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Imitation experiment of detecting the correct temperature of coal mill bearing by bimetal thermometer
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In 1998, the bearing of the coal mill of Meixian Power Plant burned the bearing of the coal mill 2 times due to high temperature; the temperature indication of the bimetal thermometer used to measure the bearing temperature of the coal mill and the protection effect did not reach the temperature value. What is the reason?
It is well known that the temperature measurement principle of a bimetal thermometer is as follows: a bimetal with two different metals with different expansion coefficients is used as a temperature sensing element; when the temperature changes; a bimetal fixed at one end; because of two metals The expansion coefficient is different and the curve is twisted; the displacement at the free end is indicated by the transmission tissue and the corresponding temperature is indicated.
The temperature sensing end of the bimetal thermometer has a certain length (such as WSSX-401; L=450mm type bimetal thermometer; its temperature sensing end length is not less than 200mm; therefore its penetration depth should be no less than 200mm); therefore its temperature measurement method It is immersed; the required medium to be measured is a movable medium such as gas, liquid and steam.
The method of measuring the bearing temperature by the bimetal thermometer is point-contact; and the measured medium is solid; therefore, it is necessary to verify by experiment; whether the bimetal thermometer can be used to measure the bearing temperature of the coal mill. There are many bimetals for power plants in the country. The thermometer measures the bearing temperature and supplies an alarm signal.
1 Laboratory calibration First check the bimetal thermometer. Take out a new type of bimetal thermometer of type WSSX-401; L=450mm (ie the type of bimetal thermometer for measuring the bearing temperature of the coal mill); Check in.
Verification conclusion: The comparison method is used to verify the standard parts and the parts to be tested in warm water; after verification; each indication value is within the scope of error acceptance; qualified.
2 Imitating the experiment using a bimetal thermometer to perform a double metal thermometer to measure the bearing temperature of the coal mill.
The experimental method is as follows: plug the electric kettle filled with water into the power source for heating; gradually increase the temperature of the outer wall of the electric kettle; find a plastic foam sponge with a thickness of 15-20 cm and stick it to the outer wall of the electric kettle (this can reduce the temperature loss) ; more and more close to the actual situation); and dig 2 small holes in the plastic foam close to the outer wall of the electric kettle. Insert the measuring end of the bimetal thermometer into a hole; make the temperature measuring end of the bimetal thermometer On the outer wall of the electric kettle, the standard platinum rhodium 10 platinum thermocouple (S indexing number) is used as the specification part; the temperature measuring end of the standard platinum rhodium 10 platinum thermocouple is closely attached to the outer wall of the electric kettle; and is fixed; The lead from the other hole of the foam sponge is placed in an ice jug.
It can be approximated that the temperature of the outer wall of the electric kettle is the same as that of the bearing temperature of the coal mill.
After the power is turned on; the temperature of the outer wall of the electric kettle is gradually increased; the data is obtained on the bimetal thermometer and the electronic potentiometer.
From the experimental data:
(1) Measurement by contact method; the value obtained by the bimetal thermometer does not reflect the actual temperature of the object to be tested.
(2) From the trend of change; the bimetal thermometer has a delay effect; it cannot reflect the temperature change in time.
(3) The value indicated by the bimetal thermometer is compared with the actual value; the difference is large; if the practical value is 84 °C; the indication value of the bimetal thermometer is 46 °C; the difference is 38 °C.
* At this moment, the water is jubilant; turn off the power.
3 Conclusion (1) The bimetal thermometer is used to measure the bearing temperature of the coal mill; the indication value does not correctly reflect the actual value of the bearing temperature of the coal mill; therefore, the bimetal thermometer cannot be used to measure the bearing temperature of the coal mill and supply the bearing temperature. High alarm and signal protection.
(2) The same; bimetal thermometer can not be used to measure the bearing temperature of the induced draft fan, blower and so on.
4 It is claimed that the bimetal thermometer can not correctly reflect the temperature of bearings such as coal mills; it is recommended to use the following methods to deal with this problem.
(1) Open a hole in the bearing bush; install the thermal resistance; instead of the bimetal thermometer (with the temperature of the thruster of the measuring machine).
(2) Pick a kind of armored thermal resistor with fast temperature reflection and small measuring end area instead of bimetal thermometer.
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