Helpful audience!

Today, I made my first spinn-casting with zinc.

It was just a first test shot to see what I can do wrong and what I did
already do wrong.
So the mold was just a plaster mold [1] and the zinc was just some scrap
zink sheet metal for roofing. That zinc proofed to be good enough and I
will use up all the rest before going to the costy zinc I ordered.
At least, the spin caster was a success. I had no other motor at hand,
so the disk is rotating with nearly 1400 RPM. Direct driven! The disk
has a diameter of 12". I thought more g-force = better surface. It
seems, that that is right. No problems with vibration, as the frame
where all the suff sits in is quite heavy.
The first casting was a (partial) success, some detail very good, other
bad. But that only where I had bubbles in the plaster. Also a partial
failure, because I didn't melt enough zinc. I have to cut the inlet (in
the center of the disk, because to much is cooling down there and
remains there and doesn't flow down into the mold.

So I will make some mods, add a brake to stop the disk spinning and add
shielding and paint.
Will put pics and explanations to my HP. This time in English, so you
don't have to babelguess about what I have written in Kraut-Language.
Will take some days, but I will keep you informed.

Oh, the silicone is damned expensive! 1kg (2 pounds) about 50 EUR, that
are 60$. :-( OK, it withstands 500°C (930 F), zink poring temperature is
400°C (750F). But that stuff is to expensive for playing around.
I will think about to put the rubber in some supporting form to save
some rubber.


[1] that showed to be my newest invention "lost plaster casting".
Also, I baked it too long in the oven. It broke in 3 parts over
night. Some super glue fixed that.
I didn't get the castings out of the mold, so I broke it apart.
It was some wothless casting anyhow.

Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

"Nick Müller" wrote in message
...
Helpful audience!

Today, I made my first spinn-casting with zinc.

It was just a first test shot to see what I can do wrong and what I did
already do wrong.
So the mold was just a plaster mold [1] and the zinc was just some scrap
zink sheet metal for roofing. That zinc proofed to be good enough and I
will use up all the rest before going to the costy zinc I ordered.
At least, the spin caster was a success. I had no other motor at hand,
so the disk is rotating with nearly 1400 RPM. Direct driven! The disk
has a diameter of 12". I thought more g-force = better surface.

But only to a point. As the G forces increase, you risk blowing the mold.
It's a problem for jewelers, casting with gold alloy with a much higher
specific gravity. If you have problems with that, you'll know you have
to slow down.

Well done!

Harold

Harold and Susan Vordos wrote:

But only to a point. As the G forces increase, you risk blowing the mold.

Yes, I'm aware of that. I will see. Plaster isn't as tight as the
silicone.


Well done!

How do you know that!? :-)
You haven't seen the pictures yet. Or do you want to push me? :-)

Anyhow, thanks for the input and hints I got there!


Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

"Nick Müller" wrote in message
...
Harold and Susan Vordos wrote:

But only to a point. As the G forces increase, you risk blowing the
mold.

Yes, I'm aware of that. I will see. Plaster isn't as tight as the
silicone.

True, but you could experience distortion, without complete mold failure,
likely only on large items, though.


Well done!

How do you know that!? :-)

Chuckle!

I have faith in you! After all, you did achieve results of sorts.

Harold

On Sun, 21 Aug 2005 19:40:10 +0200, (Nick Müller)
wrote:

Helpful audience!

Today, I made my first spinn-casting with zinc.

It was just a first test shot to see what I can do wrong and what I did
already do wrong.
So the mold was just a plaster mold [1] and the zinc was just some scrap
zink sheet metal for roofing. That zinc proofed to be good enough and I
will use up all the rest before going to the costy zinc I ordered.
At least, the spin caster was a success. I had no other motor at hand,
so the disk is rotating with nearly 1400 RPM. Direct driven! The disk
has a diameter of 12". I thought more g-force = better surface.

334 G's!

On Sun, 21 Aug 2005 21:13:42 +0100, "Triker"
wrote:


"Don Foreman" wrote in message
.. .
On Sun, 21 Aug 2005 19:40:10 +0200, (Nick Müller)
wrote:

Helpful audience!

Today, I made my first spinn-casting with zinc.

It was just a first test shot to see what I can do wrong and what I did
already do wrong.
So the mold was just a plaster mold [1] and the zinc was just some scrap
zink sheet metal for roofing. That zinc proofed to be good enough and I
will use up all the rest before going to the costy zinc I ordered.
At least, the spin caster was a success. I had no other motor at hand,
so the disk is rotating with nearly 1400 RPM. Direct driven! The disk
has a diameter of 12". I thought more g-force = better surface.

334 G's!

How do you know that?

Google on centripetal acceleration. There are lots of sites. One is
http://www.ac.wwu.edu/~vawter/Physic...etalForce.html

You do need to keep track of your units. Then, 1 G = 32.2
ft/sec^2 or 9.807 m/sec^2.

Don Foreman wrote:

334 G's!

I did the math with 1000 RPM, and if I remember correctly, it was in the
ballpark of 5 g's. Did you forget to divide by 9.81? Oh, you did divide!
I'll recheck...

I did some research and found that with pressurized zinc casting they
use in the range of 80 atm (1200 PSI) and higher. Well, I will see if I
do have distortion. Steel molds are harder than rubber, I know. :-)
And, if I do get problems, I can move the part nearer to the center or
add a rheostat.

On the other hand, there was a link (IIRC your hint?) that showed a
commercial spinn caster that had 1000 RPM with a bigger disk (judging
from the photo) and rubber molds.


Nick

--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

On Mon, 22 Aug 2005 00:26:24 +0200, (Nick Müller)
wrote:

Don Foreman wrote:

334 G's!

I did the math with 1000 RPM, and if I remember correctly, it was in the
ballpark of 5 g's. Did you forget to divide by 9.81? Oh, you did divide!
I'll recheck...

I used first principles rather than a formula, and let MathCAD keep
track of the units because I'd surely screw it up using a calculator.

Using complex rotating vector notation we EE's are so fond of,
angular displacement is: theta = r * exp(j*w*t)
velocity is first time derivative, or: v=j*w*r*exp(j*w*t)
accel is second time derivative, or: : a=j^2*w^2*r*exp(j*w*t)

j^2 = -1 so a = -w^2 * r * exp(j*w*t)

The magnitude of exp(j*x) is 1 (Euler's theorem) so accel magnitude is
|a| = w^2 * r

w was 1400 * 2*pi radians/minute , r was 6 inches. MathCAD,
magically keeping track of units so much better than I do, found |a|
to be 3276 meters/sec^2, or 334 g.








I did some research and found that with pressurized zinc casting they
use in the range of 80 atm (1200 PSI) and higher. Well, I will see if I
do have distortion. Steel molds are harder than rubber, I know. :-)
And, if I do get problems, I can move the part nearer to the center or
add a rheostat.

On the other hand, there was a link (IIRC your hint?) that showed a
commercial spinn caster that had 1000 RPM with a bigger disk (judging
from the photo) and rubber molds.


Nick

Don Foreman wrote:

I used first principles rather than a formula, and let MathCAD keep
track of the units because I'd surely screw it up using a calculator.

I only used mumath, and that was long time ago. Also don't have that
Apple ][ + Z80 card anymore.
So I (have to) stay with formulas.

a = w^2 * r
w = 2 * pi * f

w = 2 * 3.14 * 1400 / 60
w = 146.5 [s^-1]

a = w^2 * r
a = 146.5^2 * 0.15
a = 3221 [m/s^2] = 328 G

Don't know how I screwed this up. Your result is right (difference due
to roundings). Sounds a bit frightening. 8-O.

OK, lets see what pressure I have:
Average a over the whole length of the zinc column is half the a at the
end.

p = F / A (pressure = force / area)
F = m * a (force = mass * accel.)
m = V * rho (mass = volume * spec. weight)
V = A * h (volume = area * height)

assembling...
p = m * a / A
p = V * rho * a / A
p = A * h * rho * a / A
p = h * rho * a

units:
m * kg * m^-3 * m * s^-2 = kg * m^-1 * s^-2 = N / m^2 = Pa
(with N = kg m s^-2)

with ...
rho(zinc) = 7 kg/dm^3 = 7000 kg/m^3
a = 3220 / 2 m/s^2 = 1610 m/s^2
h = 0.15 m

.... I get:
p = h * rho * a
p = 0.15 * 7000 * 1610
p = 1690500 [Pa] = 16.9 bar = 245 PSI

This doesn't sound too frightening.
Or did I screw this one up too?

OK, judging from the numbers, I have to watch out for distortion. Maybe
add a metal ring at the outside of the mold or something like this. I
also have to watch out how parts of the mold will bend and orient them
to the center to minimize bending.


Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

I used to do some pewter casting of jewelry in silicone. One of our artist
friends was a pewter caster he used a two part silicone that wasn't designed
as a casting silicone for some of his moulds. It was much cheaper than the
casting silicone. It probably didn't last as long but the price difference
was worth it. I don't remember the casting temperature of zinc but it might
work.
So look around for lower cost silicones that might work.
Karl

""Nick Müller"" wrote in message
...
Helpful audience!

Today, I made my first spinn-casting with zinc.

It was just a first test shot to see what I can do wrong and what I did
already do wrong.
So the mold was just a plaster mold [1] and the zinc was just some scrap
zink sheet metal for roofing. That zinc proofed to be good enough and I
will use up all the rest before going to the costy zinc I ordered.
At least, the spin caster was a success. I had no other motor at hand,
so the disk is rotating with nearly 1400 RPM. Direct driven! The disk
has a diameter of 12". I thought more g-force = better surface. It
seems, that that is right. No problems with vibration, as the frame
where all the suff sits in is quite heavy.
The first casting was a (partial) success, some detail very good, other
bad. But that only where I had bubbles in the plaster. Also a partial
failure, because I didn't melt enough zinc. I have to cut the inlet (in
the center of the disk, because to much is cooling down there and
remains there and doesn't flow down into the mold.

So I will make some mods, add a brake to stop the disk spinning and add
shielding and paint.
Will put pics and explanations to my HP. This time in English, so you
don't have to babelguess about what I have written in Kraut-Language.
Will take some days, but I will keep you informed.

Oh, the silicone is damned expensive! 1kg (2 pounds) about 50 EUR, that
are 60$. :-( OK, it withstands 500°C (930 F), zink poring temperature is
400°C (750F). But that stuff is to expensive for playing around.
I will think about to put the rubber in some supporting form to save
some rubber.


[1] that showed to be my newest invention "lost plaster casting".
Also, I baked it too long in the oven. It broke in 3 parts over
night. Some super glue fixed that.
I didn't get the castings out of the mold, so I broke it apart.
It was some wothless casting anyhow.

Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

Karl Vorwerk wrote:

One of our artist friends was a pewter caster he used a two part silicone
that wasn't designed as a casting silicone for some of his moulds.

pewter melts at 200°C to 250°C (390°F to 480°F), that's a big
difference. They do sell silicone for pewter casting that is about 25%
cheaper than the zinc stuff (no max. temp. indicated) But I will shop
around and see if I can get something cheaper from the manufacturer.


Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

I new there was a significant difference but was too lazy to look it up.
Hopefully you can find something that will do the job cheaper.
Karl

""Nick Müller"" wrote in message
...
Karl Vorwerk wrote:

One of our artist friends was a pewter caster he used a two part silicone
that wasn't designed as a casting silicone for some of his moulds.

pewter melts at 200°C to 250°C (390°F to 480°F), that's a big
difference. They do sell silicone for pewter casting that is about 25%
cheaper than the zinc stuff (no max. temp. indicated) But I will shop
around and see if I can get something cheaper from the manufacturer.


Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...

On Mon, 22 Aug 2005 10:32:53 +0200, (Nick Müller)
wrote:



with ...
rho(zinc) = 7 kg/dm^3 = 7000 kg/m^3
a = 3220 / 2 m/s^2 = 1610 m/s^2
h = 0.15 m

... I get:
p = h * rho * a
p = 0.15 * 7000 * 1610
p = 1690500 [Pa] = 16.9 bar = 245 PSI

This doesn't sound too frightening.
Or did I screw this one up too?

MathCAD agrees.

Don Foreman wrote:

MathCAD agrees.

Thanks for X-checking!

Just doing the paint job, but it takes so long to dry (two sides, two
times).
Guess that there will be photos tomorow...


Nick
--
Motormodelle / Engine Models:
http://www.motor-manufaktur.de
Ellwe 2FB * VTM 87 * DLM-S3a * cubic
more to come ...