How to open a hot furnace without damaging it? I have a heat treatment furnace which is very similar to furnaces used to make jewelry, such as to melt gold, silver and other precious metal alloys for casting into jewelry. In fact, the manufacturer's operational video actually shows the operator putting a crucible into the furnace, which has a front loading door. This type of furnace is sometimes called a &quot;muffle furnace&quot;. It looks like this:

So, my problem is that the operating manual says not to open the furnace if the internal temperature is greater than 300C. However, if I wait for it to cool down, then my material will begin to solidify.
Now, I haven't really tested it, so maybe the chamber can be made to cool down rapidly so I can withdraw the material when it is still hot, I don't know. But I am asking here to see if anyone else has run into this problem and have a solution? According to the manual the risk to the furnace of opening it when it is hot is thermal shock which could cause the lining to crack, but that seems kind of unlikely. The lining is pressed ceramic fiber which as I understand it is pretty stable, but I don't want to second guess the manufacturer, though.
There are ovens made to be opened when hot and there are ovens not made to be opened when hot.
From what you mention what the manual says, yours can not be opened when hot.
As there are different parts that go wrong at strong heat loss or getting the full blast of the oven heat, it is impossible to predict what your oven can handle and whether you can adjust it.
Your best bet is to replace this oven with one made to be opened when hot. Your second best bet is to ask the maker or a community of oven users where someone may have more knowledge.