Enamel manufacturers know that when purchasing enamel frits, the thermal expansion coefficient of enamel is also an important attribute. We usually require that the expansion coefficient of enamel is a little smaller than that of metal. So why is this happening? The first thing to understand is what the thermal expansion of enamel is.

Thermal expansion is one of the main properties of enamel. During the firing process of enamel, the increase in temperature causes the enamel or porcelain layer to expand. The expansion of enamel or porcelain layer is generally measured by their volumetric thermal expansion coefficient, which is three times the linear expansion coefficient, that is, α body = 3α line. The coefficient of thermal expansion of the enamel should be as close as possible to that of the body metal. Because, when the expansion coefficient of enamel is larger than that of metal, the porcelain layer will shrink faster than the metal during the cooling process of the product after firing, so that the porcelain layer will be subjected to the tensile stress generated by the green body. When the tensile strength of the porcelain layer is lowered, cracks will occur, and even the porcelain will explode. If the expansion coefficient of the enamel is smaller than that of the metal, the porcelain layer will shrink slower than the green body, and the porcelain layer will be subject to a compressive stress. When the compressive stress is greater than the compressive strength of the porcelain layer, porcelain will be removed.

In fact, the compressive strength of enamel is 10 to 20 times greater than the tensile strength. Therefore, it is generally required that the expansion coefficient of enamel should be smaller than that of the metal body.

It is worth noting that since the compressive strength of the body is 10 to 20 times greater than the tensile strength, it is generally required that the expansion coefficient of the enamel should be smaller than that of the metal body.