Hardware Screw: The first method is to use Brinell hardness test. This method uses a hardened steel ball to test the surface of the hardened screw material. After a period of time, it is calculated by the value of the steel ball and the screw indentation. The hardness of the screw. This is a commonly used method.
Another method is Vickers hardness, which is a more professional method for testing the hardness of screws. Generally, the square cone of diamond is pressed into the surface of the screw using an indenter, and then the hardness of the screw is calculated according to a certain calculation formula. index.
Standard for hardware screws:
1. Product grade: According to the carbon content, we are divided into: C1008 (corresponding to 4.8), C1035 (corresponding to 8.8), C1045 (corresponding to 10.9), SCM435 (corresponding to 12.9 and 45H), including carbon. The higher the amount, the harder the material. Screws from 8.8 to above are all high-strength screws.
2, for the specification: for example, M4x8, 4 finger outer diameter is 4mm, 8 refers to the effective length of the embedded object is 8mm, the general countersunk screw is loaded with the total length, half countersunk head screw plus half head length. The pan head screw cross does not include the head size.
3. When the same material is heat treated, the higher the hardness, the worse the toughness. Heat treatment is required for plating from grade 8.8 to above. There are two kinds of heat treatments we currently do: high-strength screws require heat treatment, that is, the hardness of screws from the inside to the outside is uniform; self-tapping screws require carburizing heat treatment, that is, the surface of the screws is impregnated with a layer of carbon, which is very hard. But the inside is very soft, if the carburization is inside, the z will be burnt.