[greybeard]

Thanks Walter.
I've got an old lab balance, much used over the last 40 years of experimenting, so I'll be ok on that score.

Years ago, when I was producing polyurethane picture frames, I used a mixer blade of curious design, my own, as it was imperative that I kept the air entrapment to a minimum. With a mixing time of 25 seconds before it started to foam, I didn't have time to de-air it.
The blade was made from an old clock gear about 1.5" in diameter, still on the original shaft, with two small rectangular extensions soldered below the two arms that held the toothed rim.
The wheel was about 80 - 90% of the diameter of the bottom of the plastic mixing cup, and the effect was that the resin folded over the edge of the blade and down through the openings in it, before spinning out to the side of the cup.
The tricky bit was to lower the cup away as I turned off the power, so that the resin on the wheel spun off inside the cup, not over me.
So long as I kept my concentration, it always worked, and lasted the 10 years I was making the frames.

The resin was about 200 cps, so I shall use something similar for the epoxy, then a separate system for adding the aggregate.
we often see old kitchen mixers on the Sunday Markets we have here, so that will be added to the list.
I did wonder if a large magnetic stirrer might be another solution, but have my doubts.

John

[Zumba]

Walter, nice tests. Those two samples you recently posted do indeed look quite good.

Have you tried any vibration testing yet? I got a pneumatic vibrating unit a few weeks ago. Did some rudimentary tests on some small mixes but it didn't do much, sad to say. Still plenty of voids. Sides were slightly smoother, but that's about it. It was a small unit (150 lbs force, 20000 vpm).

[walter]

Zumba,

My experience is quite different. I think vibrocompaction works and I wouldn't even try without it. I don't use it now, but I'll be using it on my machine. I'm testing some other things at the moment and don't care about voids.

I've been using el cheapo Harbor Freight paint shaker that doesn't get above 2000vpm. For the actual pour, I'll be using this $40 HF item(s):



Keep in mind that my mixes are 16-25% epoxy and I'm using Zeeospheres (200micron ball bearings). The picture below shows Zeeospheres with very fine silica in 25% or more epoxy. Don't remember the exact figures. Pic #2 shows some of the stuff I intend to embed in my E/G gantry. The peanut butter really got me going

(the parts are just laying there- actual arrangement will be completely different)
_

[greybeard]

Cameron - are the de Larrard recipes by weight or volume?
Sorry to go on about this, but if the aggregate mix is of various materials, the differing densities will muck up the "by weight" recipe if the particle size distribution is the main criteria.

John

[ckelloug]

De Larrard's formulas are by volume. For the case of purchased aggregate with different sizes of the exact same material, weight or volume are the same. When you start adding things like zeospheres, you have to do it by volume as the densities are radically different.

Of course for shop purposes, one should still weight everything out as it's much more fault tolerant and then use the density to get volume.

[greybeard]

Thanks Cameron.
I'd reckoned on starting with a local bought crushed aggregate, analyzing the size distribution and making up any deficiencies with other materials.
One drawback with this idea is how to analyze the mix without an expensive set of sieves. The coarse fractions are not a problem, it's the sub 500 micron level that puzzles me.
I did think about using flotation, a method used by amateur telescope makers to grade abrasives down at the finest levels.

I'd like to stick with the idea of using the local aggregate mix if possible, so if anyone has any ideas on a way forward with the analysis/separation of small particles, please shout.

John

[Zumba]

Hey Walter, how deep would something like that penetrate?

I'm considering using one of those wand-type concrete vibrators.

[walter]

It might work, I'm not sure though so try it

[greybeard]

I've been looking for a supply of Zeospheres on this side of the pond, and so far zilch.
Lots of references to glass microspheres, various "sandblasting media", and other near misses, but I can't even find a 3M UK outlet other than "office supplies" type.

Somewhere I'm sure I saw a mention of zirconium silicate - is this what they are made of ?

Any suggestions/ alternatives ?

John

EDIT tracked down 3M UK -now awaiting email response, as the zeeospheres don't seem to feature on the UK site !

[ckelloug]

Hi all,

I just had a nice conversation with an apps engineer at Dow Corning. He recommended <B>Dow Corning Z6040 and Dow Corning Z6020</B> as good choices for coupling agents in our system.

Z6040 is an epoxy functional coupling agent while Dow Z6020 is an amine functional coupling agent. Since the U.S. Composites 635 Epoxy system has both functional groups the Dow Corning engineer said that either would work and that testing was the only way to determine if one was better. He also said that the Z6020 was more prone to the product discoloring in sunlight but a teaspoon of carbon black will nip that in the bud. Getting a sample from Dow Corning is as simple as clicking on the sample button on their web site. I've had good luck in the past getting samples from Dow Corning even without using my official work contact information though I did this time). I have a sample request in to them and hopefully will get some info and material back soon.

I posted a brief synopsis of what's going on on this thread over at BYK in their technical forum in hopes that they post some useful guidance. I haven't heard from them yet. I asked about BYK A500, A525, NanoBYK 3650, and BYK C8000. Our thread actually has the number 1 google reference to C8000! They also have point and click sample requests though I haven't tried yet since I am awaiting guidance from them.

I've got calls in to Reichhold and Huntsman Advanced materials for epoxy recommendations and will post more as I get more data.

Congrats to Walter on all of the good looking samples!!!

Take Care All,

Cameron

[lgalla]

John,try Lawrence Industries,Tamworth Staffordshire.They rep 3M and have all the cool stuff.
http://www.li-solutions.co.uk/product_range.html
Larry

[lgalla]

John,when buying 500 micron filler it is already sieved to 90% pass.
I have been looking at exposed concrete aggregates,planters,rubbish containers or garbage cans etc.
As far as I can see the packing looks good.Appears to be smooth rounded and oval aggregates.The larger sizes measure at 3/8",5/16"and1/4"and1/8"plus whatever fines.The packing looks very uniform and dense.
Larry

[ckelloug]

Seeing the round aggregate,

De Larrard's data shows that rounded aggregate packs better than crushed aggregate. Incidentally, he also shows that vibration with a weight applying constant pressure to the mix is twice as good at compacting a mixture as vibration alone. I think that's an endorsement for vacuum bagging the mold.

[Zumba]

What do you guys have in mind as far as order of operations? Vibrate the aggregate first before adding epoxy (for maximum fill)? Then vibrate again to make sure it fills the mold completely?

How about a vacuum? Vacuum while mixing and vacuuming again in the mold?

[greybeard]

Larry - thanks for the Lawrence link. I'll check that out.
Cameron - so d'L also goes for rounded. That will make life a bit easier as crushed stone isn't so common as rounded.
Zumba - I now plan with my spincasting to do the equivalent of that - spread a dry mix into the tube, then add the resin via a feed tube down the center at a slow spin speed. Once thats in, speed up to max revs to de-air, then slow down for the cure time.
So far I've just finished a small test rig using a 1.5" x 6" tube. Mounted in a lathe with a two speed drill for power, 900rpm + 2400rpm.
I'll just use a dried "all-in ballast" aggregate sieved to 1/8" for the tests.
Hopefully photos before the end of the week.

John

[ckelloug]

Hi all,

I just got off the phone with the apps engineer from Reichhold. He said the epoxy system that we're using: 37-127 with 37-606 is an excellent choice for this application. I talked to him about adding extra reactive dilutant to the system and he said that 10% more dilutant would be okay but that a couple percent increase hardener would be required. The increased dilutant would probably lower the maximum operating temperature of the sytem further from the approximately 160F point where the epoxy goes from glassy to amorphous.

He also said that the 37-606 hardener is well liked because it doesn't tend to cause amine blush although other hardeners tend to make for a higher glass transition temperature.

In short, this may be the first time in recorded history where cheapest we could find actually turned out to be a good engineering decision!

--Cameron

[walter]

Thank you Cameron. I appreciate your work!

[walter]

What do you guys have in mind as far as order of operations? Vibrate the aggregate first before adding epoxy (for maximum fill)? Then vibrate again to make sure it fills the mold completely?

I'm intrigued by this post. Not necessarily about the epoxy part, but about premixed aggregate part..

I think I'm starting to believe that separating aggregates is the surest way to NOT get a good mix (and distribution). Just a weird hunch..
-

[lgalla]

Walter,I have the same hunch on premixing the aggregates as far as the larger sizes.Don't know about the fines.The smooth pebbles look good at packing.Actually the pebble surfaces in concrete are broadcast on the wet concrete and tamped with a piece of wood.
Peanut butter sandwiches or epoxy.I have one everyday at lunch with silane coupling agent or jam to increase the flow or lower the viscosity.Milk or epoxy is necessary to wash or wet the peanut butter viscosity to flowability.
How about Epoxy sandwiches?Spread butter viscosity E/Qfines mix in the mold,place premixed smooth or pea gravel,tamp into the peanut butter and top off with the fines and epoxy.
Lets assume we had a perfect 10% mix looking like the picture I posted on exposed aggregate.The cured E/G will be very bumpy and if a smooth surface is required more epoxy is necessary to level,bringing us back to high epoxy ratios,at least on the surfaces.
BTW after mixing A&B pour a little in another cup and mix your usual batch.Brush on neet epoxy then pour the aggregate mix.This should help acheiving a better surface on th mold acting as a "gel coat".Al so if you get too thick a mix,it can be saved by adding the neet resin from the cup.
De Larryard

[ckelloug]

Larry,

You need the peanut-butter epoxy floppy disk I got for my parents back when people still used 3.5" floppies. Some wag took a butter knife and a floppy disk and put a dallop of pigmented epoxy that looked just like peanut butter on the knife and stuck it to the floopy disk. If you ever need to scare industrial hygiene folks or other neatniks, the epoxy-peanutbutter knife glued to something important looking takes the cake. It may also stick to your ribs. It looks like peanut butter fresh from the jar and gets 'em every time!

Regards,
Cameron