[jsage]

Igalla,

I figured military demand. Didn't realize larger fibers mucked up epoxy. Never had a need for kevlar but knew it was a bear to finish. I was just thinking big heavy materials need big reinforcement.

Did an overhaul on my waterheater a couple months back, first time, took all day. Girfriend said do today so I did. I had to use a torch to break free the elements. Wasn't heating up right the first go round so I went change an element I thought was ok. Didn't realize with well the tank would be pressurized. Had water on side of me and none on the other. A drop fell through the alarm box and burned out the circuit board. It was a lot of fun but we got hot water ; )

So I am curious, in this thread is there an example of a horizontal e/g tube. Just trying to cross the characteristics of concrete construction and frp.

[walter]

How do you put the pasted quotes in those grey boxes?

Larry, you can use the "Quote" button, under each post.

[lgalla]

Larry, you can use the "Quote" button, under each post.
Sorry Walter the box does not check for me.:withstupi
Jsage
Kevlar has its place depending on what you are trying to acheive.It does "goop up" but has the capability of eliminating sag or runs.If there is a time lapse be tween pours it helps in secondary bonding.When the K/E is sanded,only the resin is sanded away leaving Kevlar micro fibers to assist in a strong bond.The fiberes are so tough to cut sanding will not cut them resulting in difficult finishing.I have developed epoxy coatings with Kevlar pulp to reduce epoxy's self leveling to produce a textured surface.Repairs are easy as sanding exposes fiberes to lock or adhere to any type of secondary coating.The only 2 facts against Kevlar is,it absorbes moisture in raw form and deterioates under UV exposure.I have stated before 1/32 milled glassfibre would reinforce the bonds between aggregates in E/G preventing micro cracking.
Larry

[svenakela]

Please address the forum problems and questions to the Site support forum, not here.

As a bonus note, epoxy doesnt stick to aramid fibres. That's why laminating cloth is mixed up with Carbon fibres. The "checkered flag"-pattern is not a cool thing, it has a purpose.

Regards,
Sven

[walter]

Having read some of the posts this is what i can add...

Surface accuracy +/- 0.001" out of the mold.
Cost around $5k
Mold cost + $100K
Smallest feature 1mm square vacuum grooves.
Weight around 600 plus Kg
Size ~ 1.2x1.8x 1 meter high

The whole mold was placed on a giant p....

Mark, thanks for sharing. That's very interesting.

Do you have any info on aggregate type and size?

[Zumba]

Thanks for the info, Mark.

Cool stuff in that link. I really like the last one.... "Grinding Machine Base"... definitely up my alley. A large surface grinder is on my list of things to build. No way I'm going to come up with a few hundred grand to buy a commerically made grinder with 108" of X travel.

[martinw]

The whole mold was placed on a giant paint shaker to settle tha agregate mix after a initial pour of pure epoxy was used to coat the reference surfaces.
Mark Hastings

Dear Mark,

That post was really valuable. Thanks.

If I understand it correctly, you paint on a "gel coat" of epoxy to the mould surface before the main pour rather like a GRP lay-up. The difference being that the epoxy "gel coat" is not allowed to dry. Is this right?

Best wishes

Martin

[jsage]

As a bonus note, epoxy doesnt stick to aramid fibres. That's why laminating cloth is mixed up with Carbon fibres. The "checkered flag"-pattern is not a cool thing, it has a purpose.

Regards,
Sven

I did think it was some automotive cool thing. Kevlar mechanically is not ideal for an outer skin in boat building because it lacks compressive strength. Of course it can be used for abrasion resistance and a blow out cloth that holds things together after a failure. Though I don't think it is a perfectly clear rule.

On flat surfaces with multiple forces it makes sense to me.

Very good post mhastings.

ok, now somebody make something, decide on materials.

[mhasting2004]

Hi Again

I never actually went to Anocast to see it done but got this info of the guy who did. I would assume it was done very similar to a gelcoat setup like GRP. We also had a copper pipe running down the center of the drum just below the surface which was for the vacuum manifold and was drilled into from the vacuum grooves once the part was removed from the mold. I imagine some care was taken not to displace this part while thr drum was being poured.

We had one column get broken on delivery and from memory the largest piece of granite aggregate was around 1 to 2 cm3. So quite large. It also just looked like pieces of real granite (grey/ black with white flecks). The cast was black throughout so either the smaller filler or the epoxy was this colour.

Other than the drilling out or the vacuum grooves, no post machining was done to my knowledge as all the threaded inserts were molded in. I believe the tricky bit was making the curved mold drum surface and the 1mm sq vacuum groves which needed a draft angle and would make ejection from the mold more difficult. Again from very poor memory (was over 10 years ago) they may have used compressd air to push the mold off the curved drum after removing the sides of the mold.

We also had lifting eyes that bolted into large inserts in the base which would allow us to lift the whole optics assembly (around 800kg) into the machine frame.


Cheers

Mark

[Zumba]

We also had lifting eyes that bolted into large inserts in the base which would allow us to lift the whole optics assembly (around 800kg) into the machine frame.

Ah, very smart.

Makes me wonder why the cast iron guys don't do the same thing. Straps are so... mundane.

[martinw]

Hi Again

......I would assume it was done very similar to a gelcoat setup like GRP.

.......It also just looked like pieces of real granite (grey/ black with white flecks). The cast was black throughout so either the smaller filler or the epoxy was this colour.

......I believe the tricky bit was making the curved mold drum surface and the 1mm sq vacuum groves which needed a draft angle and would make ejection from the mold more difficult.

Mark

Dear Mark,

Thank-you again.

I'm speculating here, but from what you say, my best guess is that the "gel coat" epoxy has fine aggregates in it. Otherwise, the fine details of the mould surface would have been pure epoxy which is not exactly strong. Nor would it appear to be a black surface.

Any thoughts on this anyone?

Best wishes

Martin

[Zumba]

Martin, makes sense to me. Pure epoxy is not hard at all. You can cut it with a chisel or exacto knife. There must be some fine aggregate in it.

I'm curious though as to whether the aggregate is really what's making the whole structure black, or if the epoxy is dyed black?

[walter]

Ok that does sound cool. How do we get the black?

[ger21]

Add graphite powder to your epoxy "gel coat" or mold lining.

[Geof]

I think if you look into a bit deeper you will find the black pigment is carbon black not graphite. Both are forms of carbon but very different in their properties. Carbon black is the one used as a pigment in paints, plastics and tires.

[ger21]

I better stop getting info from West Systems website. They call it graphite powder, but it's not a pigment. US composites does sell a carbon black pigment.

[Geof]

Graphite powder is used in some nylons, I think, to make self lubricating bearings.

[jsage]

Graphite powder can be lubricant too can't it.

I believe you can thin epoxy and spray it. I have used a two part for boats as a barrier coat.

If you used a clear epoxy it would be more like a clear coat and a mold buffer.

Solves a few mold problems. Plus I think you can get secondary bonding for about 24 hours. Otherwise you would have to abrade the surface.

[martinw]

Ok that does sound cool. How do we get the black?

Dear Walter,

I do not do aesthetics,( whole crowds shrink away, and gasp).

Best wishes

Martin

[Geof]

Dear Walter,

I do not do aesthetics,( whole crowds shrink away, and gasp).

Best wishes

Martin

I won't shrink, you actually spelled it correctly!!!!