The Home Machinist!

A week or two ago I did my first melt with a newly acquired furnace. I'm pretty happy with the way it went, and am tweaking the equipment, and trying some new fuel types. Its been over 100 here in Virginia, so I haven't fired it up lately, but as soon as the weather breaks I'll have another go at it. I started off with charcoal which required alot of tending. I've got a couple of buckets of coal to try next, then its on to Propane and Waste oil in the future. That'll require some mods to the furnace. Heres a couple of shots of the rig and the results. This is my first post, so I hope if I crash the site or violate some rule someone will let me know. The whole story (in progress) is on my blog at:

http://bluechipmachineshop.com/bc_blog/?p=1291


1: the furnace
2:1st load
3:1st melt
4:a couple of hours work


I'm hoping that one of you guys can send me in the right direction on de-gassing agents and flux. I've heard that pool chemicals work pretty well for the home caster, and are easily available. Any suggestions are greatly appreciated.

Mick Finch
bluechipmachineshop

Virtually all of my experience with melting revolves around precious metals, although I have a keen interest in foundry work in general, and will pursue that in the near future, assuming I live long enough! I'm at the tail end of a house building project that has taken many years longer than I could have dreamed, so time is running out.

Anyway, I'd like to offer a couple comments. Please do not misunderstand them as being critical of your choices---but I think they'll serve to improve your degree of success.

Lets start with your crucible. Molten metals are very strong solvents of other metals. So much so that those that don't melt under a given temperature are often dissolved by the one with which it is in contact. Therefore, when you melt aluminum in a steel vessel, you're contaminating the aluminum to some degree. Many will argue the point that it doesn't matter, but it alters grain structure and can lead to low quality castings. If you're really sold on using steel instead of a graphite/clay or silicon carbide crucible, you might consider using a refractory wash on the inside to minimize contact of molten aluminum with steel.

You can improve the efficiency of your furnace by providing a lid with a small port on top to vent the gasses. It would be difficult with the current furnace you have, and it's likely not a big issue, but if you pursue casting of brass, it will require a lot more heat and may be difficult to achieve without retaining some of the heat that's being dumped to atmosphere with your current setup. It's fairly easy to fashion a lid that pivots, so you don't have to worry about finding a place to set it down when it's red hot. It simply pivots to the side, out of the way. I've built a few furnaces with that design and recommend it highly.

I have used natural gas and forced air for all of my furnaces, including a tilting reverberatory furnace that was used in my refining venture. That is no longer an option for me, so my future furnace (for casting bronze and aluminum) will be fired by oil. I am not versed on that type of burner construction, so anything you learn along the way would be gladly received, and I'll be willing to share anything I learn if it's of interest to you.


Because my experience revolves around precious metals, I know little about fluxing aluminum, so I hesitate to comment. I know it can be degassed by percolating nitrogen gas through the heat prior to casting, which is my intended method, assuming I get that far.

I'd like to welcome you to the Chaski board. Lots of great guys here. We're a laid back group---we try to be kind and gentle, and we tend to keep a low profile. Hope you enjoy your visits with us.

The ingots of aluminum you poured look very nice! Did you melt a variety of waste materials? I've read that bar stock doesn't lend itself well to casting, so I'm curious about what you're using. The picture of the feed wasn't really very informative---looks like aluminum plate on top, in the furnace. Having read a little on the subject, I'm lead to believe that aluminum high in silicon is a good choice. Pistons from auto engines might be a good source. I'd appreciate your comments in regards to feed stock.

Harold

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

Harold,

Thanks for the welcome and the comments. As this furnace (and accessories) was a hand-me-down, I'm dancing with the girl I brung. Its not my idea of the perfect date, but it broke the ice. I learned alot from the first go round, and plan some changes. It has a lid (with a 5" vent) that was "inconvenient" with the load of charcoal in the base. I'm sure temps would be increased with it installed. The crucibles are very heavy steel (12-15 pounders) that I plan to whittle down my 500 pound pile of mixed aluminum scrap. Better crucibles are in my future, when I learn a bit more. I've heard cast alum has all the right stuff for casting already (makes sense), and try to mix in some extruded and plate with it. The stuff in the pix is cast, which accounts for maybe 70% of my scrap.
As you might notice, the blower is straight on, the future mods are to offset it at an angle for swirl effect. That'll come when I attach the oil burner (Becket furnace head). I want to do a little experimenting with propane and coal first. this will be a little strange for me, I usually start building the big Mojo rig before I know what I'm doing. Figured molten metal might require some restraint.
Thanks for the tips, I hope you'll keep em coming. I post my progress.

Mick finch

Congratulations!
I'd say that was a successful pour, especially for the 1st pour!
I use coal for my forge and a little trick to get the coal burning is a wad of news paper and some small twigs neatly piled on the paper, then pile the coal on the twigs. Real smithys laugh at me but hell I get the fire going 1st time every time! btw it was right at a 100 here too! tt

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clueless near st.louis

Thanks, Oldgoaly. I plan on trying coal this weekend if the weather cools a bit. I'm planning on loading the coal from the bottom, so I can use the lid this time for better heat retention. I don't know how long coal burns, but suspect it'll last longer than charcoal. I'll be melting some extruded alum, to see how that flows, compared to the cast sheet mix I did last time. I'll shoot some pics when I do.

Mick

Been doing a little reading, and realize theres more to this casting thing than just dropping a match and sitting back and drinking a beer. I'm trying to get ready for the next melt, and have been trying to get some details on refractory wash. On Harold's advice, I'm planning to coat the inside of my steel crucibles. Is this stuff the same as ceramic slip? I remember using a soupy slurry in ceramics class in grade school (don't remember what for). I'm wondering if its the same stuff, and if I can get it locally from a pottery place down the road. No sense messing with it, if its the wrong stuff. If anybody has any info on a specific product I can use on my steel crucibles, I'd be grateful. I probably will pour from uncoated crucibles this weekend.

Mick

For what it is worth, I have used ciramic slip mixed with a paint base, sodium silicate, ( water glass), which is the same liquid material for making baked or dry cores as a binder. It reacts with Carbon dioxide to harden, exposure to a torch flame product sets it up. (dont burn it, just dry it).

Less is more when using this material, it is very fragile and falls off when touched with a stir rod or paddle, but serves to limit contact with the crucible , that is steel or iron, only the barest coating is enough, and can be renewed at any time the vessel is cool enough not to blow the coating off with the steam created. Foundry supply companies have washes, I have not bought any, going with graphite and carbide vessels. For the hobbiest, I see no reason to go beyond the clay-graphite vessel, for the expense. Good tongs that cradle the vessel are essential. These things get pliable and spooky when you handle them.

It should be remembered, if you are going to attempt to make a casting with all the effort involved, to preserve the quality of the metals, and get a good usable casting for the job at hand. I have preached that long hold times, adding zinc based diecast, and especially iron contamination from screws, rivets, and vessels, will flat ruin the quality of Aluminum.

I see your pig molds are well desgined and well built, for handy size. I started out that way too. I now use extra sand on the floor, and pig in the formed shapes from trimmed 2x4 right in the open sand. While you will pick up very little iron in your pigs, when they rust, they will blow on the first pour. Prolonged contact with steel or iron, will disolve into AL and make it pasty if allowed enough. It will not flow and copy fine details.

Go to your Machinists handbook and look up the various grades of AL, there are many, and figure out what can be added to the scrap stream you have. Pistons are very desirable, screen doors not so much. Things like small engines, can be iffy because they tend to have many bolts and screws that wind up in the melt. Transmission cases are about ideal, but have to be sawed or broken up, like auto wheels.

Fluxing with just a teaspoon of chlorine pool tablet crushed up and packed in a foil envelope, swished in the vessel with an infuser will do all the metal cleaning you need. These fumes are from toxic, to deadly, but easily avoided. Use common sense. You basically dont want to inhale anything coming out of that furnace. Degass with a copper or stainless tube and slow bubble Nitrogen into the melted heat just seconds before you pour, to remove Oxygen. 2 N2+ 02= 2 N02 Simple.

Ya, there is a big learning curve. But doing is only half the art, knowing what to do, assures your success.

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Big Dave

Be Alert! The world needs more Lerts.

Big Dave,

Thanks for the tip. I'll take a trip to the pottery place this coming week and see about some supplies. I guess coating my ingot molds wouldn't hurt either. Right now I'm trying to pare down the growing pile of scrap, so I can move around my shop, so any bum ingots will be turned over to the scrap dealer. So far, the stuff looks good (beginners luck, I guess), so with a few of the suggestions I've gotten here, I might not be too far off from casting parts. I've been collecting Aluminum for a while, and would guess I've got about 60-70% cast scrap. You can get an idea of the type of material from this blog:

http://bluechipmachineshop.com/bc_blog/?p=962

I used to just turn it in to the scrap dealer, till I got the furnace. This is much more fun!

Mick

MAKE THAT DEALER YOUR ALLIE. Turn in all the cans, sheet and light stuff you get your hands on. Trade him like 2-1 for any BAR or PLATE scrap you can carry off. Aluminum is a very common machine metal now, and lots of parts turn up in the trashmasher. Dont waste time and fuel with sheet trash that just burns to dross. Trade him for bearing brass and any thing else useful for the furnace. His premium should be a lot less than bar and ingot stock. It makes good stock for the lathe and mill projects, finding bar ends and heavy plate pieces. Oopsies go to the furnace. Dont melt the chips, too often they carry steel and thats a no-no. Know what the relative market is for scrap and prime metals, and commit to savings.

An old friend used to cut 4-6 inch aluminum bar for special castings, to make sure he got the good metal needed. That is an expensive way to operate, but assures the better metal quality. Still some bar materials, are not good cast, not enough silicon, so you must invest some time to research some additions for your melts from foundry suppliers.

A big drill to make a test spot on one of your ingots can be telling about how soft/hard or gassy the metal may be. The outside should be smooth. If it collapses down the centerline with grain showing, suspect that to have a lot of zinc from diecast, or other problems. Dont expect a scrapper to jump on your ingots, too many people cheat and put junk in the mold, or sand or? It all depends on if they get to know you a bit. That takes time and many passes to their yard.

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Big Dave

Be Alert! The world needs more Lerts.

This topic has been discussed in the past. For the sake of clarity, and to dispel the notion that oxygen is the culprit, readers should be properly informed.

Degassing does not remove oxygen. Oxygen readily combines with aluminum, forming aluminum oxide, which is removed as dross. That problem addresses itself quite nicely, without intervention on behalf of the operator.

Degassing is accomplished to remove hydrogen---which produces porosity in castings. Hydrogen is introduced to aluminum by various means, but melting hydrocarbon contaminated (paint and oils) aluminum is a common source.

Here's a link that can provide some useful information:

http://budgetcastingsupply.com/Aluminum ... ablets.php

Harold

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

I want to thank you guys for all the helpful info (please don't stop). I am finding this very informative. I asked a few questions at the Yahoo casting group and got no help at all. I started this venture with a plan to melt a variety of materials, and learn from my mistakes. I'm sure most of the info supplied here will shorten that learning curve. I may not implement all your suggestions all at once, but it just seems like good sense to use them, and I will. Please don't think I'm ignoring your sound advice, sometimes I just am slow getting to it.
Degassing and fluxing were two of my primary concerns, I wasn't aware of material transfer from my crucibles and molds (will address that). My raw material is aluminum oxide and hydrocarbon rich. This was partly due to some of the scrap I introduced to the melt. I learned alot from that. I will try to have my melt mostly cast, and avoid anything less than plate 1/4" thick. The rest can go to Ben (the scrapper).
I work at a water plant, and get some good stuff from the metal dumpster. Yesterday I took 100 lbs of alum reflectors from quartz lights down to Ben, cause they looked like a nightmare to cut up for a melt. Sounds like that might have been a good move. Most of what I pull from the dumpster is cast motor housings, thick plate and electrical conduit. Any thin sheet I get is usually corroded and I turn that in to Ben. I need to take a harder look at what goes into the furnace from now on.
Thanks again for the tips, and keep it coming!

Mick

Harold: I dont disagree, that hydrogen is a problem. But the question becomes why use Nitrogen? I will have to look it up in Ammens book on Casting. More later I guess. Yes, painted, coated, and plasticized aluminum is objectionable for the hydrocarbons, period.

The second part is that lighting fixtures and heads are usually a diecasting, or machine casting material, that is not all aluminum. There are a number of casting metals that are used that are zinc component, and it can be quite high. It may work for some things, but is not Aluminum as such, and may cause problems, or be OK for a detail part. Traditional 'potmetal' as it was described, is fairly hard but also brittle, and thin rodlike or finlike parts can break fairly easily if stressed. It will also corrode in odd fashions and ruin the finish if exposed raw, where aluminum can be quite stable.

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Big Dave

Be Alert! The world needs more Lerts.