[greybeard]

Walter - what's your current thinking about the maximum grain size you will use in your casting experiments ?

I'm getting the idea that the mix recipe is moving towards 3mm downwards.

Regards
John

[walter]

Walter - what's your current thinking about the maximum grain size you will use in your casting experiments ?
I'm getting the idea that the mix recipe is moving towards 3mm downwards.
Regards
John

I definitely agree. Samples with 5-15mm quartz are noticeably weaker.

Now keep in mind that anything can be made to work (my motto). Question is how hard do you have to squeeze and vibrate the mix? Commercial manufacturers have the equipment we don't have so rule of practicality may be in play. (I should add that I really like Cameron's idea of using Agsco Brown ALO2. I think I'm goint to take the four-hour drive just to get a bag!)

Notice that AkvaCNC's commercial E/G sample consists of regular crushed granite. It's a waste from granite plants, they don't even grade these things. Like I said, anything can be made to work.

Now check this out.. It's a machine used for mixing polymer concretes!
It mixes the aggregates, adds resin/hardener, adds vacuum/heat.
_

[ckelloug]

At least one of the books I saw on my last library day mentioned that natural sand greater than 5mm usually isn't very strong. This statement doesn't necessarily apply to material from other sources. I've been working on stuff with small particle sizes because a material property called fracture toughness gets higher as the particles get smaller. This is the material property that governs the stress at which brittle materials break. The smaller sizes also tend to minimize the effects of pouring into a finite sized mold etc.

The AlO2 mentioned in my last trial formula from the simulator has the advantage that the fracture toughness is about 4 times that of quartz.

Walter's motto that almost anything will work is true in the sense that as long as you remember to add hardener to the epoxy, you will get a solid Depending on what you need for material properties anything might be sufficient. What's sufficient and also sufficiently characterized for a compressively loaded machine base is much different than what I would want for a flexurally loaded hollow gantry beam.

Unfortunately, the packing density of a solid made from haphazardly graded material is not necessarily very good. The de Larrard model accounts for how tightly things are packed and can predict a limit for a given mixture. I been posting the model's value for the best packing realistically achievable (vibration plus pressure according to de Larrard) which is lower than maximum achievable.

AS for Zumba's question, I've been looking at the rule of mixtures graph for modulus I posted a long time ago. I contend on this basis that the minimum modulus achievable by the mixture doubles between 85% and 92% packing density. The maximum doesn't change near this much but since when have we ever been lucky enough to get the max achievable value for any thing. I'm trying to optimize density because I think it will help modulus and ultimate strength.

Modulus numbers for Walter's samples are unavailable but I did compute from his data that maximum fiber stress in one of the samples was over 1 ksi tensile! We don't know the ultimate tensile stress because walter ran out of weight before the sample broke.

I'm beginning to think that mixing such a high density material is not the right approach at all. I'm beginning to think that the epoxy and the aggregate both have to be placed in layers and then compressed in the mold under pressure and vibration. I'm thinking along the lines of a mold with a pneumatic ram in one side and a ball vibrator on the bottom. This might be dangerous and tricky however. This whole line of thought may be impractical. I don't know. I'm reaching the limits of what I can figure out without mixing real epoxy and sand.

One last interesting point: Round natural sand tends to pack better than crushed aggregates according to various published experimental data cited by de Larrard.

--Cameron

[greybeard]

Cameron - Is this the #6 Agsco corundum, and am I right in assuming this is US sieve size number 6 = 3.35mm ?

John

[ckelloug]

John,

Right on the first account but (I think) wrong on the second. Agsco gives a chart for synthetic abrasive sizes which is just a touch smaller than that for the natural ones. If I read Agsco's data correctly, 3.070 mm is the actual size.

--Cameron

[greybeard]

While my wife has been doing her evening sudoku puzzle, I've been sneaking round the kitchen, trying out all the sieves. It's quite a surprise just what you can find. The spark guard in front of the fireplace is a 3.5mm wire mesh for example, so that will soon be on temporary loan to the workshop !

The kitchen drawers produced 1, 0.5 and 0.4mm sieves, so the last might get diverted likewise.
Mind you, the practicality of getting even 100gms of sand through it might start me looking for a source of filter sand of the right size as an alternative.

John

[walter]

Walter's motto that almost anything will work is true in the sense that as long as you remember to add hardener to the epoxy, you will get a solid Depending on what you need for material properties anything might be sufficient. What's sufficient and also sufficiently characterized for a compressively loaded machine base is much different than what I would want for a flexurally loaded hollow gantry beam.

Let me explain myself..

I did say that anything can be made to work. The whole idea of composites seems to work around locally available materials- not some Holy Grail mail order stuff. So if all you have is 15mm quartz, please don't throw it out. It can be made to work. If all you have is fly ash- please don't throw it out either. Crushed granite? Yes, it's perfect. You do have to observe Cameron's sizing formula, of course, but anything you have is a good starting point. It's all about matching components. Not about matching the right components. Commercial manufacturers work with whatever they can find locally and that's that. Some work with fly ash, some with crushed granite, some with rabbit poop. Fly ash people use bisphenol epoxy, rabbit poop people use poly-crappy-ester epoxy, and they all arrive at the same result. Magic, isn't it? Well, it's true.

And that's all separate from sizing/packing theory. The theory is rock solid and I have nothing against theory. I respect the theory. There are some problems however.

The maximum packing theory says you can fill 1cu ft box with 92% of solids and 8% liquid, and close the box. With no air inside, and a total volume of 100%. I say you can't.



1. The 92/8% mix itself.

It will be pretty hard to squeeze the solids to 92%. I think you need a 10 ton vibrating press to even come close to 92%. And that's with air- not with epoxy. My opinion of course, but I'd like to see some tests on this.


2. 8% epoxy by volume.

Wetting 92% aggregates with 8% of epoxy is no easy task. This picture shows 16% epoxy by weight, which translates to 20% by volume http://www.cnczone.com/forums/attach...0&d=1182664205 20% by volume mix is very dry and difficult to work with. 8% mix will be powder dry.

3. Commercial 92/8% mixes.

E/Q countertop guys do 92/8% mixes - with $20million presses that press, vibrate and vacuum at the same time. What's the capacity od $20mil press? I say 100ton. Enough to squeeze 4.5" of material into 0.75" slab. So you've got 4cu ft of epoxy and aggregates and you are going to squeeze it into 1 cu ft box. I'm not saying it's impossible, but very unlikely. BTW, you can see these things in person- just go to Home Depot and knock on one of the Silestone countertops. That's what 92/8% mix looks like.

There is a wildcard, however. My "20% by volume" mix was to dry to pour, but still to wet to squeeze. Reducing it further would complicate wetting but enable press compaction. So I think there are possibilities.

btw, here's #6 Agsco Aluminum Oxide ($0.61/lb):

[alexccmeister]

Is it possible for us lot that can't use a press to have a higher mix of the epoxy. Say 25% so at least its workable to fill the mold? I am thinking of vibrating the whole mass rather than pressing. No press at my disposal I am afraid.

[walter]

Yes, that's what I'll be attempting to do. My machine parts are too complicated for press compaction.

Here's the picture of 20% epoxy mix (by volume): http://www.cnczone.com/forums/attach...1&d=1182664205

20% by volume translates to 16% by weight. Too dry for my needs.

[lgalla]

Walter says"ya gotta go with the flow"How strong would a total mix of various zeeosphere sizes be?
Walter the picture of the machine looks like The DEaTh RAy MacHine from an Austin Powers movie.
#6AgscoAlo2.My dog says looks RUF.Willnot a coarse surface demand more epoxy?
Larry

[ckelloug]

Walter,

So far in simulation I've only been able to get to 92% by using silica fume and nanopox. I've been using the values for compaction with 1 psi of pressure and vibration, not the maximum theoretical value.

The simulation I last posted about got up to 88% packing density by volume without silica fume or nanopox using the packing methodology of 10Kpa (1 psi) of pressure and vibration. (That's something like 1 psi) of pressure). That's 8 percent more than I believe you got by trial and error. What you made was already fine for machine base parts with tensile strength a bit over 1 ksi. What I'm doing here is tweaking although I believe that the nano-materials may let us get into strength territory that only guys with big presses otherwise find.

The simulator prediction is that the maximum possible density for my last mixture no matter how big your press approaches 92% while 88% is likely all we'd ever be able to get out of it. In short, the only way I think we home shop folks can get to 92% will be though the use of nano-additives (silica fume, carbon black, nanopox) which might be farther than people want to go and cause other problems. I have no idea what the mixture properties will be at that point.

Since I've got the simulator set for highest reasonably achievable packing density rather than the theoretical density, I've got some belief in actually achieving the numbers, I just don't know how the mixture will behave. Part of me thinks that you, Walter, will be vindicated and it will behave horribly and uselessly. The other part of me says that if the mixture compacts like it's supposed to that it will flow a bit and behave all right. I guess that I've reached the end of the line and have to stop pontificating and simulating and start pouring epoxy. I probably will do my experiments on aggregate sieved to my grading curve so that I get the densest possible mixture and the worst case flow behavior.

I should also point out that Walter got over 1ksi tensile stress in one of his samples without any theory at all so I hope nobody lets my rantings dissuade them. I'm posting my work on creating the strongest mixture achievable rather than a good enough mixture and since I started from first principles so I am way behind compared to folks like Walter.

Cheers all,
Local Mad Scientist Signing off for the day.
--Cameron

[Zumba]

Cameron, thanks for the info on the young's modulus in regards to packing density.

So it's clear that the goal is to make the stiffest product possible, which happens to require a very small amount of epoxy. Costing reduction is NOT a goal, nor is it a reality IMO.

Walter, I think you're right that the presses are in the 10-100 ton range. Luckily, however, bottle jacks are really cheap. I think it's possible for the average home shop user to fabricate something up to 100 tons. I have a 50 ton bottle jack that cost me $70 shipped from ebay. It can probably safely do 35-40 tons.

Wetting 92% aggregates with 8% of epoxy is no easy task.

The logical way around this problem would be to wet 92% aggregate with 16-24% epoxy (you end up with a wet mix of over 100% of the target weight), then press it with a massive hydraulic press + heater + vibrator, squeeze out the excess epoxy, skim the excess epoxy off the top, and get it back down to the target weight.

That excess epoxy can be reused immediately in another mix, or, for most of us home shop guys, discarded. Hence no cost savings. But you do end up with some wickedly cool looking silestone...

[walter]

I probably will do my experiments on aggregate sieved to my grading curve so that I get the densest possible mixture and the worst case flow behavior.

Let me know when you're ready. I'd like to chip in to help finish the formula.
It was a hell of a ride and you did a hell of a job!

Zumba, thanks for the idea. That actually might work.


Larry, Austin Powers really was the originator.

[brunog]

Cameron, Walter,John,Larry.

Keep it up Guys, you have come a long ways in the last couple of weeks!!

I'm lacking time to digest all the info you bring to the thread every day, I check the thread every time I have a few seconds to spare.

Best regards

Bruno

[walter]

Hi Bruno, good to see you!

Zumba,

Speaking of Silestone. One account says that they squeeze 4.5" of material into 0.75" slab. The other says they squeeze it to half the size. Here's what I'm wondering about..

Do they squeeze 400% of initial volume (air+material) into 100% solid block (max achievable density- in example, maximum compaction is achieved, all of the air is removed but no material is altered/contracted). Or, do they squeeze it to say 90% of the volume? Is it possible to over tighten the mix and go beyond limits? These countertops do look alien..

(Not to mention the $20mil presses. No press is worth $20 mil!)
_

[lgalla]

Cool stuff on nanoresins.Things I never knew.Nano resins have nano spherical quartz or whatever in sub micron particles,20nm.They are so small in say a carbonfibre lamate they will fit between the fibers,increasing the strength.Because of their fine nature,they are impossible to disperce in mixing.Apparently they use ultrasound for mixing. Should place a pun here,but I can't think of one.
Cool stuff,anyone know the cost?
Larry

[lgalla]

Bruno glad to see your back____.

Walter,400% to 100%?300%air?Granite does not compress,epoxy does not compress, Does not seem to add up.Some of those cool effects in Silestone are mica flakes and added sparkles.All the engineered stone guys claim 93%.Wonder what the modulus is.
If we could produce E/G like Silestone,the wives[DESPERATE]would be more into our projects,but they will steal our machine bases as kitchen countertops.Just can't win!
ALIEN COUNTERTOPS!!I agree.Look at the Nazca Lines in Peru.Looks like landing strips to me.Aliens gave us the technology thousands of years ago and we lost it.Myan and Egyptian structures are still standing after thousands of years.Concrete has a lifespan of 150years.When the Aliens return,I hope our machine bases will impress them or it maybe The DEaTh RAy MacHine for us.

[walter]

Walter, 400% to 100%? 300% air? Granite does not compress, epoxy does not compress, Does not seem to add up.

I know. They say 93% purified quartz and 7% resin/binder/pigment.

4 and 1/2 inch slab of engineered quartz vibrocompacted down to 3/4 inch slab.

You tell me.

[brunog]

I know. They say 93% purified quartz and 7% resin/binder/pigment.

4 and 1/2 inch slab of engineered quartz vibrocompacted down to 3/4 inch slab.

You tell me.

Don't forget this information is published by marketing people trying to impress potential buyers.

I am sure that what actually happens is that the mix comes out on the forms at 4 1/2" thick and then leveled and heated, vibrated and pressed to 3/4" so at least 3" is due to leveling the mix in the mould.

Best regards

Bruno

[greybeard]

Do they say how wide it was before and after ?
Just a thought.
John