Syntactic Foam?

Ian_Edwards

Ian_Edwards

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Syntactic foam, a mixture of epoxy or polyester resin and glass microspheres (or glass bubbles). This produces a lightweight and strong (at least in compression) filler.

But where can I find detailed instructions on mixing, to get a consistent light weight foam? I'm thinking of casting several litres in one go.

I've tried the 3M site, but the instructions provided are for large scale batch production, I hoping to use buckets in a garage.

It's a one off project, so I don't want to spend too much cash on equipment I may not use again.
 
It is used in the construction of ROVs for offshore use. It might be worth contacting one of the major ROV companies in Aberdeen such as Oceaneering or Subsea7. There will be guys in the shore bases that will know about that sort of stuff.
 
Several litres:nonchalance: Built a few wooden kayaks using epoxy and various fillers including microspheres. Used plastic cup such as you might find at water dispenser to mix it in. Any more than two thirds full and the heat was tremendous. Melted the cups and thought it was gonna burst into flames. Something to do with exothermic reactivity as I recall. Be careful please if you have no, or limited experience.
ps. https://www.youtube.com/watch?v=3uzRaSJFWo4
watch and read the first few minutes then click forward. The little cupful reaches 346 F in about sixteen minutes!!! A few litres might just melt your bucket, even if its a galvanised steel bucket. But trust me you will have run away long before that happens.
I keep editing this because the more I remember about it the scarier it becomes. Note the little cup requires one minute of mixing. My experience was that thorough mixing took longer than that.
You will NOT have time to mix properly "several litres" before the situation is out of control so call emergency services before you begin mixing.
 
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usernamenotvalid said:
Several litres:nonchalance: Built a few wooden kayaks using epoxy and various fillers including microspheres. Used plastic cup such as you might find at water dispenser to mix it in. Any more than two thirds full and the heat was tremendous. Melted the cups and thought it was gonna burst into flames. Something to do with exothermic reactivity as I recall. Be careful please if you have no, or limited experience.
ps. https://www.youtube.com/watch?v=3uzRaSJFWo4
watch and read the first few minutes then click forward. The little cupful reaches 346 F in about sixteen minutes!!! A few litres might just melt your bucket, even if its a galvanised steel bucket. But trust me you will have run away long before that happens.
I keep editing this because the more I remember about it the scarier it becomes. Note the little cup requires one minute of mixing. My experience was that thorough mixing took longer than that.
You will NOT have time to mix properly "several litres" before the situation is out of control so call emergency services before you begin mixing.
Click to expand...

You might have had moisture in your cup? Moisture and epoxy mix cause a lot of heat. I've probably told this here before but I was once patching up a sea water pipe on a ship with Thistlebond pipe repair tape and epoxy. It comes as two cans, you add the smaller can of hardener to the bigger can of resin. Its a case of all of both cans so as your mix is correct then stir with a welding rod or similar. I had mixed up the resin and had just set it aside to get the tape in place when I saw a solitary drop of sea water fall from the pipe into the can. Well, it went off like a volcano. The whole thing cured in about two seconds setting fire to the can label due to the heat and the welding rod was forever bonded into the can like a miniature excalibur!!! I had been sitting cross legged beside it one second but the next thing I knew I was sprinting for a fire extinguisher. However, without the drop of sea water I'm sure all would have been well. I had used the stuff before then and many times since without any trouble.
Mixing reasonable size batches of epoxy should be safe if done in proper accordance with the manufacturers guidelines.
 
You might have had moisture in your cup?
Click to expand...
Nope, cups were brand new fresh out of the wrapper. Bought specifically for mixing epoxy. Epoxy and catalyst creating chemical reaction are what causes the heat. I successfully used it many times. Just made sure to use small amounts and get it out of the large container and spread thinly really quickly. Would strongly suggest OP watches youtube and makes a sensible decision.
 
Thanks, for the posts, I use to work for SUBSEA 7, but I've been retired for 7 years now!

We use to buy almost all of our buoyancy. either as custom made units from the likes of Balmoral Glass Fibre or CRP. If we needed to make up a "special" for a tool or something we'd buy syntactic foam in sheets and machine them and then glue them together.

I know that mixing epoxy or polyester resins results in an exothermic reaction and I've experienced "thermal run a way" when mixing in a plastic cup, complete with smoke and the feeling it was going to burst into flames, coinciding with and urgent need to drop the container into a bucket of water!

But I know casting syntactic foam can be done, I've seen kits advertised to make up syntactic foam and the big manufactures obviously do it in bulk to make sheets and bespoke buoyancy blocks, without setting fire to things.

I just wonder if anyone on the forum, knew the secret, presumably some form of slow cure resin is used, but a quick Google search didn't result in anything very useful.

3M K1 glass bubbles are about £4 a Litre, so that bit is very cheap and I know I can buy Epoxy Resin in various grades, but does anyone know the secret which resin to buy and how to mix it?
 
I don't know how you would produce large volumes on a 'domestic' scale and overcome the problems caused by the large exothermic reactions involved so I googled it out of curiosity and found this: http://www.psubs.org/design/PDF/SyntacticFoam.pdf
- building your own sub! A quick look through seems to indicate their safest option was to work in smallish, manageable batches; I was also interested to see they use a mix of microspheres and macrospheres and also don't discount the use of polyester and vinylester resins, which may be much cheaper to acquire than epoxy. I would imagine industrial production would involve specialised plant to closely monitor and control temperature during reaction. Out of curiosity again, what sort of volume are you looking for, and to what end?

John
 
The Split

Rusty water has been seeping out of the joint between the grounding plate and the hull on my Southerly 46, so we split the keel and grounding plate on Saturday morning.

It's the 1st time this has been done and the boat is 8 years old.

I was concerned about what we found, the cast iron grounding plate is very rusty. It has webs cast into the upper surface, presumably to make the plate stiffer. These effectively form 10 trays and Southerly had filled the trays with foam sheet of different types. Most of the foam was sodden and all the trays full of water.

The whole assembly will be grit blasted and epoxy primed and I want to fill the trays with a good quality light weight material, which will bond the the primed cast iron and last more or less indefinitely in a wet and hostile environment, I don't want to have to go through this again!

My first thought was to use a glass sphere loaded epoxy (because of my background in ROVs and AUVs), but I then realised I didn't know the detail of how to make it!

It's hard to estimate how much I need, but a rough calculation, I guess it'll be somewhere between 30L and 50L, but definitely less than 70L.

The tray are about 50mm deep so I guess that there won't be an exothermic problem, it's quite shallow and the cast iron will form a good heat sink.
 
50mm thickness of epoxy will certainly have enough mass for a thermal runaway, but if the spheres are stirred in before the reaction gets a grip, then it is similar to pouring the mix into a shallow tray, increasing the cooled surface area. Not as effective but it will slow things down a bit. Likewise, it is possible to get a slow hardener, usually used for coating and sheathing. I'd advise a thorough visit to the Gougon Brothers (West Systems) website to bone up on the subject and a few trials before setting light to the boat!

It may be that the foam should be cast off the boat and epoxied into place once trimmed to fit.

Rob.
 
If you thoroughly mix the spheres into the resin before adding the catalyst you are already half way there. I discovered this by using an epoxy/graphite mix which in itself is a bugger to mix thoroughly and quickly. Still don't like the idea of a 50mm deep setup though. Would appear to me that if weight is important then a glass/foam/glass sandwich might be more appropriate.
 
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There are only two rules you MUST remember when mixing / using epoxy resin.

1. Only ever mix resin and hardener is wide shallow containers to give a large surface area to prevent exothermic reactions.

2. when filling thick or deep areas do so in stages so the epoxy can cool off between coats. You can reapply wet on tacky as the temperature subsides eliminating the requirement to sand between coats.

So, your answer is to fill the area in stages, as it looks like there will be a large surface you should have no problems.

PS. It's good practice to sand the final coat and apply 3 to 4 coats of resin to ensure the spheres are properly sealed. again this can be done wet on tacky.

Good luck and fair winds. :)
 
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