On 25/03/2019 16:45, Bob La Londe wrote:
Ok.. I've studied on this for a while.

Everybody says (exaggeration) you can't cast 6061 it has to be
wrought.Â*Â* If you try to cast it you get large crystals and poorly
structured metal.Â* One article I read about casting 6061 seemed to
indicate that rapid cooling of sand type castings by blasting away the
sand with water jets retarded crystal growth.Â* As near as I can tell
wrought means formed by working or under higher pressure.Â* I'm sure
somebody can provide a better definition in context.Â* I think forming
under pressure might also retard crystal growth.

Now one of the pretty well known enemies of aluminum casting is the
formation of aluminum oxides during the melting process, and of course
oxides that have already formed.Â* Rapid melting with a forced air
foundry as opposed to a naturally aspirated foundry seems to reduce
this dramatically. Surface area of the starting stock is also a factor
so even with a forced air furnace machined chips might not be a good
candidate.

So why not use a steel die (permanent mold) with a cylinder shaped
casting sprue, and then when full place it on a press with a piston to
apply pressure.Â* Then liquid cool it while still under pressure.Â* If
the process proves possible its all achievable in the conditions of a
home shop.Â* Well a home shop capable of making steel dies anyway.Â* I
would think pressure would have to be regulated so that cooling
contraction does not destroy the part. The simplest shop press might
not be upto the job as somebody would have to stand there surround by
steam pumping the jack. LOL.

The biggest issue I see is figuring out how to cap the vents when the
die is full so that you don't spray molten metal around the shop when
you apply pressure.

I don't even know if I should post this...Â* Ah what the heck.

Flame on.Â* (pun intended)



Maybe do some research into the use of chills in sand casting. IIRC the
old British Gardner Diesel engine had a sand cast aluminium crankcase
and used numerous chills in critical places to unsure rapid cooling of
critical areas for optimum strength. A mate works in engine design and
he has mentioned that aluminium cylinder heads are often done by
specialist casters as they have the knowledge to control the dendrite
formation in the castings especially for critical parts of the cylinder
head such as the head gasket face to get the maximum strength.