[Zumba]

Hey dudes,

I did a cure under vacuum a couple days ago and the foam was completely eliminated. The epoxy I have, West Systems with fast hardener, takes 2 hrs 30min to cure before I can peel away the cup. The mix was under 20inHg vacuum (there was a leak in the chamber) for 15 min. There were still traces of air bubbles near the bottom of the mix, but overall air pockets was reduced dramatically. I'm going to fix the leak, put it under 28inHg of vacuum for the entire duration of the cure and see what happens. I might build a 60Hz vibrating table as well... we'll see.

For deeper mixes (more than 2"), vibration is extremely important I think. The key is not so much to compact the aggreagate but to get those air bubbles moving up and out of the mix.

I don't really understand why mechanical pressing is necessary. Liquids and solids are not compressible. That means that after all the air pockets are gone (bubbles vacuumed out), the mix has achieved maximum compactness.

Sandi, nice experiments with the quartz bricks. I'm curious though as to why you got such a rough texture. Perhaps thin epoxy causes this problem?

The blue and red blocks I made were done with sand from Home Depot... it's much coarser than beach sand, so it's not like I used a very fine aggregate. The mix was nowhere near liquid either.... the "pour" involved scooping it from one cup to another with a plastic spoon. However, my blocks are as a smooth as a baby's fat ass (except for the top face, exposed to air).

[Zumba]

By the way... are you guys SURE that the necessary frequency is 4000Hz for vibratory compaction? Maybe the guy who wrote the article confused "Hz" with "cycles per minute".

A 4000Hz audio signal is very high pitched. It's somewhere between a B and C note at the very top of an 88 key piano. That kind of frequency with the necessary power to vibrate a several thousand pound composite mix is unrealistic.

Besides, I'm looking at industrial vibrators (ok, pour on the jokes) and the available RPMs are from 900 to 3600. I'm not sure exactly how the RPM relates to the vibration frequency, but my plan was to simply hook up my spare 5hp 3600RPM motors, bolt them to the table, and bolt on eccentric disks to the rotors. 3600RPM = 60Hz. Unless harmonics come into play....

[LeeWay]

Why not just attach something like a random orbital sander or even a palm sander to the form?
Seems to me that would do some vibrating.

[Zumba]

Using an eccetric disc on a motor, 4000Hz would require 240,000 RPM.

What's going on here?

[Zumba]

Why not just attach something like a random orbital sander or even a palm sander to the form?
Seems to me that would do some vibrating.

That would work depending on size of the form (small). A 5hp induction motor probably has 20-30 times the power of even a half sheet sander.

I'm not sure what amplitude of the vibration is necessary.... that'll rely on experimentation because it's probably a trade secret.

You can't really change the amplitude on a sander, but you can with motor + eccentric disk. More eccentric = higher amplitude. Adjustments would be similar to that of a Criterion boring head.

Who'd a thunk.... all this effort necessary to obtain vibration, in order to process a material used primarily for its vibrating damping effect. Kinda like "gotta spend money to make money"...

[LeeWay]

I don't know. I have a Ridgid 6" ROS with variable speed.
I find it very difficult to hold it with one hand at full speed.
I was only suggesting it for smaller pours. It would most likely need testing. I know with standard concrete, too much vibration is a bad thing. It can separate the mix, which isn't good.
I have used the cylinder type vibrators when pouring some walls. Some were gas powered and others were electric motor powered.
All used a flex shaft and the eccentrics were in the tip of the wand. If you weren't careful, you could get the wand stuck in there from too much separation and the aggregate would compact around it.

[brunog]

Zumba,
I believe you are right about the 60 Hz. Another important aspect is that the vibration must be vertical (up and down motion) to the mold, i read this on the German site quoted at the start of this thread (i believe it's post #30).

Best regards

Bruno

[romihs]

Sandi, nice experiments with the quartz bricks. I'm curious though as to why you got such a rough texture. Perhaps thin epoxy causes this problem?

Zumba,

Probably due to a combination of wrong aggregate sizes/quantities, poor compacting and the low epoxy to quartz ratio. I need to change the aggregate quantity ratios a bit and see what the difference will be.

Regards

Sandi

[pupa]

I'm not sure what amplitude of the vibration is necessary.... that'll rely on experimentation because it's probably a trade secret. .

200-305 Hz seems to be the concrete norm. That depending on drive mechanism used gives 12000 to 21000 VPM (Vibrations per minute) with simple rotary devices. In one of the articles I posted the frequency and amplitude is both important depending on aggregate and slump of mix. A binder and "flow" contributors can be added which should help settling.

[lgalla]

We should clear up the vibration frequency.
60Hz is 60 cycles per secondX60sec=3600vibrations per minute.This is the VPM of some concrete vibrators.
Larry

[pupa]

Thanks Martin, I enjoyed that post.

I think we're pretty close here.. We may need to rework the formula a bit and raise the epoxy to 20% but we're close. Zumba's results were pretty good and he used like 25%..

We still have to use reinforcements so what's the difference..

Larry, could you comment on that?

Strength read the document with test data in post 737. 12-14% seems to be the sweet spot for max strength http://www.cnczone.com/forums/showpo...&postcount=737

[pupa]

We should clear up the vibration frequency.
60Hz is 60 cycles per secondX60sec=3600vibrations per minute.This is the VPM of some concrete vibrators.
Larry

Thats is for some units. In the info I found and many data I read they refer to the 200-350 HZ units. I think as stated anyone in the KHZ range is rather refering to the VPM ie the 4000HZ is an error IMHO ??

[walter]

I am not sure if you have already determined that only specific epoxies are suitable for your matrix, but I have worked with structural slow epoxies before that have almost the same viscosity and surface tension as water.

That is a significant piece of information. Maybe we should look into that?

Zumba,
the 4000Hz number was taken from a Quartz countertop patent application. They're using some unique process that involves $25mil worth of machinery- we'll have to develop our own process.

I had to dig into that to get the entire picture...
Your and Sandi's results were pretty good!

[pupa]

Here is another article of a casting a large base, not a lot of detail but at least some principles are clear.

http://moglice.com/newsite/pages/newmachine.html

[pupa]

Zumba,

Probably due to a combination of wrong aggregate sizes/quantities, poor compacting and the low epoxy to quartz ratio. I need to change the aggregate quantity ratios a bit and see what the difference will be.

Regards

Sandi

Sandi just read through the PDF in post 737. They found 12-14 % the sweet spot for max strenth.

These guys use 5% ?

CHICAGO--Cincinnati Milacron Inc. has introduced a proprietary epoxy and granite composite for machine bases and is using the material for the base of the company's Model AE centerless grinding machines.

Paul Hollingsworth, sales project engineer, said one of the advantages of the bases, which are 95 percent granite and 5 percent epoxy, is that they reduce machine vibration. The product was exhibited at the recent International Machine Tool Show.

The epoxy-granite base, Hollingsworth said, has six times the dampening effect of cast iron, the material of which most machine bases are made. And with the increased dampening of vibration, he said, the machine can produce a much better part finish.

In addition, the epoxy-granite base has improved thermal characteristics, the official said. Metal bases expand and contract with changing temperature while epoxy-granite has a very slow rate of growth. With a symetrical base design, the thermal growth occurs in a controlled direction.

An average machine base uses between about 4,000 and 5,000 pounds of cast iron, Mark Kilmer, sales engineer at the Cincinnati-based company, estimated. Hollingsworth said that the cost of the epoxy-granite base is about the same as the cost of cast iron but the manufacturing lead time is shorter.

[lgalla]

Some very thin epoxies contain reactive dilutents,which affect the strength and make it a hazardous material for shipping and generally slow the cure.It also smells bad.
Larry

[walter]

Strength read the document with test data in post 737. 12-14% seems to be the sweet spot for max strength http://www.cnczone.com/forums/showpo...&postcount=737

Thanks, I appreciate the articles you posted. A lot of good info there.

I'm willing to sacrifice a little bit of strength for the sake of practicality (dry mix is difficult to handle). Here's why..

Any large frame, part of the frame or any type of gantry will need steel reinforcements, period. E/Q won't stand on it's own, 10% or not.

It may be easier to simplify (liquify?) the mix and concentrate on reinforcements. I'm just thinking out loud..

[Eson]

I belive that less epoxy means less vibrations since the vibrations rather go through the epoxy then the quartz. So if you have more epoxy you get more contact surface for vibrations to travel through.

[pupa]

Pleasure is mine, here is some more of what we already know. http://www.findarticles.com/p/articl...v93/ai_3647171 Interesting info here is the reference to product manufacturer names. Ciba-Geigy (or even Dow) seems to be someone to contact, a product expert/engineer maybe, for advise. I am sure the company's that now cast Epoxy granite bases got their info and advise from them. Ciba-Geigy have products made for the exact application I just cannot get confirmation which one to use on the net. Just to many product choices from them and I am to far away to contact their applications experts. In my view we have to deal with the Chemical manufacturing and supply companies direct to get expert advise and find solution's Why must commercial companies have monopoly on the information. Thus IMHO Cut out the local hardware supplier initially as they know as much as us anyway.

[Zumba]

Walter, I think you're spot on about needing reinforcements.

E/G and E/Q (I guess they're pretty much the same thing) have excellent rigidity at 5,000ksi (1/2 that of Aluminum, 1/6t that of steel).

But tensile strength is rather miserable at 2200psi according to the "Anocast" documents that were posted in this thread awhile back. Compare this to the yield stengths of carbon steel and aluminum - 36,000 and 60,000 psi, respectively.

I believe the 2200psi number for E/Q is ultimate strength. That stuff won't bend, so there is no yield strength number available. Those numbers for steel and aluminum are yield strength numbers. Ultimate strength is even higher, but since a bent piece of metal is useless, ultimate strength doesn't really matter in this case.

So yes, if you're not going to fill a steel tube, you should probably add rebar. One benefit of rebar is that it's so damn cheap, but I'd be cautious as to the mystery metals that might be in there. Perhaps it may be wiser to use 1018 rounds? Even those are pretty cheap from Enco with free shipping.