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Tanque 12-30-2012 01:25 PM

Building a baby foundry furnace
 
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I've been building a smaller foundry furnace, anyone here have an interest in this project?
If there is any interest I'll post more progress. It will be a small 'traditional' circulatory, with a propane fired
blower/ burner virtually identical to the larger one I made ~16 years ago except for the largest crucible it can accept is
a #4; the smallest a #2. I wanted it to be 'portable' meaning I can pick it up without assistance.

So let me know and I'll continue. Anyone could build one of these.

I started with this:



FreakyDude 12-30-2012 01:47 PM

RE: Building a baby foundry furnace
 
tag me in the interested file. Learning things like this can be invalueable even if you gain just a basic understanding of the process.
Quote:

ORIGINAL: Tanque


I've been building a smaller foundry furnace, anyone here have an interest in this project?
If there is any interest I'll post more progress. It will be a small 'traditional' circulatory, with a propane fired
blower/ burner virtually identical to the larger one I made ~16 years ago except for the largest crucible it can accept is
a #4; the smallest a #2. I wanted it to be 'portable' meaning I can pick it up without assistance.

So let me know and I'll continue. Anyone could build one of these.

I started with this:




ausf 12-30-2012 02:26 PM

RE: Building a baby foundry furnace
 
I'm in.

I'm especially interested in specifics of materials and temps. I've done all types of casting over the last 30 or so years, save metal. I have a kiln, vacuum and pressure systems, I'd love to cast some metal track links, specifically 1/16 Pz I.

Rebellion13 12-30-2012 04:38 PM

RE: Building a baby foundry furnace
 
Count me in, I love stuff like this. Mechanical and electrical and ideas like this peak my interest.

Cheers
Wade

CHIEFSONN 12-30-2012 07:09 PM

RE: Building a baby foundry furnace
 
You've got my interest.

Ronan87 12-30-2012 08:01 PM

RE: Building a baby foundry furnace
 
Same!

MAUS45 12-30-2012 08:14 PM

RE: Building a baby foundry furnace
 
Please continue!!! I want to learn.

Tanque 12-30-2012 11:18 PM

RE: Building a baby foundry furnace
 
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I'll show what I have done so far.

Of you've seen commercial furnaces you know they can get somewhat complicated and elaborate with clever ignition systems, burners and
counter balanced covers. I've dispensed with that and plan to keep this as I did my first one: very simple.

When I decided that I wished to make a smaller furnace I first set about to determine what capacity I wanted. Considering I haven't had the
need to cast a part weighing more than a few pounds including risers and gates I set the maximum capacity to be a #4 ( 4lbs aluminum) size
bilge crucible. I studied the dimensions not only of the crucible but the diameter of the furnace body's heating chamber required to allow
the use of the # 4 pullout tongs. Actually the one I have is a combination pullout tings and pouring shank common for small sized crucibles.

After I determined the dimension of the body I set about finding an appropriate housing. As luck would nave it 1 standard US 5 gallon can was perfect.
An afternoon trip to a local auto body supply house netted 2 empty tins.

I prepared one can by first cutting to an appropriate height, trimming a bit by filing then riveting a 1/16" thick steel band around the rim for reinforcement.

That's it for this part.


Tanque 12-31-2012 12:08 AM

RE: Building a baby foundry furnace
 
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I've used a commercial refractory to make the furnace bodies and covers. The one used is Pryor Giggey's Castmax 30 HR
You can find the specifications here: http://refractory.pryorgiggey.com/it.../castmax-30-hr

The key aspects for me is it is fairly easy to mix and use( although watch the water content ) and it's temperature ceiling is 3,000 F. That works for me.

I took shortcuts when preparing the body so I will tell you the proper way to do it as well as how I actually did it.

After preparing the housing as I indicated previously I also had to determine where the burner inlet would be and I made a hole through the casing
of an appropriate size. The idea is that when the gas stream/ flame is introduced into the body it will swirl around the crucible and impart heat to the
crucible and its contents. The trick also is that the flame heats up a spot on the casing wall that remains hot to ignite the incoming air /gas mixture
continuously.

In order to get the cavity in the casing one must prepare a plug. The way I've done it is to make 2 circles from wood, joined with dowels and cover the outside
with cardboard. The top is left open and I'll explain why later. I varnished my first one I made years ago but not finding my varnish I painted this one with some
ugly ( Rustoleum 'Almond') paint I happened to have. Painting to seal the plug and keep it from failing while making the casing. At this time I also made a
plug for the burner inlet which I opted only to grease and not paint; a decision I'll regret later. :-( Sorry I thought I'd taken photos of these two plugs but can't locate them. The idea is pretty simple.

Below, notice the crude diagram of the desired furnace operation ( the crucible would be the funny shaded circle).

With the plugs in had I proceeded to cast the casing. Now one of the shortcuts I took, besides the wooden plug no paint decision above was to 1)
not create a spacing mechanism to anchor the plug while filling the body and 2) not fixing the inlet plug to the casing plug. However neither of these
shortcuts has caused any serious grief thus far.

The reason the body casing plug is left open at the top is so you can fill the plug with sand. This serves 2 needs. 1) keeps the plug from
collapsing under the weight of the refractory and 2) keeps the plug from floating to the top of the refractory and stationary.

The filled body casing is seen below. Between the 30 degree weather we had right after doing this and the size of this thing I didn't touch the body for 1 week after filling it with the refractory. If you look closely you may see the sand in the casing plug. Also on the lower right is the burner inlet plug.

Next time pulling plugs and making the cover.

Jerry

Tanque 12-31-2012 05:08 PM

RE: Building a baby foundry furnace
 
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After a week had gone by I began to remove the plugs from the body casing. The central cavity plug isn't expected to come out cleanly
or easily. This one did not disappoint. As I had not actually glued the plug together I was able to remove the upper wooden disk
and the 4 supporting dowels fairly easily. After that it was just a matter of scooping out the sand from the now open plug. This may be seen in
the first photo with the second photo showing the empty cavity after the lower plywood disk was removed. As may be seen even though I was shooting for a perfectly round cavity the surface of the plug had 'flats' due to the cheap cardboard I used to make the plug... ! besides appearing odd this won't materially affect the usefulness of the body.

It would be quite some further effort to remove the burner input plug. I did get it out and it was actually better than expected. I need to remove
a ridge at the inner opening so the flame has a smoother entry into the furnace cavity.

Next up was making the furnace cover. I had planned to use a portion of the 5 gallon can that I had removed previously. I actually inverted this
portion so I could capitalize on the tapered section where the can wall meets the can top; the thinking being that the metal is simply a carrier for the
thick refractory plate that is the lid. I cleaned the cut section and riveted two 1/16" steel tabs with holes so that in use I'm able to slide a rod through them and safely remove the lid for access to the crucible. I used a poly drinking glass for the central flue hole. This worked very well and was
easy to remove.

The furnace cover being open on top and bottom actually dried fairly quickly but then our local weather had warmed up a bit also.

That is actually where the project is at the moment. I am working out the blower/ burner. I just sent off for a 10,000rpm ac motor to power the blower and I'm trying to optimize whatever blower I can make for now to get the project moving forward. I'm thinking that I may use what I have
and the very first casting exercise will be to make a better blower housing. If you explore the web you'll find all sorts of magical fanless / blowerless
burner designs but the bottom line is generally these limit you to non ferrous work, generally just aluminum.. I don't like those limits and that would also would negate using the higher grade refractory that I do. I've only had a few occasions to pour grey iron but it's nice to have the option.

Before the furnace can be fired the refractory will need to be carefully baked out or aged. By using a series of increasingly hot fires in the body with lid installed this will be done. First it's just making wood fires in it as if it were a patio fire pot, next it's fires with the blower being engaged. I think this time I'll add a step with bbq briquets and the blower just before I introduce a gas rich flame( little or no air) followed by increasingly leaner burns then finally a full out lean burn with a charged crucible.

One other thing I wanted to mention regarding the efficacy of this refractory. Now my larger furnace is substantially larger but even after a
#16 heat it is often quite possible to put your hand on the outside of the furnace body and find it just comfortably warm although after a really long heat that point along the body just outside of where the gas stream impacts the body wall may be unpleasant to touch. I am always fascinated
how relatively cool the outer part of the furnace body remains... I'm sure the baby version, even though the walls are 2" + thick will get much hotter.

So that's it for now until I get my burner together. When all is done I may repaint the metal housing.

DeadTom 01-01-2013 01:31 AM

RE: Building a baby foundry furnace
 
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Nice work, I like that you are using commercial refractory. My first furnace is made from my own mix with alumina, sand, clay and perlite. It still works great and has no cracking what so ever. I have 2 sacks of some commercial refractory that is going to make my new bigger furnace. I am working in opposite of you as I started with a smaller furnace and now I am making a larger one. My burner is pipe with a a very small hole drilled into it and then set perpendicular to a larger pipe, propane is the fuel type. This is for melting aluminum, the new furnace will be waste oil run and the commercial refractory is Kruzite Hi-Temp for over 3200 degrees, gonna try cast iron.
Keep the pics coming and thanks for sharing.

DeadTom 01-03-2013 01:29 PM

RE: Building a baby foundry furnace
 
I will post some pics of the tools that I made for my foundry setup and a couple of pics of my burner assembly tonight when I get home.

ausf 01-03-2013 04:16 PM

RE: Building a baby foundry furnace
 
Great photos and info from both of you. My sons and I have built a fir pit and a tandoor of the last few years, looks like a furnace is in order for the spring.

DeadTom 01-05-2013 10:08 AM

RE: Building a baby foundry furnace
 
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ausf,
Melting metal into what ever you need or want is very rewarding as long as you always keep safety at the forefront of each job. Aluminum melts at around 1600 degrees and cast iron around 3200 degrees definetly something your skin does need to make contact with.
Here is a few more pics of some of the tools that I made from rebar and 1/4" steel plate welded together, there is a dross spoon, feeder, a lifting the crucible from the furnace tool and a pouring the crucible tool after the crucible is out of the furnace and ready to pour the hot metal.
In the below pics I am preparing some aluminum ingots from some scrap door frame aluminum that a friend gave me, the ingot molds I also made from some angle iron that I had in the scrap pile in my back yard.

Tanque,
I hope you do not mind me adding some other information to your thread? I thought instead of starting another thread with the same type of information just add another member's information and hopefully adding some more value to an already valuable thread by a venerable member such as yourself.

Respectfully submitted,
Tom, aka DeadTom


PS - the crakcing you see in one of the pics is actually in the hot face and does not go through so the heat is retained. Also you can see the burner holder that I made out of rebar and angle iron.

ausf 01-05-2013 10:34 AM

RE: Building a baby foundry furnace
 
Tom,

I have a healthy respect for safety and processes and am very interested in any info or suggestions you have.

My goal is to cast 1/16 track links and drive spockets, particularlr Pz Is ans IIs. I'm not stuck on aluminum or iron, I'd ideally like the lowest melt alloy that will produce a viable piece, strong enough to work as a track. I assume anything with a tensile strength above ABS would work.

I originally was thinking bismut/tin and just did a search and found some very low melt temps, possibly low enough to cast in silicone molds but I still need to research that. I have a kiln that I routinely run to high 2300s, so that may be a better route for me than a furnace, since I'm set up for vacuum/pressure casting and lost wax would be another hurdle.

Any and all info is greatly appreciated.

DeadTom 01-05-2013 11:33 AM

RE: Building a baby foundry furnace
 
ausf,

Please take no offense at my safety warnings as it was a general warning for any and all who view this thread, not knowing you personally I am sure that with children around you excerise safety in all your undertakings.
As far as a low melt point metal sturdy enough to make track links from an alloy with tin might just be what will do the trick. Take a look at what another memeber did here on RCU, TheGreatestMoo's thread on his large Scorpion tank has many great ideas and castings that he did.
http://www.rcuniverse.com/forum/m_93..._1/key_/tm.htm
He used an Alumlite Epoxy for his track links, they seem to have held up well.

Regards,
DT

ausf 01-05-2013 01:53 PM

RE: Building a baby foundry furnace
 
Tom, I'm in full agreement with you, I didn't mean in anyway to come off as otherwise. I'm a champion for shop safety, including eye, respirator and vetilation in all practices. My sons are 11 and 13 and have been airbrushing/building for years and they know nothing gets started without the exhaust system on and respirator in place, regardless of materials used. I had an eight inch tumor removed from my spinal cord when I was 21, a result of ignoring MSDSs.

Smooth-On is my resin supplier and they make some high tensile resins, similar to ABS, but I think with the narrow Pz I links, I'll need some sort of metal.

Thanks for the link, I'll read over the thread. I'm set up for all sorts of rubber and stone casting here, if I could use a RTV product with low melt metal, I'd be one happy camper. Your setup looks pretty sweet by the way. [8D]

marshall 01-05-2013 02:22 PM

RE: Building a baby foundry furnace
 
Jerry, am watching you progress. Will be very interested when you go to cast parts. I have access to aluminum at 1450 degrees (work at a place that manufactures electric motors and have a diecast department for rotors). Have been plotting to do a 1/8 scale Hetzer and tracks will have to be made. Please continue sharing your work. Paul

Tanque 01-05-2013 04:08 PM

RE: Building a baby foundry furnace
 
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I agree with what DeadTom said about safety. Molten metal isn't anything to take for granted. At best you'll do it just once.

To make 1/16 scale parts I don't believe anything that is being described here is overly usable for really small parts such as tracks.
You be better off with either zinc ( ZAMACK ) spin casting or possibly aluminum vacuum investment casting although aluminum cools
too quickly for small parts in my opinion.

To DeadTom: how are you managing the temperature of your melts? Are you using a pyrometer? I have a older immersion type which is ok
but is somewhat crude. BTW I believe the melting temps you cited for aluminum and grey ( cast ) iron are a bit on the high side.
I could well be dreaming again but I believe cast iron should be in the 1300 C ( ~2500 F ) range and aluminum ~1250 F and some aluminum alloys much less than that. Zamack zinc alloy would melt around 750 F or so.

For the record I don't advise anyone to melt anything without proper precautions; even after doing for so long I'm still nervous pulling a
crucible from a furnace. Ventilation, ventilation and more ventilation. Also as Zinc is VERY toxic don't do it at all unless you have excellent ventilation.
It also requires a noxious gas producing flux to maintain alloy integrity.

Did I mention ventilation?


Anyway my progress on my blower/burner is awaiting the arrival of the motors I ordered however here's an in_progress photo. To reiterate a
previous statement- it isn't optimal but I'm trying to make the best from what I've got....

Also I've included 2 photos of a 1/10 StuG III project that I initiated many years ago. As the dust bears out I've not gotten back to this in a while.
I show it here as an example of what I've done over the years with my furnace. Nothing was purchased; I cast ( or machined) everything; hull
sprockets; tracks, idlers... everything. The track is actually Zamack and I'll never do it again. Hard as $%^$^ to drill ( that's the point of that alloy isn't it? hard). Please excuse the road wheels- made before I knew better. I made the tires also...

Jerry

DeadTom 01-05-2013 04:45 PM

RE: Building a baby foundry furnace
 
ausf,
A large tumor on your spinal cord, wow way to bounce good for you glad it all went well when you were younger.

Jerry,
You are correct sir regarding the melting temps, I guess I had more wine then I thought when I was typing last night.
I regulate my temps with an inexpensive pyrometer that I got from an older gentleman some years ago when he showed me some wonderful casting techniques.
A mentor is almost invaluable when it comes to old world artistry. Zinc, I have never done any zinc but I have not had any need for it yet. I also like the way you stress ventilation. I do most of my melting outside but I still wear a respirator as my wife is an environmental engineer and I would never hear the end of it. You should hear her when I talk of using waste motor oil for the upcoming iron melting project, I tell her that the oil is completly vaporized in the burner so no hydro-carbons should escape into the atmosphere which is mostly correct.
I see that your propane burner is receiving a blower, with that setup you should really get the temps up qutie fast.

Tanque 01-19-2013 06:26 PM

RE: Building a baby foundry furnace
 
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When I began this post I was on Christmas vacation and my return to the office has decidedly slowed my progress.
At least that's what I'll blame it on.

The central component of the blower/burner I've made was some sort of steel squirrel cage blower housing I found among my late father's things.
It has taken a substantial amount of work to modify it; as I said previously it isn't great but if it even works for a while that's all I ask. I really may well make the
first casting session a new blower housing.

It is nearly complete. I've powered it up and the 10,000rpm 1/5th hp motor really creates a substantial airstream. All that really needs to be done
it to seal the various sections of the blower, seal the gas inlet and make a mount. The furnace body is so short that the mount will be a simple wooden affair.

I hope to test the assembly with gas over the next few days aiming at fire bricks. As I've not yet cured the furnace casing I can't immediately use
the burner in the furnace.

Jerry

DeadTom 01-20-2013 10:23 AM

RE: Building a baby foundry furnace
 
Nice looking burner/blower setup Jerry.

Tanque 01-21-2013 12:41 PM

RE: Building a baby foundry furnace
 
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This day I have successfully tested the burner assembly. Next I will begin properly drying out and aging the furnace body and cover.

[link=http://www.youtube.com/watch?v=gq2xfzww5_k]Burner test[/link]

Jerry

Wozwasnt 01-21-2013 06:44 PM

RE: Building a baby foundry furnace
 
I found this site some time ago and it might be of interest to anyone building a furnace-

[link=http://www.backyardmetalcasting.com/]BackyardMetalcasting.com[/link]

Tanque 01-21-2013 06:55 PM

RE: Building a baby foundry furnace
 
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Began drying out the furnace casing this afternoon. I won't be posting all the steps but I plan on doing two more sessions with wood and or briquets with the blower running towards the end
of the session. The blower just was used as a bellows; a supplier of air. No gas. After that it will be a rich gas burn with a crucible followed by a careful run up to a leaner hotter session.
The furnace should then be ready for a melt; at that point I'll be back.

[link=http://www.youtube.com/watch?v=QRya9NDVeV0&feature=youtu.be]First wood burn.[/link]

Jerry


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