Epoxy-Granite machine bases (was Polymer concrete frame?)

[lgalla]

I gave a link earlyer to an article on type and sizing of aggreate.Search Google....machine design polymer castings....I guess nobody read it as there is still questions about aggregate sizing.Sorry having trouble linking.
The other link I left has a picture of a huge E/G machine.What is it? I will try a direct link.www.moldmakingtechnology.com/articles/040401
Larry
Woops that almost worked.use search in the top right type in 040401 If that does not work search Google"moldmaking technology secrets to hard milling

[lgalla]

I did some fieldwork today,actually visited Home Depot and a huge concrete place.Builders sand is soaking wet.Not suitable for epoxy.The bags of playsand seem promising as they are very dry and clean.The home depot suggested sandblast sand as it is graded and dry,but were out of stock.I checked the bagged gravel but it is not suitable as it is very dirty.Anything we use must be washed,to remove dust and clay.Crushed stone is not a good choice as it is jagged.Particles tend to "snag"on each other,making the mix thicker than necessary.Simply put smooth aggregates will "roll over one another like ballbearings creating a smoother mix.
On what is too big for aggregates,"If the aggregate is too large,1inch or larger it results in poor stregnth as the aggregate has different stiffness and properties compared to the binder[epoxy].The concrete place said 3/4 is their max size.Picture this 2"rough aggregate poured with cement into a 4" wide form.the rocks can lock together and not drop in forming a bridge.
Also if large aggregates are used,when you vibrate for air release and compaction the matrix becomes very fluid at certain frequincy and the large aggregate will drop like a stone[pardon the expression]to the bottom.
Is there a solution?Yes if you have read the links I posted Quartz sand is a good fine filler and max aggregate size is.375in.+smooth is better.
I don't know about you guys,but I am getting"AGREGATED about aggrates.I know a fair bit about epoxy.
Here is a few pointers.
Raw epoxy is solvent free and ships non hazmat.
Cheap reactive dilutents are used to thin the epoxy and thin the price.They also thin the properties.Ask your supplier if their epoxy contains Nonyl Phenol.
If your supplyer cannot ship non hazmat the epoxy has dangerous additaves.
Raw, neet epoxy has low vapour pressure{smell is not bad]
Reactive dilutents have very strong odour,might i add unbearable.Again if it ships non hazmat it is probably OK epoxy.To confirm request MSDS from the supplier.
We need thin epoxy to maximize filler loading.This would be called Laminating epoxy.Thinnest ? Probably 600cps which would be the consistancy of #one Canadian maple syrup.Suddenly I feel like bacon& pancakes.
Epoxy glue is 10,000cps or better.No use to us granite guys.Similar to honey.
We want a long pot life to maximize mixing time and reduce heat build up.Many times we have mixed or de gassed for too long and the epoxy is really hot.Now we are sweating granite bricks trying to get it in the mold fast before gell.
Why is epoxy such a great glue?Just before gell it thins out penetrating almost anything.I have in the past taped off mold edges only to discouver the epoxy penetrated the tape.This is also why the German guys saw pooling.Any how its near 1Am here to tired to go on and on.Hope you are not bored to death.Stay tuned for more epoxy 101 to-morrow.
Larry

[greybeard]

Chris - having ploughed through the article you linked to( loses something in translation from the Japanese I think) it seems to me to be a different ball game.
Their article uses polyester resins, and the granite aggregates are aimed at the appearance of the material. The strength of their sculpture is coming from steel rod, wire mesh and glass fibre mat.

In the ratio figures you quoted they seem to include the steel rod and a chalk filler. Like I suggested, it's not the easiest article to extract the technical details from.
Regards
John

[Mcgyver]

all sand is not created equal, as you seeing. The better stuff is considered better because for one it isn't leacherous - chemicals don't leach out of it. This 'better sand' makes its way into markets like water filtration sand or aquarium sand/gravel - two examples that require the sand to be clean as well as non-leacherous. these sands are usually granite based vs limestone as the limestone will leach, however its still rare, a lot of granite leaches as well. for the lucky owners of such deposits, the price per ton is 10x as high and water filtration sand for example is trucked distances as its is not as common. bottom line is water filtration sand should be clean and won't leach

So far as avoiding crushed stone goes, continue looking in landscaping centres or architectural suppliers of stone. These markets want aesthetics and the crushed look won't do - like surface treatment of precast panels for example or ground covers. 'river rock' for example which comes from kame deposits and is nicely rounded. construction uses don't care about leaching or ascetics so thats' the wrong supply chain to look in imo. I believe some pits even 'polish' crushed aggregates to remove the sharp edges/irregular shape.

[nMotion]

Lots of good info in this thread! I think that it is important not to over-complicate the process. Sure, as a manufacturer we have tried to perfect our formulation. Many manufacturers optimize in areas such as strict aggregate sizing, specific aggregate mineral formulations, very high granite to epoxy ratios, complicated shake and vacuum arrangements, high precision molds, and many others. Many of these optimizations are only practical when the costs and efforts associated with such optimizations can be amortized over the the product's lifespan.

As a hobbyist or someone without a need to create many machines, you are free to use materials and processes that may not be practical to a manufacturer. For example, you can simply add additional internal reinforcement to counter effects of voids created by ungraded aggregate and less complicated compaction and deaerating techniques. Also, because you are adding reinforcement you can use a higher percentage of epoxy and smaller aggregate to ease mixing and pouring and still have equivalent rigidity. Since you are not running a production line, you don't have to be concerned about the small additional cost of extra epoxy.

Here are some important notes on granite, epoxy and molds to help ensure a good casting(some of these have already been mentioned):

Granite

• Size: 3/8 to sand
• Rounded edges ease mixing and compaction
• Clean and dry aggregate well

"Decomposed granite" from landscaping places usually has a good mix of sizes and relatively smooth edges. If you want to get kind of fancy, you could probably separate the granite by size using appropriately sized wire screens, and then combine in an optimized ratio. This really isn't necessary, but I know some of us are overachievers...

Epoxy

• Low viscosity
• Slow cure
• Minimal amount of additives

lgalla did a great job with his specifications:

Raw epoxy is solvent free and ships non hazmat.
Cheap reactive dilutents are used to thin the epoxy and thin the price.They also thin the properties.Ask your supplier if their epoxy contains Nonyl Phenol.
If your supplyer cannot ship non hazmat the epoxy has dangerous additaves.
Raw, neet epoxy has low vapour pressure{smell is not bad]
Reactive dilutents have very strong odour,might i add unbearable.Again if it ships non hazmat it is probably OK epoxy.To confirm request MSDS from the supplier.
We need thin epoxy to maximize filler loading.This would be called Laminating epoxy.Thinnest ? Probably 600cps which would be the consistancy of #one Canadian maple syrup.Suddenly I feel like bacon& pancakes.
Epoxy glue is 10,000cps or better.No use to us granite guys.Similar to honey.
We want a long pot life to maximize mixing time and reduce heat build up.Many times we have mixed or de gassed for too long and the epoxy is really hot.Now we are sweating granite bricks trying to get it in the mold fast before gell.

Molds

• Masonite or similar with a smooth surface and adequate thickness for noncritical mold sections
• Aluminum or steal on areas to be precisely replicated
• Take the time to produce your precision mold surfaces to a higher degree of accuracy than you want your final product
• Don't place inserts closer than 3/4" from an edge
• Use a wax based release that is brushed on. Apply a coat, let dry, buff with a soft rag, then repeat two to four more times
• A gel coat may also be used

I hope this helps. I will post some tips later about the molding process.

Matt

[lgalla]

Thanks Matt for the good info.
I agree we are getting too complated.From all the posts I think we can agree on smooth sand and aggregate up to 3/8".I hope you agree 90% filler is almost impossible for the home guy.So what if the big guys are claiming 50times better damping than steel,if we have 80% fill what will we have?48% damping?Still better than a hollow steel tube.As I stated before I previosly did "fake granite counter tops"The mix was 50% and required vacuum degassing and vibration or entrapped air would spoil the exterior finish.I won't elaborate on vacuum de-gassing unless someone makes a request.
I found a source for black granite sand and screened and washed black granite aggregates.I found them under quarrys'in northern Ontario.They have a huge list of outlets in ontario.I emailed them for more info.As other posts have said members should be able to find aggregates locally.
Matt how about tips on mixing?I understand the German guys did it manually.Do you have to use a concrete mixer?
Here are a few epoxy mix tips.
Measure A&B in separate containers, pour into the mix bucket and scrape out every last drop.Use some kind of propellor mixer on a drill.Pause at intervals to scrape the sides of the mix bucket to the centre as the epoxy near the walls tends not to mix in.I must add to use relatively low RPM as you will whip in tons of air.I have only experience with micron spherical fillers ie 200 micron and under.We would mix the largest spheres first then the fines.Matt would this hold true for granite?Gravell first sand next?
Matt I also agree some fiber re- inforcment could help.A gell coat & carbon fiber first layer would look kool.
It is unusual for a company to help,so Matt I must thank you.
Larry

[walter]

Larry, good to have you on board, you're our epoxy expert.

And thanks to all others for their contribution. Much appreciated!

[walter]

...I don't think the full epoxy concrete approach is feasible for DIY. If you look at the German pictures they appear to have steel ways with bolts screwed in the back side and mounted in their mold. It would seem the bolts are acting to anchor the steel ways in the epoxy concrete. Some of the other links also mention making highly accurate molds for casting the epoxy concrete to tight tolerances and they also mention that it cannot be worked once cured; all threaded attachments have to be cast in situ...

That actually was the original idea- all bolts, reinforcements/attachments, mounting "devices" build into the epoxy(picture)- which would create a "plug and play" table, frame part or even entire gantry.

Polymer/concrete/epoxy may not be the best solution, but it sure beats the alternative:

I am in the process of building a welded steel frame over 10' long for my catilevered mill.
The basis is a Steel I-beam 24" between webs, 5/8 thick flanges 10' wide, with lots of 4x4x.25 wall A36 steel tubing welded in a torsion box design on bot sides between the flanges.
The cost for stress relieving something this big and massive in Northern CA is going to be between $1000 to $1200 dollars.
Blanchard grinding the long axis is going to cost another $750.
When I look at the overall cost and affect on accuracy, it seemed like a good tradeoff vs other construction techniques.
If the frame isn't straight and flat, it will be useless, hence the stress relief and grinding. Al

[lgalla]

I am in a post mood.I always worry I forgot something.
If you are having trouble with mold release,NEVER,NEVER,EVER,NEVER use "silly-cone" release agents.Silly-cone release agents will contaminate your shop forever and you will never be able to acheive secondary bonding such as painting or an epoxy pour.High end car paint shops will not let you in the door if you used Armoral on your tires.
I did not want to post this other idea on the E/G thing possibly adding a small%age of 1/32 milled glass fiber as this would greatly reduce the viscosity and result in lower aggregate/epoxy ratios.The benefit is micro fibers would reinforce the bond between the aggregates.Idon't know if this is true today but epoxies 20 years ago would not stick to cured epoxy.Repairs were impossible.I think this problem has been resolved as suppliers say secondary bonding is not a problem.Our solution in the "old days" was to add a small % milled glass.When sanded the resin would sand away leaving micro fibers on the surface promoting secondary bonding on cured epoxy.If you are casting in many pours you have to pour within the WINDOW of your epoxy usually 24 hrs.In plain english layers should be within 24hrs or secondary bonding may be a problem.cALCULATE WHAT Epoxy you need for the job.You do not to run short and wait a week for more epoxy.Make sure you have enough for the job.
Larry

[Geof]

That actually was the original idea- all bolts, reinforcements/attachments, mounting "devices" build into the epoxy(picture)- which would create a "plug and play" table, frame part or even entire gantry.

Polymer/concrete/epoxy may not be the best solution, but it sure beats the alternative:

But my point is you have to effectively build the alternative to hold all your bolts, reinforcements/attachments, mounting "devices" in the correct place within the mold in which you then cast the epoxy. And if you do not get everything in the correct place you are stuck because you cannot rework the epoxy.

[walter]

Is that a birch plywood?
Yeah...I want to use that. Seems effective

[lgalla]

Geof. you are absolutly right.
What you are talking about is beyond the hobyist.I think Walter and I are thinking is a non welded frame and epoxy surface plate to facilitate in accurate rail and gantry mounting having a flat epoxy reference plane.For the milling and lathe guys filling hollows will enhance the machines performance.I have a lot of molding and epoxy experience and would not consider a totally composite structure.I don't care if anyone follows directions or not but if you fill a hollow with any ratio sand/ epoxy you will acheive better machine performance.I know you are aware of this better damping extends tool life.The grinding people claim 30% INCREASED tool life with E/G damping.Many years ago I had a pin router at 4500lbs.I would change the bit one time per year if necessary.Weight or damping factor increases the quality of cut.I know you know this.E/G may squeze out that last thou of accuracy.
Larry

[greybeard]

But my point is you have to effectively build the alternative to hold all your bolts, reinforcements/attachments, mounting "devices" in the correct place within the mold in which you then cast the epoxy. And if you do not get everything in the correct place you are stuck because you cannot rework the epoxy.

But I would assume that all the "bolt ons" would be adjustable in position anyway. Seems crazy not to do so.
Surely the whole point of the EG is to give a well damped, simplified(!!) constructional method for frames etc.

Just my groat's worth though.

John

[RotarySMP]

I went to the library yesterday and got out ISBN 3-478-93273-4 "Mineralguss für den Maschinenbau".

It reinforces the gems of knowledge Matt has shared:

Aggregates from <0.1mm (Sand dust) up to 16mm (on the larger castings from 80mm section thickness). Whereby you want to aim for 1/5 to 1/8 your smallest feature.

Resin ratios by weight of 7% to 10%.

Shaking frequencies up to 70Hz and accelerations to 25 m/3 (2.5g) This is basically your industrial 2 pole motor with a unbalance. If you pick up a cheap motor and VFD off ebay, you can vary the speed until you hit the sweet spot for each casting.

The largest castings use a combination of a shaking table and shaking motors bolted to the outside of the form.

For optimal bond, any steel inserts you bond into the part should be sand blasted.

The practical method for prototypes and us homebuilders is wooden forms with steel sections moulded in which are subsequently milled or ground to tolerance. The big guys are going more and more to cast to tolerance, but also do grinding of the mineral to tolerance. If you have a surface plate and an eye for detail, grinding and scraping alignment rails could be a garage job.

Tolerances to +- 0,5mm should be posible with wooden molds.

Edge distance for inserts should be >3D.

If you intend to reuse the form, it should taper about 5°.

Round all internal edges.

A rule of thumb would be a polymer concrete machine base is made the same size as a cast iron part, but solid where the C.I part would be cored, should have nearly the same weight and approx 3.5x the stiffness.

As the shrinkage of epoxy occurs around the time it gels, much if the shrinkage is compensated by further filling of the still liquid mix. The final shrinkage is given as 0.02 - 0.03% linear.

[Geof]

....I don't care if anyone follows directions or not but if you fill a hollow with any ratio sand/ epoxy you will acheive better machine performance....Larry

You do not need to go to the complication of epoxy and fancy aggregate ratios.The thesis on rapid machine design, which was designing a big toolgrinding machine, that Bob gave a link to goes into damping in great depth. They found that simple concrete inside tubular structures was very good and concrete with an additive to prevent shrinkage on curing inside rubber bags in tubular structures was excellent. It is not surprising that the bag technigue worked best because they were effectively making a constrained layer damping system which is the most efficient possible. I have not found any detailed analyses but I am sure the reason the epoxy/aggregate mix damps so well is because the entire structure is in effect a constrained layer damper; it is comprised of to materials with radically different Young's moduli so vibration cannot effectively pass through in any direction.

[RotarySMP]

Geof, Polymer concrete offers a lot of advantages beyond the rigidity and damping.

You have a medium:
- you can cast at room temperature,
- which solidifies without internal stress,
- you can cast with varying cross sections,
- which doesn't shrink,
- which is stable ,
- has very limited thermal conductivity,
- electrical insulator,
- which is impervious to liquids,
- costs very little,
- you can core in your coolant lines, electrical conduit, lube lines, swarf paths,
- it's a low energy consumption process,
- the result is recycleable.

You are correct that adding a damping mass to a fabricated structure improves it's vibration response (lead shot would be a good choice), but that is not the purpose of this thread.

[Geof]

....You are correct that adding a damping mass to a fabricated structure improves it's vibration response (lead shot would be a good choice), but that is not the purpose of this thread.

This is copied from the thread starter:

"Did anyone managed to build anything out of polymer concrete? I would be interested in your experiences and materials suitable for machine frames, tables, etc."

At the DIY level I don't think polymer concrete is practical for building machine frames; my posts reflect this opinion and I don't think I have drifted too far away from addressing the topic of the thread.

[lgalla]

Found new source for granite.Search turkey grit or chicken grit.Really I am not kidding.They are graded in different sizes eg chick,chicken,turkey.I beleive birds eat stones as they have no teeth and stones aid in dijestion.
Picture this a promo for a new polymer machine.Made with 20%playsand,20%chick grit,20%chicken grit,30%turkey gravel,and high strength binder.
Larry

[walter]

Cutting heavy steel tubing, welding, end plate machining, endless drilling<---- that's what is not practical at DIY level
I don't feel like buying 8" metal saw, welding machine and drill press just to build a frame. And there is no way I'm doing any precision machining lol- I will have THAT capability when my CNC router is done


I found some more on Polymer Concrete:

"Polymer concrete (PC), or resin concrete, consists of a polymer binder, and a mineral filler such as aggregate, gravel and crushed stone. PC has higher strength, greater resistance to chemicals and corrosive agents, lower water absorption and higher freeze-thaw stability than conventional Portland cement concrete.
Polymer concrete consists of a mineral filler (for example, an aggregate) and a polymer binder (which may be a thermoplastic2, 3, but more frequently, it is a thermosetting polymer2, 4. When sand is used as a filler, the composite is referred to as a polymer mortar. Other fillers include crushed stone, gravel, limestone, chalk, condensed silica fume (silica flour, silica dust), granite, quartz, clay, expanded glass, and metallic fillers. Generally, any dry, non-absorbent, solid material can be used as a filler.

Polymer concrete composites have generally good resistance to attack by chemicals and other corrosive agents, have very low water sorption properties, good resistance to abrasion and marked freeze-thaw stability. Also, the greater strength of polymer concrete in comparison to that of Portland cement concrete permits the use of up to 50 percent less material. This puts polymer concrete on a competitive basis with cement concrete in certain special applications"

Montmorillonite polymer concrete: Zero-shrinkage and expanding polymer concrete with enhanced strength

"Conventional polymer concrete (PC) suffers from setting stresses, generated during the cure of the resin binder, when polymerization shrinkage is hindered by the close packing of filler and aggregate particles. Setting stresses impair significantly the strength of the cured PC. Current zero-shrinkage and expanding PC formulations achieve these properties with a sacrifice in strength. Here we present a novel method for producing zero-shrinkage and expanding PC systems with concomitant enhancement in strength. This is achieved by dispersing small amounts of the mineral montmorillonite (MMT) into the resin. As the system cures, the resin interacts with the hydrated mineral: at temperatures above 100°C some of the hydration water is released, creating expansion forces, which counteract resin shrinkage. MMT contents of 0.2 percent or less give rise to zero-shrinkage polyester PC systems with flexural strength 30 percent greater than the corresponding conventional PC.."

[greybeard]

I think it's imperative to keep clear in mind the difference between "polyester" resins(familliar as glass reinforced plastic materials), and "epoxy resins" more familliar as potting compounds.
The first has large shrinkage in polymerisation and contains lots of viscosity lowering solvents adding to the problem, and the later with next to zero shrinkage.

The idea of introducing a compound to release water into the mix just to counter shrinkage seems a backward step to say the least !!!

John