[bloefeld]

Hi,

Welcome aboard Chris. Walk-in ovens, are going to be a great addition to the process, nothing beats a good post-cure heat.

From CK's last post it seems that there are concerns with brittleness in some of the formulations. I suggest that reading the Huntsman document I posted should point toward some good solutions. The shrinkage factor as a result of heating the resin is nil.

There are many options available to add toughness to the resin pack. I suggest adding 10 to 20 percent Inhance HD 1800 particles to the resin. They will both toughen the mixture, improve adhesion to the aggregate, and increase the bulk properties of the resin. Obviously reactive rubberisers are available and require some simple calculations to adjust the stoichiometry. I prefer to keep my resin systems as neat as possible and alter their characteristics with particles.

Because you have an oven available, I would suggest that the matrix be cast and then cured at around 200F for about 2 hours. This will reduce the likelihood of cracks forming in the resin. Then follow one of the post-cure schedules laid out by Huntsman.

The main idea behind my preference for systems like Huntsman curatives and accelerators is that they have been very well investigated and are zero or very low VOC systems.

Cheers,

Tony

[lgalla]

Chris be careful.
Sorry I have not posted in a long time and may not be up to date.Basically glass fiber carbon fiber and the like as cloth or rovings under vacuum infusion plus injection is cool as the fiber/resin ratio is about 50/50 by weight.Trying to get 90/10 epoxy aggregate is not possible with a small % age of glass fiber no matter how much vacuum or injection pressure you have.The space between the aggregates is minimal and the glass fiber will complicate the procedure.The fibers will "wash" at the injection point plugging the resin path and building high pressure in the mold.If you are infusing with a high pressure pump,good luck.The mold must be very strong to resist the pressure buildup.Forget the glass fiber for now.
Larry

[crr]

Larry-

Thanks for the input. The carbon/glass that I would be using is not in cloth form, but rather, 1/4" loose chopped fibers. For the test samples that I am going to do, I am going to make a split mold, with the resin injection points at either end and the center on the bottom. I am then going to put the whole thing in a vac bag and compress and vibrate simultaneously. I'm going to try and get as many of the sizes as close as possible to save the effort of cutting too many edges on the wetsaw. The first trial that I am going to do, I am going to see if I can get the resin in purely under vac after the resin has been heated.

On a side note, I have all of the supplies en route, so I look to be contributing more fruitful information in probably 2 weeks time.

-Chris

[Calthorp]

I think the loose fibers would be good as it will act as large aggregate.
Going to cast a sample today if I can get my vaccum pump to go.

[Low-Alloy]

Bloefeld wrote:

"Pump the epoxy into the mold while drawing with vacuum."

Instead of using a gear pump to pump the heated epoxy, would a paint pot at around 50psi do the job? It would certainly be easier rig and clean up would be a lot simpler as well..

I was also thinking that heating the aggregate to around 140f pre-infusion shouldn't be too hard; and if the casting was massive enough it would stay warm long enough to pump the epoxy and keep it's viscosity thin during the entire process.

Possible problems I see with the procedure is that it may cause loss of accuracy as the different aggregates cool their coefficients of expansions may stress the casting out of shape. Also the heated aggregate may cause cause too fast of a cure of the epoxy.

However, I like the idea of heating the epoxy to lower its viscosity if it allows for a superior casting, but the aggregate would have to be heated as well, because I doubt that it would stay warm after infusing though more than just a few pounds at room temperature.

What do you all think?

[probinson]

My thoughts on......

Using a paint pot:

You can use air pressure to drive the epoxy out of a sealed container (I use a pressure cooker with the safety plug filled myself) but you will be using MUCH lower pressure than if you pumped the epoxy directly, approximately 100 PSI instead of a few thousand PSI.

Thermally induced stress:

One of the most attractive properties of the aggregate is low thermal expansion so you don't need to be worried about that. If the aggregate expanded significantly with such a low temperature differential it would be worthless as a machine base to begin with.

[crr]

This is what I was going to use for the test articles. This way I can keep it cheap until I'm ready to do something big.

If you don't want to follow the link, they are basically refillable caulking tubes. I figured I could put the mix in, de-gas, and heat it up in a easily transportable and workable manner. Considering how thick caulk is, heated epoxy should be a piece of cake.....or pie.


http://www.westmarine.com/webapp/wcs...4&classNum=165

[Low-Alloy]

My thoughts on......

Using a paint pot:

You can use air pressure to drive the epoxy out of a sealed container (I use a pressure cooker with the safety plug filled myself) but you will be using MUCH lower pressure than if you pumped the epoxy directly, approximately 100 PSI instead of a few thousand PSI.

I was hoping that heated, low viscosity epoxy would get around that high of pressure. Even at 50psi it would take a pretty stout mold to hold shape. If it takes say 100psi to pump through the aggregate the mold walls would be reacting the load pretty early on during the infusion I would think. It would'nt be a matter only seeing the load when the epoxy/aggregate is 100%.

What do you say?

[probinson]

Sounds perfect a a first trial. Should be more than sufficient to give insight into what it will take to make thing work.

[probinson]

Actually, I really don't see how you can get complete air removal in a large mold trying to force the epoxy in to compacted aggregate. My thought is that you need to premix with excess epoxy then vibrate and compress the mixture forcing out excess.

That's not to discourage your attempts, just my untested opinion. I am sure we will all be tickled to death if it works.

[lgalla]

Resin transfer molding and infusion are similar.Usually in RTM a heafty mold is necessary as resin is injected at 1500psi or more.The reinforcements of choice are continuos mat and cloth or rovings.Compared to E/G there is tons of space for the resin to flow.The pressure on the mold is low as long as the resin has somewhere to go.When a closed mold is full it must withstand the full injection pressure.The problem with a good aggregate mix is there is little space for the resin which will cause pressure build up right away.Addition of fiber will cause more packing and local build up of pressure.
Infusion is just vacuum pressure but would be too slow.
RTM and Infusion are great methods for molding parts with fiber,but not to wetout well packed aggregates.
The big boys use vacuum mixing and vibration tables and this is the proper path to follow.
Larry

[ckelloug]

Howdy all,

I wanted to say that I too will try the pressure/vacuum approach out of interest as Tony definitely has some experience in the area that I lack. If Walter were still tracking this however, he'd have a fit because molding under pressure and vacuum in heavily prepared molds will turn out to be the very antithesis of easy: even if the results are great.

Pressure and vacuum may very well be the way to go for volume manufacture of machine parts and I'm also in favor of vacuum degassing. I'm not so sure however that a pressurized resin vacuum infusion process will work well for guys trying to build routers with improvised tooling.

For all the work done on this thread, we still have a ways to go. I just sawed some samples of Hexion 813/IPDA with different cure cycles. Some of the samples appear quite rigid but due to other tests I needed to do on this set of castings, I will only get to take a small amount of ASTM D790 data on them until I make some more castings.

Regards all,

Cameron

[qroger]

I hope I am not repeating. In the current issue of Civil Engineering, there are two places where "waterless concrete" is announced for possible use in poured in place structures on the moon. Peter C. Chen working at NASA proposes to spin cast a reflecting telescope dish using epoxy, carbon nanotubes and lunar dust.

Houssam S. Toutanji, and Richard N. Grugel, report that NASA has also considered using molten sulfur reinforced with glass fibers to cement lunar aggregate together, creating a waterless concrete suitable for construction purposes. The thrust of the article was the effect of the glass fiber on the strength of the concrete.

[jhudler]

Just a note:
Lest we forget (John Wayne; She Wore a Yellow Ribbon).

Buying the epoxy and aggregate is 1/4 the battle. (Ignoring the 3385 previous posts .

You now have to mix, vibratory compact, and cure that mass you think you're about to pour.

Also, one must not take the attitude of DFU (a rather vulgar acronym), so buy extra.

[ckelloug]

snookered1ca,

What did crosslink recommend?

[snookered1ca]

Cameron,
crosslink recomended their CLH 6520 product and I've attached their product data sheet. However after reading a lot of the previous posts, I'm at # 85 thus far, I don't think this is the correct product. It is described as a semi-flexible end product.
When I was talking to a rep from a supplier of PTM&W products he proposed a novel method of introducing a steel shot filler. That was to pour in a determined quantity of mixed resin and then add the shot until it came to the top of the epoxy and then repeat as necessary. In theory this would enable the maximum amount of filler to epoxy ratio and it would eliminate or reduce the probability of voids.
One concern that does come into play is would a casting with a steel shot filler have the same dampaning properties as one with crushed granite filler.

Bruce

[crr]

Hello all-

Here is a picture of the mold I am going to build so that I can make 5 samples at once.

I also have all of the materials necessary (Resin, hardener, aggregate additives) and hope to have some samples by the end of next week.

The plan with the mold is to put the resin feed lines in the rounded ends of the individual cavities, then add the aggregate. vibrate, vacuum, infuse and cure.

[snookered1ca]

I'm new to this group and would like to get up to speed relatively quickly, is there any compilation of the posts that one could read without going through all 3388 of them. Even a current status overview would be helpful.

Bruce

[snookered1ca]

Sorry to reply to reply to my own thread but I just came across post 3320 - 3324 that has shed a great deal of light on the subject. Any other info would be greatly appreciated.

Bruce

[ckelloug]

snookered,

Check the sticky index thread at the top of the forum that the EG thread is in. That summarizes the contents of the first 1500 or so posts. Indexing is labor intensive and it hasn't been updated in a while. Thanks for the link to crosslink's reccomendation.

crr,

That looks like an impressive mold. I've been out in the shop turning the cranks on my bridgeport to make a block casting mold to cast 8x8 by 1/2 blocks. Your CNC will probably have your mold made before I even get all of the stock square Thanks for your work!

Regards all,
Cameron