Fastener product basics
Basic knowledge of fastener products:
The standard of the screw is: product name (standard), material, strength grade, specification and surface treatment
1. In terms of product type, the torsion force of the outer hexagonal screw is relatively larger, the torque of the inner hexagonal screw is smaller, and the torque of the cross recess is smaller. In the product supporting use, we generally recommend that the screw grade be one level higher than the nut grade, which is the most economical.
2, product material grade, here mainly talk about the carbon steel commonly used by our Hongyi screws, according to the level of 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), the higher the carbon content, the harder the material. Screws from 8.8 to above are all high-strength screws.
3. For specifications, such as M4x8, the outer diameter of the 4 finger tooth is 4mm, the effective length of the 8 finger embedded in the loaded object is 8mm, the general countersunk screw is loaded with the total length, and the half countersunk head screw is added with half head. length. The pan head screw cross does not include the head size.
4. 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 screws will be burnt.
5, under normal circumstances, hardness > 32HRC, plating has the risk of hydrogen embrittlement. When hydrogen embrittlement is the product pickling (oily stain), H+ enters the inside of the metal to form bubbles, and the screws are used on the spot and break after 24 hours. Therefore, this product with a risk of hydrogen embrittlement needs to be dehydrogenated after electroplating.
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