Compressed Air vs Nitrogen for Autoclave Cures

[vinguy]

Morning,

I was wondering if anyone had any insights into using compressed air vs nitrogen gas for autoclave cures for temperatures of up to 350F. We are trying to save on costs from using nitrogen gas and was wondering if 100% compressed air cures were a viable/safe option for these types of cures, and what factors should be considered when making this decision. The considerations of this project currently are safety, practicality, and effectiveness. Whether or not we can obtain the same quality of a part, as easily, and as safely as we can with using nitrogen gas.

I appreciate your time, and any insights you could give me on this matter.

 

[SWComposites]

https://www.apexgasgenerators.com/p... process the,an inexpensive and inert option.

 

[WKTaylor]

Aircraft tires under very high inflation pressures... often 500-to-750-PSI... experience high heat from braking and/or brake fires which increases internal pressure substantially. IF the 'slow-blow melt fuse plugs' in the wheel works as advertised, then the tires deflate before rupture... then all is well. IF the fuse-plugs fail, then the over-pressurized tires will burst like balloons, sheading very VERY dangerous fragments of Rubber. For this reason, aircraft tires are often called 'rubber bombs'. CAUTION... these 'dangerous ruptures' are are non-explosive, since high pressure tires are universally serviced with 'dry nitrogen' ~99%.

It was discovered that high pressure tires... when super-heated by brakes or fires... will cause the rubber to decompose and out-gas hydrocarbon fumes. On the outside of a tire, the fumes dissipate fast at atmospheric pressures and with minor breezes. Some hydrocarbon fumes/hot-rubber MIGHT feed fires... but effect will be very mild. However, within the pressurized cavity inside the tires, the outgassing hydrocarbons are smothered by the 99% nitrogen atmosphere... even as it heat up. No fire or explosion is possible... if the fuse plugs relieve the pressure build-up.

IF these same tires had been serviced with a high % of air at 750 PSI... and encounter the same over-heating emergency criteria... overheating and outgassing hydrocarbons at extreme pressures... then... when the lower-explosive limit of fuel [hydrocarbon fumes] and air [35%n oxygen] and high heat are reached... often before the fuse-plugs can rupture to bleed-off pressure... then pressure-ruptures are always exaggerated by an 'O2-hydrocarbon detonation'... boosting the burst energy by several orders of magnitude... a truly horrific ['atomic'] RUBBER BOMB.

CAUTION. A few years ago, the high pressure autoclave nitrogen system used by an aircraft manufacturer [Wichita KS] ruptured during 'off-hours'. It sounded like a bomb... and the felt like a mini-earthquake... when the rupture occurred... which destroyed a good portion of the composites building and removed MOST of roof. Thank God no one was hurt.

The accident investigation pinpointed the 'cause' of the N2 system rupture to winter conditions creating an ice-plug over the system's outdoor N2 pressure relief valve... allowing N2 gas pressure to slowly-build to the point of piping rupture'... instead of harmlessly venting to the atmosphere, as it should have.

PS1. Dry nitrogen is ~99.8% nitrogen with virtually NO DETECTABLE MOISTURE [H2O]... which can freeze within system components... and especially valves!

Regards, Wil Taylor
o Trust - But Verify!
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[EdStainless]

You might get ways with lower purity N2, such as 98% that is generated on site.
But you need zero water, usually at least a -40 dew point.
If there is any moisture it will condense on depressurization and cause all kinds of problems.

 

[IRstuff]

High temperature and air would seem to be the ideal environment for aging materials...

 

[georgeverghese]

Why on earth would you want to switch to air?
Preferably use cryogenic quality N2 from liquid nitrogen tank/vaporiser or from compressed N2 cylinders.