The project followed an energy appraisal by AAR Powerdrives at Voestalpine Metsec's Oldbury plant, aimed at identifying applications that could benefit from VSDs.
In fact, the VSD now controls the speed of the bending machine's hydraulic pump motor, with the savings achieved primarily during non-active times in its cycle.
"The machine makes frame components for the cabs of JCBs," explains Voestalpine Metsec maintenance manager Eddie Raymond.
"This was suitable because of the high idle times the machine has in its cycle. Depending on the parts being manufactured, the component can take anything from 20—40 seconds to make," he continues.
"As an example, for a component that takes 20 seconds to form, there can be 30—40 seconds of idle time, accounting for some 60% of the total cycle time," he explains.
The machine's energy appraisal showed that the average current drawn was 14—18 A, reaching a peak of 46A at the start-up of the pump.
Following installation of the drive, the average current reduced to 10—13 A, with a start-up peak of 34A.
AAR Powerdrives supplied, installed and commissioned a 22kW ABB ACS550 drive for the installation. The full load speed was slowed by 17% to 1,185 rpm and the no load by 42% to 830 rpm.
Raymond says one challenge on this application was how to receive the signal from the bending machine to initiate the motor to start the hydraulic compressor.
"Initially, we used a pressure switch but we could not find the correct place on the hydraulic pack to get the right signal," he says.
"We found that the drive was ramping up and down continuously, causing the part being bent to distort and go out of tolerance."
To solve the problem, Raymond changed over to a timer on the drive. The machine controller now sends an 'in cycle' signal to the drive. When this signal is not present, the drive is in idle mode. After receiving this signal from the machine, the drive waits for two seconds, then ramps up the speed for the motor.
"Sometimes the operator might press the cycle start and then find he wants to pause the cycle due to the part slipping between the jaws," explains Raymond.
"The two seconds is the check time to allow the cycle to get in full motion, and ensures the part is at the correct angle for bending."
As well as the energy saving, the lower pressure on the hydraulic system means less heat build-up, yielding a longer lifetime and reduced noise. Additionally, Raymond says machine oil is also now lasting longer.
"We also predict a longer life for the motors as they are not running at full speed constantly as previously," he adds.
Voestalpine Metsec now intends to convert four more of its machines to VSD operation over the next few months, with a total of 50 being candidates for drive installation in due course.