Metal Casting question

[Piggiron]

I've often wondered if a metal alloys properties change from the original when melted and cast aside from any heat treatment process it had undergone by the manufacturer.
Anyone know ?

I'm also curious to know if the end result is changed when a mixture of hot rolled and cold rolled scrap were mixed when melted and cast.
I'm currently not set up to cast, but would like to in the future. Knowing the answers would make the decision easy of whether to keep various alloy scrap separated or not.

[TerryWerm]

I believe I can answer most of that for you.

Yes, alloys do change a little each time they are melted and poured. Pure metals such as aluminum do not change as much, but some changes do occur.

Brass, for example, loses zinc each time it is melted, so the alloy changes.

I cannot answer for steel but I suspect that it changes also. The scrap mill that I used to haul into would make a "recipe" for pouring. This mill would pour into ingots, then hot roll them into either round bar stock or rebar. They did not produce any cold rolled nor did they produce any flat bar stock. They had a continuous furnace process, and the magnet crane operator was always feeding the furnace different steels or cast iron based on what the chemists asked for. It was an ever-changing process and it varied with what they were planning to make from the resulting ingots. It was interesting to watch (what parts I could see) but even more interesting to listen to some of the guys there talk about various aspects of the process.

Are you eventually planning to melt and pour steel??   Keep in mind the equipment required for aluminum or brass and bronze is far different from that required for cast iron or steel. Steel and cast iron are usually outside the realm of the backyard foundry, but some folks have done it.

@Uglydog has gotten into doing quite a bit of aluminum casting and has done some brass and bronze. I have been there for aluminum and a little bit of brass, but I have not been present for bronze quite yet.

[Piggiron]

If I get into it, I would mostly cast aluminum. Possibly copper, brass and/or bronze. I don't think I'd try steel or CI, take a lot of heat for that.
Most of my scrap aluminum from the shop is 6061, although I will be cutting some 7075 in the near future. I wondered if I should try to keep the saved scrap separated.
I do have other aluminum alloy scrap collected for selling to the local recycle plant, but no idea what most of it is.

[TerryWerm]

Yes, I would keep it separate. As I recall the 6061 and 7075 alloys are not the best for casting. You can feed them into the melt a little here and there, but it does not work as a major component of the melt. Lots of guys swear by aluminum pistons and such, or small engine castings.  Basically, you want aluminum that has been cast before but you have to watch out for high magnesium alloys like lawnmower decks. You can add a little bit of other alloys, but not a lot. Years ago we found that extruded aluminum worked well if added in small amounts. This helped to stretch our good cast aluminum scrap a bit further. 

If you find your interests going that direction do yourself a favor and find a new friend that does aluminum casting. Learn what you can from those who have done it. The time spent will be well worth it.  HINT: Daryl (Uglydog) does a couple of aluminum pours each year and makes a big day of it. I sometimes manage to get up there for such things but not always. You might consider a trip to northern Minnesota in your future. 

[savarin]

My favorite aluminium for casting is scrap ally wheels.
I use a propane burner to get it hot enough to break up with a hammer into smaller bits to fit the crucible.
When molten I use up small amounts of extruded fittings but havnt noticed any difference in the final product.
The best casting I had was a mistake, I melted it in a stainless bowel where it leaked through what I assume was dissolved holes in the stainless so it didnt get as hot or as fluid as I usually pour.
When I cut the bowel up for use I found it to be the best ever with zero porosity of any kind and no shrinkage voids.

[kvt85]

Very interesting subject.   I wanted to get into pouring some AL,  and brass.  did some but needed to find what to use as Degasser for AL and flux or whatever for the brass.   My AL pours were full of gas bubble holes which caused me problems.   The brass was Ok,  but did not come out quite like I was wanting.   

Was using a butane setup, and thought about trying to make a waist oil burner to use. Then other things come along and I keep moving it to the back burner.

[34_40]

I saw what you did there..  move it to the back burner indeed Lol     

[savarin]

I find with using propane that a highly oxidizing flame really cuts down the porosity.
I've tried degassing with soda and pool chlorine, neither made much of a difference.
Tried lost foam for brass, that was horrible so all my brass is just sand cast. Still horrible on the outside but once through the sandy skin its fine.

[Uglydog]

I don't pretend to be any sort of guru.
But anyone here is welcome to northern Minnesota to do a pour(s) as an individual or large group.

I've done more brass lately, and am hoping to experiment with aluminum brass this summer.

Using petro bond in a sand table through a muller.

Am secretly hoping that I can team up with Terry and get the other furnace operable. This vintage propane furnace is huge. The crucibles will require a mechanical lift due to weight.

Daryl
MN

Daryl
MN

[TerryWerm]

That big furnace would be a bit of a project!  I suspect it is designed for natural gas, but we should be able to get propane to work. 

[Uglydog]

Broberg gave me a couple dozen igniters and other foundry furnace related he had in his barn and wanted gone.
Am hoping to someday get to this....
I need to call Mifco and ask for tech assist.
OEM parts are evidently still available.
Perhaps I should preemptively call them.

Nahh... That would be to much like reading the directions before attempted assembly on Christmas Eve.

Daryl
MN

[TerryWerm]

If I remember correctly, the larger Mifco furnaces all have an automatic ignition system with flame detection, etc. Due to the size of the burner, I assume it is probably best to have a pilot light of some sort and the controller will not open the main gas valve without proving draft and a flame at the pilot first. That would probably be the safest way to go.

I know that if the control panel is missing, we can make one by using a generic Honeywell controller for a home heating furnace, available brand new on Amazon for about $100. As I have learned making control panels, the main component is the cheap part. Adding an enclosure, switches, indicator lights, wire, and terminals is the expensive part.

So far it sounds like a project that I would love to help you with. REALLY starting to wish I was retired now but I still have 22 months to go.

[Uglydog]

You may not recall. But you've already studied this specific set up. The sensor and controls work. What we don't have is the pipe to the furnace and the igniter.

Daryl

[TerryWerm]

That's right!!  After my last post I knew that I was missing something and that there was a part or parts missing but right off the top of my head did not remember what. Thanks for the refresher!

[4GSR]

Going back to Jimmy's original question about loosing elements in the melt. 
It's been my experience with investment casting that you loose carbon in the cooling of a investment casting.  That's if there is a sizable amount of carbon in the melt.  If the casting has a fairly thick section to it, you only loose carbon near the surface.
As for loosing any other elements, I've never encountered any other elements in a heat of material being lost. Most of the time when a heat of material is melted, they generally add elements to get the correct grade of material needed.
As for the cases of loss carbon, they do a carbon restoration in the heat treat furnace, the same furnace as used to do carburization in. You just don't quench the parts. It has to be cool down gradually until 400-600°F is reached and maintain a carbon rich atmosphere by running a gas flame in the furnace.