[ckelloug]

I'm sorry to jump in so far from the start of the thread, but epoxy is my life :wee:

Huzzah! An epoxy chemist!

If you can give me a bit of background on your objectives, I am sure I can give you some good and inexpensive solutions.


Obviously you are a sophisticated user of epoxies, and from the looks of your experiments are using high quality products.

I have learned from the wisdom of many on this thread and cnczone like lgalla and probinson and walter as well as reading many books and datasheets. There are some sophisticated epoxy users here but alas, I'm not one: I'm just a crazy engineer who decided he wanted to figure out this E/G stuff.

I am a big fan of pure Bis A or Novolac systems. Huntsman makes a line of jeffamine curatives and accelerators that create systems that yield numbers considerably higher than what you are showing here. I can give you some stoichiometry to work from.

It seems to me from the little bits of the string I have read that you are going to need some filler materials to help stabilize the material as it cures and to reduce the chances of stress cracking. You will also probably need to cure in heat and then do a post cure heat to get maximum performance from the materials.

I would really like to help out on this project, and if you can give me a small amount of background, I'm sure that I have some value to add.

Cheers,

Bloefeld

So, Welcome aboard Bloefeld and here's the scoop:

The idea is to produce a dimensionally stable epoxy mineral composite for accurately casting machine parts. Such work has already been done in the past by Studer in Germany and their patent expired a long time ago. Several folks here who preceeded my interest got this thread off the ground.

I've done a lot of research on the filler aspects and believe I have the correct data to get the filler loading up to between 88 and 92% if the mixture rheology doesn't become too horrible.

The epoxy on the other hand is more troublesome because there isn't a lot of good data to go on. There is one product on the market in europe only that is for this purpose Hexion 556 mineral casting epoxy. The datasheet is attached but Hexion said they won't market it here in North America.

The original formulation we started out with was reichhold 37-127 and 37-606 because it was cheap, slow setting, low viscosity (600cps) and readily available. This is a diglycidyl ether reactive diluted Bis A system with a hardener composed of Amino-Ethyl-Piperazine and a bunch of nonyl phenol. This stuff has flexural strength of about 10ksi and modulus of about 380ksi. The viscosity is a touch high compared to the hexion 813/3046 I just tested.

In general, I'd like to see an epoxy that has viscosity of 300-600 cps when mixed, a modulus of at least 500ksi, a gel time of about 6 hours. I'd also like it to be non-toxic enough that it could be supplied to our readership here on good conscience without creating superfund sites all over the country. . .

This link gives a couple of the more numeric comparisons I've made recently between the epoxy modulus and the needed filler percentage with quartz filler. http://www.cnczone.com/forums/showpo...postcount=3302

The Reichhold 37-127/37-606 and the Hexion 813/3253 combinations were suggested by the respective apps engineers.

The hexion engineer said that that combo is used in several of their customers machine grouts. The hardener is a reaction product of TETA and tall-oil. I've concluded that this hardener is not a real winner in this application.

One of the folks who makes E/G for a living said that they use isophorone diamine as their hardener. I don't even want to crack open the bottle of Vestamin IPD or the Hexamethylene Diamine I got from Evonik Degussa until I get a fume hood. I know however that Reichhold and Hexion both make IPDA adduct hardeners that appear to be much less toxic and corrosive so I'm hoping that one of these pans out.

I think that the Hexion or Reichhold Resins are probably about what we need but I think the hardeners we have leave a lot to be desired.

Having given the specifics of the epoxy, The idea is to use carefully sized mineral fillers to get the filler density up in to the high 80% range ensuring bonding and viscosity control with a combination of silanes from DUpont, titanates from Kenrich, fluorosurfactants from 3M, and deairing agents from BYK. I've written software using the works of French concrete researcher Francois de Larrard to predict the density to which a given aggregate distribution will pack. De Larrard claims that the model is good to within 3%.

Any advice would be appreciated by the large following here. I seem to recall somebody suggesting that the Jeffamines weren't going to be good for this but I don't remember the rationale and I haven't tried them.

Regards all,

Cameron

[krazatchu]

I found this 2 axis centrifugal mixer a while back, thought it might be of interest here...

Although the capacity is rather small, it looks like it would mix and de-air E/G quite well...

The demo video is worth viewing, esp. the mixing of the 2 tone clay...

Linky: http://www.thinky.co.jp/english/index.html

It certainly might open up some possibilities of using higher viscosity epoxy...

[ckelloug]

krazatchu,

Thanks for posting about that mixer. It is very interesting. I also have the feeling that it is an expensive piece of hardware but I don't know for sure. Such mixing will become more important as bigger batches get made.

Regards all,

Cameron

[jhudler]

Wow the red clay on white clay did it for me! (10 minutes in to demo video).
It should be easy to make one of these!
The de-aerating feature might be a bit of a challenge but not necessary.
Design should easily scale up multi-liter batches.

Jack

[lerman]

It isn't obvious to me what the rotational speeds are along the two axes. What sort of linkage is used to achieve that motion (or is it just geared)?

Is the deairing caused by the motion or is a vacuum also applied?

It sure does sound like a good idea, though.

How does it differ from the paint mixer at my local hardware store?

Ken

[krazatchu]

I haven't done a patent search on it, but I would guess it's probably not geared... Perhaps a smaller motor mounted near the major axis and belted to the mixing cup (minor axis)....

I think that it probably mixes first, where both axes are functioning...
And then only rotates the major axis for de-airing...
I don't think it uses vacuum for de-airing, I think it is just exploiting the effect of the g-force on the difference of density...
The paint mixers I have seen just shake and agitate..

The rotational speed of the major axis can be calculated from radius and the G force (Ok, Ok, it's not a REAL force) ...
http://www.centrifuge.jp/cgi-bin/calc-e.cgi
On the Tech page of the site, it states "over 400 G's"....
So probably less than 500, which for comparison, is just a bit higher than the average commercial washing machine ...
However, a lower G force would mix just as well given a longer time...
Maximum speed would depend on materials of construction, resonant modes, safety...

I don't think the the minor axis rotates very fast, but it may depend on what is being mixed...
A higher viscosity wouldn't need as fast a rotation along the minor axis as a "stickier" lower viscosity mix...

Anyhoo... these are just my speculations, I may be completely off base...

[krazatchu]

Hehe... I was wrong...

It seems they do apply vacuum depending on the material...

"To improve degassing quality and accelerate dispersion of powder, THINKY apply vacuum pressure on the mateiral addtionally. The most of applications can satisfy with non-vacuum mixer, however, we offer vacuum mixer for extream degassing or for some mateirals that requires vacuum to degas. "

They have an American site as well... Seems to have more info than the Japanese one...
http://thinkyusa.com/performance.aspx

[krazatchu]

Speed ratio's are here...

http://thinkyusa.com/thinkypower.aspx

1:25 and 1:36.7 ...

It mentions it can vary vary the speed dynamically, so it's probably driven off a separate motor...

[jhudler]

All is revealed!

[krazatchu]

Woot! Good find!

[lerman]

After reading the document, I've concluded that you could make the basic device without infringing IF you didn't have a hose connecting to the container.

One way to apply a vacuum without such a connection is to pump out the whole device. That would mean it would have to be stronger and sealed.

Ken

[jhudler]

Having messed with vacuuming EG... I wouldn't bother with it.
I use to think it was important however, I've since changed my mind.

Jack

[rowbare]

After reading the document, I've concluded that you could make the basic device without infringing IF you didn't have a hose connecting to the container.

One way to apply a vacuum without such a connection is to pump out the whole device. That would mean it would have to be stronger and sealed.

Ken

This patent seems to be a derivative. The Thinky patent is from 1989 so has probably expired. They have the ARV series of machines that use vacuum but several of their models don't. The demo was done with the AR 250 so I am assuming that no vacuum was used there. Pretty impressive demo but I wouldn't want to try casting a 250 KG machine base using those little 250 ml cups....

[jhudler]

I was thinking of a several gallons!
Imagine slinging that around at 2000 rpm!

Hmmm ~19 lbs per gallon (assuming 2.262 g/ml).
Say 4 gallons in a 5 gallon bucket.
That's 76 lbs, 35 kg or about 1/2 cubic foot...

assuming 2000 rpm... 2 * PI * 2000 / 60 = 210 radians/sec (omega) or is it the OMG factor!!!

Guessing a 5 gallon bucket on said angle would have a radius of ~500mm (0.5 meters)(hair is standing up on my back)

centrifugal acceleration a = (210^2) * 0.5 = 22050 m/s2

centrifugal force = ( ma ) = ( 35 * 22050) = 771750 Newtons!!!!! Whoa!!
I know its late... did I do dis right? Thats 86 tons!

Considering that you need rotating frame with equal mass to balance this... multiply that times 2!!! 172 tons the frame has to hold!
This thing let go and that pail of EG would lay waste to a herd of elephants!!!!
Or vaporize any human in its path!

Hmm... keep talking this much mass and a discussion of Lagrange points will break out!

[rowbare]

That is a lot of force... The largest Thinky machine listed on the Japanese site holds 3L and weighs about 500 KG. I wonder how massive this machine would have to be.

Since we have to counter-balance the mixture, it might make sense for our purposes to split the mixture into two buckets of equal weight. This makes the mechanics a bit more complex but also reduces the amount of revolving mass and should allow a shortening of the moment arm.

Also we should be able to spin our mixture at a substantially lower speed and still get the 400G force that these machines generate.

bob

[lerman]

Why not six buckets of equal weight? Of course, there is the issue of having to measure the components out multiple times, and then combine them.

Ken

[rowbare]

Why not six buckets of equal weight? Of course, there is the issue of having to measure the components out multiple times, and then combine them.

Ken

That might not be all that difficult. Put appropriate amounts of resin and hardener in each bucket, spin up the machine for a minute or two to mix it up, then dump in your aggregates. It might not even be necessary to premix the aggregates -- guessing here...

[bloefeld]

Centrifuges are designed to stratify, not to homogenize. The machine will mix materials but for the most part it will work on small quantities of micro or nano particles that are difficult to disperse in epoxy solutions because they have high surface energies relative to the surface tension of the epoxy.

If your intention is to mix high ratio aggregates, this machine will simply sling all the heavy stuff to the bottom of your container and stratify everything else out by mass.

The same principle of this machine is used in medical labs to stratify and de-gas plasma.

Think more along the line of a paint mixer at your local Home Despot.

However I think that a better approach is to create an emulsion of the aggregate in both your resin and curative, de-gas with vacuum and then combine, mix, cast and apply another vacuum.

I think there is some underlaying confusion about the viscosity of a resin system and its ability to wet-out materials and adhere to them.

Adhesion is achieved by having (as a handy rule of thumb) a difference of at least 10 dynes/cm2 between the surface energy of the solids and the surface tension of the liquid. Epoxy is about 42 dynes, so the particles have to 32 dynes to spontaneously wet-out. I can get wet-out with resins that are 200,000 to 400,000 centipoise with no difficulty. Ya just gotta squish them harder.

This means that for the gravel you are mixing you will need a silane coupling agent applied to it and cured prior to trying to adding the epoxy. The viscosity of the resin is nearly irrelevant if the surface energy issues are dealt with.

Without spontaneous wet-out, you cannot create a composite mass. I believe at this stage that the best you can achieve is a cohesive mass of basically poorly adhered to particles suspended in cured epoxy. The compressive, flexural, tensile, and modulus properties will be relatively lower as a result.

I recommend the use of zero VOC epoxy systems and either functional (chemically functional to allow cross-linking to available carbonyl, hydroxyl and other organic groups) particles or high-aspect ratio particles such as wolostanite.

The addition of small amounts of ceramic whiskers, nano-clays (stupidly expensive) or products such as Inhance TiC particles with short and long strand Fiberglas filaments are more likely to get the mass wanted to decrease harmonics and the much higher levels of physical properties that are desirable.

If I were building a machine I would start first at seeing which parts I could make using honeycomb and Fiberglas composite sandwich panels and those that need to be casted.

Finally I would design it so that the differential thermal expansion of the metal linear devices are left free to float, or entirely bonded to the composite components. Done properly, the metals should constrain the thermal expansion of the composites down to the level of the surface interface a dozen or so molecules down.

Just some random thoughts that I thought may add to the discussion.

Cheers,

Bloefeld

[jhudler]

If this were strictly a centrifuge, I would agree.
However, if you examine the pat app in an earlier post, you will see that it rotates the mixing chamber which is at an angle (45deg?). This is how it mixes.

I've experimented with several methods of mixing EG, and short of a cement mixer... this is probably this best method I've seen yet.
As for vacuum, the pro's rarely use it and then only to handle unique molding applications. They mount the mold on large vibratory compaction tables (see http://www.knauer.de/index.php?id=114&L=2).

[bloefeld]

Hi;

Yes I understood it to be an orbital mixer. Not the point really. If you want to mix micro or nano particles into your solution this is a great way to go.

On the topic of vacuum and what the 'pro's' use; I do this for a living. I have made a wide array of robotic devices from all sorts of materials. I have also designed several casting systems for urethane. I do not cast anything until I have drawn a vacuum on it. There is simply no better way to avoid voids (ouch bad sentence).

However I agree with you that the addition of a vibratory table with the vacuum would be great in this application.

Below is a product data sheet link to a material that is in the tool-box of most maintenance people.

Belzona, take a look at their ceramic material

http://www.belzona.com/prod1k.aspx

And Novocoat, which makes an infinitely superior product.

http://www.novocoat.com/EN/_literatu...eet_ec_310.pdf

These are both epoxy systems that have huge amounts of solid materials held in suspension. In the case of the Novocoat product, I know exactly what those materials are. Obviously they are proprietary, but in principle they meet the requirements I outlined in my earlier post.

The issue in making a composite product is the ability of the adhesive component to bond in a preferably polar manner to the solid materials. This results in a matrix where the strong solid materials are held together by the relatively weaker thermo-set resin.

While it may be true that an epoxy composite cast base has worked to some degree in the past. It is not necessarily the best method of making such a base.

One can use a true composite to make the base, make it much stronger, and much lighter than the faux concrete attempted here.

If you go to the Novocoat site, you will find a product called 1100. It is one of the world's lowest surface tension epoxies. I have mixed it with sand, gravel, aluminium oxide, silicone dioxide, wolastanite, long-strand and short strand fibreglass, and Inhance particles and made a literally bullet proof plate with it.

From memory a gallon of the 1100 held about 10 gallons of the above junk together very well. If I were doing it again, I would use the Novocoat 3000 in knit Fiberglas (about 12 oz per square yard 0/90)and hand lay-up into the mold. As this material cured to tacky (like scotch tape) I would add my mixed solids until the mold was full, draw a vacuum and then mix in the 1100 using the vacuum as the means to infuse the materials.

I predict an incredibly strong matrix with great density. As I get time, I will put an experiment together and share the results with the forum.

Cheers,

Bloefeld