GB/T 7991.7-2019 "Test methods for vitreous and porcelain enamels — Part 7: Determination of the mean coefficient of linear thermal expansion" applies to the determination of the mean coefficient of linear thermal expansion of vitreous enamel frits below the transformation temperature within the range of 20°C to 400°C. It specifies the test principle, equipment, procedures, and calculation of results. The test requires the use of a push-rod dilatometer with a resolution of 2×10⁻⁶L₀, a heating furnace with temperature control accuracy of ±2°C, and a digital caliper with an accuracy of 0.01 mm. By heating, holding, and collecting data from the pressed and dried enamel powder samples, the coefficient of expansion is calculated using a correction formula. Two samples are tested per group to ensure the reliability of the results, providing data support for the compatibility of vitreous enamel materials.