In Reply to: Re: A casting of aluminum with a copper tube posted by Lee on 05/31/00 at 10:06 PM:
Ok, here is the long of it... ;>
I'm trying to come up with a inexpensive way of producing, in low volume (50 per
month), a device to create a stream of steam. I chose Aluminum for the
block because I have a foundry near by that can do aluminum. (and it can transfer
heat quickly) The copper tube (standard pure copper 1/8" od or 3/16" but is is less
common)would be easy to connect to, coil, hold in the sand mould, and relatively
inexpensive (esp. when compared to getting sand cores made, and that is just strait
cylinders...can't imagine the cost of a cork screw... if it is even possible) Heat would
be provided by a water heater type heating element cast right into the block. Some
where on the order of 1000 watts. I have a controller that can keep the block at a
preset temperature via a temperature sensor drilled into the core and a piston pump
to move the water at a variable rate. The block will be wrapped up in insulation
(ceramic baton?) and that will be the whole system (minus the box to put it all in).
Copper tube I thought was a good choice as it is cheap, easy to form and had a
higher melting temp than the aluminum... too bad it dissolves like a sugar cube in a
cup of water... Gave some consideration to Stainless Steel tube but it is more
expensive, harder to work with, and thought it may not be in the best environment,
heat, water and attached to a big block of aluminum. Besides... I believe some
where I read that I'd have the same dissolving issue as with the copper.
So, now I'm thinking I just need some coating that would keep the copper from
physically touching the aluminum. I've considered cold galvanizing sprays, anti
weld splatter... Ideal would be something that I could just dip the coiled copper
tube into and let dry the day(s) before a pour. Any insulative effect the coating
would have, I imagine, would be small and not a factor. If I need more time for heat
transfer I'll just put more coiled copper tube in...
Have done some test runs with different types of mould release (the foundry guy
had some on hand... one was Slick 50?) but didn't work. Copper tube was breached
in several places when we cut the cores open... (and a few places showed no trace
of the tube!)
But I have seen examples where this has been done, the copper cast into
aluminum... but I'll be damned if I can find someone who knows or is willing to tell
HOW. Is it that hard that it is a "trade secret"?