[Geof]

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......

My experience parallels this.

I did notice in the link that 'high voltage' and 'critical air free applications' was mentioned. I suspect that the very good vacuum they say is essential is not just removing air it it is removing adsorbed water which is a real no no in materials working with high voltage.

Also recognise that they are trying to convince you to buy their system. A little hyperbole in sales literature is to be expected.

[ckelloug]

Graybeard,

Awesome post about vacuum!!!!! 15 torr from your venturi is about what the pump I think Larry has is rated for. I believe either harryn or groger also reccomended venturi vacuum systems earlier but I incorrectly assumed the vacuum was a bit low.

The 5-10 torr numbers from Advanced Process Technology that I had been citing are from people who make equipment to vacuum degas critical stuff like MRI coils and potted high voltage components where it might be an issue if there were any imperfection. As Geof quite cleverly points out, thoroughly removing water vapor might be the reason they go so low. Geof's comment about hyperbole in manufacturer data is also valid. Water vapor is bad for epoxy aggregate adhesion in our case too.

From the consensus on the thread, it looks like 15 torr is realistically the minimum vacuum level for degassing epoxy. This is at the lower limits of the Advanced Process Technology Numbers and substantially higher than the millitorr numbers from Marks handbook.

<B>Does anyone disagree that a reasonable recommendation for vacuum on this thread is "Any vacuum source equivalent or better than 15 torr gage pressure and economically feasible". This is equivalent to 29.3 inches Hg of vacuum.</B>

[lgalla]

From the APT site.
30" Vacuum = 0.0 mmHg (Torr) = 0.0 microns = Perfect Vacuum
0.05 mmHg (Torr) = 50 microns
0.1 mmHg (Torr) = 100 microns
0.5 mmHg (Torr) = 500 microns (Resin is degassed at 50 to 500 microns to vacuum
pot and encapsulate high voltage components.)
1.0 mmHg (Torr) = 1,000 microns (In-chamber vacuum levels from 500 to 1,000
microns are required for most vacuum potting and encapsulating applications.)
2.0 mmHg (Torr) = 2,000 microns
5.0 mmHg (Torr) = 5,000 microns (2 to 5 mmHg is needed to make low to medium
viscosity resins visibly air-free. This range of vacuum levels is five to ten times
better than 29" of vacuum.)
10.0 mmHg (Torr) = 10,000 microns (Very little degassing is done at this level.)
29" Vacuum = 25.4 mmHg (Torr) = 25,400 microns (Not a sufficient
vacuum level for degassing most epoxy and urethane resins.)
28" Vacuum = 50.8 mmHg (Torr) = 50,800 microns
15" Vacuum = 381 mmHg (Torr) = 381,000 microns
0" Vacuum = 762 mmHg (Torr) = 762,000 microns = Ambient Air
I saw this and said what??the hec?I think we are reading the charts wrong.I think possibly they mean 29"will not de gas the epoxy formula.E/G if you were de-gassing polyester,29"would boil out the styrene and ruin the chemistry.Max for polyester is something like 25"
Cameron from the Mechanical Engineers hand book,29.9 again this must refer to what point the epoxy vaporizes.If so this would translate to epoxy is safe to de-air at perfect vacuum.Perhaps we are using the wrong terminology.
De-gassing is different from De-aring?
Only guessing,but 25"should be sufficent for De-airing epoxy while mixing.
I will try to research that later.Late for work.
A cheap Gast pump should be able to do the job.
A realy cool item is a vacuum bell jar.You can see your mix boiling.
Larry

[walter]

Thanks for stopping by Larry, always good to see your insights here~!


btw, I hear that $300 refrigeration service pump can get down to 25 microns..



http://www.rparts.com/Catalog/Tools_...cuum_pumps.asp




They also have a $290 hand pump that will pull 29" of vacuum.
_

[brunog]

Are you all sure that vacuum degasing is a must??

Walter,
take a close look at the samples you got from France, I have seen a lot of air bubbles on their surface.

What do you think? Were these samples degased, i personally doubt it.

Best regards

Bruno

[walter]

Bruno, better pics of that 36mm EG core will be here tonight, stay tuned.

re: Vacuum

I'm not sure what to tell you.. There is a chance that a vacuum chamber would make the whole job a lot easier. Actually, I think it would make this a real cakewalk. Some manufactures go to great lengths to fight air - some are placing aggregate in the mold and then slowly pump the resin (from the bottom!) just to avoid air. Have a look at the pic in post #1355- 30% of that block is air.

Of course you can get rid of it - heat the epoxy, put it in the kitchen sink, heat the pan, heat the stones, dance around that 200lb mold with a heat gun, whatever. But I can tell you that you that you will not enjoy that process- how in heaven are you supposed to work that out with large molds? That's silly..

But hey.. A man's got to do what a man's got to do! I drew a line in the sand and $500 vacuum equipment is on the other side of that line. And no, I am not building one. Btw, if it wasn't for the no-shrink feature, I'd be out of epoxy business long time ago. Another thing is with the flex strength- I really don't think that de airing and some other small refinements will up the strength 10 fold (which we need to get to the pro level). I broke one of the 36mm EG core pieces and it didn't seem all that strong- except for the surface hardness maybe.

But anyway, let me cheer you up:

I will stay my course - use just a few random components that I have on hand, maybe a heat gun and some good shaking. No calculators, no math formulas, no vacuum. My idea is to mix it, dump it into the mold, flip the shaker switch and go watch a movie. Just kidding. Maybe not..
I've learn so much on this thread- I hate not to use this knowledge! But practicality will eventually have to kick in and my caveman approach will probably win the day.



I do however appreciate all the work being done here on this thread. The pursuit of commercial E/G should definitely continue because not everyone is a hobbyist like me. Some people want big machines and will have to use the proper tools and Formula. I have no doubts.

Peace.
_

[ckelloug]

Here is an excellent paper on degassing from crosslink technologies, a Canadian epoxy and urethane formulator:

http://www.crosslinktech.com/degassing_materials.htm

What do y'all think??!

They suggest 29 inches of vacuum for general use and give 2mmHg=29.84in as their number for production applications. They also say 5-10 minutes should be enough to degas most anything as too much degassing will boil off components of the mixture as Larry warned. I may have taken the info from the Marks handbook out of context about degassing in the millitorr range in that the section was on picking a high vacuum pump or an ultra-high vacuum pump. Nonetheless, it seems like the crosslinktech guys are also using some pretty high vacuum.

We don't really know if vacuum is absolutely necessary nor do we know if the additives mitigate the air entrapment sufficiently to bypass the need for vacuum. As a research approach, vacuum is worth checking and I suspect it's almost a foregone conclusion as echoed by the chat harryn had with a chemist.

The unfortunate part of E/G is the work needed to figure out how to make E/G is much harder than just making the part. I need a vacuum pump anyway for some other stuff that I am working on so I will be testing the vacuum effects when the squall line of tempests in teapots subsides in my forecast area. This could be up to a few months away

Walter, I hope you will continue to hang out on this thread even once you succeed at making a usable machine. You've had a lot of good insights into making the ultimate E/G and I hope you're still having fun here. Most of the useful results from the theoretical approach will come long after you are done with your machine at the rate things are going. If there is anything I can do specifically for your machine, please don't hesitate to ask as I'm trying to study making E/G thoroughly before doing much building and haven't posted much that's been directly helpful to a machine builder lately.

Best Regards,

Cameron

[walter]

Ok, we have some close ups. First, the entire E/G core:



Now onto the slices - first one is polished on all sides, both sides pictured. Other two are saw cut and will be pictured in next post.
_

[walter]

Here are two saw cut samples, wetted for the photograph.
(front and back pictured)
_

[walter]

Last post, all samples dry and natural looking- just in case there is someone who can identify the matrix. Any material engineers out there..?

And once again, big thanks to Leif (AkvaCNC) for sending it all the way from France, I really appreciate it! :cheers:

[lgalla]

Hey Walt,
Going back to caveman type E/G,WilliamD had sledge hammer proof E/G with 25% epoxy and a bag of sand,no vacuum,no vibration.I beleive he had thick epoxy and the mixes were like bread dough pushed into the mold by hand.I would assume apparent high strength due to better wetting and bonding with excess epoxy.
Air release additives,wetting agents exc,do not magically get rid of entrapped air,they assist in the vacuum process.
Vibratory compaction is vibratory compaction.It may release air but its main contribution is to compact the aggregates into a formation thats locks them to gether.Too much vibratory compaction is also a bad thing.The cores you have look good,not much air.Your last samples look like you discouvered epoxy foam.Sorry for being the negatory type guy,but I must post any downsides I see.Sure,with unlimited capital its do -able but I hope to see simple solutions for the home guys.
The Busch R-5 pump I have was run 8hrs a day for 10 years with no service other than changing the oil.Really good product.Opon receiving the pump I acctually read the instructions first.It stated the pump must be shipped without oil or damage may result.Apparentally the oil will get on the wrong side or the rotary vanes and may break the vanes upon startup.Simple solution is to manually turn the pump for a minute to place the oil on the right side of the vanes.
JICYAI:Just In Case You Are Interested,Ifiberglassed coated plywood with a chopper and vacuum baged it.The pump could suck the resin right through the plywood.Talk about good bonding.This was for flight case manfacturing.The compition glued ABS to plywood and cut their pricing to knock me out of the market.It worked as my price was higher.I still have the pump and tank and the thread has convinced me to dust off the equipment and do some Vacuuming.
Larry

[ckelloug]

Formulator epotek recommends 29 inches of vacuum but says that it should be applied and released as quickly as possible.

http://www.epotek.com/SSCDocs/techti...%20Tip%204.pdf

Formulator resins-online.com in the UK recommends brief degassing at 5 mbar= 3.75 torr gage pressure = 29.77 inches Hg Vacuum.
http://www.resins-online.com/resin-online-faq.php
This thread actually comes up in page 2 for epoxy degassing in Google!

Formulator PTM-W Recommends greater than 28 inches of vacuum.
http://www.ptm-w.com/dynamicdata/dat...procedures.pdf
PTM-W also has some high strength cast iron filled epoxies which look like they might be the kind of thing we like!!!

So it looks like 3 epoxy formulators (counting Crosslink from my last post) recommend more than 29 inches and one formulator just says it is more than 28.

Since Crosslink, Epotek and Resins-Online all recommend values very close to 29.75 inches of vacuum, I'm not so sure this was out of line as a target vacuum value, especially considering the fact that several of the vendors state that as short a degas time as possible is recommended. Less vacuum for a longer time may work but it doesn't seem reasonable to me to deliberately purchase a vacuum pump for this application which won't produce 29.75 inches Hg of vacuum.

It's still possible that an adequate mixture can be produced without vacuum using additives but I am convinced but the very strongest mixtures will still require vacuum.

It might not have any granite in it but it looks like we could just buy cast iron filled epoxy from PTM-W and be done early with higher strength and likely decent vibration damping. . . Sigh.

--Cameron

[fyffe555]

Conversations moved back to degassing and vacuum?

So, Why not approach it from the other direction - just don't get gas in there in the first place.

Use the standard cascade mixers to mix epoxy. As Larry mentioned before they're intended and produced to fully mix epoxy/hardener without introducing air. You should now have an airless epoxy mix.

If you're intent on using vacuum then use an economically viable 28" pump. Put the mixed airless epoxy into the pot with the aggregate UNMIXED, and then put it under 25-28" or so. THEN mix epoxy and aggregate under vacuum. Anyone see why this wouldn't produce an mostly airless E/G mix?

In molding process use vacuum to assure packing, As someone mentioned before bag it down to ~28" to provide a compacted airless mix, then bag again and pressure the external bag 2bar.

You'll need a very strong mold.....

The bigger problem is still getting complete wet coverage, a voidless cast and reasonable distribution of aggregates. You can run a 'wet' mix to assure full coverage and void filling and remove the excess under bagging in the mold.

Distribution is more tricky but the commercial samples Walter recieved seem be be rather sparse in aggregate fill and what there is is randomly spread so distribution might not be an issue in practice.

Any more discussion on how you're actually going to use the material, machine designs ?

Andrew

[walter]

Thanks Andrew, that makes sense.

Here are some of the uses for home brewed E/G, these are only examples, please don't pick on them. The main advantage is that you would be able to build a machine without any welding or metal working tools. Today, there is no such possibility- hobbyist has to use MDF of expensive aluminum, and both are pretty weak materials- not suitable for any real machine. There are no choices really! E/G is also weak but you can use more of it- just buy another bag of sand/gravel and dump it into the plywood mold. How hard is that? At $0.80 per lb is a no brainer really. I wouldn't use steel tubing even if you pay me to - I think it's crap and only the big manufacturers can make it work in machine tools. I hear there's one guy here who bought a ton of steel tubing, was welding it for 2 years and now he's able to take light cuts in aluminum. Laughable if you ask me.
_

[ckelloug]

I think Andrew's suggestion of using a static mixer to mix the epoxy and then adding it to the pot and mixing it with the aggregate under vacuum is a good suggestion in practice. My main concern is that most of the commerical metering pumps with manifolds and cascade mixers on the end for epoxy that I've seen are almost as expensive as a surplus vacuum pump. Grebeard's suggestion of DWV pipe for the vacuum chamber is ingenious.

See http://www.michaelengineering.com/ for example costs on static mixing epoxy dispensers.

The 1975 paper by gamski said that setting under pressure was not effective in removing air voids but that it helped maintain good aggregate distribution and produced stronger samples. It's my opinion that bagged setting under pressure will do better for keeping air out of the cast and good aggregate distribution than vibratory compaction unless thixotropes are used to help maintain the spatial aggregate distribution and they require vibration.

I'm getting the impression that a carefully poured mixture that isn't too viscous and was properly deaired will be able to be poured into a mold and work ok though vacuum bagging and pressurizing ought to work better.

The biggest problem with air that I see is that it doesn't just sit around forming voids in the matrix. The air is concentrated in pockets around the aggregate effectively reducing the mix to pure epoxy for strength and modulus.

I agree with Andrew that the commercial samples Walter got are a bit sparse. I recall walter saying that they were from a machine base which I'd guess probably didn't need the high test stuff. To me, they appear to have only a few large voids around the edges which would indicate they were made from vacuum deaired epoxy poured into a mold at atmospheric pressure.

The distribution of aggregate uniformly throughout the sample ought to be random. When it isn't: that's when there's a problem. The Machine Design article way back written by folks from accures castings indicates that accures uses accurately graded aggregates to ensure the proper size distribution.

Finally, I'll have to politely disagree with Walter about steel tube generally being bad. While light gage steel tube, the stuff you'd voluntarily cut with a hacksaw, is going to be tough sledding for machine building, heavy wall stuff or I beam is likely infinitely easier to get to perform well than E/G. Most of this could be put together by bolted joints with epoxy grout in them so they stay square (this is the E/G thread).

I'd guess that with an oxy-acetylene welding cutting setup, an angle grinder, a hack saw, a drill with lots of sharp metal drilling bits, a big square, epoxy grout, and some stuff like 80/20 channel for the precision parts one could build a very nice machine. I'd also go out on a limb and state that such a brute force approach might be less difficult and less expensive than E/G. The secret is that none of the metalwork is precision work: it's just holding the precision parts up. I'd also suspect that the tools to make the metal one will ultimately be cheaper and more generally applicable than the tools for E/G.

My neighbor is a composite materials expert for Boeing on the international space station. He said to me the other day that if composites had been invented first that everybody would be rushing to aluminum as the miracle material for most applications. He recommended aluminum filled epoxy as used by industry for "soft" dies in forming operations for what we are doing.

In short, I like E/G for the reasons that Walter does: it's theoretically inexpensive and easily formed with wood molds into complex shapes that home shop types couldn't form without extensive metal cutting tools. On the downside however, it is apt to require relatively bizarre equipment like vacuum pumps and because E/G isn't particularly strong, it will require heavily engineered parts to avoid metal reinforcement.

If all a person wants to do is make a big CNC router, I'd think that several other cast materials besides E/G will be less work and have a more predictable good outcome. Metal dust filled epoxy and metal whisker filled epoxy like some of the stuff in the PTM-W catlog might be a lot easier if they aren't prohibitively expensive. Using E/G for a router, it will be a lot easier to reinforce with rebar where necessary and accept the theoretical few percent vibration increase than to design metal free parts. My own interest is to create an open E/G design that will work without reinforcement for machine applications but it doesn't mean I think that this is the easiest way. It is however the most interesting way and the road less traveled. It's probably also the cheapest way for a <u>mass produced</u> part.

Hope I've been playing devil's advocate here and not the devil,
Cameron

[greybeard]

A thought for those intending to use some random mix of sand/crushed granite/rocks.
If a "perfect" mix of different sizes is to make such a big difference to the ultimate strength of the E/G, there needs to be some method of checking if the mix we have in front of us is good/bad/indifferent.
Could this be a dry check of the density ?
Take a small box of known dimensions. Fill it with the largest size rocks and weigh it. This will give me the lowest "density" of my E/G( I'm ignoring the weight of the epoxy for simplicity.)
If I now pour in smaller rocks, shaking the box as I do so, till I can get no more to go in below the rim, and weigh again, this gives me an improved "density".
Now I pour in another smaller sized fill, and repeat the process.
I can, by this method, see what I can make with a mix of segregated, and known sizes of fill particles.
If I now take a "random" mix of crushed stones and pour it into the box, shaking it as I do so, the weight/density figure will give me a check on how good a particular sample is. Pushing it a bit, it might let me see if the mix could be improved with an addition of some particular size, but I'm not sure if that's worth considering. I'd need to separate the "random" mix through a set of seives to see how the size distribution was.
What I'm looking for is a simple method of checking that I'm starting with the best mix from whatever is available to me locally.

Thoughts ?

[ckelloug]

Greybeard,

You're exactly right. The only thing that I would suggest is using two measuring vessels. Fill the first with your aggregate to a known volume and then add water from another vessel until the water reaches the same mark where the top of the aggregate is. The volume you filled the aggregate vessel to minus the volume of water added divided by the volume you filled the aggregate vessel to will be the fill percentage.

This won't tell you what aggregate mixture to use but it will tell you how well you did. This assumes of course that none of the aggregate is water reactive.

--Cameron

[walter]

New bits of info.

Some 'polymer concrete' machine base manufacturers use fluids/binders with viscosity of 1-10cP. Water is 1cP, automotive antifreeze is 20cP, Motor oil SAE 30 is 200cP. My epoxy is 600cP.

http://www.freepatentsonline.com/4670208.html

Here's another one (before you buy the aggregate):

High grade quartz contributes to great wear resistance but also lowers elastic modulus. In another words, buy stuff other than quartz to get the best Young's modulus.
_

[ckelloug]

New bits of info.

Some 'polymer concrete' machine base manufacturers use fluids/binders with viscosity of 1-10cP. Water is 1cP, automotive antifreeze is 20cP, Motor oil SAE 30 is 200cP. My epoxy is 600cP.

http://www.freepatentsonline.com/4670208.html

Here's another one (before you buy the aggregate):

High grade quartz contributes to great wear resistance but also lowers elastic modulus. In another words, buy stuff other than quartz to get the best Young's modulus.
_

The fluid they speak of in that patent is acrylic resin which I thought was rejected on this thread due to high shrinkage.

According to the nist paper brunog posted some time back, http://fire.nist.gov/bfrlpubs/build99/PDF/b99032.pdf

crushed quartz does better than natural granite on young's modulus but not quite as good as basalt. I suspect that there is a huge amount of variability depending on exact particles sizes so I have no idea what data to believe about aggregate.

My belief is that whatever material has the highest value of a parameter called fracture toughness which is particle size dependent is going to work best.

[brunog]

Greybeard,

This won't tell you what aggregate mixture to use but it will tell you how well you did. This assumes of course that none of the aggregate is water reactive.

--Cameron

Cameron,
Even if 15% of the water is absorbed by the aggregate, you will stil get a very good idea within 4% precision overall, and the aggregate mixture will always be underestimated which is ok.

Best regards

Bruno