NB/T 10291-2019Test method of equivalent accelerated aging of daily-use metallic tube electric heating elements for air-heating (English PDF)

3.1 Accelerated life test

Accelerated life test accelerated aging test.

On the premise of maintaining the original failure mechanism and failure mode of the product and not adding new failure factors, increase the test stress and strengthen the test strip To accelerate the failure of the received sample, so as to predict the reliability or life characteristics of the product under normal working conditions in a short time And a test method for evaluation.

3.2 Daily-use metallic tube electric heating elements

The metal tube is used as the shell, the alloy heating wire is used as the heating element, and the dense magnesium oxide powder or similar insulator is used as the insulating medium between the two.

And through the lead rod connected to the power supply for heating element.

3.3 Predefined working condition

The rated conditions and requirements of product design specified by the manufacturer.

3.4 Failure mechanism

Internal causes such as physical and chemical changes that cause failure.

3.5 Failure mode

The manifestation of the malfunction of the product that can be observed or measured.

3.6 Failure factor

The external cause or condition that caused the failure.

3.7 Testing stress

The input factors that directly affect the component during the test.

3.8 Working condition for testing

The test conditions and requirements during component test specified in the corresponding test clause.

3.9 Damage

The components are damaged or some electrical indicators lose their effectiveness.

Note: In this standard, a component is considered damaged when it has one of the following conditions.

--The leakage current at the operating temperature of the component cannot meet the requirements of 8.3 of this standard;

--The electrical strength at the working temperature that the component can withstand cannot meet the requirements of 8.4 of this standard;

--When the component is working, the shell produces flame, melt or other damage that cannot be repaired.

3.10 Normal use

Use the components or connected equipment according to the designed purpose and the method predetermined by the manufacturer.

3.11 Normal working condition

When the component is connected to the power supply, it is in a working state according to normal use (conditions).

3.12 Heating surface

The surface of the metal tube corresponding to the heating length of the component.

3.13 Surface load

Note: The common unit of surface load is watts per square centimeter (W/cm2).

3.14 Rated surface load

The surface load of the component under rated power conditions.

4.1 Component failure analysis

The components have different degrees of surface roughness, work hardening, residual stress, cracks, unreasonable distribution of heating wires or insulating media, etc. trap. In the life test, the material of the component undergoes continuous oxidation and shedding and other failure mechanisms, which aggravate these defects and gradually deteriorate the performance of the component.

Retreat. The heating wire and insulating medium deteriorate, age, fuse, and decrease the electrical insulation in the high temperature environment and electrical shock of the test, which are important components Failure mode.

4.2 Design principle of accelerated life test

Accelerated life test by increasing test stress, strengthening test conditions, amplifying failure factors, quickly exposing the defects of components, in a shorter time Within time, it is predicted whether the components can meet the designed life requirements.

5.1 Information required by the manufacturer

The component manufacturer shall provide sufficient information to ensure that the tests related to this standard can be carried out to confirm that the component meets the requirements of this standard.

The data required for the component testing of this standard is as specified in Table 1.

These information should be provided to the testing organization in the form of documents.

5.2 Main technical parameters and units

The main technical parameters and units involved in the components.

a) Power supply voltage, in volts (V);

b) Power frequency, in Hertz (Hz);

c) Rated voltage, in volts (V);

d) Rated power, in kilowatts (kW);

e) Working temperature, in degrees Celsius (°C);

f) Overall dimensions, in millimeters (mm);

g) Surface area, in square centimeters (cm2);

h) Time, in hours (h); i) Heating medium.

6.1 Test device

6.1.1 Regulated and regulated power supply

The output voltage should be steplessly adjustable, the output voltage fluctuation value should not exceed ±0.5%, and the power supply voltage deviation should not exceed ±3%.

6.1.2 Power on and off control device

The preset power-on time and power-off time can be adjusted separately, the power-on and power-off can be automatically cycled and the number of cycles can be preset, and the time accuracy is not Less than 0.1 s.

6.1.3 Working condition simulation device

The components are installed in electrical appliances or under simulated conditions. The test conditions should be simulated in accordance with the test conditions specified in Chapter 7. Test under working conditions.

6.1.4 Measuring device

In all tests, the measuring instrument or measuring device should not significantly affect the measured value.

a) Electrician measuring instruments such as electric strength detectors, leakage current detectors, etc., with an accuracy level of not less than 0.5;

b) For temperature measuring instruments, the allowable error is ±1%;

c) For humidity measuring instruments, the allowable error is within ±6% RH of the measured relative humidity.

6.2 Test environment

The temperature and humidity of the test environment shall meet the technical requirements of the corresponding use environment of the test product specified in the technical documents. If there is no document requirement, The room temperature should be maintained at (20±5) °C, the relative humidity of the surrounding air should not exceed 85% (when the temperature is 25 °C), and the atmospheric environment should be at an altitude of 2 000 m or less.

There should be no flammable, explosive materials and gases in the test site.

The test personnel should make appropriate safety protection, and should use appropriate devices to fix and protect the components to avoid factors in the test process.

High temperature or insufficient electrical protection can cause personal injury or damage to the surrounding environment. There should be no personnel frequently in the test site.

7.1 General requirements

The total number of samples required is 6 pieces, divided into 2 groups, 3 pieces in each group, and in the format of "group-serial number" from 1-1, 1-2, 1-3, 2-1 to 2-3 Encoding mark.

7.2 Test procedure

7.2.1 The samples of the first group shall be subjected to 8.2 overload fast on-off test.

7.2.2 The sample should meet the above test requirements.

7.2.3 If a sample is unqualified, select the same number of unqualified samples from the second group of samples and perform the corresponding test again.

If the test is passed, it is judged that this item is qualified, otherwise the remaining samples of the second group are selected for the test. Until the second group of samples are all tested If there are still unqualified conditions, it is judged as unqualified.

7.2.4 Components with a rated surface load greater than 10 W/cm² are not applicable to the test requirements of this classification. Test plan by test agency and manufacturer Negotiation.

7.2.5 If it meets 8.2 overload fast on-off test for 3,000 cycles, it is considered that the life of the product under normal working conditions meets the requirements of this standard Claim.

8.1 General requirements

8.1.1 For components with current protection or disposable temperature protection device, the protection device should be removed or short-circuited.

8.1.2 Unless otherwise specified, components with multiple rated voltages or one (multiple) rated voltage ranges shall be within the specified range The most unfavorable voltage is tested.

8.2 Overload fast on-off test

8.2.1 Put the components in the most severe product design conditions, according to the different rated surface loads of the components, load different rated loads according to Table 2.

For the test power of the power multiplier, a cycle of 0.4 s when the power is applied and 0.8 s when the power is disconnected is a cycle, and the continuous continuity test is performed. The component under test is not Take cooling measures in addition to design requirements.

8.2.2 When necessary, the temperature controller or temperature control system should be installed to limit the operation of each part of the components not exceeding the limit specified in Appendix A temperature. Once a component reaches the limit operating temperature, the test should be suspended immediately, and the test should be continued after waiting for the component to cool to room temperature naturally.

8.2.3 Qualification of the test is determined by the following two.

a) During the test, no phenomena that affect safety, such as melting, spraying fire, and releasing harmful gases, shall occur;

b) The sample after the test should not be damaged.

8.3 Leakage current measurement at operating temperature

After the relevant tests required by this standard, the components work under normal working conditions, and the test voltage should be adjusted to make the input power equal to 1.15 times the maximum rated input power. After reaching a steady state, measure the leakage current. For the measurement method, see 13.2 of GB 4706.1-2005. The leakage current value should not exceed 3.5 mA.

Note: Before the test, the moisture in the components is allowed to be drained.

8.4 Electric strength test at working temperature

The test shall be carried out immediately after the test of 8.3 according to the provisions of 13.3 of GB 4706.1-2005, and shall be carried out within 5 s. The component should withstand the duration of 1 min, the voltage of the basic sine wave with a frequency of 50 Hz or 60 Hz, the test voltage is determined according to Table 3, the setting current of the electric strength test equipment It is 5 mA.

The insulation of the component should be able to withstand the corresponding electric strength test, and there should be no breakdown during the test.

Note: The glow discharge that does not cause a voltage drop can be ignored.