Southern Industrial Drive Technologies • Experts in solid-state AC & DC drives and machine controls
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CLIENT: BAY MOTOR WINDING
ABOVE: Ancient monster electric motor built in 1902 to run a massive rotary boring machine. It was used to machine turrets for tanks in World War II. SID-TEC was able to build a new motor control cabinet to give it decades of additional productive life.
This shot shows the front end of the boring machine's massive 62-inch rotating table. Materials are rotated past machining and cutting tools.
Here is the "after" solution created by SID-TEC to control the boring machine. The new electronics eliminated arcing and other operational problems, and provide additional life to this century-old machine.
All the components in the photo at left are housed in the professional metal cabinet shown above. The cabinet was assembled off site and shipped to the customer for installation.
1. Determining the advantages and disadvantages of keeping the original DC motor or buying a new AC motor.
2. Building a custom DC controller with all the modern benefits of current-day technology to coax several more highly useful decades out of this aging monster.
This large DC motor is original to this 100 year old dual turret boring machine made by the King Machine Tool Company in Cincinnati Ohio USA at the turn of the last century. The machine has quite a history and was used to machine the tank turrets that were made and used in the Second World War.
The machine was built to last and the ridged structure and mechanical drive system of the 62 inch diameter rotating table are still true and work perfectly, even though the new owners, Specialty Machine of Gulf Port Mississippi, do not make the aggressive cuts this machine was once designed for.
The motor made by Crocker and Heller is only 30 Horse Power and boasts a maximum base speed of only 500 RMP and a top speed of 1500 RPM. The motor was originally built as a Compound Wound DC Motor and was controlled by a Ward Lenard Motor Generator set. Most of the companies that looked at rebuilding the control system wanted to get rid of this motor and replace it with an AC motor and VFD.
When SID-TEC was approached, the head of engineering did the math and figured out the output torque curve of the motor, he found that it was delivering 315 ft/lbs. of torque from 0 to 500 RPM. In addition the motor is capable of taking 200% for 30 seconds and 125% for extended periods of time, so this motor could produce an astounding 630 ft/lbs. of torque for short periods, and 400 ft/lbs. for extended periods.
Replacing this motor would require a 150HP AC motor and VFD to get the same job done, in addition the motor would have to be a 1000 to 1 torque over speed range vector duty motor and would require a lot of programming to handle to no load to full load changes as the cutting tool is applied to the job during machining. This AC option was becoming an expensive and unattractive option for the customer.
SID-TEC’s engineering department decided to keep the old motor and do away with the motor generator set and fit a new state-of-the-art processor-controlled DC Drive onto the motor. A 3 phase Reactor was added into the armature circuit to soften the rate of rise of the current pulses produced by the DC Drive and the motor was overhauled. The compound winding was removed, allowing for a regenerative 4 quadrant controller to be used.
In addition a 1000PPR Encoder was mounted to the back of the motor shaft and this was used as a speed feedback device which provided the motor with a highly accurate speed regulation that provides the machine with a truly stable cutting ability and a very small no-load to full-load speed regulation.
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