GB/T 17394.2-2022Metallic materials - Leeb hardness test - Part 2: Verification and calibration of hardness testers (English PDF)

5.3 Inspection of Mass and Geometric Dimensions of Impact Body

5.3.1 The mass of the impact body shall satisfy the requirements specified in Table 1.

5.3.2 The impact body shall consist of a ball head and a bracket. If the impact signal is read

through the electromagnetic induction coil, then, the impact body shall contain a permanent

magnet.

5.3.3 For D, D + 15, S, E and C-type impact devices, the tip of the ball head shall protrude from

the grip by at least 0.3 mm. For G-type impact device, the tip of the ball head shall protrude

from the grip by at least 0.6 mm. For DL-type impact device, the diameter of the gripped round

steel bar is (2.5  0.1) mm, the length is (55.15  0.1) mm and the tip of the ball head shall

protrude from the grip by at least 2 mm.

5.4 Inspection of Geometric Dimensions and Hardness of Ball Head

5.4.1 In order to inspect the geometric dimensions and hardness of the ball head, randomly take

a sample from a batch of balls to test its diameter and hardness. This batch of balls shall be

provided with a certificate of conformity or evidence of the required hardness. Balls subjected

to the hardness test shall be discarded.

5.4.2 The diameter of the ball head shall be determined by measuring different positions on the

ball to obtain the arithmetic mean of not less than three diameter values. The difference between

a single measured value at any position and its nominal value shall satisfy the requirements in

Table 1.

5.4.3 The ball head shall be made of tungsten-cobalt cemented carbide, ceramics or synthetic

diamond (as shown in Table 1). The hardness test shall be carried out in accordance with the

stipulations of GB/T 4340.1, and the hardness value shall comply with the stipulations of Table

1. The steel ball can be tested directly on the spherical surface, or sliced inside the steel ball.

Synthetic diamond balls do not need to be inspected for hardness.

5.4.4 When conducting an inspection under a magnifying glass of 100 times, the surface of the

ball head shall be smooth and free of defects.

5.5 Inspection of Geometric Dimensions of Support Ring

The thickness of the support ring shall be determined by measuring different positions on the

support ring to obtain the arithmetic mean of not less than 3 thickness values. The difference

between a single measured value at any position and its nominal value shall not exceed 0.1 mm.

5.6 Inspection of Impact Velocity

5.6.1 The impact velocity shall be directly measured in the direction of gravity, and the velocity

value shall be read at the maximum height above the surface of the test piece listed in Table 1.

5.6.2 If a direct inspection of the impact velocity is not possible, then, conduct an indirect

inspection on the impact velocity. For example: replace the impact body of the impact device

with a reference impact body that complies with the parameters specified in Table A.1 of GB/T

17394.3-2022. Connect the impact device to the standard display device and vertically

downward test the reference test block, compare the displayed measurement signal with the

standard signal value, as shown in Appendix B. The signal waveform response before the

impact shall be peculiar to the hardness tester and irrelevant to the material being tested.

5.7 Indirect Inspection of Hardness Tester

After the direct inspection is qualified, in accordance with the requirements of Chapter 6,

conduct the indirect inspection.

6.1 General Rules

6.1.1 The indirect inspection should be carried out within the temperature range of (23  5) C,

and the reference Leeb hardness test block used shall comply with the requirements of GB/T

17394.3 If the inspection is carried out beyond this temperature range, then, it shall be indicated

in the inspection report / calibration certificate.

6.1.2 Conduct a visual inspection on the appearance of the impact device, impact body, support

ring and display device, and there shall be no damage.

6.1.3 The resolution of the display device shall be at least 1 HL.

6.1.4 For the hardness testers, select three reference Leeb hardness test blocks from the hardness

range specified in Table 2 to test the hardness value (one reference Leeb hardness test block

shall be selected for each hardness range).

Appendix A

(informative)

Measurement Uncertainty of Calibration Results of Hardness Testers

NOTE: Figure C.1 of ISO 16859-1:2015 shows the structural diagram of the metrological

traceability chain used to define and distinguish each hardness scale.

A.1 Direct Inspection of Hardness Tester

A.1.1 Inspection of impact body and support ring

The impact body is equipped with a ball head and support ring made of tungsten-cobalt

cemented carbide, ceramics or synthetic diamond, and cannot be inspected or calibrated on site.

The geometrical deviations, physical properties and chemical composition of the ball head need

to be proved by a valid inspection certificate issued by an accredited laboratory (see 5.3).

A.1.2 Use reference impact body and reference display unit for the inspection of impact

device

Under laboratory conditions, use a reference impact body and reference display unit to conduct

an indirect inspection on the impact device (see 5.4).

A.2 Indirect Inspection of Hardness Tester

By using the reference Leeb hardness test block for the indirect inspection, the overall

performance of the hardness tester can be checked. Meanwhile, in accordance with the

calibration value of the reference Leeb hardness test block, determine the coefficient of

variation and relative error of indication of the hardness tester.

The composite standard uncertainty during the indirect inspection of the hardness tester (see

ISO/IEC Guide 98-3) shall be calculated in accordance with Formula (A.1):

Where,

uCRM---the standard uncertainty provided by the calibration certificate of the reference Leeb

hardness test block (k = 1);

uCRMD---for the reference Leeb hardness test block, since the latest calibration, the standard

uncertainty introduced by the drift of the hardness value with time (when the reference Leeb

hardness test block that satisfies the requirements of the standards is used for inspection, this

item can be ignored);

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