GB/T 6187.2-2016Prevailing torque type all-metal hexagon nuts with flange, style 2 -- Fine pitch thread (English PDF)

4.6 Tensile strength, nominal strain at break, tensile strength at 5% nominal strain

The test shall be carried out in accordance with the provisions of GB/T 1040.1-2006 and GB/T 1040.3-2006, using type 2 specimens which have a specimen width of 15 mm; the initial fixture spacing is 100 mm; the test speed is (100 ± 10) mm/min; the longitudinal and transverse directions are tested, respectively. The number of specimens is 5 each. The results are taken as the arithmetic average.

4.7 Thermal shrinkage

4.7.1 Test instruments

The test instruments are as follows:

a) Oven, temperature accuracy ±1 °C;

b) Vernier caliper, accuracy 0.02 mm.

4.7.2 Specimens

The specimen size is 100 mm × 100 mm; the number of specimens is 5. Mark a line each in the longitudinal and transverse directions, indicating the longitudinal and transverse directions. Use a steel ruler, which has a graduation value of 0.5 mm, to measure the length of the two lines.

4.7.3 Test steps

Adjust the oven temperature to (150 ± 3) °C. Quickly put the specimen in and start timing. The specimen is placed flat, kept for 30 minutes. Take it out. After cooling to the test environment temperature, measure the longitudinal and transverse lengths of the specimen. Calculate the thermal shrinkage of the specimen. Take the arithmetic mean as the measurement result, accurate to 1 decimal place.

4.7.4 Calculation

See formula (3)

Where:

S - Heat shrinkage, %;

L0 - Length before heating, in millimeters (mm);

L1 - Length after heating, in millimeters (mm).

4.8 Surface roughness

Test according to Chapter 8 of GB/T 13542.2-2009.

4.9 Friction coefficient

Test according to GB/T 10006-1988.

5.1 Group-batching

Acceptance is carried out in batches. Films of the same specification produced under the same formula and process conditions are considered as a batch. Each batch shall not exceed 50 t. If the output is less than 50 t for one week of continuous production, the output of one week shall be considered as a batch.

5.2 Sampling

Appearance and specifications shall be in accordance with the normal inspection sampling plan specified in GB/T 2828.1-2012, using the general inspection level I and the acceptance quality limit (AQL) of 6.5, see Table 5. Each roll of film is a sample unit.

For physical and mechanical properties, it shall randomly select from the qualified appearance samples and inspect it according to the provisions of 3.4.

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