Development of self-tapping screws


Self-tapping screws were introduced to the industry in […]

Self-tapping screws were introduced to the industry in large quantities in 1914. The earliest design (essentially imitating wood screws) is a type of thread forming screw made of hardened steel with a type A end, which is mainly used for thin metal passages connecting heating and ventilation systems. It is also called: "thin metal screw".
By the end of the 1920s, with the expansion of the market and new applications, the emphasis on new designs has greatly improved its application performance. The following describes four different stages of self-tapping screws in the 40-year development: thread-forming self-tapping screws, thread-cutting self-tapping screws, thread-twisted self-tapping screws, and self-drilling self-tapping screws.
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)
Due to the normal self-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 harder, brittle and other materials with 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 orifice 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 performance are strictly controlled.
4. Self-drilling self-tapping screws (self-drilling screws)
People have done statistics: Among the ten items that constitute the total assembly cost, the highest one includes the processing of the hole. 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 one operation for drilling, tapping and fastening.
These are the four main stages in the design and development of self-tapping screws. In addition, two newly developed products are also worth introducing. Both types of screws are available in special thread types. One is designed for use in plastics and other low-strength materials; the other is used in the construction industry to connect cement wall panels, so it is also called wall-wall self-tapping screws.