Talk Composites - The Forum for Advanced Composites

CF air tank [10 bars]

http://www.talkcomposites.com/Topic20043.aspx

By rapidos - 12/18/2015 2:59:57 PM

Good morning,

I have to build a +- 2.5 liter CF air tank that hold 10 bars continuously.
My plan is to shape a cylinder (7.5 cm diameter and 15cm long) in a block of foam that need to resist epoxy resin under vacuum, wrap it with 6 layers of CF, after cooking I will drill two holes where I will later install some plugs, filling through them acetone to dissolve the foam and get a final clean inside piece.

My questions are :

- is my plan the easiest or do you have a better idea ?
- which foam to use (I want to avoid glue in the process and 10cm height is your only option) ?
- how many layers of 400gr CF would you recommend (my intention is 6) ?

Thanks for your kind advice.

               
By ChrisR - 2/6/2016 12:35:13 PM

You've actually just highlighted the two main concerns I have with this which may lead to premature failure.

100degC+ environment - did you post cure the tank to higher than this? most off the shelf epoxies have a Tg around or lower than this so you'll loose a lot of strength as the temp rises, even if the epoxy has a Tg higher than this do you really want this component post curing in service? I certainly wouldn't.

vibration - the threaded connections where you've tapped directly into the laminate - a) as already pulled to note by others, this is not an ideal way to fix the sensors/inlets/outlets etc b) I've used/got similar sensors as the ones in your picture so I know they are relatively heavy, shake those suckers around in the back of a car for a while and something is going to give.

I've built a number of cars over the last 20 years and I can pretty much guarantee that although it may work on the bench or for a while on the car, something will give and you can be certain it will happen when you least expect if or really don't want it to happen. The underhood/clam of a car on the road and even worse on the track is a very nasty place and will cause failure of any component not 100% up to the job. The best case senario at failure is a small leak and loss of pressure causing you to limp back to the pits or pull over, the worst case I wouldn't want to imagine the fallout but I know from cars I've worked on, a clam shell does not really offer much protection from a failure from inside the engine bay.

If you want to see what can happen when a pressure chamber fails at temperature, take a look at the mythbusters heater clips https://youtu.be/jbreKn4PoAc?t=2m34s

different materials but you get the general idea.