Cartridge heaters are a versatile style of heater. Sheaths can be sealed, flanges added, thermocouples incorporated, bushings and couplings installed, non-stick coatings applied, plugs and different types of lead protection added – all are available. Finned cartridge heaters are available for heating fluids or gases. Different watt densities (called distributed wattage or zoned wattage) are available to produce a heated profile.
Band heaters have many options available for heating objects. Options for clamping or attachment, different fittings can be attached, leads can be any length and protected by different materials, watts and volts can be changed to provide exact heating requirements and balance, holes can be cut to allow for thermocouples or fasteners. Band heaters are usually cylindrical, but can be square, conical, and less than 360 Deg circumference. Band heaters can be used to heat the outside of an object or the inner surface of an object. Diameters from 1″ to 36″ or larger are available
Strip heaters are straight band heaters. Finned strip heaters are popular for heating air flows to medium temperature. Sealed strip heaters are used in harsh environments. Most strip heaters are used for platten heating. Like cartridge and band heaters, strip heater elements are constructed different ways depending on end use, and sheaths with different mechanical options to achieve different results.
Cartridge, Band and Strip heater construction can be divided into two general configurations: high temperature and standard construction. These configurations are called different names by different manufacturers: MI Bands®, Better Bands®, mica bands, high temperature, and standard construction are ways of indicating the difference between high watt density and low watt density construction. The difference between the two categories is watt density capabilities of the heater. Heaters capable of operating at higher watt densities are constructed differently than standard elements, and are usually more expensive.
Importance of Construction
Construction style does not impose limits on wattage or watt density, but watt density and operating environment will impose life limits on a heater. A $30 heater may match all the electrical and mechanical specifications of a $65 heater (watts, volts, leads, size and mechanical construction), but have three times the failure rate as the $65 heater. Similarly, it makes little sense to pay $65 for a heater when the $30 will have a similar useful life. The total cost difference can be determined by taking into consideration the number of heaters used per unit of time, the maintenance (labor, time and material) cost to replace the heater, and machine downtime for the procedure.
Mechanical Factors to consider when specifying a heater:
1. Operating environment (wet, corrosive, mechanical abuse, etc.)
2. Electrical connections (leads, terminals, terminal box, plugs, etc.)
3. Most efficient way to heat target (heating surfaces available, interior space, target material)
4. Attachment to the target object
Non-Mechanical Factors to consider when specifying a heater:
1. Operating temperature
2. Ambient temperature
3. Heat transfer characteristics of object heated
4. Total Wattage required to achieve results
5. Watt density on the element
6. Cost of maintenance for replacement and machine downtime