Thermophysical properties of certain ferroalloy and graphite powders

Thermophysical properties of certain ferroalloy and graphite powders

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Powder Metallurgy and Metal Ceramics. Vol. 35. Nos. 1-2, 1996 THERMOPHYSICAL PROPERTIES OF CERTAIN FERROALLOY AND GRAPHITE POWDERS I. N. Zegalo, Yu. N. Grishchenko, A. P. Stovpchenko, and S. I. Zigalo UDC 621.762:669.412 The thermophysical properties of certain ferroaUoy (FS3OR3M30, FSZr50, FTi-30) and graphite powders, used for the composite microalloying of steel castings, were determined using an experimental--calculation method. A substantial difference in the heat conductivity of powder and monolithic materials was revealed. The nature of change of these properties with temperature was investigated. In developing techniques for the manufacture of composite ingots microalloyed with ferroaUoy powders [ 1], it has been established that the use of thermal conductivity coefficients for these materials in the compact (cast) state leads to significant errors in calculating the heating rates of the materials in powder form. The authors of the present work have determined the thermophysical properties of the powder materials using the experimental--calculation method proposed by N. Yu. Taits and E. M. Goldfarb for steel [2]. This is based on graphical solution of the heat-conductivity differential equation, carried out with the aid experimentally determined heating rates for the bodies. A schematic of the experimental equipment, constructed on the basis of a Tamman furnace, is given in Fig. 1. The experiments were conducted as follows: a steel tube 2, filled with powder (or a monolith) of the investigated material 4, and closed above and below by refractory plugs 3 (to decrease heat loss), was situated within a graphite block 1, placed on a support and heated to 1100-1150°C." Temperature changes in the graphite block, in the center of the specimen, and in the tube wall were measured with the aid of a system of type VR 5/20 thermocouples, and registered on the multipoint self-recording potentiometer KSP-4. The measurement error at 1000*C was +4 degrees, according to the thermocouple wire certification. The dimensions of the specimens were chosen so that they could be located in the zone of constant temperature along the length of the furnace ( - 150 mm), but be of a diameter large enough to provide a noticeable temperature difference through the cross section in the initial period of heating. The steel tubes were 48 mm in diameter and 3 mm in wall thickness. The length of the specimens was twice the diameter, which obviated the occurrence of heat loss through the ends. Results of the temperature measurements during heating were transferred to special tables, in which the temperature ranges were delineated. From the initial and final temperature differences At o and At, and the heating rate over the time interval T, the criteria Ato/C T and At/C T were found. Then, using the graph given in [2] for various values of At0/C T, the Fourier criterion F 0 = c~z/R 2, where ~ = temperature conductivity, m/sec; r = time, sec; R = specimen radius, m, was determined for the different values of Ato/C r.
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This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.

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Thermophysical properties of certain ferroalloy and graphite powders

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