Need help with this dentist vacuum furnace

N

Natlek

Joined
Jun 9, 2015
Messages
6,182
Ok , thanks to Stacy https://bladeforums.com/threads/some-shop-time-and-a-nice-surprise.1796019/ i will convert this oven for melting cooper , bronze , silver.............if i can make it work !
I get it from friend who service dentist equipment .But he is not familiar with ovens... I took off from this oven all parts from vaccum part of oven and used them in my low vacuum HT oven which i work on ...
Now i can t find any thermocouple on it ? It has two independent coil inside ceramic fiber cylinder and four outlet for them from vacuum chamber .Nothing else ! So i can t figure how this thing control temperature .I can t find any manual on net .
Anyone know something about this ??
First picture is from net ... mine is disassembled
Dental Eurotherm Docx Automatic MK II ceramic dental furnace
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Back side of one controller , on contact 7 and 8 are connected HT element
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It has electric motor for up / down ...close /open
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What's connected between terminals 7 and 8 on your PID? That will be your thermocouple.

If there's nothing there, somebody likely removed it before you picked it up.
 
Drew Riley said:
What's connected between terminals 7 and 8 on your PID? That will be your thermocouple.

If there's nothing there, somebody likely removed it before you picked it up.
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Drew , only hole from outside of aluminium body of oven are for two kanthal coil , which mean four hole .......no other access to mount something which will reach hot zone inside .On terminal 7 and 8 are connected ends of HT coils .That is what confuses me , where would go thermocouple if it was say removed from someone before i get it ? HT oven was complete when I get it , just burn coils .......??
 
Picture from back side , and from top .
On first picture you can see four hole where HT coils exit chamber . Actually there are sealed connectors , wires from heat elements are connected from inside .Other two parts which can be seen are inlet for vacuum pump and inlet for vacuum gauge and that is all...no other way to get inside ?? If there was TC once how would be attached to read temperature ?
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Can I see a better picture of the back of the PID connections? What is the yellow part? Is it possible the TC goes up through the bottom, inside the center shaft?

The schematic symbol between terminals 7 and 8 is pretty standard notation for the thermocouple. Does the oven heat at all as is?
 
Drew Riley said:
Can I see a better picture of the back of the PID connections? What is the yellow part? Is it possible the TC goes up through the bottom, inside the center shaft?

The schematic symbol between terminals 7 and 8 is pretty standard notation for the thermocouple. Does the oven heat at all as is?
Click to expand...
Ok guys ,thanks for help :thumbsup: I think that I figured how this thing work ..............They use resistance change in one or in both coils as thermocouple......... it is only way i think since there is no other input or output to get inside chamber ..
Coils are embedded in ceramic fiber insulation and that mean i can t fix them because they are melted .Only way would be to make change and to use modern PID and thermocouple........

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smaller controller............
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In that last photo, what is the device hanging down on the bottom right? It looks like a thermal limit switch, but could be a thermocouple.
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Stacy E. Apelt - Bladesmith said:
In that last photo, what is the device hanging down on the bottom right? It looks like a thermal limit switch, but could be a thermocouple.
View attachment 1588354
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I took that picture last night so it is not clear , sorry ...........It s power cord
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here is othe clear picture from down side , nothing there except motor and some kind of limit switch for movement of lift part
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What do you think about using resistance change in elements for temperature control ? I can t see any other way they can do that in this oven .....there are no other parts which can do that ?
When elements start heating resistance of wire change , that can be meausred in any temperature .....so ?
 
I don't have much experience with this specific style of vacuum kiln, but when I worked in a lab we had one, and about 1/4 of my job ended up being to service the thing. One thing I did was add 2 1/4 sheets of graphite over the heating elements to even out the temperature. With no internal convection, heat sensitive parts got ruined due to the heat drop off from near the elements to the center
 
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