Heat Treat Oven for Iron Build

I started another thread dedicated to a standoff production method here:

http://forums.thehomefoundry.org/in...nded-mullite-based-refractory-standoffs.1695/

Denis

 

I finished assembly of the heat treat oven last night and did a test run and then a stress relief load today. The furnace performed better than expected. It heats very rapidly and the skin temp got up to an estimated 130 to 140 degrees.

Incidentally, today's runs were done with no gasket between the lid and body of the oven.

A good thing noted was the benefit of using quadruple thickness leadouts vs the ususal double leadouts. The leadouts did not become red hot at all and the junctions with the mains stayed relatively cool too. On the kiln project I only double the leadouts and they became quite hot. No trouble so far, but they get to a low red color and that stresses the junction of the leadouts with the mains connection. That is why I decided to try the quad twist this time. Seems like a good plan going forward.

As expected, the Bartlett board is extremely easy and quick to program and does just what it is supposed to do. On note on putting it together. I did search around and found a 12V AC mechanical relay to use with it. But, AC mechanical relays are few and far between. Still the board requires a center-tapped AC transformer putting out to 12v leads with a center neutral. That is no problem to find. And the board outputs a 12v dc signal to drive a relay. That was the rub. I felt compelled to use an AC relay. But, what I could have done and what most people probably do is to use a dirt cheap and very common bridge rectifier to convert the AC output from the board to a DC signal. Next time that is what I will do.

The other note on the board is that it offers an output pin to "do something" for an over-temperature condition. I have not yet utilized that feature. But I think I will find a way to trigger a mechanical switch to open and, once tripped, to remain open until reset. Can someone suggest a simple mechanism for that. I guess it would be similar to the reset button often included on power strips etc. I have not yet done any searching for such. But I will begin tonight.

The standoffs worked great. They were easy to install and secure the heating coil nicely. I spaced them every 5 inches, but I do not know what the maximum spacing might be.



The copper crimped main-to-heater connection is in each of the two smaller box. I drilled a sizable grill of vent holes in the bottom and inside wall of the boxes. I used 10 ga mica wire as mains to the resistance wire.


Denis

 

I made a new thread on making a safety power interruption circuit for the furnace.

http://forums.thehomefoundry.org/in...ptor-for-an-electric-furnace.1697/#post-38337

Denis

 

ERROR IN POST 14 above. My apologies and my bad.

The output pins"Safety," 1,2,and 3 are 12v DC not AC as I erroneously stated above. My apologies for my incorrect reporting.

Here is a link to their tech manual:https://binst.s3.amazonaws.com/uploads/manual/asset_path/36/v6cftechnicalmanual.pdf

And here is their contact info. They do answer the phone and did connect me to a tech guy right away. Kudos to a "real" company supporting their quality product.

Address: 1032 Ave H, Fort Madison, IA 52627
Hours:
Open ⋅ Closes 4:30PM
Phone: (319) 372-8366
Contact Email: information@bartinst.com crunchbase.com

Denis

 

Today I decided to add 1" of insulation to my heat treat oven. It does fine getting up to 1150 for iron stress relief. But, annealing iron calls for 1750 F and that was possible with the 2" insulation, but required nearly continuous current in the heating coil. Adding the the inch on wool and improving the gasket on the lid should help considerably. There was a modest gap between the body and the door in the original build and I had not yet gotten to adding clasps at several points to pull the lid down onto the body of the furnace. That comes soon.

I did "discover" a way to make it easier to pass the tie wires through the insulation so that I could come closer to hitting the crossing of the two SS welding filler rod used as retaining bars for the insulation.

For the tie wire I used approximately .030 SS tie wire that I got at my local (good) hardware store. One problem is that it is sold by the foot from a 3" reel of wire. That means it has all the turns bent into it and is something of a rats nest when you take it home. The solution for the waviness is to put one end in a vise and then use a vise grip to stretch a maybe 10 foot section. That straightens it nicely. I was fascinated to actually feel the wire stretch when I pulled on it after it was made straight and taut. You could clearly feel that a fairly strong pull caused it to lengthen PERMANENTLY and it remained nice and straight. I would guess the lengthening might have only been an inch or two in ten feet. But it was noticeable.

Then I cut the wire into about 6.5" lengths and grasped each length with a needle-nose plier at its midpoint and applied pressure close to the pliers in such a way that a long-legged staple was formed but the legs of the staple were not bent. From that point it was pretty easy to carefully insert each of the legs in the paired holes in the steel outer plate and straddle a crossing point of retaining bars and then use the special pliers to twist the wire as before.

Here is the layer of wool secured to the lid. There is a "set-back" to the added layer as the side walls will soon be thickened in the same way. The set-back allows clearance for the side walls.




A segment of wire ready to bend.


A bunch of "staples" ready to insert and twist. If they have fairly straight legs,
they track more truly and do not veer off from the desired direction in the wool.
Crooked legs make directing them nearly impossible.


Denis