[ckelloug]

Plastic Worker,

I don't know whether "flashing" would significantly modify the surface energy of aggregate or not. It would probably help to drive off water and other molecules of crap stuck to the aggregate however.

My intuition is that since plastic bottles are composed from hydocarbon molecules that quickly "flashing" them will modify the chemistry at the surface of the plastic perhaps oxidizing it ever so slightly. I've read about using corona discharge and plasma treatments to get things to stick to difficult plastics which uses a similar principles.

Most aggregates like Quartz, Sand, Alumina, etc. are composed of relatively chemically inert oxides close to what they line furnaces with. I'd suspect without proof or reference that it might be difficult to get aggregates hot enough to see any effect whatsoever in permanent surface energy modification.

OT: I learned about the plasma etch stuff when I was busy trying to figure out how to get epoxy to stick to teflon. It turns out that for that problem there is some stuff called fluoro-etch which modifies the surface chemistry a few atoms deep in a block of teflon and renders it epoxiable. There's also an older formulation called tetra-etch which sounded so nasty I'd avoid touching the ten foot pole that touched the ten foot pole that touched the stuff.

Thanks for the post and if you think of anything else, enquiring minds want to know.

--Cameron

[ckelloug]

Mazaholic,

That liquid crystal polymer stuff looks neat but I am out of my depth in determining what to do with it. The tensile strength looked nice however.

--Cameron

[brunog]

Is there a way of approximating the viscosity of that mix immediately after mixing, and before it starts to cure ?
This would help in deciding how useful a starting point this epoxy would be, or should I be looking for something with a much lower figure for the resin ?

John

John,
you should be able to get a "mixed" viscosity from the supplier or manufacturer, this is standard info.

Best regards

Bruno

[walter]

_
A new tasty bit of E/G info.


"[...]A number of different types of polymer-based concretes have been developed which can be used to cast machine tool quality structures. For example, Fritz Studer AG, a prominent manufacturer of precision grinders in Switzerland, discovered that special polymers can be used to bind together specially prepared and sized aggregate to yield a stable, essentially castable, granite-like material with a damping coefficient much higher than that of cast iron. By carefully controlling the manufacturing process and selection of binder and aggregate, properties can be varied somewhat to suit the user. The polymer concrete material and process developed by Studer is known as Granitan™ and its composition and manufacturing process was patented. Numerous companies have licensed the process and will make castings from Granitan™ to order. Other companies have developed their own proprietary polymer concretes with similar high performance properties. For polymer concrete castings, the same rules for draft allowance apply as for metal castings if the mold is to be removed. Instead of ribs, polymer concrete structures usually use internal foam cores to maximize their stiffness-to-weight ratio. Unlike metal castings, a polymer concrete casting will not develop hot spots while curing even in thick, uneven sections. Polymer concrete castings can readily accommodate cast-in-place components such as bolt inserts, conduit, bearing rails, hydraulic lines, etc. It should be noted that a bolt will fail before a bonded-in-place insert. With appropriate section design, polymer concrete structures can have the stiffness of cast iron structures and much greater damping than cast iron structures.** However due to polymer concretes’ lower strength, heavily loaded machine substructures (e.g., carriages) are still best made from cast iron. Polymer concretes do not diffuse heat as well as cast iron structures and thus attention must be paid to the isolation of heat sources to prevent the formation of hot spots in a polymer concrete structure. In addition, their modulus of elasticity is about one fifth that of steel, and their strength is an order of magnitude less, so they are used primarily for machine bases[...]"

** See, for example, Capuano, T. September 10, 1987. Polymer concrete. Mach. Des. 133–135; Jablonowski, J. August 1987. New ways to build machine structures. Am. Mach. Automat. Manuf. 88–94; and McKeown, P.A. and Morgan, G.H. 1979. Epoxy granite: a structural material for precision machines. Precis. Eng. 1(4): 227–229
_

[walter]

Cheer up. I don't think we're in a bad shape at all.

We've been joking about our crappy samples and many of you are probably thinking "Yes, very crappy". Let me assure you, it is not as bad as you think. The only reason we don't have the E/G machine is because we don't want to epoxy our expensive rails and ballscrews in something that we know is only half decent. Especially knowing that we can add 2 components and make it a whole lot better.

My mixes aren't even properly cured/de-aired. Still, you could use them on a large machine base and smoke most of the hobby CNC stuff.



Take this for example. No real aggregate, just some powder, pool sand and zeeospheres.




Pretty hard nonetheless. The size is 1 3/8" x 2 1/4".




I set it up on two supports (12") and tested with some weight on it.




Each of these boxes contains 50lbs of quartz.




I put 200lbs on it and took the picture. Then I added another box (250 lbs total). It didn't budge. I'm sure it can hold 300-350 lbs. And that's not even real E/G!



Here's the "crappy mix" from post #1548. I was filling column of my mini drill and didn't even weight the aggregates. It was a quick sloppy job. I didn't use heat so the whole mix became unworkable, with too much epoxy and zero flow. Still, I dumped it into the column and it did it's thing.




Done and ready to go!




Why is it crappy? Well, if you don't use heat, viscosity gets high. At 20-25% epoxy the mix has almost zero flow- you can't mix it, you can't vibrocompact it. That's bad. The cost is another issue- epoxy is the most expensive component, you don't want 25% mixes. (Keep in mind that this was a small batch- large batches create their own heat so there will be no problem).

Anyway.
I dumped the leftovers into small plastic container. Results are below.
This is how crappy/unworkable mix looks like. Now imagine what non-crappy will be like.

[lgalla]

Walter,your latest post is saying what me and Andrew have been saying from the beginning.Use E/G to its greatest advantages.Damping steel structures or surface plate uses.Adding re-bar,carbon fibreglass ect.may not have the dampinating factors required.
Oh,Oh,I have used foams as cores for stiff structures and will share the knowledge if asked.Older guys like myself are cautious to new ideas.Keep up the good work Walter
Larry
Adamant that should read second last post.You youngsters are too fast.

[ckelloug]

Walter,

The maximum stress on the beam in the picture is about 350psi tensile on the bottom of the beam given your data that:
width=1 3/8
depth=2 1/4
Length =12
Force P=200lbs

and the formula S=3*P*L/(2*b*d^2)

The important point is that since it didn't break yet, the ultimate breaking strength is higher than 350psi. Since this one was done with weights and distances only, this is likely a good number. The hypothetical material I was using in calculations was only 5 times as strong as this and accures's materials is claimed to be about 8 times as strong. Of course since yours didn't break, we don't know the ultimate strength because it is still holding together.

FWIW when last I tried to estimate the strength of samples broken in your jig, I had gotten around 170psi. I don't know the magnitude of the error in the old 170 psi estimate. Invoking the improper technique of wishful thinking however, I'd like to believe (without appropriate proof) that this means progress is being made.

To the rest of the audience:

In deference to the remarks of Andrew and Larry, I still think that filling weldments and beams with E/G is much easier than building parts out of it. For anybody who is afraid of the risk of ruining a lot of parts or wasting money on a bunch of epoxy, almost any E/G formulation will work as a damper when poured inside a beam already capable of carrying the load. So will the technique from Bamberg's thesis of placing a rubber bag in the beam and filling it with ordinary concrete as posted by Bob Warfield. I personally am moderately obsessed with seeing what the stiffest and strongest Epoxy Aggregate material I can figure out how to make is. My intended application is certain metalworking machine parts for a machine that hasn't been designed yet. I'd also like to be able to make a Router gantry beam out of E/G which means that I need a material that is both quite strong and very well characterized. I'm trying to incorporate came-out-of-the-lab-last-month grade materials science into the framework of older materials engineering as best I can and am trying to finish the paperwork before testing anything.

At any rate, Nice test results Walter. Good Job on Keeping it real!

--Cameron

[walter]

Thanks!

And speaking of came-out-of-the-lab-last-month grade materials- I've got a hot one for you..


"Apr 20, 2007 BYK-Chemie develops the first polymeric coupling agent for filled radical curing systems.
Filled, radical curing systems like polymer concrete must be able to withstand tremendous loads. Thus their mechanical properties - such as flexural strength, compressive strength, tensile strength and impact resistance - affect their quality directly.
BYK-Chemie has developed an additive that improves these key characteristics by up to 50%. This impressive figure is achieved by means of a totally new mode of action. Normally, the filler is only mechanically embedded in the resin. BYK®-C 8000, however, - as the UP resin a polymer - creates genuine chemical bonds between resin and filler.
The mechanical strength achieved in this manner can even allow the thickness of components to be reduced without any loss of quality, thereby saving considerable costs. At the same time, BYK®-C 8000 improves the processing properties of the filled resin by reducing the viscosity.
Source: BYK-Chemie"


What say you?

[ckelloug]

Geez Walter,

This one is so hot the vapor hasn't condensed yet. It's still vaporware in terms of buying it but since nobody will sell us anything, the fact that samples are available bodes well for this crowd.

Here's the datasheet. The datasheet is not as complete as the blurb you posted. http://www.byk.com/output/download/E500_USA.pdf

Because they cite results of an amine titration in the datasheet, it will increase the required hardener in our epoxy.

You do work miracles finding some of the stuff you find by the way.

--Cameron

[walter]

Continuing on 'Internal Foam Cores'.


This appears to be the cross section of a typical large E/G base.
The old-timers seemed to use 2 stage approach:


1. Cast the main base first, with light cores for high structural stiffness to weight ratio (and cure it for 6 hrs).

2. Then cast other precision parts/surfaces (able to hold accuracy of 1um per 1m), on top of the main base.

Bonding epoxy type resin 'has been developed' to provide high wetting of aggregate (which is few microns to 15mm). Its low exothermic curing property is said to be critical in causing negligible internal stresses in the material.


Another piece of the puzzle falling into place.. So Larry, how about those Foam Cores?
:cheers:

[greybeard]

Congrats Walter on a picture that gives me a great boost, and a determination to develop my own ideas.

John

[walter]

Glad to help!


Continuing on 'Epoxy Toughening' (from post #1562)


Andrew suggested that adding (any) tougheners would lower flexural on tensile modulus. I understand what rubber does, but there are other tougheners. Tests with ABS, PC and PMMA clearly show positive effect. Check out Young's modulus.


These silk-epoxy composites are tested for their mechanical properties and "it is found that the strength of the composite increases after toughening epoxy resin with ABS polymer"
_

[walter]

Walter,
The maximum stress on the beam in the picture is about 350psi tensile on the bottom of the beam given your data that:
width=1 3/8
depth=2 1/4
Length =12
Force P=200lbs
and the formula S=3*P*L/(2*b*d^2)
The important point is that since it didn't break yet, the ultimate breaking strength is higher than 350psi.

Up to 327 lbs now. I'm running out of weights.

[ckelloug]

Wow Walter,

With 327 pounds of weight on it, That's withstanding 566 psi of tension on the bottom! Is there anything special in that one?


Also, that foam core construction idea is excellent for hollow structures. The foam itself doesn't likely add any strength but it is an easy way to make the part hollow.
--Cameron

[lerman]

Put a dial indicator under that beam and tell us how much it deflects as a function of load.

I'm sure that would provide more useful information.

Ken

[walter]

Nothing special. It's exactly the same as my 32 ft*lb sample from <A href="http://www.cnczone.com/forums/showpost.php?p=294370&postcount=1183"> post #1183</A>.


That sample just oozed respect. It was tough as nails and ready to go on my gantry. Just imagine.. cheap pool sand, silica powder and zeeospheres. No vacuum. Only vibrocompacting; And, a very liquid mix- 15-20% epoxy.



BTW, I ran out of weights at 532 lbs. The beam is still going strong but I'm done testing, the structure is becoming unstable.




366lbs in boxes, 166lbs in metal junk on top. Total 532lbs.
Sorry, no indicator test. Not a good surface.


You're right about foam cores. And it's a special hard foam, not the Home Depot stuff.
Light core bases have higher structural stiffness/weigh ratio when compared to total E/G bases.
_

[ckelloug]

Holy guacamole Walter!

At 532 lbs, the tensile stress in the bottom is 920psi. You've almost surely managed 1ksi (engineer speak for 1000psi when the numbers start getting big) since it still didn't break!

I have no idea what you're doing but by all means keep doing it.
:cheers:

[lgalla]

Foam cores could be simply stryofoam with no added stiffness.Added strength is a result of lowering the mass of the E/G.The beam's mass is lower and has less self weight to support.Polyurethane foams are available at 16lbs/cu ft which is similar to pine and may add strength.
PVC foams are heat foramable.
There is glass foam,aluinium foams etc.
Epoxy foam is used in deep sea vessels to withstand 20,000feet depth.Basically it is epoxy mixed with hollow glass microspheres.
Foam cores,honey comb etc.Nida core is cool.
In large boat cruisers Nida is used in the hulls amd as a lightweight core for granite countertops.Each sibe or skin or the core should be ballanced or equal stiffness.Any information I have is in my head from 20 years ago.Applied to E/G this opens a can of worms.I will not post on the subject unless asked specific questions.Foams or lightweight cores may have no use for E/G but are an interesting subject.
Larry

[walter]

Thank you both. That is good info!
_

[lgalla]

Walter,in your pictures you have foamular 150.This is 15psi foam.Wonder how 2 one inch thick skins of E/G on each side would perform.In cores generally the further apart the stiff skins,the modulus goes up.This is really high tec stuff and beyond my capabilities.An engineer such as Cameron would have to de-cifer the properties or advantages.
The subject is like "treading on thin ice"Take information"with a grain of granite".
Larry