Cooling of Enamel Products
When the enamel product is taken out of the furnace, it is in a hot state. During the cooling stage, all parts of the product should dissipate heat evenly.
If the local cooling rate of the fired product is faster than its adjacent parts, there will be a temperature difference between the two parts, and a certain stress will be generated at the same time. The greater the temperature difference, the greater the stress. Of course, when the stress exceeds the tensile strength of the enamel frit, it will Cracks or peeling occurs. The following experiment proves this point:
Three products fired at the same temperature, immediately take one of them and place them on a copper plate with a temperature of 25℃, the bottom of which is in contact with the copper plate, and the other one in water (most of the green body remains outside the water layer) and the bottom of the product. Cold water, the other one is left on the grill to let it cool naturally. As a result, it was found that the enamel layer of the first one had cracks on the bottom of the enamel frit, the bottom of the second had decayed porcelain, and the body had serious cracks, and the third had no cracks and no decayed enamel, and the porcelain surface was intact.
The test results fully show that uneven cooling is the main reason for the fracture of the porcelain layer. In actual production, in order to ensure the quality of enamel products, uniform cooling must be achieved. The following points should be noted:
1. The skewer, plastic appliances, etc. must be preheated.
2. Apparatus for placing freshly baked enamel products should absorb as little heat as possible, such as turntables or conveyor belts with hollow enamel plates.
3. The fan in front of the furnace should not directly blow the enamel products just out of the furnace, so as not to cause excessive local temperature difference of the products and affect the quality.
4. The thick-walled products fired in the box furnace (such as cast iron enamel bathtub, large industrial enamel reactor, etc.) should be placed in the 80~100℃ insulation room for slow cooling after being discharged.