A study of the thermomechanical properties of the graphite-bearing refractores

Abstract

Determining the properties of the graphite-bearing refractories is of considerable importance in view of the wide application of these refractories and the stringent specifications on their properties [I].This paper presents the test results on the strength and the thermal shock resistance of the corundum-graphite refractories used in continuous preform casting machines. The tests were carried out on the laboratory specimens made from the industrial (No. i) and the experimental (Nos. 2-6) hatches that are used for producing submerged nozzles and monoblock stoppers. Table i gives the composition of the specimens under study.The laboratory specimens were made on a hydraulic press at a pressure of i00 MPa, and were fired at 1620-1670~ in a coke-powder charge.The high-temperature strength and the compressive creep were determined in argon atmosphere. The heating elements, the loading pads, and the protective screens of the heating chamber of the test set-up were made from graphite [2]. For determining the ultimate compressive strength, cylindrical specimens measuring 50 mm in height and 36 mm in diameter were heated at a rate of 180~ up to 1470~ at a rate of 720-900~ in the 1470-1770~ range, and at a rate of 120-180~ up to 18200K; at a given test temperature, the isothermal holding period amounted to 0.5 h. Table 2 shows the test results along with the data on the ultimate tensile strength obtained using the radial (diametric) compression method [3]. For all the specimens the temperature of strain initiation under load (determined according to GOST 4070-83) was above 2020~For the purpose of comparison, we measured the high-temperature strength of the specimens cut out from an imported monoblock stopper. It was equal to 8.4 MPa at 1820~ Almost all the experimental specimens, except specimen No. 6 having combined (alloyed) graphite, were found to be inferior to the specimens of the monoblock stopper with respect to strength. The temperature dependence of the ultimate compressive strength was determined in the 1720-1870~ range for the specimens of the batch No. i used for producing submersible nozzles. Composi~ tion number