While most maintenance men understand basic thermal principles, even the seasoned engineer needs help determining maximum allowable watt densities for cartridge heaters.
The Maximum Watt Density-Heating Metals Chart
The Maximum Watt Density-Heating Metals chart will tell you either the maximum hole fit or the recommended watt density of the heater. Enter the chart with either known variable, part fit in hole dimension, or W/in². Then find the application temperature by reading up or over on the chart. If the fit of the heater in the hole dimension is not known, it is easily determined. Subtract the minimum diameter of the cartridge heater (normal diameter minus tolerance) from the maximum hole diameter.
For example, take a hole diameter of 0.00 minus a heater diameter of 0.496 ± 0.002 inches. The hole fit would be 0.006 inches. For cartridge heaters in square holes or grooves, contact your Proheat sales engineer or account manager for the fit in hole dimension
Correction Factors: Also note, this graph depicts cartridge heaters used in steel parts. Therefore, for either stainless steel or aluminum and brass, refer to applicable correction factors: