Butterfly valve, gate valve, globe valve and ball valve are the four types of valves with the most consumption. Butterfly valve can be divided into soft seal and hard seal according to the material of the sealing surface. The pressure range of the hard-sealed butterfly valve is PN0.6MPa-PN160.MPa, and the valve body material must reach a certain hardness standard value.
Hardness indicates the ability of a material to resist the pressing of a hard object into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.
1. Brinell hardness (HB)
Press a hardened steel ball of a certain size (generally 10mm in diameter) into the surface of the material with a certain load (generally 3000kg) and keep it for a period of time. After the load is removed, the ratio of the load to its indentation area is the Brinell hardness value ( HB) in kilogram force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement is used instead. It uses a diamond cone with an apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18mm, which is pressed into the surface of the tested material under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the different hardness of the test material, it is expressed in three different scales:
HRA: It is the hardness obtained by using a 60kg load and a diamond cone indenter. It is used for materials with extremely high hardness (such as cemented carbide, etc.).
HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm. It is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: It is the hardness obtained by using a 150kg load and a diamond cone indenter, and is used for materials with high hardness (such as quenched steel, etc.).
3. Vickers hardness (HV)
Use a load within 120kg and a diamond square cone indenter with an apex angle of 136° to press into the surface of the material, and divide the surface area of the material indentation pit by the load value, which is the Vickers hardness value (HV)