[crr]

Well, you take some time off for the holidays and look what happens!!
I have not fallen off of the map, but was taking some much needed time witht he family.
It is really nice to see the interest though.

Cameron-
Impressive stuff! After talking with you previously, I have changed my mold design, and will be re-cutting it soon.
I will be posting so that I can get feedback on this one as I did the first one.
This has inspired me to get cracking.

-Chris

[ckelloug]

As long as a combination of forward looking predictions on epoxy and the danger of using models to predict performance where you don't personally have data don't get us, it seems exciting. Looking at the Agsco aluminum oxide however, the standard size range is only 3 orders of magnitude so the optimum mix is likely to have densities only in the 80% range unless I find some bigger and smaller particles.

--Cameron

[romihs]

Cameron,

Regarding the size range of available aggregates: What if you were to sieve the aggregate yourself into (more than 3) size ranges?

Really good work on the epoxy there, thanks for all the effort! :cheers:

Regards

Sandi

[greybeard]

Hi Sandi.
Sieving quartz sand was my own approach to getting six fractions, but I was surprised at how narrow the size distribution was in the "wild" sources I was trying.
The whole area around us is ancient sand dunes and I assumed there would be quite a spread of sizes.
It turns out that the geological processes that produced the dunes made about 90% of one particle range with a marked tail-off on both sides.
Not the uniform ie random sizes that I expected.
Regards
John

[romihs]

Hi John,

Wow... I was not expecting that... I was also under the assumption that we should not have a problem getting quartz..

Well, the supplier that I have sells 3 or 4 sizes of sand, which I was thinking of splitting further into more accurate size grades.. Maybe I should reconsider before paying for expensive sieves.

How about a supplier of nano particles, or resins with nano particles, have you found anyone supplying this in Europe?

Regards

Sandi

[ckelloug]

Hi Sandi,

Here's what I know:

For nano-particles, it looks like nanoresins whose headquarters in in Germany are the go-to guys. Their U.S. branch seemed cooperative when I spoke to them a year or so ago but I haven't requested samples or used the material yet. A $4000 ultrasonic mixer is required to mix your own nanoparticles effectively enough to get the effect so mixing your own isn't exactly practical for ad-hoc work.

Nanoparticles are expensive and may not be warranted for non-critical parts but their use may make it easier to put together mixtures that are very rigid using thin epoxy and less attention to detail. For example with quartz, it looks like you could get the filler content down to 83% from 88% to get the modulus of the commercial stuff using nanoresins material.

There are many manufacturers of non-nano abrasives and particles so unless one really has a need to sieve it himself, I don't think it's really cost effective to sieve your own unless you can locate the sieves and the base material for scrap prices. Think Grinding media and blast media. Abrasives are graded tightly for sandpaper and made accurately in industrial quantities.

I suppose I am going to have to start measuring particle packing densities as the ultimately achievable density depends on it and I've been using numbers from the books that are only plausible guesses.

The packing densities are also likely to differ between quartz and alumina. Quartz is cheaper but if all the cards are right, alumina could make a composite that has a modulus almost that of steel without needing a foundry if you can get mostly spherical particles and figure out a way to process it.

The number of fractions required is a function of the smallest and largest sized particles. If an OOM is the number of (O)rders(O)of (M)agnitude difference between the biggest and smallest particles, the number of fractions predicted by the model as optimum is:

1 OOM=3 fractions
2 OOM=5 fractions
3 OOM=7 fractions
4 OOM=10 fractions

To achieve the 4.5e6psi elastic modulus of a commercial formula with 440,000psi epoxy , they key is getting the particle packing density up to 88% with quartz. With alumina you still have to get the particle packing density to about 80%. You can see from the graphs I've posted that the response is very non-linear and the 5% packing density improvement between 88% and 93% makes for a 20% improvement in the modulus with quartz and a 60% improvement with alumina.

The mixtures that are almost as stiff as steel that I've mentioned can probably only be achieved with high pressure vacuum infusion (if at all) and I haven't tried it yet.

Heres a model run for alumina using the 3 order of magnitude size distribution for the smallest and biggest obtainable from a certain supplier (agsco). Alumina abrasives can be had in almost any size desired and each of these sizes is matched closely by one in the abrasives suppliers standards. Beta is assumed to be .66 for angular particles. It is about .71 for spherical particles.

The fields are fraction number, size in microns, volume percent, and cumulative volume percent.

Phi=0.880596 Assuming Beta=0.66

6 3.000000 0.066077 0.066077
5 10.241966 0.069167 0.135243
4 34.965953 0.085642 0.220885
3 119.373364 0.111616 0.332501
2 407.539296 0.146948 0.479449
1 1391.334488 0.202410 0.681859
0 4750.000000 0.318141 1.000000

As for epoxy, The Hexion 556 is available to you Europeans and sounds like a much smaller hassle than the epoxy research I've been doing on Hexion 813 and or the constituents of it.

I also have to say that Hexion 813 with Roach's suggestion of IPDA cured at 85C looks decent though It might give better numbers to use the same base epoxy but less of the cresyl glycidyl ether in Hexion 813.

Regards all,

Cameron

[altaic]

Hello all, I've been sort of absorbing bits and pieces of this thread for a few weeks. So much information! Most of you guys are in a different league from me when it comes to composites, so I'll try not to make an ass of myself.

Anyhow, I have a couple findings and a couple questions...

First off, AGSCO and the Cary Company have both been very pleasant to deal with. It's always nice when professionals are friendly and good at communicating with laymen.

Now, the last I read about vibrating moulds in this thread (perhaps a hundred pages ago, so I may have missed something more recent), people had asserted that E/G companies use >= 4kHz vibration, but actually ~100Hz was fine. I'd think that such a low frequency would be less effective for small particle distribution, so I'd like to test out higher frequencies. McMaster Carr has a pneumatic turbine vibrator capable of moving 450lbs @ 683Hz (yep, that's 41000RPM), which uses a mere 3cfm @ 60psi. It's part #5794K22, and weighs in at $185.57. I'd love to use electric motors instead (my air compressor drives me nuts), but they are usually pretty expensive or max out at around 100Hz.

Now for some questions... Do you guys know of a distributor for Hexion in the US that doesn't require a business account? An online distributor would be even better.

Similarly, I understand that a lot of people like US Composites resins because of their reasonable prices; how do they compare to Hexion and Reichhold? Is there one that's particularly suitable for E/G? I'm especially interested in very low shrinkage for precision casting.

Finally, what can I expect of E/G machinability? Is there anything I should watch out for, any especially suitable cutter types, etc.? I'm guessing the quartz and alumina will be very hard, necessitating grinding or some such... I would be thrilled to learn that normal carbide endmills and facemills do the trick

Anyway, this thread has been and continues to be a great read. Thanks to everyone for their insightful and informative contributions.

Cheers,
Will

[ckelloug]

Welcome Will,

A lot of us have worked on this for a long time. I've spent a lot of time studying the parts but I'm only nearing the point of pouring my first E/G sample after much research on aggregate and epoxy characteristics. <U>The most critical aspect of E/G is getting the aggregate distribution right</U>. I've been trying to see what is possible and come up with a formula which behaves well and predictably.

Having made no samples with aggregate yet, I can't comment on the vibration aspects although I will use a tiny electric bin vibrator from FMC Syntron on my sample mold when I get to that point since one came as part of a vacuum chamber assembly I got on Ebay. Solutions for real parts are more difficult.

I have been working with Hexion samples so far during my formulation work and haven't figured out the purchasing aspect yet. If you wait long enough, I'll probably offer the epoxy formulation I settle on for sale after posting the formula here since I'd like to produce parts and getting a hold of all the ingredients (especially obscure additives) can be a touch on the tough side. I've got a 2 year head start on this aspect from working on it a bit each day.

U.S. Composites from my conversations with them is a repackager of Reichhold resins and hardeners. They confirmed for me that their thin epoxy and slow hardener are reichhold 37-127/37-606. So far, from my work with Hexion 813, I'd say that Reichhold 37-137 (the Reichhold equivalent) is likely to be more appropriate although I think that a non-standard mixture with the same components but less cresyl glycidyl ether would be a better fit and I aim to try it soon. I have no idea how hard it is to get 37-137 although to buy it from the Reichhold distributor will mean buying 55 gallon drums. U.S. composites stocks a relatively small number of resins and hardeners and while it isn't proven, I think they may be the wrong ones for E/G. For laughs however, I should try 37-127 with some of the better hardeners I have in stock so see how it goes.

For machinability, I'd suggest that diamond grinding is the right and likely only approach unless all you are trying to do is drill. Wear will probably get you with carbide milling tools. You want to cast things to shape with accurate molds in E/G as machining it is apt not to go well. If you want something that's machinable and ceramic, I think something like Corning Macor would be better.

In my epoxy-only tests, I have been able to see the impressions of a fingerprint and a scratch in the mold (the rest of which is polished to 3000grit) in the final epoxy sample so if you make the mold right, you should be able to reproduce details so small that you don't want to reproduce them. E/G may smooth a few of those bad details but the intrinsic accuracy should be about the same. It's the kind of material that you want to make right in the mold because it goes down hill from there.

--Cameron

[BillTodd]

It turns out that the geological processes that produced the dunes made about 90% of one particle range with a marked tail-off on both sides

.
Fasinating. I wonder if tide and time has already done the sifting (i.e. has sorted the particals already), or whether there is some natural mechanism that has produced a consistant fracture size in the rock

[brunog]

Cameron,
As stupid as it may sound:

50ml play sand + 25ml filtration sand + 25ml aquarium pebbles = 84ml aggregate

It makes a very stable dry mix, no apparent seggregation regardless how I shake it by hand, however it needs a little bit of tweeking' I have about 3ml of pebbles that stay uncovered on the top.

Next step revise my mix to:
50ml play sand + 30ml filtration sand + 20ml aquarium pebbles and check total volume and seggregation of dry mix.

Best regards

Bruno

[altaic]

Hi Cameron, thanks for the quick response. I'm definitely in the beginning stages of understanding E/G, but I hope to be able to offer some results eventually. I'm still pretty far from being able to produce parts-- no vacuum generator/chamber or vacuum mold, and no epoxy (kind of important).

Plus, there are a few things I'm ruminating on... I think once I have some very-low viscosity epoxy, I'll have a better idea of how to cast things to shape as you said. It's too bad about the machinability, but there are always tradeoffs; surface hardness and durability are important features of E/G to me.

Edit: I wish CNCZone had an integrated wiki. It would be awesome to compile all this information in a nicely formatted page.

[ckelloug]

Bruno,

Very Interesting Result! Can you describe your measurement procedure? If your aggregate formula consistently holds 88%, I think we're done with the general formula. Plugging that number into the chart I made from Kinloch's book back in April, the modulus model predicts that we will have duplicated Accures/Zanite performance. See <A href=http://www.cnczone.com/forums/showpost.php?p=444339&postcount=3119>post 3119</A>. In practice, some silane may be needed to actually achieve the numbers as Kinloch's book said that you can't achieve the predicted strength or modulus without the complete bond ensured by silanes or titanates.

Anyway Bruno, if you happen to have grading curves for your mixture, I'd love to model it. If you actually have some, I'd be interested in making a sample and testing it. I worry a bit that random sand may also not have quite as good a modulus as pure quartz but it's probably not as critical as I worry about.

The difference between now and then is that the epoxy we had was not quite that good and maybe also that the obsessiveness on my part for optimal declined yielding the recognition of the fact that it should be possible to have it work pretty well with 88% packing density and the epoxy we have. I've also noticed an interesting phenomenon in the model: Mixing up most stuff that isn't blatantly badly behaved tends to yield 80-85% packing density under the model's vibrated under pressure criterion.

The difference between making epoxy-dog$hit with a modulus of wet-noodle and Epoxy Granite like Zanite or Accures at 4.5 million psi is only a slight variation in packing density between say between 85% and 88%. Making a 92% mixture, even in the models, is a female canine and locating the spherical materials for it is an entirely new challenge.

I'm pretty anal about getting the numbers good and consistent because a formula that only works half the time or makes low modulus numbers like the initial samples jhudler and greybeard were kind enough to send will generate a bad reputation. (With the amount that the commercial guys tout their material grading; I suspect that inconsistent performance when this was a new technology was probably why there aren't many suppliers in the market today).

Using the modulus chart from post 3119 with the 440,000psi epoxy you get by using Hexion 813 and IPDA cured at 85C, that duplicates the performance of zanite and accures. The 420,000 you get from Hexion 813/Jeffamine T403 cured on the cure schedule they suggest in the datasheet also comes out very close. The latter also is also quite tough and likely meets the criteria that lgalla had that if you drive a forklift into the casting it breaks the forklift and not the casting. The former behaves somewhat more like glass although there is still probably no way to break a casting in practice. The unfortunate part is that IPDA is nasty enough according to the MSDS that isn't something you want near your house, and Jeffamines, while nicer, still are DOT and OSHA hazardous materials.

Looking forward, Using a DER331 type epoxy diluted with cresyl glycidyl Ether dilutant to the point of the modulus anomaly at 15 pph and DETDA as hardener, as Preston suggested back in April it should be possible to to make a formula that's a drop in replacement for Zanite using no Hazmat stuff. Throw in some titanates and silanes to keep adhesion up (and maybe a bit of cobalt acetyl acetonate for good measure) and I think we've got a contender.

Thanks Bruno! If you could kindly post the technique used to make your measurements and any grading curves or datasheets for the material you have, that would also be appreciated.

Regards all,

Cameron

[altaic]

Hi Bruno, did you vibrate (by tapping by hand or with a machine) the components before and after mixing? Just thinking there might be some error due to loose vs. tight packed.

[brunog]

Cameron,
Actually the result is a little better 84%, I just edited the previous post.

The method I used was very simple:
I used a 250ml graduated cylinder and measure each product individually and did the dry mix in a separate container, then placed the mix back in the graduated cylinder. After approx 2 minutes of shaking and tapping, I took a reading of 84ml (I had mistaken the 2ml graduations for 1ml)

Note: I also did some minor tapping when measuring each material separately

I have no specs for the aggregate and sand used, however I evaluated the grain size as follows:

Play sand is the equivalent size of fractions #2 to #6 in your post 3447

Filter sand is an average fraction #1

Aquarium rocks are average #0

The material was either purchased at a local hardware store (both sand material) or at a local quarry.

I need to make a few other tests using a different mix as per post 3451, I want to make about ten separate mixes and use an orbital sander to vibrate the mix to evaluate aggregate seggregation of the mix.

Will,
I hope the post also answers your question.

I will make photos of the material as soon as I can reach my stock in the shed, we had about a foot of snow yesterday, I'll have to to a bit of shovelling to reach it.

Best regards

Bruno

[ckelloug]

Bruno,

If I understand your methodology correctly, you are calculating the volume that an initial 100 ml of loose pack bulk volume mixture compresses to. This isn't how packing density is defined in the literature so you and I are measuring different things when we say packing density.

I believe the more commonly accepted definition, at least in the books I read, comes from multiplying the specific volume for the material by the mass of the aggregate in the sample to get an absolute volume of the solid portion. The packing density is this absolute volume divided by the pi*r^2*h volume that a cylindrical slug of this aggregate occupies in a cylinder of radius r after compaction.

This gives you a ratio between the absolute volume and the packed bulk volume which lets you see how the mixture compacted and is also the precise volume fraction of solid per unit of empty space. I've come to live with this definition and understand it but I would not have thought it up.

Unfortunately, I can't provide any insight into the meaning of what you measured because the models I've been working on use a different definition of packing density than you did and I am unable to derive the packing density, as it is commonly defined, from your data.

Regards,

Cameron

[altaic]

I did some testing today...

I first mixed according to the recipe in post #3422. Vibrating this mix dry at low frequencies caused it to quickly separate into layers, largest particles atop. I tried higher frequency vibration, and it seems that low amplitude works pretty well for mixing and packing, although I could still mechanically pack it a bit more by tamping it down. Then I tried mixing in 12% water by volume (12% of totaled individual component volume), since this will tell me what ratio of epoxy to use with a similar mix. Surprisingly, a little water pooled at the top, so I poured it off and measured it. It was about 1/4 of the total water I'd poured in, so 9% or 10% epoxy should do it. Not bad!

So, I did a test using epoxy... The stuff I used was Mas Epoxies Low Viscosity Resin and Slow Hardener, 2:1 mixture. Not ideal, but I thought it'd make for a good test (we shall see tomorrow). I did discover that its viscosity, at 550-650cps, is simply too high when dealing with such high levels of fill. Vibrating helped liquify it so I could mix it more, but it was a pain. I definitely would use an ultra-low viscosity epoxy for actual parts, perhaps one intended for infusion. Anyhow, I added in the extra 2% epoxy for a total of 12% to help out with the stiff mix. The mix was starting to set up by the time I finished vibrating and degassing with a torch.

I also noticed that the bottom of the water mix contained more large particles, and the top almost none. The bottom was very dense, with small particles well packed between the large. This leads me to believe I may want to increase the quantity of large particles, perhaps 3 parts #6 alumina, 2 parts #4 quarts, 2 parts #2 quarts, 2 parts #2/0 quartz, 2 parts G-800 Microspheres, and 2 parts G-200 Microspheres.

Finally, the pneumatic vibrator I'd posted is not as powerful as I'd imagined. Also, as expected, the rotary vibration does interesting things involving stirring and moving material to one side or another (not ideal). I think I need to bolt it to a mold for it to really work well. Anyway, it may be good for small batches, but there's no way it'd do a 200 lb. machine base, regardless of its 450 lb. rating.

Cheers,
Will

[romihs]

Will,

The people on the German forum 'Peters CNC-Ecke' "discovered" that the EQ should be vibrated in a linear manner and not in a circular manner. They built a vibrating table that was pivoted at one end and had a spring on the other end, with a vibrator bolted to the bottom of the table. This allowed the table top to move in one direction only (almost linear).

We also discussed the issue of vibration a long way back in this thread (#2542), but check this out. Jhudler was talking of building a similar table to this, but I don't know what happened to the build...

I also believe that one must weigh down the the top of the EQ in the mold when vibrating it so that it is compacted better. This could also be performed with a light vacuum.

I am one of those guys who believes that vacuum is not of much use when molding EQ. I also believe that one can not infuse epoxy successfully into the aggregate with a vacuum. For that reason I believe vibrating is the only way to go with this material.
But I have ZERO experience, so I might be wrong....

Jhudler, if you still visit this thread, and if you see this, did you get around to building that table?


Regards

Sandi

[brunog]

Will,
Sandi is right the vibration should be vertical and good mechanical bond must be made from the vibrator to the mold or preferrably the vibration table. Also plan on some adjustability in the height (as per 'Peters CNC-Ecke', there might be some photos in this thread in the earlier posts). Last but not least, direction of rotation is also an important aspect that must not be neglected. As a general rule, when the base is in a vertical position, the rotation should be in a downward direction.

I hope this information is usefull.

best regards,

Bruno

[altaic]

I had read those posts regarding linear (or constrained) vibration, however I wanted to test out the rotary vibration. The mixing effect may be good for initial particle dispersion... It's hard to say. I do, however, plan of building a steel table for linear vibration, with rare earth magnets to hold molds.

Interesting thought about weighing the top of the E/G down, Sandi. I'd been thinking about how to do an enclosed cast, and it occurred to me that one could make a lid that fits inside the top of the mold, with a small vacuum port in the center. Line the lid with the breather and perforated peel-ply stuff used for vacuum bagging fiber lay-ups, then vacuum the lid down, compacting, degassing, and removing excess epoxy all at once.

Note that I'm not talking about vacuum infusion; the epoxy and aggregate are already mixed and wetted at the point of vacuuming/compacting and vibrating. I do however think an infusion epoxy (i.e. ultra-low viscosity, perhaps 300cps or less) would be very beneficial for air bubble removal, particle dispersion, prevention of small particle clumping, etc.

[romihs]

Will,

I did not think that you were planning on infusing the epoxy into the aggregate when you mentioned the low viscosity epoxy, I was just voicing my opinion and understanding of EQ properties.... no problem. :rainfro:

I have been giving vibration compacting a lot of thought. I believe that the lower parts of the EQ in the mold will compact together quite well due to the mass of the material above it, but as you get closer to the top of the mold, the EQ will not compact together as well. That is why I would devise some way of applying pressure to the top part of the mold so it can also compact optimally. This would only be required while vibro-compacting the EQ...

When I experimented with this a long while back, I noticed that vibration compacting is the only way to get this stuff to compact at all... Ok, I did not do any serious experimenting, nor did I use vacuum, but I did get a feeling for the material and how it behaves..

Regards

Sandi