GB/T 7991.7-2019Test method of viterous and porcelain enamels—Part 7: Determination of coefficient of mean lincar thermal expansion (English PDF)

Foreword

GB/T 7991 "Test method for glass lined layer" is divided into 10 parts.

--- Part 1. Determination of corrosion resistance of alkaline solutions;

--- Part 2. Determination of resistance to boiling acids and their vapor corrosion;

--- Part 3. Determination of resistance to sudden changes in temperature difference;

--- Part 4. Determination of mechanical shock resistance;

--- Part 5. thickness measurement by electromagnetic method;

--- Part 6. High voltage test;

--- Part 7. Determination of the average linear thermal expansion coefficient;

--- Part 8. Determination of scratch resistance;

--- Part 9. Determination of tensile strength;

--- Part 10. Determination of lead and cadmium dissolution.

This part is Part 7 of GB/T 7991.

This section is drafted in accordance with the rules given in GB/T 1.1-2009.

This section replaces GB/T 25144-2010 "Determination of the average linear thermal expansion coefficient of glass-lined glaze", which is in line with GB/T 25144-2010 Compared with the editorial changes, the main technical changes are as follows.

--- Added Chapter 4 Principles (see Chapter 4);

--- Modified "Push rod expander should be able to measure 2 x 10^-3L0 change" to "Push rod expander should be able to measure 2 x 10^-6L0 The amount of change "(see 6.2, 4.2 of the 2010 edition);

--- "The axial or radial movement of the dilatometer in the heating furnace by 2mm should not affect the measurement accuracy" was modified to "the dilatometer is in the heating furnace Axial or radial movement of 0.5mm shall not affect the measurement accuracy "(see 6.3.1, 4.3 of the 2010 edition);

--- Added "Before the sample is fired, the glass-lined glaze should be dried at (110 ± 5) °C, the drying time should be not less than 5h" and "Fired The rear sample must be free from defects such as cracks, bubbles, partial shedding, and abrasion "(see 7.2);

--- Added the requirement of "sample size. length (45mm ~ 50mm) ± 0.5mm, cross-section diameter phi 10mm ± 0.5mm" (See 7.4);

--- Increased the provision of test temperature range selection (see Chapter 8).

1 Scope

GB/T 7991 specifies the method for determining the average linear thermal expansion coefficient of glass-lined glazes below the transition temperature.

This section applies to the determination of the average linear thermal expansion coefficient of glass-lined glaze.

2 Normative references

The following documents are essential for the application of this document. For dated references, only the dated version applies to this document. For undated references, the latest version (including all amendments) applies to this document.

GB/T 21389 Vernier, Band Watch and Digital Caliper

3 Terms and definitions

The following terms and definitions apply to this document.

4 Principle

Within the test temperature range, heat or cool the sample to the test temperature at a certain heating rate and cooling rate, and measure the length of the sample The degree of change in temperature is recorded at the same time, and the linear thermal expansion coefficient of the sample is calculated based on the recorded data.

5 Factors affecting measurement accuracy

5.1 The materials used to make the dilatometer will have a greater impact on the test accuracy.Therefore, when selecting the dilatometer material, the expansion performance of the material should be determined