First, the type and type of self-tapping screws and threads Standard self-tapping screws can be identified by letter code, each code represents a variety of different combinations of tooth shape and end shape. Each self-tapping screw is generally available in two thread types: machine thread or self-tapping thread.
Second, materials, heat treatment and surface treatment Self-tapping screws are made of carbon steel, stainless steel, brass or aluminum. Carbon steel self-tapping screws account for more than 99% of the total amount of self-tapping screws. In fact, in the published materials, except for carbon steel, it is reported that the mechanical properties and workability of self-tapping screws of other materials are almost absent.
Carbon steel self-tapping screws are made of low carbon steel (commonly considered by various analyses), heat treated (due to small product size, good heat treatment effect) and surface hardening, and have sufficient hardness for cutting or forming internal threads.
For self-tapping screws, the relationship between the depth of the carburized layer and the surface hardness and core hardness is critical. If the carburized layer is too shallow, the screwing effect is poor; if it is too deep, it will adversely affect its torsional strength and screw toughness. In the SAE J933, SAE J78 and SAE J81 standards, the surface hardness and core hardness of the screw are specified accordingly. For ordinary self-tapping screws and self-cutting self-tapping screws, it is recommended to follow the SAE J933 standard.
The SAE J933 standard can be found at: http://
The SAE J78 standard can be found at: http://
The SAE J81 standard can be found at: http://
Most self-tapping screws are galvanized or phosphated. If higher quality of appearance is required, nickel or chrome plating may be considered. Two problems associated with plating: high hardness, small size self-tapping screws can increase sensitivity to hydrogen embrittlement. Therefore, in order to avoid hydrogen embrittlement, it becomes a problem that must be paid attention to in the manufacturing process of self-tapping screws. Self-tapping screws are required in the above three SAE standards. After electroplating, the drying and dehydrogenation treatments are performed. SAE J81 even specifies the drying time and temperature.
Not only does the coating increase in size, but different coating materials can affect the relationship between screwing in and tightening torque. Because the aperture is very sensitive to normal screwing and fastening. Therefore, it should be tested to determine the correct pore size. Moreover, the surface treatment of the screws used in the test should be the same as the surface treatment of the screws used in the production.Third, the length of the screw
When selecting the length of the screw in the application, it is important that the screw be of sufficient length to ensure that the full thread passes through the full thickness of the material being joined. This requires that the calculated length of the screw must be equal to the length of the clamp (total length of each joint) plus the length of the end of the screw (the length of the drill end should also be included for the self-tapping end of the drill).Fourth, the main features of self-tapping screws
Although there are many types of self-tapping screws, they all have the following in common:
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