The tools, quantities, molds and molds used in mechanical manufacturing should have sufficient hardness to ensure the performance and life of use.
Hardness is the capacity to measure the resistance of the material to local deformation, in particular plastic deformation, indentation or scratches. Generally, the more difficult the material is, the better its abrasion resistance.
Type of hardness
As the above figure shows, there are so many types of hardness … Today, I will present you the common and practical indentation hardness tests in the metallic hardness.
Definition of hardness
1. British hardness / Bronnel hardness
The British hardness test method (HB symbol), among the hardness of recognized specifications, is the first development and summary method.
The principle of the British hardness test is: the test force F (steel ball or alloy hard ball, DMM diameter) is applied to the test force F. Once the sample is removed, improve the pressure head The ball in the concave diameter D (mm (mm) left by the pressure head. The symbol when the head is the steel ball is HBS, and the hard alloy ball is hbw. K is constant (1 / g = 1 /9.80665 = 0.102).
2. Vickers hardness
Vita hardness (HV symbol) is the most used test method that can be tested with any test force.
The hardness of the meat is the value obtained by the contact zone (MM2) between the test force f (N) with the standard film and the head. The standard film for calamity on the standard film is calculated. K is the constant (1 / g = 1 / 9.80665).
3. The hardness / hardness of Nude Knoop
As the following formulas shows, the hardness of naked (HK symbol) is calculated by dividing the test force of the divided projection zone A (MM2). 30 ‘and 130˚).
The nude hardness can also be measured by replacing the Victorian head of the microscopic hardness test machine at the naked head.
4. Rockwell Hardness
Before measuring the hardness of the dress (HR symbol) or the duct of Luoz, you must use the diamond head (cutting angle: 120˚, tip radius: 0.2 mm) or spherical head ( Steel ball or hard alloy ball) The standard film applies pre-loading, then the test force is applied to restore the pre-added capacity.
The hardness value is concluded by the hardness formula, and the formula is expressed by the difference between the depth of indentation H (μm) between the pre-added capacity and the test force. The dress hardness test uses a 98.07n pre-load, and the Romas surface hardness test uses a pre-added capacity of 29.42N. The specific symbols provided by combining the type, the test force and the hardness formula are called the rule. The industrial standards of Japan (JIS) define various standards of related hardness.
The operation of the hardness test machine is relatively simple and fast, which can be tested directly on the surface of the raw materials or parts, so it is widely used.
Hardness selection guide
Hardness selection conversion
1. The conversion of the hardness and hardness of nude vita
(1) Based on the resistance equal to the head of Victoria de Nu with the same hardness, derives the constraint of the two types of pressure on the loading load on the load load, then obtained from σhk = σhv: HV = 0.968hk. This formula is measured under a low load and the error is relatively important. In addition, the formula error is important when the hardness value is greater than the HV900 and the reference value is lost.
(2) The formula of the converting formula of the hardness of the nude and the hardness of the Victoria after the derivation and the correction are
After the actual data verification, the maximum relative conversion error of this formula is 0.75%, which has a high reference value.
2. The conversion of the hardness and hardness of the lot
(1) For the Qvarnstorm converted formula proposed by Hans · Qvarnstorm
After the revision, the conversion formula for the hardness of the roses and the hardness of the Vita is:
This formula uses standard black metal hardness data published by my country.
(2) On the basis of σhrc = σhv of the different pressure head, the formula is obtained by the analysis of the deep relationship curve of the hard hardness and the revelation of the Victoria hardness
Unlike the national standard experimental replacement value, the error in calculation calculation results and the standard experimental value is ± 0.1hrc.
(3) According to real experimental data, the conversion of the hardness of Lowl and the hardness of Vicani is discussed by the linear regression method.
This formula has a small scope and large errors, but it is easy to calculate and can be used when the precision requirements are not high.
3. Conversion of the hardness of the lowl and the hardness of the blade
(1) Analyze the depth relationship of the British indentation and the low cane, and obtain the conversion formula as a function of the stress σhrrc = σhb of the pressure head
Compared to the national national experimental value, the error in the result of the conversion calculation and the standard experimental value is ± 0.1hrc.
(2) Obtain formulas according to the actual method of experimental data
The formula error is large and the use range is small, but the calculation is simple and can be used in the case of low precision.
4. The conversion of the hardness and hardness of the Bélisée
The relationship between the harshness and hardness of the blade, the formula is also obtained according to σhb = σHV
The conversion result of this formula is compared to the national standard replacement value, and the conversion error is ± 2 hp.
5. Converting the hardness of the hardness of nude and low
Because the hardness of naked and the corresponding curve of the hardness of Lowl are similar to the parabolic lines, the curve has obtained an approximate conversion formula as
This formula is more precise and can be used as a reference.
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