WilleyB wrote:
JBarca wrote:
Do you have any of the affected fitting area and the probe interaction?
Hi John, By "the affected fitting area" if you mean the element holder and the welded area. no I don't have a photo of that. I have a photo of the new element being inserted into the "Element Holder"
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Cheers Willis
Willis
Thanks, we are getting closer. Right now I'm trying to just see and understand the internals and the temperatures involved. I deal with thermal failures in machines at work. Actually working on one right now. The machine heats and cools every hour. 80 F to 260 F and back down real quick. And the difference in metal thickness create different stress levels in this cyclic situation.
The thick part heats slower and then cool slower. When the differences in thermal expansion are large enough between adjoining metal parts high stresses in them can come from this. On this machine we are literally ripping 1 1/2" thick metal apart. Over time low cycle fatigue starts to set in and then over more time metal breaks.
Most likely the welds in a RV fridge are not stress relieved after welding. There is not normally a need to. So high stresses are left over from the welding operation. If you heat and cool that high stress heat affected zone enough and different metal thickness are involved, the stresses can rise fast. Over time those stresses become destructive. The weld cracks was the place that let go to relieve the stress.
The design way out of this problem in machinery is normally, even metal thickness, stress relived parts after welding and or to allow uneven members in thickness to have expansion joints.
In the case of this fridge, if the affected metal does not get hot enough, it will not expand as much and thus not create the high stresses. People running 120 or 125 Volts have the problem worse and then there is the tolerance on the wattage of the elements or a high wattage element. If this is a thermal expansion cracking problem, then they are sitting on the edge of the expansion stress situation.
I'm not saying this is the case here, but the little bits and pieces we keep learning are starting to put some of the puzzle pieces together.
Thanks
