Self-tapping screws, or fast-screws, are fast-acting fasteners that are galvanized and passivated on steel. Self-tapping screws are often used for connections between thin metal sheets (steel plates, sawing boards, etc.). When connecting, first make a threaded bottom hole for the connected piece, and then screw the self-tapping screw into the threaded bottom hole of the connected piece.
1. Ordinary self-tapping screws (thread-formed self-tapping screws)
Ordinary self-tapping screws are a direct result of early sheet metal screws. The principle is that when screwed into the preformed hole, the internal thread connected to the screw is formed by the displacement of the material around the hole and the pushing of the material into the gap between the threads.
2. Self-cutting self-tapping screws (thread cutting self-tapping screws)
Because ordinary tapping screw thread formation is only quite thin. And the toughness of the material can be easily realized. Development of the use of self-tapping screws to thicker sections and materials that are harder, brittle and have poor deformability. In this way, a self-cutting self-tapping screw was developed: a cutting groove or a cutting edge was machined at the end of the screw rod. When the screw is screwed into the pre-made hole, the screw acts as a tap and actually cuts the thread connected to itself.
3. Self-squeezing self-tapping screws (threaded self-tapping screws)
In the early 1950s, fastener engineers began to realize the potential advantages of self-tapping screws with "structural" rather than just light loads. This led to the development of a new self-tapping screw threaded self-tapping screw (self-squeezing self-tapping screws). According to the cold forging forming tap design principle, the screw and the end are specially designed for the screw, so that the screw can be formed by applying intermittent, periodic pressure on the crest of the thread instead of the side of the entire thread. Internal thread for connection. By concentrating and limiting the forming pressure, the compressed material against the hole is more easily flowed and better filled (squeezed) into the flank and the bottom of the self-tapping screw thread. Since the frictional resistance of the screwing is much lower than that of a conventional self-tapping screw, the threaded self-tapping screw (self-squeezing self-tapping screw) can be screwed into a thicker section. At the same time, it has better screwing control and tightening torque, and greatly improves the joint strength and overall firmness. The engineering standards for such self-tapping screws stipulate that material selection, heat treatment mechanical properties and work performance are strictly controlled.
4. Self-drilling self-tapping screws (self-drilling screws)
People have done statistics: among the ten items that make up the total assembly cost, the highest ones include the processing of holes. Self-tapping screws require machining of pre-formed holes in practical applications. Moreover, in order to make the preformed holes work well in practical applications, it is necessary to control the size of these holes to a relatively strict range. In the early 1960s, self-drilling self-tapping screws appeared. Since there is no need to machine prefabricated holes, a major step forward is made to reduce assembly costs. In summary, self-drilling self-tapping screws enable a single job of drilling, tapping and fastening.
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