[jhudler]

I think Gupta's claim that an average of 31 microns of epoxy times the surface area of all of the particles is correct. This explains why I see such a large variation in resin volume for different fomulas.
As a test, it took 40% epoxy to wet out 100% of 200 Zeeosphere's.

Jack

EDIT: So I guess that blows my earlier observation out of the water. Wetting out the current formula with 10% takes about 10 minutes of hard vibration.

[ckelloug]

Jack,

Interesting post!

Gupta's model used the specific surface area times the mass of the particles to extrapolate the epoxy needed. De Larrard's model models the empty space in the mixture that must be filled. From the de Larrard model, the minimum volume of empty space in 100 percent zeospheres is 28% since the random packing of spheres yields 72% packing density both from numerical random packing simulation and experimental data. Since zeospheres aren't perfect, their intrinsic packing density may be even lower. Approximately 61% is the intrinsic packing density for crushed aggregate although the exact Beta value varies with the aggregate and must be measured. (Beta is the number de Larrard uses to designate the theoretical packing density of a single particle type.)

The specific surface area from Gamski/Gupta's model is difficult to measure compared to the volume of empty space in a given mixture which can in principle be measured by the amount of water that can be added after the particles are packed to a given volume to the proper density. De Larrard describes another technique for measuring intrinsic packing density but I'd have to look it up.

Using the de Larrard model of the packing density, it's definitely true that the epoxy that can fill the empty space is the smallest possible amount though not necessarily the optimal amount. Gupta used Gamski's theory to estimate the amount needed as equivalent to occupying a 31 micron shell around each particle.

I like de Larrard's theory more because it is based on direct physical measurements and is more general but it gives only the lower limit of the epoxy amount required and since more is needed, comparison studies are needed. I suspect Gupta's result is dependent on variables related to the aggregate which he didn't really control for.

If we can figure out a good way to get specific surface area data for our aggregate, maybe we can get more accurate estimates of the epoxy needed. One method I read about from the Texas A&M concrete research laboratory, that might allow a good determination of specific surface area, coats the particles with ultramarine blue dye and then measures the mass difference on an analytical balance IIRC. I only have a .01g increment scale and not ana analytical balance so I can't do this test yet.

The flexural strength of a given mixture is not easily predicted however the stiffness will be proportional to the percentage of aggregate in the formula according to the rule of mixtures until there is not enough epoxy. We don't know the not enough epoxy amount and it will vary depending on the aggregate mixture used.

Regards all,

Cameron

[jhudler]

I"m using vibration and vacuum on the first set of test pieces.
Given how had this stuff is to make at very low resin levels, it looks at though I'll have to increase the resin ratio for hand mixed.

Walter, how are you mixing your batches? Anything mechanical? How much resin?

[walter]

Walter - double checking - did you obtain that flat surface (I know with the fan stuff) with just gravity settling? Now I wonder if I should just pour a thin EG layer on the garage floor - maybe 1/4 - 1/2 in thick.

I need to go back and look - maybe I can just pour some of that epoxy that is being used in the EG formulation on the floor and let it cure as is.

Yes, definitely. You can use filled epoxy on the bottom and 1/4" unfilled on top.
Table top epoxy self levels at 1/8" and creates uniform and tough surface. I hear this is not always the case with low viscosity epoxies (TT epoxy being thicker than honey).

And yes gravity does work.


Jack,

Gelcoat does sound interesting. We also need release agents- maybe you can kill two birds with one stone. I did the tests with ordinary spray and wax and I highly regret it.
_

[walter]

Given how had this stuff is to make at very low resin levels, it looks at though I'll have to increase the resin ratio for hand mixed.
Walter, how are you mixing your batches? Anything mechanical? How much resin?

Everything goes through the old kitchen-aid mixer, 5-8min per batch. I hand stir epoxy-Al2O3-quartz for 10 sec, then add zeeospheres and send it through the mixer.

15-20% epoxy by volume, depending on part complexity.

[jhudler]

Walter, Thanks, I see the need to create a process where a shell can be made that is then filled with EG. That shell can be the "sporty" exterior where you can personalize it or used to add real structural support in the form of woven fiber mats.

But all things a side; the need to create molds and the methods used needs to be ironed out and well documented.

I find that UHMW material is an excellent mold material for EG. I've used small holes in the mold to allow air to escape and to blow air back in to demold.

[greybeard]

I've just done a quick calculation on the amount of epoxy required, as per Gamski/Gupta ( 31 micron thick layer on average) for two different particle sizes.
I took 100 ccs of 200 micron particles in the first case, and 2mm particles in the second.
This gives a volume of each particle as 0.004189 cu mm for the first, and 4.189 cu mm for the second.
Assuming both to have a packing value of 72%, the total number of particles is 1.72 x 10^7, and 1.72 x 10^4 respectively.

However the surface areas are 2.16 x 10^4 sq cms and 2.16 x 10^3 sq cms, so the volume required to fulfill G/G's requirements will be 67 ccs and 6.7 ccs epoxy for 100 ccs of 200 micron and 2mm particles respectively.

I think that as an approximation this bears out Jack's observation of the amount required to wet G200 at 40% by volume, which at first sight seems a lot.

Jack, is your "UHMW" material referring to ultra high molecular weight polythene ?

John

[jhudler]

Jack, is your "UHMW" material referring to ultra high molecular weight polythene ?

John

Yes

[jhudler]

Just mixed my first batch of thick epoxy 3:1 US Composites.

It seem to take a bit more to wet out and requires a bit more force to mix but other than that I do not see any reason this cannot be used. I did use 525 and 969 agents.

I also don't think the BYK-A 525 is doing much for us when mixed with aggregate. Mixed alone with neat epoxy the effect is very dramatic, but other than that...

Jack

[Steven.ji]

For the ploymer concrete, it's called as "expoy granite", "expoy marble", as my opinion that's not exact name. With respect to ploymer concrete, the filler is not only granite and marble, but also other minerals. So the exact name is "plymer concret","mineral casting" etc.
Genman studied the subjet since the second world war, till now polymer concretr is a poven technique. Polymer concretr has been widely applied in machine tool for metal work, wooden work etc due to the performance and price advantage.
Concerning the polymer concrete, the integration is the first advantage. it can be cast in pipes, wires, hydraulic tube etc. Precision is the second advantage. If somebody want more detail advantage, I will provide.
For the proportion of sand and expoy, sand is more than 93%, and expoy is less than 7%. So the price is much cheaper than cast iron.

[jhudler]

I am not sure what you are trying to explain; that our use of the phrase "epoxy granite" is incorrect?
Granite is primarily composed of quartz and feldspar, the two most common mineral composites on the planet.
Generally Granite is 72% Quartz, 15% Aluminum oxides, and others which if you look at our current formulation, is a close approximation (though accidental) of Granite.

I just had a email from a well known supplier of epoxy where I used the phrase "polymer concrete", they told me that they did not work with concrete. I wrote back using the phrase "epoxy granite" and they understood; I wanted to "Glue a box of rocks together".

Call it "polymer concrete", "mineral casting", "thermoset composite", "particulate composite", or what ever you like.

Here we refer to it as "Epoxy Granite" because simply; it saves time.

We here "Glue a box of rocks together"... who coined this phrase? Walter?

[ckelloug]

Stephen.ji,

We're interested everything people have discovered about mineral composite machine parts whatever name you want to call them by.

This thread settled on the name "Epoxy Granite" because polymer concrete usually implies a polyester resin based formulation according to Ken Lipovsky, the applications engineer for polyester resins at Reichhold. The nomenclature has also changed since the 1970's when some of the technology for epoxy based particle composites was originally researched.

If you have any information on the proportions of rocks and sand to epoxy used in other formulations, I'm interested. I've done a lot of research and believe we are near the optimal formula. My calculations, based on the work of French Researcher Francois de Larrard, indicate that between about 7 and 12% epoxy by volume should work although practical considerations make the lower epoxy mixtures a touch tricky. Lower epoxy mixtures also require carefully graded aggregate.

Thanks for your post and if you have more to say about what you have learned, please feel free to post it as we are always interested.

Regards all,

Cameron

P.S. The lack of posting here doesn't signify a lack of activity on the subject lately. I know that both Jack and Walter have been busy working on this as have I and most likely others.

All of my work lately has been involved in getting my shop and lab area set up to do effective research on E/G which doesn't make for good posts here. My machine shop now has power and the lab will have a 48x36x36 oven for post curing parts later this week. I've got my Bridgeport mill up and running although there are issues but my big accomplishment of the day was crashing my lathe and breaking the two iron castings that hold the half-nuts (chair)

I've already communicated with harryn about meeting this week, but I'll be on travel in the san francisco bay area from the 11th to the 18th if anybody else who follows this thread and lives in the bay area wants to get together. Just send a PM if you're interested.

[jhudler]

I'd make some nasty joke about turning on a lathe with the half-nut engaged only...
I wrecked the blade insert in my table saw today by trying to tilt the blade while it was running. Not a problem when you have an insert that's designed for a tilting blade.
Good thing my head was below the table when the insert took off at 400 MPH!
Now I have to realign the trunnion. Just one of those says when you just, walk away.

[lgalla]

Lucky Jack!
I suppose your insert was just a piece of wood.Kickbacks are no fun.One of my employees got a kickback from a piece of 18mm birch,2'X3'inthe(nuts).He was off work for a week and naturally I paid his wages.I would swear his voice is higher.Amazing what a 10Hp/14" saw can do.This is why I want a large E/G router.I hope it is safer than pushing sheets through a saw.
Jack I think Walter coined the"Glue a box of rocks together"I coined the E/G,E/Q,ESP terminology.Perhaps the final aggregate mix should be termed:
E/G/E/Q/AL02/ZeO2.Naw! E/G should be fine for a bunch of rocks glued together.
Larry

[jhudler]

No just your average melamine faced, high density phenolic laminate insert.
http://www.woodcraft.com/family.aspx...e=details#tabs
Sheared the hold down tabs clean off!

[walter]

Epoxy-granite is more of a symbolic name. While original formulations of polymer composites came from concrete filling of machine tool bases and included concrete, more recent formulations consist mainly of quartz or granite materials in an epoxy composite. Also note that Fritz Studer AG of Switzerland, who invented the technology in the early 1970s, did it with epoxy and granite http://findarticles.com/p/articles/m...v93/ai_3647171

I like the term "mineral casting". Note that polymer concrete is used for pipes, airport runways and trash cans, which only confuses everyone.

* * *

BTW, here's the table that I made last week. Pretty good for a prototype, although I'm seeing lots of small voids. I placed a layer of aluminum oxide then poured E/G without vibrating it.
_

[robpiaz]

I know a company that puts a dunham headstock on a surface plate. Then mounts linear bearings on it to make a gang tool machine. It designed to make small precision parts. This could be another alternative. All you would have to do is find someone or a way to drill and tap your mount holes. I know this works quite well they've built a few of these machines.

[jhudler]

Walter,
How did you hold all those inserts in position while you pour the EG?

Jack

[jhudler]

2500 messages.... I've got bagsies

[walter]

I glued them in place with epoxy. It sealed the hole perfectly.