[ckelloug]

greybeard,

First, from what I've read about Silicon dioxide sand, the grains are relative spherical at least much more so that something like garnet. Secondly, and this is pragmatic to use fyffe555's euphemism for not thorough, everyone else doing packing studies seems to assume assumes spherical sand.

The paper you cited from NISS was random packing of spheres of different sizes. The 70% fill rate that they achieve with random packing is only 5% less than the packing of uniform sized identical spheres. They also state that as the size of the spheres added approaches 0 the packing approaches 100%. They got 70% stopping at an arbitrary size some ratio away from the biggest sphere. My gut instinct is that it will scale well to most semi-spherical shapes. Something I saw said the some types of packings actually work better with ellipsoids ?!

Gupta et. al in the paper brunog posted talk about something called binder skin theory and they talk about it accounting for the non spherical nature of the particles as well as some other effects. I have ordered reference 1 from Gupta which is a book of proceedings from the first conference on polymers in concrete, London, 1975 in hopes of it explaining what gupta cited it for.

Lastly, above all of the aggregate theory, we have the Reichhold aggregate formulation for polyester polymer concrete which is undoubtedly at least decent. I have a hunch that a formula based on the NISS paper will work better than one based on either Fuller's Formula or the Reichhold reference formulation. That being said, I'll have to track down brunog and buy him a beer if I'm wrong.

Ultimately, there are probably an uncountably infinite number of good aggregate sizing strategies. Fuller's Formula, a formula based on the NISS paper, and the Reichhold formula are but three. Fuller's formula has 100 years of testing in ordinary concrete. I don't have an implementable formula from the NISS paper yet. Finally, the Reichhold formulation was recommended to help them sell resins so it was obviously thoroughly tested.

One must remember that randomness is not something to fear in engineering. It can be controlled and often used to advantage. The niss paper when extended down to the tiniest particles actually approaches 100% packing. Dense packed spheres of any single size do not and I imagine that Dense packet spheres of any number of uniform sizes also may very well not.
Randomness in particle size should essentially cancel out randomness in particle placement.

For those who are interested in getting machines out the door pronto, I'd suggest considering the formula for the aggregate in old style polymer concrete posted here http://www.cnczone.com/forums/showpo...postcount=1201.

I'd also recommend writing up what you want in terms of percent retained on different sieve sizes rather than just winging it and calling a specialty sand manufacturer such as www.agsco.com to sieve you a batch. If we use custom sand mixes prepared by somebody with the right sieves, we will have a better chance of comparing results and duplicating published formulas.

[lgalla]

Jim&john:Furfurol

Flavour compound in cheapo whisky that gives a burnt taste. Undesirable in large quantities.Tastes bad in epoxy too.:nono:
Alcohol compounds do thin epoxyies,but act as an accelerator.Beleive me,I once added methyl hydrate,an alcohol to epoxy and got epoxy foaming and smokin.
Any solvent will thin,but upon evaporation will shrink.
Reactive dilutents do not evaporate but compromize the epoxy parameters.E/g nonyl phenol.This also acts as an accelerator in epoxy.Thinner epoxyies may contain nonyl but it crosslinks with the epoxy and does not shrink.Thinners and reactive dilutents are best left to the formulator who can spec gel time etc.

[Udayan Patel]

Welcome Udayan!

This is about the most useful forum I have ever come across, hope you enjoy your stay here- these guys really know their stuff and are incredibly friendly too

Yes, I reckon this is by far the best thread, so far I have come across. I regularly read CR - 4 Engineers place for Discussion -- Blog of Global Spec -- but this is superb.

One feels like sitting in a conferance room watching experts talking / discussing .

Thanks Greybeard for your Welcome msg and tips. After going through all the 104 pages , I may think of doing my own expriments by picking up threads from this forum. I have read only 20 pages so far, First 11 and from 90 onwards.

I had seen some samples of E/G produced by Granitek-- UK and found that it looks very much similar to Granite but at the bottom of this small blocks, there were pin holes as big as 2 to 3 mm dia. What could be the cause ? Can it be filled by some epoxy ? If so , what about hardness where epoxy is filled ?

Thanks once again to all for their valuable in-puts

Can we ask modewrator to give printer friendly link ?
Udayan Patel

[lgalla]

this just hit me.(chair)
I have been following the posts and learning countless things,thanks guys.
You may know I have been against a total E/Q machine and that is still my opinion,I am the steel frame,damped with epoxy,surface plate for rail mounting accuracy,wonder if a forklift bump will crack my plate type guy.
If casting a beam,the mold must have the accuracy you desire???or cast off a surface plate or your machine bed.What is the answer to casting a .0001 beam?
How heavy would anE/G gantry be?Can your steppers or servos handle the weight?These are issues I have not seen answers to.I will stick to E/G as damping for weldments and surface plate uses.Maybe blind but still cannot see a total E/G machine.I am sure someone can prove me wrong and hope this happens.Any answers?

[walter]

That gives me an idea...

Maybe we could talk one of these big manufacturers into sending us a tiny E/G sample?

It would't hurt to actually see what's inside of the latest and greatest in E/Q technology :stickpoke

[walter]

That's a great question Larry..

My personal choice will always be a "moving table" type of design.
Even the tiniest 36" gantry will top 100lbs and I wouldn't feel comfortable moving this thing around. With moving table I can make the gantry as heavy as it needs to be and doubling the size of the table is a small price to pay.


re: Accurate Castings

I don't need that either, all my metal parts will be mounted to metal surfaces, E/G will serve as an outer jacket.

I should be able to post some sketches this weekend.
_

[greybeard]

greybeard,

First, from what I've read about Silicon dioxide sand, the grains are relative spherical at least much more so that something like garnet. Secondly, and this is pragmatic to use fyffe555's euphemism for not thorough, everyone else doing packing studies seems to assume assumes spherical sand.

The paper you cited from NISS was random packing of spheres of different sizes. The 70% fill rate that they achieve with random packing is only 5% less than the packing of uniform sized identical spheres. They also state that as the size of the spheres added approaches 0 the packing approaches 100%. They got 70% stopping at an arbitrary size some ratio away from the biggest sphere. My gut instinct is that it will scale well to most semi-spherical shapes. Something I saw said the some types of packings actually work better with ellipsoids ?!

Ultimately, there are probably an uncountably infinite number of good aggregate sizing strategies. Fuller's Formula, a formula based on the NISS paper, and the Reichhold formula are but three. Fuller's formula has 100 years of testing in ordinary concrete. I don't have an implementable formula from the NISS paper yet. Finally, the Reichhold formulation was recommended to help them sell resins so it was obviously thoroughly tested.

One must remember that randomness is not something to fear in engineering. It can be controlled and often used to advantage. The niss paper when extended down to the tiniest particles actually approaches 100% packing. Dense packed spheres of any single size do not and I imagine that Dense packet spheres of any number of uniform sizes also may very well not.
Randomness in particle size should essentially cancel out randomness in particle placement.

Thanks c for the posting.
Having some drink taken last night while trying to explain close packing to number one grandson, I think I got random packing of one size particles mixed up with random sized random packing. (chair)

I think it's the former that gives the much lower fill now the head is a little clearer. :tired:

I, too, have some dim memory(25 years ago ?) of the discovery that ellipsoid packing could achieve higher fill ratios than 75% for spheres.


Re mixing and placement of the mix. I have had two ideas.
1. Could a better packing be achieved for the diy molder by mixing all the aggregates except the biggest with the total volume of epoxy first. This would give a lower viscosity "sludge".
Pour a thin layer of this into the mold, followed by a single layer of the largest stones, which would then be pushed down into the sludge, such that excess sludge oozes up just enough to fill the gaps under the stones.
Then another thin pour of sludge, followed by another single layer of stones.
Repeat till the mold is full.

If possible, vacuum reduction of air entrapment, vacuum bagging or vibrating could each or all be applied during the process, along with any other embeddings(sp?) needed.

The idea is to calculate all the different component quantities first, but handle them in a different way. Leaving the stones out of the small aggregate mix giving a better pour, and placing the largest separately giving more controlled distribution, but bringing the final mix back to the required fill density.

2. Could spinning the mold be used as a method of compaction/air release ?
I envisage taking two (for balance)rectangular steel hollow sections held together and parallel, and spun about their central long axis. Each filled with E/G, spinning would drive the fill to the outer sides and the air toward the inner sides of each beam. These would then become the bottom(tension) side of the finished beams.

John

[ckelloug]

John,

I think Larry suggested a similar method for mixing the epoxy with the aggregate some posts back and will hopefully elaborate seing your more detailed post. I don't have much experience when epoxy stops being something with shear strength equal to 19ksi and starts being a gooey semi-fluid muck that will become a rock.

Spinning is a great idea. Spinning the mold will be too hard as it will be huge, heavy and oddly shaped. Spinning the epoxy batch might work quite well however it's a lot of epoxy and you will spin the aggregate down too and have to remix it thus maybe introducing air you removed.

I predict that a spun batch will be much better than an unspun one because the air that is trapped will be somewhere random in the matrix rather than around the aggregate grains causing the effective cross section of the material to be pinhole filled epoxy with no reinforcement. Vacuum might be a bit easier to achieve however.

Also, on the subject of deairing, check this out from: http://advancedprocess.com/apt/Vacuum%20Casting.htm

Vacuum Levels Required for Degassing Resins
and Potting Components Under Vacuum:

30" Vacuum = 0.0 mmHg (Torr) = 0.0 microns = Perfect Vacuum
0.05 mmHg (Torr) = 50 microns
0.1 mmHg (Torr) = 100 microns
0.5 mmHg (Torr) = 500 microns (Resin is degassed at 50 to 500 microns to vacuum
pot and encapsulate high voltage components.)
1.0 mmHg (Torr) = 1,000 microns (In-chamber vacuum levels from 500 to 1,000
microns are required for most vacuum potting and encapsulating applications.)
2.0 mmHg (Torr) = 2,000 microns
5.0 mmHg (Torr) = 5,000 microns (2 to 5 mmHg is needed to make low to medium
viscosity resins visibly air-free. This range of vacuum levels is five to ten times
better than 29" of vacuum.)
10.0 mmHg (Torr) = 10,000 microns (Very little degassing is done at this level.)
29" Vacuum = 25.4 mmHg (Torr) = 25,400 microns (Not a sufficient
vacuum level for degassing most epoxy and urethane resins.)
28" Vacuum = 50.8 mmHg (Torr) = 50,800 microns
15" Vacuum = 381 mmHg (Torr) = 381,000 microns
0" Vacuum = 762 mmHg (Torr) = 762,000 microns = Ambient Air

[AkvaCNC]

Hi Walter,
Very, very nice forum, it would be wonderful with a kind of nomenclature/classification of the threads in this forum, because it’s now very huge, but I suppose we can have it all.
But you can have a slice of this dia. 36 mm E/G Core, if it can be to any help.
Let me know how and where to ship it!
Professionals don’t seem to be too concerned about air bubbles ( see left photo x60 ); they can be filled afterwards if necessary. When blending the the epoxy it’s a good idea to shortly put it under vacuum. It’s amazing to watch the amount air coming out, it become like boiling water. When blended with the granite the vibration table take care of the rest or almost.

[harryn]

Hi, FWIW, here is an inexpensive concrete mixer that I have used for backyard projects.

http://nga-gardenshop.stores.yahoo.net/13-1015.html

It is essentially a small drum with a baffle that you roll around on the ground to mix. The really nice thing about it for me, was that I was able to easily mix small qty of a fairly dry mix to obtain a bit higher strength than I could do otherwise. I bought mine several years ago at a local Orchard or Home Depot, but they are around. No idea if this is a good price or not.

[walter]

Hello AkvaCNC,

That is pretty cool!

Is that the E/G for commercial machine bases? I would love to take a closer look

How can I pay you for it?

[uhrgerat]

Sorry, made a mistake on the furfural alcohol. The reference in the patent was to the possibility of using a resin based on same. The dilutant should be non-reactive, and the examples given for polyester resins were acetone, methylene chloride and 1,1,1, trichloroethane. None were given for epoxy resin. But the net result for the patent was the ability to produce polymer concrete with approx 10% resin binder.

Regarding the spherical aggregate. I think you're heading in the wrong direction. I believe you should be looking at angular and subangular particles. As an example, in foundry work you're warned against using "beach" sand for the molding sand. It's rounded and doesn't hold together. The angles and edges of rough sand interlock. Also, if the sizes are appropriately chosen, angular particles are going to form a closer bond with fewer spaces then spheres.

In Patent #4,696,839 (assigned to Fritz Studer AG, later acquired by Hardinge?--I think this is actually the basis for Harcrete), the inventors specify essentially cubic (1:1.4 edge to length) broken rock such as basalt, flint, gabbro, greenstone, diabase and diorite to be mixed with smaller particles such as aluminum oxide, silicon carbide, silicon nitride or, our old friend, quartz. The former rock types are sorted in five steps from ~4 microns to 16mm and larger. Those below 1mm are discarded. The fines replace this <1mm group. The resin is a biphenolic A-epoxy resin with a hardner of aliphatic polyamines with a minimum viscosity of betwen 100 to 300 mPa sec. (Someone will have to translate this!) Unfortunately, the patent doesn't describe the particle size distribution used in the final mix--a trade secret I suppose.

A good source for flint, at least, is pottery supply houses. You can probably get the others as well, all in various mesh sizes, pre-sorted. I'm going to see if I can't use some of the flint grog I have with some silica sand to make a sample.

Regards,
jim

[BigAl1]

Hi All,
Been very interested in this thread, and toyed with the idea of a complete cast machine for a while now. By some web-searching, I have found several sites with pics of raw material (presumably the aggregate being used in their mixes?), and noticed that they showed sharp, broken material instead of rounded or spheres. Also see this in the pics of the EG core sample just above this post. Besides the packing theory for spheres already stated, is there another reason to avoid the sharp, broken stone? With the use of a wet mix, and vacume applied to de-gas the poured mold, and a vibration applied, I wonder if the shape of the aggregate is really that important? Not questioning the size - that is obvious for the most fill packing, just the shape.


Allan

[uhrgerat]

Hi,
another correction--Studer was not acquired by Hardinge, I was thinking of Tschudin. Studer's version of e/g is Granitan.

But, it looks like Allen and I were on the same track--angular particles rather than spherical. I'm going to try a quick and dirty with polyester resin, flint, and silica sand this weekend. Don't have the epoxy or a vacuum chamber. But, I do have a grinding wheel with some serious vibrations!
Have a good weekend!
Jim

[ckelloug]

I'm supposed to be digging for my sprinklers but. . .

I just got hold of Proceedings of the First International Congress on Polymer Concretes 5th to 7th of May, 1975. Published in 1976 by the Construction Press Limited in London.

Section 7.1 is an article by some researchers at Brighton Polytechnic in the UK that worked with CEIBA GEIGY (now Huntsman).

Their formula is 10-12 mm aggregate and sand used with huntsman gy-250 epoxy and HY830 and HY850 hardeners.

Huntsman gives a formula for Epoxy concrete on page 33 of the linked pdf: http://www.huntsman.com/performance_...theramines.pdf

60% 3/8 aggregate, 30% coarse sand, 10% flu ash as the percentage of aggregates out of total aggregates. Their aggregate to epoxy, hardener and accelerator ratio is 11:1 by weight.

I also found out that EEW means epoxide equivalent weight after calling huntsman advanced materials and talking to an apps engineer. The huntsman literature calls for epoxide equivalent weight 188 which is Huntsman GY6010.

The EEW of our epotuf 37-127 is 197 which is very close to the formula except that ours has reactive dilutents.

The proceedings book says that getting all of the air voids out is not critical, however compacting the mixture as walter discovered is critical. They say that letting the epoxy harden under pressure is the best way; which for us likely means we will have to devise a vaccum technique like vaccuum bagging. Vaccum deairing will be required. Beyond bone dry aggregates are a must.

We can probably also greatly improve results with a deairing agent like BYK525 and we would probably also be very well served by using a coupling agent. We do have the right general type of epoxy although the version used in the reference formula has no reactive dilutents. Finally, the book says that the material must be cured for 3 days at 40 degrees celcius.

Jim,

Somebody with concrete experience posted earlier that overly angular granules interfered with the process. I would suspect that the more angular grained materials would be more friable and thus more likely to fail and let a crack form. I really don't know. Based on the research results I've put into this post, I suspect that servicable E/G can be made if we use anything approximating a good aggregate design and aggregate, get some additives to make sure we're wetting the materials correctly, and a deairing agent.

Our first step is to make a sample with a modulus higher than that of cheesecake. We can work towards 10MPa compressive modulus later.

-Cameron

[walter]

We can probably also greatly improve results with a deairing agent like BYK525 and we would probably also be very well served by using a coupling agent. We do have the right general type of epoxy although the version used in the reference formula has no reactive dilutents.

These additives are a good idea. I'm still having doubts about epoxy though.

Are you sure they're using regular epoxy?



Doesn't seem all that well packed and there's a lot of resin in here.

The resin would have to be hard as hell to make that work. That's not what I have...:tired:

[walter]

But, it looks like Allen and I were on the same track--angular particles rather than spherical.

This could very well be true. It's better at interlocking but I read somewhere (here?) that also creates tensions in the mix (if not done properly).
I have to double check that.

[qroger]

First post to this forum, so please forgive me if I break any rules. The aggregate, (filler) is very familiar to me from concrete. In concrete, strength is the key characteristic. Here damping is also important. In concrete, the portland cement portion is just enough to stick everything together. Ultimate strength depends on the aggregate strength and on the bond between the aggregate and the cement. If your broken concrete doesn't show broken aggregate, something was wrong. The aggregate pulled out of the cement, which is Bad. This link: http://www.eng-tips.com/ is another great forum and you can find all you want to know about concrete, etc. I noticed that one note referenced curing under pressure, and another referenced vacuum. If your sample is under pressure, any contained gas is under the same pressure and the bubbles will disolve into the epoxy, or whatever. It is the same as when you open a carbonated drink. There are no bubbles until you let off the pressure. ( It is probably easier to find an air compressor than a high volume, high vacuum, vacuum pump.)
Thanks
roger

[walter]

I think we're EXTREMELY CLOSE TO MAKING THIS WORK.

Some pieces of the puzzle are still missing so please speak out with your ideas and concerns. Could be the size, could be the shape. Whatever it is, we have to find it.

I just talked to Harvey at Agsco Illinois www.agsco.com and it looks like it would be a several hundred dollars to have them mix up 50 or a hundred pounds of a test mix for us if we can get our specifications written in such a way that they are comprehended by sand guys. While this may be more expensive initially, it saves having 50 pound bags of 10 kinds of sand shipped to us. It also means that they can tell us exactly what we got and if it works, we can all get the same thing.

I'm very interested and willing to give it a shot.

We can mix random components for months or just come up with the formula and bet the farm on it.



How sure are you about your math Cameron? :violin:
_

[ckelloug]

Walter,

I think we have the same general kind of epoxy than Huntsman used with the exception of the fact that ours has reactive dilutants reducing it from 11,000cps to 200. The reactive dilutants may lower strength some according to the Huntsman datasheet. The Huntman formulation does use an accelerator however which we may consider adding. Nanoresins used cobalt acetyl acetonate for an accelerator.

In terms of the experiments that you've described, I think that the mixing of the components is incomplete and that the cure is also incomplete for some reason. There's also a lot of very very fine aggregate in the commercial formulations for countertops that means that the surface is mostly aggregate, not epoxy and thus pretty hard.

After what I've seen today on aggregates and I'm not done reading the new book, our biggest problem is getting the materials to wet out properly and the epoxy to stick to the aggregates.

While it is true that the best aggregate recipes will be better than bad ones, I think we need a thread wide discussion on mixing processes right now. I am thinking that for small batches a kitchenaid is the right tool like I was discussing with harryn in a PM. For machine size batches, we probably need a small cement mixer that's never had cement in it. We also probably need one of the vaccum paint pot deairing systems talked about.

I'll go double check my translation to sieve numbers of the Reichhold formulation and then ask AGSCO for a quote on Monday. No math involved on that part thankfully! I now suspect that optimum aggregate engineering won't be as critical as mixing, compaction under high pressure, bonding agents and deairing agents in that order. Since I have the book that Gupta cited, I think I need to make sure there's nothing we've missed.

Finally, I need to figure out how to get some deairing agent and some bonding agent pronto since these are our problems and they are what the apps engineers recommend.