Protecting the foundry

[David Durman]

I'm putting together a home foundry following some plans, but they haven't discussed the subject of high heat paint to protect the steel of the body and I was hoping someone here would have some insight. I've roughed out the body of my foundry and coated the outside with high heat paint (see attached) to prevent the steel from oxidizing; the paint is rated up to 2000F and my thinking was that if the exterior gets to the point of 2000F then I have bigger problems than paint vaporizing. I am tempted, however, to paint the inside wall as well; the lid and the bottom will be protected from oxidation by the refractory I plan to line them with, but the walls are simply going to use kaowool to contain the heat and I am worried that if I paint the interior that I could be risking temps that will vaporize the paint, especially at the seam of the kaowool. I really want to protect the steel as much as possible to extend the life of the foundry but I draw the line at any safety risks. I've considered lining the walls with refractory as well, but I am very reticent to deviating from plans. Here are the plans I'm using for reference. Any advice would be greatly appreciated.

 

Additionally, I am planning on buying a burner rather than constructing one as per the plans; I'm certain that I could make one but there are practical concerns and I like the craftsmanship of the burners I'm eyeing in eBay. These plans are for a burner where the tube is 3/4", but I think I can manage to attach something with a 1" tube as I can't seem to find any made to the specifics of the Reil EZ burner that the plans call for; would this be too much for this small a foundry? I could obviously just turn it down, but I would prefer to not over-stress what I'm working with. Thanks again; these forums have been a lot of help.

[ThomasPowers]

Well since you must live out here where relative humidities are often in the single digits; rusting is not that big an issue! I don't paint the outside of my forges; of course the one I use the most is only a bit over 15 years old now and still going strong.  Now if you lived in a damp or salty environment things would be different.

A foundry will need to be lined with some sort of refractory: Insulative will save hundreds of dollars in fuel but be fragile, hard refractories will be fuel hogs; but last longer between relines

[David Durman]

Thanks! I was fairly certain I was being overly cautious with the paint, but it seemed a pretty inexpensive step and the annual humidity here is 70. I'm thinking that I will use refractory on the walls as well; I'm not sure why those plans are calling for kaowool on the walls, but it seems like there shouldn't be an issue with refractory.

[ThomasPowers]

See the "save 100's of dollars using an insulative refractory like kaowool"

[David Durman]

Save hundreds seems unlikely unless the castable refractory I'm considering buying isn't sufficient; I suppose he could mean over the course of relining the foundry. I'm planning on using U.S. Refractories Lou Cast 3000, which seems like it is up to the task.

[ThomasPowers]

It's your fuel bill(s).  Remember that a lot of commercial foundries are more concerned with uptime and shutting one down for a reline can take weeks.  Tough liners are often more cost effective for them over ones that have the most fuel efficiency.   Sort of like the difference between driving a dumptruck and a minivan; both will get you there but if a minivan will do it will save a lot in running costs.

[David Durman]

I see; I thought you were referencing something in those plans rather than your previous post, for some reason. Thanks!

 

EDIT: Assuming I want to go with kaowool to save on fuel, and that humidity is relatively high where I am, do you still think that it wouldn't be worth it to paint the interior wall of the foundry?

[ThomasPowers]

Will the paint and time cost more than replacing the shell?   I consider pretty much everything in my blacksmithing shop a consumable; though some items have been in use over 100 years now...   If you are in a damp climate and it will be used sporadically and stored without climate control and you dislike building/rebuilding your equipment then a very high temp paint might help.  For me I am more likely to use it until it starts failing and then next reline time rebuild the whole thing. (most likely reusing the burners if they are still ok)

[mutant]

I didn't paint the interior of my propane foundry. It already comes rust proof since the manufacturers don't want them rusting from the inside out. Either way, your setup will last a long time. I also highly recommend the use of Kaowool. Don't over think it, if you really get into casting, you'll probably make another foundry anyways. Most of us do. Heh.

[ThomasPowers]

Rebuilding gives you a good excuse to try tweaking things...About time for me to rebuild my coal forge for the 5th? time for that firepot; I've got some ideas to make it easier to transport...

[David Durman]

When I spoke with the place I'm planning on buying the refractory from the guy on the other end said just to ask when I get there if there is any scrap kaowool in the dimensions I need and they will just give it to me since they only sell it in giant rolls, so there isn't really any cost difference for me between kaowool and the refractory I'm buying anyway. You are right, though, I am probably overthinking it.

[Frosty]

I don't know of a real melter that isn't insulated. 1' of hard refractory has an R1 value and it's a tremendous heat sink. Thomas' estimate of 100x the fuel is is probably on the optimistic side. By "real" I'm not talking about things like the Gingery charcoal fired foundry or melting beer cans and al. shards in a tin can in the camp fire kind of "melter."

EXCELLENT, you're hooked up with a company that supplies or service HVAC. Code restrains the service guys from using drops so they often have dumpsters full of Kaowool or equivalent and various fire brick "scraps." It's gold to us but they can't legally use it. I drove into Anchorage yesterday with a friend and picked up around 4-5 sq ft. of rems. Unless I actually need a 2'x2' piece they just aim me at the scrap bin. The cost to me was about 3gl. of gas and I had lunch at Taco Bell.

Frosty The Lucky.

 

[David Durman]

I finally finished this foundry. Here are some images of it; does anyone have any suggestions? It still needs a first firing, but I am going to wait until I get the crucible I am going to use so I can cure them both at the same time. 

[ThomasPowers]

what are you planning to melt in it?  (temp ranges are an important part on choosing refractories, an Al foundry would use different stuff than a steel foundry...)

[David Durman]

Planning on making bronze with it, so copper-melting temps are the highest. The ceramic wool is Cerablanket 2400F and the castable refractory is a commercial mix rated for 2600F.

[Frosty]

How much space is around crucible?  I'd certainly have put 2" of Kaowool or equivalent blanket in the melter but that's just me. The casters I know call their studio the "foundry" and the furnace they melt metal in a "melter". I know I'm bordering on semantic nit picking but it's the same misnomer you see so often when people call a blacksmith's shop a "forge." The forge is the fire place you heat the iron/steel in, not the building.

Bronze has a lower melting temp than copper, it's the eutectics of the alloy. If you break the copper up small enough and add the tin before you start the melt the whole mass will melt at a lower temp than copper.

Frosty The Lucky.

[ThomasPowers]

On the other hand he intends to *make* bronze and so will start by melting the copper and adding the lower melting temp alloys.

I would get the crucible and get the lifting tongs you plan to use on it and see how much side room you have to pull the crucible without hitting the walls.

[David Durman]

1 hour ago, Frosty said:

How much space is around crucible?  I'd certainly have put 2" of Kaowool or equivalent blanket in the melter but that's just me. The casters I know call their studio the "foundry" and the furnace they melt metal in a "melter". I know I'm bordering on semantic nit picking but it's the same misnomer you see so often when people call a blacksmith's shop a "forge." The forge is the fire place you heat the iron/steel in, not the building.

Bronze has a lower melting temp than copper, it's the eutectics of the alloy. If you break the copper up small enough and add the tin before you start the melt the whole mass will melt at a lower temp than copper.

Frosty The Lucky.

Fair on the terminology; I would think, though, that calling the building the foundry would be the same type of misnomer as calling the shop the forge. The caster's building is a shop and the melter is the foundry. This might simply be a matter of regional usage.

I would prefer that method but all of the examples I've seen where the bronze is made prior to casting have the tin being added at the last moment. The material I've read warns against 'boiling' the bronze, presumably due to the tin in the alloy being roughly 4 times past it's melting point. But this could all be just caster superstition, similar to blacksmithing superstitions like a forge that has had copper in it being unusable for steel.

1 hour ago, ThomasPowers said:

On the other hand he intends to *make* bronze and so will start by melting the copper and adding the lower melting temp alloys.

I would get the crucible and get the lifting tongs you plan to use on it and see how much side room you have to pull the crucible without hitting the walls.

Yeah, the instruction I have had was to up the tin in after the copper melted, then give it a few minutes to melt but be careful not to 'burn' the bronze.

I plan on a couple of cold runs before even thinking of firing it; as Frosty said, I would have preferred 2 inches of wool, but I was concerned about he #10 crucible I need to use not having sufficient room.