Fabricating Crucibles

Home enthusiasts discuss their Foundry & Casting work.

Moderator: Harold_V

Post Reply
AllenH59
Posts: 469
Joined: Wed Mar 16, 2011 1:26 pm
Location: Prince George BC Canada

Fabricating Crucibles

Post by AllenH59 » Tue Jan 04, 2022 1:53 am

It is winter, and things are very cold and the snow is deep. I am thinking of building a forge in the spring, and casting a bit of brass and bronze, and aluminum. For metals in these melting ranges is it appropriate to just make a crucible? I would think that mild steel would be ok. I am new at casting, I have not cast anything since metal work class in grade 10, in 1975. Part of what I want to do is just salvage material and make it into useful pieces of rod or tubing etc, although no doubt there will come a time when a part needs to be cast. Thanks, Happy new year.

Harold_V
Posts: 19353
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Fabricating Crucibles

Post by Harold_V » Tue Jan 04, 2022 2:24 am

I am not a fan of metallic crucibles. My years of experience refining precious metals taught me the importance of not exposing fluid metals to other metals, as they are strong solvents. Said another way, if you melt aluminum or copper alloys in steel, you can expect the molten metal to dissolve the steel vessel. It's bad enough that the melting vessel enjoys a short life, but much worse considering the iron dissolved tends to ruin the qualities of the melted metal. It's just not a good idea, in spite of the fact that many do exactly that.

Why don't you consider buying the proper crucible? They are available made from graphite/clay or silicon carbide. The silicon carbide variety are considerably more shock resistant than the graphite/clay variety. They're not prohibitively expensive, and should last you for multiple heats, assuming you limit the use of fluxes.

If you must use steel, consider applying a refractory wash, which will limit the dissolution of the vessel.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

AllenH59
Posts: 469
Joined: Wed Mar 16, 2011 1:26 pm
Location: Prince George BC Canada

Re: Fabricating Crucibles

Post by AllenH59 » Tue Jan 04, 2022 5:01 pm

Harold, I am not so much cheap as not knowing what to buy, Silicon Carbide sounds like the ticket, thank you. I saw you mentioned that you had some crucibles with size numbers, what do the numbers mean? I am looking to be able to do something like 5 lbs of brass/bronze max.

jscarmozza
Posts: 553
Joined: Mon Mar 03, 2014 5:09 pm

Re: Fabricating Crucibles

Post by jscarmozza » Tue Jan 04, 2022 7:30 pm

Check out PMC Supplies, they have a nice variety of crucibles, brush up on your metric conversions from Kg to Lbs and Cm to In, they list everything in metric units.

User avatar
10KPete
Posts: 428
Joined: Wed Sep 30, 2015 5:29 pm
Location: Nordland, WA, USA

Re: Fabricating Crucibles

Post by 10KPete » Tue Jan 04, 2022 7:38 pm

I've been told that the crucible number is the weight of bronze it will hold when full.

?????

Pete
Just tryin'

choprboy
Posts: 309
Joined: Sat Oct 29, 2011 11:23 pm

Re: Fabricating Crucibles

Post by choprboy » Tue Jan 04, 2022 8:47 pm

Some places say the number represents the pounds of aluminum that the crucible can hold, others say it is the kilograms of red brass/copper it can hold. Seems like everybody has a bit different definition and you need to look at the actual dimensions as a #50 on one site may be virtual identical in dimensions to a #55 or #60 on another site... They also tend to come in some basic shapes: "A" shape which is a basic vase, narrow at the bottom with a moderate middle diameter and slightly wider at the top; a "B" or "bilge" shape, narrow at the bottom, wide in the middle , and slightly narrower at the top; and a "C" shape, straight walled with a spout. But again exact shapes can vary a lot...

In addition to PMC Supplies there is also (no particular order or experience with all of them):
- Legend Mine Supply (LMine)
- Pieh Tool Company
- Budget Casting Supply (BCS) / Budget Foundry**
- Small Foundry Supply
- MIFCO

** Years ago I bought stuff from BCS and had no problems at all. I had heard that they were going under or had been having problems of some sort/customers were unhappy Their website is completely different now and has almost nothing listed... so I don't know if they are the same entity now.

FKreider
Posts: 292
Joined: Fri Feb 02, 2018 8:44 pm
Location: Sturbridge, MA

Re: Fabricating Crucibles

Post by FKreider » Tue Jan 04, 2022 9:10 pm

Just buy a graphite crucible off amazon - perfectly good for hobby use:

https://www.amazon.com/Foundry-Graphite ... 116&sr=8-8
-Frank K.

RONALD
Posts: 668
Joined: Sun Oct 26, 2003 7:27 am

Re: Fabricating Crucibles

Post by RONALD » Tue Jan 04, 2022 9:29 pm

It is the pounds of aluminum that a crucible holds that determines its number.

Look thru the information posted by Kramer: http://www.hkramer.com/foundry-data-handbook.html

In the attached photos, there is a McEnglevan B30.

It is made for a #30 Crucible: https://mifco.com

https://mifco.com/shop/crucibles/30-sta ... -crucible/

I also have a larger B700, made for a #70 Crucible.

The crucible in the photo, a #30 can hold 30 pounds of aluminum, or ~ 90 pounds of copper alloy.

In reality, if you fill to its limit you are heading for trouble, better to be at 75% than flowing over the top with the slightest misstep!
DSC_0692.JPG
DSCN0024.JPG
DSC_0722.JPG
DSC_0758.JPG
DSC_0761.JPG

Harold_V
Posts: 19353
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Fabricating Crucibles

Post by Harold_V » Wed Jan 05, 2022 2:36 am

AllenH59 wrote:
Tue Jan 04, 2022 5:01 pm
Harold, I am not so much cheap as not knowing what to buy, Silicon Carbide sounds like the ticket, thank you.
Welcome! This tends to be a very touchy subject (steel crucibles) with some folks, but it doesn't hurt to be well advised, so you can make a good decision. One thing you should know----graphite clay crucibles must be tempered (slowly heated before use) to expel moisture. They are prone to cracking otherwise. Silicon carbide doesn't suffer that problem. It's a great choice.
I saw you mentioned that you had some crucibles with size numbers, what do the numbers mean? I am looking to be able to do something like 5 lbs of brass/bronze max.
As others have so nicely stated, the number designates the amount of aluminum (in pounds) a crucible can melt. It's three times that amount in copper alloys, as they are much heavier than aluminum.

As far as your projected use, don't make the mistake of buying too small. While larger crucibles cost more, they are also thicker, so they not only allow for a larger pour, but they'll last longer, too. I used to use a #8 crucible for melting silver, and it was an excellent size for my operation.

It's not hard to build a melting furnace (and that's what it is---it's not a foundry, a term that designates the place where castings are poured). A forge could be used, but they aren't built to accommodate crucibles. If you need a little guidance, speak up. A great source for the air supply is an old vacuum cleaner (often found in thrift stores), with the upright types a lot easier to convert. A couple of gate valves for air and gas control, a large can for the body, some refractory and some creativity and you have a furnace. You can build for a hundred fifty dollars what may well cost you a thousand dollars if purchased commercially, and that's assuming you could find what you need.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

AllenH59
Posts: 469
Joined: Wed Mar 16, 2011 1:26 pm
Location: Prince George BC Canada

Re: Fabricating Crucibles

Post by AllenH59 » Wed Jan 05, 2022 6:04 pm

Thank you Harold: Yes, I understand that it is a melting furnace I am looking at building, and it will probably be inside an expired 30# propane bottle. I have a buddy who is a master blacksmith, who will help me, it is his suggestion that I use castable refractory, he makes excellent burners. I may use it for heat treatment once in a while, but I do not have a lot of interest in beating iron into shape. It is my plan to use it as a heat source to melt lead, although I will not be putting it inside, just putting a melting pot over the top. I Think it will be a useful tool around the shop. Like everything else I will build it bigger than I imagine I need.

Post Reply