[Geof]

Geof,

Good comment regarding alkaline generally inhibiting corrosion in steel.

I also note that the concentrated KOH solution around my lab tends to do bad things to most everything it comes in contact with. . .

All I'm trying to say by "null out the deflection" is that you can reduce the strain to zero in the beam under static loading by adding a tension member and tension such that it creates an opposite deflection to that of the beam under gravity and cancels out the beam's own static deflection.

Yes concentrated Potassium Hydroxide will eat just about anything, you included. It is the region around 7.5 to 8.5 that corrosion of steel is minimal.

I thought ab bit more about your tensioning and realised you are also possibly dealing with a pseudo modulus because voids in the composite close up under compression. Tension will close these up so you will get a true modulus and of course you do get a combined one taking into account the two materials.

[ckelloug]

Geof's right about the alkalinity: Page 6-106 of Marks Standard Handbook for Mechanical Engineers, 9th edition says that ". . . an overbalance of hydroxyl ions (high pH) depresses electrochemical corrosion and may provide excellent protection even without film formation--as when caustic, ammonia, or amines are added to condensate or demineralized or completely softened water.

On the pseudo-modulus idea, Geof has an interesting thought about tensioning the material closing up cracks. I haven't personally considered the voids yet mainly because I and others are trying to come up with a reasonable way using either additives or vacuum to reduce the void content to near zero.

Completing the KOH anecdote, one of the few things that is nearly impervious to concentrated KOH is NI-200 Nickel which is pure annealed nickel.

I've been studying my reference materials on the acceptable tensile strain for cast iron. In some types of Ductile Cast Iron, the ultimate tensile strain is only 1% ! (Marks Handbook for Mechanical Engineers Ninth Edition Pg 6-50, right column, paragraph 3.) This is the same value as the 1% expansion given for Hydrocal B11 which means that it could easily fracture the unspecified low elongation iron from the cited reference. What is safe for a small engine block with a few pounds of material in small cavities and one alloy of cast iron might not be safe for something with a huge cavity in a different iron alloy.

Hydrocal B11 is probably not as big a danger as some of the higher expansion plasters but I would worry about it very much in a large cavity in a casting. I would definitely not fill my own Bridgeport column with it. For homebuilt machine tools with steel beams, the worst that is likely to happen is a very small deformation in the tool which will likely go unnoticed by most gantry router folks. In something with iron castings, I contend that one could fracture the casting or use up the strain margin such that further loads might cause the casting to fracture without warning.

While others may have insight that proves this case further one way or the other, I would think that filling an expensive cast iron .0001 inch precision metalworking tool with Hydrocal B11 is only marginally less of a bad idea than letting your water pipes freeze during the winter. I personally think the portland cement in the rubber bag suggested by Bamberg is much safer and likely to perform better at damping due to the non-linear spring/damping response of the rubber bag. E/G is more expensive but unlike Hydrocal B11 has no potential to damage the casting by expansion.

While Hydrocal B11 may be appropriate in some situations, Bamberg's concrete in a bag, and E/G are both preferable solutions. In short, Servo, it's an interesting suggestion for some applications but I wouldn't say it is a good general solution as a damping material for machine tools.

Switching topics, on the E/G front, I have an idea that it might be possible to make a cheap and effective vacuum chamber/ vacuum deairing epoxy mixer out of a decommissioned welding oxygen cylinder but I haven't done the math yet.

--Cameron

[the4thseal]

I am making some samples of e.g. that are working...I think. I was wondering if any of the people who are testing and posting would like to test some of my samples so that there would be continuity. I like the results that I am getting and would be glad to tell everyone what I have done if the samples turn out to be good.the reason for doing this is I think that we need some continuity so even if the process is flawed it is the same process. Thoughts?

[walter]

I was wondering if any of the people who are testing and posting would like to test some of my samples so that there would be continuity. I like the results that I am getting and would be glad to tell everyone what I have done if the samples turn out to be good.

Absolutely. Davo already offered his sample, I hope others join in and the process moves forward. My testing slowed to a crawl as I'm busy with some other stuff. I apologize.

More updates later today. I have to run to the post office and pickup the E/G core sample sent all the way from France! Courtesy of AkvaCNC
_

[the4thseal]

Could you post a dimension so that i can give you something that is similar to what you have been testing,,,,, in case you would like to standerize your units?
O....Thanks

[Zumba]

I've been out of the loop for a bit. I see Walter has performed some nice tests. Good work.

Here's a question... has anyone figured out how exactly they want to perform the vacuum degassing? I tried many pages ago, and vacuum degassing will barely get the bubbles out of a 2" deep cup. If you've got a 5 gallon bucket of the stuff, it will not de-gas.

You guys mentioned a chemical degassing additive... I forgot the name of the stuff. Can anyone remind me what it is? Has anyone tried it? $$??

[walter]

Could you post a dimension

My testing rig is very crude, sample thickness should be no less than 1". Maybe something the size of a pack of Marlboro?

I will get back to you later, have to run to the post office.

[ckelloug]

Helping out Walter a bit since he's busy, he gave sample sizes back in post 1178 when I was bugging him trying to calculate the approximate flexural modulus of the samples:

http://www.cnczone.com/forums/showpo...postcount=1178

2 inches wide, 1.45 inches high and about 5 inches long seemed to be his standard size. His jig was set up for 3.7 inches of spacing between the supports.

Hope this helps.

<B>P.S. I'm pointing this out here because since we don't have a known correlation between torque/turns and actual sample modulus yet, we can't compare data usefully if the samples are not the same width and height. As long as the jig stays at 3.70 between supports, length doesn't matter.

Also, we shouldn't forget that to try to get a flexural modulus number, we need a torque value at each 1/4 (or better 1/8th) turn along with how many fourths (or better eighths) of a turn till breakage. If this data gets posted, I'll post a flexural modulus estimate graph for the sample.</B>

--Cameron

[walter]

If this data gets posted, I'll post a flexural modulus estimate graph for the sample.

Still haven't done the jig calibration, hopefully this weekend..(chair)


On the more positive note: I picked up the cool E/G core sample pack! (Courtesy of AkvaCNC, France) I'm still drooling over it so you'll have to wait a bit for an update.


I can only say that my reservations about matrix and surface hardness (posts #1257/1262) went deeper. This doesn't look like epoxy to me! They don't even use pure quartz-more like a random crushed granite.. But it's rock hard and a chainsaw wouldn't be much good for cutting it.

It's the complete opposite of my sorry @$% samples.
_

[ckelloug]

Zumba,

From the research that I posted a few pages back, it looks like vacuum degassing won't work until the vacuum level is better than 29.75 inches of vacuum. Pardon the pun but that's going to really suck. It looks like a rather serious vacuum pump is necessary to have any luck degassing.

I've been scheming about making a vacuum degasser/mixing chamber out of an oxygen bottle that failed hydrostat but I haven't started designing it yet. I also don't have a cheap source for the serious type of pump necessary.

As for additives, BYK A525 from BYK chemie is the degassing additive. I've also wanted to DOW Corning Z6040 bonding agent which when added directly to the mixture may have a very similar effect to BYK A-525. See post 1280 http://www.cnczone.com/forums/showpo...postcount=1280 for my last sample formulation. From Walter's data it appears that carbon black is causing the epoxy to set improperly so I'd leave is out for the moment.

These additives can likely be obtained by calling BYK chemie or dow corning and asking for a sample. I haven't tried this yet but I have gotten some dow defoaming agents that way for an unrelated project. There's probably no way that any one of us could buy any because they sell huge drums of the stuff.

So, you probably can't buy any but you probably can get all you will need for free. Note that the quantities used are infinitismal! Maybe we can talk US Composites into selling them if we show that they work well.

[walter]

AkvaCNC says this core was drilled out of a huge E/G mold designated for a machine tool. I'm not sure if it's E/G or polymer concrete/crushed granite, but it's rock solid. Aggregates are random and highly angular, I don't see any math here...
_

[ckelloug]

I've thought a lot about the aggregate and I've identified four principles from materials science which govern what the optimum aggregate mix is. There may be more principles but I believe these to be the most important.

<OL>
<LI>Rule of Mixtures
<LI>Griffith Fracture Theory
<LI>Random Packing Theory
<LI>Binder Skin Theory
</OL>

The Rule of Mixtures tells us that the strongest composite will contain the highest percentage of the stronger component. The effect of the rule of mixtures is balanced by the other three rules.

Griffith fracture theory says that the most effective aggregate will be that whose pieces are smaller than the average flaw size for the maximum stress in the part. Griffith fracture theory also tells us that the smaller the flaws in our parts due to bubbles and failed adhesion to the aggregate, the stronger the parts will be. See (Callister 195). (also Google "Size-scale effects in the failure mechanisms of materials and structures" to get a google book search result from conference proceedings on fracture mechanics. )

Random packing theory says that the mixture must be packed randomly such as the NISS paper explains how to do. Mixtures that exhibit only a single size of particle will have pronounced shear planes (thanks to Andrew for pointing this out) and thus minimal strength. Random packing also allows arbitrarily high packing densities to be achieved as particle size approaches zero while ordered packings approach a density of only pi/sqrt(18) which is 75%.

Finally, Binder Skin Theory described in Gamski's 1975 paper along with Gupta's paper indicates that there is a minimum thickness of epoxy below which bonding is not effective. According to Gupta, this is 30-36 micrometers.

<B>
The optimal formula for E/G will thus contain a wide array of particle sizes in order to keep the random packing theory assumption valid. It will balance the need to use small aggregate for maximum strength with the difficulties in getting defect free mixes using small aggregates while taking into account the binder skin theory result that 30-36 micrometers of epoxy coating is required around all particles.
</B>

Making it work

The NISS paper teaches us that it is easier to get higher fill densities with aggregate distributions that have more small particles than Fuller's rule would predict. Griffith fracture theory tells us that these small particles will have greater fracture toughness (which is the limiting factor in the strength of brittle aggregate like that used in E/G).

Griffith fracture also theory tells us that we must minimize the critical flaws such as voids and adhesion flaws which will cause the material to fail early and in the epoxy portion. To me this means bonding agents and vacuum degasing.

Gupta's result says that as we approach 30 micron aggregate size from above that we have a huge increase in the required epoxy percentage for a tiny increase in small aggregate thus ruining the high aggregate ratio. This says to me that we need to have the minimum macro aggregate sized 30 microns or greater and to add only up to about 10% dispersion hardener in the .1 to .01 micron range leaving an at least 30 micron gap between the smallest macro aggregate and the dispersion hardener. This appears to be handled by the Reichhold reference formulation's aggregate distribution which uses 60 micron as it minimum aggregate size.

I believe from these results:
<OL>
<LI> Large rocks are of limited usefulness. (Too many flaws in aggregate. Griffith)
<LI> Adhesion must be maximized and voids minimized (Avoid flaws in Matrix. Griffith)
<LI> Significant aggregate below 30 microns ruins the fill density (Binder Skin Theory: Gupta, Gamski, Reichhold)
<LI> Dispersion hardeners must be kept to reasonably low percentages and should be much much smaller than the aggregate .1 to .01 microns to avoid affecting the epoxy aggregate ratio. (Dispersion Hardening from Callister Chapter 17, Nanoresins, Cabot Apps Engineering, Gupta)
<LI> Aggregate must be widely distributed in size while as small as reasonble. (Random Packing Theory, NISS)
</OL>

While this list of rules is not a complete formulation, I hope it will keep the discussion of what needs to be done moving forward. Like Walter said, I think we are pretty close.

[ckelloug]

Walter,

Thanks for the cool pictures of the core sample from AkvaCNC!!!!!!

Randomness is exactly what the math says you want. Most of the math that gets done on this stuff is making sure that the aggregate is sufficiently and precisely random but has enough of each size to be good. There are multiple paths to making a mix that is sufficiently strong and most certainly many formulas.

The formula for this core sample is designed on different principles than the ones that I am working towards and it has a different makeup. It may have the benefits of practical experience that the references and equations I've been using don't give me.

My own opinion on the sample is that it reinforces my belief that we need fewer voids, better compaction and better adhesion.

Your pictures of the sample show that there is a relatively large amount of small aggregate present along with the big aggregates as well as the fact that they are uniformly mixed and have relatively few air bubbles or signs of poor adhesion.

I'm not sure what dissolves epoxy but if you really want to be pedantic, you could always dissolve all of the epoxy out of the sample and then have someone like agsco sieve the resulting aggregate and tell you the distribution. Probably an expensive way to go.

At any rate, your pictures of the sample were awesome and thanks for the shot with the ruler. Best of luck on catching up with your other tasks, Walter. I'm nearing the point where I can put my lab doors up and also the point where the dang sprinklers are done.

--Cameron

[walter]

The NISS paper teaches us that it is easier to get higher fill densities with aggregate distributions that have more small particles than Fuller's rule would predict. Griffith fracture theory tells us that these small particles will have greater fracture toughness (which is the limiting factor in the strength of brittle aggregate like that used in E/G).

There is a Catch-22, however.

- It is easier to get higher fill densities with aggregate distributions that have more small particles, but

- Small particles restrict flow and create a massive air entrapment problem;

- Vacuum degassing won't work until the vacuum level is better than 29.75 inches of vacuum.:tired:


This sample has a "typical" mix of large rocks and sands down to maybe 100 micron. Picture shows that using "proper" mathematical formula without vacuum actually leads to a total disaster and about 30% air content.
_

[ckelloug]

Walter,

You have a good point. I tried to say that all these factors have to be balanced in order to get a good formulation. My recent posting on aggregate theory is what I think that the driving factors behind aggregate mix design are. These are qualitative and provide discussion points more than anything.

A good mix is still governed by the same rules as an optimal one but you don't have to push the limits on each property in every formula. Other than the 30 micron minimum aggregate size that I take from interpreting Gupta, none of my other rules have numbers to go with them which means that I don't know their relative importance. None of them in the form in my post cover the effects of mass air entrapment other than what I draw from Griffith which predictably says it is bad. Duh!

Our number one priority in my view has to be reliably deairing the mixture to the point where the epoxy sticks to the aggregate. My post about aggregate theory was based only on the realization I had the other day that Griffith Fracture Theory plays a major role in the ultimate tensile strength of an E/G mixture. (I'm hoping my rantings induce another highly knowledgeable lurker to post!!!!!)

With the current rash of lousy results with small aggregate, perhaps Bruno's mix designs based on Fuller's formula with the larger quartz aggregate you posted about having in stock will work better in a home shop setting. We don't know the critical flaw size for quartz or epoxy yet (needs some more book work) so I don't have any comments on the maximum reasonable size of quartz aggregate or the maximum acceptable air bubbles. It might be huge.

I suppose in order of importance I'd figure this is what's needed:

<OL>
<LI>Get Epoxy to stick to Aggregate (Bonding Agent)
<LI>Adequately deair the mixture (Deairing Agent, Vacuum)
<LI>Use a high density aggregate distribution for the chosen sizes (Math on aggregate distribution)
<LI>Minimize the largest aggregate size (Pick smaller value for largest aggregate)
<LI>Cure epoxy at above ambient temperature (Heat Lamps)
<LI>Introduce dispersion hardener (Carbon Black, Silica Fume, Nanoresins Nanopox)
<LI>Introduce accelerator (Cobalt Acetyl Acetonate)
</OL>

I suppose I need to call Dow and BYK and scrounge up some additives so I can get to testing once my shop is done. Sorry if I've posted some not-overly-helpful discussion points today. Just trying to keep people thinking about all the aspects of optimizing E/G in hopes that one of the optimization theories also makes it easier to produce.

--Cameron

[brunog]

AkvaCNC says this core was drilled out of a huge E/G mold designated for a machine tool. I'm not sure if it's E/G or polymer concrete/crushed granite, but it's rock solid. Aggregates are random and highly angular, I don't see any math here...
_

Walter,
Nice samples!!!

What is the diameter of the samples?

Is it possible for you to photograph the samples individually, this way it could be possible to estimate the aggregate mix in them, I be curious to see if all samples are very different in aggregate mix.

Bes regards

Bruno

[ckelloug]

Just spotted a site with industrial grade refurbished vacuum pumps under a grand and with more than adequate vacuum. I was looking at the less expensive edwards pumps listed on the page. Looks like $500 would buy a more than adequate pump. The http://www.bocedwards.com site lists several of these inexpensive pumps as good for epoxy degassing. Look at an E2M1.5 or an RV3 or something similar at bocedwards.

The site I found selling the surplus pumps is http://serviceforvacuumpumps.com

I haven't done business with them but I am considering it once I have more time and fewer projects in process.

--Cameron
Some people say I'm one circuit short of a sprinkler system.

[lgalla]

Sorry for being absent,but I have a note from my mother.
29.92 vacuum is perfect.29.75 is obtainable at extreme cost.The last few inches Hg gets expensive.I have a Busch R-5 pump 1Hp 15cfm pump.It is 28 point something and cost me 1,800 bucks 20 years ago.It was fine to de-gass my 50/50 mixes.A 5 gallon pail half full was put in a 10 gallon pressure pot,tilted on an angle and rotated like a concrete mixer for 10 minutes.This resulted in zero air,but much thinner mixes.
I sugested Monarch 800 as a pigment at low concentrations:not as a filler;
Zeeospheres were sugested as an additive to lower the viscosity.
If you have a mix viscosity of peanutbutter,ya aint gunna de-air on the shuttle.Sorry for no answers.
Larry

[ckelloug]

Larry,

This is what I was looking at when I cited 29.75 inches of vacuum which I would love your further opinion on:

http://advancedprocess.com/apt/Vacuum%20Casting.htm

Does this reference seem reasonable? I'll stop citing it if you disagree, I just don't want to cite too low a number for the required vacuum and disappoint anyone who goes out of their way to buy a pump. I checked my copy of Marks Standard Handbook for Mechanical Engineers ninth edition and it cites 29.916 to 29.919 inches HG as the range for degassing on pg 14-47.

From Zumba's post, it looks like he has tried degassing at low vacuum and it didn't work too well. I have never done any vacuum degassing personally, everything I've posted about the subject has come from reading the web site above because it looked rather authoritative and a few others.

I think that the 28 inches of vacuum number you gave me is too low or a typo. I'm guessing you meant 29. I researched the vacuum pump specs you gave me. I believe that given the Busch R5, 1 horsepower, and 15 cfm that you posted, your pump is an RC5-0021. This appears to have 15 torr of vacuum pressure which amounts to 29.3 inches of vacuum. This is consistent with the above reference as near the minimum for any sort of degassing. What I don't understand is whether visibly air free and degassed enough for good aggregate adhesion are similar or not from an engineering perspective.

I can say though that the prices from the site I posed on used vacuum pumps mean that a used 15l/min pump that goes to 29.91 inches of vacuum costs between $400 and $1000 today. The cost gets insane somewhere between 29.91 inches and perfect vacuum, not between atmospheric and 29.91. we don't need perfect vacuum, just decent vacuum.

The busch specs are at http://www.buschpump.com/busch2004/d...205%20data.pdf which may require annoying registration.

Your idea about tilting the pail inside of the paint pot and turning it is ingenious. This is the kind of thing we need to be doing to the epoxy for E/G. I've got a much less refined concept on the drawing board for making a vacuum tight mixing chamber out of a decommissioned oxygen cylinder. . .

I was the one who suggested the carbon black as a dispersion hardener instead of a pigment based on the info in my materials engineering text. I still think it would work given some tweaking. It is however messing up the epoxy cure at least somewhat and DAK3333 who is an expert suggested that silica fume would be a better dispersion hardener in this case. I'm suggesting the silyated silica fume or Nanoresins nanopox at this point over carbon black until I have enough time to do my own lab work as they do not effect viscosity adversely and don't interfere with curing.

I don't think we'll end up with peanutbuttery goodness for our mix but I agree that there isn't enough vacuum in the world to degas it if it's too viscous er vicious

Thanks for the comments. I miss having you around more often here. Scrutiny is how we insure that we don't propagate bad information.

--Cameron

[greybeard]

I've had a few years experience degassing medium viscosity silicone rubber mixes for mould making, and my initial reaction to the figures you've been quoting are that they seem a bit extreme.
I started with a lab water-powered venturi and that did a reasonable job with a rubber that was thicker than "runny honey" but thinner than peanut butter.
I've no idea on measurements in stokes or poise or whatever, but if you took a pint glass half full and tipped it up, it would take about 10 seconds to reach the edge(20 secs on a cold day )
When you start to reduce the pressure above a fluid mix containing bubbles, there is a steady air loss that accelerates as the pressure goes down, until some critical pressure is reached. At this point, the fluid erupts to about 3 times its original volume, so you need a vessel 3.5 times the volume of the mix if you don't want it to go into the pump.
Once that point is reached, you can allow the air back in, as virtually all the removable air has just come off.
If you can reduce the pressure still further you might reach the vapor pressure of the fluid at room temperature, when it will start boiling.
This is why even the best water powered vacuum system cant get below about 15 torr, the vapor pressure of water at 15 degrees C.

I've also used an old two stage fridge pump from a butcher's cold store, by re-jigging the piping.
Then went on to an Edwards high vac pump which I found in an auction, but I only found the convenience of not needing to get to the kitchen sink better, not the degassing.
In all cases the container I used was a 12" length of 6" diameter plastic soil pipe, with an epoxied on plywood base, and a removable top of 1/2" perspex(Plexiglas).
Just my bit of experience if it helps