Monday, January 28, 2008

Changing a Tire

I came across a new collection of Library of Congress photos that are being posted on Flickr as Flickr: The Commons. The intent is to use Flickr to get wider dissemination of the photos and hopefully some additional identification and comments on those that are not well documented.

The collection contains some beautiful color photographs from the 1930's and 1940's. One that particularly caught my eye was an image of changing a "tire" on a steam locomotive drive wheel. Funny, I had never thought about the fact that steel tires could be changed in the same way rubber tires are changed. But as the photo demonstrates, changing a tire in the locomotive shop can be a hot job. The steel tire has to be heated to a red-hot temperature to allow the steel to expand and slip off of the inner wheel. Reversing the process, the hot tire is put back on the wheel and allowed to cool and contract to keep it anchored in place.

In both the steel tire and the rubber tire, the principle is the same: pressure keeps the tire anchored to the wheel. In the case of the steel tire, the pressure is in the form of high stresses within the tire compressing it to the wheel. For the rubber tire, it is air pressure forcing the edge of the tire against the rim of the wheel.

If you have an interest, it is worth the time to browse this collection of color photos. There are some amazing shots that cover both towns and industries and, in the later years, the war production efforts. Who knows? You might even see places or people that you know.

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