Replacing bearings on a new motor for my 1948 9A
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  1. #1
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    Default Replacing bearings on a new motor for my 1948 9A

    Through the kindness of a PM member, I got a used inverter rated motor and VFD.

    The motor is a 1/2 HP Baldor IDXM7006. It was removed from service by the member's company and trashed. He rescued it and its three brothers, along with their little Baldor VS1ST VFDs.

    The motor and VFD worked, except the motor made a strange thumping sound, which I attributed to worn bearings.

    When I examined the motor prior to disassembly, I was mystified by these two large bolt heads on the pulley end.
    Baldor's drawing shows them:

    baldow-motor-pulley-end.jpg

    The bolts were retained by two 1/8" spring pins -- just barely visible in the drawing.

    This drawing, which I didn't have at the time, shows their only apparent purpose is to cover the recesses for the 10-32 bearing retainer screws, as shown in this drawing.

    baldor-bearing-retainer-drawing.jpg

    I cut the pins flush and was able to remove the bolts using a 3/4" socket. It didn't completely clear the recess in the casting, so I probably should have ground its OD a bit smaller, but I got the bolts out. I was then able to remove the retainer screws. They were Phillips/hex head, but there was no chance of getting a socket into the recess. I thought they were excessively tight, but I got them out.

    After this, the end bell came off as easily as the other end had.

    I was amazed to see the inside of the motor was EXCEPTIONALLY clean! There wasn't a speck of dust. I guess "explosion proof" also means dust proof, which is reasonable.

    I pressed on new bearings, reassembled the motor (sans new spring pins), and tested it. Success! It purred smoothly from 1 to 2000 rpm. Fortunately for me, I can't hear the 15 kHz carrier frequency, but my wife says she can.

    If anyone can enlighten me as to the purpose of the huge pin-retained "dust cover" bolts, I will be most grateful.

  2. #2
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    Thats a very versatile motor it has foot mount and flange mount.I think thats what was on the end housing.

  3. #3
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    An explosion proof motor has to be able to withstand an explosion internal to the motor without igniting a hazardous atmosphere outside the motor. Leakage of the hot gases does occur through threads, but the long path cools the gases below the ignition temperature in the outer atmosphere. The small screws for the bearing retainer do not have the long path length necessary to quench the flame, so the big screws are installed to provide the long path length.

    You can also see the long tight clearance between the shaft and the end bell (.006 to .004) that serves the same purpose.

    I worked for decades in a building with potentially hazardous solvent concentrations, and the electrical classifications and wiring techniques were very interesting.

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  5. #4
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    Quote Originally Posted by wheels17 View Post
    An explosion proof motor has to be able to withstand an explosion internal to the motor without igniting a hazardous atmosphere outside the motor. Leakage of the hot gases does occur through threads, but the long path cools the gases below the ignition temperature in the outer atmosphere. The small screws for the bearing retainer do not have the long path length necessary to quench the flame, so the big screws are installed to provide the long path length.

    You can also see the long tight clearance between the shaft and the end bell (.006 to .004) that serves the same purpose.

    I worked for decades in a building with potentially hazardous solvent concentrations, and the electrical classifications and wiring techniques were very interesting.
    Thanks very much for the explanation, Wheels17!

    Jon


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