Heat Treatment Oven Build Process
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Posted 30th November 2024
Time is running out! Okay, that's a bit of an exaggeration as there isn't really a dead-line for this project. However, I've got two weeks off work over the Christmas break. Most of one of those will be occupied with family stuff but I'd like to use the second week to start building this oven. I doubt I'll finish it in that time, but I'd like to make some solid progress if possible.
Given that most suppliers will be closed over the Christmas break, that means I need to start ordering stuff very soon if I'm going to get it before the break.
Following some conversations on the MIG-welding forum, I now feel like I'm getting close to a shopping list of stuff I need to acquire:
Heat Zone Stuff:
- Insulating Fire Bricks, Grade 23 (plus spares!)
- Fire rope (for the door seal)
- Kanthal Wire (I already have this)
- K-Type Thermocouples (3)
Note: I'm not going to buy high temperature mortar or ceramic wool as both are apparently unnecessary.
Control Cabinet Stuff (some of this is probably overkill, but overkill can be fun!):
- PID Controller
- Thyristor / controller of some sort (I don't think I'll do anything very fancy with this, just set a target current).
- Two SSRs (and heatsinks if they need them)
- Mains voltage relay (for over-temperature safety trip)
- Something to measure temperature from a thermocouple and trip the relay (I'm not sure what options there are for this at the moment, but hopefully something fairly simple and reliable)
- A current transformer (not strictly necessary as current monitoring will mostly be for interest)
- Some DIN rail
- Cable glands and such-like
- Fuses & fuse holders
- Switches (including a couple of mains-rated ones), potentiometers, LEDs (I've probably already got some of this)
Other Chamber Stuff:
- Angle iron for the frame (I've got loads of box section, so I had pondered cutting it in half diagonally; that would result in a lighter frame as it's 2 mm wall rather than the 3 mm typical of angle iron, but it's probably a lot more faff than I can be bothered with)
- "Bullet" hinges for the door
- Door interlock switch(es)
- Ceramic terminal blocks for the electrical connections to the chamber
- Thermocouple extension cables?
- High temperature rated power & signal wire
I think that's everything at the moment. I'll have to make a control cabinet but I've got some sheet steel to use for fabricating that. I'm sure there are other minor bits and bobs I've forgotten but hopefully that lot will get me most of the way there.
Anything you can think of that I've forgotten?
I'm working on the premise that the control cabinet will be relatively big, but I'm planning to make it a separate piece to the main chamber rather than having the cabinet permanently fixed to the side of the chamber. There are two reasons for that:
- It will make it much easier to re-use the control cabinet with a different chamber if I decide I want a different cavity size or something like that.
- It will make it easier to transport to/from storage as I can carry the chamber in one trip and the cabinet in a second.
The main disadvantage of that approach (that I can think of) is that I'll have to make sure that all the connections (thermocouples and heater) to the chamber are relatively easy to disconnect/reconnect and extremely easy to identify (so the right connection goes back to the right place).
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