A - It depends on specific grade of cast iron used: Class 30, 40, or 50. The class number indicates its minimum tensile strength, in pounds per square inch (PSI). The maximum allowable peripheral speeds, in feet per second (FPS), are:
ASTM A-48 Tensile Speed Class 30 30,000 PSI [ * ] FPS Class 40 40,000 PSI [ * ] FPS Class 50 50,000 PSI [ * ] FPS
These values are based on [ * ] degrees Fahrenheit maximum temperature. Some manufacturers avoid using Class 30 cast iron because of quality and machining issues with commercial sand castings.
The calculation for peripheral speed (S), in feet per second, is:
S = [ D x N ] / 229
By rearranging, the equation can be rewritten as:
D = [ S x 229 ] / N
N = [ S x 229 ] / D
D - impeller diameter, in inches N - rotational speed, in revolutions per minute (RPM) S - peripheral speed, in feet per second (FPS)
What is the biggest diameter a cast iron impeller can be used safely at 3560 RPM, at ambient temperature?
Answer: D = [ * x 229 ] / 3560 = [ * ] inches
[ * ] Some information are excluded in this article. Read more.
R: 1109-CAIR C: design, operation F: impeller cast iron