[jhudler]

Hi gang!

Silicone?!?!? that's no ordinary rabbit, that's the most cruel, vile and vicious rodent you ever set eyes on! (oops deprecated into Monty Python again... hmm could be defecated).
Just a funny reminder to use the silicone outside! Especially if you intend to paint or stain anything in the room where its use was originally intended.

Clean the part and your hands using a liquid dish washing soap like DAWN.
And leave that cruel, vile and vicious can of silicone far away from your work area.

Funnier still want to know how to screw up a paint and body shop? Casually stroll into the paint prep area and spray a can of this stuff for a few seconds .

[jhudler]

Oh one other thing. Vibrate the bucket of EG before you pour it in to reduce entraped air; then pour into the mold. Then give it a few taps with the shaker or a very low setting while you pour.

[veteq]

Hee Jhudler,

Silicones aren`t you`re best friends.....?

But really, is it that bad? Heard painting afterwarts is a pain... but does it the job of releasing the mould, thats the most important thing.

[jhudler]

Hee Jhudler,

Silicones area`t you`re best friends.....?

But really, is it that bad? Heard painting afterward is a pain... but does it the job of releasing the mould, thats the most important thing.

Of course Silicone is your friend when used as intended. Just be aware of where your use it and clean up.

For example my workshop is my wood shop. Aerosolized Silicone release agent will contaminate the surface of everything with tiny droplets of Silicone. Who's distribution is probably based on some inverse-square-law . Think of it as brushing the hair of that most cruel, vile and vicious hare; goes everywhere. (hmm might crunch that down into a haiku)

[lgalla]

I refinished some pro speaker cabinets with a 6 second gell polyurea bedliner.The coating fell off.The guy had used Armour all every week.Hours of sanding with 40 grit cured the problem.Our shop named the product...SillyCone and StupidCone.
If you never plan on secondary bonding or painting StupidCone release is fine.Larry

[jhudler]

I forgot all about the most vile and vicious Armour All death spray! The stuff is banned from my household.

[veteq]

Thanks guys, think i encounterd a problem in my design....
Igalla, you said bonding...i want to glue some insert for the rails in my EG with Moglice.
So stupidcone isn`t the product for that part...

Hmmm...didn`t thought off that..

[ckelloug]

Hi Roy,

There are zillions of types of commercially available release agents. See this one for example which says that it can be removed for painting or secondary bonding operations:
http://www.mann-release.com/erelese3.htm

Out of curiosity however, why aren't you embedding metallic parts for some of this?

Regards,

Cameron

[veteq]

Hee Cameron,

If i pour them in the mould in 1 setup, my moluld has to be very precise,
in my way i use a precision jig, easier to make...

Another question about the silicone:
If i grind the insert holes after removing the mould, then the silicon is gone right?
Like really hard grinding etc, like taking 0,5mm away?

[lgalla]

Sanding or grinding does not remove SillyCone 100%.SillyCone is round slippery balls,which tend to just roll under the sandpaper.As Cameron says there is zillions of paintable release agents out there.An old fashion release agent is PVA or polyvinyl alcohol.Trade name is Partall.It is used over wax based agents to ensure an easy release.It dissolves readily with water.
http://www.rexco-usa.com/part.htm

[Steven.ji]

Hee Cameron,

If i pour them in the mould in 1 setup, my moluld has to be very precise,
in my way i use a precision jig, easier to make...

Another question about the silicone:
If i grind the insert holes after removing the mould, then the silicon is gone right?
Like really hard grinding etc, like taking 0,5mm away?

it's not necessary to make a very precise mould. You can cast steel bar in polymer concrete, then drill the hole on the steel bar.

Steven

[Steven.ji]

Sanding or grinding does not remove SillyCone 100%.SillyCone is round slippery balls,which tend to just roll under the sandpaper.As Cameron says there is zillions of paintable release agents out there.An old fashion release agent is PVA or polyvinyl alcohol.Trade name is Partall.It is used over wax based agents to ensure an easy release.It dissolves readily with water.
http://www.rexco-usa.com/part.htm

Hi

did you recieve my e-mail?

Steven

[Steven.ji]

Hey Cameron,

Nice to see you got results with your nice lab-setup. cool.

Could you tell a bit more about the process off demoulding, did you had some trouble with it? Since the mould is vibrated and maybe the release agent gets broken? What did you used for the release agent.

For my own machine i`m making some progress to, i got a wooden mould cnc machined and i have to put it together the next few weeks. Then i can take the mould with me to Germany to a big EG manufacterer, here i cann use there mixture and vibrating table etc, they are going to help, so thats pretty cool for me...

Kind regards.

Roy

PVA release agent is available

[Palms]

We use polymer granite for our laser base because of its vibration dampening, temperature has no effect on it, sets up in a day or so, repeatability, non-magnetic, solid, acid spill has no effect and no rust. And, it needs no special foundation like cast/metal laser frames. PRIMA Lasers.

Sam Dyke
847-452-1721

[RomanLini]

Do you manufacture your own polymer granite bases? If it is not violating any trade secrets, could you share any info on your material or casting process? Thanks.

[osiervt]

I did a few runs this afternoon. Cameron was kind enough to run my aggergates through his simulator. Most of my aggeragrates are small, all of them under 2 mm. After mixing in the epoxy it turned into a paste of sorts. Not something that will flow into fine details of an elaborate mold, but would compact in well enough. I had extra epoxy mixed up at the end so I did to more runs with the same small agregrate mix but with granite chunks mixed in to increase the volumn a bit.

I've attached a few pics, including my sorry excuse for a vibration table. It work well to get the bubbles out of the epoxy but there was no point to but the mix back on the table as it was so thick.

[jhudler]

Not something that will flow into fine details of an elaborate mold, but would compact in well enough.

That looks like an almost perfect mix but a bit runny. I would use less epoxy on the next run.
As for fine details; trust me it will flow when vibrated just like liquifaction during an earthquake.

One other thing. Clamp your mold to the vibration table (board).

[ckelloug]

In a discussion with osievrt, he made a good point about what happens when the particles and the epoxy mix:

I may looking at this wrong but even with an excess amount of epoxy the packing model should still be relevant. With an excess amount of epoxy around the particles I would think that having the right amounts of each size so everything fits together right would matter. The only difference between the 'perfect' amount of epoxy and and excess amount would be the space between the particles, no?
I am thinking of it in this way a container full of basket balls, tennis balls, and golf balls. If you dump it in a vat of water (simulates a little epoxy) and shake it, it will settle better than if you dump it in a vat of yogurt(simulates lots of epoxy). However even the later will be better than container of only basket balls in any amount or type of liquid.

Your intuition is very good I believe. I think the water vs. yogurt analogy is more valid for viscosity of epoxy than for quantity of epoxy although it is somewhat apt either way. The question that needs to be answered is what actually happens, and I don't have a satisfactory answer.

I've been using a model in my head where the particles separate to the maximum extent possible given the volume of epoxy and particles in the container. The more epoxy there is in that model, the farther the particles can move apart in the mixture. My model is definitely oversimplified and what other problems it has remain to be seen.

With an excess of a hypothetical near-zero viscosity ideal fluid with no surface tension, you can mix up the particles to any desired extent and the difference in density will cause the particles to settle to the bottom at equilibrium packing themselves according to their size distribution. You end up with particles on the bottom and liquid on the top with a definite separation as far as I can tell. The viscosity and surface tension of the the ideal fluid are not likely great enough to alter the achievable packing density much via forcing the particles apart: thus, I think the ideal liquid's main effect is to act as a lubricant.

Replace the ideal fluid with honey, yogurt, (or epoxy) and you have a different case. These fluids have a high viscosity so an external force is required to get particles to move in the fluid. Gravity might not be enough for the particles to settle in any reasonable amount of time.

I've seen in the lab with small particles and medium viscosity epoxy that a combination of surface tension and viscosity causes particles to group together in blobs as the epoxy is mixed with the particles.

There is almost certainly an epoxy viscous enough that large particles could be suspended in it such that the volume of the particles but not the shapes was the determining factor in the density of the solid when the epoxy hardened. If you have that much epoxy such that the particles are not in intimate contact, you have a suspension, not a packing and the de Larrard packing model doesn't directly apply.

We know from our thought experiment with an ideal fluid that given enough epoxy, at least some particles will settle out. We know from measured packing densities that there is some minimum quantity of epoxy required to fill the voids in a given aggregate mixture. Of course, what we really need to know is what happens with quantities of epoxy between enough for particles to settle out and not enough to fill the voids. Like in most of physical science, of course the target range is the one where the behavior is difficult to understand.

I contend that when you have more epoxy than is required to fill the voids in the aggregate that you get a suspension and for this excess epoxy the modulus of the resulting mixture suffers. On the other hand, one does need enough epoxy so that all the surfaces of all the particles stick together and this is probably a slightly greater quantity than merely filling the voids.

If the amount to fill the voids and the amount to wet all particles sufficiently are similar, then the model will help design a good mixture. If they're too far apart, I think you end up with a suspension containing relatively large regions of pure epoxy.

I don't know if anybody is still reading this thread but a good discussion of what happens when there is more epoxy than required to fill the voids might be valuable.

Regards all,

Cameron

[jhudler]

I think the water vs. yogurt analogy is more valid for viscosity of epoxy than for quantity of epoxy...

Personally I like the marange model... stiff peaks! (chair)
You know air bubbles are the aggragate... well maybe it not such a good analogy... sure taste good though... hmm Lemon Marange pie. Off to the kitchen!

-Jack

[rowbare]

Cameron,

With regards to using an excess of epoxy, if the volume of the aggregates is such that they fill the mould, shouldn't it be the case that the excess epoxy will simply spill over or rise to the top where it can be skimmed while an ideal amount of epoxy will remain to fill the voids?

bob