Being new to this hopefully this isn't an ignorant question. My question is specifically about sand. Does sand get stuck to the sprue's? Do you cut or grind it off before re-melting? Does it matter? I've been acquiring the needed materials for sandcasting and was thinking about this today. Thought I would ask before I got to that point. Thanks in advance. Matt
I think you will get lots of opinions. Nobody will be wrong. I try to not put extra trash into the crucible but most extraneous materials come off with the dross or slag. I think sand is pretty benign so any that can't be brushed off goes back in. Same goes for chrome plating on brass, it floats away. Solder goes into solution so plumbing fittings which have been soldered contaminate brass with lead, tin, and whatever else was in the solder. It's aminor point if you aren't just melting soldered joints.
Cleaner is always better. Paint, grime, excessive dirt are best cleaned or removed as much as possible. Compare it to welding prep: you can get away with shortcuts, but it'll get you somehow, someway. Clean metal should really be at the top of the list. If you have stuck-on sand alittle effort with a wire brush will get you close enough. Pete
I bead blast my bronze before remelting it. I hear bits of shell are a real no no when remelting so I get rid of it.
I couldn't agree more. My lost foam coating will prevent sand adhesion on the majority of casting and feed system but sometimes I get a little on the sprue and pouring cup. But as Petee said, a few strokes with a wire brush removes almost all of it. Dirty metal makes for more dross, lower yield, and gassy metal. Silica is very close to the density of aluminum, but I usually find if there is any, it's retained in the small thin heal of an empty crucible after an aluminum melt, so I just discard it. However, a few grains of sand in a casting can wreak havoc with machine cutters if post machining is required. Best, Kelly
It's a big hassle with aluminium and much less of a problem with denser brasses and bronzes, I'll attach the same identical casting made in dirty bronze scrap (fluxed) and in aluminium from recycled runners with a generous coating of sand. You can see sand grains embedded in the aluminium and the bronze looks perfectly clean.
Love that bronze finish!. The aluminium was sand all the way through however, nothing that high speed steel couldn't cope with.
I can't say for certain but it's likely, mainly old marine plumbing fittings recycled. If brass has a machinability rating of 100 then 85-5-5-5 bronze relative machinability is in the 80's I think...
In most alloys sand and other lightweight contaminants will float as it is lighter than the melt charge and can be cleaned during slagging. However with lighter metals some trash may be heavier and may not float. It would be easier to wire brush it off than to slag it out of a crucible in my opinion. I generally try to clean any return melts as best as I can before melting.
With bronze I don't bother. It doesn't get stuck in metal. Only floats to the top and can easily be skimmed before pouring. I guess aluminum is a different animal tho.
Glad I found this thread before posting my question. I have an old piston with oil and carbon on it. I take it I should clean as best as possible before melting. Sounds like a silly question now...but I guess wondering what would just melt off in the melting process.....having melted nothing yet, I don't know what I don't know. Thanks for starting this thread.
Shawno, The carbon shouldn't be a problem. But you want to get as much of the hydrocarbons (oil, grease, etc) off as is feasible before you drop it in your crucible. A wipe with a rag and a quick shot of degreaser and a scrub brush never hurts. You don't have to get carried away no need for a trip through hot caustic or a vaper bath. just not fresh from the motor either. However you clean it make sure it's Dry, Dry, Dry before it meets molten metal!!!
I will be honest though...you can clean the metal with slagging and such to compensate for a slightly dirty melt and if you do a good thorough job the casting should be good. Loose sand in the mold and especially in and around the ingates is the biggest source of inclusions in sand molding. Even bad gating will usually give you pretty decent castings if you have clean metal and a good clean mold as long as it is not too pressurized which will wash the sand out.
Thank you for the input. I finally got around to melting the old lawn mower motor today. I cleaned it up with a parts cleaner and we will see how the castings look. I have no particular needs right now for anything so am just pouring the melt into soup cans. I have not stolen my wife's muffin tins yet...
