The worst seems to be Aluminum for me. I get into the habit of welding a while then setting the torch down to cool. When I set the torch down to cool I always disassemble it to keep the heat saturation down.
The bummer is once I get the aluminum up to temp where it is welding well I have to let the torch cool.
Next thing that happens, I short out the torch on other projects where it melted.
Here are 2 things which pretty much tore up this torch: