In the course of the diploma work we performed measurements of the thermal properties of two enamel grades, used for kitchen appliances, by transient plane heat source method (Hot Disk TPS 2200) in accordance with the international standard ISO 22007. Since we could not perform direct measurements of the thermal properties of enameled steel sheets, samples of enamels were also prepared in the form of thick layers. The results obtained from the measurements of the thick layers are within the expected values of the enamels thermal properties. However, it has been established, that the density of the enamel layer has a significant effect on the thermal properties.
The samples of the enameled steel sheet were metallographically prepared and analyzed by scanning electron microscopy (SEM-EDS) and optical microscopy (OM). We found out that the layer of analyzed enamels has multiphase structure, consisting of amorphous regions with different chemical composition, crystalline phases and pores. From the microchemical analysis results of the enamel powders it can be seen, that certain crystalline phases in the enameled layer originate from the process of preparing enamel powders.
From the microchemical analysis (SEM-EDS) of the steel – enamel phase boundary, it is evident that chemical reactions occur during the firing of the enamel at certain points on the phase boundary, whereby the cobalt diffuses into the steel.
An assessment of the influence of enamel layer thermal conductivity on the thermal transmittance of enameled steel sheet is also calculated.
|
