How are infrared thermometers used in hot rolling?
JISCO hot strip mill is a semi-continuous rolling line with an annual capacity of 2.5 million tonnes, which mainly consists of: two step heating furnaces, a four-roll reversible roughing mill with front standing rollers, a cutting head flying shear, a six-stand finishing mill unit, a set of strip laminar flow cooling device, two coiling mills, a set of coil transport system and other equipments. In order to measure the surface temperature of steel parts and control the quality of rolled parts, infrared pyrometers are set up at four points in total, which are roughing mill exit, finishing mill entrance, finishing mill exit and coiling machine entrance.
1.Basic Principle
All objects with a temperature higher than zero degrees are constantly sending infrared radiation energy to the surrounding space. Infrared radiation characteristics of the object: the size of the radiant energy and its distribution by wavelength and its surface temperature has a very close relationship. Therefore, through the measurement of the infrared energy radiated by the object itself, it will be able to accurately determine its surface temperature, which is the objective basis for infrared radiation temperature measurement.
Infrared thermometer, also known as infrared radiation thermometry, is a technology that uses infrared radiation emitted by the object itself to measure the temperature of the object. Infrared radiation or infrared is the wavelength is located between 0.76 μm ~ 1000 μm electromagnetic radiation, for the ideal black body its unit surface area to the hemispherical space emitted by all the wavelengths of the total radiant power (referred to as the full radiant degree or intensity of radiation) and the temperature of the object is proportional to the fourth power:
Mb(T) = σT4 (1)
This is the famous Stephen Boltzmann law. Where σ = 5.6697 x 10-8W/m2K4 is called the Stephen Boltzmann constant.
(The equation (1) is used for real objects and needs to be multiplied by the radiance:
Mgb(T) = εσT4
It can be seen that the intensity of spontaneous radiation Mgb(T) of any object is related to the temperature of the object and the emissivity of the object. The emissivity ε of an object is directly related to the nature of its material (composition, metallic non-metallic, crystalline non-crystalline, etc.), the state of the surface (surface smoothness and roughness, degree of oxidation, contamination or surface coating, etc.) and the temperature of the object. As long as the correct choice of the object's emissivity, the actual temperature of the measured object can be accurately derived.
Infrared thermometer is composed of three parts: optical system, detection unit and signal processing. The main role of the optical system is to collect the radiant power of the target to be measured, and make it converge on the infrared detector. The role of the infrared detector is to receive the infrared radiation into an electrical signal output.
