<br><font size=2 face="sans-serif">I did not mean to leave everyone hanging, but I had to go...more on this subject. Concerning composite built pipes of any brand. First the main problem with the pipes made from epoxy is not the fact that the resin matrix is epoxy, but more from the epoxy that was chosen. Most of the pipes that I have seen are made by taking commercially available carbon fiber braid and conforming it down to a male mandrel. This braid is dry and needs to be wetted out with epoxy. Since most of our Pattern equipment is produced by innovative small business guys, working out of their garage or something, most of the epoxies that could survive are not feasible to use in this method of producing the pipe. The choice is limited by two factors, one-the need for the resin to be liquid at room temperature, Two- the need for the resin to "set" at room temperature, then maybe postcure after room temp gel. These two factors force the manufacturer !
to use an epoxy resin similar to the adhesive I mentioned earlier, Hysol 9394, supposedly a 350F system. Technically speaking, this is and aromatic amine cured epoxy. The temperature resistance of the epoxy comes from the use of the aromatic amine. Two problems that relate to aromatic amine....they are soilds at room temperature and they really need elevated temperaures to cure-hence violating the fab needs stated earlier. So Hysol 9394, and other "liquid" aromatic amines usualy have copius amounts of regular primary amine, which are liquid and cure easily at room temperature---and have low temp resistance. </font>
<br><font size=2 face="sans-serif">So at 350F these epoxy systems work, albeit at dramtically reduced strength (75% reduction), and that is one reason for crushed inlets. Even at about 400F the epoxy does not burn but has little to no strength. Along comes the hot day and slightly lean run, the exhaust temp goes up and bye-bye inlet tube. Long aluminum headers and rich runs protect the inlet from that temperature. As you can see these type of epoxy systems are absolutely borderline effective. That is why half of you guys say never had a problem and the other half burn up your inlet tube.<br>
Concerning the post directing people to sources of 600F epoxy.....Sorry no such thing- period. Look closely at the web site info. No structural data, because these are potting compounds, AND guess what...they need high temperatures to cure. As a potting compound these materials can take short duration spikes up to 600F and not burn up, but the will be soft rubbery gels with zero strength, which works for those applications because it is a potting compound only.</font>
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<br><font size=2 face="sans-serif">The only way to get high temp properties from an epoxy is use an epoxy that cures at high temp, but this has problems of its own. Applying-Using an aromatic amine cured epoxy at 250F is just like using a liquid epoxy at room temperature......only the humanoid operator has cooling problems at this condition so this is not feasible (without an asbestos suit). Attempts to wet out braids with viscous epoxy/A-amine goo with a heat gun will work, but as the temperaure is raised to cure at 350F, all the trapped air expands creating voids in the laminate and leaks in the pipe....bad-bad. Curing under a vacuum enhances the expansion of trapped air BUT if you can get it all out the no pinhole leaks.....but there is no way to really do this perfect everytime.</font>
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<br><font size=2 face="sans-serif">Epoxy of any type WILL NOT absorb oil. But pinhole leaks, microcracks and sanded outter surfaces exposing the fiber will. Pinholes come from the process problems mentioned above, microcracks come from stress at temperature, and sanding the outside of the pipe is a cosmetic REQUIREMENT from all you totally anal retentive pattern types that gotta have a "Good Lookin" pipe......one word here-function! Hats off to Bolly! they use a high temp Bismaleimide resin (I think) AND they do not sand the outside of the pipe. Granted, it looks like something that shoulda gotten flushed, but it does not burn out, and it does not absorb oil. It is also for this reason heavier by a couple of ozs.</font>
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<br><font size=2 face="sans-serif">The answer.....do it the way the B-2 was done.....epoxy-aromatic amine (or bismaleimide or cyanate ester) prepreg cured in an autoclave.....Now can you afford this? Perhaps. To avoid blatant advertising I will stop here. Anyone interested please email me offline at Aeroslave@comcast.net.<br>
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Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>