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The purpose of applying infrared imaging technology to the detection of the surface temperature field of hot roll is to judge the cooling condition of the roll by detecting the distribution of the surface temperature field of the hot roll just off the machine, and to effectively control the working temperature by improving the cooling system, so as to reduce the number of roll changes and improve the utilization rate of the working roll.
1.Influence of roller temperature on service life
Modern rolling mills have high rolling speed and power, part of which will cause the temperature rise of rolled pieces and rolls. If the roll temperature is too high, the roll is easy to cause peeling and cracking of the roll working layer under the action of rolling stress and thermal stress during steel rolling, resulting in defects such as roll peeling and increased thermal crown, thereby increasing the number of roll changes, and the shape of the strip is not easy to control. Therefore, the rolling mill has a cooling system to reduce the roll surface temperature, but how to control the temperature and whether the cooling system makes the whole roll surface temperature cool evenly have not been systematically tested at present. It is only a unilateral guarantee that the cooling system works normally, and little consideration is given to the cooling effect of the roll and whether the local temperature is high. Applying infrared thermal imaging technology to detect the surface temperature of hot rolls can judge the distribution of the surface temperature field of rolls, so as to judge the cooling condition of rolls. By improving the cooling system, the working temperature can be effectively controlled, the number of roll changes can be reduced, and the utilization rate of working rolls can be improved.
2.Application of infrared imaging technology in roller surface temperature detection
2.1 Detection methods and steps
① After the roll is pulled out, it is placed on the site for infrared detection 30 minutes later.
② Adjust the instrument parameters, start to test the inlet side and outlet side of each work roll, and record each test position.
③ Use the software to analyze and find out the maximum surface temperature of the work roll.
2.2 Analysis of detection examples
The infrared test was carried out on the rolls of a hot rolling plant. The infrared diagram and test data are shown in Table 1: the surface temperature of the work roll of the rolling mill is required to be less than 60 ℃ after cooling. From the data in Table 1, the maximum temperature at the inlet side of the work roll of F1 rolling mill is 63.9 ℃, indicating that the cooling condition is poor.
3.Analysis of the causes of the errors in the detection of roll surface temperature by infrared imager
In the process of using infrared imager to detect the surface temperature field of hot roll, it is found that there is a great difference between the detected temperature value and the result of using contact thermometer. The main reason is that the ability of an object to reflect external radiation is directly related to its own material and surface roughness. The smoother the surface of an object, the smaller the ability to reflect heat radiation. Due to the needs of production technology, the surface of the roll has been processed by lathe, and the surface roughness is low, which leads to the situation that the temperature value detected by infrared imaging is less than the actual temperature value of the roll.
4.Method of eliminating the temperature error of roller surface detected by infrared imager
Because the surface roughness and material of the same roll are basically stable, that is, the error caused by using infrared imager is basically stable. If the atmospheric temperature, relative humidity, measurement distance and other parameters remain unchanged, adjust the "emissivity" parameter to correct the influence of the surface roughness of the object on the reflected energy, so that the instrument can get the test results close to the actual temperature, as shown in Table 2:
5.Epilogue
(1) When using infrared imager to detect the temperature of objects with smooth surface, it may cause large measurement error. At the same time, other means should be taken to detect and compare the actual temperature value.
(2) By modifying the "emissivity" parameter of the infrared imager, the detection result close to the actual temperature value of the object with smooth surface can be obtained. For the hot rolling work roll, the set value of emissivity is about 0.4.
(3) If you want to use the above method to detect the temperature value of a smooth surface object, you should make the infrared imager shoot the measuring point as far as possible to reduce the error.
