Why use Calorised Emitter tubes?

Why do SPACE-RAY use Calorised Emitter tubes? The comparison tables below show the relative merits of emitter tube materials.

Tube Material Internal Absorptivity External Emissivity Radiation Performance Corrosion Resistance

Calorised Very Good Very Good (0.86) Very Good Excellent Excellent
Stainless Steel Very Poor Very Poor (0.20-0.25) Very Poor Excellent Excellent
Stainless Steel Painted Very Poor Very Good (0.85) Average Excellent Excellent
Aluminised Steel Very Poor Poor (0.25-0.30) Very Poor Good Good
Aluminised Steel Painted Very Poor Very Good (0.80) Good Very Good Very Good
Mild Steel (Hot Rolled) Average Average (0.66) Average Poor Poor
Mild Steel Painted Average Good (0.75) Good Poor Average
Tube Material Peeling and Flaking Resistance

At Burner Downstream
Scratch Resistance Site Time to Clean & Paint Each Tube
Calorised Excellent Excellent Very Good n/a
Stainless Steel Excellent Excellent n/a n/a
Stainless Steel Painted Poor Average Extremely Poor 15 Minutes
Aluminised Steel Good Good Good n/a
Aluminised Steel Painted Poor Average Poor 15 Minutes
Mild Steel (Hot Rolled) Poor Average n/a n/a
Mild Steel Painted Poor Average Extremely Poor 20 Minutes
  • Calorising gives protection to ferrous metal by providing a self-forming, self-healing coating of practical infusible material (alumina) which is impervious to oxygen, carbon, sulphur and the products of combustion of all common fuels.
  • Various grades of the process are available according to the article and the use for which it is intended up to maximum metal temperature of 950 degrees centigrade for calorised aluminised mild steel or cast steel.
  • The process is accomplished by fusing aluminium into the surface of the base metal with which it forms a homogenous alloy.
  • The protective action is due to the aluminium oxide formed on the surface by the action of heat.
  • Under working conditions the exposed surface of the alloy is converted to alumina which has a fusion point in excess of 1,000 degrees centigrade.
  • Due to the protection given to the base metal, calorised aluminised mild steel has improved resistance to deformation and scaling at elevated temperatures.
  • It is particularly useful for parts subjected in service, at elevated temperature, to sulphurous gases and for case-hardening boxes and pots, cyanide, salt and lead baths. Also for steel protection tubes for thermo-couples.

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