Low viscosity epoxy

[rocketcharlie]

I have been using Aeropoxy and Rocketpoxy for structural joining of rocket parts. Is there anything out there that has a low viscosity but is still strong? I'm trying to push this epoxy through a syringe with an 8 gauge dispensing needle on it.

Thanks,

Charlie

 

[Tobor]

West Systems makes water thin epoxy. IIRC it is their "105 System".

Note: I too have used Aeropoxy to inject internal fillets. I've just thinned it out a tad with denatured alcohol. If you go this route, do not use isopropyl alcohol as that contains water, which is not good for epoxy.

 

[G_T]

West is fairly thick compared to some other laminating resins.

MGS. https://www.wicksaircraft.com/shop/mgs-epoxy-system/ for one source, though I haven't used that source. I've used a lot of the epoxy. It isn't cheap and it isn't available in small quantities. Sorry. Anyway, much thinner than West.

Gerald

PS - Just saw the post on thinning. The appropriate alcohol to thin with is Isobutyl... good luck. Denatured etc thinning about 5% by weight reduces ultimate strength by on the order of 50%, going by memory. That's a pretty bad penalty.

 

[G_T]

Instead of injecting, how about leaving the lower centering off? Then can use a stick to put epoxy where you want it on the inside, if you feel the need for internal fillets. Then put on the lower centering ring. I've done it that way before.

Gerald

 

[boatgeek]

I use System 3 Silvertip for laminating. I haven’t tried getting it through a needle, but I did just push some through one of those curved dental syringes with the small end.

(Edit) I just looked up needle sizes. 8 gauge looks like about 1/8”, so any laminating epoxy will be fine. The dental syringe I used was around 1/32”.

 

[JohnCoker]

AeroPoxy has multiple formulations as well. You're probably using the bonding epoxy which is thick, but they also have a laminating epoxy which is much thinner.

 

[afadeev]

I have been using Aeropoxy and Rocketpoxy for structural joining of rocket parts. Is there anything out there that has a low viscosity but is still strong? I'm trying to push this epoxy through a syringe with an 8 gauge dispensing needle on it.

Just about any epoxy out there will have lower viscosity (will flow more easily) then Rocketpoxy.
I usually fall back on West Systems 105 + 205 for larger jobs, and BSI 30 minute for when smaller quantities are needed. Both are clear (vs. black and gets everything black Proline), flow equally well, and are easy to inject through a syringe.
I would suggest ditching the needle for injection, and poking the tip straight into the injection areas. Needle is too much of a flow constrictor, and creates yet more parts that need cleaning afterwards.

BTW, if you are in a pinch and only have Rocketpoxy on hand, warming up its ingredients in a microwave before mixing will drop the viscosity and make it almost injectable. Higher temps will speed up the epoxy cure and reduce working time. Working time for Rocketpoxy's gets reduced in half from 30-40 minutes. Not ideal, but doable, in a pinch.

 

[rocketcharlie]

John, i have watched your video. Do you feel that laminating epoxy would be as strong? I realize that it is lower viscosity.

Gerald, I have left off the aft centering ring. When I use a dowel to try and place the epoxy it seems to get on a lot of places that I dont want it to. I had hoped to use a syringe and be a little more accurate with the placement.

I did try heating it to thin it out. With a 10 second time in a microwave oven it went off in less than a miniute.

Thanks to all who replied.

Charlie

 

[dr wogz]

adding alcohol to epoxy just weakens it.

another alternative is to 'paint on' the epoxy, then hit it with a hair dryer. It'll run like water once heated, but it'll also cure in a second!

 

[JohnCoker]

John, i have watched your video. Do you feel that laminating epoxy would be as strong? I realize that it is lower viscosity.

Probably not "as strong," but most likely "strong enough." I try to use each epoxy for its intended purpose, but it's probably not critical for sport rockets.

The fillers add some structure to the bond to reinforce it instead of just having a glob of cured epoxy. Take a look at the different fillers available with West Systems to get an idea of how the epoxy properties are modified.

Epoxy Fillers - modify marine grade WEST SYSTEM Epoxy

WEST SYSTEM Epoxy Fillers modify the consistency of epoxy, tailoring it for a specific job. Fillers help bridge gaps when bonding, and can ease sanding.

www.westsystem.com

When I used West Systems, I would generally thicken with 404 for bonding. The nice thing is that you can control the viscosity to match the application.

 

[rharshberger]

BTW "water thin" epoxies are typically used as laminating epoxies for composite layups. My favorite is US Composites 635 with 3:1 hardener. US Composites 150 is their structural resin and its about like honey consistency.

 

[David Schwantz]

Try holding the rocket nose down at a bit of an angle. that way I like to dribble the epoxy off the stick along the fillet. Then you can either let it run down or smear it in place with the stick Also, if you add the dye to rocket poxy, it will make it thinner.

 

[rocketcharlie]

That's interesting David. When I opened the bag the rocketpoxy came in and saw the dye, I wondered why anyone would want to dye it. At least it would make it thinner and easier to work with.

 

[David Schwantz]

Itt does make it thinner, but on a black glass rocket with black fins, using the black dye on your fillets makes it so you do not haveeee to paint.
Sorry sticky keys. Need new tablet

 

[afadeev]

When I opened the bag the rocketpoxy came in and saw the dye, I wondered why anyone would want to dye it. At least it would make it thinner and easier to work with.

Itt does make it thinner, but on a black glass rocket with black fins, using the black dye on your fillets makes it so you do not haveeee to paint.

That's definitely part of it - matching epoxy color to the airframe is a nice side benefit (one can order many colored dyes).
The other benefit is that evenly mixing the dye into the epoxy gives a perfect indication that one has mixed resin and hardner completely and thoroughly. Achieving that thorough mix is a bit more of a challenge with higher viscosity epoxies, like RocketPoxy. Getting swirls from a bright dye to disappear into the mix is indicative of the resin and hardner have mixed well as well.

 

[rocketcharlie]

Yes. I can see the point. I didnt think about only adding it to one of the components. Also I hadnt thought about using it on say a carbon fiber build.

 

[David Schwantz]

The dye also helps in seeing the epoxy through a fiberglss tube as it runs down doing internal fillets.

 

[rklapp]

Another option...

https://www.amazon.com/Disposable-Graduated-Calibrated-Essential-Laboratory/dp/B07MSNQYTV/ref=sr_1_4

 

[dr wogz]

When I used West Systems, I would generally thicken with 404 for bonding. The nice thing is that you can control the viscosity to match the application.

I'm a big fan of their 405 fairing filler! whip it up like peanut butter, draw / pull it with a hotel room key-card. Lays smooth, keeps it's shape, and sands super easy!

 

[JohnCoker]

I'm a big fan of their 405 fairing filler!

Yeah, the different fillers all have different purposes: 404 for strength and 405 or 410 for shapeability.

 

[Rob702Martinez]

Aeromarine 300/21

 

[G_T]

Just to note, I wouldn't be heating epoxy in a microwave you intend to use for food.

I may not be a big fan of West Systems for lots of uses though I certainly have used it a lot, but I am a big fan of their fillers.

If you look around enough you can find other interesting fillers as well. But the West ones are readily available.

BTW, if you ever use them, handle carefully cotton flox and Kevlar flox. You don't want to breathe the dust. That probably applies to ceramic fillers as well.

Gerald

 

[prfesser]

Just to note, I wouldn't be heating epoxy in a microwave you intend to use for food.
Gerald

I've found that when the epoxy and curative are mixed, microwaving not only thins the mix, but also speeds up the cure. A lot faster than I'd expected. Haven't done it in a long time but I seem to recall that some mixtures would partially harden while in the microwave---less than a minute. (These weren't fast-cure mixtures, either.)

 

[G_T]

Perhaps the frequency of the microwaves is such as to excite an epoxide functional group and/or a reactive hydrogen, or have some other specific affect that would increase reaction rates beyond just the results of general heating. Anyway, I'm speculating and no expert on it.

Microwave heating tends not to be uniform, epoxy has poor thermal conductivity, and enough viscosity to slow convective heat transfer in the fluid. Since epoxy reaction rates tend to double roughly every 10 degrees C (very crude estimate) it may not take much time in the microwave oven to reduce the cure time for some parts of the epoxy volume to less than the time spent heating in the microwave!

A better way is to warm up the epoxy not the hardener using some source of gentle heat. Warm it up in bulk before dispensing. This has the added advantage of re-dissolving any crystallized components in the epoxy. You might have to get it a little over 50C in some cases I understand. However I've seen lower temp than that work.

Gerald

 

[rocketcharlie]

OK, OP here. There have been some good thoughts on my efforts to get some epoxy through an 8 gauge needle. It seems like the options are...
1) find some lower viscosity structural epoxy.
2) use laminating epoxy.
3) use laminating epoxy with additives (but wouldnt this thicken it?)
4) heat the epoxy carefully.
5) add denatured alcohol to. the epoxy (but this weakens it)
6) ditch the needle and use a
dowel to apply the epoxy.
(I'm not always happy with
this method, I find this to be messy and I dont always get the internal
fillets as even as I
would like.


Which one is strongest do you think?

And thank you to all who posted.

 

[boatgeek]

I'd go with either 1 or 3. The advantage of additives plus laminating epoxy is that you can control how thick you make it by controlling the amount of additives.

 

[DeepOvertone]

Just a thought, and maybe you've already considered and rejected this solution... But what about foaming the can? Thats the method I use in conjunction with other techniques. For instance, I groove the root edge of my fins with a dremel to give more surface area for the epoxy to grab on to the fin. I also do the "multi dip method". I'm not sure if thats exactly what its called but it goes like this> lay bead of epoxy onto root edge, insert into fin slot and seat onto motor tube, pull straight out and lay a new bead of epoxy. I do this 4 times. At the end I have a nice fillet of epoxy built up around the root edge and motor mount. After all the fins are installed, I just foam the can with 2 part HD foam. Sure is easier than tons of internal fillets. Of course I don't fly at crazy speeds or extreme conditions. I also use large chutes to land gently.

 

[Back_at_it]

I can't speak for all epoxy but I can tell you that BSI 30min becomes very thin when warm and holds that heat well enough that it will flow down into rocket bodies to form fillets in sears that you can't otherwise reach. You can also use a hair dryer or heat gun to warm the rocket itself to help with the flow.

 

[3stoogesrocketry]

Don't mind the dirty bottles , we buy 5 gallon kits and I "save" the last qt or so the pumps do not pick up.

 

[prfesser]

OK, OP here. There have been some good thoughts on my efforts to get some epoxy through an 8 gauge needle. It seems like the options are...
1) find some lower viscosity structural epoxy.
2) use laminating epoxy.
3) use laminating epoxy with additives (but wouldnt this thicken it?)
4) heat the epoxy carefully.
5) add denatured alcohol to. the epoxy (but this weakens it)
6) ditch the needle and use a
dowel to apply the epoxy.
(I'm not always happy with
this method, I find this to be messy and I dont always get the internal
fillets as even as I
would like.


Which one is strongest do you think?

And thank you to all who posted.

Strongest will be careful heating of the epoxy; use a slow curative if possible. Laminating epoxy will be a close second, as very little of the reactive diluent is needed, and being reactive the effect on the properties of the cured resin is negligible. My old copy of Lee and Neville says no more than about 15% of the diluent is preferred. Just 10% of allyl glycidyl ether reduces the viscosity of DGEBA (standard epoxy resin such as DER-331 or EPON 828) by a factor of 12.

Heated laminating epoxy will probably run like water. Don't heat too much as the diluents can evaporate somewhat.

Instead of denatured alcohol, xylene is a decent choice for a nonreactive solvent. 6% xylene reduces flexural strength from 18,500 psi to 17,900 psi. Very strong odor.

And finally: there's only one person who will know what your internal fillets look like. Even if they're really pretty...you can't show them off...

Best -- Terry