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How hard is the hardness of the cold drawn tube? How to measure the hardness of the standard
Apr 17, 2018

Cold drawn tubes are produced at relatively low temperatures and have many performance and advantageous features. Cold-drawn tubes can also be used in the construction of various buildings. The more important feature of cold-drawn tubes is that the hardness is relatively large, the hardness is large, and they play an important role in various fields. . Since the production and operation of cold-drawn tubes have a relatively important impact, the use of cold-drawn tubes is also more extensive. What is the hardness of a specific cold drawn tube?

 

Among them, the scales commonly used for cold-extrusion tube hardness test are generally A, B, C, namely HRA, HRB, HRC. The hardness value is calculated using the following formula: When tested with the A and C scales, HR=100-e When tested with the B scale, HR=130-e Where e--the residual indentation depth increment, which is specified The unit of 0.002mm means that when the indenter is displaced axially by one unit (0.002mm), it is equivalent to a change in Rockwell hardness. The greater the value of e, the lower the hardness of the metal, and the higher the hardness. The scope of application of the above three scales is as follows: HRA (diamond conical indenter) 20-88 HRC (diamond conical indenter) 20-70 HRB (diameter 1.588mm steel ball indenter) 20-100 Rockwell hardness test is currently widely used The method, in which HRC is used in steel pipe standards, is only inferior to Brinell hardness HB. Rockwell hardness can be applied to the determination of a very soft to extremely hard metal material, it makes up for the Brookfield method is not, simpler than the Brookfield method, can read the hardness value directly from the dial of the hardness machine. However, due to its small indentation, the hardness value is not as accurate as the Brookfield method. C. Vickers Hardness (HV) The Vickers hardness test is also an indentation test method in which a positive quadrangular pyramid diamond indenter with an opposing surface angle of 1360 is pressed onto the test surface with a selected test force (F). The test force was removed after the specified holding time, and the length of the two diagonals of the indentation was measured. Vickers hardness value is the quotient of the test force divided by the surface area of the indentation, and its calculation formula is: Where: HV - Vickers hardness symbol, N/mm2 (MPa); F - test force, N; d - The arithmetic average of the two diagonals of the indentation, mm. The Vickers hardness test force F is 5 (49.03), 10 (98.07), 20 (196.1), 30 (294.2), 50 (490.3), 100 (980.7) Kgf (N), etc. The range is 5 to 1000 HV. An example of the expression method: 640 HV 30/20 means that the Vickers hardness value measured with a test force of 30 Hgf (294.2 N) for 20 seconds (seconds) is 640 N/mm 2 (MPa). The Vickers hardness method can be used to determine very thin metallic materials and surface layer hardness. It has the main advantages of Brinell and Rockwell, and overcomes their basic shortcomings, but it is not as easy as Rockwell's method. Vickers is rarely used in steel pipe standards. HB is the use of a certain force to a certain diameter (2.5,5,10) ball pressed against the surface of the material to be measured, and then measured the diameter of the indentation of the steel ball surface to determine the hardness of the material. The original state of the material and annealing, normalizing or tempering of the cold-drawn tube is commonly used HB. HR has three types of A, B and C3

 

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