What happens to the diameter of a steel ring when heated?

What happens to the diameter of a steel ring when heated?

When assembling a bearing onto a shaft or axle, will it be better to freeze both parts, heat both, or heat only one? Most bearings make a tight fit when assembled, so gaining just a fraction of an inch will be favorable.

Bearings are made to be press fit onto shafts or into holes. I general there should be no reason to heat up or chill one or the other. Make the parts in accordance with the manufacture recommendations when it comes to tolerances.

There are a limited number of applications where you do need to heat and chill parts but they are very few and far between.

Niel Leon
engineering.com

heating the out part will make it expand, freezing the inner part will have it contract. When I was in an auto shop we would heat up a very tight collar to get it off, but this was a rare event. As for putting on new ones they were sized correctly, just the rust had to be removed and a hammer to get it into place (use something to soften the blows as not to wrap the bearing).

I concur with Niel’s response. The only time you would need such an extreme force fit is if high torque transmission is required. Extreme force fits will reduce bearing clearance and lead to early bearing failure as well.

Unless absolutely necessary, I would not rely on the force fit alone to retain the bearing as it can “walk out” during operation, especially if the shaft is highly loaded.

Randy Karambelas, PE (Mechanical)