Thermal Expansion Coefficient of Enamel Frit
Thermal expansion performance is one of the most important properties of enamel frit. Thermal expansion refers to the phenomenon that the enamel frit or porcelain layer expands with the increase of temperature during the firing process. It is measured by the volume thermal expansion coefficient of the enamel frit. , the volume expansion coefficient is about 3 times the linear expansion coefficient, namely: α body = 3α line.
When the enamel manufacturer chooses the enamel frit, the thermal expansion coefficient of the enamel needs to be as close as possible to that of the metal body. If the expansion coefficient of the enamel is greater than that of the metal, the enamel layer will shrink faster than the metal in the cooling stage after the enamel product is fired, resulting in the ceramic layer being subjected to tensile stress from the metal body. Once the tensile stress is greater than the resistance of the ceramic layer Tensile strength, there will be cracks and even cracks and other defects.
If the expansion coefficient of the enamel is smaller than that of the metal, the porcelain layer will shrink more slowly than the metal, and the porcelain layer will receive the stress. Once the stress is greater than the compressive strength of the porcelain layer, the defect of de-porosity will occur. Whether the expansion coefficient is too large or too small, it will have a bad influence on the quality of enamel products.
Under normal circumstances, the compressive strength of the enamel will be 10 to 20 times greater than the tensile strength, so we will require the expansion coefficient of the enamel frit to be smaller than that of the metal body.
Of course, because the cooling speed of each part of the metal blank is different, the stress generated is also different, the enamel manufacturer should choose the enamel whose thermal expansion coefficient is close to that of the metal blank, and the parts with small curvature radius need to pay more attention.