tom jelly wrote:
Funny thing about forming tubes- I saw what nasa did- they used SILICONE
RUBBER of all things inside a 2 piece mold- 2 half round aluminum parts and
a silicone male cylinder core. unlimited pressure available as we all know
now....pushing on the ends of the silicone pushed it out, compressing the
matrix in the mold.
Tom>
That is good to know. The florescent light bulb trick is only good for one
or two
sizes but that trick will work for all sizes. Furthermore you get a good
finish
on the outside of the tube.
Method: Get a piece of thick wall aluminum tube.
Slice it in half on the band saw. Weld bar stock on all four edges.
Match drill holes in the bar stock. Fill it with RTV. Now that can get
expensive. I guess you could use an RTV coated smaller inner tube.
Viola you have a male and female composite tube mold.
Sounds like this trick will
work for all sorts of shapes for composite parts. The red silicone will
take the cure oven temps as well. Perhaps this is the trick they use
for co curing wing ribs into wing skins. I have been wondering how they
do that for the last ten or so years.
A vacuum bag would apply pressure to both male and female mold.
Now I am getting ideas for a molded composite rotary intake manifold
laid up on 1.5 inch diameter RTV rubber rods and a cast concrete
female mold. The RTV rods could have copper wire inside them to
hold the rough curve while the composite was hand laid before they
went into the female mold to be final cured. Or the RTV rods bent into
shape can be used to cast the concrete female molds. There are variations
on this theme where the female concrete molds can be used later to cast RTV
male core molds. This looks like a good low initial investment
business for someone to get into as the concrete female molds and maybe
the RTV male molds may be used over and over again.
Do we need a sketch or does everybody follow this?
We spent a lot of time a couple of years ago trying to figure
out a quick way of making composite intake manifolds. Hand carved
blue foam male molds were determined to be about the best way then.
The blue foam must be removed chunk by chunk from inside the cured tube.
I think this idea beats that. Here is a picture of one that Perry made
with blue foam male molds. That's Perry's son.
I looked into having a cast aluminum intake manifold pattern made
and the cost was about $5000.
Paul Lamar
Be VERY careful or you'll break your mold. I analyzed an attempt at
this at work. The upper RTV and lower solid (?) mold pieces filled a
~12" diam 2" wall steel tube about 18" long. The lower mold insert was
fixed, the RTV upper a slip fit. A blob of a difficult to mold material
about like modeling clay was dropped in, the RTV upper insert added
and the 2" thick steel lid bolted on with 1" studs on about 3" centers.
They popped it into an oven at something like 350F for a few hours.
The plan was to form and cure the part with inexpensive tooling since
it was a low volume item.
I wish I had kept the picture they brought me. This "can" had a 45 slope
about 2" deep (max) of grey "sand" around the base. The "sand" was
cured RTV that had extruded itself out between the lid and the sides,
shearing itself into granules, and plastically deforming the lid about 1/16"
between studs and dishing it slightly,too.
Kid's don't try this at home, leave it to the professionals. Well,
we ARE professionals and we screwed it up. ;-) They wanted an
explanation of what happened, so I 'splained it to them.
Ya'll be careful out there. The laws of physics will be strictly enforced.
Bill Freeman
Long EZ builder & pilot
BSME, MSME
EAA Technical Counselor
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