Though they may sometimes have a similar appearance, cartridge heaters and tubular heaters each serve dramatically different applications.
A cartridge heater is an industrial heating element. It consists of an outer metal enclosure called a sheath containing resistive wiring separated from the sheath by electrical insulation. Most cartridge heaters are straight cylindrical tubes and have diameters designed to slide into holes drilled with common English or metric drill sizes.
A cartridge heater consists of the metal sheath, power pins, resistive wire, insulation, sealing at one end of the sheath, an electrical connection between the resistive wire and power pins, a termination of the resistive wire into wire leads, and the leads themselves.
Tubular heaters are used for immersion and air heating. They often get clamped to objects such as vessels and tanks, fitted into milled groove platens, immersed directly into a liquid, or even are mounted in ducts for heating air and gas. They may also be available in single and double-ended versions.
Sheaths: Both cartridge heaters and tubular heaters may use Incoloy nickel-based alloys and stainless steels in their sheath materials. In addition, tubular heater sheaths may often be copper, when used in water heating, or low-carbon steel, when used for heating tar, asphalt, or similar materials.
Electrical leads: Cartridge heaters typically have both electrical leads brought out to one end of the sheath. The electrical leads can be insulated with various materials depending on the amount of heat the leads must withstand. Tubular heaters typically have one electrical termination at each end of the tube. The terminations may be wire leads but more typically are threaded studs or lug terminals separated from the body of the heater with a ceramic or mica insulator.
Mounting:Cartridge heaters typically slide into open holes, rather than blind holes, drilled to accept them. Installations generally stay away from blind holes because the extraction of the heater from a blind hole can be problematic in the presence corrosion or debris.
Tubular heaters may be brazed, soldered, or welded onto surfaces they heat. But the most widely used mounting approach is with a mounting collar or bracket, particularly for containers that are not pressurized and which aren’t sealed to hold liquid. The usual way of attaching the heater to the bracket is with staking or crimping. Bulkhead fittings are used to mount heaters through tank walls. The connection method to the heater depends on such factors as the amount of pressure or vacuum present and the qualities of gas or liquid being heated.
Article Source : machinedesign