~78% (mass) aluminum refractories. Five of these refractories were selected for use in different furnaces in the steel industry and the thermal and mechanical properties associated with these refractories were determined. Water quenching 8.319) Determine the thermal shock stability of the sample. Based on the properties of the material and the heat transfer conditions, two equations related to the temperature difference are used. Under free convection conditions, the cylinder is placed in a static position in the tank and the heat transfer coefficient is calculated using the Holman equation.
The calculated temperature difference is compared with the number of quench cycles tested, and linear regression analysis is used to determine the correlation between the calculated value of the critical temperature difference and the water quench test results. From the results, it can be seen that several equations are recommended for predicting the thermal shock properties of aluminum refractories.
Introduction The thermal shock resistance of ceramics is of great importance in a wide variety of applications. In order to meet these applications, many different methods of describing the susceptibility of a refractory material have been made. These methods are based on material properties such as resistance parameters. The critical temperature difference (ATc) required for initial thermal stress fracture represents a quantitative measure of the thermal stress of a particular refractory material. The quantitative interpretation of this data is based on the thermoelastic theory of convection-induced heat transfer. The most commonly used experimental method to determine the thermal shock stability is the water quench test. The author of this article discusses the use of thermal shock resistance to describe the properties of steel refractories based on their experience. The purpose of this study was to compare the predicted performance and experimental performance of the five selected refractories under thermal shock conditions by means of a water quench test. In order to predict thermal shock resistance, different equations are used to calculate the temperature difference.
Materials The standard laboratory procedures were used to determine the thermal and mechanical properties of selected materials. The results obtained were described in previous studies. As a test method, water quenching method 8.319) was used to measure the thermal stability of the refractories. The sample was dried at 110 and then placed in an electric furnace of 950 for 15 minutes. The sample was taken out and put into the water for 3 minutes, and then sent to the electric furnace of the 9501, and this process was repeated until the sample broke. The number of water quenches for this cycle until the sample breaks is used as a measure of the thermal shock resistance (Table heat transfer coefficient is used to place the cylinder in the tank and the heat transfer coefficient under free convection conditions is calculated using the Holman equation ( h).
Since the value of h given in Equation 1 is a function of the temperature difference, for all calculations, the set temperature (T.-! is 930. The temperature difference for the water quench test is the same as the selected value. The needle is clearly indicated. The a-SiA10N structure can be achieved by using p-Si3N4 starting powders or nucleation during sintering.Different microstructures are obtained through SEM studies, (B-Si3N4 raw material powders can be sown during sintering. The resulting acicular a-SiA10N particles are formed, and acicular a-SiA10N particles can also be produced with industrial a-Si3N4 powder by first nucleating and then growing at a low temperature. This improves the robustness. Due to the low thermal conductivity of a-SiAlO, this type of material cannot be used for cutting tools, but at low temperatures it is the best choice for wear areas such as ball bearings.
(: July 2002) For sinks, it is assumed that the heat transfer coefficient is caused only by free convection. In the past, metallurgists have made some efforts to apply vaporization heat transfer theory and relate it to the quenching process.
Due to the very complex heat transfer of vaporization, it is not expected that one equation may be related to the vaporization curve, which often represents the characteristic, in all states. For this reason, some useful contrast relations apply to individual vaporization states. For the sake of simplicity, this article only assumes free convection.
Table 1 Performance Characteristics of the Samples Thermal Expansion Coefficient/% Compressive Strength a/MPa Surface Breaking Energy 7/(km2) Young's Modulus E/GPa Poisson Number U Water Quenching Test (cycle number) 4 Temperature Difference Thermal shock resistance The assessment is based on the critical temperature difference required to cause a significant loss of strength observed during cooling or heating. It has been observed that the critical temperature difference depends on the heat transfer rate. Water is often used as a quench medium, and these rates show several orders of magnitude change in the temperature range. The general form of the equation for thermal stress generated by cooling or heating reflects the importance of specimen size and heat transfer rate.
Young's modulus; AT - temperature change; Bi = ah/k - Biot number.
It is generally assumed that a critical value of ΔTc can be obtained when the thermal stress generated by the thermal gradient curve is equal to or exceeds the fracture strength of the material. The formula used to calculate AT is as follows: Transfer coefficient.
Without breaking, the sample is subjected to quenching. The maximum temperature difference is given by the following formula: 5 Test 5.1 Heat transfer conditions Parameters Using Equations 1 to 3, the relevant calculation parameters for the heat transfer conditions for the flume are listed in Table 2. Table 2 Heat The transmission condition is calculated using the parameter performance convective heat transfer coefficient h/-CnfsK)-1 5.2 Results and Discussion ~ 4 The critical temperature difference or the maximum temperature difference is calculated. In order to calculate the temperature difference, the compressive strength was used. Using the difference of the standard equation Bi (the functional relationship between the maximum number of cycles required by the water quench quenching experiment and the range 4), it is a function of the water quenching experimental results. From the results obtained, it can be seen that there is a linear relationship between the temperature difference AT and ATa and the water quenching test results. The calculated value AT was compared with the experimental value. Linear regression analysis was used to determine the relationship between temperature difference and water quenching experiments. Some linear regression analysis results are shown in Table 3. Table 3 Linear regression analysis results Relationship between AT and N R times standard deviation Approximate function relation Linear regression analysis results confirmed Graphical results. In previous studies, the relationship coefficient for the linear relationship was considered to be greater than 0.85. This higher value of the selected relationship coefficient was used as a safety factor to study aluminum refractories with high porosity.
6 Conclusions Different methods can be used to predict the thermal shock resistance of refractories. In this paper, thermal shock is analyzed using temperature difference and water quenching tests. To calculate the temperature difference, two equations provided by different authors were used. The calculated value of the temperature difference was compared with the measured value of the number of quench cycles resulting in the fracture in the water quench test. The regression analysis results show that in both cases, the linear relationship between AT and water quenching results can be obtained by two equations. The analysis provided herein can be used to predict the thermal shock properties of aluminum refractories. To determine the thermal shock stability of refractories, a temperature difference method can be used. The data calculated based on the temperature difference of the material and the performance of the quenching medium (water) is related to the number of quench cycles. The number of water quench cycles is often used to determine the thermal shock stability of the refractories.
118 Xu Qingbin School (August, 2002) - The development of C bricks The effect of special additives is obvious even when compared with conventional products.
Table 1 Chemical composition and physical properties of the sample Chemical composition /% Fixed C additive apparent porosity /% bulk density / (Kcm3) bending strength of the sample A: no fired sample; B: in coke in 800t, Samples treated after 3 h; C: Specimens treated in coke at 1400 T for 3 h; D: High-temperature flexural strength after coke treatment at 14001 C, 3 h in the use of alkali in recent years In various furnaces of refractories, chrome-free, carbon carbide, low thermal conductivity, etc. are required, and in particular, the low carbonization of MgO-C bricks is required. However, when the amount of carbon raw materials used is reduced, there is a fear that the thermal shock resistance and the like will be reduced. Therefore, in order to reduce the carbon content and ensure the mechanical strength and heat resistance, the material ratio was studied. This article reports the results of studies using special additives.
2 Test results 2.1 The main physical properties of strength. In addition, in order to understand the effects of the special additives, products (4) for comparison were also produced. The strength properties were evaluated using the flexural strength under A4 to A4 conditions.
The measurement results are shown and the following points are made clear: due to the effect of special additives, the flexural strength of the specimen can be maintained at a relatively high level; the flexural strength of the specimen after heat treatment in the coke bum, using special additives is 10 MPa Above, it can be kept at a more ambitious level;
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