Pressurized box 5

[pedrox]

Hi, I am a Mechanical engineer and I´m developing a pressurized box (600x500x200 mm^3) that will contain electronics. The problem is that I have to keep a pressure of 1 atm in the inner, while in the outer I have almost 0 atm. I woul like to know if it is a good idea to develop the box as a rectangular prism (no cilindrical or spherical shapes, but flat rectangular plates). Another question is the kind of material, becouse of weight is a mandatory question in the project, I´m thinking in al 6082 or al 7075.
For manufacturing I´m thinking in empty a block of aluminum then I will have a box and a cover. I would like to know the way to join the box to the cover (screws, seal, thickness..).

If someone know something about these topics, anything will help me.

thanks in advance,
Pedro.

 

[prex]

As weight is a major concern, it is certainly a bad idea to build it in parallelepiped shape. Also the idea of carving it from a block is quite odd.
If weight is definitely of major concern (going to space?) you should first of all choose the most effective material for minimizing weight: I'm not particularly expert with this, but guess that besides cold stretched aluminum also titanium might be of interest.
Concerning the shape a sphere or two ellipsoidal heads should be chosen, depending on your internal and external size requirements.
The opening will impact very much on mass: also here you should decide the required size. If you need a full size opening, the two heads above would be joined with a full diameter flange, but this will likely weigh more than the rest of the container.

prex

http://www.xcalcs.com

Online tools for structural design

 

[pedrox]

thanks for your quick reply. I was thinking in the conceptual design that you have advised, of a cylinder with two heads (spheric, ellipsoidal,..) joined through a full diameter flange and fixed with screws and nuts. Now I have to develope the new concept and let see if the volume is acceptable.
It´s not for space, but near. It will fly at 40 km height. My next problem is the temperature differences and the different thermic expansion coefficient of aluminium hull and steel of titanium screws.

Thank you again,
Pedrox

 

[arto]

For rectangular Pressure Vessel design, see Appendix 13 of ASME B&PV code, Sec VIII, Div. 1. Usually they end up relatively thick - curved surfaces [sphere, cyl., elliptical] are better.

 

[sreid]

Aircraft electronics are often housed in rectangular boxes that see a one atmosphere pressure differential (the boxes are air cooled usining bleed air from the engine compressor). The good news for these (and you) is that 15 PSI is not a large pressure differential. To keep the weight down, the box panels can be made thick and then pocketed to reduce weight

 

[fredt]

As noted by sreid 15psi is not a large pressure in a box this size particularly if it has internal divisions as suggested. Any good mechanical engineer should be able to design you a simple rectangular box using sheet aluminium of appropriate thickness. It is doubtful that pressure vessel code would apply to a box like this.

 

[pedrox]

does anybody know where can I find a .pdf or a text copy of ASME B&PV code, Sec VIII, Div. 1????

 

[pmover]

the asme codes are available for purchase at:

http://www.asme.org

sorry, these codes are not free. perhaps your firm has these codes. at least , i would think so.

good luck!
-pmover

 

[quark]

Sometime back, I got a copy of rectangular tank design from one of the eng-tips members (taken from one of the reputed monthly journals). This basically deals with water storage tanks. The basic principle is to consider the vertical plates as columns and subsequently checking for bending moments. This may help you and if you want a copy of it give me your e-mail id.

Regards,


Eng-Tips.com : Solving your problems before you get them.

 

[arto]

try Engineering College Libraries too

 

[pedrox]

ok quark, here is my non-official mail:

pedrodmar@ono.es

thanks for your help.

 

[quark]

There seems to be a problem with the id. Mail returned back.

Eng-Tips.com : Solving your problems before you get them.

 

[hockchong]

Dear quark,
Can I have a copy of this spreadsheet. Please email to hockchong.lee@akerkvaerner.com

 

[pedrox]

ok, sorry, try with this one:

pedro.rodriguez@uv.es

thankyou.

 

[RWR100]

Dear Quark:

Please send me a copy of the spreadsheet also. Send to info@rowald.com

Thanks

 

[AndrewTX]

Quark,

Could you also send me a copy of the rectangular tank design document.

Send to: alarson2@houston.rr.com

Thanks.