[thehairs]

So, it sounds like as long as I use epoxy I won't even have to wax the foam. Have you done any mineral casting? If so what do you think of the casting in layers.

D.Hair

[keebler303]

I work in composites, no mineral casting but some resin casting with other things in them. If you just use the foam, it will be stuck, but you can rip the foam out and you will be left with a fairly clean shape. Wax will make it a PITA to bond to later if that is your intent.

Casting in layers is not recommended because you may not get a good mechanical bond between the layers.

Can epoxies be bonded to cured epoxy?

[thehairs]

OK. What if the layers were about 1 1/2 hours apart. That would still be in the early cure stage. The reason I was wanting to layer the bed is where I could work all the air possible out of the first layer before pouring the second. Sorry to be picking your brain, but this is my first attempt and I hope to get it right thr first time.

David Hair

[keebler303]

I'm not a chemist so I can't say what the effect will be. If you rough up the surface between layers, it should be fine. All the casting I do is vacuum degassed before pouring or while in the mold. In some cases, a propane torch quickly moved over the surface will help to burst the bubbles near the surface.

Matt

[thehairs]

Thanks Matt, I'm learning. I think I will cast a small base for a tool grinder I'm building first. I'm ordering my epoxy in the next day or so to do both projects. Planning on usind crushed granite 3/8" or less sand blasting sand and rock dust from where the cut granite counter tops. I don't have the means to vacuum so I will be using a small metal rod to pack the mix into all of the tight corners. This is going to be interesting, but at least I'll learn a bit first hand before I cast on top of my lathe bed way. I'm afraid I will only have one shot at that.

David Hair

[thehairs]

sorry double posted

Can you not delete your own post on this forum?

David Hair

[johnohara]

Hi David~

An easy way to experiment and not break the bank is to make small samples using Laticrete SpectraLock Epoxy Grout.

It's sold as a "three" part system. Part A and B is the epoxy resin and hardener. Part C is the aggregate. If you read
the msds sheets on Part C you'll find it's a mix of Silica Sand (fine), Aluminum Oxide (fine blast) and Iron Oxide for
color. This blend will save you a lot of time and hassle trying to derive your own recipe. Buy a bag of pea gravel
for another $5.00 to add larger pieces to your mix. The gravel should be dried for 24 hours beforehand (you'll see the
moisture inside the bag.

The epoxy costs $20.00 and the aggregate is $4.00 for 2.5 lbs. --- plenty to experiment with.

Lowe's has it in the tile section. Home Depot doesn't carry it.

Buy some plastic bowls at the grocery store for your molds. The goal is to test the pot life and
de-airing and get used to casting with epoxy before you try something bigger.

~john

[vigneshpsg18]

is it possible to machine polymer concrete?if yes,how?

[eloid]

what happen to this thread? did anyone complete and testing with these castings cast

[made2hack]

Here are my tests for making various epoxy granite mixes. All of my measurements are BY WEIGHT. I tested the following formulations:

1 - Silica Sand 80um size (US mesh 170 - 200) + Epoxy in various amounts
2 - Aluminium Oxide aka Alumina aka Al203, 75um size (US mesh 170 - 200) + Epoxy in various amounts
3 - Silican Sand 50% by weight mixed with quartz (silica) pebbles from 1mm - 3mm size 50% by weight. This is the type of quartz / silica gravel you get for your aquarium
4 - Aggregate (epoxy granite aggregate) + Epoxy in various amounts

For the aggregate, I used from 40% - 50% by weight a gravel aggregate I bought from a local granite / marble counter top distributor. They call it granite gravel, but it also has bits of marble and other stone in it. It ranges in sizes from maybe 6mm up to 20mm. They are all jagged pieces, not round.
For 25% - 30%, I used the quarts gravel from the aquarium (1mm - 3mm) and for 25% - 30% I used the silica sand of 80um size. Once thoroughly mixed, I added Epoxy.

For my epoxy, I used an off the shelf epoxy for garage or industrial flooring. It is a 2 part epoxy (ISOMAT Durofloor PSF) in a ratio almost 2:1. It is actually 100:55 or 1.82:1 resin to hardener. This was mixed for 3 minutes and then mixed in to the sands or aggregates. I then kind of vibrated the mass, but not much, in order to try and eliminate some bubbles. They were cut out of the plastic cups after 24 hrs.

The pieces that were cut in half were cut using a diamond grinder blade used for masonry.

I find that the ideal mix of epoxy to aggregate is somewhere from 12.5% - 15% epoxy and 85% - 87.5% aggregate. Most of the literature on the subject seems to favour a maximum of 15% epoxy. After that, it is too much resin wasted.

[RCaffin]

A good spread indeed.
Will you be posting any test results - strength or whatever? That would be really useful.
Did any of them seem at all 'soft'?

Cheers
Roger

[made2hack]

A good spread indeed.
Will you be posting any test results - strength or whatever? That would be really useful.
Did any of them seem at all 'soft'?
Cheers
Roger

Hello Roger,

I do actually want to make a video on the subject, more detailed. I am not so much concerned with strength as I am with damping. What I plan to build (a 7x16 lathe) will have armature on the inside (think reinforced concrete). I don't know how to make a test for damping. From the literature, others have used a piezo resonator at both ends of a piece under test and various frequencies were transmitted and received. Perhaps I can maybe setup something similar.

As for them being soft, I wouldn't say so. I would liken them to "hard as a rock", especially the ones with very little epoxy. If there is a thick layer of epoxy on the edges, I suppose you can maybe characterize them as "softer", insofar as the resin has some plasticity. However, I would call them quite hard. I've yet to take a hammer to any of them.

Best regards,

[RCaffin]

Ah - damping. Yep, definitely of interest, but harder to measure.
Cheers
Roger

- - - Updated - - -

Ah - damping. Yep, definitely of interest, but harder to measure.
Cheers
Roger

[rocketflier]

Waterjets use fine garnet to abrasively cut through metal. You can pickup bags at abrasive suppliers, or.. the waterjet folks just toss it after it looses it's bite. I've been meaning to ask if they'd save me off a bucket...

[Halbmond]

Well done mate impressive, masterpiece study it is.
I appreciate it. Alumina test made me surprised that I never imagibed such thing before. But it seems brittle though. Allumina is the second hardest following diamond yea?

[made2hack]

Well done mate impressive, masterpiece study it is.
I appreciate it. Alumina test made me surprised that I never imagibed such thing before. But it seems brittle though. Allumina is the second hardest following diamond yea?

Hi, yeah it is at the top in terms of hardness, but you can go harder (think Carbides such as Silicon or Titanium Carbide. Although, I don't know if it matters in our case, since I am not trying to cut or sand another surface. I just want an epoxy composite to act as a vibration damper.

So in an epoxy matrix, it is no more brittle than the epoxy granite or quartz granite, unless you try to break it with a hammer.

However, as a ceramic (think Aluminium Oxide crucible), I imagine it is quite brittle (such as porcelain, maybe even more so). Then again, I guess a silicon oxide ceramic or titanium oxide ceramic would also break as easily.

The problem is that I don't think many companies sell Aluminium Oxide as stone or pebbles. You generally find it as a fine powder, usually purified for special use. Or sometimes you might find it as a larger particle for sand blasting.

Whereas Quartz (Silicon Oxide) is readily sold everywhere and is quite cheap. You can find it at the hardware store as silicia sand and at the pet store as aquarium quartz decoration.

[RotarySMP]

These are all very "wet" samples. Industrial experience shows that you need:
- to get the epoxy down to 8-12% for decent stiffness.
- a near fullers curve packing density.
- plenty of vibration, with the frequency tuned to your mould
- extremely fine finest aggregate
- largest aggregate 1/5 the smallest mould feature
- round rather than sharp aggregate.

I you can acheive that, you should be able to acheive a youngs modulus of aprox 60GPa.
Mark

[made2hack]

These are all very "wet" samples. Industrial experience shows that you need:
- to get the epoxy down to 8-12% for decent stiffness.
- a near fullers curve packing density.
- plenty of vibration, with the frequency tuned to your mould
- extremely fine finest aggregate
- largest aggregate 1/5 the smallest mould feature
- round rather than sharp aggregate.
I you can acheive that, you should be able to acheive a youngs modulus of aprox 60GPa.
Mark

Hi Mark,

Thanks for the input. My most recent acquisition has been quartz pebbles up to a max of 7mm size which are much rounder. That large sharp aggregate is nice for looks, but it doesn't help for packing density. Where did you find the 1/5th smallest mouuld feature? My understanding was that it should be max 1/2 smallest mould feature?

I read so many papers on the subject so far that all the information is starting to jumble together. However, I think there was a paper from 1995 (Kim, A study on the epoxy resin concrete for the ultra-precision machine tool bed) and the largest mesh size they used was 2?).

They recommend weights as follows: 50% pebbles (where a pebble is defined as anything larger than 6 mesh - 3.35mm), 42.5% sand (anything less than 3.35mm) and 7.5% Epoxy.

[RotarySMP]

Where did you find the 1/5th smallest mouuld feature?

ISBN 3-478-93273-4 "Mineralguss für den Maschinenbau".

Trying to get optimal ~8% epoxy mixes to flow is rather differcult, but that is what you are aiming for. If you had 1/2 wall thickness largest aggregate in there, you are going to get logjams stopping areas filling.

Fuller and Thompson researched packing density of aggreates back in 1907. Not sure why a researcher today would want to cut corners with non-optimised recipes like you mentioned, as getting close to a optimal fuller curve density is not that difficult.

Here is the spreadsheet which Thomas Zietz created to optimise packing density as close as possible to the Fullers curve, with whatever aggregate sizes you can get.

[rocketflier]

Here are my tests for making various epoxy granite mixes. All of my measurements are BY WEIGHT. I tested the following formulations:

1 - Silica Sand 80um size (US mesh 170 - 200) + Epoxy in various amounts
2 - Aluminium Oxide aka Alumina aka Al203, 75um size (US mesh 170 - 200) + Epoxy in various amounts
3 - Silican Sand 50% by weight mixed with quartz (silica) pebbles from 1mm - 3mm size 50% by weight. This is the type of quartz / silica gravel you get for your aquarium
4 - Aggregate (epoxy granite aggregate) + Epoxy in various amounts

For the aggregate, I used from 40% - 50% by weight a gravel aggregate I bought from a local granite / marble counter top distributor. They call it granite gravel, but it also has bits of marble and other stone in it. It ranges in sizes from maybe 6mm up to 20mm. They are all jagged pieces, not round.
For 25% - 30%, I used the quarts gravel from the aquarium (1mm - 3mm) and for 25% - 30% I used the silica sand of 80um size. Once thoroughly mixed, I added Epoxy.

For my epoxy, I used an off the shelf epoxy for garage or industrial flooring. It is a 2 part epoxy (ISOMAT Durofloor PSF) in a ratio almost 2:1. It is actually 100:55 or 1.82:1 resin to hardener. This was mixed for 3 minutes and then mixed in to the sands or aggregates. I then kind of vibrated the mass, but not much, in order to try and eliminate some bubbles. They were cut out of the plastic cups after 24 hrs.

The pieces that were cut in half were cut using a diamond grinder blade used for masonry.

I find that the ideal mix of epoxy to aggregate is somewhere from 12.5% - 15% epoxy and 85% - 87.5% aggregate. Most of the literature on the subject seems to favour a maximum of 15% epoxy. After that, it is too much resin wasted.

Thought this interesting. Note the cream on the 25% sample. I wonder what percent that is. Vibrate mold in a vacuum bag with perf and breather to suck out the excess.