Calculate pressure on a gasket from screw joint 3

[Bjorn92]

Hello!
How do you calculate the pressure on a gasket from two flanges that is being pressed together by screws.
Say you have 5 x M10 screws and you apply 50NM torque on every screw.
The surface area of one flange that is in contact with the gasket is 225 square centimeters.

See picture explanation here:

https://imgur.com/a/1d6KN47

 

[desertfox]

Hi

Using Torque = force * K * d. d= bolt diameter, K= friction factor,

50 * 10^3 = force * 0.2 * 10 transpose to find force :- Torque/ (0.2*10)

Therefore axial bolt force in one bolt is equal to 25000N.

Multiply the force by five bolts :- 25000 * 5 = 125000N

Divide the above force of 125000N by gasket area :- 125000/(225*100)= 5.55 N/mm^2

This is a rough approximation and assumes no thread lubricant. I used formula from this site

https://roymech.org/Useful_Tables/Screws/Screw_loads.html

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[3DDave]

Something that happens is that thin flanges flex, particularly when used with thin gasket materials, concentrating the force and pressure very near the screws, easily leaving some areas with little to no contact pressure at all.

 

[GregLocock]

Rule of thumb is that the line linking adjacent bolt holes should be in the middle half of the gasket, which your diagram fails. I don't know if that means you can have a funny shaped gasket that adheres to this rule.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianE22]

Is your drawing to scale? My gut feeling is that you need more bolts and/or thicker flanges. I see the flanges bending and not much compression on the gasket halfway between the bolts.

 

[drawoh]

Bjorn92,

Your contact force is the sum total of the tensions of your screws. Desertfox has provided the standard equation which gives you some ability to predict the screw torque needed to achieve a required screw tension.

How flat are your flange faces?

How flat are your gasket faces? This will massively affect your contact force.

--
JHG

 

[Strook]

Gasket principles require a combined bolt force to apply a stress to the gasket that is equal to or (ideally) exceeds the stress required for the gasket to seat (a.k.a. seal) properly.

Challenges arise when determining the appropriate gasket area that is influenced by each bolt, especially in the instance of thin flanges and large bolt centre distances, as 3DDave has identified.

Rubber/polymeric gaskets are generally self-energising and require a seating stress > 0 MPa, but harder gaskets require specific seating stresses.

You could look at standardised flanges such as ASME B16.5 for informative guidance on suitable bolt-centre and thickness ratios to design your flange.

Some flange designs call for non-linear FEA to identify areas of zero gasket contact ie. leakage potential. This is an (expensive) option if your application requires it.

 

[Tmoose]

Bjorn92's last login was on Monday, February 15, 2021.

https://cache.desktopnexus.com/thumbseg/1130/1130904-bigthumbnail.jpg