Since the Leeb Hardness Tester measures the hardness of metal under the action of power, there are many factors that affect the accuracy of the test results, so these factors should be limited to a certain extent, mainly including: test conditions, test objects, operating techniques and data processing, etc. Several key links, let's discuss some specific issues below:
1. The influence of sample curvature on accuracy
In field work, samples with curved surfaces are often encountered, and various curved surfaces have different effects on the hardness test results. Under correct operating conditions, the instantaneous position of the impactor on the specimen surface is the same as that of a flat specimen, so it is commonly used. A support ring is sufficient. However, when the curvature is small to a certain size, due to the obvious difference between the deformation of the plane condition and the elastic state, the rebound speed of the punch will be very low, and the Leeb hardness display value will be very low.
2. Errors caused by data conversion
The error when converting the Leeb hardness to other hardness includes two aspects: one is the measurement error of the Leeb hardness itself, and the error when converting the Leeb hardness to other hardness includes two aspects, one is the measurement of the Leeb hardness itself Error, which involves the dispersion when repeated testing with the same method, and the error of multiple Leeb Hardness Testers of the same model. On the other hand, errors arising from comparing hardness measured by different hardness testing methods are due to the lack of a clear physical relationship between the various hardness methods and are affected by the unreliability of measurements in mutual comparisons.
3. Errors caused by special materials
Conversion tables stored in the Hardness Tester may differ from the following steel grades:
high alloy steel
◆All austenitic steels
◆ Among high-speed steels, heat-resistant tool steels and chromium steels (tool steels) and hard materials (such as lead carbides such as M7C3 and M6C) will cause an increase in the elastic modulus, resulting in a lower HL value. Such steels shall be subjected to cross-sectional tests.
◆ Localized cooling and quenching, eg due to improper cutting or specimen preparation, can also lead to high HL values.
magnetic steel
◆When testing the hardness of magnetic materials, the HL value will be very low due to the influence of the magnetic field. If the magnetic field is very strong, this test method is not recommended.
case hardened steel
◆For surface hardened materials, especially surface treated steel, the HL value will be very low due to the soft matrix. When the hardened layer is larger than 0.8mm (0.2mm for C-type impact device), the HL value will not be affected.
For special materials, the following methods can be used to establish the comparative relationship by yourself.
◆The test surface needs careful preparation
◆If coupling is not performed, the selected sample size should be as
Large The hardness of the sample is within the conversion range of the Hardness Tester
◆Check the accuracy of the static Hardness Tester and the hardness block of the corresponding measurement range.
◆Use a static Hardness Tester to measure three points on the sample, and use a Leeb Hardness Tester to measure five values around the indentation, and take the average value. Compare the hardness values measured by the two methods to obtain the error range. A set of different hardness samples can also be used to plot the conversion curve for the above method.
4. Gear detection error
In general, the Leeb Hardness Tester can further guarantee the detection accuracy of the gear tooth surface with a modulus greater than 7, but when the gear modulus is less than 7, the test error is relatively large due to the small tooth surface. Corresponding tools can be designed according to the situation, which will help reduce errors.
5. The influence of material elasticity and plasticity
In addition to hardness and strength, the Leeb value is also related to the modulus of elasticity. The hardness value is a characteristic parameter of material hardness and plasticity, because the composition of both needs to be determined together.
In the elastic part, it is first obviously affected by the E modulus, in this respect, when the static hardness of the material is the same, but the E value is different. Materials with low E values have higher HL values.
According to the modulus of elasticity of the material. Alloy type and heat treatment state can classify various materials.
6. Structural error caused by hot rolling direction
When the workpiece to be tested is formed by a hot rolling process, if the test direction is consistent with the rolling direction, the test value will be very low due to the large elastic modulus "E", so the test direction should be perpendicular to the hot rolling direction. For example: when measuring the hardness of the cross section of a cylindrical piece, the test should be carried out in the radial direction (usually, the hot rolling direction of the cylindrical piece is the axial direction).
7. The influence of other factors
The following points should be noted when testing fittings:
◆Pay attention to the stable support of pipe fittings
◆The test point should be close to the support point and parallel to the support force
◆When the tube wall is thin, put a proper core in the tube
During processing, the metal material sometimes changes (for example, 20Cr steel is carburized and quenched from alloy structural steel to low alloy tool steel). In this case, care should be taken to select the appropriate metal material.
The hardness dispersion of the workpiece itself will also cause errors in the test values. The hardness distribution should be analyzed empirically, and the error of the test value should be reasonably explained. Incorrect operating methods, sample preparation, and probe configuration can also cause errors.
in conclusion
All durometers are not versatile and cannot solve all problems! The portable Leeb Hardness Tester has simple measurement value, small wiring, wide hardness value measurement, easy to carry, and is not limited by space and direction. It is a useful addition and extension to your benchtop Hardness Tester! Widely used in mold, roll making, container manufacturing, forging and other industries!
