In high-temperature industrial metallurgical furnaces heat transfer occurs mainly by radiation. In carrying out heat calculations in such equipment is necessary to know the radiation characteristics (coefficients of radiation and reflection) of all the components of the working space, and in the first case of the refractory lining materials. However, existing information on the thermal radiation properties of refractories is very limited, and the data on spectral characteristicsof infrared reflection is practically completely lacking.This article deals with an experimental investigation of the reflecting properties of industrial corundum in the IR spectrum both at room temperatures and also when heated to 1500~ with subsequent cooling in air. The spectral relationship with the coefficients of reflection for these materials was obtained from spectrophotometric measurements, and the heating of the specimens was carried out by focusing the thermal radiation of an optical furnace. The plan of the experimental equipment is shown in [I]. Using the IKS-21 spectrometer we measured the intensities I, and l,p of the reflected radiation respectively from the surface of the standard (magnesium oxide and sodium chloride) and the specimens being studied. The ratio (19 and I,)/R, -rA, where R, is the reflecting capacity of the standard, enable us:to determine the coefficient of reflection (bidirectional reflective capacity) rA for different angles of incidence e' and reflection e in the wavelength range A from 0.75 to 6 ~m.The objects of the investigation were specimens of corundum refractory produced by the Podolsk refractories factory. The chemical composition of the refractories (OST 14-46-79), % was: A1203 97, Ti02 1.5, SiO 2 0.5, FezO 3 0.1; the porosity reached 21%. To clarify the possible changes in the optical properties of the surface of the refractories under the action of prolonged heating we studied corundum specimens obtained from the Volgograd Red October Factory which had been used in a heat-treatment furnace at a working temperature of 1500~ for 1.5 h. Figure 1 shows spectral curves for the reflection coefficients for the original and worked material obtained at room temperature with an angle of incidence and angle of reflection close to the normal. The coefficient of reflection of corundum refractory possesses a clearly expressed selectivity. In the close IR region of the spectra (A up to 2.3 ~m) we observe an increase in r A. Further scanning over the spectrum showed that with increase in the wavelength there is a sharp reduction in the coefficient of reflection with the formation of a minimum on the spectral curves when A -3.5 ~m and a slight increase in the region of = 4-5 ~m~In the entire spectral range studied the levels of r A of the used material in absolute values were lower than in the original material, although the qualitative character of the spectral curves was the same. This is connected with the irreversible changes in the surface roughness of the worked refractory. Measurements of this factor ca...

In contemporary metallurgy the role of refractories is extremely important, both technologically and also from the point of view of accelerating the heat processes and rational utilization of energy.This makes it necessary to conduct all-round investigations into refractories, including their radiation characteristics, which have a substantial influence on the heat exchange in the working space of the furnace.The present work deals with an experimental investigation of the integral normal degree of blackness ~tn of fibrous refractories during heating to 1500 K in oxidizing and in inert gas atmospheres.Measurements were made on experimental equipment described in [i]. Specimens were heated in the radiation optical URAN-I furnace in which the source of intensive thermal radiation consisted of a xenon high-pressure lamp, DKsR-10000, located at the first focus of an elliptical mirror reflector.The temperature of the materials being studied was measured with chromel-alumel thermocouples 0.2 mm in diameter, the hot joints of which were attached to the surface of the specimens with refractory cement, and the cold ends were thermostatically controlled at 0~The source of radiation energy consisted of a semiconductor bolometer BKM-5 placed in a thermostatically controlled frame with an automatically maintained temperature (303 • I)K. The temperature of the specimen and the bolometer signal were measured on a digitial metering complex F30K.The rate of heating the specimens was fixed and regulated with an automatic potentiometer KSP-4.The bolometer was graduated with respect to a model of an absolutely black body, consisting of a graphite cone with an opening angle of 13 ~ , pressed in a molybdenum block, which was heated in vacuum in a tungsten resistance furnace.The integral normal degree of blackness etn in the case of equality of the resulting currents of radiation of specimen and black body was calculated from the equation T0--T~2t~t"~ where T0, TI, and T z are respectively the temperature of the black body, the specimen, and the heat receiver.The total error of the determination of ~tn was 12-13%.The investigations were made on the following fibrous materials: ShVP-350 from 75% aluminosilicate fibers (SiO z 49-50%, AIzO 3 48-49%, FezO 3 0.8-1.3%, CaO 0.6-0.8%, MgO 0.3-0.9%, S 0.2-0.8%) and 25% clay bond; ShVP-350 with a coating about 0.5 mm thick of 10% silica sol (water solution of SiOz) ; high-temperature refractory made of 95% mullite-silica fiber (SiO z 46-47%; AIzO 3 46-48%, CaO 2.8-3.5%, NazO 0.9-1.2%, FezO 3 0.9-1.1%) and 5% silica sol bond. The surface of the latter refractory was coated with a layer of 22% silica sol, about 0.5 mm thick.The apparent density of the fibrous material ShVP-350 was 350-380 kg/m 3, and of the high temperature refractory 240-260 kg/m 3. The diameter of the fibers for these materials did not exceed 8-10 ~m. The specimens of diameter 30 and thickness 4-5 mm were cut so that their working (radiating) surfaces formed the face of a standard brick.The thickness of the specimens was selecte...

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Refractory materials (refractories) are products made on the basis of mineral raw materials, and are widely used as construction linings of industrial furnaces and a whole range of other thermal-energy units. In conditions of high-temperature heating the refractory lining not only delineates the working space, but also takes a direct part in the processes of heat exchange, and above all in such processes through radiation, which as a rule are the dominant processes. Therefore, the effectiveness of the work of industrial furnaces, their reliability and economic effectiveness largely depend on the proper choice of refractory materials and a knowledge of their reflective and radiating capacities (radiation characteristics). The study of the properties of the thermal radiation of refractories is extremely important, both technologically and from the viewpoint of speeding up heating processes and the rational use of energy [1][2][3]. All this leads to the need for a detailed investigation of the radiation properties of materials.Refractory materials can be classified into several groups. The main ones are siliceous, aluminosilicate, magnesia, chrome-magnesite, high-alumina, zirconia, and oxide materials [4]. In Soviet scientific literature several reviews have appeared dealing with the measurement of the properties of thermal radiation of refractories. Noteworthy are the reviews and summaries given in the handbook under the editorship of A. E. Sheindlin [5], in the work of Landa and Glazachev [6], and in the factual data [7]. The reviews cover a wide range of experimental works and so we shall concentrate mainly on investigations which for one reason or another have not found the necessary reflection in publications [5-7]~ Of great practical importance is a study of the influence of prolonged industrial use of articles on their radiation properties. These questions are examined in [8][9][10], in which measurements were made of the spectral normal radiation capacity SAn of high-alumina and chamotte (fireclay) refractories with different services periods in metallurgical furnaces.Measurements were made by comparing the radiation of specimens and a model of an absolutely black body, which was used in the form of a tubular resistance furnace. The design of the apparatus was described in detail in [ii]. Heating was done by using flat specimens, tightly pressed to a metal plate made of nichrome or molybdenum, coated with molybdenum disilicide, through which an electric current was passed. The temperature of the refractory materials was measured with two chromel-alumel thermocouples which were placed in special channels 0.6 and 1.2 mm deep, and attached to the specimen with a refractory cement. The temperature of the working (radiating) surface was determined by extrapolation to the zero depth of the reading of the thermocouple. Investigations were made in the range 973-1273 K and a wavelength of 0.95-15 ~m in air. The experimental error is assessed at 8-10%.It is established (Fig. i) that the considerable change in the spec...