<p>There are ovens made to be opened when hot and there are ovens not made to be opened when hot.</p>
<p>From what you mention what the manual says, yours can not be opened when hot.</p>
<p>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.</p>
<p>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.</p>

CC BY-SA 4.0
2021-05-04T08:17:11.553Z
2021-05-04T14:11:24.837Z
2021-05-04T14:11:24.837Z
Willeke
<p>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:</p>
<p><a href="https://i.sstatic.net/CbZ16m.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/CbZ16m.png" alt="enter image description here" /></a></p>
<p>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.</p>
<p>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.</p>

CC BY-SA 4.0
2021-04-18T21:55:20.180Z
Easy.  Operate the furnace in a 300C room, then no temperature difference when you open the door.  How to do that would be the subject of another question.  :-)  You might need to use a different type of furnace.
fixer1234
CC BY-SA 4.0
2021-04-19T13:59:15.813Z
Curious, why use a closed furnace? It doesn't seem like the right tool for the job; I never used anything but an open crucible for heating metal, because of the need to transfer it to a mold. My personal inclination is that the solution here is "use the right tool for the job."
Allison C
CC BY-SA 4.0
2021-04-19T19:36:14.290Z
Send this question to the customer service of the manufacturer. Explain your motive. Ask for a method of workaround. If the manufacturer is hesitant to recommend unofficial (potentially risky, not guaranteed to work) workarounds, look up the repair agency in the warranty. They may feel less obliged to keep their mouths closed when it comes to empirical experience & solutions over the prescribed procedure. If they also don't help, look up other, similar companies who repair things like this, and send your question there too.
Levente
CC BY-SA 4.0
2021-04-20T13:53:56.717Z
Does the manual actually state that not opening at >300°C is to avoid damage to the furnace?  Could they mean for safety reasons?
Chris H
CC BY-SA 4.0
2021-04-20T14:44:04.780Z
@ChrisH The manual says the lining could crack if subjected to thermal shock. The lining is pressed ceramic fiber and actually there are two hairline cracks in the lining already which were present when it was delivered.
Tyler Durden
CC BY-SA 4.0
2021-04-20T14:47:56.483Z
@TylerDurden that's reasonable - sort of.  Thermal shock from air seems unlikely as its specific heat capacity is so low.  Splashing water in there or putting a cold piece of metal on the floor would seem to be far worse at 200°C than air at 400°C
Chris H
CC BY-SA 4.0
2021-04-25T12:49:35.073Z
@ChrisH If you open the front door, the back wall of the furnace will cool quickly by *radiation* through the open hole. The thermal contraction at the surface of the back wall will start micro-cracks which will grow every time you repeat the procedure. The furnace walls are designed to cool down slowly from the outside in, not quickly from the inside out.
alephzero
CC BY-SA 4.0
2021-04-25T16:54:05.417Z
@alephzero good point, if the opening is a large part of what it can see.  The door lining would be even more vulnerable
Chris H
CC BY-SA 4.0
2021-05-04T04:40:07.907Z
@everyone I'm just feeling nice today and gave away 10% of my rep. good luck getting those 50 points! ...remember: best answer = free 50 points
Isaac750
<casting>
How to open a hot furnace without damaging it?
Tyler Durden
# How to open a hot furnace without damaging it?

(Asked by: username_0 on 2021-04-18)

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 "muffle furnace". It looks like this:

[![enter image description here](https://i.sstatic.net/CbZ16m.png)](https://i.sstatic.net/CbZ16m.png)

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.

**Tags:** casting

> **Comments:**
> **username_1**: Easy.  Operate the furnace in a 300C room, then no temperature difference when you open the door.  How to do that would be the subject of another question.  :-)  You might need to use a different type of furnace.  
> **username_2**: Curious, why use a closed furnace? It doesn't seem like the right tool for the job; I never used anything but an open crucible for heating metal, because of the need to transfer it to a mold. My personal inclination is that the solution here is "use the right tool for the job."  
> **username_3**: Send this question to the customer service of the manufacturer. Explain your motive. Ask for a method of workaround. If the manufacturer is hesitant to recommend unofficial (potentially risky, not guaranteed to work) workarounds, look up the repair agency in the warranty. They may feel less obliged to keep their mouths closed when it comes to empirical experience & solutions over the prescribed procedure. If they also don't help, look up other, similar companies who repair things like this, and send your question there too.  
> **username_4**: Does the manual actually state that not opening at >300°C is to avoid damage to the furnace?  Could they mean for safety reasons?  
> **username_0**: @ChrisH The manual says the lining could crack if subjected to thermal shock. The lining is pressed ceramic fiber and actually there are two hairline cracks in the lining already which were present when it was delivered.  
> **username_4**: @TylerDurden that's reasonable - sort of.  Thermal shock from air seems unlikely as its specific heat capacity is so low.  Splashing water in there or putting a cold piece of metal on the floor would seem to be far worse at 200°C than air at 400°C  
> **username_5**: @ChrisH If you open the front door, the back wall of the furnace will cool quickly by *radiation* through the open hole. The thermal contraction at the surface of the back wall will start micro-cracks which will grow every time you repeat the procedure. The furnace walls are designed to cool down slowly from the outside in, not quickly from the inside out.  
> **username_4**: @username_5 good point, if the opening is a large part of what it can see.  The door lining would be even more vulnerable  
> **username_6**: @everyone I'm just feeling nice today and gave away 10% of my rep. good luck getting those 50 points! ...remember: best answer = free 50 points  

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## 1 answers

### Answer by username_7 on 2021-05-04. Score: 2

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.


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