A customer in the Health Services Industry ordered a mica insulated band heater from Tempco at a specified inner diameter (ID) of 16". Upon receiving the heater and test fitting it, our customer discovered that the actual outer diameter (OD) of their mandrel was 15-7/8”. In a typical installation of a band heater, the ID of the heater should be identical to the OD of the barrel. In this case, the discrepancy between their mandrel OD and the heater ID caused the heater’s gap of 3/8” to be lost. This resulted in a loose-fitting installation. While the difference between 16” and 15-7/8” may seem small, that difference translates to approximately 0.39” in the heater’s case length.

The heater was originally fitted with built-in brackets which extend out of the case by 3/16” on each end. These brackets are typical of one-piece and two-piece micaband heater construction styles and come with a standard 3/8” gap between them when mounted on the appropriate diameter. The heater in question was returned to Tempco and the standard built-in brackets were carefully removed. New, weld-on brackets were spot-welded onto the heater. These weld-on brackets were positioned so that they were even with the heater ends allowing the 3/16” that was lost on each side initially to be gained back. This increased the gap from 3/8” to 3/4”, which allowed the heater to properly fit the 15 7/8” mandrel even though it was sized to fit on an outer diameter of 16”.

This repair saved our customer time and money because Tempco did not have to make a new heater. Once the customer received the repaired heater, they again tested the fit on their application and found that they were able to use the heater with the new clamping. This situation shows that a larger gap may be useful if the barrel OD is not precisely known. Using a non-standard gap can help compensate for slight mismeasurements of barrel diameters and help prevent situations like this from happening.