Straight & Formed Tubular Heaters
Industrial tubular heaters are highly adaptable to most applications where electrical heating is required. They can be used in their straight form or bent into various shapes. Tubular heaters can be used in free air, clamped to a surface, placed inside a groove or cast into metal. These versatile heating elements are available in Steel, Copper, Stainless Steel or Incoloy outside sheath and can be utilized in application temperatures of up to 1400º F.
Bucan tubular heaters use 80% Nickel 20% Chromium high grade coiled resistance wire as a heating core. This core is welded at both ends to pins that provide a cold section that varies in length depending on the application requirements. The coil-pin assembly is precisely centred inside a heavy gauge, oversize metal tube, and embedded inside a 96% pure, high-grade MgO insulating medium. This assembly is then compacted through a roll-reducing process that reduces the outside tube diameter to its final size, and transforms the MgO matrix into a rock-hard solid that acts as an excellent heat transferring medium, as well as an electric insulation with high dielectric strength. Finally, heaters are annealed inside a high-temperature furnace to eliminate internal stresses accumulated during the cold-forming and roll-reducing process to make them soft. Heating elements are then formed into special shapes, or supplied in their straight form. Proper electrical terminations are added to the final product.
HEATING MOLDS & PLATENS
IMMERSION INTO LIQUIDS
RADIANT & CONVECTION HEATING
EMBEDDED OR CAST INTO METAL
Tubular Heater Specifications Table
|Tubular diameter (inches)||Maximum voltage||Maximum amps||Minimum Ohms per heated length (inches)||Maximum Ohms per heated length (inches)||Minimum sheath length (inches)||Maximum sheath length (inches)|
|Overall length (inches)||11-20||21-40||41-70||71-100||101-140||141-170||171-200||201+|
|Tolerance in sheath length (+/- in)||0.1||0.125||0.16||0.19||0.22||0.25||0.375||0.5|
|Tolerance in heated length (+/- in)||0.25||0.5||0.9||1.130||1.4||1.65||2||2.38|
|Min. unheated length (inches)||1||1.25||1.5||1.625||1.75||2.25||2.25||2.5|
The MgO insulating medium inside a tubular heater is highly hygroscopic and can absorb moisture from its terminal ends. Moisture resisting seals are barriers that resist or stop moisture and contamination.
This seal is a silicone-based resin that is applied to tubular heater terminal ends. The seal penetrates a short length of the MgO insulation and transforms it into a moisture and contamination resistant medium suitable for temperatures below 200°F.
This is a silicone room temperature vulcanizing seal that can resist moisture and contamination for up to 350°F.
This is a liquid resin which is thermally cured to reach solid state. This moisture barrier is adequate for temperatures up to 400°F.
Tubular heating elements may absorb moisture if they sit idle for a long period of time or get exposed to a humid environment. This might lower the dielectric characteristics of the MgO insulation and cause electrical shorting and premature failure. In order to prove the electrical integrity of a tubular heater, the insulation resistance of each circuit to ground should be checked using a 500 VDC megger. An initial reading of 500,000 ohms or more is acceptable in the field. If heaters do not pass the megohm test they should be dried out. An ideal drying procedure is oven-drying at 3750F after removing the terminal hardware. An alternate procedure is to apply a lower voltage (please consult factory for instructions). The target is to attain at least 20 megohms.
The two most critical factors that affect the durability of a tubular heater are:
â– Sheath material
â– Watt density
The sheath material type of a tubular heater depends on the operating temperature and the corrosivity of the medium within which the heater will operate. The watt density distribution on the surface of a tubular heater is critical for two reasons. First it determines the temperature that a heating element sheath will attain within the conditions that the heater is subjected to. The second reason is that every material has a specific maximum watt density that it can tolerate during its heating cycle. Table 1 below lists various sheath materials, maximum allowable temperatures and mediums within which they are recommended to operate. Table 2 lists recommended maximum watt densities and maximum operating temperatures for different materials. Graphs 1, 2, 3 and 4 show the relationship between the sheath temperature of a tubular heater and its watt density in different conditions.
|Sheath Material||Maximum Sheath Temperature||Applications|
|Copper||3500 F||Immersion into water and non corrosive low viscosity liquids|
|Steel||7500 F||Oil, wax, asphalt, cast in aluminum or iron|
|Stainless Steel 304-316||12000F||Corrosive liquids, food industry, sterilizers|
|Incoloy||15000 F||Air, corrosive liquids, clamped to surfaces|
Maximum Watt Density Ratings for Various Solutions
|Solution||Maximum Watts/in2||Max Operating Temperature (0 F)|
|Bunker C fuel oil||10||160|
|Caustic soda 2%||45||210|
|Caustic soda 10%||25||210|
|Caustic soda 75%||10||180|
|Fuel oil pre-heating||9||180|
|Machine oil, SAE 30||18||250|
|Heat transfer oils||12-20||500-650|