Crucible Problems

Home enthusiasts discuss their Foundry & Casting work.

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ShorelineJohn
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Joined: Thu May 29, 2014 1:55 pm

Crucible Problems

Post by ShorelineJohn »

Hello all
I hope I am in the right place, if not just tell me.
A while ago I took a weekend type class on casting and setting up a home foundry. Since then I have built a furnace, sand table, lifting and pouring tools. Here is a general picture of my set up.
Image

The problem is that after a few pours my silicon carbide crucible develop cracks and turns to clay. This is a picture of my first crucible.

Image

This crucible had 3 aluminum pours and then a brass pour when this happen. After talking to the store I bought it from they replaced it at no charge even though I told them it might not be their fault.
This is a picture of the second one after 3 aluminum pours.

Image

No where near as bad but after 3 aluminum pours shoudn't be like new?

I got these crucibles at Budget Casting Supply http://www.budgetcastingsupply.com/Crucibles.php
The size is a A10 which they don't seem to sell any more and the crucible looked like the one on the right in the picture than the one in the middle.
I have also followed the steps listed on their web site as to baking and preheating the crucible.
I have gone ahead and ordered a new crucible at http://smallfoundrysupply.com/store/pro ... ucts_id=84
I believe this will be close to fitting my tools and I will be able to adjust them to fit.
The other thought I had was to bake the crucible for a few hours before every pour.
I am really hoping someone can tell me whats going on here and or how to fix it. I hope I haven't been too long winded but that first crucble scared me and this problem is keeping from moving forward. Any help or insight anyone could provide would be greatly appreciated.
ShorelineJohn
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Harold_V
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Location: Onalaska, WA USA

Re: Crusible Problems

Post by Harold_V »

Please accept my comments in the spirit in which they are offered.

That is NOT a silicon carbide crucible. If it has been sold as one, it has been grossly misrepresented.

I've used a huge number of small (#8) crucibles, both silicon carbide and graphite/clay. Neither of those two degrade to what you've shown, and I've used them until they were perforated (from flux). In other words, I've seen the innards of both types on many occasions. I can think of no reason for the color of a crucible to wash out as yours appears to have done, not even if it's graphite clay. What I see is a glaze that is failing. Silicon carbide is black through, and remains so. If it does not, it is no longer silicon carbide, and I know of nothing that will change the composition, although fluxing does dissolve the material (without changing the color).

The crucible you've shown is, in my opinion, nothing more than a clay crucible, and a poor one at that.

Welcome to the board!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
hammermill
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Re: Crusible Problems

Post by hammermill »

not what you thought it was. Good work putting the kiln together.
ShorelineJohn
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Joined: Thu May 29, 2014 1:55 pm

Re: Crusible Problems

Post by ShorelineJohn »

Thankyou Harold.
I am new to this field and can't identify one crucible type from another much less levels of quality. I found the company easy to deal with and they replaced the first one at no charge including shipping, but again they don't list the A10 size any more. They also have a disclaimer on the page saying that the A shape crucibles were not the same quality as their B shapes but the price is right. Should of been my first clue.
I hope I am not going down the same road with the one I just bought, the price is not that bad compaired to others, but I ordered it on tuesday and the guy today said he thinks it shipped but he was not sure.
Are there crucible manufactures You would recommend and or web sites? Google doesn't tell one much about quality.
The other question I had is could these cracks be caused by not baking it before each pour?
ShorelineJohn
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Harold_V
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Re: Crusible Problems

Post by Harold_V »

ShorelineJohn wrote:I hope I am not going down the same road with the one I just bought, the price is not that bad compaired to others, but I ordered it on tuesday and the guy today said he thinks it shipped but he was not sure.
The crucibles I purchased came from a commercial foundry supply (Larsen Foundry Supply, in Salt Lake City, where I used to reside), and they didn't sell anything that may be suspect. I do not recall the brands they carried, but I was satisfied with the performance I experienced, in spite of the fact that some of them were good for only eight heats. I used a lot of flux (including soda ash, which is very hard on crucibles), so the lifespan I experienced was short, but in keeping with the operations I performed. I used them in the refining of precious metals, not for casting base metals, so my application was somewhat irregular from that of the typical foundry.
Are there crucible manufactures You would recommend and or web sites? Google doesn't tell one much about quality.
I have been away from melting for almost 20 years now. I have not pursued crucibles in all that time, although I expect I will in the future. I have much to learn about the current market, having been away for so long. As a result, I hesitate to make any suggestions. I think I would recommend you stick with a major US based producer, though, and ensure that your choice is silicon carbide, or graphite/clay, in that order . I think your experience speaks volumes about why.
The other question I had is could these cracks be caused by not baking it before each pour?
They very well could be. I used clay melting dishes, which are VERY susceptible to fracturing if not heated properly before being put to use. Clay melting dishes were difficult to use, even when properly annealed. The later models were not made of brown clay, and were far more resistant to cracking. I suspect they may have been made of fused silica with a clay bond.

If you live where humidity is high, that may be part of the problem. If so, you can address the issue by using silicon carbide exclusively, not even graphite/clay, which is also moisture sensitive. However, if your choice is graphite/clay, you may enjoy success by simply heating the crucible on a hot plate, keeping the temperature below boiling, so the moisture doesn't flash to steam. Once dry, you can then use the crucible without concern. It is very important to expel the residual moisture if your crucible is not made of silicon carbide.

A little suggestion for you. We are a pretty friendly bunch of guys here---no flaming---no bad language, no personal insults---so you'd be well served to provide your approximate location in your profile, so folks like me have a clue where you reside. No need to provide an address, just narrow it down to the state, and maybe the county, if you're comfortable in doing so. That way, if someone is local to you and can offer assistance, they'll know to speak up. Some folks won't contribute to those who prefer to remain invisible, and I don't blame them. :wink:

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
RONALD
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Joined: Sun Oct 26, 2003 7:27 am

Re: Crusible Problems

Post by RONALD »

I have used #30 and #60 Starrbide Crucibles from Morgan for years.

Here is their web site, they have PDF's available that contain good information.

http://www.morganmms.com/
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steamin10
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Re: Crusible Problems

Post by steamin10 »

My thoughts parallel that of HV. It is a clay crucible, and not very durable.

Clay graphite is good for aluminum, higher heats (Bronzes, Iron) benefit from having silicon carbide vessels as they will erode less over time, making them economic. Iron is not good in a crucible furnace, it is usually run in a lab furnace of induction design, but can use a crucible. They wont be found in a home shop.

The setup you have looks good from here, The lifting tongs and pouring shanks are easily built at home. The limits are how much you can handle by the Armstrong method.

All vessels need to preheat to avoid thermal shock, and put to a pilot flame in the furnace regardless of time out to eliminate moisture. Once the vessel begins to warm, put some metal in and let it button. This gets you a good transfer of heat to the cool metal. All metal should be warm, so that putting it in the vessel does not chill the dew out of the furnace atmosphere. Dont jam material into the vessel, thermal expansion may damage it. Dont ever leave a skull in the vessel to cool. If you lose your furnace during a heat, immediatly dump your charge, or flirt with disaster.
Always use a separate vessel for Al, and Bronzes. This prevents unwanted cross contamination of metals that change the properties. If you have invested the money to build such a system as you have, invest the time to read some books by Ammen or others about professional casting and step up from home guestimates. Buy or build a pyrometer for non ferris heats. Many types of metals are defined in the Machinery hand book, and that is a good place to start to understand what scraps you may run across, and be usable for you, given it is a SWAG at times. Otherwise use bar metal, and dont contaminate it. Heat, and pour, without holding, your best bet.

If I am preaching to the Choir here, I apologise, but this is my basic mantra of casting. I worked in a huge commercial steel and iron foundry, but I am not it. My 3 furnaces at home serve me well when I can use them. Otherwise life gets in the way. Cheers! move forward with confidance.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
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hammermill
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Re: Crusible Problems

Post by hammermill »

I buy from these fellows a lot, http://lagrandindustrial.net/ friendly to the small guy.
ShorelineJohn
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Joined: Thu May 29, 2014 1:55 pm

Re: Crusible Problems

Post by ShorelineJohn »

Thanks everyone for the replys.
I live in Shoreline Washington, just north of Seattle, it's wet here but the humidity is low. I will update my profile as soon as I figure out how.
I have got a couple of books but none by Ammen I will look for it.
This crucible was sold as silicon carbide and I just don't have the experience to say different. I should recieve a new one this week and will follow a strict porcedure of preheating before each firing. Hopefully this will produce better results.
Thanks again.
ShorelineJohn
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Harold_V
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Re: Crusible Problems

Post by Harold_V »

ShorelineJohn wrote:Thanks everyone for the replys.
I live in Shoreline Washington, just north of Seattle, it's wet here but the humidity is low.
Chuckle!
Well, that's a relative comment. Now that I understand that we're "neighbors", I'd suggest to you that humidity, here, isn't all that low, keeping in mind that I came from an environment where it wasn't unusual to see single digit readings in the winter.

I run several dehumidifiers, and they run regularly, trying to keep humidity at or below 50%.
I will update my profile as soon as I figure out how.
I'm going to assume that you use the default program (subsilver2). Use the User Control Panel button, located at the top right hand corner of your monitor (top of this page). That will open a second page. Select the Profile button, which you'll see at the left hand side of the monitor, located near the center, vertically. That should open the page on which you can place your location. It's the 7th. line, counting down.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
DavidF
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Location: Delaware

Re: Crusible Problems

Post by DavidF »

i get crucibles from here..http://www.lmine.com/mm5/merchant.mvc? thier clay graphite have been holding up well for iron melts...
OddDuck
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Re: Crusible Problems

Post by OddDuck »

It's the crucible. This problem surfaced several years ago on Alloy Avenue (and perhaps Backyardmetalcasting.com, not sure of the exact date...) specifically with that "silicon carbide" crucible from BCS. Many casters had the exact same problem you did. If I remember correctly, as long as the crucible passed the "ring test" aka flicking it with your finger and listening to it before you used it (dull flat sound means cracks, don't use it) it was okay and lasted about the same amount of time as a regular clay graphite. The "silicon carbide" is just that outer layer that's flaking off.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
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