Top loading Kiln question

NLite said:
I recently acquired a small top loading kiln with an element in the lid. The kiln is 110v, with a heating cavity that is 9 inches deep (two bricks tall,) and 17.5 inches wide (simple dial control, but a thermocouple and analog temperature display were included in an accessory box.) I was thinking it could be used for heat treating with a few improvements, but wanted to see if anyone had some wisdom to share before I get too involved.
Click to expand...

I agree with the others that this would be difficult to convert to a heat treating furnace. If you are on a budget, perhaps you could find a used digital enameling kiln. They have a swing-style door. While most enameling kilns are shorter than a knife making furnace, they are suitable for heat treating knives.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
 
I know the shipping cost is a bummer but if you don't just bite the bullet and pay it you may be compromising the quality of your end product. Spend the cash. If time is money the Evenheat will pay for it self pretty fast. Use the one you have now for a tempering oven thus saving you even more time. Just my 2cents. I was once in Eggeggik and a they had one watermelon in the uhhh store the price was $25 haha. But a Mora knife was $12 . I went with the Mora. LOL
 
Thanks for the advice.

I was looking at the Evenheat KO 22.5 (since it heats up to 2400 degrees,) however it is a little short. I was hoping to find an oven with at least a 24 inch long chamber. That leaves the KM24D (max temp 2350) or the KF 27 (max temp 2200.) The reason why I want an oven with a higher max temp is only to try and make the the oven as future-proof as possible (in case some new steel comes out that requires the higher temp.) I sent an email to mackilns (already left a voice mail message) to see what they would charge for shipping as a comparison (to the first place I contacted.)

In looking at building an oven and the components required, it looks like I could possibly build one that has a max temp of 2400, and is 24 inches long for around $700.00-800.00 (including shipping.) That is about half (more if talking about the KMD24D) what purchasing an oven and having it shipped will cost. Of course, this does not include my time, but this is a hobby for me...

I know many of you have said to not mess with the fusing kiln I have, but I am curious if I can get it to perform better if I decrease the heating chamber size and increase the insulation on the lid. I found some vermiculite locally and was thinking about putting a 4-6 inch layer of it in the heating chamber and on the lid (using aluminum foil or something to hold it in place.)

I guess I will make a decision once I hear back from mackilns & perform my vermiculite test.

Thanks again for all the input.
 
Howdy.

Here are the results of my vermiculite test:

5 minutes to 500 degrees.
11 minutes to 800 degrees.
19 minutes to 1000 degrees.
56 minutes to 1500 degrees.
85 minutes to 1700 degrees.
162 minutes to 2000 degrees.

Adding the vermiculite to the heating chamber and to the lid halved the heating times.

Here is what I did (so far):

http://imgur.com/yyUItdk
http://imgur.com/c7ZaoLN
http://imgur.com/667CoAg

I plan to put something on the top to keep the vermiculite from coming out, and probably add a PID.

I have not heard back from Mackilns yet...
 
YOu could make light castable refractory bricks with fire clay and perlite, either one solid or some smaller fire clay bricks for the top and use straps to hold them in. fire clay = gray clay layer that you can see in excavations. Stove cement and perlite works too.
 
You can't make soft fire brick that will work in a kiln like that. Those bricks are fired in a very hot oven from an alumina/silica mix. The air in the spacing of the refractory is part of why they are light, soft, and insulate well. Kitty litter and fireclay makes a fine lining for a coal forge firepan, or the floor of a damascus forge.... but won't work well at all as cast bricks.
 
If you are adding insulation on the outside of the lid, you don't need super-high-temperature stuff. Something like Rockwool mineral-fiber slab or blanket should do the job and will be easier to fix than loose vermiculite. I'd expect it to be fairly easy to find locally too. Rockwool is a UK brand name, but I'm sure there's a local equivalent.

There's no reason it can't be used round the outside walls and on the floor too. You'll just need to bear in mind that what was originally the cold face will be at a much higher temperature because it'll be somewhere nearer the middle of the insulation.
 
bladsmth said:
You can't make soft fire brick that will work in a kiln like that. Those bricks are fired in a very hot oven from an alumina/silica mix. The air in the spacing of the refractory is part of why they are light, soft, and insulate well. Kitty litter and fireclay makes a fine lining for a coal forge firepan, or the floor of a damascus forge.... but won't work well at all as cast bricks.
Click to expand...

It's not going inside the kiln, as I understand the problem, it is going on top of the fire bricks that are already in the lid, to provide for some extra insulation.
 
In my first test of the kiln I noticed that at about 1500 degrees the outside of the kiln became really hot (almost too hot to touch.) I was thinking that part of the original problem of it taking too long to get up to temperature may be due to the kiln losing too much heat (it is only comprised of a single wall of k23 firebrick.) I thought that by adding some additional insulation to the kiln, that it may reduce the amount of time it took to heat up. I was also thinking that the heating chamber was too large - at least too large for what I needed it t o do. I originally just wanted to add some K23 firebrick in the heating chamber to reduce its size. Unfortunately, no one in town had any (at least that I could locate.) I could however, find some vermiculite at a hardware store, so I thought I would try a little experiment to see what would happen.

In my second test I noticed that I could see in between the lid and the base after it was closed (just a little). I also did not put vermiculite all the way up to the height of the lid in the heating chamber as I am unsure what that would do to the heating element (I am thinking that there may need to be some space/air gap around the heating element - even if I do not want to use that part of the heating chamber.)

I am thinking that I could further improve the heating times of the kiln by adding more insulation to the heating chamber, and removing the very small gap between the lid and the base. All I really need in the heating chamber is a straight path - the rest of the octagon is wasted space for knives.

I am proposing to cut out one brick in the side wall (opposite the brick with the temperature probe hole) and use that for a door, as well as sealing the lid to the base with some stove cement (or some other way to remove the gap,) and adding as much vermiculite as possible in the heating chamber.

Unfortunately, no one sells rockwool/mineral wool in Juneau (they only sell fiberglass, foam, and cellulose insulation. Rockwool can be purchased via "special order." :)

I would have experimented with K23 firebrick, but my contact in Fairbanks is out of town until next week (and then I have to wait for it to arrive.)

The top of the kiln only gets slightly warm now (even at 2000 degrees,) so I probably could get away with using some plywood as a new lid base. However, I am going to experiment with some metal screen first.
 
You know you might be able to find someone willing to drop the evenheat off at the ferry in Seattle, so you can just pick it up at the terminal. I don't know if that would work, but it might end up being a cheaper option...
 
I was able to cut the door out this afternoon as well as install some window screen to keep the vermiculite in place. Here are some pics:

http://imgur.com/EXCZ7tC
http://imgur.com/BregttS
http://imgur.com/ppgckdD
http://imgur.com/BHBuBcg
http://imgur.com/mbpUxws
http://imgur.com/5FQ5hty

I also added some more vermiculite to the heating chamber, and played around with the lid/base fit. I was surprised I was able to reduce the heat up times even more:

4 minutes 30 seconds to 500 degrees.
9 minutes to 800 degrees.
14 minutes 30 seconds to 1000 degrees.
41 minutes to 1500 degrees.

I then pulled the door out, waited 35 seconds to simulate inserting some knives (temperature dropped to 1400 degrees) and then put the door back in. It took 2 minutes to get back up to 1500 degrees.
 
Sweet deal! Might take a bit longer with putting cold mass in there but still seems pretty efficient.
 
I have serious doubts about how well this will work for doing HT, but you certainly get an A for ingenuity :)

What you have now is a blade sitting on an insulator material, in a very small air volume, directly exposed to the radiant heat of the coils a few inches away. Ask any engineer who deals with thermal things like metallurgical ovens and I bet he will say that is the perfect storm of bad things.
One thing to consider is that short thermocouple is reading the low "K" (thermal conductivity) air, while the coils are directly heating the high "K" blade The vermiculite under the blade probably has the lowest K in the group. This is not a good thing in doing HT.
 
Thanks for the input.

I will probably try heat treating a 1080 blade with the kiln as it is (still need to add a PID,) and then replace some of the vermiculite with firebricks when they are available (hope to order them next week.)
 
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