What is durometer?
is a hardness testing instrument. Metal hardness measurement was first defined by Reoml as hardness, which indicates the ability of a material to resist the pressure of a hard object on its surface. It is one of the important performance indicators of metallic materials. Generally, the higher the hardness, the better the wear resistance.
Shore hardness is a standard for expressing the hardness of a material, proposed by American Albert Ferdinand Shore (1876-1936) in the 1920s and invented the corresponding hardness tester.
Shore hardness is a measure of the hardness of non-metallic materials such as plastics, rubber, and glass in HA, HC, and HD, measured by static extrusion. Shore hardness is a measure of the hardness of metallic materials in HS, measured by dynamic rebound. Both the measurement method and the object are different and the two cannot be mixed. Therefore, although both were proposed and invented by Albert Ferdinand Shore, they are two concepts.
Shore hardness is measured by a Shore hardness tester, which is divided into three categories: Type A, Type C, and Type D. The measuring principle is exactly the same, the difference is the size of the stylus, especially the diameter of the tip is different, type C is the largest, type D is the smallest.
Type A is suitable for general rubber, synthetic rubber, soft rubber, polyurethane, leather, wax, etc.
Type C is suitable for rubber and plastic and plastic containing foaming agents made of microporous materials.
Type D is suitable for general hard rubber, resin, acrylic, glass, thermoplastic rubber, printing board, fiber, etc.
Type A hardness tester is inaccurate when the indicated value is lower than 10HA or higher than 90HA, it is recommended to replace Type C and D accordingly for measurement.
It is worth stating that the Type A Shore hardness test method is the most long-established and widely used means of measuring rubber hardness, and the Type A Shore hardness tester accounts for about 90% or more of the rubber hardness tester currently in use in China. For example, common polyurethane hardness is 50, 70, 90, etc.
Test method of Shore hardness
Shore hardness tester
is inserted into the material under test, the pointer on the dial is connected to a piercing needle through a spring, and the needle is pierced into the surface of the object under test, and the value shown on the dial is the hardness value.Shore hardness tester
measured the value of the reading, its unit is "degrees", its description method is divided into A, and D two, respectively, on behalf of different hardness ranges, 90 degrees below the Shore A hardness tester test, and yield data, 90 degrees and above with Shore D hardness tester test and yield data, so, in general for a rubber or plastic products, in the test, the testers can be based on experience before the test The pre-determination, and thus decide to use Shore A hardness tester or Shore D hardness tester to carry out the test. General feel more elastic or soft products, testers can directly judge with Shore A hardness tester test, such as stationery class glue bottles, TPU TPR plastic film bags, and other products. And feel basically no elasticity or hardness, can be tested with Shore D hardness tester, such as PC ABS PP and other products. If the degree is Shore Axx, indicating that the hardness is relatively not high, if it is Shore Dxx that its hardness is relatively high.
Common hardness classifications of durometer
The hardness test is one of the simplest and easiest test methods for mechanical properties testing. In order to be able to replace certain mechanical property tests with hardness tests, a more accurate conversion relationship between hardness and strength is needed for production.
A. Dietmar Leeb
Richter hardness is designed according to the latest Richter hardness test principle using the most advanced microprocessor technology.
B. Brinell hardness (HB)
Brinell hardness (HB) with a certain load (generally 3000kg) and a certain size (diameter generally 10mm) of hardened steel ball pressed into the surface of the material, maintained for a period of time, after de-loading, the ratio of the load and its indentation area, that is, the Brinell hardness value (HB), the unit is kilogram-force / mm2 (N/mm2).
C. Rockwell hardness (HR)
Rockwell hardness (HR) When HB>450 or the specimen is too small, the Brinell hardness test cannot be used, and the Rockwell hardness measurement is used instead. It is to use a diamond cone with a top angle of 120° or a steel ball with a diameter of 1.59 or 3.18 mm to press into the surface of the material to be measured under a certain load, and probe the hardness of the material by the depth of the indentation. According to the different hardness of the test material, there are three different cases.
HRA: is the hardness obtained by using a 60kg load and diamond cone indenter, used for materials with very high hardness (such as cemented carbide, etc.).
HRB: is the hardness obtained by using a 100kg load and 1.58mm diameter hardened steel ball, used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: is the hardness obtained by using a 150kg load and diamond cone indenter, used for materials with very high hardness (such as hardened steel, etc.).
D. Vickers hardness (HV)
Vickers hardness (HV) is obtained by pressing a load of up to 120 kg and a diamond square cone indenter with a top angle of 136° into the surface of the material and dividing the load value by the surface area of the indentation crater of the material, which is the Vickers hardness value (HV).
E. Knoop hardness (HK)
Knoop hardness (HK) is suitable for hardness testing of high-hardness materials (general HV1000 Hardness and above hardness measurement).
F. Wechsler hardness tester (HW)
Wechsler hardness tester (HW) is suitable for the measurement of the Wechsler hardness value of aluminum alloy products.
G. Plaster hardness tester
Plaster hardness tester is suitable for measuring the hardness of building plaster. A steel ball is placed on the test piece, the depth of the ball mark under a fixed load is measured, and the hardness of the test piece of plaster is calculated.
Type of durometer
A. Richter hardness tester
a. The main functions of the Richter hardness tester are the ability to select the test material, hardness system, test direction, and a number of tests by pressing a button.
b. Conversion between six types of hardness (HLD, HRB, HRC, HB, HV, HS) is possible.
c. Repeatedly display the results of each test and automatically or manually delete the test results by mistake.
d. Output single test average or overall output of all stored data at any time.
e. Automatic detection of battery voltage. There is a power display icon in the test state.
Working principle of Richter hardness tester
Using an impact body with a certain mass to impact the surface of the specimen under a certain test force, the hardness is calculated by measuring the ratio of impact velocity to rebound velocity at 1mm from the surface of the specimen.
Formula: Richter hardness HL = 1000 × VB (rebound velocity) / VA (impact velocity).
B. Rockwell hardness tester
Digital Rockwell hardness tester is an electromechanical integration of hardness testing instruments. Digital Rockwell hardness tester has a novel appearance, large screen display, menu structure, and microcomputer control, and the hardness value is directly displayed by numbers. Hardness test results can be directly printed out, automatic feedback locking between the lifting screw and rotating wheel, external RS232 super terminal setting, and external printer, with good reliability, operability, and intuitiveness; except for the test bench lifting, completely automated, eliminating the operation and reading errors.
The digital display Rockwell hardness tester also has the functions of Rockwell scale selection/plastic Rockwell scale selection (optional function)/hardness conversion between each hardness, etc.
Digital Rockwell hardness tester is suitable for hardness determination of ferrous metals, non-ferrous metals, and non-metallic materials.
Rockwell hardness tester, take the test sample surface roughness requirements less than or equal to 0.8μm.
C. Brinell hardness tester
Automatic turret digital display Brinell hardness tester with unique dual-core dual-chip, changing the previous hammer-press type loading method. Adopt the closed-loop control system of CPU control, sensor collecting signal, and stepping motor loading. With 10 levels of test force, it can test 10 scales of Brinell hardness respectively. Easy to operate.
D. Micro hardness tester
The microhardness tester is a new microscopic Vickers and Noah's hardness tester using precision mechanical technology and photoelectricity. It has good reliability, operability, and intuitiveness. The microhardness tester is novel in appearance, microcomputer-controlled, with software to select the Vickers and Nuss hardness measurement, adjust the intensity of the measuring light source, and preset the test force holding time, with LCD display, and through the operation control keys to select the hardness scale HV or HK, test force, holding time, and light source brightness can be steplessly adjusted. The diagonal length D1 and D2 values can be measured with the microscope and the hardness value can be displayed on the LCD after key input, which is easy to operate. The hardness value is read out directly on the screen by inputting the diagonal length of the indentation through the panel, which simplifies the tedious task of checking the table. Micro hardness tester adopts unique indentation measurement conversion and microscopic eyepiece once measurement reading mechanism. Easy to use, high measurement accuracy. Micro hardness tester can also be equipped with a photographic device according to the user's special requirements and can be a measured indentation, and material metallographic organization for photography. Widely used in the determination of microhardness of tiny, thin specimens, surface permeation plating and other specimens, and the determination of glass, ceramics, agate, artificial gemstones, and other brittle and hard materials Nucleus hardness, scientific research institutions, factories, and quality control departments for material research and testing of the ideal hardness testing instruments.
The scope of the application contains heat treatment, carbonization, quenching and hardening layer, surface cladding, steel, non-ferrous metals and tiny and thin-shaped parts, etc.
a. The durometer generates two types of errors: one is the error caused by the deformation and movement of its parts; the other is the error caused by the hardness parameters exceeding the specified standards. For the second kind of error, the hardness tester needs to be calibrated with a standard block before measurement. For Rockwell hardness tester calibration results, the difference within ± 1 qualified. The stable value of the difference within ±2 can be given as a correction value. If the difference is outside the ±2 range, the hardness tester must be calibrated and repaired or changed to another hardness test method.
The Rockwell hardness scales have a de facto range of applications and should be used correctly according to the 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 beyond its specified test range, the accuracy and sensitivity of the hardness tester are poor, the hardness value is not accurate and should not be used. Other hardness testing methods are also specified with corresponding calibration standards. The standard block for calibrating the hardness tester cannot be used on both sides, because the hardness of the standard side and the back side is not necessarily the same. The standard block is generally valid for one year from the date of calibration.
b. When replacing the indenter or anvil seat, you should pay attention to the contact parts to wipe clean. After the change, use a certain hardness of the steel sample test several times until the hardness value obtained twice in a row is the same. The purpose is to make the contact part of the indenter or anvil and the testing machine pressed and in good contact, so as not to affect the accuracy of the test results.
c. After the hardness tester is adjusted, the first test point is not used when starting to measure hardness. Because of the fear of poor contact between the specimen and the anvil, the measured value is not accurate. After the first test point is finished, the hardness tester is in the normal operation mechanism state and then conducts a formal test on the specimen and records the measured hardness value.
d. In the case of test pieces allowed, generally choose different parts to test at least three hardness values, take the average value, and take the average value as the hardness value of the test piece.
e. For the complex shape of the test piece use the corresponding shape of the pad, fixed before testing. Round specimens generally should be placed in the V-shaped slot test.
f. Check whether the loading handle is placed in the unloading position before loading, and the action should be light and steady when loading, don't force too hard. The loading handle should be placed in the unloading position after loading, to avoid the long-term load state of the instrument, and plastic deformation, affecting the accuracy of measurement.
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