Differences is casting technique depending on mold material?

[That'll Do]

So here goes:

I recently purchased a 360-180-WFNGC from NOE. It is my first mold that is of aluminum construction. All the others are cast iron. I had a nice long casting session tonight, and all the iron molds spit out pretty boolits. The aluminum mold gave me nothing but wrinkled boolits.

All molds spent about 30 minutes on my hot plate before being put into casting service. My alloy is WW with 2% tin, 4% antimony, and 0.25% arsenic (Group Buy WW Alloy), and I usually cast between 700F and 750F (at least that's what my Lyman thermometer tells me).

Do I need to cast differently with an aluminum mold?

[JIMinPHX]

I vary my casting technique slightly depending on the individual mold, alloy being used & even ambient temperature. That aside, aluminum molds usually like to be run a little faster than iron molds do. If you are running around 700-750 degrees, you probably have the pot hot enough. You probably just need to pick up the pace a little so that the mold can't cool down as much between pours. Aluminum doesn't hold heat like iron does. I would say that is 80% likely to be the problem. It is also possible the the mold is not clean (oil residue?).

[That'll Do]

I vary my casting technique slightly depending on the individual mold, alloy being used & even ambient temperature. That aside, aluminum molds usually like to be run a little faster than iron molds do. If you are running around 700-750 degrees, you probably have the pot hot enough. You probably just need to pick up the pace a little so that the mold can't cool down as much between pours. Aluminum doesn't hold heat like iron does. I would say that is 80% likely to be the problem. It is also possible the the mold is not clean (oil residue?).

Thanks for the reply Jim.

I cast pretty darn fast (using the speed casting technique), so I think my pace is alright.

I'll bet that I need to scrub the mold with brake cleaner again. I scrubbed it once before setting it on the hot plate, but I have a feeling that I missed some residual oil.

[JIMinPHX]

When you say that you're using the speed casting technique, if that means that you're cooling off the mold or sprue plate with a damp rag or something like that, then try not doing it. The aluminum molds loose heat fast enough by themselves. You don't want to speed up the heat loss if you can help it.

[That'll Do]

When you say that you're using the speed casting technique, if that means that you're cooling off the mold or sprue plate with a damp rag or something like that, then try not doing it. The aluminum molds loose heat fast enough by themselves. You don't want to speed up the heat loss if you can help it.

OK, I'll give that a try tomorrow and see what happens.

[stubshaft]

Try Kroil in the mould. It seems to creep into those microscopic pores in the aluminum and get debris out. I don't know why but it works for me.

[mooman76]

I cast hotter with aluminum moulds than with steel. Ike said they loose heat quicker. They also heat up quicker but loose heat faster. If you are using your normal temp for steel jus turn it up a little more. You have to change for bullet size also. Smaller bullets don't heat or keep it as hot has so you need a hotter lead also as well as big bullets like for the big BP rifles heat and keep the mould hot so you turn the heat down. I think people get too hung up on their thermometers thinking it should be working instead of just adjusting the heat so it does work.

[That'll Do]

Well, I scrubbed the mold again, and cranked up the heat (800 degrees), and I was able to get good boolits as long as I kept a brisk pace.

I think I'll Kroil the mold for good measure and give it another go tomorrow.