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Do you know the application standards of screws

2021-02-22

The standards for screws include: product name (standard), material, strength grade, specification and surface treatment.

1. In terms of product types, the torsion force of the hexagon socket screws is relatively greater, the torque of the hexagon socket screws is smaller, and the torque of the cross groove is smaller. In the supporting use of the product, it is generally recommended to select the grade of the screw one level higher than that of the nut, so that * has economic benefits.

2. Product material grade. Here we mainly talk about carbon steel commonly used for screws. According to the level of carbon content, it is divided into: C1008 (corresponding to 4.8 grade), C1035 (corresponding to 8.8 grade), C1045 (corresponding to 10.9 grade), SCM435 (corresponding to 12.9) Grade and 45H), the higher the carbon content, the harder the material. Screws of grade 8.8 and above are all high-strength screws.

3. For specifications, such as M4x8, the outer diameter of the 4-finger tooth is 4mm, and the effective length of the 8-finger embedded object is 8mm. Generally, the total length of the countersunk head screw is loaded, and the half countersunk head screw needs to add half the 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 electroplating of grade 8.8 and above. There are two kinds of heat treatments currently done: high-strength screws require quenching and tempering heat treatment, that is, the hardness of the screw is uniform from the inside to the outside; self-tapping screws require carburizing heat treatment, that is, the surface of the screw is carburized, which is very hard. But the inside is very soft, if carburizing to the inside, the screw will be burnt.

5. Under normal circumstances, hardness>32HRC, electroplating has the risk of hydrogen embrittlement. Hydrogen embrittlement means that when the product is pickled (oil stain), H+ enters into the metal to form bubbles. The screw is used continuously on the spot, and it breaks after 24 hours. Therefore, this product with the risk of hydrogen embrittlement needs to be dehydrated after electroplating.

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