[Eson]

Even if the resin is shrinking it wont matter. If there is enough aggregates the casting wont change. Say that you filled a cup with 90% sand and 10% water to a level. If you later dry the water out the sand will still be at that very level. The small sand stones rest on each other and the water just fill the empty space.

In the resin case, it will also bond the sand stones to each other. And when the resin is shrinking it do not want to let go of the stones. So there will be tensions but i belive this is why the E/G dont expand when heated. When heated the resin will expand a litle but not enough for the tensions to be canceled, thus there will always be forces that are trying to compress the stones.

[martinw]

Hey Martin
Try www.granitek.co.uk/news and google search rk series centerless grinders.Point 1 micron [.000004]"machine resolution does not happen with"creepy " materials
Larry

Dear Larry,

Sorry, I couldn't get that granitek link to work.

I do not know the structural properties of different typesof epoxy/granite composites. As regards creep.....

"Creep is the continued extension or deformation of a plastic part under continuous load"according to this article

http://www.eng-tips.com/viewthread.cfm?qid=94905

Does epoxy creep? Well if you type creep, epoxy, and deflection into google,you will find a whole bunch of learned papers on the subject, so my guess is that it does.

OK, now if we can agree that epoxy does creep, it might seem reasonable to assume that a composite that contains epoxy might also exhibit this behaviour. It may do so to a lesser extent than solid epoxy, but it may still creep. It may well be that this presents no problem in a particular application.

Anyway, I'm still unconvinced that the composite will be as rigid as a lump of solid granite of the same dimensions. It may well have other desirable qualities , eg, it might be less brittle.

Best wishes

Martin

[Geof]

This link gives thermal expansion coefficients for a variety of materials but does not include polymer concrete.

http://www.supercivilcd.com/THERMAL.htm

Granite does have a lower expansion coefficient than most of the others but it still does expand with heat. I do not understand how it could be possible for E/G to have zero thermal expansion because both the granite particles and the epoxy expand. I expect that E/G will have a slightly larger coefficient that solid granite because some of the expansion has to come from the epoxy. However, if the epoxy content is small compared to the granite content the overal coefficient should be very close to granite.

Just as a matter of interest compare quartz sand concrete with iron; both are very nearly the same which is why reinforced concrete works. Both the steel and concrete expand at the same rate with temperature.

[romihs]

Shannon,

I have looked into R&G resins (L1100 + EPH294), and their data sheet specifies curing time to be 24 hours at room temp (I'm assuming that the exothermic reaction is quite slow, so the epoxy will not heat up much durring the cure at room temp). + 15 hours at 60 deg C. Would this annealing cure at 60 deg C harden the epoxy?

The R&G documentation say that the annealing process improves the bonding strength of the epoxy. If I remember correctly, from 98% or 99% to 100%, which does not sound like much.....

Sandi

[Big S]

Is this the resin used in polymer concretes?

I don't think it will be, it is more likely to be an epoxy.

Sposl,

I have noticed that with the epoxy I use, if I cure it at a higher temperature, the finished article ends up harder than if it is given a very slow cure. I remember reading about this somewhere. It may only be applicable to certain epoxies.

Shannon.

[lgalla]

Here is a link that gives answers to the vibration damping and thermal TCE of E/G and some good pictures to boot(nuts)
http://www.rockwellautomation.com/an...df/anocast.pdf
Larry

[martinw]

Here is a link that gives answers to the vibration damping and thermal TCE of E/G and some good pictures to boot(nuts)
http://www.rockwellautomation.com/an...df/anocast.pdf
Larry

Dear Larry,

Thanks. There machines look pretty impressive.

I think the "blurb" is a bit naughty though when it says "superior dimensional stability compared to metallic structures"

The linear coefficient of thermal expansion for mild steel is 12.6 x 10-6/degree C

For anocast it is 16.9 x 10-6/degreeC


Incidentally granite is 8.5 x 10-6/degreeC.

Best wishes

Martin

[Geof]

...I think the "blurb" is a bit naughty though when it says "superior dimensional stability compared to metallic structures"....Martin

Maybe not; it depends how you define dimensional stability. If they are meaning that the Anocast remains more stable than metal castings or weldments post curing they could be correct. Regular cast iron is not stable and will move before, during and after machining. Ductile or malleable cast iron is very stable because the manufacturing process includes a post-casting heat treatment process, however I doubt whether any machine castings of a significant size use ductile. Welded structures can move significantly unless they are normalized after welding and even when normalized some additional movement can occur following machining.

[martinw]

Maybe not; it depends how you define dimensional stability. .

Dear Geof,

That's a fair comment. I was only looking at the thermal issue, not that of strain relief.

As you can see from my previous ramblings, I still think the stuff will creep. Whether or not that could be a problem, I do not know.

Many thanks

Best wishes

Martin

[lgalla]

Ger I don't know but maybe stress is the difference.I think we are getting too technical or critical about the subject.E/G is used for sub-micron machines which is good enough for me.We are not building diamond cut machines or centreless grinding machines or optic inspection machines.The most important feature of the material is vibra damp and ease of accurate design or use in existing weldments.
Larry

[lgalla]

Posting time is here.My transmission blew-up,30 car train de-railment,one foot of snow in the last hour,I'am bored.Lets do mega posts to-day.
BTW william has taken the plunge and started a new thread "polymer concrete tests"Thankyou william

[the4thseal]

would using a heating blanket help in the curing and "hardening" of the E/G?

[walter]

Larry, isn't the 'polymer concrete' just like the regular portland minus shrinkage?

One of the original ideas was to use actual polymer concrete and top it off with epoxy.

[walter]

The linear coefficient of thermal expansion for mild steel is 12.6 x 10-6/degree C

For anocast it is 16.9 x 10-6/degreeC


Incidentally granite is 8.5 x 10-6/degreeC.

Martin,

Here's the big selling point: E/G is brilliantly simple to use- can be done in your garage, requires no tools, can be used by virtually anyone.

Try that with mild steel, anocast or granite...

[lgalla]

Walter
I have always considered "polymer concrete"to be polyester resin and aggergates.Polyester shrinks 2 to 5%,which maybe worse than regular concrete.Polyester is like other materials we have been discussing.It can continue to cure and shrink for years.This is why your boat or yatch will show print through of the roving years later.This does not happen with epoxy as it is stable after one week.I have tried to distinguish the different names in other posts to catagorise what we are talking about.That is why I named E/G epoxy granite to distinguish it from polymer concrete.
Anything that shrinks with age,and polymer concrete may be worse than reg concrete is not suitable for our purpose.Your design of the filled channels is a good one and worth consideration.The E/G volume would be minimal so forget the concrete coated with epoxy.
Larry

[Geof]

...As you can see from my previous ramblings, I still think the stuff will creep...Martin

Again maybe not. Creep in plastic is a bit analogous to fatigue in low carbon steel; provided your stress is below a certain limit it does not occur. I think that the type of stress that these epoxy granite structures are subject to may be below the limit.

[lgalla]

Walter you posted while I was posting.
I agree from your previous posts we hoby or semi-pros are trying to eliminate welding,blanchard grinding,vibratory stress releif.heat stress releif Prozak stress releif etc.The process is simple.Mix A&B throw in some sand throw in some rocks presto we have a non vibrating machine structure.
Larry

[lgalla]

Martin maybe this will help the plastics are creepy theory.I am out on a limb here as I have no links to confirm.As far as i know epoxys are based on soybean type oils and are not plastics,which are petrolium based.Most plastics have solvent bases while epoxys are 100%solids.There is no solvents to cause shrinkage.
Larry

[walter]

I agree about Prozac stress relief, it is a big issue...

[martinw]

Again maybe not. Creep in plastic is a bit analogous to fatigue in low carbon steel; provided your stress is below a certain limit it does not occur. I think that the type of stress that these epoxy granite structures are subject to may be below the limit.

Dear Geof,

I do not know what "fatigue" in low carbon steel means. That is not meant to be a gentle insult; it is a statement of fact!

Steel: elastic deformation. It goes back to where it came from if the load is removed.

Plastic deformation: it does not go back to where it came from when the load is removed. A continued application of the load will cause no further movement.

Polymers


Some polymers exhibit "creep". Under a continual load, the material will keep on deflecting.

I do not know if polymers exhibit elastic/plastic behaviour up to a point at which they start creeping. Each formulation will certainly behave differently.

Best wishes


Martin