ONLINE ELECTRICAL ENGINEERING STUDY SITE

Materials used for Heating Elements

Many heating equipment’s or appliances such as electric furnace, electric oven, electric heaters etc. utilizes the electrical energy to produce the heat. In these equipment’s or appliance heating element is used to convert the electrical energy in the form of heat. The working of heating elements is based on heating effect of electric current. When a current is passed through a resistance, it produces the heat. To produce the heat, the electric energy consumed by resistance is given by, Where, ‘I’ is the current through the resistance (in A) ‘R’ is resistance of element (in Ω) ‘t’ is the time (in seconds)

The performance and life of heating element depend on properties of the material used for heating element. The required properties in material used for heating elements-

  1. High melting point.
  2. Free from oxidation in open atmosphere.
  3. High tensile strength.
  4. Sufficient ductility to draw the metal or alloy in the form of wire.
  5. High resistivity.
  6. Low temperature coefficient of resistance.
Following material are used for manufacturing heating element-
  1. Nichrome
  2. Kanthal
  3. Cupronickel
  4. Platinum

Nichrome

Composition of Nichrome Properties of Nichrome
  1. Resistivity : 40 µΩ -cm
  2. Temperature coefficient of resistance: 0.0004 /oC
  3. Melting point: 1400oC
  4. Specific gravity: 8.4gm /cm3
  5. High resistance to oxidation
Use of Nichrome Used in making heating elements for electric heaters and furnaces. Note Nichrome is best suitable and ideal material for making heating element. It is having comparatively high resistance. When the heating element is heated first time, chromium of alloy react with oxygen of atmosphere and form a layer of chromium oxide on outer surface of heating element. This layer of chromium oxide works as a protective layer for element and protect the material beneath this layers against oxidation, preventing the element wire from breaking and burning out. Heating elements made of Nichrome can be used for continuous operation at a temperature up to 1200oC.

Kanthal

“Kantahl” is trademark name for alloys made by composing Iron-Chromium-Aluminum (Fe-Cr-Al). These alloys are used in wide range resistance and heating applications. Composition of Kanthal Properties of Kanthal
  1. Resistivity at 20oC: 145 µΩ -cm
  2. Temperature coefficient of resistance at 20oC: 0.000001 /oC
  3. Melting point: 1500oC
  4. Specific gravity: 7.10gm /cm3
  5. High resistance to oxidation
Use of Kanthal Used in making heating elements for electric heaters and furnaces. Note When the element made of “Kanthal” is heated first time, the aluminum of alloy react with oxygen of atmosphere and form a layer of aluminum oxides over heating element. This layer of aluminum oxides, is an electrical insulator but have good thermal conductivity. This electrical insulating layer of aluminum make the heating element shock proof. Heating elements made of Kanthal can be used for continuous operation at a temperature up to 1400oC. Therefore, it is very much suitable for making heating elements for Electric Furnaces used for heat treatment in ceramics, steels, glass and electronic industries.

Cupronickel

Cupronickel is also called as copper-nickel. It an alloy made by composing copper, nickel and strengthening elements such as iron and manganese. Composition of Cupronickel Properties of Cupronickel
  1. Resistivity at 20oC: 50 µΩ -cm
  2. Temperature coefficient of resistance at 20-500oC : 0.00006 /oC
  3. Melting point: 1280oC
  4. Specific gravity: 8.86gm /cm3
  5. High resistance to oxidation
Use of Cupronickel Used in making heating elements for electric heaters and furnaces, for making coins. Note Cupronickel is having high electrical resistance, high ductility and good corrosion resistance. Heating elements made of “Cupronickel” can be used for continuous operation at a temperature up to 600oC.

Platinum

Platinum is a chemical element. It is having the chemical symbol Pt and atomic no. 78. Platinum is least reactive metal. It has remarkable resistance to corrosion, even at high temperature. Therefore it is considered as noble metal. Properties of Platinum
  1. Resistivity at 20oC : 10.50 µΩ -cm
  2. Temperature coefficient of resistance at 20oC: 0.00393 /oC
  3. Melting point: 1768.30oC
  4. Specific gravity: 21.45gm /cm3
  5. High resistance to oxidation
  6. High ductility
  7. Highly malleable
  8. Good mechanical strength
  9. Good stability with temperature and mechanical stress
Use of Platinum
  1. Platinum is an incredible material with high resistivity and melting point. It is very much suitable for electrical heating elements, rheostats. But due to very high cost, its use in electrical engineering is limited to laboratory furnaces with a working temperature of 1300oC, rheostats, and resistance thermometers.
  2. Platinum is a precious metal, it is very popular for making jewelry.
  3. In medical platinum is used in chemotherapy for treatment of certain types of cancers.

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