INSULATION TYPE:

Mica-insulated bands are the least expensive and are the most cost-effective bands for standard wattage applications. Most users prefer Mica for nozzles bands.

For higher wattages, High-Watt-Density mica bands can be used; but their longevity is limited and their cost is higher.

Mineral insulated and ceramic insulated bands are the most expensive, but their watt densities are high and their service life is normally the longest. Mineral and ceramic bands also must be heated slowly at low voltage to evaporate any moisture before full voltage is applied. That practice is also recommended for mica but is not as important for mica.

WATTAGE:

Try to match the wattage as closely as possible to the heating that is required. The following formula works for mica material heater bands, which normally have a watt density of 35 watts/square inch:

3.14 (pi) x Band ID (in inches) x Band Width (in inches) x 35 (watts per square inch) = heater band wattage

Example:
3.14 x 1-1/2" ID x 1-1/2" Wide x 35 watt/inch² = 247.275 Watts

DESIGN AND CONSTRUCTION:

Choose a band where the sheet metal has been carefully folded around the insulation to provide a tight seal against penetration by any melted plastic. Cheap bands often scrimp at this point.

Choose the lock-up type. Normally you will replace the existing band with the same type. Most nozzle bands have a strap that holds them to the nozzle. Some are bent into a pair of flanges that are held together by screws. Others use barrel nuts. Key-lock bands are low-profile, to allow them to fit where other bands cannot.

Choose lead-wire length. Most nozzle bands have lead wires. Stock bands normally have relatively short leads to prevent money being wasted by too-long leads. Post terminals are also available, but are more common on bands for barrels.

LONGEVITY:

Be sure the heaters fit tightly to the nozzle or barrel. Direct metal-to-metal contact is the most effective method for heat transfer. A loose fit will shorten a heater’s life time by allowing a pocket of air that inhibits the transfer of heat. Check bands often because the heating cycle can cause the heaters to loosen over time. A burn spot on the ID of the band is evidence of a loose fit.

We recommend using a little heat transfer compound as a good precaution. A little bit between the heater and the nozzle will help bridge any air gaps. You are still going to want to keep the bands as tight as possible. The heat transfer compound contains metal powders that conduct more heat than air does, but there is nothing like good metal-to-metal contact.

A. Top and Bottom Sheet Mica Insulating Covers.
B. Center Mica Core or Strip with Resistance Wire Winding.
C. Inner Sheath: Rust Resistant Dull Finish Steel for maximum conductivity