what I'm asking about is the materials used to build the casting
moulds for little model engine crankcases. ones cast in alooominumm.

what sort of head do you need in the aluminium to get a reliable mould
filling?

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

how much venting do you guys find necessary?

how long do your moulds last?

TUMESFFFFFF

In article ,
Stealth Pilot wrote:

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

More from reading than from doing thus far, but obviously if starting
with scrap, start with _nice_ _cast_ aluminum scrap - a good source of
which is old computer hard drive casings.

I'll be interested in the responses to your questions from those doing
more.

--
Cats, coffee, chocolate...vices to live by

On Oct 20, 12:25 pm, Ecnerwal
wrote:
In article ,
Stealth Pilot wrote:

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

More from reading than from doing thus far, but obviously if starting
with scrap, start with _nice_ _cast_ aluminum scrap - a good source of
which is old computer hard drive casings.

I'll be interested in the responses to your questions from those doing
more.

--
Cats, coffee, chocolate...vices to live by


Here is a qualitative description of what I know about this topic:

Metal molds, aka die-casting dies, are made from MOLD STEELS.

A variety of steels is available for different temperature ranges,
life expectancy, and of course, costs.

The molten aluminium is injected into the mold under PRESSURE to
ensure strength and absence of voids and leaks.

Aluminium can be sand cast; cylinder heads, older model transmission
cases and differential housings spring to mind. Surface finish and
dimensional accuracy are quite a bit coarser than die castings or
INVESTMENT CASTINGS.

Investment casting is an alternative for the model maker. A wax
pattern is produced (for mass production these may be molded in a
die!) and "invested" in a ceramic slurry. The wax is removed by
melting it out, and the ceramic shell heated and the molten metal
poured in (very abbreviated description).

The pressure required to fully fill the mold depends on a number of
variables such as alloy, mold complexity, size of the mold cavity,
etc. For simple dies I would think that 12" of head would suffice.

Simple steel molds have been made by modellers using common hot rolled
or cold rolled steel. For a dozen or so castings this metal is just
fine. A simple plunger injector can be arranged to force the metal
into the mold.

If you wish to carry out this process in your home workshop try to
read some reference works on this topic dated from the 1930's or so.
Early die casting used simple equipment and was used for producing
automotive radiator grilles.

As for the alloy to use....I would start with modern transmission
cases or cylinder blocks. I know for a fact that the TOYOTA small 4
cylinder block is a die casting.

Wolfgang

wrote in news:1192899432.935450.189020
@k35g2000prh.googlegroups.com:


The molten aluminium is injected into the mold under PRESSURE to
ensure strength and absence of voids and leaks.


There is also gravity permanent mold aluminum casting. The mold is again
made from steel, usually a specific grade of H13. The mold is vented at
the top, with the gate at the side. Depending on equipment, fairly tight
tolerances can be held, but not as tight as pressure die casting. In the
case of a cylinder head, you would want excess material on the vent side so
that when you machine it, you don't have oxides left in the surface. The
vent should be about 1/3 or so of the volume of your part to be available
in the vent and another 1/3 in the gate.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Stealth Pilot wrote:
what I'm asking about is the materials used to build the casting
moulds for little model engine crankcases. ones cast in alooominumm.

what sort of head do you need in the aluminium to get a reliable mould
filling?

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

how much venting do you guys find necessary?

how long do your moulds last?
Nobody uses reusable molds for hobby projects. I'm not sure the
auto makers use them, either. Either iron or aluminum engine
blocks are usually sand-cast. There are several variations on
the system. The old traditional system is wood patterns and
molding sand, with a clay-petroleum based binder. Another
system is lost-foam casting, where the sand is rammed arounds a
pattern made out of styrofoam, like the blue stuff used for home
insulation. I watched Rick Chownyk do some lost foam pours at
this year's CNC Workshop in Galesburg, IL. Very interesting.
We have a guy in St. Louis who has set up a very elaborate
casting shop, and I've watched and helped him ram up some wood
patterns and then pour them. There is also the lost-wax method,
usually used on small projects. Investment casting is a
time-consuming process, but gives amazing detail. A wax pattern
is made, sometimes in a mold also, then coated ("invested") with
a refractory slurry that is painted on in layers and allowed to
dry. The pattern/investment is then packed in sand to support
it, and the wax is melted out in a furnace. The metal is
usually poured while the mold is still hot.

A 6" head is plenty for mold filling with aluminum, often 2 -3"
will suffice. More head is needed with the lost foam, as the
foam is burning out with huge greasy flames as the aluminum is
being poured in. Too much head forces the mold flask apart, and
the aluminum starts leaking out.

Venting is often done with coat hanger wire or small welding
rods. Molds last one time if you do anything with the sand
processes. Alloys are rarely controlled, as most backyard
casters don't have a metallurgical analysis lab on site. You
use nice castings of known purpose, like hard drive cases or
pistons.

Jon

"Jon Elson" wrote in message
...
Stealth Pilot wrote:
what I'm asking about is the materials used to build the casting
moulds for little model engine crankcases. ones cast in alooominumm.

what sort of head do you need in the aluminium to get a reliable mould
filling?

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

how much venting do you guys find necessary?

how long do your moulds last?
Nobody uses reusable molds for hobby projects. I'm not sure the auto
makers use them, either.

Just to clear up a point, high-pressure diecasting, squeeze casting, and
permanent-mold casting are all used in making car engine blocks today, along
with traditional baked sand, thin-wall refractory-lined sand, and lost-foam
sand. The old B-O-P V8 from the early '60s was made in a steel, permanent
mold. Ferraris are made in plaster molds that are similar to investment
molds.

--
Ed Huntress

what I'm asking about is the materials used to build the casting
moulds for little model engine crankcases. ones cast in alooominumm.

what sort of head do you need in the aluminium to get a reliable mould
filling?

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

how much venting do you guys find necessary?

how long do your moulds last?

Sand casting is probably your first choice, both for cost and
something the home shop can accomplish. Oil bonded sand,
often called petrobond, is the easiest to work with. Water
bonded sand, sometimes called green sand, needs a little
more work to keep it in condition and needs more venting.
It usually isn't necessary to vent petrobond molds for aluminum.

Sand casting is a one shot mold that you simply remold for your
next casting. The pattern lasts a long time.

356 alloy aluminum is a good starting point or you can remelt
aluminum bell housings, etc., to get a feel for how the process
works. Stay away from extrusions and beverage containers
unless you are prepared to experiment with additives.

A couple inches of sprue should give you enough "head",
however, to get complete castings gates and runners will
likely be necessary.

Take a look at this video on YouTube:
http://www.youtube.com/watch?v=NKXj5Ng3X58 and
also by looking at "more from this user" you will find a short
video about investment casting. If you follow the link to my
projects page, there are a couple examples of lost foam and
also a project using gates and runners.

Rod

An interesting link to whet your appetite
http://images.google.com/imgres?imgu...icial%26sa%3DG

On Oct 21, 7:52 am, Gerry wrote:
An interesting link to whet your appetitehttp://images.google.com/imgres?imgurl=http://www.dmdaustralia.com.au...

Here's a better link I hope http://www.dmdaustralia.com.au/block.html

On Sat, 20 Oct 2007 21:38:27 -0500, "chips-'n-swarf"
wrote:


what I'm asking about is the materials used to build the casting
moulds for little model engine crankcases. ones cast in alooominumm.

what sort of head do you need in the aluminium to get a reliable mould
filling?

what aluminium alloys do you use for casting?
which alloys do you avoid like the plague?

how much venting do you guys find necessary?

how long do your moulds last?

Sand casting is probably your first choice, both for cost and
something the home shop can accomplish. Oil bonded sand,
often called petrobond, is the easiest to work with. Water
bonded sand, sometimes called green sand, needs a little
more work to keep it in condition and needs more venting.
It usually isn't necessary to vent petrobond molds for aluminum.

Sand casting is a one shot mold that you simply remold for your
next casting. The pattern lasts a long time.

356 alloy aluminum is a good starting point or you can remelt
aluminum bell housings, etc., to get a feel for how the process
works. Stay away from extrusions and beverage containers
unless you are prepared to experiment with additives.

A couple inches of sprue should give you enough "head",
however, to get complete castings gates and runners will
likely be necessary.

Take a look at this video on YouTube:
http://www.youtube.com/watch?v=NKXj5Ng3X58 and
also by looking at "more from this user" you will find a short
video about investment casting. If you follow the link to my
projects page, there are a couple examples of lost foam and
also a project using gates and runners.

Rod


I've not made a melt for some years now but I am well versed in
greensand casting. I made my own casting sand using washed sand and
about 5% bentonite rubbed to coat each sand particle and 5% moisture.
If anything my sand is just a shade coarse but it vents extremely
well.

I have two nemisis projects.both are tiny compression ignition model
aircraft engines.
one is to remake a 0.1cc Nano that actually runs beyond a prime this
time.
the other is to make a mills 0.75cc replica. it is the steel mould for
gravity casting the crankcase that I was asking about.

I think the key to good micro size screwthreading is to use an alloy
harder than 1214 free machining steel. it is wonderful for general
turning but useless for threading because it tears.
I havent given up trying on this quite yet though.

TUMESFFFF

On Sun, 21 Oct 2007 06:03:59 -0700, Gerry wrote:

On Oct 21, 7:52 am, Gerry wrote:
An interesting link to whet your appetitehttp://images.google.com/imgres?imgurl=http://www.dmdaustralia.com.au...

Here's a better link I hope http://www.dmdaustralia.com.au/block.html

now THAT was impressive.

Tumesffff

Jon Elson wrote:

I'm not sure the
auto makers use them, either. Â*Either iron or aluminum engine
blocks are usually sand-cast.

I'm sure that at least valve heads (out of aluminium) are cast in steel
moulds. Just the ports and water ways are sand cores. Sand casting is too
expensive for high volume productions.


Nick
--
The lowcost-DRO:
http://www.yadro.de

"Nick Mueller" wrote in message
...
Jon Elson wrote:

I'm not sure the
auto makers use them, either. Either iron or aluminum engine
blocks are usually sand-cast.

I'm sure that at least valve heads (out of aluminium) are cast in steel
moulds. Just the ports and water ways are sand cores. Sand casting is too
expensive for high volume productions.


Nick
--
The lowcost-DRO:
http://www.yadro.de

It depends on the accuracy, size and reusability desired. Plaster, rtv, sand
are common materials. For big
metal objects there are other choices in foundry practice.
There are plenty of good books out there on the processes.

Regards,

Edward Hennessey

Stealth Pilot wrote:

it is the steel mould for
gravity casting the crankcase that I was asking about.

Did you ever try petrobond?
A friend made his very first casting (with lots of mistakes; riser, feeder)
and the result was just incredible. Walls with 1mm thickness came out
perfect.


Nick
--
The lowcost-DRO:
http://www.yadro.de