Page 16 - MetalForming November 2010

Hydraulic Presses
Turn Green with Variable-Frequency Drives
The return on investment for outfitting a hydraulic press with a variable-frequency drive (VFD) shortens the more a metalformer pays for electricity, the more said company’s hydraulic presses sit idle waiting for work and the bigger the press motor. Many VFD installations pay for themselves in two years or less.
Hydraulic presses use electric motors to supply the workforce/horse- power required to build tonnage. Most (if not all) of these motors use AC (alternating current) and run on volt- ages between 120 to 600 VAC. Motor horsepower ratings can range from 1 to several hundred—here we’ll focus on larger motors, 50 hp and greater, which can consume a massive amount of elec- tricity and become a big number on a metalformer’s balance sheet. One ener- gy-saving device that’s well known in many segments of industry, but per- haps less understood among metal- formers, is the variable-frequency drive (VFD).
Developed decades ago to allow the use of AC drives rather than DC drives in large machines, VFDs allow accu- rate control of an AC motor—its accel- eration and deceleration, startup times, boost torque and a host of other vari- ables. In manufacturing plants, VFDs can be found anywhere that operating speed needs to be varied—conveyors or mixing operations, for example.
But when it comes to hydraulic presses, many metalformers need more education, which is why we spent some time discussing the topic with Rob Bis-
This small 10-ton hydraulic press, with a 7.5-hp motor, went to a metalformer that was able to justify the addi- tion of a variable-fre- quency drive because the press runs at only 1 to 2 cycles/min. The VFD, an Allen-Bradley PowerFlex model seen in the top- left corner of the electri- cal-cabinet photo, gener- ates significant energy savings for the stamper.
BY BRAD F. KUVIN, EDITOR
14 METALFORMING / NOVEMBER 2010
www.metalformingmagazine.com
bee, senior automation engineer with press builder Greenerd Press, Nashua, NH.
“While our customers with applications less than 50 hp typi- cally cannot justify the investment in a VFD, presses with larger motors and, in particular, with applications that cycle a part every few minutes rather than continuously more readily can see an ROI that makes