Self-tapping screws are generally manufactured by cold […]
Self-tapping screws are generally manufactured by cold heading process, hot heading (pressing) process, cold extrusion extrusion process or cutting process, for self-tapping screws with a nominal diameter of 0.750 in or less and a nominal length of less than or equal to 10 nominal diameters or 6 in. (The smaller one) should be produced by the cold heading process. For self-tapping screws with a nominal diameter greater than 0.750IN and a longer nominal length, the cold heading or hot rolling (pressure) process can be used. The option is in the screw manufacturer. For self-tapping screws with a nominal diameter greater than 1.5in, the forging process can be used for machining processes, and the option is at the screw manufacturer.
If the user has no other special requirements, the thread of the self-tapping screw should be twisted, that is, twisted or threaded. Especially for screws with a nominal diameter of 0.625 in or less and a nominal length of 4 in or less, the thread must be machined. For self-tapping screws with a nominal diameter greater than 0.625 in. and a nominal length greater than 4 in., the thread should be machined as much as possible. Only when machining is impossible, the cutting or grinding of the thread can be considered.
Self-tapping screws must be heat treated - quenched and tempered. Moreover, oil should be used as the quenching medium. The tempering temperature should exceed 700F.
Self-tapping screws should be tempered at 680 °C and moisturized for 30 minutes to verify the minimum tempering temperature of the self-tapping screws. When tempering, the average hardness of the three points on the radial section of the self-tapping screws, and then The average hardness before tempering should not differ by 20 Vickers hardness values.
When self-tapping screws are used for plating, etc., necessary measures should be taken. To prevent the self-tapping screws from being brittle due to electroplating hydrogen embrittlement.