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+--- Thread: First try at melting metal (/thread-92.html)
RE: First try at melting metal - dallen - 10-01-2012
(10-01-2012, 05:15 AM)big job Wrote: This has been on my mind a long time, I have pails of brass swarf that I have always
wanted to put back on the shelf.
your better off to take it to the scrap yard unless you have an electric inert gas furnace, its really a loosing battle trying to melt swarf, it will oxidize and you will throw most if it away.
(10-01-2012, 07:29 AM)SnailPowered Wrote: I have a buddy who's dad was short on ingot molds so he went to all of the local antique stores and bought up all of the cast iron cornbread molds he could find. He uses them for lead ingots but I don't see why they couldn't be used for brass as well.
I have a couple that I have poured everything into them from aluminum to cast iron. molten cast iron won't stick if they are clean it cools faster then it can raise the mold temp to melting.
RE: First try at melting metal - Sunset Machine - 10-01-2012
Yes indeedy, air is for cooling. Amongst other things, I used to service and repair landfill gas extraction flares. The EPA set regs as to temps, they were monitored with overpriced Honeywell digital temp controllers which controlled simple motorized shutters on the secondary atmospheric air intakes on the sides of the flare stacks. The gas was from constant speed blowers through manually adjusted butterfly valves. That adjustment determined the quality of the gas coming from the field, if too rich then open the valves a little and build a bigger fire. It needed to hold a negative in the field to prevent methane from getting into houses and was influenced by who-knows-what-all. All very basic stuff, just large. I could light the sky or rattle windows for miles around with those things. Lots of control.
'Twere me, speaking as a 30 year industrial burner mechanic in a variety of installations, an air shutter would be preferred over blower speed control. I can honestly say that I've never seen speed control used for that. Look at blower performance curves and you'll see why. Not that it won't work, it just works better if you throttle the air. More precise control.
Speaking of rattling... I've wandered. Melting cast iron! I bought Colin (The Artful Bodger) Peck's book on backyard foundries using waste oil - very interesting. British, I think. He's melting cast iron with old motor oil. ISBN 0-9546895-1-8
RE: First try at melting metal - Rickabilly - 10-01-2012
(09-16-2012, 04:56 PM)Rickabilly Wrote: Often the easy way to regulate flow when using a centrifugal blower is by use of a butterfly valve, as RPM vs flowrate curves are far from linear and with little back pressure just plain difficult to manage, but, with a correctly sized butterfly; a closed butterfly is closed and at half open the flow is around half of full flow and open is full flow.
Yes Mr Sunset,
That is exactly what I was saying when I posted this above, to get good simple control just throttle the flow rather than mucking around with expensive RPM control and fighting with pump delivery charts.
On a few of the other posts listed;
When using a hair dryer for blast air, make sure you use the heating element as it will help keeping the combustion process going and also make the process more efficient. better still use a paint stripper gun as more heat is "more good" and I find them to be cheaper to buy as a general rule.
Regarding the loss of swarf to oxidation, covering the pot and mixing the brass swarf with crushed charcoal, or at least adding a second pot inside the melt pot full of crushed(6-15mm) charcoal or coke, as the coke oxidizes the oxygen inside the closed pot is used up which prevents the swarf being lost to oxide, it works with most metals, use it where carbon content in the final metal is not an issue, it is a common metallurgical practice and has been used as long as metal has been smelted, as a matter of fact add a little flux, (crushed limestone or borax) and you can even convert some of your oxides back to metal!
When heat treating, this added carbon method prevents scale build up on the surface of most metals especially iron based metals, but keep the carbon away from the steel in the furnace.
Regards
Rick
RE: First try at melting metal - Sunset Machine - 10-04-2012
I like the tip about using a heat gun. Wouldn't have thought it would make that much difference, but an extra few hunnert degrees it is. :)
One nit - don't bother with a butterfly valve. Too expensive unless you already have one. Just a tin shutter in a slot, held with a wing nut or something is all that's needed. Slot the air tube with a hacksaw.
Probably not an issue with solid fuel, but one of the scariest jobs I had involved a large Cleaver-Brooks Scotch Marine firetube boiler, gas fired (400 HP, I think it might have been the largest skid mounted package made in this country at the time). The operators were in a panic. Brand new high pressure steam boiler, they started it up and and as soon as it went into high fire everyone's clothing would start fluttering. It's caused by over-firing, the flame actually leaves the burner and then snaps back. If it didn't snap back, the combustion chamber would fill with an explosive mix - it had .8 seconds to shut down.
Anyway, if your oil/gas flame starts to pulsate you need to stop and fix it, lest it blow flaming bits of metal and brick everywhere. Look towards reducing burner velocity by using larger piping.
RE: First try at melting metal - Rickabilly - 10-04-2012
The heat gun just helps when firing up, run the heat for a while before starting with the fuel and you can forgo some of that nasty start up trouble that is common with some burners when cold. But the most important part is that you're not cooling the fire with cold air, if combustion adds 800 degrees to your airflow, and you start with an ambient 20, you've got 820, but start with 100 and you've got 900, and every little helps.
Re, the valve I used to use an old efi throttle body that cost nothing on a burner rig I built ten or more years ago, the sheet of tin in a hacksaw slot is what we used to call a slip plate, in the boiler house I worked in as an apprentice, of course the professional version was a bit more sophisticated
And one last thing, if anyone is going to try the anti oxidisation trick I posted, don't use coal, it has too many impurities and will give trouble,
A further tip when heat treating tool steel or any thing you don't want to oxidise heavily is to use plain flour with a little water, knead into a dough and cover the areas to be protected, dry it on low heat and then bring to full temperature, the flour will turn to carbon and as it encases the workpiece will protect it very well from oxygen damage
Regards
Rick
RE: First try at melting metal - the artfull-codger - 03-03-2013
Just looking at past foundry threads with regards to various ways of controlling the air supply to your furnace, when I built my first furnace with my late Dad over 40 yrs ago with very little info' around then I used an old ''snail fan'' that we cannibalised from a central heating blower, it did me for many years melting brass,bronze, alloy & iron, till I bought a bouncy castle blower which I now use & is much more powerfull[you can blast the coke out of the flue] if you want to!!! the way I ajust the air without valves,shutters, thyristors etc is to just move the blower further away from the furnace,dead easy fine control & nothing to go wrong,this is for solid fuel,I've never changed to gas[ allthough I do use one at work & very convenient it is too] 'cos we allways have plenty of coke in for the rayburn cooker. [& it comes out of the ''family budget'' he he.]
RE: First try at melting metal - stevec - 03-04-2013
There may be others (besides me, that is) who have no idea what a "bouncy castle blower" is.
RE: First try at melting metal - Highpower - 03-04-2013
Something for kids to entertain themselves for awhile.
Basically an air filled trampoline that is normally supplied by a 1.5 - 2.0 hp squirrel cage blower.
http://en.wikipedia.org/wiki/Inflatable_castle