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Roger
01-10-2011, 10:43 AM
Since I enjoy building things I decided to build my own heat treat oven. At a local pottery supply I got all the parts for a 110v oven. I was thinking of 220v but the guy there convinced me I could get to 2000* using 110v. After finishing I had it on high for a couple of hours and could only reach 1360*. I am using K23 bricks and followed all the instructions. The guy made up the heating coils for me and said to stretch them double.

Could I have stretched the coils to far or not enough? They got a dull red at the 1360* but that was about all.

12345678910
01-10-2011, 11:35 AM
We need MUCH more info

What is the volume of the oven?

What are the specifications of the element?
Wire type, diameter, length..etc

what wattage, amperage is your system calculated to be?

In general, 110 can work, but will take longer and is only practical with a small oven.

Roger
01-10-2011, 12:06 PM
Oven ID is 6" wide X 4" tall X 12" deep. Supposed to be 1500W @ 15A. Not sure what wire it is but the place I got it from builds kilns and had a rack full of pre-made elements. The guy working there said for what I wanted he needed to make a special element and brought me back one that was 4' long and said to stretch it double and be sure that in the bends none of the coils were touching each other. I also got the bent hi-temp 'staples' to hold the element in the grooves. The control he gave me had infinite control from 'Off - High' and seemed to vary the temperature ok but 'High' just wasn't 'High' enough. I also have the bricks in a steel 'case' like on the British knives website. Being green at this I fugured I'd glue the bricks together with high temp furnace cement to hold them and seal the seams from heat loss.

Thanks for your help in this.

ARCustomKnives
01-10-2011, 01:25 PM
Are you sure your controller is set to Farenheit and not Celsius? I've heard of guys having similar issues, wondering why their adhesives were bubbling at such a lower temperature than the product rating stated... ;)

Other than that, you may have your controller/element wired incorrectly, or you might be using the wrong type of thermocouple. Also make sure that your are getting 120VAC across the contacts that your element is connected to.

By the way, what type of controller are you using? How did you wire it? How are you setting it? If it's a digital controller, it may need to be "programmed" before it functions correctly. If it's an analog controller, or something that you can't set a specific temperature for, it may not operate up to 2000*F. Some controllers are only rated for use up to a certain temperature, such as 1000*F or so. You may have been sold the wrong kind.

ARCustomKnives
01-10-2011, 01:45 PM
Also, I hope that the furnace cement you used is rated for 2300*F and not the kind used for fire boxes. Otherwise, your bricks may not hold together very long.

Not all refractory cement is created equal.

Roger
01-10-2011, 02:59 PM
Thanks AR for the tips. Might be that the controller won't pass enough 'juice'. It was a cheap-o to use till I got a programmable one. I'll try just running it with just an ON/OFF switch to see if it heats up with direct power. I'm using a K thermocouple with a Fluke and an off-brand temp display and they both read the same in F. The cement isn't actually to hold anything together, I just added it to help seal off the seams to retain heat.

Roger
01-12-2011, 05:33 PM
I bypassed the temperature controller and it took an hour to get to 1000* and was still climbing but very very slow. I still don't think it will get to 1500+. The internal dimensions are 13" deep, 5.5" wide and 5" high and sealed tight. Anyone have any ideas on how to raise the temperature?

Rudy Joly
01-12-2011, 05:59 PM
You might try a shorter run on the heating element. Instead of stretching it out double, try less and still keep the coils apart. If 110v is actually enough juice then it's a resistance problem with the element. (probably too long )

Personally I'd rewire for a minimum of 208v if the controller or infinite switch will handle it and keep the kiln on a dedicated line. You may also have to get a larger guage element.

Rudy

ARCustomKnives
01-13-2011, 11:43 AM
At only 1500W/110VAC, it's gonna take a bit longer to get up to 4 digit temps, but I would think it shouldn't take an hour or more.
I personally use a 3000W element on 220VAC, but it only takes about 15 or 20 minutes to get to 1500F for me.

As for being a possible resistance issue, I'm sure this might contribute some, but I can't imagine it's a lot.
How are you actually connecting the voltage to your element? Are you sure you're getting the full 110V across the element itself?

Roger
01-13-2011, 12:43 PM
In the brick in back I drilled holes for the twisted ends of the elements. I used the SS crimps that were supplied with high temp wires to the controller, used the correct crimping tool and filled the holes with high temp cement. I have a 15A breaker that hasen't tripped and none of the wiring or the connections get even the slightest bit warm. My connections are good, I think the problem is either element length or I should have trusted my gut and went 220V.

Rudy Joly
01-13-2011, 04:44 PM
Trust your gut.

Rudy

Roger
01-13-2011, 05:56 PM
For the knowledge I'll shorten it and try again....but, I have a digital controller and relay coming so I'll get 220V coils. Any idea where the best (sends you stuff that works) place to get correct elements is?

ARCustomKnives
01-13-2011, 06:01 PM
For the knowledge I'll shorten it and try again....but, I have a digital controller and relay coming so I'll get 220V coils. Any idea where the best (sends you stuff that works) place to get correct elements is?

http://www.duralite.com/store/scripts/prodView.asp?idproduct=108

That's where I got my element and staple wire from. Very reasonable prices too.

Rudy Joly
01-13-2011, 07:16 PM
These guys give some specs on thier elements. It may help match what you have built already.

http://www.budgetcastingsupply.com/Heating-Elements.php

Rudy

Roger
01-17-2011, 08:07 AM
As an FYI....I played around with the oven this weekend. I figured I wasn't out anything if I ruined the elements I had so I started by cutting a foot off of it. That didn't help and its a PITA to re-assemble so the next time I cut 2 feet off. Danged if it didn't start getting hot faster. In 50 minutes it gets to around 1550. With the oven style control I have I could adjust it to stay within +- 30*, 40*. After cycling it 5 times over Saturday and Sunday I figured it was working. I started to try and figure out the PID and the manual was written for a Chinese electrical engineer with a Phd. I got the one from Ebay that had been recommended here. Is there a simple way to program these things?

Wolfe
01-17-2011, 03:07 PM
If you have the simple controller from Ebay like I have, the manual tells nothing. I just punch in the temp I want and it goes there and cycles at that temp. The programmable ones are about twice the cost and do have to be programmed.

Roger
01-20-2011, 07:54 AM
I now have the oven 99% done and it gets hot. I've attached a few pictures of what I've ended up with. The elements will probably need to be replaced, sooner than later. Since I experimented trying to get it up to temp. I cut and re-configured the wire twice so it took some re-bendend and straightening. The door gasket is 'glued' on with 2000* furnace cement and took 10 minutes off of my heat up time.195291953019531

ARCustomKnives
01-20-2011, 09:20 AM
As an FYI....I played around with the oven this weekend. I figured I wasn't out anything if I ruined the elements I had so I started by cutting a foot off of it. That didn't help and its a PITA to re-assemble so the next time I cut 2 feet off. Danged if it didn't start getting hot faster. In 50 minutes it gets to around 1550. With the oven style control I have I could adjust it to stay within +- 30*, 40*. After cycling it 5 times over Saturday and Sunday I figured it was working. I started to try and figure out the PID and the manual was written for a Chinese electrical engineer with a Phd. I got the one from Ebay that had been recommended here. Is there a simple way to program these things?

What type of controller are you using? Do you have a link to the manual?

I know that with mine ($40 model from Auberins.com) there was a very simple way of "configuring" it by selecting a particular setting when I first turned the oven on. The controller then used some kind of "intelligence" to determine the best way to control the element based up input from the thermalcouple and what not. Once I set it the first time, I was good to go.

Before I configured my controller, I was getting temperature sweeps of 15 to 25 degrees with the door closed. Now I'm holding within +/- 1 or 2 degrees at the most.