Leeb Hardness Tester

In the Leeb hardness testing method, the hardness value can be calculated from the energy loss of an impact body after impacting upon a metal. This Leeb quotient is equivalent to the measure of that energy loss due to deformation. The impact body rebounds faster from harder samples than the softer ones, resulting in a larger value 1000* vr / vi which is quoted as the Leeb rebound hardness unit HL.

When an impact device accelerates an impact body with the help of spring force, the velocity of the impact body gets segregated into three phases:

Approach Phase
The impact body is accelerated in the direction of the test surface with the help of the spring force.

Impact Phase
The impact body as well as the specimen remain in direct contact. The specimen gets plastically or elastically deformed and the impact body comes to the standstill. This elastic spring-back nature of the impact body, as well as the specimen, helps the impact body to rebound.

Rebound Phase
The impact body is again accelerated out of the impact phase with the resultant energy.

Bench Hardness Tester
This bench hardness tester is a traditional type used to determine the hardness of a sample employing the standard methods of Rockwell, Vickers, Brinell, or Shor. Hence, they can be called ‘bench Rockwell hardness tester’ or ‘bench Brinell hardness tester’. There are many other bench hardness testers used to measure the hardness of the sample not only using just one scale but varied hardness scales.

There is a bench hardness tester used to measure hardness using Brinell, Rockwell, and Vickers scales. All these bench hardness testers are very large and heavy, weighing more than 50 kg. Therefore, these testers are installed either on a table or a floor. Its advantages include the standard implementation along with the easier and direct method of hardness determination.

Portable Hardness Testers
Unlike the bench testers, portable hardness testers are smaller in size with lightweight. These testers are compact in nature, which determines the hardness using various hardness scales. Moreover, the modern portable hardness testers can detect the hardness by employing all hardness scales. Its major advantages include user convenience as well as portability. There is no need to carry samples into the testing units or workshops.

The modern portable hardness tester can electronically save the test results in the internal storage, followed by transferring them to a computer to generate a report. These reports employ a specialized program named ARM, which is provided along with the portable testers. At times, there might be a requirement for the bench hardness testers, though it is too rare. Anyway, 99 cases out of 100 users always prefer portable devices.

Introduction
Rebound hardness testers , otherwise known as “ Leeb Hardness Testers “ are the alternative to traditional counter hardness testers , installed in laboratories . The revolution represented by rebound hardness testers is primarily related to their portability combined to very high precision and to the type of non-destructive test which are able to make .

This method is based on the Leeb principle introduced by Dietmar Leeb in 1975. Conceptually it’s defined as the ratio between impact speed and impact body rebound velocity , then multiplied by 1000 . Depending on metal type the Leeb method indicates hardness value that can be converted to other scales ( for example HB , HV , HRC etc. ) .
Using the same principle is also possible to measure tensile strength in relation to steel . The operating principle is based on the application of a certain force to an impact body of a certain weight , that will go to touch the measuring surface .

The instrument respectively measure impact and rebound velocity when spherical striker is located to 1mm from the measuring surface . The calculation formula is the following:

HL=1000×(VB/ VA)
HL → Hardness value HLD
VB → Rebound speed of impact body
VA → Penetrator impact velocity

With This Method We Can Measure Many Materials , Like :
• Steel and fusions ;
• Cold work tool steel ;
• Stainless steel alloys ;
• Gray cast iron ;
• Nodular cast iron ;
• Mergers and aluminum alloys ;
• Brass alloys / zinc brass alloys ;
• Bronze alloys ;
• Copper alloys

A hardness tester is an essential tool in various industries and applications, aiding in determining the hardness of materials. Hardness is a vital material property that reflects its resistance to deformation, wear, and scratching. Different materials require different hardness levels based on their intended use. By measuring hardness, engineers can assess material quality, make informed decisions for material selection, and ensure product reliability.

Metallurgy And Manufacturing
In the field of metallurgy, hardness testers play a pivotal role in quality control and material characterization. Manufacturers use hardness tests to assess the strength and durability of metal components such as gears, shafts, bearings, and tools. For instance, the Brinell hardness test involves indenting a material's surface with a hardened steel ball and measuring the diameter of the resulting impression. This method is commonly employed for testing castings and forgings, ensuring they meet the required hardness specifications.

Automotive Industry
In the automotive sector, portable hardness testers are used to evaluate the hardness of critical components like engine parts, brake systems, and transmission components. Ensuring optimal hardness levels in these parts is essential for their longevity and performance. Hardness tests help manufacturers identify materials prone to wear and tear, leading to improved vehicle safety and reliability.

Aerospace Engineering
The aerospace industry demands materials with high strength and durability due to extreme conditions experienced during flight. Hardness testing is used to examine aircraft components such as turbine blades, landing gear, and structural elements. By accurately determining hardness, engineers can prevent failures caused by excessive stress, fatigue, or corrosion, ensuring the safety of air travel.

Construction And Civil Engineering
In construction, hardness testers are employed to assess the quality of building materials like concrete and asphalt. The rebound hammer test, a non-destructive method, measures the surface hardness of concrete structures, providing insights into their compressive strength and durability. This information is vital for maintaining the structural integrity of buildings, bridges, and roads.

Material Science Research
Hardness testing is fundamental in material science research and development. Scientists use it to study the behavior of newly developed materials, alloys, and composites. By analyzing the relationship between hardness and other mechanical properties, researchers gain insights into a material's potential applications in various industries, from electronics to medical devices.

Quality Control In Electronics
The electronics industry relies on hardness testing to ensure the reliability and performance of components like microchips, connectors, and circuit boards. Proper hardness levels are crucial to prevent damage caused by mechanical stress or thermal expansion. Hardness testers aid in identifying materials susceptible to deformation or cracking under the conditions these components experience.

Oil And Gas Industry
The oil and gas sector often deals with harsh and corrosive environments. Hardness testers are utilized to evaluate the hardness of pipeline materials, drilling equipment, and refinery components. This ensures that these materials can withstand the stresses imposed by drilling, transportation, and processing of oil and gas resources.

In site work we often encountered surface test pieces. Various surfaces have different effects on the hardness test results. In the case of correct operation, the impact falls on the surface of the specimen at the same moment as the plane specimen, so the universal support ring can be used.

However, when the curvature is as small as a certain size, the elastic state of the deformation of the plane due to a significant difference in the impact of the impact of the body is low, so that the Indies hardness is low. Therefore, for the specimen, it is recommended to use a small support ring when measuring. For specimens with a smaller radius of curvature, it is advisable to use a profiled support ring.

According to the principle of the Richter, as long as the material has a certain rigidity, can form a rebound, you can measure the exact value of the Richter hardness, but many of the material and other standard hardness of the standard does not have a corresponding conversion, so the current hardness tester The conversion of nine kinds of materials. Specific materials are as follows: steel and cast steel, alloy tool steel, gray cast iron, ductile iron, cast aluminum alloy, copper and zinc alloy, copper and tin alloy, pure copper, stainless steel.

For some special material samples, the user can use the company to provide the fitting curve to do a special conversion table. In the actual production, the use of a wide range of metal materials, due to the hardness of the material on the material processing methods, materials, alloying elements of the composition of sensitive, and Richter hardness chip stored in the hardness table can not meet the needs of users , The user in the test, you can use the fitting to do their own dedicated hardness conversion table.

The Data Conversion Error
The error in the hardness of the other hardness includes two aspects: the one is the measurement error of the hardness of the hardness itself, which involves the dispersion of the test method by the method and the measurement error for the same type of internal hardness tester.

On the other hand, it is the error of the hardness measured by the different hardness test methods. This is due to the fact that there is no clear physical relationship among the various hardness test methods and is affected by the unreliable influence in the comparison.

The Error Caused By Special Materials
The conversion tables stored in the hardness meter may deviate from the following steels:
All of the austenitic steel heat-resistant tool steel and the chrome steel (tool steel) hard materials cause an increase in the modulus of elasticity, resulting in a low L value. This type of steel should be tested on a cross-section. Local cooling Hardening can cause a high L value. The magnetic properties of the magnetic steel will cause the L value to be low. Surface hardening steel, the base is soft, will make L value is low, when the hardening layer is greater than 0.8mm (C-type impact device is 0.2mm) does not affect the L value.

Gear Detection Error
Under normal circumstances, because the tooth surface is small, the test error is relatively large, which, the user can design the corresponding tooling, according to the situation, will help reduce the error.

The Material Elasticity, Plastic Effect
In addition to the hardness and strength, the value is related to the elastic modulus, the hardness value is the material hardness and plasticity of the characteristic parameters, because the two components must be co-measured.

In the elastic part, the first is obviously affected by the E modulus, in this respect when the static hardness of the same material, and E value of different size, E value of the material, L value

The Direction Of Hot Rolling Caused By The Error
When the measured workpiece is hot-rolled process molding, if the test of the Richter hardness and rolling direction consistent with the elastic modulus E is too large to cause the test value is low, so the test direction should be perpendicular to the hot rolling direction. For example: measuring cylindrical cross-section hardness, should be in the radial test as well. (Generally cylindrical hot rolling direction is axial).

The Impact Of Other Factors
When measuring the hardness of pipe fittings, note that the pipe should be firmly supported. The test point should be close to the support point and parallel to the supporting force. The pipe wall is thinner and put into the appropriate core in the tube.

Traditional hardness measurements, e.g., those of Rockwell, Vickers, and Brinell, are stationary, requiring fixed workstations in segregated testing areas or laboratories. Most of the time, these methods are selective, involving destructive tests on samples. From individual results, these tests draw statistical conclusions for entire batches. The portability of Leeb testers can sometimes help to achieve higher testing rates without destruction of samples, which in turn simplifies processes and reduces cost.

The traditional methods are based on well-defined physical indentation hardness tests. Very hard indenters of defined geometries and sizes are continuously pressed into the material under a particular force. Deformation parameters, such as the indentation depth in the Rockwell method, are recorded to give measures of hardness.

According to the dynamic Leeb principle, hardness value is derived from the energy loss of a defined impact body after impacting on a metal sample, similar to the Shore scleroscope. The Leeb quotient (vi,vr) is taken as a measure of the energy loss by plastic deformation: the impact body rebounds faster from harder test samples than it does from softer ones, resulting in a greater value 1000×vr/vi. A magnetic impact body permits the velocity to be deduced from the voltage induced by the body as it moves through the measuring coil. The quotient 1000×vr/vi is quoted in the Leeb rebound hardness unit HL.

While in the traditional static tests the test force is applied uniformly with increasing magnitude, dynamic testing methods apply an instantaneous load. A test takes a mere 2 seconds and, using the standard probe D, leaves an indentation of just ~0.5 mm in diameter on steel or steel casting with a Leeb hardness of 600 HLD. By comparison, a Brinell indentation on the same material is ~3 mm (hardness value ~400 HBW 10/3000), with a standard-compliant measuring time of ~15 seconds plus the time for measuring the indentation.

● Keep the measurement object's surface level and clean, free of debris and blemishes.

● When the measured object's mass and thickness are smaller than the required minimum mass and thickness, coupling the object to a sturdy support is required for measurement.

● When measuring, the space between any two indentations on the material should not be less than 3mm. And the space between the center of the indentation and the edge of the object being tested shouldn't be less than 5mm. Additionally, it is best to avoid performing multiple tests at the same location.

● It is essential to briefly push the power button to enter the configuration interface, pick the material, and then carry out the measurement operation when it is necessary to convert other hardness values.