Study On The Emissivity Of Spring Steel,Brass And Nickel-chromium Alloy

Emissivity,also known as optical density,refers to the ratio of the radiance from a real surface to that of a blackbody at the same temperature.It is one of the thermophysical parameters and an important basic characteristic of objects.It's of great value to reference and application in agriculture,civil industry,military industry,aerospace and other fields.However,due to many factors affecting,such as temperature,wavelength,angle of emission,material,surface state and so on,accurate measurement of emissivity has always been a problem.So far,researchers have put forward many measurement methods and designed a variety of measurement devices,but no method or device occupies an absolute dominant position in the field of emissivity measurement because of the diversity of measurement conditions and requirements.Therefore,it is necessary to provide more theoretical methods and experimental data on emissivity measurement.With the wide application of metallic materials in various fields,people pay more and more attention to their purity and quality.Accurate temperature control and measurement are very important in the production process of metallic materials and directly affect the quality of desired product.In actual production,metallic materials are always moving and the surface state is very unstable.The traditional contact thermometry is not applicable.Most temperature measurements of metallic materials are done by radiation thermometry.The production process of metallic materials is always in the air and the surface will inevitably undergo oxidation reaction.An oxide film will be produced,which will affect its emissivity.Therefore,the accurate measurement of emissivity in complex conditions is very important.In the second chapter,an experimental device for emissivity measurement is introduced.Its structure and measuring principle are described in detail,and various factors affecting emissivity measurement are analyzed.In the third,fourth and fifth chapters,we measured the emissivity of spring steel 65 Mn,brass H85 and nickel-chromium alloy Cr15Ni60 at 1.5?mand 800-1100 K.The position and cause of strong oscillations were analyzed and explained during the growth of oxide layer.The variation of emissivity with heating time,temperature,heating time-temperature was studied.In this paper,11 fitting models of emissivity varying with heating time and temperature were evaluated.And two fitting models of emissivity varying with heating time-temperature were evaluated.The fitting function which best fits the variation of emissivity is determined according to their fitting results.Based on the emissivity obtained from experiments,the emissivity measurement and the temperature measurement errors caused by surface oxidation are calculated.Spring steel 65 Mn,brass H85 and nickel-chromium alloy Cr15Ni60 are three common and important materials in life.They are widely used in various fields.Their spectral emissivity data are very scarce.Only few can be seen in literatures.These data are supplemented by our work.In this paper,the relationship between the spectral emissivity and the oxide film of these materials were discussed.The variation of emissivity with heating time and temperature was studied.The temperature errors caused by oxide film were calculated.These works provide reliable reference for related theoretical and experimental researches and are of great significance for industrial production and practical application.