[greybeard]

It's great to have people's experience of vacuum degassing epoxy posted here .
However, could I make a plea to everyone doing so, to say what type of epoxy they were using.
If we're looking at low viscosity 100% epoxy, then I'd expect the degassing to occur without any "boiling". By which I mean that though there will be bubbles expanding and bursting quite dramatically, no component is lost that will affect the chemistry of the curing, nor any strength issues.

Obviuosly the value of the residual pressure you've dropped to is going to have an effect also. I don't know what the vapour pressure of typical epoxy resin components is at room temperature, but I'd be suprised if that would be a problem for most people, high vac pumps not being that common among the readers here, I suspect.

If we're looking at a low viscosity resin that contains a thinning agent like styrene monomer, then yes, it will boil off under vacuum at room temerature. Any other volatile components present will also come off, so possible effcts on the post cure strength etc. would be pretty unpredictable.
Regards to all,
John

[jhudler]

Good point!

The epoxy is US Composites 635 thin 2:1 which is Reichhold EPOTUF 37-127/37-058 and 37-606 hardener.

Resin:
37-127 is a low viscosity 100% reactive diluted liquid epoxy resin based on 80% pbw Bisphenol A (CAS 25085-99-8) and which contains 20% pbw EPOTUF 37-058 (C12 - C14 glycidyl ether) (CAS 68609-97-2).

Hardener:
37-606 is is a modified, aliphatic, polyamine curing agent ( ~6% pbw Amino Ethyl Piperazine, ~12% pbw CAS 68391-18-4, 34% pbw Nonylphenol (CAS 84852-15-3), 46% pbw Polyoxypropylenediamine (CAS 9046-10-0)

Pretty much your basic epoxy with added reactive diluent.

[jhudler]

Last night's test of boiling epoxy in a vacuum:

Using the aforementioned epoxy mixed 2:1 without any fillers or additives, was boiled err "vacuum degassed" for 30 minutes at 28 microns pressure.

It did not harden overnight.

I'm trying an oven curing at 50C for 1 hour to see what happens. But I don't have any hardness testers to validate any results other than "it's cured" or "it's not cured".

Jack

[ckelloug]

I think these experiments demonstrate that the proper approach is probably to hold the epoxy for an extended time period at a pressure above the boiling point (like say 5mm) and then briefly dip to a lower pressure but not as low as 28 microns.

http://www.cnczone.com/forums/showpo...postcount=1249

I might also point out that Jack's result correlates quite well with the info in the link above which I posted 1100 posts ago (!) about recommended degassing levels from a company that builds vacuum degassing equipment. The original is linked in that post.


But now we have it confirmed in the lab which is much better.

Regards all,

Cameron

[MaX-MoD]

Has anybody tried using these sort of vibrating -dunno, my english is poor- stick, pick whatever that wou directly dip into the concrete?

I read something on it (in French) saying it was the best way for degasing concrete, but they usually work at much higher frequency, like 200-300Hz.

I know from using plaster that a low freq makes the thing flow easyly, but oddly that at higher freq it degases far better, whereas it flows less easyly.

Maybe it could be the same thing for E/G, and a well chosen vibration method would be more effective than a 50microns vacuum.

[ckelloug]

Bonjour Max-Mod,

Je voudrais assayer "le stick", mais je n'ai pas un "stick". C'est dommage. J'ai etudier la "ultrasound" systeme vibratoire a 20,000Hz maiz il coute chere! $9000 USD. Je pense qu'un combinacion de vibracion et "vacuum" est mellieur. Je ne parle pas le bon Francais mais merci beaucoup pour votre note. Votre anglais est meilleur que mon Francais!

--Cameron

[MaX-MoD]

Bonjour Max-Mod,

Je voudrais assayer "le stick", mais je n'ai pas un "stick". C'est dommage. J'ai etudier la "ultrasound" systeme vibratoire a 20,000Hz maiz il coute chere! $9000 USD. Je pense qu'un combinacion de vibracion et "vacuum" est mellieur. Je ne parle pas le bon Francais mais merci beaucoup pour votre note. Votre anglais est meilleur que mon Francais!

--Cameron

You don't have to be ashamed about you're French, it is a faaaaar more complicated language than English

To finish with the "stick", in french it's "aiguille à béton" it looks like this : http://www.enar.es/Vie/fotoAmp.aspx?...g&idLanguage=3
(just to be sure everybody's thinking of the same thing)

But I was wrong, it is actually 12-15KHz that is used for concrete!
But it is FAR less monex than the Oh-Damn!-EXPENSIVE! ultrasonic system

[greybeard]

Just a last thought before I turn in - doyou think the optimum frequency to interact with the bubbles will relate to the dimension of the bubble and the speed of sound in the epoxy ?
So that at the appropriate frequency, the bubble resonates, picks up the maximum energy, and......
I think I'll go to bed.
Night all.
John

[qroger]

I just checked into the last page after a long absence. I would point out that if you over apply the vibrator to the concrete it will segregate. A bad thing. Also if you search for concrete vibrator on google, you may be shocked at what it finds. The little shock waves that the vibrator sends through the wet cement, or dry sand for that matter, liquify it.
roger

[vacpress]

is there any agency that goes around giving awards to high quality message board threads that transcend anything that should be expected of the medium?

that said, has anyone started any wiki or anything for all this?

[lgalla]

Guys,ya ain't boiling the epoxy.Many posts ago,Cameron posted links to how much vacuum can epoxy take.I beleive it is over 29 "Hg.John mentions Vapor pressure which is very high for epoxy as it has no solvents but not the case for styrene based polymers.
If you had a vacuum bell jar and observed a neet epoxy mix with no fillers,it will expand three times its volume appearing to boil.It is not boiling only the entrapped air is expanding.
If you were actually boiling the epoxy and vaporizing components the epoxy would not properly cure as it is sensitive to accurate ratios.
Jack,I wouldn't worry about sucking chemicals into the pump as it is just air.If worried just change the oil.I was vaporizing styrene based polymers through my Busch R5 pump for years although we regulated the vacuum below the vapor pressure of the polyester resin which was 25"Hg or so.The vapor pressure of epoxy is higher than most pumps can acheive.
Larry

[jhudler]

If you had a vacuum bell jar and observed a neet epoxy mix with no fillers,it will expand three times its volume appearing to boil.It is not boiling only the entrapped air is expanding.

Larry,
I just completed a second test using 37-127 and 27-606.

The total volume of my epoxy (neat) was 6 cc's comprised of 4 cc resin and 2cc harder in a pyrex test tube. There were two identical tubes each with 6cc's.

It expanded as you described however, it took over 20 minutes for the bubbling to reduce to the point it could take 25 milliTorr/microns (.025 mm or 0.98703 inches).

After 30 minutes it still had froth on top and I gave up.

After 12 hours, the one exposed to 30 minutes of vacuum had not hardened at room temperature (it was highly viscous and would pour out had I let it), the control had.

After a 5 hour cure at 50C the vacuum exposed sample hardened,

Supposition: Something in the 37-606 is out gassing.

Sounds like it's time to call Reichhold or get a sample from them to make sure I or US Composites hadn't contaminated it in some way.

Comments?

Jack

[ckelloug]

After a bit of googling, I noticed that the 37-058 that is a component of 37-127 has a vapor pressure of 11600 microns at 100F. It's kind of a stretch since I don't know the whole vapor pressure curve for the stuff but I'd say that's evidence enough that if one holds really high vacuum that it will boil along with other components.

I agree with Jack that the sample probably did boil and was outgassing. Jack said he was achieving 28 microns which is pretty low pressure. The reference I posted was suggesting that 5000 microns was the pressure to degas epoxy. I believe this test means that molding under vacuum with slow curing epoxy is out and that 28 microns is too low and a case where more (or less in this case) is not better.

I've been worried for a while that the 37-127 / 37-606 system that we are using will require oven curing for maximum strength and hardness anyway but I suspect that the stoichiometric ratio of the epoxy was way off at the end of the vacuum application. (I vote for too much hardener at that point based on my theory that the reactive dilutant boiled off.)

The data sheet I got the vapor pressure from uses trade name heloxy modifier 8 for the dilutant in question:

http://www.resins.com/resins/am/pdf/SC1416.pdf

Jack,
I've got epoxy, hardener, and reactive dilutant on the way direct from Reichhold now. Should be here in the next week or so, I think.

MaxMod,

Those concrete vibrators look interesting. I'd be worried about the difficulty of sticking something in the molded E/G as our solids percentage is a lot higher than concrete.

groger,
Segregation may be a problem but the size distribution that I published and Walter used during testing is ver y close to the provably the least likely to segregate according to de Larrard's theory. As a result, I'm not that worried about it. Segregation is a much bigger problem using traditional concrete mix designs and especially gap graded mixtures.

vacpress,
I've considered starting an archive using the Open Source Alfresco Enterprise Content Management System but the community here on the zone is so supportive that it seems like it would dilute the effort to stop conducting our daily business here. I think I can speak for all of the regular contributors here in thanking you for the compliment!

greybeard,

I suspect that you are right that the vibration frequency can be tuned to the bubble size. I suspect the best degassing frequency is both related to that and also the "resonant" frequency of the particles suspended in the epoxy. I imagine that the absorbtion is pretty broad band as this is a vibration damping material. . . I also think it is going to be complicated and hard to figure out other than by lab work.

Congrats to everyone on the great progress.

Regards all,
Cameron

[jhudler]

I believe this test means that molding under vacuum with slow curing epoxy is out and that 28 microns is too low and a case where more (or less in this case) is not better.

I wouldn't say out, just keep it above 12 mm or 1/2 inch of vacuum and vibrate it.

A quick test of this at 12-15mm with fillers doesn't boil or rise much, but vibrating it does produce an air free mix.

So molding with lite vibration would create a very nice product.

[lgalla]

This should be self explanatory,from Crosslink Technology

Formulated Epoxies, Urethanes and Custom Cast Electrical Parts

"Our strength is in our Formulations"


ISO 9001: 2000 Quality System

"Our Mission is to profitably meet the needs of our customers through customized, innovative, high quality formulations and reliable components, accompanied by the best customer service in our industry, while being recognized as a trusted reliable supplier and employer, achieving steady growth by retaining our customers and discovering new business opportunities"

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DEGASSING EPOXY AND POLYURETHANE COMPOUNDS

Although most, if not all, suppliers of formulated Epoxy and Polyurethane materials manufacture products under vacuum. This being the case, there may still be some undesirable trapped gases that appear while using these compounds.

The following are some of the most common causes of bubbles;

1. Air inclusion during mixing the resin and hardener together.

2. Air trapped in moulds.

3. Air trapped due to improper casting/moulding techniques.

4. Air introduced by suction as the material shrinks or due to a leaking tool.

5. Trapped residual solvent vapours from certain types of mould releases.

6. Volatile components being stripped out of the materials while casting under vacuum.

7. Gases generated during the reaction (hardening) process.

8. Gases formed during improper storage (moisture contamination etc.)

9. Gases introduced through pressurized systems.

10. Air from improperly de-aired resin and/or hardener.



The first and most important step in eliminating the problems caused by bubbles is simply taking care not to introduce air while handling the materials. If it is unavoidable to introduce air during mixing, such as during mixing by hand, it is highly desirable to remove the trapped gases under vacuum before using the mix. Gaseous bubbles trapped in a liquid, although initially microscopic in size, will expand when heated and can grow to become large enough to cause problems.

Polyurethane products are moisture sensitive. In fact they crave moisture and should not be mixed during days when the humidity is high. Urethane resins and hardeners should be protected from picking up moisture by applying a layer on Nitrogen on top of the material in the containers. Mixing urethane resin and hardener components together is best achieved under vacuum or at least under a blanket of Nitrogen.

Moisture contaminated polyurethane products will exhibit a large number of tiny bubbles on the surface or, in extreme cases, will rise to produce foam. These type of bubbles are next to impossible to remove.

As a rule, epoxy compounds are less moisture sensitive except for certain hardeners. Moisture contaminated epoxy hardeners can be usually recognized by the formation of a crust around the edges of the container. Moisture contaminated epoxy hardeners, depending on the formulation, will react faster than expected with the resin.

Bubbles tend to rise to the surface of the material and will, under ideal circumstances, given enough time, will eventually release from the liquid. In reality, most applications do not allow for the required time or the proper conditions for products to self de-air, vacuum must be applied to speed the removal of trapped gases from the mix.

Some of the key factors that effect the removal of gases are as follows;

1. The viscosity of the mix.

- The higher the viscosity the more difficult it is to remove gases

2. The surface tension of the materials

- Can be reduced by heating and the addition of surfactants

3. The temperature of the epoxy or urethane mix.

- Heating the material will reduce the viscosity. Be sure to consider the pot life and gel time before heating any mixed materials.

4. The amount of epoxy or urethane material being de-aired at one time.

- The depth to surface ratio is important. The larger the surface that is exposed to the vacuum the better.

- The lower the amount of product the rising bubbles have to travel through the better.

5. Agitation

- Agitation (mixing) during the de-airing process (while under vacuum) will speed the removal of air considerably.



Alternate methods to remove or minimize the impact of trapped gases.

Thin film de-airing; The material is exposed to vacuum in a thin film. This is probably the best and fastest method of removing trapped gases.

Centrifugal force: Trapped gases may be forced out of the product by centrifugal forces by spinning at high speeds. This is not a widely practiced method and has limited possibilities in common applications.

Pressure: The application of pressure during the gellation process will reduce the size of the bubbles. The amount of pressure necessary will have to be determined by experimentation. Depending on the component configuration it is not uncommon to use 80 to 100 psi.

Vibration: Placing the mixture on a vibrating table will assist the bubbles in travelling to the surface.

Basic steps to produce bubble free epoxy or urethane castings:



1.

Careful selection of the epoxy or urethane compound to be used.

- The least number and amount of volatile ingredients.

- The lowest possible viscosities (individual components and mixed)

2.

Mixing

- Hand Mixing

i. De-air each component containing fillers individually.

ii. Do not use violent motion during mixing and scrape the sides of the container to insure a thorough mix. De-gas the mixture under vacuum if possible.

iii. If vacuum is not available, allow the mix to stand for a period of time to allow the coarse bubbles to escape prior to pouring (don't forget to consider the pot life).



- Mix/Dispense Equipment

i. Take precautions to minimize air entrapment while topping up the storage tanks. Slow, steady pouring into one spot will minimize air inclusion. De-air the materials in the storage tanks if possible.

ii. Keep the fittings, valves and dispense pistons in good repair. Defective components will allow air to be sucked into the dispense lines.

iii. Cavitations and lead/lag problems can be sources for air inclusions.

3.

Pouring

- Pour slowly into one corner of the mould or container. Pouring slowly will allow the rising material to push the air ahead of it minimizing air entrapment.

- Pour with the least amount of turbulence.

5. Curing

- If possible, de-air the poured assembly prior to cure. This step is not necessary for parts involving small volumes. Large mass castings or castings with complicated shapes, conducive to air entrapment, should be de-aired prior to cure for best results.

- Establish and use the appropriate temperatures that result in slow, even gellation. Provide a sufficient reservoir of cool material to replenish the shrinkage that takes place during gellation and cure.



Other suggestions:

- Hydraulic hose fittings on vacuum lines allow for leak free connections and better vacuum.

- 29” Hg of vacuum is sufficient for most applications.

- 2 mm of vacuum has been found sufficient for high volume production.

- Always use a large enough container to allow the material to rise under vacuum.

- It may be helpful to add a drop or two of a suitable surfactant.

Precautions:

Almost all formulated epoxy and urethane materials contain at least some volatile ingredients. These ingredients are an essential part of the product and will start flashing off under vacuum. This is evidenced by the fact that the mix being de-aired never seems to be totally free of bubbles no matter how long it is vacuumed. Care should be taken not to vacuum strip the material. In most cases vacuum at 29” Hg for 5-10 minutes will sufficiently de-gas the mixture.
Larry

[jhudler]

Anyone have a source for "milled carbon fiber" that doesn't require a truck load?

[ckelloug]

I call Home Court Advantage! Toray Carbon Fibers North America HQ is in town. I can drive over and try to get a sample. I think 1 inch or 3/4 gets the maximum benefit according to the theory of chopped fiber reinforcement.

Regards all,
Cameron

[jhudler]

Would be nice to have a sample of milled CF to test out with, might come in handy on edge reinforcement. Trying to get Toho Tenax to part with a batch.

[ckelloug]

Jack,

Can you give me some more idea of what you are trying to get hold of? There are a huge array of carbon fibers manufactured here in the Huntsville area (in Decatur, AL actually) at Toray.

[jhudler]

There's apparently two types other than fabric; chopped and milled.
Chopped seems to refer to anything longer than 1 or 2 mm, while Milled is less than. From what I've found so far, Milled is 1 to 400 microns.

Nice time to quantify the tensile benefits of CF.

Jack