Calculating number of bolts for piston cap 1

[shears]

I am trying to figure out what size and number of bolts I need to attach a piston cap to the cylinder barrel. It's for a 250ton brake with 2 cylinders, so I figure 125 tons of pressure on each cylinder. I am using the formula for allowable stress = load/bolt tensile stress x # of bolts. Is the correct formula? And how does that get me to my amount of bolts I need?

 

[MiketheEngineer]

First of all don't assume that each cylinder will get 1/2 the load. I could be 2/3 / 1/3.

If each bolt is good for 10,000 lbs then you need 13 bolts assuming half and half.

That said - I think you need to seek some professional help on this one.

 

[shears]

How do I know what the bolt is good for? And what size it is? I am trying to understand what I need to be looking for in the design of the cylinder. The FEA software is giving two different answers.

 

[CoryPad]

You get the bolt properties from a specification like ASTM A 325 Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength or ISO 898-1 Mechanical properties of fasteners made of carbon steel and alloy steel -- Part 1: Bolts, screws and studs .

The size is the thread stress area, which is found using various equations such as those found in ISO 898-1.

It sounds like you would benefit from the Guide to Design Criteria for Bolted and Riveted Joints, available here:

http://www.boltcouncil.org

Regards,

Cory

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

 

[JakeAdkins]

Thanks for the link CoryPad. That is a great referance for anyone

 

[Tmoose]

We made hundreds of hydraulic actuation cylinders for a machine tool drawbar with a bolted on end cap.

One day the application called for a boost in hydraulic pressure.
Basic calcs said the specified torque's clamping due to preload would be exceeded with the new pressure.
Oil all over the test area confirmed the cap lifted enough to unload the o-ring. The bolts did not break.

 

[Twoballcane]

Hmmmm…well first tons of pressure makes no sense. Is this the load on the cap? Have you done any hand calcs before you went to FEA? Did you calculate your tensile forces and preload? Because from there you can calculate your tensile stress and then compare that to the yield stress of the material / bolt you are using. Then figure out a factor of safety that you want and then you can come up with the number of bolts you want to use. If you are basing your decisions on the FEA without the hand calcs, you may be going into something you do not understand, GIGO. As MikeTheEngineer said, please seek a professional Mechanical to help out.




Tobalcane
"If you avoid failure, you also avoid success."