GB/T 30824-2014Testing method for temperature uniformity of gas heat treatment furnace (English PDF)

3.1 Temperature control system error

An offset to the temperature measurement results produced by the temperature control system composed of temperature sensors, extension and compensating cables, display adjustment instruments, etc. Its value is the algebraic sum of the errors of temperature sensors, extension and compensating cables, display adjustment instruments and other components.

3.2 Maximum permit error

The allowable error limits of measuring instruments and measuring systems specified in technical specifications and standards.

5.1 Implementation conditions

To determine whether the temperature uniformity of the effective heating zone of the gas heat treatment furnace complies with the provisions of the heat treatment process document, any of the following methods shall be used.

5.2 Test cycle

5.2.1 The temperature uniformity test cycle of the gas heat treatment furnace and the calibration cycle of the temperature control instrument are shown in Table 2.

6.1 Composition and connection method

The test device consists of thermocouples, extension and compensating cables, test instruments (or computers), transfer switches and temperature measurement frames.

The wiring diagram of the test device is shown in Figure 1.

6.5 Transfer switch

For signal switching between channels, the parasitic potential shall be tested regularly, and the test cycle shall not exceed 1 year. The parasitic potential of a transfer switch connected to base metal thermocouples with graduation numbers such as K, N, and E shall not exceed 4 µV.

6.6 Temperature measurement frame

The size and shape of the bracket or frame used to fix the thermocouple depends on the test method.

7.1 Test requirements

7.1.1 The gas heat treatment furnace shall realize automatic temperature control, and the qualified test status shall be able to be reproduced in the production process.

7.1.5 During the no-load test, the measuring ends of the test thermocouples distributed near the burner and flue shall be protected with protective covers. It is also recommended to add protective covers to the measuring ends of test thermocouples distributed in other locations to reduce the impact of temperature fluctuations on the test results.

7.1.6 The gas heat treatment furnace shall be heated at the heating rate specified by the process. The furnace temperature shall not rise above the test temperature and then drop to the test temperature.

7.1.7 During the test process, all parameters of the furnace shall reflect the normal production operation process of the equipment.

7.2 Determination of test temperature

7.2.1 Initial test

Select the lowest and highest temperature points of the operating temperature range. If the operating temperature range exceeds 330 °C, temperature test points shall be added so that the test temperature interval is no greater than 330 °C.

7.3 Determination of number and location of test points

7.3.1 Test methods and applicable objects

7.3.1.1 The test methods are classified into fixed test point method and moving test point method according to the state of the thermocouple during the test process. Where the thermocouple position is fixed during the test, it is called the fixed test point method, also known as the volume method;

7.3.1.2 The volume method is applicable to cyclic (box-type, pit-type) gas heat treatment furnaces and continuous heat treatment furnaces which can be hardly realized by the moving test point method;

7.3.2 Determination of number and location of test points of volume method

7.3.3 Determination of number and location of test points of unit volume method

A unit volume is the volume of pallets, frames, etc. loaded according to the rated loading capacity. The number and location of test points of the unit volume method are determined according to the size of the unit volume, and the distribution of test points shall be able to reflect the temperature distribution within the unit volume. The determination method is as follows. […]

7.4 Test sequence and method

7.4.1 Check the test instruments, test thermocouples, extension and compensating cables, transfer switches, etc. of the test system, which shall be within the validity period of the calibration.

7.4.6 Record all test data truthfully in Appendix A