Building of a digitally monitored heat treating kiln

S

Spela

Joined
Mar 16, 2014
Messages
44
Hello everyone:)

It has been a while since I've last written anything on this forum, which translates to being busy all the time hehe
Anyway, I was thinking (already started) of building a gas powered, digitally monitored, heat treating kiln.

I want to present you my ideas and post a couple of pictures about the idea itself.
Let me know if that ''do-able'' and if I'm going in a right direction :)

For starters, I plan on building a sheet metal housing, from 1/64'' or 1/32'' sheet metal.
Overall measurements will be:
-aprox. 13'' wide,
-aprox. 19'' deep (long)
-aprox. 10'' high.

After all the welding has been done, I plan to line everything with fire bricks, bind everything together with refractory cement, let it dry and cure.
After that, I would line everything with 2'' thick layer of mineral wool and apply ample amounts of rigidizer over that lining.
When the kiln main structure will be done, I plan to put in a 6'' dia. tubing in there, to prevent direct flame/centralized heat to touch the blades and enabling only the ''air''/atmosphere to get hot. Inside that tubing, there will be a firebrick, with holes drilled in it and steel rods inserted to hold the blades edge up.
That idea with steel tube inside the main structure should work, to enable even temp. for accurate treating right?

I'm just not sure about how many burners I should use and where they should be located to ensure the best ''eveness'' of heat and fast temp. climb.
Will one burner suffice to EVENLY heat all the atmosphere?

Anyway, let me know, what you think ;)

Best, Vito

heat_treating_kiln_front_side.jpg
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I'm not sure about a gas oven. If this is for heat treat, I would just make it electric. Your already doing all the work it would take to make an electric one. I just built an electric oven for around $350. 14 amp, 1600 watt element was $30-35, K-type thermocouple was 30 or so and then the controller was 45. A Solid state relay and heat sink and you have your controller. Is there a reason you want gas?
 
You are building a muffled oven. They work fine for carbon steel HT, but aren't good for stainless temps and their more complex temperature steps
.
Your build will be more than efficient, heat retention wise.

A HT oven does not need a lot of heat source to get to and maintain a temperature of 1400-1600F. One good burner or two small ones would be more than sufficient.

Simple PID control will run the burners. You want to build a two-stage system with blown burners, as venturi or single stage control would not work well in this situation. The stickys have the diagrams and info.
 
Rookie25 said:
I'm not sure about a gas oven. If this is for heat treat, I would just make it electric. Your already doing all the work it would take to make an electric one. I just built an electric oven for around $350. 14 amp, 1600 watt element was $30-35, K-type thermocouple was 30 or so and then the controller was 45. A Solid state relay and heat sink and you have your controller. Is there a reason you want gas?
Click to expand...


Rookie, yes, I have been thinking of an electric oven, but I changed my mind mainly because of energy consumption of electricity vs. cheap prices of gas.
+ I wan't to build it out of stuff I have, and rather spend my money on steel ;) I only need the burners, everything else I already have.
Maybe I change my mind again and eventually go to electricity but I really don't know about electricity consumption...bills could go high right?


Best, Vito
 
Stacy E. Apelt - Bladesmith said:
You are building a muffled oven. They work fine for carbon steel HT, but aren't good for stainless temps and their more complex temperature steps
.
Your build will be more than efficient, heat retention wise.

A HT oven does not need a lot of heat source to get to and maintain a temperature of 1400-1600F. One good burner or two small ones would be more than sufficient.

Simple PID control will run the burners. You want to build a two-stage system with blown burners, as venturi or single stage control would not work well in this situation. The stickys have the diagrams and info.
Click to expand...

Stacy, why do you think that it couldn't reach stainless temps? I've seen people melt steels in gas furnaces? Well, that's good to hear (that the build is efficient hehe), do you think that I will be able to reach and maintain a stable, EVEN HOT AIR, temperature inside the tubing or do I run a risk of getting ''hot spots''?
Where should I place a burner? On the top, on the side?

Stacy, just one more thing, I don't really understand those expressions, ''two stage system with blown burners''? What do you mean by that?

Thank you and all the best, Vito
 
I don't blame you for using what you have. I had all of the electric controllers for mine so I came out cheaper. You could probably convert it later if you needed/wanted to. Stainless steels require higher temps and closer tolerances for proper heat treat. I'm just getting into all this heat treat stuff but for most stainless it's around 1900 degrees and needs to be +-25.
Spela said:
Rookie, yes, I have been thinking of an electric oven, but I changed my mind mainly because of energy consumption of electricity vs. cheap prices of gas.
+ I wan't to build it out of stuff I have, and rather spend my money on steel ;) I only need the burners, everything else I already have.
Maybe I change my mind again and eventually go to electricity but I really don't know about electricity consumption...bills could go high right?


Best, Vito
Click to expand...
 
Ok rookie,

let's say that I would wan't to build an electric heat treating oven. Any good tutorials anywhere?

Best, Vito
 
I did one on mine and there have been a few others. You can search around. The only thing I didn't show was the wiring because mine was already together. As Stacy said I think a gas one would be fine for 1084 or some other carbon steels.
 
Rookie25 said:
I did one on mine and there have been a few others. You can search around. The only thing I didn't show was the wiring because mine was already together. As Stacy said I think a gas one would be fine for 1084 or some other carbon steels.
Click to expand...



Yes...well, I was thinking...and I decided to go for an electric powered kiln.
I just can't find anywhere, what kind of resistance wire (heating wire) should I get...how much Ohms of resistance wire do I need to be sufficient?
And what exactly do I need (components) to wire everything together?
And what's the deal with the heat sink? what's it for?
I'm sorry, but I'm not good with electronics :/
Best, Vito
 
I think I understand where you are coming from, but you've not mentioned how much use it is going to get or whether it's for professional or hobby use. It can make a difference.

You've also not mentioned what you'll be Heat-Treating in it.

I think I've built something that will do the job you are looking to do. The guy who's been testing it for me took a short video while waiting for a blade to soak. 816 degC is 1500.8 degF.

https://www.youtube.com/watch?v=1xvWkXBXY6U&feature=youtu.be

It's the second one I've built to the same basic design. The first one went to a guy who makes razors.

It works fine on single knife blades and should work OK on 2 or 3 at a time. The opening is too small for axes and the like. It's very much a hobby-maker setup: the pros could not realistically afford the time needed to make the manual adjustments.

The background to it is that I'm in England and about the only readily-available blade steel here is O1. As a result it gets used by beginners and those with minimal HT facilities in a way that is probably inappropriate and is perhaps not the case in the USA.

Getting the best out of O1 needs a good soak at a controlled temperature, which usually means fairly pricy equipment. I thought it might be useful to try to come up with a reasonably foolproof design for a HT forge that could be built by anyone from readily available (in the UK) parts.

I'd seen a 55-gallon drum HT forge, built I believe by Don Fogg, at a hammerin, and had been very impressed by the simplicity, low cost and performance of the design, but it was too big for most of the hobby makers I know to accommodate.

The aim was to scale it down and to use a burner that had sufficiently sensitive air:fuel ratio control that it could be run with a rich (reducing) atmosphere in order to reduce scaling (anti-scale compounds are also very hard to find over here).

I was pretty sure that the size was a big factor in the even-ness of the chamber temperature in the original, so scaling down presented an interesting challenge.

The rich mixture reduces scaling of Carbon steels (and, early results suggest, decarb, though to a lesser extent) compared to an air atmosphere in an electric oven, but does not eliminate the problem altogether. Antiscale compound definitely still improves things.

The forge itself is a piece of 10" thinwall pipe, lined with rigidized 1" thick Kaowool blanket, and the ends are 1" thick ceramic fiber board, also rigidized.

The burner is built on a commercial 1/2" "Amal" atmospheric injector from Burlen Fuel Systems. It is fitted with a size 30 jet, which is, as close as I can measure, 0.5mm (.020"). The injector cost me about 35 GBP ($55) as a walk-in customer and I'd expect something very similar to be available in the US. It is pretty much an ideal Venturi mixer and gives the sort of mixture control many smiths tend to associate with well-sorted blown burners. We've used the Amal injectors for the last 25 years at work, so I knew they'd do the job.

http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf

I am fairly sure I could build a DIY burner with fine enough control, but suspect my communication skills are not good enough to ensure that anyone else could reliably replicate it. The commercial mixer takes care of that.

The Don Fogg design has the burner low down at one end and the exhaust/workpiece port high up at the other end. I tried almost everything but could not get an even temperature on the small version until I turned it upside down. Burner high, workpiece low made a world of difference.

The Pyrometer is a Chinese TM902C bought off ebay for 2.86 GBP (under 5 bucks) delivered. The thermocouple is a 6mm (1/4") dia Mineral Insulated type K, scrounged from work.

I'd only really intended it to treat O1 and other Carbon steels, sticking the thermocouple in, adjusting the temperature until it holds at the desired soak temperature, then replacing the thermocouple with the workpiece. Mark took it one better, permanently mounted the thermocouple in its own hole and manually adjusted the burner to ramp up the temperature with the workpiece in.

It looks very much like it will cope with stainless blade steels, for which it will obviously need foil. It will certainly achieve forging temperatures, so the higher HT temperatures for stainless are no problem.

There are obviously a few things I did differently to your thoughts and I'll try to explain why.

I'd had the benefit of seeing the Don Fogg setup with only 1" of kaowool and one small burner, so I knew it worked. It seemed sensible to aim for the smallest possible thermal mass in order to get the time taken to set the temperature as short as possible, so the insulation stayed at 1".

A single 1/2" burner is more than adequate for the job in this case. Had it not been sufficient, I would have gone for one bigger burner rather than 2 small ones. The reason is that the air gap (choke) adjustment controls the flame temperature and only having one burner eliminates the possibility of having 2 burners adjusted to different temperatures.

A muffle tube is useful for evening out temperature differences. If the forge design is right, there should be very little temperature difference to even out. Muffles usually keep the forge atmosphere and the workpiece apart, losing the benefit of the reducing atmosphere. There are workarounds, so it's not a big problem, but it seemed better to purpose-design for HT from the outset and avoid the need for add-ons like a muffle.
 
Hello,

thank you for reply,
I'll be using it about 3-4 times a week, maybe more (5 times a week, for about 3-4hours per day), so yes, pretty serious.
I specify my steel selection to mostly low alloyed high carbon steels, but that's just the personal preference, I've been asked many times to use high alloy carbon steels, or steels that require longer soaks at higher temps. which is very close to impossible with only a coal forge.
Therefore, I plan to build an oven that will last and will withstand regular use.
Also, I'm very very interested in starting to use Sandvik steels, because I got a really good deals on several steels that they manufacture.
So, yes, I do need highly reliable, ''controlable'' oven, that'll do the job.

Thank you for replying mate:)

P.S.: I'm not from USA, I come from Slovenia, Europe ;)
 
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