Estimating Stress Relaxation

[hodag]

Here is my problem:
We make split, babbitted bearings for our customer. The wall of the bearing is approximately, 3/8" thick and after splitting it, there is a "free spread" dimension on the print that is to be met. If the part is not at this free spread dimension, the bearing half is "sprung" to size (basically we manually deform it to meet the drawing requirement.) The problem is that these are repair/replacement parts and that while they conform to the drawing dimensions at the time they are made, and would conform to the mating housing into which they are going, but our customer shelves them for when they need them, and after time, the part relaxes so that the free spread dimension is oversized when pulled off the shelf.

So my question is this: Is there a way to estimate the amount of stress relaxation a part will endure over time, such as a time/stress curve, for a particualr material. We cannot run the parts thru a stress relief cycle because it would result in melting out the babbitt.

 

[plasgears]

I recommend sizing the halves by forming them in oversize diameters. They will spring back to near required size. Of course you need to develop this with a few trials.

 

[israelkk]

You could supply them with an inner and outer rings that will prevent them from relaxation. Or you can do some stress relieving process after splitting while the two halfs are confined in an inner ring and an outer ring that will keep them from relaxation during the stress relief.