Hi Howard,
I need some casting advice. What happens if I pour some molten aluminum
into an existing casting like a Mazda water pump housing?

Any drawbacks in melting the aluminum in a steel container?

Paul Lamar

Howard Wilkinson wrote:

Paul:
        From what I understand it doesn't work very well.   The temperature
differential doesn't make for a decent bond, not to mention the aluminum oxide which
makes a skin almost immediately on the surface of any aluminum and melts at a
considerably higher temp than aluminum itself.    Not pouring a mold fast enough will
result in a flawed casting, and stopping and starting a pour absolutely is a no no.
You can and many people do melt aluminum in a steel container.... the only
drawback is that the aluminum picks up some impurities from the steel.... not too
serious a problem in most cases.    Remember in doing aluminum to melt pieces that
are clearly castings.... do not use such things as 6061, 6063, 2024, 7075, etc.... the
common aircraft structural alloys do not cast worth a damn.   Such items as pistons,
bell housings, lawnmower engines, etc.... are much better choices for casting alloys.
Exercise caution in what you use.... Magnesium is found in a lot of VW stuff and can
be a real adventure as you cannot easily or safely put out the fire.

        My recommendation for your water pump project would be that you use
parts from one of the many small automotive water pumps in which the bearing and
impeller are one assembly and the impeller housing and water channels are a
second.   This will allow you to easily design a casting which will only need a
machined face for the bearing & impeller assy to bolt to and another to mate to the
block.   Carve what you want from blue xps foam and smooth the surface with a thin
layer of wax.   If more than the standard thickness of foam is needed (2") a dot of
epoxy to glue the pieces together...   Use a thermostat  housing for your water outlet
rather than bothering to cast it in.... there are lots of 90 degree thermostat housings.
Pour the whole piece.   Water pumps are so simple that it should be easy to build
one.    All you need is a way to channel water to the center of your impeller, and
space around the impeller to channel water away..... they are dirt simple and actually
rather crude.   You don't even need the fancy swirl shape most pumps have inside
for it to work.
        Invest your piece by pouring plaster of paris around it leaving several
vents, and leaving several sprues gathered to a single ingate for pouring.   Allow it to
dry damn well, and pour it.

        I'm not sure what the purpose of this exercise is.....    The problem with
most automotive water pumps is that they pump water into the engine and draw from
the radiator.... this results in the impeller facing the wrong way round forcing you to
have more channels than would otherwise be necessary.  The ideal compact light
water pump would be mounted to the engine such that the impeller would draw right
from the engine, and exhaust sideways.   This would allow the impeller to run very
close to the engine and reduce overall dimensions & weight.... I don't know how well
reverse flow cooling would work though.... You'd still push the water down through
the radiator, but it would flow opposite through the engine unless you could draw
from where the water outlet currently was.  Continental made extensive use of an
external water pump on their industrial engines.   This pump was mounted beside the
engine and was driven from an accessory shaft rather than a belt..... something to
think about.... the pump need not be mounted right to the block.

        I would suggest simply designing the pump you want from blue foam, and
having one of the people on my hobbicast mailing list do the casting.   Quite a few of
them have small businesses which have developed from their casting hobby and are
quite good.  Using the foam method would allow you control of the result, minimize
shipping problems, and free you to do what you are good at.... design.... and let
someone else do the part they are good at.... casting.....    I strongly recommend this
approach.    Below are two excellent small scale metal casters who are considerably
beyond hobby class expertise.   Of the two I would recommend Jerry as he does
some foam work already and can advise you.    I don't know if Charles does.   Hope
this helps some...... do it right.

                                        H.W.


Charles Logan
hfd220@aol.com
http://hometown.aol.com/hfd220/index.html

Jerry Twaddell
Custom Castings by Twaddell
foundryman@igateway.net
http://members.igateway.net/~jtwad/

Thanks Howard.

Paul Lamar
 
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