When an electric current passes through, almost all conductors can generate heat. However, not all conductors are suitable for making heating elements. The correct combination of electrical, mechanical, and chemical characteristics is necessary. The following are the characteristics that are important for the design of heating elements.
Resistivity: To generate heat, the heating element must have sufficient resistance. However, the resistance cannot be high enough to become an insulator. Resistance is equal to the resistivity multiplied by the length of the conductor divided by the cross-sectional area of the conductor. For a given cross-section, in order to obtain a shorter conductor, a material with high resistivity is used.
Antioxidant properties: Oxidation can consume heating elements, thereby reducing their capacity or damaging their structure. This limits the lifespan of the heating element. For metal heating elements, forming alloys with oxides helps to resist oxidation by forming a passivation layer.
Temperature coefficient of resistance: In most conductors, as the temperature increases, the resistance also increases. This phenomenon has a more significant impact on certain materials than on others. For heating, it is usually best to use a lower value.
Mechanical properties: As the material approaches its melting or recrystallization stage, it is more prone to weakening and deformation compared to its state at room temperature. A good heating element can maintain its shape even at high temperatures. On the other hand, ductility is also an important mechanical property, especially for metal heating elements. Ductility enables the material to be drawn into wires and formed without affecting its tensile strength.
Melting point: In addition to the significantly increased temperature of oxidation, the melting point of the material also limits its operating temperature. The melting point of metal heating elements is above 1300 ℃.
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Post time: Sep-16-2023