What to use to make a mold?

I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

On Mar 22, 5:23*pm, AK wrote:
I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if *mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

High temp RTV rubber can withstand up to 1000deg F. It's not cheap
stuff, but it will work quite nicely...

If you use gypsum or plaster products, just make two molds, (after
your first mold is made make a male model from it to cast new females
off of...) as it would be difficult to get out your lead w/out
breaking it, assuming it survives the thermal shock of the pour. Heat
up your plaster mold in an oven to within 100deg of your pour first to
avoid that pitfall, but you must very slowly heat the plaster up since
it may have micro water in pores that will superheat and make it crack
as the steam exits. Take at least 4 hrs to bring your mold up to temp
(after 24 hrs minimum cure) , ramping up 100deg/hr until at
400ish... plaster is cheap and easy to work with, so it will
probably be most practical. note-plaster expands 1-3% when cured, so
take this into account for allowances if you have critical tolerances.

If you need precision plaster/gypsum there is a product called
Ultracal (in 30 or 60 minute cure versions) made by US gypsum that
does not expand or shrink. it's cheap enough to use too at like
$30/50# . It feels and mixes just like plaster of paris but is
gypsum based so it cures like cement. Phenomenal product actually...

There's always the option to just trap your lead shot in epoxy
thickened with cabosil or microballoons etc, which seems much easier
but will obviously not provide the same density as a solid block...

-Paul

sisu1a wrote:

There's always the option to just trap your lead shot in epoxy
thickened with cabosil or microballoons etc, which seems much easier
but will obviously not provide the same density as a solid block...

It does avoid the breathing of lead vapors, something even a pilot
should avoid.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

For a single pour mold, you can even carve it out of wood, like a 2 by 4.
It will smoke, burn the wood (you can blow out the fire), but it will hold
up for a single lead weight making. How heavy a weight are you trying to
make? And about how big?

You could then make the glass cup from the lead part, or even from a block
of foam that you cut to about the same shape.

A friend once got in trouble with his wife by using one of her frying pans
to make lead disks for putting in the seat pan of our old club two place!

One thing to watch out for (may not be this way with the gypsm stuff that
Paul mentioned), but anything that used water in its making, can trap
water inside. Put molten lead in it, and it can be a bad thing.

Happy slug making!

Steve Leonard

At 02:30 23 March 2009, Steve Leonard wrote:
For a single pour mold, you can even carve it out of wood, like a 2 by 4.

It will smoke, burn the wood (you can blow out the fire), but it will
hold
up for a single lead weight making. How heavy a weight are you trying
to
make? And about how big?

You could then make the glass cup from the lead part, or even from a
block
of foam that you cut to about the same shape.

A friend once got in trouble with his wife by using one of her frying
pans
to make lead disks for putting in the seat pan of our old club two
place!

One thing to watch out for (may not be this way with the gypsm stuff
that
Paul mentioned), but anything that used water in its making, can trap
water inside. Put molten lead in it, and it can be a bad thing.

Happy slug making!

Steve Leonard
Lead has a melting temp of about 500 degrees C commercial moulds for
casting batches are usually cast iron as are some pans.
If you make a mould using sheet steel this would then encapsulate the lead
after pouring and prevent the soft lead from deforming under pressure from
the fastening bolts.

On Mar 22, 5:23*pm, AK wrote:
I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if *mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

sand

On Mar 23, 8:28*am, wrote:
On Mar 22, 5:23*pm, AK wrote:

I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if *mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

sand

http://en.wikipedia.org/wiki/Sand_casting not quite that simple in
practice and would also req the purchasing of some specific setup
materials which are not found at Home Depot etc...

You should go the wood or plaster route.Wood is dead simple if your
shape is not to complex. I saw that Steve quite rightly mention of
worry of plaster and residual water/steam being an issue... hence
the very specific directions I layed out for preheating/drying your
plaster mold BEFORE lead is poured in. If it survives the 4 hr
incremental ramp up to 400deg, it will not break from the pour since
all the water will have been evacuated by then. If in doubt, leave it
in the oven for an extra hr or 2 at 400ish...

I dabble in investment casting, and the same methodology applies for
pouring 1700-2100 deg metal (bronze, slver, gold, etc) into a plaster
mold, except the heatup/dryout process brings it up to 1000deg over a
5, 7, or 12 hour ramp up (usually spending some an hr or 2 at 1300deg
to vaporize out the wax remnants before ramping back down to
1000ish).

-Paul

On Mar 23, 12:12*pm, sisu1a wrote:
On Mar 23, 8:28*am, wrote:

On Mar 22, 5:23*pm, AK wrote:

I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if *mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

sand

http://en.wikipedia.org/wiki/Sand_casting* not quite that simple in
practice and would also req the purchasing of some specific setup
materials which are not found at Home Depot etc...

You should go the wood or plaster route.Wood is dead simple if your
shape is not to complex. * I saw that Steve quite rightly mention of
worry of plaster and residual water/steam being an issue... * *hence
the very specific directions I layed out for preheating/drying your
plaster mold BEFORE lead is poured in. If it survives the 4 hr
incremental ramp up to 400deg, it will not break from the pour since
all the water will have been evacuated by then. *If in doubt, leave it
in the oven for an extra hr or 2 at 400ish...

I dabble in investment casting, and the same methodology applies for
pouring 1700-2100 deg metal (bronze, slver, gold, etc) into a plaster
mold, except the heatup/dryout process brings it up to 1000deg over a
5, 7, or 12 hour ramp up (usually spending some an hr or 2 at 1300deg
to vaporize out the wax remnants before ramping back down to
1000ish).

-Paul

Thank you a lot to all who responded, especially to Paul for the
details he provided and Steve for the safety warning.
I was already aware of safety issue, but I appreciate you mentioned
it.

For safety in an accident I would use the lead pellets
and make a containter.

Plus you will be able to make adjustments to your weight if you use
pellets in a containter.

A big chunk of lead could become a very dangerous projectile in a hard
landing or crash.

Ray

On 23 Mar, 02:01, Eric Greenwell wrote:
sisu1a wrote:

It does avoid the breathing of lead vapors, something even a pilot
should avoid.

Is the sublimation rate of lead at room temperature significant?
Church roofs seem remarkably resistant to evaporation after hundreds
of years, as do the 120 year old lead water pipes in my house.

Ian