H stands for hardness! As for the hardness, it depends on the value in front of H.
The hardness of plastic is the resistance of the plastic material to imprints and scratches. According to different test methods, there are Barcol hardness, Brinell hardness, Rockwell hardness, Shore hardness, Mohs hardness, scratch hardness and Vickers hardness. (vickers) hardness, etc.
Generally speaking, plastic materials mostly use Rockwell hardness.
For information about Rockwell hardness, you can refer to /view/204900.html?wtp=tt
The ability of a metal material to resist the indentation of the surface by hard objects is called hardness. According to different test methods and application scope, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. There are three commonly used hardnesses for pipes: Brinell, Rockwell, and Vickers hardness.
A. Brinell hardness (HB)
Use a steel ball or cemented carbide ball of a certain diameter to press into the surface of the sample with the specified test force (F) and maintain it as specified After a certain period of time, remove the test force and measure the indentation diameter (L) on the sample surface. Brinell hardness value is the quotient obtained by dividing the test force by the surface area of ??the indented sphere. Expressed in HBS (steel ball), the unit is N/mm2 (MPa).
The calculation formula is:
In the formula: F--the test force pressed into the surface of the metal sample, N;
D--the steel used for testing Ball diameter, mm;
d--average diameter of indentation, mm.
Measuring Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2 (MPa), and is not suitable for harder steel or thinner plates. Among steel pipe standards, Brinell hardness is the most widely used. The indentation diameter d is often used to express the hardness of the material, which is both intuitive and convenient.
Example: 120HBS10/1000130: It means that the Brinell hardness value measured by using a 10mm diameter steel ball under the test force of 1000Kgf (9.807KN) for 30s (seconds) is 120N/mm2 (MPa).
B. Rockwell hardness (HK)
The Rockwell hardness test, like the Brinell hardness test, is an indentation test method. The difference is that it measures the depth of the indentation. That is, under the sequential action of the initial test force (Fo) and the total test force (F), the indenter (cone or steel ball of the gold steel mill) is pressed into the surface of the sample. After the specified holding time, the main force is removed. Test force, use the measured residual indentation depth increment (e) to calculate the hardness value. Its value is an anonymous number, represented by the symbol HR, and the scales used include 9 scales, including A, B, C, D, E, F, G, H, and K. Among them, the scales commonly used for steel hardness testing are generally A, B, and C, namely HRA, HRB, and HRC.
The hardness value is calculated by the following formula:
When testing with A and C scales, HR=100-e
When testing with B scale, HR =130-e
In the formula, e--the residual indentation depth increment is expressed in the specified unit 0.002mm, that is, when the axial displacement of the indenter is one unit (0.002mm), it is equivalent to Changes by one number on the Rockwell hardness scale. The larger the e value, the lower the hardness of the metal, and vice versa.
The applicable range of the above three scales is as follows:
HRA (diamond cone indenter) 20-88
HRC (diamond cone indenter) 20-70
HRB (diameter 1.588mm steel ball indenter) 20-100
Rockwell hardness test is a widely used method at present, among which HRC is second only to Brinell in steel pipe standards. Hardness HB.
Rockwell hardness can be used to measure metal materials from extremely soft to extremely hard. It makes up for the shortcomings of the Brinell method. It is simpler than the Brinell method and the hardness value can be read directly from the dial of the hardness machine. However, due to its small indentation, the hardness value is not as accurate as the Brinell method.
C. Vickers hardness (HV)
The Vickers hardness test is also an indentation test method. It is a regular square pyramid diamond indenter with an included angle of 1360 between the opposite faces. Press into the test surface with the selected test force (F), remove the test force after the specified holding time, and measure the length of the two diagonals of the indentation.
The Vickers hardness value is the quotient of the test force divided by the indentation surface area. The calculation formula is:
In the formula: HV--Vickers hardness symbol, N/mm2 ( MPa);
F--Test force, N;
d--The arithmetic mean of the two diagonals of the indentation, mm.
The test forces F used in Vickers hardness are 5 (49.03), 10 (98.07), 20 (196.1), 30 (294.2), 50 (490.3), 100 (980.7) Kgf (N), etc. Level six, measurable hardness value range is 5~1000HV.
Example of representation method: 640HV30/20 means that the Vickers hardness value measured with a test force of 30Hgf (294.2N) for 20S (seconds) is 640N/mm2 (MPa).
The Vickers hardness method can be used to determine the hardness of very thin metal materials and surface layers. It has the main advantages of the Brinell and Rockwell methods and overcomes their basic shortcomings, but it is not as simple as the Rockwell method. Vickers method is rarely used in steel pipe standards.
---Xiao Xu