View Full Version : New crucible installation 300# Stadelman Furnace

Tim Bassett
01-29-2012, 05:00 AM
I am about to replace the crucible in our furnace. I will tilt the existing crucible with a brick before we cool down to facilitate removing the old crucible . The thermocouple protrudes into the chamber so I will have to pull it out at least an inch or so.I am concerned that the thermocouple may be glazed in place. Should I remove the thermocouple completely from the furnace or just pull it back so it no longer protrudes? I am aware to take plenty of care of the elements and will leave the element straps on the elements and take plenty of care.
I will also put some timbers to brace the roof when I remove it.
My crucible arrived 2 months ago and as yet I have not opened the crate. The crate looks in good shape and I am trusting the crucible is good. (Hey, its summer here and we have been really busy)
Any suggestions on the best way to do this job will be gratefully accepted.
Because we are about to replace the crucible we decided to see if we could have some fun and make some coloured glass. We use gaffer batch which we buy from the local manufacturer 70 miles away. We probably have 60# of transparent glass left in the bottom of the crucible.Charged 60# gaffer batch mixed with elemental selenium, next two charges(120#) just batch and then the last 60# gaffer batch mixed with nickel oxide. It will be interesting for us to see what happens.If it works o.k. I will try to post some photos.

Pete VanderLaan
01-29-2012, 05:20 AM
I have taken pieces of plywood and pre drilled them with holes for the ropes to lift the crown Tim. Put them on the inside of the furnace when lifing. Any way you can distribute the stress is good. If you can get the thermocouple loose without breaking the tube, do that by rocking it gently. If it isn't sticking far in to the furnace and it isn't really in the way of the pot coming out, I'd leave it alone. We have what we call Sod's Law here which is " If you disturb it it will break". I think you are no worse off if an accident happens to the tube since it's likely it would break trying to remove it. Those tubes are good for about a year, not much more, and Gaffer batch being high in Boron will melt everything together. When I want a pot out of the furnace, I just smash it. It's easier to get it over with.

Bad to not check the pot right away. If it is damaged there is no way to make any kind of a claim after that much time. Cross your fingers. That is true of elements as well. Look at them immediately. I guess your friends there have major transformer issues on the road for going electric. We suggested we could build propane as well but have not heard anything.

Tim Bassett
01-29-2012, 06:05 AM
Thanks Pete. The thermocouple protrudes too far for me to consider removing the crucible in one piece and would also make me wary of installing the new pot.Should I organize a new tube...we have been hot now for about 30 months so the tube has done well.The furnace has amazed us, we have done no maintenance apart from cleaning spilt glass through the cleanout port in the bottom. I was very careful to use the noalox and tightened all my element connections to the best of our ability. The door has been eaten a bit but I never knew to vent until it was a bit too late. I will cast a new door and put a vent in place. Better than a Mercedes.

Pete VanderLaan
01-29-2012, 06:49 AM
I've heard a lot about Mercedes lately.

30 months is a long time to not do a sustained maintenance on the element parts. Check each heavy cable, at both ends for oxidation ( blackening). If in doubt, cut those cables back to fresh wire. Do it in the transformer as well. The Buss blocks holding the wires will not come apart well at all. You should have new ones ready to go. In this country we call it a 600MCM buss block. Always have at least one spare. They always seem to fail on Fridays at 5:01 PM. Inspect and tighten the wires leading from your relay to your SCR to your transformer as well. Clean and cut as necessary. Inspect your cables for fraying between the elements. Re- noalox everything and tighten.

If you can get a new thermocouple tube easily, do it. Having a spare is wise. They really have an 18 month life span for the most part. I'm sure I will now hear about one installed in 1978 that still works.

Make sure you have spare fuses.... now. They can be hard to acquire.

Allan Gott
01-29-2012, 05:26 PM
Hi Tim...one thing for sure........open that crate and check the new crucible before you shut your furnace off......it'd be awful to find it cracked after the furnace is cold.........your colour experiments sound like fun....be cool to see some pics....my best regards to you and Tali

Pete......does High Temp nest pots for shipping if you order a couple or pack individually?

Pete VanderLaan
01-29-2012, 05:47 PM
we individually crate. Nesting vitreous stuff breaks things. We never did it at EC either. It's not a good idea. Checking your crate after it's traveled 12,000 miles is a good idea too.

Steve Stadelman
01-29-2012, 06:25 PM
Oh those peripatetic crates!

Barb Sanderson
01-29-2012, 06:41 PM
When I do my pot changes I make sure to remove the thermocouples completely and pack them in insulated fibre as soon as I turn off the furnace. You are right to use the brick to tilt the crucible but be very aware of the angle since the front elements on either side of the door can come pretty close to the pot if angled too much.
Once cool I undo all connections up top and carefully remove those damn elements. Carefully! Be sure to have a safe flat secure space to place them while doing everything else.
Then I take four rachet straps and thread each one down one element opening and back up an opening on the other side of the crown. Repeat four times. Then I tie the straps to the hoist and lift it off. Move the furnace out of the way and place the crown on a marver or someplace large enough to support it for a while and preferably on wheels.
Then I use C Clamps (4) and attach them to the outgoing crucible and tie it to the hoist and lift it out. Repeat in reverse for the new crucible.
Reverse everything for starting back up - check and recheck your elements for continuity before reattaching the straps and wiring. Listen to Pete about checking all connections and make sure your wire is not cracking or looking black anywhere. If so, cut back to good wire and reattach.
Good luck - here's some pictures...

Pete VanderLaan
01-29-2012, 08:32 PM
you look like a toddler in a playpen Barb.

Barb Sanderson
01-29-2012, 08:40 PM
With a ventilator on? :)

Pete VanderLaan
01-30-2012, 05:12 AM
We call those respirators where I come from Missy. You ain't quite old enough for a ventilator.

John Riepma
01-30-2012, 02:51 PM
I thought it was the Hannibal Lecter model pacifier

David Russell
02-01-2012, 07:42 PM
i have not attempted the tilting of the pot before shut off. It looms in my future sometime this year.

It seems such a tight space i fear i will whack the wall or an element when leverging the pot, as touched upon by barb.

How is this done with finesse?

Jordan Kube
02-01-2012, 08:18 PM
Apply steady firm pressure. Don't go crazy. A lever is nice. It will come loose.

Barb Sanderson
02-01-2012, 08:23 PM
I use a spare firebrick and have someone slowly winch with a pipe between the pot and the wall just enough to get the brick in there (using long tongs), hold the brick there and let them release the pot. Also one other very important lesson learned....
When removing the elements and bricks up top, make sure to label each element and where it came from - over time these puppies sag and turn so knowing where they fit is best once putting things back together.

David Patchen
02-01-2012, 09:46 PM
We used a crowbar to tip the pot back a little, then inserted a half brick by drilling a hole in it and setting it in place on a small punty. You can stay further away from the heat this way vs. tongs. But if you have a smaller furnace maybe it doesn't make a diff....we were doing this on a 600lb Stadelmelter.

Pete VanderLaan
02-02-2012, 05:41 AM
I took a five foot long piece of 2x2 inch squarestock steel tubing and ran one end of it through a trip hammer and flattened it. It slides very nicely down in front of the pot. Only try this with the furnace really hot, as in, really hot! Put the lever in and as Jordan says, just apply steady pressure. It will come loose after about 30 seconds. Then let it go and turn the furnace off. Come back in fifteen minutes and do it again. It will come loose far easier. It will come completely free when cold with just a mild tap on the pot.

Steve Stadelman
02-02-2012, 09:54 AM
One more problem with the stadelman furnaces. The extra expense of a trip hammer ;)

Pete VanderLaan
02-02-2012, 11:53 AM
And the flatbed White freightliner to haul it around!

Doesn't everyone have a triphammer? Harbor Freight lists one, doesn't it?

Rollin Karg
02-02-2012, 12:51 PM
I want a trip hammer !!! How did you come to have one ?

Pete VanderLaan
02-02-2012, 01:25 PM
I used Tom Joyce's trip Hammer back in Santa Fe. Tom called it "Profit Margin". God what a beast! I really enjoyed working with him. He has done well for himself.

Scott Dunahee
02-02-2012, 06:21 PM
For breaking crucibles loose while hot, we always used a breaker bar. It's a 5' solid flat crow bar that is 1"ish square in the bottom 2 feet and tapered to an easy to grab round handle on the "top." It cost like $20 at the local farm store.

I never managed to bend the breaker bar on this or any other project, but I sure as hell tried. It did not care about furnace temps at all for all the times we used it for this.


Tim Bassett
03-03-2012, 06:18 PM
Thanks to everyone who replied to this thread, it certainly made the crucible change easier. I opened the drain port and removed any glass on the floor and then used a lever placed through the drain port to tilt the crucible and used the soft brick on a punty to keep it tilted, the crucible broke free with a small amount of pressure once everything was cold. I numbered all the elements and straps and took photos to help me reassemble. I used 4 g clamps to remove the old crucible but did not feel comfortable reversing that procedure with the new crucible so I used webbing which was not too hard to remove once the crucible was in place. I cast a new door with a vent in it which was pretty easy. The door arch on the furnace was a bit crapped out and I thought I might patch it with rammable which I tried to do but it did not look like it would hold so I removed the rammable and spent an hour or so with a diamond grinder and ground the arch pretty flat. I replaced the first three layers of fibre on the roof as it had started to detiorate, there were no chimneys and all my wires looked in good shape. I am now at 400c after 24 hours so hopefully tomorrow I can start to charge. Thanks again to everybody that helped.I would be really stuck without the wonderful resources that reside within Craftweb.

Michael Ahlefeldt-Laurvig
03-04-2012, 08:47 AM
You have another 800 C to go in 24 h?- thats 33 C an hour straight without counting the quarts inversion zone, sounds a bit fast?

Pete VanderLaan
03-04-2012, 08:51 AM
I tend to agree that it's fast and quartz inversion should be paid its due. It's particularly true in Molys since they have no convection flow. The difference between the lip temp and the foot temp can be remarkable. I suggest stopping at 1000F for four hours and then going to 1100F over six hours, then stop at 1100F for four hours again. Then proceed at about 35-40F per hour until it glows. Then, turn it up.