Plastics catalog - Watlow - #37

Use as low a watt density rating as your application permits. A close match of the heat supplied to the actual require­ments will reduce temperature overshoot, reduce cycling and increase the life of any band heater you use.

Calculate the safe maximum wattage

for your heater using:

Calculate the heated area of your barrel heater by subtracting the no-heat area from the total area in contact with the cylinder (3.14 x I.D. x width). Subtract the no-heat area at the terminals (from table) and any additional no-heat area caused by holes, slots or oversize gaps. Determine the maximum watt density of your heater from the graph on this page. The curves are based on narrow heaters mounted on a smooth, steel cylinder. Apply the necessary correction factors:

• For heaters 57 mm (2.25 in.) to 127 mm (5 in.) wide, multiply watt density by 0.8.

• For high expansion cylinders (aluminum or brass), reduce the watt density by 0.46 W/cm² (3 W/in²).

• For heaters 57 mm to 127 mm wide (2.25 in. to 5 in.) installed on a high expansion cylinder, reduce watt density by a total of 0.46 W/cm²

(3 W/in²) only.

• For regular cylinder surfaces other than smooth, machined finish, reduce watt density by 0.46 W/cm² (3 W/in²).

• For heaters that will be insulated or enclosed, contact Watlow for specific watt densities.

• For units greater than 355 mm (14 in.) diameter, consult recommended clamping graph on page 39.

• For units used in vertical applications, consult factory for application assistance.

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