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# Snap action of Disc

## Snap action of Disc

(OP)
Hi,

I am designing a pressure switch using metal diaphragm disc.
To find The deflection at the center of the disc I am using an equation which has stifness associated with bending and stretching as presented in the following link

http://www.stanford.edu/class/me220/lectures/lect07/lect_7.html

This formula does not calculate the ping pong (oilcan) behaviour of the disc. Please let me know if there is any other theory or equations that can explain oil canning effect of thin disc

Thanks and Regards

Surendhar

### RE: Snap action of Disc

A snap disc has to have a conical or other non-flat shape to it, otherwise it won't snap.  The equations you're using assume a flat disc.  For a conical disk you can try an analysis using the equations for Belleville washers, see Roark's Formulas for Stress & Strain, Warren C. Young, McGraw-Hill.  There are websites out there with Belleville washer formulas on them as well (Google "Belleville Washer").

### RE: Snap action of Disc

Snap-action diaphragms involve buckling.  I'm sure their behaviour is well documented.

Timoshenko is the man for bucking of thin sheets, start by looking for stuff from him.

### RE: Snap action of Disc

(OP)

The disc dimensions that I have are .003" thick and .5" diameter with a differential pressure of 30 psig.

The disc is pre formed to conical or circular shape with a blister of .375" dia.

You guys still think I should use Belleville Washer design guide lines.

### RE: Snap action of Disc

FEAinfotech

I have designed and built snap belleville springs for low force 2-12kg and for high forces such as 200kg.

The process is quite complicated because the snap force to one side and the return force are need to be specified and they may not have to be equal. In addition to that the spring deflection between the two stable position is not arbitrary.

One more issue is that the snap forces are highly sensitive to the disk thickness variations. The smaller the thickness the larger the variations.

http://www.webspawner.com/users/israelkk/

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