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Turn-of-the-century stamping press gets new life with variable-speed drive

Oct. 10, 2013
Adding a variable-speed drive to an old cast iron stamping press lets it do modern production work.

Upgrades that included a constant torque flux vector variable-speed motor let a pre-1912-vintage stamping press handle modern production duties.

The cast-iron press, salvaged for $80, weighed about 3,500 lb. and was made by the Toledo Machine & Tool Co., a firm eventually acquired by the press builder Aida.     

Engineers at Patriot Engineering Co., Chagrin Falls, Ohio, first rated the press using finite-element stress analysis.  At a 60-ton shock loading, only small areas of the frame showed stresses near 19,800 psi.  These results affirmed that a nominal 32-ton rating was fairly conservative. 

The rebuilt press was refurbished with new ac drive controls that include a speed control potentiometer, start-stop switch, reset switch, top-dead-center light and a large braking power resistor that shunts motor power when operators suddenly switch off power. Developers added the braking resistor to provide a margin when stopping the press. This set-up lets operators slowly feed in metal strip, then bring the press up to production speed. Blower cooling is necessary when the motor handles full tonnage at slow speed.

A 32-in. OD flywheel on the device had stress cracks in its spokes from the many millions of cycles over nearly 100 years of use.  These were repaired by welding.  Patriot either reground or replaced other wear parts such as journal and crank bearings.

To bring the press in line with modern safety standards, Patriot engineers replaced the old mechanical pin clutch with a Magnetek GPD series ac drive which is now marketed by Yaskawa.   

Analysis revealed an oversized variable speed electronic drive and motor could replace the old mechanical clutch and brake.   Oversizing the motor is key to controlling flywheel momentum.  Earlier in its life, the press had been “modernized” from an overhead leather belt drive to a 2-hp electric motor.  Patriot engineers calculated that replacing the 2-hp motor with a 3-hp version provided enough margin to bypass the mechanical clutch for starting and stopping the press electronically.

The replacement electronic drive system consisted of a vector-duty, closed-loop, blower-cooled motor from Reliance Electric (now part of the Baldor Electric Co. division of ABB Ltd.)  teamed with a flux-vector-duty constant-torque general purpose ac drive.  The original mechanical clutch was permanently engaged and the only parts modified were a slide for tensioning modern multiple V-drive belts. 

Resources

Patriot Engineering Co., Chagrin Falls, Ohio,  www.patriotengineeringco.com

Baldor Electric Co., Fort Smith, Ark., www.baldor.com

Yaskawa America, Inc., Waukegan, Ill., www.yaskawa.com

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