Quote:
Originally Posted by ithacaartist
The interference fit is great--it will never be shot loose, and there's no mess to clean up.
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Cool story!
I have one too...
Back when I was a millwright, one of my recurring jobs was rebuilding pulverizer gear reducers for the boiler in our paper mill. Coal dust got in everything (especially lungs
) and gummed the reducers up to the point they would break 3" shafts. To replace the bearings we'd heat up the cast iron gearbox, refridgerate the race overnight, and press the outer race (about 6" dia) in with a six foot hydraulic press. The outer race was an interference fit. You only had one chance to get it right. If you got it wrong, the race had to be torched in half and do it all over again.
To get the cast iron gearbox to expand the exact amount needed to drop the race in, we'd use two oxy-acetylene torches with rosebud tips. The millwright heading the job [me] would run a Tempilstik [pic below] over the area. The stik was like a candle but only melted at a specific temperature. 262º F in this case. When it melted & ran when you touched it to the gearbox, you [me again] dropped the race over the gearbox shaft opening, slammed a long steel sleeve over it, tilted it under the hydraulic ram, and started pumping like Hell!!!
I did at least a dozen rebuilds...I don't recall ever having a hangup...But there was evidence in at least one of the four reducers we had that it had happened (torch cut in the cast iron body)...
It was a four man job...And once the ram slammed down we all took turns pumping...Welders, millwrights, machinists - anyone walking by!!!
It was a stressful job...Lots of time spent by the machinist making the shafts...Expensive bearings...6" in dia, 3" wide races...
A reducer lasted about three months...We always had one standing by for when one of the two in use failed...The dust got in the oil ways and made a hard paste that had to be drilled out...
IIRC, the interference fit was ~1 1/2 thousandths [.0015"]...You couldn't let the reducer body get any hotter or it would take the hardness out of the bearing race...We had to have air hoses ready to start cooling the reducer down as soon as the press reached 20 tons...
They had all been painted gray originally...I had our painter paint them different pastel colors to tell the four apart...Baby blue, pink, light green, and gray...My way of rebelling against conformity...
