Ⅰ. Test methods of leeb hardness tester
The impact body with a hard metal indenter is pushed to the surface of the specimen by spring force, and when the impact body hits the test surface, the surface will be deformed, which will produce kinetic energy loss. The energy loss is calculated from the impact and rebound velocities measured at 1mm from the surface.
The permanent magnet inside the impact body generates an induced voltage in the single coil of the impact device. The voltage of the signal is proportional to the velocity of the impact body.
With a certain mass of impact body impacting the surface of the specimen under the action of spring force, the ratio of the impact velocity and rebound velocity of the impact body at 1 mm from the surface of the specimen is expressed as the leeb hardness.
Using the electromagnetic principle, the permanent magnet inside the impact body produces an induced voltage in the coil of the impact device, and this voltage is proportional to the speed of the impact body. The formula is as follows: HL = 1000 × VB/VA
leeb hardness tester is one of the most commonly used instruments to assess the mechanical properties of metal materials. The essence of hardness is the ability of a material to resist being pressed into another harder material.
How can an accurate hardness value be measured? For the measurement instrument error is inevitable, so what are the factors affecting the measurement accuracy of the leeb hardness tester?
Ⅱ. The error generated by the data conversion will affect the measurement accuracy of the leeb hardness tester
The error when converting the leeb hardness tester to other hardness includes two aspects: on the one hand, the measurement error of the leeb hardness tester itself, which involves the dispersion of the test by method and the measurement error for more than one leeb hardness tester of the same model.
On the other hand is the error arising from comparing the hardness measured by different hardness test methods, which is due to the reason that there is no clear physical relationship between various hardness test methods and is influenced by unreliable measurements in mutual comparison.
Ⅲ. The errors caused by special materials can affect the measurement accuracy of the leeb hardness tester
All austenitic steel heat-resistant tool steel and Leyland chromium steel (tool steel category) hard materials can cause an increase in the modulus of elasticity, which results in a low L value.
Such steels should be tested in cross-section Local cooling hardening causes high L-values Magnetic steels cause low L-values due to the influence of magnetic fields Surface-hardened steel with a soft base will make the L value low, when the hardening layer is greater than 0.8mm (0.2mm for C-type impact device) will not affect the L value.
Ⅳ. The error in gear testing will affect the measurement accuracy of the leeb hardness tester
In general, because the tooth surface is small, the test error is relatively large, for which the user can design the corresponding tooling according to the situation, will help reduce the error.
Ⅴ. The error caused by the direction of hot rolling will affect the measurement accuracy of the leeb hardness tester
When the measured workpiece is hot-rolled process molding, if the test direction and rolling direction, will be due to the elastic modulus E is large and cause the test value is low, so the test direction should be perpendicular to the hot rolling direction. For example, when measuring the hardness of a cylindrical section, it is better to test in the radial direction. (General cylindrical hot-rolled direction for the axial direction).
Ⅵ. The material elasticity, plasticity will affect the measurement accuracy of the leeb hardness tester
leeb value in addition to hardness, strength, more related to the elastic modulus, hardness value is the characteristic parameters of material hardness and plasticity, because the components of both are necessarily measured together.
In the elastic part, the first is obviously influenced by the E modulus, and in this respect when the material has the same static hardness and different E value sizes, the material with low E value has a larger L value.
--The weight, roughness and thickness of the specimen can affect the measurement accuracy of the leeb hardness tester
--Measuring the hardness of pipe fittings must be noted: pipe fittings pay attention to solid support, the test point should be close to the support point and parallel to the support force, the pipe wall is thinner in the pipe into the appropriate core.