings wanted its new, three-story hydraulic press to consume less energy than its predecessors. Traditionally, presses use electric motor control to rotate the hydraulic pumps at the nameplate revolutions per minute (rpm) whenever a machine is on, even if the press is in idle - wasting energy, and increasing wear and tear on a machine.
Other types of machines typically use drives to cut the power when it is not needed. But machines the size of the ERIE presses - many weighing millions of pounds - have long been considered too large to cost effectively install variable frequency drives (VFD). Without drives, conventional press operators have the option to turn the motors off during idle periods in an attempt to limit energy use. Unfortunately, restarting the motor with a full voltage starter negates any energy saved, since a motor typically draws five times the motor's full load amperes (fla) during startup. This method also shortens the life of the motor due to the motor-generated heat from multiple restarts.
"Think of it like a car. Slamming your foot on the gas, going from zero to 60 as fast as possible, requires a lot of fuel -much more than starting at 5 mph and gradually speeding up to 60," said Bill Goodwin, sales manager for ERIE Press. "Hard stops and starts are also hard on the hydraulics, leading to more maintenance and potential breakdowns."
With the need for energy efficiency and a desire for improved machine diagnostics, ERIE sought a new control solution for the McInnes Rolled Rings press - a control that is precise yet fast and efficient. They found that solution with Rockwell Automation.
Collaborating for Solutions
"Both ERIE Press and McInnes Rolled Rings had a long history of working with Rockwell Automation," Goodwin said. "The collaborative capacities and fully integrated components convinced us that Rockwell Automation was the right partner for this project."
For the first time, ERIE designed a drive system into one of its presses. Based on an Allen-Bradley? PowerFlex? 755 VFD from Rockwell Automation, the system has a power range that extends up to 2,400 hp. Provided and configured by a Rockwell Automation Local Support Center, the system controls the frequency of electrical power supplied to the motor, thus adjusting the motor speed to match the press cycle requirements, including allowing it to idle between press cycles.
The hydraulic power unit consisted of eight 300 hp motors driving four 118 gpm fixed-volume pumps and four 118 gpm variable-volume pumps. The requirements of this forging press are to form the billet as quickly and accurately as possible, and then reverse quickly to reduce billet heat loss during die contact time. With the addition of the VFDs, the press performed this task admirably.
When a pressing cycle is initiated, all eight VFD-controlled motors accelerate the pumps to 1,800 rpm, outputting maximum flow. As the press closes to the programmed target position, the output of the four fixed-volume pumps is reduced by lowering the motor speed as the press nears the target position. The four variable-volume pumps remain in the cycle longer because their output can be reduced through the motor speed and the electronic volume control.
The ability to reduce the motor speed by using VFDs, along with the electronic volume control, allows the variable-volume pump's output to be reduced much faster than the traditional 350 ms required if the pump rpm remains constant. Typically, metering large volumes of oil proportionally with a fixed-speed motor requires expensive electronic-controlled variable-volume pumps (with a limited response time) or costly large-flow proportional cartridge valves.
All eight pumps are employed during the forging cycle. When the press reaches the target position, it opens using only four pumps. Implementation of the VFDs allows the controller to shut down four of the pumps when they are not needed during the cycle. After the forging is completed, the remaining four motors can go into idle mode until the next billet is loaded into the press.
In the past, ERIE would employ multiple safety relays and input/output channels to communicate the machine's status with the process controller. Now, an Allen-Bradley GuardLogix? controller helps simplify this process by linking the safety circuit directly to the machine control process. This allows the safety I/O modules to be placed near the safety devices, reducing excessive wiring, and improving system debugging and commissioning times.
To further ease the operating, monitoring, and maintaining of the McInnes Rolled Rings machine, ERIE installed an Allen-Bradley PanelView? Plus 6 15-in. touchscreen at the press operator's pulpit and an industrial computer running the FactoryTalk? View SE human machine interface software. These HMI interfaces provide users with a "window" into the press through extensive on-screen diagnostics, animated hydraulic schematics, "pass/fail" status indicators that show press startup progress, and error messaging and logging.
Electrical and hydraulic schematics, as well as operator and maintenance manuals, are readily accessible on-screen in PDF form. Operators and maintenance personnel then have the necessary documentation to troubleshoot critical components without ever leaving the machine, reducing downtime.
A virtual private network (VPN) connection point is installed in the control enclosure of each machine. This point links to authorized computers across the world, enabling customers to monitor their machine without being in the factory. This also allows customers to remotely share their machine interfaces with ERIE personnel, who can assist them with their maintenance challenges.
Through the use of EtherNet/IP,? the control system has improved access to production data, reduced machine wiring, and improved the functionality, flexibility, visibility, and diagnostic capabilities of the safety devices. The safety features integral to the PowerFlex 755 VFD remove rotational power to the motor without removing power to the drive - ensuring that there are no unintentional startups. Employees within the McInnes Rolled Rings plant - from the plant floor to the corporate level - can view communication between the industrial control system and the machine on the HMI.
Getting the Right Results
Thanks to the upgraded solution, the new ring preform press has met all of McInnes Rolled Rings' requirements, including higher throughput, simplified commissioning, easier maintenance, and less noise.
In terms of operational savings, the new machines use about 30% less energy than conventional presses. The PowerFlex 755 drive also reduced the need for variable volume pumps, allowing ERIE Press to select fixed-volume pumps for projects, which are 35 to 40% less expensive. Considering that this particular press utilized four large fixed-volume pumps, the savings were significant.
In addition, the drives allow hydraulic pumps to run below 1,800 rpm. This not only saves energy, but reduces pump noise and heat, lessening the need for sound protection and cooling capacity for the hydraulic fluid. Since pump life is largely based on the number of rotations, reducing the speed of the pumps and shutting them down during idle periods increases their life by reducing wear and tear on the pump rotary group.
"The drive, controller, and other components from Rockwell Automation were critical in meeting the needs of our customer," Goodwin said. "Equally important was the collaboration we received from the people at Rockwell Automation. They did for us what we try to do for our customers - develop a unique solution by innovating together."
Based on the application knowledge gained on this project, ERIE has begun applying VFDs to other press applications. One is a powdered metal compaction press, where motor speed is reduced to 600 rpm during the necessary long-dwell pressure. This results in energy savings and, most notably, a sizeable reduction in the pump noise level. Another application uses VFDs to drive electronically controlled variable-volume pumps on a press that require a wide range of precise velocity control down to 0.0005 in. IPS.
"Thanks to the PowerFlex drive's ability to manipulate the speed of the motor, our pumps are always in the sweet spot, operating at maximum efficiency," Goodwin said. "They never apply too much flow or too little flow - it's always in the perfect control range for the pump electronics to maintain accurate velocity control."
