CraftWEB Hot Glass Talk

CraftWEB Hot Glass Talk (http://talk.craftweb.com/index.php)
-   General Hot Glass Discussion (http://talk.craftweb.com/forumdisplay.php?f=4)
-   -   Casting a new crown. (http://talk.craftweb.com/showthread.php?t=11622)

Mike Kaplan 07-12-2017 01:40 PM

Casting a new crown.
 
I'm looking for some advice. I am building a new furnace and looking at my old crown I see that the skin it is peeling in layers.
Are used to cast a light 30. Are there any recommendations for a crown that would last longer without peeling?

Eben Horton 07-12-2017 03:18 PM

Can't beat castolite 30 imho..... crowns are meant to be replaced every 10-15 years I think.

That said, a friend used huge silicon carbide kiln shelves as a crown and swears by them.

Kenny Pieper 07-12-2017 05:15 PM

Quote:

Originally Posted by Mike Kaplan (Post 135571)
I'm looking for some advice. I am building a new furnace and looking at my old crown I see that the skin it is peeling in layers.
Are used to cast a light 30. Are there any recommendations for a crown that would last longer without peeling?

If you are melting batch I would recommend that you use something harder and more durable than cast a lite 30. Ask your refractory source. There are so many options now days.

Mike Kaplan 07-12-2017 11:42 PM

Thx for the advice. I always seem to forget to ask the experts first.

Mike Kaplan 07-13-2017 09:57 AM

I would say this crown lasted 3 yrs and i use cullet. It didnt crack but it is pealing

Justin Zotynia 07-13-2017 11:35 AM

I used kastolite 30 for my crown and used cullet worked well no peeling. maybe every furnace environment is different due to design. don't know just that it worked for me.

Jordan Kube 07-13-2017 11:40 AM

I would use something a little heavier duty than Kast-o-lite. Some people have good success with it. It doesn't seem to be the case in your furnace. Make sure you mix thoroughly and to manufacturer's instructions as well.

Eben Horton 07-13-2017 12:44 PM

I'd bet you a case of beer that when you made your crown 3 or 4 years ago, you made th mix too wet. If you mix it right, it will last a long long time. Mix it wet and the casting will be brittle and won't last. I learned this with glory hole and furnace doors. Also, make it thick. At least 4 inches and give it a nice arch to give it strength

Eben Horton 07-13-2017 12:44 PM

Oh.... I forgot to mention, I would use castolite 30 plus. Not the stock castolite 30

Sky Campbell 07-13-2017 01:21 PM

Quote:

Originally Posted by Eben Horton (Post 135587)
I'd bet you a case of beer that when you made your crown 3 or 4 years ago, you made th mix too wet. If you mix it right, it will last a long long time. Mix it wet and the casting will be brittle and won't last. I learned this with glory hole and furnace doors. Also, make it thick. At least 4 inches and give it a nice arch to give it strength

That has been my experience. To much water and it spalls over time. Don't forget to vibrate air voids are weak points.
I really can't imagine a better product for a crown. I have never found a product that compares. Green cast for an early furnace failed miserably.

Art Freas 07-13-2017 08:26 PM

OK, I am almost ready to post my door learnings but want one more round before I do it. However one thing I would say for doors. If it vibrates down it is probably too wet. If you put 9 pints with 55lbs you can tamp it but not really vibrate it. So far extremely dry and tamped is working pretty well. Not sure how that would work with a dome form though.

Eben Horton 07-13-2017 09:50 PM

Quote:

Originally Posted by Art Freas (Post 135595)
OK, I am almost ready to post my door learnings but want one more round before I do it. However one thing I would say for doors. If it vibrates down it is probably too wet. If you put 9 pints with 55lbs you can tamp it but not really vibrate it. So far extremely dry and tamped is working pretty well. Not sure how that would work with a dome form though.

Spot on. I mix mine so dry you'd think it's way too dry but it hardens rock solid. When I fill forms to cast parts, I add small amounts at a time and trowel it down and compress it into corners to assure there are no voids. That said I have never tried the vibration technique

Peter Bowles 07-15-2017 09:08 PM

I would urge you to find a way to vibrate the castable as it goes into the mold - it will make a significant difference to the final density of the casting.
It does mean you have to have the mold very securely braced and any gaps filled, but you will get a much better result than by just tamping alone. It also means you can use the specified quantity of water too - which as already mentioned is a critical aspect of these materials.
There are many inexpensive pneumatic vibrators available now - a seriously worthwhile investment I think. I used to set molds up on an old reciprolap with great success, but now use a wee hand held thing.
Once you see these castables flow under vibration you'll understand how tamping just won't cut it - particularly for structural castings.

Peter Bowles 07-15-2017 09:24 PM

If your molds are reusable, permanently mark on them the final volume or weight of the castable used. Will make the whole process much more economical in time and materials next time around.

Steve Stadelman 07-16-2017 12:12 AM

Peter is right on with sage advice. Harbor Freight makes a pin vibrator that's practically disposable for just these occasions.

Dennis Hetland 07-16-2017 02:57 AM

Is this a combustion furnace? I Don't understand why you would run a combustion furnace for cullet.
It's not one of those electric furnaces the have u shaped elements dropping through the roof is it? Those furnaces have holes in the roof where your money flies out.
IF It's an electric furnace and you're melting cullet I wouldn't use castable. It has very poor insulating properties compared to IFB.

Michael Ahlefeldt-Laurvig 07-16-2017 08:56 AM

In my oil fired 350 kg pot furnace I got talked into using the lite 30 by a salesman- in spite of having had a crown like that fail on me before- After 2 years it failed and I replaced it with Greencast 94- after 15 years when that furnace was retired the crown looked like it was new.
Dennis , in my case the choice of combustion furnace was due to the power company- I needed 100 amp 400 volt 3 phase main fuses. My studio was a couple of miles from the transformer they would have to upgrade from. out in the country.The cost proposal almost 30 years ago was 30,000 just to do it + change a local transformer 7000, then the labor and cost of 300 meters cable to my studio- that money would have bought a small farm at the time.
Also, dense cast crowns are usually insulated on the outside :-)

Pete VanderLaan 07-16-2017 09:58 AM

I would not be inclined to make the hot face of a crown with insulating castable. I would make it out of a high alumina castable and make damn sure that I didn't have to remove the crown to change the pot. Cheyenne is making his moly's that way now. The vibrator is critical to a good casting, particularly if it's five inches thick.
The single best high alumina castable I've ever used is MORCO 95 ( Missouri Refractory Company). High Temp in Fenton Missouri handles it and accept no substitutes. I had a crown in service for five years with it and it looked brand new. I would insulate the snot out of it with both 2600F and standard 8lb density fiber. Then I would go to enormous lengths to never touch it again.

As to cullet, it can be very deceptive stuff. The borax that keeps winding up in those products has a poor ionic bond and dissociates pretty easily. Boron is really good at attacking both silicates and fireclays. It's that yellow fluff near your door that is dissolving everything. There's no free lunch. If your cullet melts easily at low temperatures, there's a reason. Put a vent on your electric units if you do use cullet. Just plug the vent when you aren't melting.

Dennis Hetland 07-16-2017 12:06 PM

I designed front loading electric furnaces. The front tears away in two stages. You can just disassemble the archway, but you can disassemble the bottom as well to get inside for maintenance. It's all machined IFB. No walls to demolish and recast. You can simply replace single bricks. (that you can buy from me for only $10)
I've met Cheyenne a couple of times. He's a friend of a friend and makes a good product. I don't have anything against Cheyenne, but my furnaces are much more efficient. I have 27" of insulation on top of the crown with no penetrations. Plus my design creates firing chamber that is 25% smaller than a molly furnace.

Eric Trulson 07-16-2017 12:45 PM

Quote:

Originally Posted by Peter Bowles (Post 135611)
I would urge you to find a way to vibrate the castable as it goes into the mold - it will make a significant difference to the final density of the casting...Once you see these castables flow under vibration you'll understand how tamping just won't cut it - particularly for structural castings.

One more voice in the chorus of agreement here. Vibrating is 100% necessary for castables that are intended for it (it will usually say in the manufacturer's datasheet whether a castable is intended to be vibrated or rammed).

There are good cheap commercial vibrators available, but in a pinch I've used a sawzall with the blade taken out, just pressing it up hard against the side of the mold and holding down the trigger, and giving the mold a little shimmy back and forth by hand at the same time. You will be able to see when the vibration "takes", the castable starts to flow much more quickly and gets a very faint liquid sheen on the surface (NOT water pooling up on the top of the castable. That generally means you have over-vibrated and it's time to stop)

David Hopman 07-17-2017 01:40 AM

The cheap air hammer I bought to chisel through glass buildup on the furnace also worked great as a vibrator for the castable.


All times are GMT -5. The time now is 10:36 AM.

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.