Selection And Application Scope Of Hardness Tester

Hardness tester is a metal hardness measurement tool. The definition of hardness was first proposed by Leo Muhl, which indicates the ability of a material to resist a hard object from pressing into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance.

According to different principles, hardness measurement is divided into Leeb hardness tester, Rockwell hardness tester, Brinell hardness tester, Shaw hardness tester, Shore hardness tester, Barcol hardness tester, microhardness tester, Mohs hardness tester, Vickers hardness tester, etc.

Brinell hardness tester and Rockwell hardness tester are the most widely used. Steel and cast steel, alloy tool steel, stainless steel, gray cast iron, ductile iron, cast aluminum alloy, copper-zinc alloy (brass), copper-tin alloy (bronze), pure copper, forged steel, heat treatment, carburization, quenching hardening layer, surface coating, steel, non-ferrous metals and tiny and thin parts, rubber, plastic, IC wafers, jewelry, etc. can all be tested with it.

There are several points to note about the hardness tester.

1. The hardness tester itself will produce two errors: one is the error caused by the deformation and movement of its parts; the other is the error caused by the hardness parameter exceeding the specified standard. For the second error, the hardness tester needs to be calibrated with a standard block before measurement. The Rockwell hardness tester is qualified if the calibration difference is within ±1, and the stable value within the difference is within ±2, and the correction value can be given. When the difference is outside the range of ±2, the hardness tester must be calibrated and repaired or replaced with other hardness test methods.

2. The hardness tester has different applicable ranges and should be selected according to regulations. For example, when the hardness is higher than HRB100, the HRC scale should be used for testing; when the hardness is lower than HRC20, the HRB scale should be used for testing. Because when it exceeds the specified test range, the accuracy and sensitivity of the hardness tester are poor, the hardness value is inaccurate, and it is not suitable for use.

3. When replacing the indenter or anvil, pay attention to wiping the contact area clean. After replacement, use a steel sample of a certain hardness to test several times until the hardness values ​​obtained twice in a row are the same. The purpose is to make the indenter or anvil press tightly and contact well with the contact part of the testing machine to avoid affecting the accuracy of the test results.

4. After the hardness tester is adjusted, when starting to measure the hardness, the first test point is tested with a standard test block to exclude the situation where the contact between the specimen and the anvil is not good and the measured value is inaccurate. After confirmation, the hardness tester is in the normal operating mechanism state before the specimen is formally tested and the measured hardness value is recorded.

5. If the specimen allows, generally select different parts to test at least three hardness values. The distance between the three points is ≥3mm, and the average value of the three is taken as the hardness value of the specimen.

6. For specimens with complex shapes, corresponding pads should be used, and they can be tested after being fixed. Circular specimens are generally placed in V-grooves for testing.

7. The hardness tester must be calibrated according to regulations. The standard block used to calibrate the hardness tester cannot be used on both sides, because the hardness of the standard surface and the back surface may not be consistent. It is generally stipulated that the standard block is valid for one year from the date of calibration.

‌The applicable scopes of various hardness testers are as follows‌:

Brinell hardness tester‌: Mainly used for hardness testing of forged steel and cast iron with uneven structure, and also suitable for non-ferrous metals and mild steel. The Brinell hardness test is suitable for the inspection of raw materials and semi-finished products. The advantage is that the indentation is large, which can reflect the comprehensive performance of the material and has high precision; the disadvantage is that the indentation is large and is generally not used for finished product inspection.

‌Rockwell hardness tester‌: Suitable for hardness testing of various ferrous and non-ferrous metals, including quenched steel, quenched and tempered steel, tempered steel, annealed steel, surface hardened steel, carbide materials, powder metallurgy materials, thermal spray coatings, etc. The advantage is that it has a wide range of applications and is suitable for hardness testing of various ferrous and non-ferrous metals; the disadvantage is that the indentation is small and is suitable for thin plate metals, thin-walled pipes, etc.

‌Surface Rockwell hardness tester‌: Suitable for hardness testing of thin plates, carburizing, nitriding, surface treatment hardened layers, stainless steel and aluminum alloys, etc. ‌ Vickers Hardness Tester: Used to measure tiny parts, thin steel plates, metal foils, IC sheets, wires, thin hardened layers, electroplating layers, glass, jewelry, and ceramics. The advantage is that the indentation is small, which is suitable for testing tiny parts and thin materials; the disadvantage is that the operation is relatively complicated. Suitable for testing tiny parts, thin steel plates, metal foils, and other materials.