[jhudler]

I think an often overlooked problem is that if you vibrate the aggregate before the epoxy has been added, there is a strong tendency for the particles to "segregate". This will defeat the purpose of having the mixed sizes.
While I would like to have the epoxy "sneak" down amongst the aggregate, my brief experience with spinning a mix, where the G forces have reached about 50G so far, when I poured the epoxy into the middle and spun it up, it was very obvious that its viscosity still had a hard job getting it to replace the air heading for the spin axis of the tube.
Where I'd pre-mixed the E/G, the air was escaping through the mix as it was compacting. The G force being greatest at the outer surface was working to my advantage in this process.

John

John,

After working with vacuum and vibration, I think I may have another way for you to achieve your goal.
I take it you have the molds for the various items you want to cast, why not try what I'm doing with the test samples. I'm using a thick walled 4 inch PVC s schedule 40 (though I don't know what you lot call it over there) capping one end and putting a 1/2 inch sheet of lexan (polycarbonate) sealed with silicone on the other.
I'm mounting it with 3 rubber bushing about 2 inches long and 1 inch diameter, then attaching the whole thing to a motor with a rod attach to an offset cam then attached to the PVC pipe.
This way I can pull a full vacuum and vibrate the mix at the same time.

I was going to do this just for mixing E/G when Gordon Bennett! that's what greybeard needs! You can find this PVC pipe from sizes all the way up to 24 inches, thought not likely to find this size down at the local DIY.

Jack

[Eson]

jhudler

Wear gloves!
Anyway my idea sort of worked. I saw the aggregate 'bubbles' didnt mix well. Maybe if you can alter the vibration frequency you can crush the bubbles.

[jhudler]

jhudler

Wear gloves!
Anyway my idea sort of worked. I saw the aggregate 'bubbles' didnt mix well. Maybe if you can alter the vibration frequency you can crush the bubbles.

I've tried that (not on camera) it really didn't have much effect, the only effective means of removing air entrapment is vibration while under vacuum.

If you notice the epoxy never returned to its before vacuum level when I released the vacuum. This tells me air is still entrapped in the mix and when I vibrated it later, it reduced back some, and air bubles are still visible just under the surface.
What I believe is preventing it from deairing is the epoxy skinning over. Perhaps that's where BYK-A-525 comes into play.

The real test is doing both at the same time.

That's tomorrow!

Jack

[greybeard]

Segregation is a function of aggregate design. Without digging up the De Larrard book and looking stuff up, I'll say that the mixture with the #6 aluminum oxide was designed with the formula that minimizes segregation potential. I don't know how bad the segregation would be in an actual implementation but according to the theory, variations from the formula will only make segregation more likely for the given aggregate sizes.

greybeard might be right but it may also be a very small effect. Hard data is needed.

Regards all,

Cameron

Hi Cameron. I agree that the effect may be small, but if memory serves, all of de Larrard's work used a mixing method that involved subjecting the mix to a positive pressure while the particles were being vibrated. This ensured that each time a particle could move and fill a space it did(the vibration), but it couldn't move far(the pressure) so the initial mixing was retained.
If the system was vibrated without any pressure constraint, there is nothing to stop the particles moving in a random fashion, and this inevitably leads to segregation, with the smallest particles falling, and the largest rising.

Obviously we have the presence of the epoxy to complicate matters, which de L didn't, but I think it important to keep in our minds that the recipe and methodology will interact. We don't want to loose the gain that the recipe with the measured mixture brings, by a mixing/vibrating/compaction method that might(and I stress "might") counteract it.

Again, I think it important to keep in mind that the gains that we're looking at once we move beyond a two or three component mix, are going to be proportionally smaller, and the "Law of Diminishing Returns" will almost certainly kick in.
For those like myself who are working towards a wood router set up, a two or three component(+resin) may well prove to be more than adequate.
Those looking for a metal milling machine bed, where we're pushing de L's work onwards, will almost certainly need all the extras that this amazing thread can squeeze in.

Jack, thanks for your suggestion. In fact that is the sort of pipe that I'm using. However the mold designs are made to fit the pipe, and to be spun. Bear in mind that I am producing beams, not blocks, and the spinning methods that I'm developing are aimed at an alternative methodology.
I'm starting with the same de Larrard type recipe, but with a higher resin ratio, probably nearer 20%. By packing this down into a pipe and spinning it, and I'm looking at about 150G at the outer surface, I aim to get several benefits.
1. The outward force on all the particles will be the equivalent to de L's pressure component(see above).
2. My inadequate engineering will ensure that there will be a vibration component, possibly of frightening proportion.
3. As in 1 , the force on the aggregate/resin will push the air towards the centre, (my equivalent to vacuuming out the air) along with any excess resin that is sqeezed out by the aggregate particles being denser, thus bring the resin % content down at the surface.

I'm hoping this method will remove the need for any additives, and keep the recipe as simple as possible for anyone who would not be able to obtain them.

Regards to all,
John

[greybeard]

Cameron - what are you doing on line -you should be off taking your exams?

[jhudler]

If the system was vibrated without any pressure constraint, there is nothing to stop the particles moving in a random fashion, and this inevitably leads to segregation, with the smallest particles falling, and the largest rising.

In my testing I do not see any segregation at all. Let me scan in the cross sections of my 3 test samples and post them momentarily (err shortly).

Jack, thanks for your suggestion. In fact that is the sort of pipe that I'm using. However the mold designs are made to fit the pipe, and to be spun. Bear in mind that I am producing beams, not blocks, and the spinning methods that I'm developing are aimed at an alternative methodology.

I too am producing beams at the moment.

I do understand the desire to try alternate technologies however, you have only to purchase a vacuum pump (like those used by refrigerant techs) and supply a vibration source to start manufacturing.

What size are the beams you are producing?

Jack

[jhudler]

Ok here are the pictures from the top are sample 1,2 and 3.
1200 DPI Color in PNG. (I use PNG because it's lossless)
White paint was used to highlight voids.

Too big to show in an image link:

http://www.hudler.org/pub/eg/Three Samples edge.png

The large black chucks are the quartz aggregate.

Notice the random distribution.

Jack

[greybeard]

Hi Jack. As a matter of fact I've got three vac pumps including a two stage Edwards, but as I said, I'm more interested in spinning at this moment. The beams will be from 2x1 to 4x2 inches and up to 36 inches long.
Were the three samples you've posted the ones that you gave the recipe for a couple of days back, and were they 1,2, and 3, top to bottom ?
Regards
John

[jhudler]

Were the three samples you've posted the ones that you gave the recipe for a couple of days back, and were they 1,2, and 3, top to bottom ?
Regards
John

Yes they were.

Ahh I just sussed it; you want to play!

I was looking at this to save you the effort and complication of spinning.

Jack

[greybeard]

Yes they were.

Ahh I just sussed it; you want to play!

Jack

That's my cover blown then.

[svenakela]

Mixing under vacuum can definitely improve the quality but I would never cast under vacuum. That's not how pro's are doing it http://www.cnczone.com/forums/attach...2&d=1186331184
I'd like to see some vacuum bagging tests though.

Oh, I missed to comment on this one. Casting in vacuum is very good. When I was working with plastics all day long I was mixing AND casting in vacuum. The company has a uge vacuum chamber with an automatic mixer that poors the resing down into the mould. I made extremely nice airless castings in that chamber.
But I think your casting is too big to fit in a chamber, it must be pretty big. When mixing in vacuum you have to calculate that the resin raises about 300-400 % in the cup when the air bubbles expands. It requires a lot of space...
But if you can get a chamber big enough, air evacuation with vacuum is really good.

I think your work is excellent, Walter!

Regards,
Sven

[jhudler]

Ok someone checkout my thinking here:
I made a list seives to grade local aggregate to the agsco sizes in the current formula.

#10 - anything that doesn't pass is junk
#30 - anything not passing for #4 (should be 25 only I don't have a 30)
#80 - anything not passing for #2
#270 - anything not passing for #2/0
PAN for everything that passes #270, we don't use.

Here's the PDF that shows Agsco sizing.
http://agsco.thomasnet.com/Asset/Par...rain-Sizes.pdf

Can add more sieves if we create/have a more precise formula.

Thanks,
Jack

[romihs]

Jack,

Great results!! Thanks!

I was wondering where you get sieves from?
I was thinking of doing the same, but gave up on the idea when I could not find a source for sieves....

Thanks

Sandi

[jhudler]

I found all I needed on eBay.
Google sieves.
http://www.humboldtmfg.com/sieves.php
http://www.benmeadows.com
www.ascscientific.com
tons more from the looks of it... however Slovenia? Don't have a clue.

Jack

[walter]

When mixing in vacuum you have to calculate that the resin raises about 300-400 % in the cup when the air bubbles expands. It requires a lot of space...
But if you can get a chamber big enough, air evacuation with vacuum is really good.

Thanks Sven, I appreciate the info!

[lgalla]

Walter& Sven I had the same restrictions or limits to the 300 to 400% rise,requiring Only de gassing say 1gal in a 5 gal pot.Jacks video shows the rise is minimal due to the low resin content and the heavy weight of the fillers.
Larry

[jhudler]

When mixing in vacuum you have to calculate that the resin raises about 300-400 % in the cup when the air bubbles expands. It requires a lot of space...
But if you can get a chamber big enough, air evacuation with vacuum is really good.

Sven,
What you said is valid if you're not vibrating in a vacuum. Otherwise when you see it start to rise, slow or stop the vacuum and let the vibrations and vacuum liberate the entrapped air until it falls back. Then resume the vacuum and continue to vibrate until air bubbles are no longer seen on the skin.

There's no need to pull a full vacuum all at once.

Jack

[lgalla]

Woops!Jack,didn't know you were backing off the vacuum as it rose.The vacuum bell jar is a good idea as you can monitor the rise and back off as required. Larry

[jhudler]

Larry, in the video and the 3 samples I didn't. But what I saw suggested this. During some testing today I proved it. So you would not need extra volume in the mold to capture expansion, but you will need release the vacuum to add more mix to the mold as it deairs, and then pull the vacuum again to finish.

Actually if you pull the vacuum slowly while vibrating I doubt you'd ever see it rise.

Jack

Jack

[jhudler]

Oh tested mixing with the System 2000 Epoxy Laminating Resin from
http://www.fibreglast.com/documents/345.pdf

I have the 2060 version at 950 Cps (37-127 is 600) and could not tell the difference in mixing between the two.
The 2060 shows a tensile strength of 45,170 psi while EPOTUF 37-127 shows 10,000.

Should be an interesting set of D-790 tests.

Jack

BTW I remember someone buying the thicker stuff from US Composites.
If your not using it.... could have it... or a sample of it?