- 著者
- 佐々木 茂弌
- 出版者
- 公益社団法人日本セラミックス協会
- 雑誌
- 窯業協會誌 (ISSN:18842127)
- 巻号頁・発行日
- vol.68, no.780, pp.283-294, 1960-12-01
For the purpose of investigating the effective way of preventing the thermal fracture of various bricks for bottom casting pit in teeming of molten steel, the equation of thermal shock resistance has been deduced from thermal stress equation, and the physical-mechanlcal properties of various bricks have been determined by testing. On the basis of the results obtained, considerations have been made concerning the effect of these properties and the size of each brick on thermal shock resistance.<br>Important results obtained are summarized as follows:<br>i) In the thermal stress equation σ=<i>E</i>α/(1-μ)⋅(θ<sub>0</sub>-Θ)⋅<i>f</i>, thermal shock resistance (R) are expressed in σ<sub>max</sub>/σ′, putting σ′ as max. thermal stress in tension, <i>f</i>′ as factor <i>f</i> corresponding to σ′, σ<sub>max</sub> as max. tensile strength of a brick.<br>ii) Heat-transfer coefficient from molten steel flowing at temperature θ<sub>0</sub> to the surface of the brick at temperature Θ being in contact with molten steel flow is very large, and therefore, thermal shock resistance is expressed by the following two equations.<br>In the earliest stage, when heat does'nt begin to flow within a brick:<br><i>R</i><sub>2</sub>′=σ<sub>max</sub>/<i>E</i>⋅(1-μ)/α⋅1/(θ<sub>0</sub>-Θ)<br>In the next stage, when heat flows within a brick:<br><i>R</i><sub>1</sub>′=σ<sub>max</sub>/<i>E</i>⋅(1-μ)/α⋅1/(θ<sub>0</sub>-Θ)⋅(<i>kt</i><sup>1/2</sup>/γ)<sup><i>a</i></sup><br>or <i>R</i><sub>1</sub>′=σ<sub>max</sub>/<i>E</i>⋅(1-μ)/α⋅1/(θ<sub>0</sub>-Θ)⋅(<i>K</i>/<i>γh</i>)<sup><i>a</i></sup>′<br>iii) The relation between the mechanical properties and porosity may be expressed by a hyperbolic curve.<br>iv) The ratio of bending strength to Young's modulus, an effective factor for increasing thermal shock resistance, is larger in pyrophillite-clay brick than that in grog-clay brick. This ratio shows a trend to decrease with increasing porosity. It is presumed from the data in technical literatures that this ratio is approximately constant at high temperature below the critical temperature of pyroplastic property.<br>v) Based on the equation of thermal shock resistance determined in the case of runner brick, it is estimated that bending strength/Young's modulus ratio, linear thermal-expansion coefficient (α), poisson's ratio (μ) and temperature difference (θ<sub>0</sub>-Θ) have an influence of first power. On the other hand, the thermal conductivity (<i>K</i>), specific heat (<i>C</i><sub>ρ</sub>), density (ρ) and wall thickness (γ) have an infiuence of 0.040 and 0.081 powers, respectively, on thermal shock resistance. In addition, considerations have been made concerning the degree of the effect of porosity, which is in functional relation to mechanical properties and thermal conductivity, on the thermal shock resistance.<br>vi) It is presumed that there is a limit in the improvement of thermal shock resistance by changing the properties of a fire clay brick and that most important factor for the prevention of thermal fracture is the moderate pyroplastic property.