.........The Fusion of Art and Science tm .........

G. Finkenbeiner Inc. 33 Rumford Ave Waltham, MA 02453. Telephone: (800)552-6182, 781-899-3138. Fax 781-647-4044

PRESSURE

Since fused quartz is utilized in applications involving internal pressures, it is sometimes helpful to know the maximum pressure which can be applied to a certain size tube. The following formula will approximate this information at room temperature.

CFQ Rupture Formula For Tubing

S = p*r/t

Where:
S = Hoop Stress in Pa
p = Working pressure (Pa)
r = Inside Radius of Tube (mm)
t = Wall Thickness (mm)

This formula is not applicable when the internal pressure exceeds 7x10 ⁵ Pa (100 psi).

CFQ Rupture Formula For Discs And Plates

Calculating pressure differential is also required for many applications of stressed fused quartz discs, plates, and sight glasses.

The formula which follows can be used for room temperature applications of circular parts with either clamped or unclamped edges.

Clamped	Unclamped

Where:
p = Pressure differential, PSI
d_o = Unsupported disc diameter, mm (for plates substitute width)
Smax = Maximum stress (approx. 7 to 1 safety factor) 1000 PSI
t = Disc thickness, mm

However, the following factors will affect the strength of these parts and must be considered when using the formulae:

• Surface should be highly polished and free of scratches.
• Means by which a sample is clamped into a pressure device.
• The gasketing material used.
• The thermal gradients expected across the surface and between the surfaces.
• The rate of pressure increase which will be applied.
• Temperature of specimen.