정전분무법에 의해 코팅된 가정용 법랑제품의 물성이 균열발생에 미치는 영향 Effects of the cracking by properties of the household porcelain enamel product coated by electrostatic spraying원문보기
Generally, the porcelain enamel is applied to the oven cavity coating among home appliances because it has some useful properties including chemical resistance, corrosion resistance, and especially exceptional thermal properties at high temperature. The environment temperature of the oven cavity...
Generally, the porcelain enamel is applied to the oven cavity coating among home appliances because it has some useful properties including chemical resistance, corrosion resistance, and especially exceptional thermal properties at high temperature. The environment temperature of the oven cavity as the cooking utensils is 250 ℃ . However, recently developed oven has a self-cleaning mode in using the high temperature of 450 ℃ for cavity cleaning. The self-cleaning mode is identical to thermal cycling process, cracking of the porcelain enamel coating sometimes occurs due to excessive tensile stress. That is caused by the mismatch of coefficients of thermal expansion between porcelain enamel coating and steel substrate. The cleanliness and corrosion resistance of the product are degraded by the cracking. The aim of this paper is to evaluate the effects of the cracking by properties of the porcelain enamel for additives under the self-cleaning mode. The behavior of the porcelain enamel coating under tensile stress is explained with the :fracture mechanics model of Hillerborg. The brittle :fracture criteria are composed of failure stress and energy release rate. The brittle :fracture properties of the porcelain enamel were determined by Impulse Excitation Testing method, Vickers Indentation Fracture (VIF) test, and uniaxial tensile test, respectively. The properties by each method were used to predict the favorable additive for the effects of cracking. As the result, enamel for Al-additive is predicted to favorable additive for the suppression effect of cracking. In order to evaluate the effect of cracking under realistic condition of the oven product, two steel substrate are manufactured by press forming process and firing process with porcelain enamel frit for either Al-additive or Ti-additive, respectively. The experiment of self-cleaning mode is performed according to constraint. As the result, the cracking is occurred on the coating layer in first thermal cycle. The thermal cycling is conducted for a total of 30 times. Then the results are evaluated by crack density. As the results of thermal cycling experiment, the crack density value of enamel for Al-additive is measured less than the crack density value of enamel for Ti-additive. The residual stress of the enamel coating changed by thermal cycling is measured by Vickers Indentation Fracture test. The thermal cycling experiment is performed without constraint. The residual stress in every 10 cycle is measured at observed point while the thermal cycling is conducted for a total of 30 times. As the conclusions, the residual stress changed value of enamel for Al-additive is measured still the compressive residual stress. But, the residual stress changed value of enamel for Ti-additive is measured the tensile residual stress after 30cycling. thus, Al-additive is determined to has advantageous suppression effect of cracking. Eventually, the results of verification experiment agree well with the prediction by properties value, therefore this technique can be used as a convenient way to predict advantageous additive.
Generally, the porcelain enamel is applied to the oven cavity coating among home appliances because it has some useful properties including chemical resistance, corrosion resistance, and especially exceptional thermal properties at high temperature. The environment temperature of the oven cavity as the cooking utensils is 250 ℃ . However, recently developed oven has a self-cleaning mode in using the high temperature of 450 ℃ for cavity cleaning. The self-cleaning mode is identical to thermal cycling process, cracking of the porcelain enamel coating sometimes occurs due to excessive tensile stress. That is caused by the mismatch of coefficients of thermal expansion between porcelain enamel coating and steel substrate. The cleanliness and corrosion resistance of the product are degraded by the cracking. The aim of this paper is to evaluate the effects of the cracking by properties of the porcelain enamel for additives under the self-cleaning mode. The behavior of the porcelain enamel coating under tensile stress is explained with the :fracture mechanics model of Hillerborg. The brittle :fracture criteria are composed of failure stress and energy release rate. The brittle :fracture properties of the porcelain enamel were determined by Impulse Excitation Testing method, Vickers Indentation Fracture (VIF) test, and uniaxial tensile test, respectively. The properties by each method were used to predict the favorable additive for the effects of cracking. As the result, enamel for Al-additive is predicted to favorable additive for the suppression effect of cracking. In order to evaluate the effect of cracking under realistic condition of the oven product, two steel substrate are manufactured by press forming process and firing process with porcelain enamel frit for either Al-additive or Ti-additive, respectively. The experiment of self-cleaning mode is performed according to constraint. As the result, the cracking is occurred on the coating layer in first thermal cycle. The thermal cycling is conducted for a total of 30 times. Then the results are evaluated by crack density. As the results of thermal cycling experiment, the crack density value of enamel for Al-additive is measured less than the crack density value of enamel for Ti-additive. The residual stress of the enamel coating changed by thermal cycling is measured by Vickers Indentation Fracture test. The thermal cycling experiment is performed without constraint. The residual stress in every 10 cycle is measured at observed point while the thermal cycling is conducted for a total of 30 times. As the conclusions, the residual stress changed value of enamel for Al-additive is measured still the compressive residual stress. But, the residual stress changed value of enamel for Ti-additive is measured the tensile residual stress after 30cycling. thus, Al-additive is determined to has advantageous suppression effect of cracking. Eventually, the results of verification experiment agree well with the prediction by properties value, therefore this technique can be used as a convenient way to predict advantageous additive.
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