Help me with Bolt Sizing Calculation 2

[cryopumps]

Can someone tell me how to calulate the size and number of bolts I need to secure a cylinder that is holding internal pressure. Simply a cylinder with an OD and ID and one end is open that needs to have a plate screwed on to the top to hold the pressure. This should be very easy calculation.

 

[CoryPad]

This is one of the test cases for VDI 2330. You can download a demo copy of SR1 software from Hexagon that will do this for you:

http://www.hexagon.de/sr1_e.htm

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Cockroach]

Given the internal pressure, compute force on the end cap which is your top plate holding back pressure. Divide this by the number of bolts intended to be utilized in the end cap. This is the force that each bolt shall experience.

I would carry a factor of safety of three. Presumably you are to use some sort of Grade 8 bolt, so SAE J429 will come it at around 130, 150 ksi yield and tensile strength. Use 43 ksi as your allowable stress and compute the cross sectional area given the bolt force above. Now compute the resulting diameter from the area. This will represent the nominal bolt size allowed in the design.

Go to the Machinist Handbook or use a thread program. Specify the closest commercially available bolt GREATER than the said allowable diameter. This will most likely be a UNC thread form, although it could be a UNF if you need more length of screw.

Your next step is to determine the length of screw. This is specified as the shear area per screw. You can use the Machinist Handbook or use the threading program. I use a shear stress of 0.577 that of normal; compute the area and divide through by the shear area PER UNIT LENGTH of thread. This is the resulting length of screw. Pick a length round off to the nearest quarter inch OVER the theoretical length.

Now you know. Without numbers to the problem, this remains a philosophical discussion. No doubt others will have different approaches.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Barry1961]

In many applications the majority of the force in tension the bolt sees is due to torque put on the bolt during tightening. The Machinery's Handbook goes over this fairly well.
Here is a link someone posted months back showing some common clamp forces at recommended torques for standard bolt sizes.

http://www.team.net/sol/tech/torque.html

Considering your name "cyro" you might also need to consider thermal expansion.

One common mistake I have seen made when using aluminum and SHCS is not having enough contact area under the bolt head and yeilding the aluminum, sinking the head into the material. You may need hardened washers to prevent this.

Barry1961

 

[ScanHead]

How is the allowable stress of the bolt determined?

 

[cryopumps]

what about bolt circle diameter

 

[unclesyd]

Are you designing a pressure vessel that may need to be designed under some code or standard?

Comeback with all the physical parameters and enviroment the vessel in question will see

 

[pennpoint]

cryopumps
If your designing a Vacuum Chamber of sorts,why can't you specify a equivelant size flanged port from ASA/ANSI vacuum supplier catalogs? Such as Key High Vacuum, NC Vacuum, Varian, and or/others.
Try not to re-invent the wheel. There are standard flanges and O-ring sized flanges available without having to estabish your own custom size. Your customer will be grateful in the end.

Best Regards

pennpoint

 

[arto]

Easy.....if you don't want to include bending moments.


Look @ ASME B&PV Code SecVIII Div.1 UG-34 & Appendix 2 for a raised face design, Appendix Y for a metal-to-metal outside the bolt circle. [Class 3 = flat head]

Also you want "pi" bolt spacing [#bolts = BCD in inches, round up to nearst multiple of 4] max to prevent scalloping between bolts.