Junichi Kon

Determination of the thermal shock resistance of graphite by arc discharge heating

Abstract This paper presents a technique to determine the thermal shock resistance of graphite by a basic analysis of non-steady thermal stress in a circular disk heated by an arc discharge at its central part. The thermal shock resistance is defined as Δ = σ θ k Eα , α θ , circumferential tensile thermal stress; κ, thermal conductivity; E , Youngs modulus; α, thermal expansion coefficient) and is determined en bloc only measuring the electric power of the arc discharge using the specific non-dimensional thermal stress S ∗ which is calculated theoretically as the maximum saturation stress in the non-dimensional diffusion time τ > 1 4 . This technique is also available to measure simultaneously the thermal diffusivity k = k cp ( c , specific heat; ρ, density) using the specific non-dimensional diffusion time τ ∗ calculated theoretically as the heat reaching time from the center to the periphery of the disk after the arc discharge is started. The experimental studies for several kinds of graphite were carried out and the results are compared with the values of σ θk Eα and k cp estimated indirectly from the individual mechanical and physical properties.

An analysis of thermal stress fracture in a graphite electrode used in an arc steel making furnace

Abstract In this paper, the thermal stress in the graphite electrode, which is connected typically three rods of 20 in. dia., is analyzed by an elastic theory as an axially symmetrical thermal stress of cylinder with finite length. The axial and radial temperature distributions in electrode during the regular power (RP), high power (HP) and ultrahigh power (UHP) operations in arc steel making, are assumed with reference to the actual data of steel making arc furnace measured by Nedopil and Storzer. For the reason of convergency of analytical solution in the center of cylinder, the hollow cylinders with a small hole in the center are treated. These hollow cylinders are used partly at present because of the arc stability. The distributions of principal stress components were calculated numerically using the anisotropic mechanical properties of graphite at the temperature as a function of operating conditions of RP, HP and UHP. The results of hollow electrode with small hole obtained here may be extended to the case of solid electrode for the evaluations of maximum thermal stress which occurs at the outer surface of electrode. The values and the positions of maximum stresses are discussed in comparison with the anisotropic properties of mechanical strength of graphite, and are investigated the current carrying capacities of graphite electrode. These analytical results agree very well with the actual fracture phenomena of graphite electrode observed in a model arc furnace.