[martinw]

Vacuum forming wet layups usually use a peel ply and bleeder ply inside the bag incontact with the layup. The peel ply, is usually something like polyester that the epoxy won't stick to that is perforated to allow epoxy through but not the layup. The bleeder ply is the transport to move the excess epoxy thats pushed through the peel ply by the vacuum (yup thats right ). Excess epoxy is removed without passing the layup or in this case the aggregate.

.

Dear fyffe555,

Thanks for that. In the case of E/G, are you saying that the peel ply and bleeder ply would act as a "filter" to retain the fine aggregates in the compacted mix? I know I'm still being dumb.

Best wishes

Martin

[ger21]

How do you keep the bag from distorting the mold?

[lgalla]

Andrew thanks for the explaination.
I might add the success of the process is the autoclave is heated and pressurized to 100psi or so giving high quality laminates.
Thanks
Larry

[lgalla]

Gerry
How do you keep the bag from distorting the mold?
__________________
Gerry
The vacuum pressure would be equal in all directions not distorting the mold.If the mold had any internal large voids,different story,the mold may collapse.
Larry

[martinw]

Dear Larry,

But if the mix has air bubbles in it to begin with when you turn on the vacuum,
would that still apply?

Best wishes

Martin

[LeeWay]

Someone who made samples earlier in the thread said it didn't get hot, just warm (Zumba?). If it was just epoxy, then yes, it would get very hot, but it's only 10-20% epoxy, so the aggregates keep it cooler.

Thanks Gerry.
You are probably right, but when it is surrounded by a bag, the heat formed wouldn't have anywhere to escape. That is unless it's pulled out through the vacuum. I know the one guys thread I have seen spoke of it getting pretty hot if you poured too much at one time. I imagine his mixture is far more epoxy than we are talking here with this formula though. Has anyone nailed down the thickness we are talking yet? Will thicker slabs have to be done in stages?
Just really curious on this, because in the near future, I will be filling some 3060 80/20 extrusions with something. The intent right now is hydraulic anchoring cement with small rebar and #8 shot, but if we get some formula's for this figured out in the mean time, I may go that route.

[brunog]

This link might help us understanding the vibrating process of concrete:

http://www.precast.org/publications/...nVibration.htm

Best regards

Bruno

[Stepper Monkey]

I dont have any clue about the best way to handle the finer details of making machine tables with this process, as I haven't used or seen it used for this exact purpose. The process is pretty straightforward, but just like anything there will likely be details for this exact purpose that will only be discovered with practice.

A few bits that might help though;

The de-bubbling really needs to be done before compaction, whether using vibration, vacuum, or a combination of the two.

Sorry I didn't do a very good job of explaining earlier, you were right in that there needs to be a porous "filter" to pass the binder, but can even be just small vent holes in the top plate or the small gap around it as the aggregate should hopefully not really want to extrude while under compaction.

The vacuum doesn't distort the mold, as the mold is rigid, and so is the plate placed over the mix that acts as a ram. They do however move relative to one another so the top plate acts like a piston compressing the mix evenly and squeezing out excess through and around it.

No heat problems - the vinyl doesn't need to stay on through cure, only compaction. Vacuum left on until cure would kill a vac pump! It isn't like after compaction it is going to really expand again, and anyway you just clamp or use a press to hold it until cure.

The cross-sectional density here is different than anything I've done before. Vacuum force is directly related to surface area which is why it is so beautiful for big or irregularly shaped stuff.
For the linited surface area involved for this project, do you even need to vacuum to compact if you have a hydraulic press to drive the ram? You could still get 1 ton/sq ft.+ pretty easy even with a small press.

I'm going to have to try that later.

[martinw]

Dear fyffe555 and Stepper Monkey,

I understand, at last. Sorry for taking so long to get there.

They were really useful posts.

Thanks

Best wishes

Martin

[lgalla]

I don't see useing Vacuum bag molding techniques as being very useful for our purposes.De-gassing a2or3mm fiber laminate compared to 4"of E/G is entirely a different animal.You willnot pull air through 4" of material.If you use a caul or pressure plate without vibratory compaction the press will not do to much.The 10% or less mixes are not even of trowl consistancy.You are not going to pull air out of this heavy mix.
On sucking out excess resin,there is no excess resin at 10% or less.
I am not discounting the process only stating some downsides.It is worth discussing and would require lots of experimentation.Doable??I don't know.The bag method would have to be modifyed to work.
Larry

[lgalla]

In a previous life I made"densifyed marble countertops"This is a repeat,but for anyone missing previous posts.The mix was 60% fill,40% resin.The resin was 100cps.This is a very porable mix which was vacuumed mixed for 5 minutes,poured into the mold and vibrated.Any higher ratios of fill would not acheive good surface quality from entrapped air problems.This is why I am against 5to10% resin ratios.would prove difficult with our resorces.
I am not against trying.We may come up with a solution.
My.02Pesos worth
Larry

[Zumba]

Now that this thread has broken past the 800-post mark, I think we should start talking about practical solutions.

Let's pretend were using this recipe:
Aggregate: fine sand, course sand, and little pebbles, 85% by weight
Epoxy: US Composites Thin with slow cure hardener. 15% by weight
Coloring: Blue dye for aesthetics.

1.) Mixing. It is unlikely that anyone here will want to invest money in a vacuum mixing device. Hence we will have to mix in a bucket in open air, which means there will tons of air bubbles in the mix.

2.) Degassing prior to pouring. We will have to place the mix in a vacuum chamber. I've already tried using vacuum alone on a 3" deep mix. It didn't eliminate all the air bubbles, especially the ones at the bottom. Vibration is mandatory. What's the best way to vibrate the mix while under vacuum? Note that the vacuum chamber cannot collapse under 28 inHg, and the bucket of mix needs to be rigidly connected to the vibration device, otherwise the vibrations will not pass through.

3.) Pouring. Assuming the air bubbles are completely gone, we'll need to use vibration by itself to ensure that the mix fills every crevice of the mold. Best way to do this would be to rigidly mount the form to a vibrating table. How do we build a large enough vibrating table on the cheap?

P.S. The West Systems medium-viscosity epoxy with FAST hardener generated very little heat in a 3" deep pour. It was warm at best. Clearly, the high percentage of aggregate by weight acts as a very good heat sink. We can eliminate heat as a potential source of problems.

[BobWarfield]

Geez guys, as Zumba says, time to get practical and start converging this thread towards getting something built. There's a mill base that's been done, but nothing else in over 800 posts!

Much ado about degassing, but why? Is it to create a precision surface? The only precision surfaces discussed in any detail were the "surface plate" floors. There's no vacuum bagging or vibration being used there. How did they get it to work? There must be a simpler way than building giant degassing tables and vacuum mixing chambers, even if all you did was purchase and pour their material.

It has been said that heat will facilitate a reduction in bubbles. Great! Build your mold in 1/4" steel, pour the aggregate sans epoxy, heat that whole assembly up, and then add the epoxy. Plenty of thermal mass in the aggregate and steel. The epoxy will find a nice warm resting place that should make it very thin. Use some slower curing material. First, the heat will speed curing, and second, it will give more time for the bubbles to leave.

I still have heard no discussion or demonstrated samples of how you're going to make the precision surface aside from all the degassing chatter. How does the surface get smooth and true? There seems to be a lot of hope the epoxy itself will just work out for this if you pour a little above the aggregate. How are you going to get that to line up just right with the inserts you'll need? Who will try an experiment to proove how smooth it can be and work out those bugs? The pix of machine bases are extremely smooth and uniform.

If the degassing is not about creating a precision surface, why bother degassing? Or, if it is going to be so hard to create a precision surface that no one has yet done it on the thread, why not focus discussion on machine designs that don't need a precision surface? If you're just dampening fabricated structures of one kind or another, extrusions, weldments, or even mdf torque boxes, there is no need to worry about degassing. Pour the E/G in the voids as the fellow did with his mill base and move on.

It seems to me that moving table gantry mills are ideal for use of E/G mix. Take a look at this fellow's build:



It's over here:

http://www.cnczone.com/forums/showth...172#post281172

Put a 1/4" bottom plate on that, weld some inserts to hold linear rails, and pour E/G around the inserts to dampen the whole works. Should make for an awesome gantry mill.

Use aluminum extrusions and bolts if you don't weld.

Cheers,

BW

[lgalla]

Good posts Bob&Zumba.
Bob the guys are worried about air entrapment as it weakens the mix.I really would not worry about it much as E/G should mainly be used for damping steel structures.A home constructor should not try a total E/G structure.
I am just repeating what I previously posted:
I mix sand and epoxy in a 5 gal plastic pail until it is very thick.Place the pail in a tub of hot water 90DegreesF or above.the 600cps epoxy will thin to 100 to 200cps allowing tons more sand to be added.Dropping the pail from 6"above the floor rapidly helps to compact and you will see air bubbles appearing and possibly pooling on top.A mix done this way should be fine for filling weldments and easy with minimal tools.
Next if you have the equipment.I place the less than half full bucket in a 10gal paint pressure pot and draw a vacuum.My tank has a mix propellor.If you do not have the mixer.tipping the pot and rocking back and fourth will help,similar to a concrete mixer.
I have said it many times before 5to10%resin mixes are beyond use home guys.If you are a large machinery co.and aggregates are20 bucks a ton and epoxy20,000 a ton.It is worth spending millions on vacuum.vibrating tables etc.
Larry

[brunog]

Larry,
I still believe that building a building a total E/G structure is possible without spending a fortune in equipement.

I also believe that is all our responsability to read what has been posted so far and stop repeating ourselves, it just doesn't bring anything constructive to this thread. I will not post anything more unless it makes this thread evolve.

I think we have come a long way since the first post and that I personally have learned a lot through this thread, let's stop looking behind and move fore ward with this thread.

I have a pile of data to read and I will be ready to work on designing a total E/G machine.

best regards to all

Bruno

[speed33317]

Hi,

Jumping in on this ride :-)

I have been doing my own experiments, actually they are curing right now.

I have tried my formula by volume which works out to 10% epoxy.

Yes it is very stiff and tiring to the hands while mixing.
You have to ram it into the mold.

I used slow cure epoxy.

1st mix I used pool filter sand ,pretty coarse but clean no dust.

2nd mix I used ground up granite paver base, kind of a dirty mix
I just used it as is, dust and all.

I was at Harbor Freight during my lunch hour today and found
a cement mixer for $99 , when it comes time to mixing up
1000 pounds of this stuff it will be money well spent.

[lgalla]

Zumba,Bob,Bruno I agree this seems to be going nowhere as we have been stuck on air bubbles for the last 500posts.In reality guys building machines can take years to complete.Patience is warrented as this is a new thing requiring much thought.3or4 members have taken the plunge and started experimenting.Have patience Bob.I feel bad as I am the guilty one repeating and repeating and repeating myself over and over again.
FromBruno Quote
I also believe that is all our responsability to read what has been posted so far and stop repeating ourselves, it just doesn't bring anything constructive to this thread. I will not post anything more unless it makes this thread evolve."I have spent countless hours researching and giving advice especially If I see a definate NoNo.Any problems or questions will be accepted via Private E-mail on the Zone or [email protected]
Larry

[Zumba]

I actually have no problem with the repeat posts. As time passes, we look back at what we said earlier and may have a different take on things.

Anyway, let's discuss vibration. Realistically, none of us are going to get the vibrations above 300-400Hz, due to the units that are readily available. I'm willing to bet that 60Hz would be sufficient for what we're doing.

I'm looking through McMaster's offerings and see several different types, linear/all-direction, pneumatic/electromagnetic/electric, etc Before deciding on exactly which type, does anyone here know how much force is required to vibrate 2-3 gallons of mix? The available units range from 20 lbs of force to several thousand.

There's this pneumatic rotary ball vibrator (vibrates in all directions), the puts out 689 lbs of force at 200Hz and costs $99.78 (5807K73). Draws 15CFM @ 60psi which my compressor can handle. I thinking about bolting this to a table for making my own vibrating table. Then strap down a pressure pot (vacuum chamber) to the table.

[LeeWay]

I have seen this type used on dump trailers. They turn it on for seconds only and it literally cleans out anything that was clinging to the sides when dumping.
On trailers, they are extremely loud.
I imagine you would have to have a solid work bench that was bolted together or welded. Might not work well with something nailed together.

I know a ROS is a repeat suggestion here, but I guarantee you that they are sufficient to vibrate a 5 gallon bucket with whatever mix might be inside.
VS would allow you to try a range of frequencies. Even a HF air sander, impact wrench, air chisel etc would all have pretty good vibrating characteristics on the cheap. Set the bucket on a foam pad and attach the vibrator choice to the bucket. As long as the mix is slow cure and the air is lighter than everything else in there, the bubbles will rise.
You can get a HF bench grinder and I bet the wheels are so bad that they would do enough vibrating to tackle the issue. DAMHIKT.

[brunog]

I feel bad as I am the guilty one repeating and repeating and repeating myself over and over again.
FromBruno Quote
I also believe that is all our responsability to read what has been posted so far and stop repeating ourselves, it just doesn't bring anything constructive to this thread. I will not post anything more unless it makes this thread evolve."I have spent countless hours researching and giving advice especially If I see a definate NoNo.Larry

Larry,
Don't feel bad about it, the reason why you have repeated yourself is mainly because peopel have brought questions that have been discussed in this thread many posts ago and that is the reason I brought in that comment.

best regards

Bruno