CZĘSTOCHOWA UNIVERSITY OF TECHNOLOGY FACULTY OF MATERIALS PROCESSING TECHNOLOGY AND APPLIED PHISICS Department of Industrial Furnances and Environmental.

CZĘSTOCHOWA UNIVERSITY OF TECHNOLOGYCZĘSTOCHOWA UNIVERSITY OF TECHNOLOGY

FACULTY OF MATERIALS PROCESSING FACULTY OF MATERIALS PROCESSING TECHNOLOGY AND APPLIED PHISICSTECHNOLOGY AND APPLIED PHISICS

Department of Industrial Furnances and Environmental ProtectionDepartment of Industrial Furnances and Environmental Protection

„„PRECISE MEASUREMENTS OF THE SURFACE PRECISE MEASUREMENTS OF THE SURFACE TEMPERATURE OF SOLID BODIESTEMPERATURE OF SOLID BODIES””

Author: mgr inż. Agnieszka KlosAuthor: mgr inż. Agnieszka Klos

IntroductionIntroduction

The heating of metal charge before hot plastic working is a very The heating of metal charge before hot plastic working is a very important process which influences both the quality of rolled important process which influences both the quality of rolled product and the costs of processing.product and the costs of processing.In a properly conducted technological process, following the charge In a properly conducted technological process, following the charge heating programme should assure the proper quality of the process, heating programme should assure the proper quality of the process, that is prepare the charge at the specific temperature and with that is prepare the charge at the specific temperature and with permissible temperature differences. In the case of heat treatment, permissible temperature differences. In the case of heat treatment, temperature differences on the surface are also important.temperature differences on the surface are also important.

In industrial furnaces, the continuous measurement of charge In industrial furnaces, the continuous measurement of charge surface temperature is very difficult, or even impossible.surface temperature is very difficult, or even impossible.There is no method for controlling the charge surface There is no method for controlling the charge surface temperature during the heating process. We presume that this temperature during the heating process. We presume that this control method can be provided in the future by computer-aided control method can be provided in the future by computer-aided measurement using digital photopyrometry. Research into such measurement using digital photopyrometry. Research into such measurements are being conducted at the Department of measurements are being conducted at the Department of Industrial Furnaces and Environmental Protection of the Industrial Furnaces and Environmental Protection of the Czestochowa University of Technology.Czestochowa University of Technology.

Digital photopyrometryDigital photopyrometry

Digital photopyrometry is a contact-less method. The measurement Digital photopyrometry is a contact-less method. The measurement and recording of temperature is done using a digital camera. The and recording of temperature is done using a digital camera. The method consists in making a photograph of the radiating object method consists in making a photograph of the radiating object under examination. under examination. The digital photograph is transformed in The digital photograph is transformed in greyscale image.greyscale image.Such transformation enables the temperature of the examined object Such transformation enables the temperature of the examined object to be represented as a funkction of the absolute greyscale level. to be represented as a funkction of the absolute greyscale level.

The digital pictures exempleThe digital pictures exemple

Measurement methodology

Tests were carried out on a steel sample. The sample was Tests were carried out on a steel sample. The sample was heated directly in the chamber of an electric & gas furnace with heated directly in the chamber of an electric & gas furnace with a precise temperature control capability.a precise temperature control capability. The reference sample temperature was measured with an Ni-The reference sample temperature was measured with an Ni-CrNi thermocouple with the simultaneous photographic CrNi thermocouple with the simultaneous photographic recording of the image of the test sample.recording of the image of the test sample.Using the obtained image, the readout of the temperature being Using the obtained image, the readout of the temperature being measured was done with two methods. The first method was by measured was done with two methods. The first method was by manual reading out the average greyscale level of for the manual reading out the average greyscale level of for the assumed surface. The value of the greyscale level readout was assumed surface. The value of the greyscale level readout was then converted into the temperature value.then converted into the temperature value.In the second method, the temperature value was also read out In the second method, the temperature value was also read out directly using a developed computational program.directly using a developed computational program.

t0

t=f(r)

Number photo

Value t0

oCValue r Value

t1oC

It has been established that the effect of temperature on the It has been established that the effect of temperature on the greyscale level can be described with the following equation:greyscale level can be described with the following equation:

d

ra

barcrt

ln)(

where:where:a, b, c, d – constant value,a, b, c, d – constant value,r – degree greyss,r – degree greyss,t – temperature, °C.t – temperature, °C.

The values of the constants in relationship (The values of the constants in relationship (11) were established by ) were established by using the results of measurements carried out for developing the using the results of measurements carried out for developing the correlation between the temperature value and the greyscale level. correlation between the temperature value and the greyscale level. Thus, relationship (Thus, relationship (11) for S=1/60s was obtained in the form, as ) for S=1/60s was obtained in the form, as below:below:

73,6785,261

73,25985,261ln75,1013)(

r

rrt

(1)

(2)

Comparison of Comparison of thermovision and digital photopyrometrythermovision and digital photopyrometryMeasurement results obtained by three different methods are shown Measurement results obtained by three different methods are shown on the graphon the graph. . The temperature values obtained using the digital camera differ from the reference The temperature values obtained using the digital camera differ from the reference temperatures to a considerably lesser extent compared with the temperature values temperatures to a considerably lesser extent compared with the temperature values measured with the thermovision camera.measured with the thermovision camera.

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termocoulpe

thermovision kamera

digital kamera

Results of temperature measurements with utilization of three methodResults of temperature measurements with utilization of three method

In the case of the digital camera, a larger error is observable at lower temperatures. By contrast, for the thermovision camera, the error increases with the increase in specimen temperature.

The masuring precise of digital photopyrometryThe masuring precise of digital photopyrometry

The diagram The diagram is presented the is presented the preciseprecise of temperature readout from a digital of temperature readout from a digital

picturepicture manuallymanually and from and from using the developed computer program.using the developed computer program.

600650700750800850900950

100010501100115012001250

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Number measurements

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pera

ture

,0C

t0 t1 t2-computational program

The accuracy of temperature readout from a digital picture manually by reading out the average greyscale level is placed at a measuring error level of 3-4%.This error is greater for lower temperatures. Whereas, the measuring error for temperature read out using the developed computer program is approx. 1%, which is indicative of high accuracy of this measurement method.

The temperature characteristic for different solid bodiesThe temperature characteristic for different solid bodiesThe digital photopyrometry can be used to measurement of temperature The digital photopyrometry can be used to measurement of temperature different solid bodies. For the comparision were carry out the measurement for different solid bodies. For the comparision were carry out the measurement for some materials.some materials.The temperature characteristic for chamotte, steel and graphite are shown on The temperature characteristic for chamotte, steel and graphite are shown on the diagram.the diagram.

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average degree greyss, r

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chamotte steel graphite chamotte L6

SummarySummary

The analysis of measurement results shows that the results The analysis of measurement results shows that the results of temperature measurement using a digital camera are of temperature measurement using a digital camera are taken with high accuracy. In addition, the use of a suitable taken with high accuracy. In addition, the use of a suitable computer program enables a considerable automation of computer program enables a considerable automation of the process and facilitates reading out, while enhancing the process and facilitates reading out, while enhancing the accuracy of temperature readout (measurement).the accuracy of temperature readout (measurement).By using the program, the punctual readBy using the program, the punctual read out of steel out of steel and and the other materials the other materials surface temperature is possible.surface temperature is possible.

Thank you for attentionThank you for attention