On Fri, 12 Oct 2007 21:34:22 -0500, Ignoramus12693
wrote:

I have a scrapper with whom we have done a lot of stuff together (I
sold him a lot of scrap, he sold me 625 Signode banding cutters, etc).

He has a truck (similar to Ford F-550) with a big steel "box" (5 ft
tall) for hauling stuff. That "box" has steel doors in the back that
swings open like a gate. Each door hangs on two hinges.

One of the hinges broke. It is a second time it failed. It failed
before and was welded back rather atrociously. The weld looks very
bad. It failed around the weld. The failed area is close to where the
flat part of the hinge is welded into the gate.

The "big issue", in my opinion, is that the hinges are undersized for
the sort of stuff that he hauls around, as evidenced by gouges from
inside the box, etc.

I promised to fix it for him. I told him that if he continues o abuse
these hinges, and drives with heavy things unsecured inside, they will
fail again. Nevertheless, I feel that I can weld them in such a way
that something will fail other than the welds.

Anyway, the purpose of my post is mainly to see if there are some
non-obvious things that I am missing.

i

Often the gate material around the hinge fails rather than the hinge
breaking or the weld failing. There's a lot of vibration in a truck
door and vibration eventually results in fatigue. We sometimes had to
design and test stuff to considerably better than mil spec to have it
survive on trucks.

If the gate material is failing, the remedy is to use more hinges
and/or use stress-spreader plates under or around the hinges. You
can't fix bad design merely by making good welds.