Tubular heaters vs. cartridge heaters

06-03-2015

Tubular heaters vs. cartridge heaters

Although they can sometimes have a similar appearance, cartridge-electrical heaters have different applications to tubular heaters.

Although they can sometimes have a similar appearance, cartridge-electrical heaters have different applications to tubular heaters.

A cartridge type heater is an industrial heating element consisting of a metal sheath containing resistive cable isolated from the sheath by ceramic pieces or magnesite. Most of the cartridge heaters are straight cylindrical tubes and the most common diameters range that we manufacture is from 6.3 mm to 32 mm. In the same way happens with the length that can vary from 35mm to 1500mm. Apart from these measures, although the manufacture of cartridge heaters would be possible, Resistencias Tope does not advise its manufacture or its use because in the cases of small diameters and very short lengths the powers are very limited by the small surface of the cartridge.

Both the cartridge heater and the tubular heater usually carry inside a coil of nichrome wire isolated from the tube by magnesite or MgO material. The resistive element ends at the end of the tube for an external connection point. The cartridge heater use flexible electrical conductors that connect to the connections, whereas in the tubular heaters have connections usually with faston or threaded terminals. We can manufacture electrical heaters with different types of connection according to the diameter of the tube.

The cartridge heaters are generally straight (cylindrical or square), being able to form an elbow at an angle of 90 degrees, but in any case they never acquire curves or other geometric conformation as tubular heaters do. In this way the cartridges can be inserted into drilled blind holes. In contrast, tubular heaters can form curves and complex geometries with an infinite variety of lengths, diameters and shapes. In this way, if we mold the spiral tube, more power can be applied in a small space because the development of the tube can maintain the same load per square meter. This solution is very useful to reach higher temperatures and highly recomended for heaters of electric ovens which are on metal surfaces, elements for air duct heaters.

The connections: the tubular heaters usually have a threaded pin in the connection, with or without ceramic or mica insulator.

The tubular heaters are used mainly in the immersion of liquids (to heat water, oil, corrosive liquids, etc.) and for the heating of air. They are often attached to containers or tanks, fit into molten plates, immersed directly in a liquid or even mounted in the heating and gas air ducts.

The internal composition of the tubular electric heaters resembles that of the cartridges. They also contain a coil of resistive wire that is welded to the ends of the pins. The coil is isolated from the outer tube by the magnesite which is compacted to fix the coil and facilitate the transmission of heat to the outer tube of the resistors, as in the cartridge type resistors.

Because the cartridge heaters have a simpler geometry, they can sometimes provide a higher watt surface density than tubular heating resistors. The reason is that its heating surface can be put closer to the surface than in the tubular electric heaters in which the resistive wire must have to conform to curves or changes in geometry. Also as a consequence of the simple geometry, the cartridge type resistors can be manufactured in diameters of up to 4mm when the tubular electric resistors must bemanufactured i with a minimum diameter of 6mm.


Materials used for cartridge type resistors and tubular resistances.

Sheath: Both types of resistors can use alloys based on nickel and stainless steels, but the tubular resistances can also be formed by copper tube, if its application is to heat water; or stainless steel, when used for the heating of tar, asphalt, or similar materials.

Electrical wiring: In the case of cartridge electrical resistors, the connections are always on the same side. The electrical cables, in addition, can be insulated with different materials depending on the temperature that will have to support the wiring.

In contrast, the tubular electrical resistors have a terminal at each end of the tube and these terminals can be connected to the cables but more often we find threaded pins or faston terminals separated from the resistor with a ceramic or mica insulator.