Blot quantity and spacing formula

[whteglve]

I found it once years ago and now I'm trying to figure it out again. I'm trying to create a watertight container and I can't remember or find the formula/calculation to figure out the optimal number of bolts along the flange length. Everything I'm finding is based on pipes and my design is more of a box. So I need to calculate everything along a straight edge and not a diameter. All I remember of the process from before is I needed to know the bolt diameter, flange thickness, gasket thickness, and desired compression.

 

[SnTMan]

whteglve, seen this? thread292-462286

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Geoff13]

Another source could be this posting : thread404-191936

About halfway down Zimann quotes a formula from Taylor Forge Bulletiin 502 that I've used in the past. Can't think of any reason why "a" couldn't be a straight line as it's certainly not far off one on a large diameter flange.

 

[mskds545]

An alternative to the Taylor Forge method is to treat the flange as a beam on an elastic foundation using formulas in Roark's. Use the gasket stiffness as the foundation stiffness. 2a+t can give awfully close spacing for thin plate flanges, and with 2a + 6t/(m+.5) you have to worry about someone bending the flange during seating if they crank down too hard on the bolts. If you do the beam calc, you can get the foundation stress at the mid-point between bolts. With a thin flange and wide bolt spacing, it will go into tension. Optimize the bolt size, spacing, and flange thickness to keep the gasket stress suitably uniform and the bending stress in the flange below your design limit. When you check the bending in the flange at the bolt location, subtract the hole area before calculating the section modulus.

Depending on your gasket, you might also just treat it as a beam under uniform load, assume the gasket reaction load is constant and limit the beam deflection to some fraction of your total gasket compression.

Both of these ignore the stiffening effect of the hub. Depending on your geometry the hub can help considerably.

If there is any pressure or other loads transmitted through the hub, or if the gasket sits inside the bolts rather than on both sides, you'll need to look at bending across the width of the flange and into the hub as well.

-mskds545

 

[r6155]

See Taylor Forge Bulletin 45 Design of flanges for full face gaskets.

Regards