Application analysis of bimetallic sheet in thermal protector
2022-03-01
The most important element in the thermal protector is the bimetal. Today, I will take you to understand the application of the bimetal in the thermal protector.
The role of the bimetal sheet in the thermal protector is: when the temperature changes, because the expansion coefficient of the high expansion side of the bimetal is much higher than the expansion coefficient of the low expansion side, bending occurs, and we use this bending work. in the thermal protector.
The hot bimetallic raw materials of various manufacturers are basically the same, the matrix is iron and copper alloys, and elements such as nickel and manganese are added to change their expansion coefficients, resulting in high-expansion side and low-expansion side alloys, and then composite composition. Master alloys are sometimes added in order to change the resistivity of the material.
Before assembling the thermal protector, the bimetallic sheet forming is a very critical step. First, the hot bimetallic strip is punched and blanked into a sheet shape, and then pre-formed into a disc shape. At this time, the dish-shaped thermal bimetal has a fixed action and reset temperature. The main parameters of bimetals that should be considered before punching: specific bending, elastic modulus, hardness, dimensional accuracy, resistivity, operating temperature range. First consider the temperature range that the bimetal sheet can be used in, and then consider the force and torque of the action that the bimetal should generate, and select the appropriate specific bending and elastic modulus. Then select the size, hardness and elastic modulus of the hot bimetal suitable for the respective molding process and equipment. Then select the appropriate resistivity according to the current time requirements of the protector and the effect of the heat capacity cavity.
According to the bimetal's current thermal effect formula Q=∫t0I2Rdt, it can be known that selecting a bimetal with high resistance will generate more heat, shorten the operating time of the thermal protector, and reduce the minimum operating current. The opposite is true for bimetals with low resistance. The resistance of the bimetal is affected by the resistivity, the size and thickness of the shape.
The role of the bimetal sheet in the thermal protector is: when the temperature changes, because the expansion coefficient of the high expansion side of the bimetal is much higher than the expansion coefficient of the low expansion side, bending occurs, and we use this bending work. in the thermal protector.
The hot bimetallic raw materials of various manufacturers are basically the same, the matrix is iron and copper alloys, and elements such as nickel and manganese are added to change their expansion coefficients, resulting in high-expansion side and low-expansion side alloys, and then composite composition. Master alloys are sometimes added in order to change the resistivity of the material.
Before assembling the thermal protector, the bimetallic sheet forming is a very critical step. First, the hot bimetallic strip is punched and blanked into a sheet shape, and then pre-formed into a disc shape. At this time, the dish-shaped thermal bimetal has a fixed action and reset temperature. The main parameters of bimetals that should be considered before punching: specific bending, elastic modulus, hardness, dimensional accuracy, resistivity, operating temperature range. First consider the temperature range that the bimetal sheet can be used in, and then consider the force and torque of the action that the bimetal should generate, and select the appropriate specific bending and elastic modulus. Then select the size, hardness and elastic modulus of the hot bimetal suitable for the respective molding process and equipment. Then select the appropriate resistivity according to the current time requirements of the protector and the effect of the heat capacity cavity.
According to the bimetal's current thermal effect formula Q=∫t0I2Rdt, it can be known that selecting a bimetal with high resistance will generate more heat, shorten the operating time of the thermal protector, and reduce the minimum operating current. The opposite is true for bimetals with low resistance. The resistance of the bimetal is affected by the resistivity, the size and thickness of the shape.
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