[Zumba]

As to the the thermal issue, I think someone got it wrong. Hopefully it wasn't the Anocast documents.

Thermal expansion of E/Q: 9.4 x 10^-6 in/in/°F
Thermal expansion of steel: 6.4 x 10^-6 in/in/°F

Steel expands LESS than E/Q.

[romihs]

Pupa,

Earlier on in this thread it was discussed that epoxy is the week link in the mix, so if you want to benefit from the good properties of quartz or granite, you have to keep the epoxy quantity to a limit.

Also, this link was posted some time ago, in this thread, stating that it is theoretically possible to fill 95% of a defined volume using different sized particles and ratios.
This article does refer to spheres, but I believe that it is possible to achieve similar results using irregularly shaped particles.

My goal is to try and get a mix working well with an epoxy content, by weight, of between 5% and 10%. I plan to go the same route that the German guys went here (you will need to register to view it).

Hoe gaan dit in Suid Afrika?

Regards

Sandi

[LeeWay]

So yes, if you're not going to fill a steel tube, you should probably add rebar. One benefit of rebar is that it's so damn cheap, but I'd be cautious as to the mystery metals that might be in there. Perhaps it may be wiser to use 1018 rounds? Even those are pretty cheap from Enco with free shipping.

Part of the strength you get from rebar is in its gription. It doesn't slip easily through. Any smooth rod would not do as well. Threaded rod might work okay. Acme would be better, but rebar is hard to beat for its purpose and cost. You can always step it up in size if you are worried about its strength. Then again there are ratio's for that too. I do know that 1" rebar is some very strong stuff when surrounded by concrete.

[pupa]

Pupa,

Earlier on in this thread it was discussed that epoxy is the week link in the mix, so if you want to benefit from the good properties of quartz or granite, you have to keep the epoxy quantity to a limit.

Also, this link was posted some time ago, in this thread, stating that it is theoretically possible to fill 95% of a defined volume using different sized particles and ratios.
This article does refer to spheres, but I believe that it is possible to achieve similar results using irregularly shaped particles.

My goal is to try and get a mix working well with an epoxy content, by weight, of between 5% and 10%. I plan to go the same route that the German guys went here (you will need to register to view it).

Hoe gaan dit in Suid Afrika?

Regards

Sandi

Baie goed, dankie. Only crime to high.

My point exactly. I think the drive should be ultimately to go as low as possible with epoxy and get the help of the epoxy makers to get a solution to the slump of the mix. We have time so a low slump mix that could give up the excess fluids during curing with minimal shrinkage is the key. The fact that the aggregate cannot shrink if well distributed and compacted I think it is not a issue as the final self leveling surface topping will compensate for any shrink to get to the final level accuracy.

[walter]

So yes, if you're not going to fill a steel tube, you should probably add rebar. One benefit of rebar is that it's so damn cheap..

Check out the rebar "cage" in post #404 on page 34.

I thought the 8020 idea was pretty good too.. We've got 8020, steel tubing, I beams, C channels.. You name it.

I should just go buy the 8' of C channel and encapsulate it with E/Q. That would be a good test..

[ericdwilso]

You can get pneumatic vibrators on the 300+ Hz range... McMaster Carr sells them... look-up "Air-Powered Rotary Ball Vibrators". They have some higher performance versions that go up to about 700Hz.

[lgalla]

Which is better?A5to10% epoxy ratio being rather dry and full of air bubbles or 10 to 20% epoxy with the possibility of using a concrete vibrator.With the higher ratio the vibrating will compact the mix and excessive resin will pool on top.Just sprinkle some sand and small aggregates to suck up the excess.With this method I will bet the aggregates will pack as close as they can.Another thought,the pooled resin could be your surface plate if desired.
If filling a structural tube is re-bar necessary?The steel is for strength, the E/G for damping.Re-baring any E/G mix may bring back resonance????
Just my .05 pense
Larry

[LeeWay]

Rebar would still add strength to it.
It would help to spread any load on the channel or extrusion over a wider area than just a filled shell would.
Think of a span or a concrete floor in a high rise. They pour these spans on top of steel floor sometimes, but without rebar, it still couldn't carry much of a load.
Fill two small channels. One with rebar, the other without. You can set it up in a shop press and the one without will fail before the reinforced one will, even though they both have a steel or aluminum shell.
The bar is helping with the distribution of stresses and spreading that stress out along the rebar.
Smooth bar would fail also before rebar would because it can't grip.
Smooth bar is used sometimes though as long as it has a hook on the end. That keeps it from slipping through just as the ribs an rebar does.

Not sure about the resonance. Rebar doesn't have to be used to gain strength either. Sometimes fiberglass is added for this purpose. Wire mesh especially in smaller pours may be all that is needed to increase the concrete's strength. Either of these would be less likely to induce resonance.

[lgalla]

No doubt rebar will add strength,But i am thinking of a self supporting steel structure with E/G to damp.None of the E/G machine builders use rebar or steel re inforcements.There must be a good reason against its use.
Larry

[lgalla]

Walter always gives strength to E/G issues.We must thank him for the reviews and all the time spent as the unofficial moderator.:cheers:
As the Michal Jackson song says"Heat it,heat it or is that beat it,beat it".Either way Mike is right.Heat it heat it, to reduce viscosity and beat it beat it to release entrapped air.
Perhaps the use of audio transducers will compact our mixes.Place your molds on you Cervin Vegas,add Thriller and compaction and degassing may happen.Martin beat the pun.:stickpoke
Larry

[Stepper Monkey]

Which is better?A5to10% epoxy ratio being rather dry and full of air bubbles or 10 to 20% epoxy with the possibility of using a concrete vibrator.With the higher ratio the vibrating will compact the mix and excessive resin will pool on top.

In using epoxies for aerospace they get the best of both worlds - excess epoxy is used during the initial stage, and then removed from the matrix during the vacuum compaction stage.

Vacuum compaction solves all of your concerns at once; It allows vibration to be used, causes de-bubbling, an extremely large force for physical compaction, allows the advantages of a >10% epoxy ratio during mixing for optimal wetting and cavity removal, allows a <5% final epoxy ratio for optimal strength, positive removal of excess, and smooth surfaces on ALL sides.

easy mixing/pouring
full wetting and de-bubbling
no inclusions
physical compaction
optimal strength
no pooling
all sides surfaced

All the extra equipment needed to do this in one step?

Vinyl sheet for vacuum bag
pvc pipe for the drool can

Other than it can be messy the first time you try it, what else do you need or want? It's not only cheap and easy, it is actually the pro way to do it. It may sound hokey, but it is still the way F1 cars and spaceships get built.

I don't think this needs to be as complicated as we are making it. Most are looking at large-scale mass-manufacturing techniques which are out of context here, but in looking at processes for this project, we might be better served looking at aerospace, racing, and laboratory practices.

[martinw]

In using epoxies for aerospace they get the best of both worlds - excess epoxy is used during the initial stage, and then removed from the matrix during the vacuum compaction stage......

All the extra equipment needed to do this in one step?

Vinyl sheet for vacuum bag
pvc pipe for the drool can

.

Dear Stepper Monkey,

That's a really useful post. Thank-you.

The one thing I don't understand is how you ensure that the stuff you remove is all epoxy, and not a mix of epoxy and aggregates. Is the excess epoxy allowed to "pool" at the top before you apply the vacuum?

BTW, "drool can"???? Crazy name!

Best wishes

Martin

[brunog]

Dear Stepper Monkey,

That's a really useful post. Thank-you.

The one thing I don't understand is how you ensure that the stuff you remove is all epoxy, and not a mix of epoxy and aggregates. Is the excess epoxy allowed to "pool" at the top before you apply the vacuum?

BTW, "drool can"???? Crazy name!

Best wishes

Martin

Martin,
slow curing epoxy will have time to pool at the top and "drool", however I prefer Larry's solution of adding sand to absorb excess epoxy.

best regards

Bruno

[Stepper Monkey]

Dear Stepper Monkey,

That's a really useful post. Thank-you.

The one thing I don't understand is how you ensure that the stuff you remove is all epoxy, and not a mix of epoxy and aggregates. Is the excess epoxy allowed to "pool" at the top before you apply the vacuum?

BTW, "drool can"???? Crazy name!

Best wishes

Martin

It doesn't pool, it is actively displaced. You use a relatively close-fitting "pusher" block on top of the aggregate, and small holes in the ends of the form itself. You essentially enclose the whole thing in a bag. When you draw vacuum on the bag, unlike in a rigid chamber you get two things to happen (other than not needing a giant rigid chamber!) - first the aggregate is compacted evenly at almost 1 bar, or almost a ton a square foot, by the pressure differential. Secondly, this squeezes out all of the excess epoxy rather the same as if the block was being pushed down by a hydraulic press, which can also be used for additional longer-term clamping if needed so you can turn the pump off and not lose holding force.

The excess epoxy needs to go somewhere, so to keep it from getting into your vacuum pump you use a "drool can", essentially a short chunk of PVC pipe with two end caps and hose fittings. The vacuum pump hose attaches to a top-mounted hose barb, the hoses from the form to side-mounted barbs.
This allows any excess liquid to pool in the bottom of the can while vacuum draws out through the top, this saving your pump and all but the short chunks of hose to the form.

This is how even thin, curvy items get made as well as thick ones - the bag then just goes around two blocks with mating shapes with the epoxy filled matrix in between. The vacuum "clamps" the two blocks together and squeezes out excess epoxy.
This makes for thinner, lighter, stronger, more consistent thickness race car and aircraft panels than old-fashioned hand layment.

[lgalla]

Hi Stepper.
Do you need a perforated release film and bleeder material?This is necessary making aircraft parts.I assume in our appalication thing are simplified?
I may be wrong on this but I thought the highest glass fiber/ resin ratio was 60/40.
Larry

[LeeWay]

If you use a vacuum bag, you need to take care what type plastic or vinyl the bag is. The Epoxy will heat up pretty good.
For smaller pours, they have plastic they use in ovens that would work.

The pour could also be done similar to molding something. With sprue's. Granted there would be some cleanup, but if poured from the bottom, the top should have a pristine shiny surface when complete. Most all the air bubbles and excess epoxy would wind up in the sprue's I would think. Some of these same issues are conquered when thermo forming plastics. They generally do it in a mold under pressure with irregularities in the pour being at the pour point.

[martinw]

Dear Stepper Monkey,

Thanks for that.

I'm being stupid, but I still do not understand why the "drool" is epoxy and not a mix of epoxy and aggregate.

If you are laying up carbon fibre and epoxy, or glassfibre and polyester resin,
I can see how (if you compact the mix) you are effectively "wringing" a wet sponge. In other words, if the fibres are all joined up, they will not migrate with the resin. With E/G, the aggregates, especially the smaller ones, would be mixed up with the epoxy being squeezed out would'nt they?

Sorry if I'm being dumb.

Best wishes

Martin

[lgalla]

Hay Martin.

Sorry if I'm being dumb.

Best wishes

Martin
I join your club, also as I don't understand either.Maybe we are missing something and are dumb.Possibly the aggregates are to heavy for the vacuum to suck them out?More info on the process is necessary for the slow guys.
Thanks
Larry

[ger21]

If you use a vacuum bag, you need to take care what type plastic or vinyl the bag is. The Epoxy will heat up pretty good.

Someone who made samples earlier in the thread said it didn't get hot, just warm (Zumba?). If it was just epoxy, then yes, it would get very hot, but it's only 10-20% epoxy, so the aggregates keep it cooler.

[fyffe555]

Martin, don't worry , you're just missing a piece of the puzzle, or in this case the vacuum bag.

Vacuum forming wet layups usually use a peel ply and bleeder ply inside the bag incontact with the layup. The peel ply, is usually something like polyester that the epoxy won't stick to that is perforated to allow epoxy through but not the layup. The bleeder ply is the transport to move the excess epoxy thats pushed through the peel ply by the vacuum (yup thats right ). Excess epoxy is removed without passing the layup or in this case the aggregate.

For the last decade or two race cars and aerospace have used prepreg's of glass, carbon or other layups. These are dry laid in the form in accordance to schedule and vacuumed dry. The autoclave then heats the layup releasing and mixing the resin and hardner in situ and assuring perfect layup resin contents. Mike F. who posts here on the Zone knows way more about prepregs than I can remember.