Rocket Man VW Heads... What alloy?

On Sat, 10 Jan 2009 11:15:40 -0800 (PST), "
wrote:

356-T6 is usually selected for its HIGH STRENGTH rather than its
ability to pass heat

While I don't disagree with you, my ASME Metals Properties (1954)
shows the 356 alloy to be well above average in thermal conductivity.
What alloy is usually used in aluminum heads?

George

On Jan 12, 7:17*am, GeorgeB wrote:
What alloy is usually used in aluminum heads?
--------------------------------------------------------------------------------

I don't know, George. My data is probably out of date. The Navy code
is (or was) MM212a... which I was told is equal to A.S.T.M. B26-37T ,
cited as suitable for Aluminum Sand Castings (Cylinder Heads,
Crankcases, Etc.) It has 4% copper and has about the same thermal
conductivity of the other copper-bearing alloys ( ie,
0.0000125 ...meaning that's it's coefficient of expansion between 68
and 392*F ). Not very strong, though... 32kpsi (Tension)
-------------------------------------------------------------------------------------------------------------

While I don't disagree with you, my ASME Metals Properties (1954)
shows the 356 alloy to be well above average in thermal conductivity.

-------------------------------------------------------------------------------------------------------------

It's okay to disagree with me, George :-) I'm just whipping most of
these numbers out of my ass anyway. When I was the leading Chief at
COMCRUDESPAC's computer shop we were just across the street from the
Pattern-makers school at the 32st Naval Station, and me & the Chiefs
over there were about the only Chiefs for some distance around, so we
were always bumping into each other. I picked up a little bit of
knowledge about casting & pattern making. Enough at least, to cast
little do-dads. Our local junior high usta teach that; showing kids
how to make ash trays and the like. All gone now, of course. Too
dangerous or something.

But it doesn't really matter. Because I'll be using old pistons any
way :-)

It's not a question of strength, money nor physical properties, but
more a question of time & convenience. With about a thousand people
'subscribed' to this group, and everyone TALKING about the subject,
odds are I'll be the only one to actually DO anything about it :-)

Pretty exclusive club, Doing Things.

My muller (the thing that you use to mix the oil or what-have-you with
the sand) is one of those humongous mixers you drive with a 1/2" drill
motor (usually used to mix mortor). I use #100 sand from Dixieline
Lumber in Escondido... costs about two bucks a bag (or did). I've got
several flasks around the place, plus a small furnace that uses a weed-
eater flame nozzle. My 'furnace' is a big bucket lined with fire-
clay. Steel pot for the melting. Dipped in a slurry of refractory
material, allowed to dry then 'cooked' in the furnance until it's
cheery red and allowed to cool. The aluminum gets heated then chunked
up with a BIG iron bar. Anything left over goes into a couple of
steel molds.

The tricky bit is making the patterns. I think I've got it figured
out but I haven't tried making the core boxes as yet.

To make cores I use some molasses and paste-flour, plus a bit of
water. #100 sand. Pack it good & tight then dismantle the core-box
and hope it don't crack. Put them in the over to cook overnight @ 250
degrees. Next morning (or eight hours later) you've got a light --
hopefully porous -- core that will fit the holes in your pattern.
High tech it ain't :-)

-Bob

wrote in message
...
On Jan 12, 7:17 am, GeorgeB wrote:
What alloy is usually used in aluminum heads?
--------------------------------------------------------------------------------

I don't know, George. My data is probably out of date. The Navy code
is (or was) MM212a... which I was told is equal to A.S.T.M. B26-37T ,
cited as suitable for Aluminum Sand Castings (Cylinder Heads,
Crankcases, Etc.) It has 4% copper and has about the same thermal
conductivity of the other copper-bearing alloys ( ie,
0.0000125 ...meaning that's it's coefficient of expansion between 68
and 392*F ). Not very strong, though... 32kpsi (Tension)
-------------------------------------------------------------------------------------------------------------

While I don't disagree with you, my ASME Metals Properties (1954)
shows the 356 alloy to be well above average in thermal conductivity.

-------------------------------------------------------------------------------------------------------------

It's okay to disagree with me, George :-) I'm just whipping most of
these numbers out of my ass anyway. When I was the leading Chief at
COMCRUDESPAC's computer shop we were just across the street from the
Pattern-makers school at the 32st Naval Station, and me & the Chiefs
over there were about the only Chiefs for some distance around, so we
were always bumping into each other. I picked up a little bit of
knowledge about casting & pattern making. Enough at least, to cast
little do-dads. Our local junior high usta teach that; showing kids
how to make ash trays and the like. All gone now, of course. Too
dangerous or something.

But it doesn't really matter. Because I'll be using old pistons any
way :-)

It's not a question of strength, money nor physical properties, but
more a question of time & convenience. With about a thousand people
'subscribed' to this group, and everyone TALKING about the subject,
odds are I'll be the only one to actually DO anything about it :-)

Pretty exclusive club, Doing Things.

My muller (the thing that you use to mix the oil or what-have-you with
the sand) is one of those humongous mixers you drive with a 1/2" drill
motor (usually used to mix mortor). I use #100 sand from Dixieline
Lumber in Escondido... costs about two bucks a bag (or did). I've got
several flasks around the place, plus a small furnace that uses a weed-
eater flame nozzle. My 'furnace' is a big bucket lined with fire-
clay. Steel pot for the melting. Dipped in a slurry of refractory
material, allowed to dry then 'cooked' in the furnance until it's
cheery red and allowed to cool. The aluminum gets heated then chunked
up with a BIG iron bar. Anything left over goes into a couple of
steel molds.

The tricky bit is making the patterns. I think I've got it figured
out but I haven't tried making the core boxes as yet.

To make cores I use some molasses and paste-flour, plus a bit of
water. #100 sand. Pack it good & tight then dismantle the core-box
and hope it don't crack. Put them in the over to cook overnight @ 250
degrees. Next morning (or eight hours later) you've got a light --
hopefully porous -- core that will fit the holes in your pattern.
High tech it ain't :-)

-Bob

-----------------------------------------------------------------------------------------------------

First, I would recommend you double check your source on sand. Most building
supply folks sell "river" sand. If you examine it closely, you will find it
is made up of round granules that look simply like pea gravel. Silica sand,
the white sand used for years in public ash trays and some blasting
operations is much more suitable, and well worth the addtional cost. Olivine
is also very popular for green sand molding, although it cost a good bit
more. The shape of these sands are much more irregular, and thus will form
much stronger molds regardless of which binder you choose.
http://en.wikipedia.org/wiki/Olivine

I'm not familiur with your binder recipe, but might want to try a sodium
silicate based solution to simplify your process. You can mix a one part
liquid with your sand, ram up your core boxes, and simply gas them with CO2
gas to set them in less than 60 seconds. There are also catalists available
that will cure them in 10 minutes or so, if you have a mixing process that
allows you to mix the sand and get it in the mold that quickly. I have
friends in the business and could probably get you a gallon sample freebe if
you would like to try it. I'm told it's about $75 for 5 gallons if you get
addicted to it, but it only takes about 2% if you have a good mixing
process.

As for the metal and the melt process, to each his own. But I can say from
experience you stand a good chance of having porosity problems with the
method you discribe, and there are cheaper ways to do things. Having the
ability to fabricate the patterns are the real challange here, and I have no
doubt you can do that. Once they are complete, a small shop could probably
cast you some heads for less than your time and supplies are worth.

There is also the possibility of molding this in plaster, but that's another
story.

On Jan 12, 8:38*pm, "Maxwell" #$$9#@%%%.^^^ wrote:
-----------------------------------------------------------------------------------------------------

First, I would recommend you double check your source on sand.
------------------------------------------------------------

BT, DT (big Smiley)
This is good quality 100% silica. They don't even store it in the
same shed, to prevent errors (They'll load stuff for you.).

I've got a couple of bags of #80 but I've found it's a bit too
coarse. (But works fine in the blast cabinet.)

------------------------------------------------------------

I'm not familiur with your binder recipe,

-----------------------------------------------------------

I may not be either :-) I think I used 'Karo Syrup' the last time I
made cores but I had a rather unfortunate accident with the
materials. We have cats and... perhaps that's enough said :-)

----------------------------------------------------------

but might want to try a sodium
silicate based solution to simplify your process. You can mix a one part

----------------------------------------------------------

I've seen this used to make some brass castings, literally while the
'customer' was waiting (circa 1975) I've always wanted to try it but
applying the gas makes it appear rather complicated. Of course, guys
who HAVE used it tend to make it sound like mother's milk, whereas
guys who have TRIED to use it make it sound like WWIII. I assume
it's somewhere in the middle :-)

---------------------------------------------------------

. I'm told it's about $75 for 5 gallons

---------------------------------------------------------

Then it's beyond my means. (The cancer has attacked my pocket-book
with even more success than my spine :-)

And besides, I still have the patterns to finish and prove. The last
time I worked with fins I had a HELL of a time before I got the patten
to 'rap' free. Indeed, it made cores simple by comparison.

I will also have to develop the procedure for afixing the valve seats,
hopefully like Stephen.... what's-his-name... the fellow who did so
well racing the Type IV's. His foreman let me try my hand swaging the
seats into a modified Type IV head and that puppy was HOT -- it came
right out of the oven. (Do it COLD -- which was VW's recommended
procedure -- and you'd end up with a loose seat for sure.) Plus the
racer's seats were something like 5/8" deep; VW's appeared to be less
than 1/2". So there's a bit of tooling needed on the production side,
assuming I can get the thing to give me some fins.

....but you've got me thinking about using the CO2 method for the outer
mold as well. Give me another hundred years... or even ONE :-)
--------------------------------------------------------------------------

There is also the possibility of molding this in plaster, but that's another
story.
---------------------------------------------------------------------------

I think I mentioned the dentist. He was casting some exotic STEEL
alloys for bridge-work using the lost-wax process. Had a little
centrifuge, tiny ceramic crucibles -- the whole nine yards but in
miniature. He let us use his oven to heat-treat the hinges for the
Varieze. But only once :-) When I tipped the tray of hinges into the
ice water it drove everyone out of the lab. I guess he'd never seen
it done before.

-Bob

On Mon, 12 Jan 2009 22:38:54 -0600, "Maxwell" #$$9#@%%%.^^^ wrote:



There is also the possibility of molding this in plaster, but that's another
story.


unless you've tried it you would have no idea how dangerous that
suggestion actually is.

firstly the strength of plaster vanishes to nothing beyond a certain
temperature. that temperature is just 5 degrees celcius above the
melting point of aloominum.

I have tried the technique to cast a mills 0.75cc diesel crankcase.
this is a tiny thing about an inch and half by an inch and a half in
overall dimensions. relatively tiny and easy to work with.
it was done lost wax.
a day after the plaster was set the mold went into the oven to melt
out the wax. it was then cooked up to about 180 degrees farenheit for
a while (2 hours afaik) to evaporate off the moisture. it stayed in
the oven overnight (I've never been allowed to use the oven again) it
was then given 15 minutes in the microwave to really dry it out.
it was wrapped in a cloth and raced out to the workshop hot.

it looked alabaster white and as dry as a piece of chalk.

when the aluminium was poured into the mold a guyser of molten
aluminium ejected to the ceiling of the workshop. this seemed to
continue for some time. an examination of the mould later showed it to
be totally empty. I dont know how dry you need to get it but I gave it
a fair go at getting a bone dry mould.

I have to ask you what your experience is in casting.
have you ever done any of this yourself or is it something you've
watched?

Stealth Pilot

"Stealth Pilot" wrote in message
...
On Mon, 12 Jan 2009 22:38:54 -0600, "Maxwell" #$$9#@%%%.^^^ wrote:



There is also the possibility of molding this in plaster, but that's
another
story.


unless you've tried it you would have no idea how dangerous that
suggestion actually is.

firstly the strength of plaster vanishes to nothing beyond a certain
temperature. that temperature is just 5 degrees celcius above the
melting point of aloominum.

I have tried the technique to cast a mills 0.75cc diesel crankcase.
this is a tiny thing about an inch and half by an inch and a half in
overall dimensions. relatively tiny and easy to work with.
it was done lost wax.
a day after the plaster was set the mold went into the oven to melt
out the wax. it was then cooked up to about 180 degrees farenheit for
a while (2 hours afaik) to evaporate off the moisture. it stayed in
the oven overnight (I've never been allowed to use the oven again) it
was then given 15 minutes in the microwave to really dry it out.
it was wrapped in a cloth and raced out to the workshop hot.

it looked alabaster white and as dry as a piece of chalk.

when the aluminium was poured into the mold a guyser of molten
aluminium ejected to the ceiling of the workshop. this seemed to
continue for some time. an examination of the mould later showed it to
be totally empty. I dont know how dry you need to get it but I gave it
a fair go at getting a bone dry mould.

I have to ask you what your experience is in casting.
have you ever done any of this yourself or is it something you've
watched?

Stealth Pilot


Both. http://www.gp.com/build/product.aspx?pid=1569

On Jan 13, 1:00*am, Stealth Pilot
wrote:
On Mon, 12 Jan 2009 22:38:54 -0600, "Maxwell" #$$9#@%%%.^^^ wrote:

when the aluminium was poured into the mold a guyser of molten
aluminium ejected to the ceiling of the workshop. *this seemed to
continue for some time. an examination of the mould later showed it to
be totally empty. I dont know how dry you need to get it but I gave it
a fair go at getting a bone dry mould.

Stealth Pilot

Your experience pretty much matches mine. I was able to get dry
enough plaster to make castings without porosity, but it took WAY to
long to dry to that point. My first pour too resulted in a steam
geyser and I would have sworn I baked that thing long enough. I was
also having fill problems. One plaster cast per go made the
experimentation too time consuming. I gave up and went back to sand.
I was trying to make fined valve covers for my1/2VW and was having
trouble getting molds in sand to stay together while puling the
pattern. At that time I didn't have a muller and could not get oil
based sand to work at all - thus the try at plaster. I finally
managed to modify my sand formula and got satisfactory results. A
touch of sugar did the trick.

The fins on the valve covers were enough of a challenge that I won't
be trying to do any head casting in sand, oil or bentonite based.
IMHO buying/building a muller is worth the time and trouble as the oil
based sand is good stuff. The humidity in my part of the world is
such that an uncovered covered heap of sand will dry out too much in a
matter of hours. Oil doesn't and for that reason alone I made the
switch.

Just in case you don't have the formula, even though I'm sure you
do...........................

http://www.foundry.ray-vin.com/k-bond/k-bond.htm
http://users.hal-pc.org/~lwhill/sandsystems.html

=======================
Leon McAtee

On Tue, 13 Jan 2009 08:42:55 -0800 (PST), "
wrote:

On Jan 13, 1:00*am, Stealth Pilot
wrote:
On Mon, 12 Jan 2009 22:38:54 -0600, "Maxwell" #$$9#@%%%.^^^ wrote:

when the aluminium was poured into the mold a guyser of molten
aluminium ejected to the ceiling of the workshop. *this seemed to
continue for some time. an examination of the mould later showed it to
be totally empty. I dont know how dry you need to get it but I gave it
a fair go at getting a bone dry mould.

Stealth Pilot

Your experience pretty much matches mine. I was able to get dry
enough plaster to make castings without porosity, but it took WAY to
long to dry to that point. My first pour too resulted in a steam
geyser and I would have sworn I baked that thing long enough. I was
also having fill problems. One plaster cast per go made the
experimentation too time consuming. I gave up and went back to sand.
I was trying to make fined valve covers for my1/2VW and was having
trouble getting molds in sand to stay together while puling the
pattern. At that time I didn't have a muller and could not get oil
based sand to work at all - thus the try at plaster. I finally
managed to modify my sand formula and got satisfactory results. A
touch of sugar did the trick.

The fins on the valve covers were enough of a challenge that I won't
be trying to do any head casting in sand, oil or bentonite based.
IMHO buying/building a muller is worth the time and trouble as the oil
based sand is good stuff. The humidity in my part of the world is
such that an uncovered covered heap of sand will dry out too much in a
matter of hours. Oil doesn't and for that reason alone I made the
switch.

Just in case you don't have the formula, even though I'm sure you
do...........................

http://www.foundry.ray-vin.com/k-bond/k-bond.htm
http://users.hal-pc.org/~lwhill/sandsystems.html

=======================
Leon McAtee

priceless references.
I've never tried oilsand just a seemingly continuous tweaking of my
bentonite based mix getting it better and better.

maxwells investment reference gives little actual detail but they must
do some cunning stuff with the additives that they allude to in their
plaster. they've certainly developed the process way beyond what I've
achieved.
Stealth Pilot

"Stealth Pilot" wrote in message
...
On Tue, 13 Jan 2009 08:42:55 -0800 (PST), "

maxwells investment reference gives little actual detail but they must
do some cunning stuff with the additives that they allude to in their
plaster. they've certainly developed the process way beyond what I've
achieved.
Stealth Pilot

It wasn't an investment reference, just a casting plaster.

On Jan 13, 3:00*am, Stealth Pilot
wrote:
On Mon, 12 Jan 2009 22:38:54 -0600, "Maxwell" #$$9#@%%%.^^^ wrote:

There is also the possibility of molding this in plaster, but that's another
story.

unless you've tried it you would have no idea how dangerous that
suggestion actually is.

firstly the strength of plaster vanishes to nothing beyond a certain
temperature. that temperature is just 5 degrees celcius above the
melting point of aloominum.

That is because it is water molecules that bind the other molecules
together when the plaster cures. When you heat it, you break those
bonds and drive off the water.

You can test this out by weighing the water and plaster you mix,
then weigh the cured solid when it appears dry. It will still weight
a lot more than the dry plaster did. After baking it, weigh it
again.

As long as the weight is greater than the original dry plaster, you
know there is still water in there.


I have tried the technique to cast a mills 0.75cc diesel crankcase.
this is a tiny thing about an inch and half by an inch and a half in
overall dimensions. relatively tiny and easy to work with.
it was done lost wax.
a day after the plaster was set the mold went into the oven to melt
out the wax. it was then cooked up to about 180 degrees farenheit for
a while (2 hours afaik) to evaporate off the moisture. it stayed in
the oven overnight (I've never been allowed to use the oven again) it
was then given 15 minutes in the microwave to really dry it out.
it was wrapped in a cloth and raced out to the workshop hot.

it looked alabaster white and as dry as a piece of chalk.

when the aluminium was poured into the mold a guyser of molten
aluminium ejected to the ceiling of the workshop. *this seemed to
continue for some time. an examination of the mould later showed it to
be totally empty. I dont know how dry you need to get it but I gave it
a fair go at getting a bone dry mould.


I've no experience, but there is a nice newsgroup called
rec.crafts.metalworking or something like that where you
can get good advice from people who routinely have a
less exciting experience.

Plaster of Paris retains water of crystalization when it is
cured. It takes a lot of heat for a long time to get all of that
water out, like maybe 5 or 6 hours at 500 F and you should
keep it hot when you our. If I understand the chemistry, by
the time it is dry enough to cast aluminum you will have returned
it to much the same material that it was before you mixed
it. Since you didn't do that, it was the molten aluminum
that decomposed the plaster releasing the water with the
observed result.

Jewelers work with much higher melting point metals, platinum
even. They use investment, sometimes called investment plaster.
The difference between that and ordinary Plaster of Paris is that
it has materials added like silica that do not decompose when the
mold is burnt out, and other materials (maybe wood flour) that are
there to create microporosity when it is burnt out. A high quality
investment may be overkill for casting aluminum, but it will be
better than a molten aluminum geyser.

But please do check with people who, unlike myself, have
actually done this.

On to the subject of cooling fins:

I HAVE designed cooling fins back in a former life when I
was working in the nuclear industry. I believe you will
get the best heat transfer with pure aluminum. Alloys
will have a lower thermal conductivity, although the
more important parameter is heat capacity, the product
of thermal conductivity with density. But for an airplane
you probably don't want denser (and therefore heavier
materials).

You can improve the heat transfer and reducing the
weight by tapering the cooling fins from root to tip. A
good undergraduate engineering book on heat transfer
should address the optimization of cooling fins.

Remember also that convective heat transfer is
governed by Newton's law of cooling:

q = mdot * h * A * deltaT

DeltaT is the temperature difference, A is the surface
area (which you increase with fins), h is the convective
heat transfer coefficient (usually a function of Reynold's
number) and mdot is the mass transfer rate of the cooling
fluid.

Bumping up the flow increases both mdot (directly) and
h, by increasing the Reynold's number. It helps a lot.

IOW, concentrating on improving the airflow may be more
helpful than improving the fins.

Hope this helps

--

FF