High Temp Resin Recommendations

Discussion in 'Composites' started by Toobuilder, Mar 12, 2019.

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  1. Mar 12, 2019 #1

    Toobuilder

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    I'm considering fabrication of an exhaust augmented duct for the cowl on the Rocket. It will be a single, flattened oval approximately 4hx8wx18l. This duct will handle all of the cooling exit air so it will see substantial volume of "warm" air, but will be augmented by raw exhaust flow (like a jet pump). I intend to line the inside with stainless foil tape, but I'm thinking a resin better suited to elevated temps than my typical West Systems would be a good idea.

    Anyone have a line on a good high temp "hobbyist" product?
     
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  2. Mar 13, 2019 #2

    wsimpso1

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    Vinylester resin has a Tg of about 300F. Get it from Aircraft Spruce and Specialty. Lots of homework is appropriate. While I have not used it yet, I do plan to shortly for my header tank and heat/defog stuff. Fiberglast and Aircraft Spruce & Specialty are among the sources.
     
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  3. Mar 13, 2019 #3

    Marc Zeitlin

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    While a high temp epoxy (or the Vinylester that Bill suggests) would work fine, the canard community has long built substantial parts of baffles and very close fitting cowls from the standard set of room temp. cure laminating epoxies with good results. Particularly if you're going to have flowing air between the exhaust pipes and the duct, and given that the duct is not structural, I'd have no hesitation about using room temp. laminating epoxies for this part (especially if you're going to line the inside with fiberfrax and either SS or AL tape).

    Either way should work just fine.
     
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  4. Mar 13, 2019 #4

    Victor Bravo

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    I'm pretty sure that some of the guys at Scaled will be able to let you have a cup of something that they use for higher temps. Or at least tell you where to get it.

    If you have some reason for not taking advantage of resources that may be nearby, I'd call E. V. Roberts in Los Angeles, they were one of the larger supply houses for resins which would sell to the public. I used to go pick up resin there for sailplane repair when I was hanging around the repair shops in Tehachapi. One of the technical people there might be able to offer a recommendation.
     
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  5. Mar 13, 2019 #5

    BJC

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    Glasair Aviation used a high temperature vinyl ester resin for FWF for many years, but now uses the same resin FWF as for FWA with no adverse result.

    IIRC, most epoxy resins will adhere to VE, but VE does not reliably adhere to epoxy.


    BJC
     
  6. Mar 13, 2019 #6

    pictsidhe

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    Cotronics makes a thin high temperature epoxy.
     
  7. Mar 13, 2019 #7

    wsimpso1

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    I will not argue with success, but I wondered for a while how that could be reliable... CHT's at the temp probe will spend a lot of time near and above 400F, while the Tg for most standard epoxies is only 160-180F. I understand that the Tg will rise some when the part is exposed to higher temps, and that the head is somewhat cooler out at rocker covers, but that still seems to explain only part of it. Somewhere between rocker cover temp and core temp of the heads we must hit the limits for RT cure epoxy and require a change to higher temp resins and/or put in heat shields and/or put in insulation.

    Does anyone have any rules on what conditions require a switch to high temp resins and/or aluminum tape, stainless tape, and Fiberfrax? Empirical results are great...

    I expect that this can be particularly important near exhaust pipes or in conventional cabin heat systems where air can come off the red hot pipes...

    Billski
     
  8. Mar 13, 2019 #8

    Vigilant1

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    A related question: Is there a significant difference in flammability/flame spread/smoke properties of an epoxy part and a vinylester part in the case of inadvertent contact with an ignition source (headers/exhaust pipe, etc)? Maybe the MSDS info from the manufacturers of the specific resins would provide some useful information on this.

    As far as keeping the temps tolerable, I would think a radiative barrier (reflective metal tape, etc) would be a big help in reducing heat transfer to the part.
     
  9. Mar 13, 2019 #9

    BJC

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    There are VE formulations that will not sustain combustion. The more common will burn.


    BJC
     
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  10. Mar 13, 2019 #10

    Topaz

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    I don't have answers to your questions or the OP's, but it seems to me that the critical condition is on the ground, right after shut-down. Everything is still very hot, and there's no cooling airflow. Exhaust system components are usually fairly thin metal and will cool down quickly, but the engine itself is a pretty big block of metal and would do a nice job of heating everything around it, after a flight.
     
  11. Mar 13, 2019 #11

    Toobuilder

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    I've measured components after a good heat soak and even at the top of the engine I didn't see much more than 200f. Not bad.
     
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  12. Mar 13, 2019 #12

    wsimpso1

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    Gougeon Brothers' stuff is always good, if pricey. Check out https://www.prosetepoxy.com/wp-content/uploads/HTP-182_HTP-284.pdf. Tg of 300F when post cured at 140F and 275F. That may make it a bit tough to finish off in the average home shop, but maybe you have the equipment or can arrange use of an oven someplace.

    Their standard cure resins can be cured at 180F and make a Tg of 207F. We can get 180 F even here in Michigan by wrapping the assembly in black visqueen and setting it in the sun on a warm summer day. Watch a remote reading thermometer so you can open the bag if it tries to get too hot.

    Fiberglast 1110 has a Tg of only 209 F. Derakanes go from 210 to 250 F, and you can get their stuff through Aircraft Spruce & Specialty. Not having any luck finding a 300 F vinyl ester, but I know that I have seen them...

    Billski
     
    Last edited: Mar 14, 2019
  13. Mar 13, 2019 #13

    BoKu

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    We're in the process of evaluating high-TG epoxies for a couple of projects in the works. We've considered this one, but the viscosity of 3k cP is a bit high for my taste. For a laminating resin I prefer something down around 1k cP.

    I'll post more when we've actually had a chance to work with one or more candidates.
     
  14. Mar 14, 2019 #14

    Rconc

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    Hysol EA9396 is good to work with but I've always cured it at 150 F.
     
  15. Mar 15, 2019 #15

    TFF

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    I know you talked about the shape on another thread, but I don’t remember. Is it a complicated shape? Why not stainless for the whole thing or titanium? Soft Titanium sheet could be shaped and be pretty trick.
     
  16. Mar 15, 2019 #16

    Toobuilder

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    My original plan was two metal pipes of 4" diameter. I might still go that way if the right material drops in my lap, but the I still need to spin a pair of inlet tulips. By the time I do that I could have made a simple plug and popped out the oval duct in composite (I think).
     
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  17. Mar 16, 2019 #17

    Victor Bravo

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    Has Jon Sharp retired yet? If I recall correctly he and some of the Nemesis team members were in the composite materials engineering division of an aerospace company. If you can reach Jon he would certainly be able to give you, or get for you, a recommendation for an epoxy resin that would have XYZ temperature capability.

    Ralph Wise would also possibly either know of some particular resin form his experiments, or I would bet he can pick up a phone and get a recommendation.
     
  18. Mar 16, 2019 #18

    Toobuilder

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    Jon hasn't been around these parts for years now. Last I heard he was out of aviation to care for family out of state.

    I have one half of the duct curing with RT epoxy now. I'm going to try it as is and see what happens. Worst case, it fails and l build a new one out of HT resin. NBD.
     
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  19. Mar 16, 2019 #19

    blane.c

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    Since NOMEX is used as a fire barrier, I wonder what resin is used in conjunction with it?
     
  20. Mar 16, 2019 #20

    wsimpso1

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    Waiting anxiously for your results...
     

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