First of all, We Need to Understand What is a Self-Tapping Screw.
In most cases, self-tapping screws are used for the connection between thin metal plates such as steel plates and saw blades. 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.
The Development of Self-Tapping Screws
1. Ordinary Self-Tapping Screws
The principle of the ordinary self-tapping screw is: that when it is screwed into the prefabricated hole, the internal thread connected to the screw is formed by the displacement of the material around the hole and pushing the material into the space between the threads.
The thread of an ordinary self-tapping screw is the self-tapping thread, also called coarse thread. Surface treatment is mostly in the form of electroplating.
2. Self-Cutting Self-Tapping Screws
Because ordinary self-tapping screw thread forming can only be used conveniently on relatively thin and tough materials. When the use of self-tapping screws is expanded to thicker sections and materials with hard, brittle, and other poor deformability, self-cutting self-tapping screws are required.
The principle of self-cutting and self-tapping screws is to machine a cutting groove or cutting edge at the end of the screw shank. When this kind of screw is screwed into the prefabricated hole, the screw acts as a tap and actually makes the thread that connects with itself.
There are several types of self-cutting self-tapping screws: cross-recessed pan head self-cutting self-tapping screws, cross recessed countersunk head self-cutting self-tapping screws, cross recessed half-countersunk head self-cutting self-tapping screws, and hexagon head self-cutting self-tapping screws.
3. Self-Extrusion Self-Tapping Screws
The threads and ends are specially designed for this type of screw according to the principles of cold-forged tap design. Allows the screw to form a connecting internal thread by applying intermittent, periodic pressure on the crest of its thread, rather than on the side of the entire thread.
By concentrating and limiting the forming pressure, the pressurized material against the hole can be made to flow more easily and better fill the flanks and roots of the thread of the self-tapping screw. Since the frictional resistance of screwing in is much lower than that of ordinary self-tapping screws, self-extrusion self-tapping screws can be screwed into thicker sections. At the same time, it has better screw-in control and tightening torque, and greatly improves the connection strength and overall firmness.
The threads of self-extrusion self-tapping screws are generally machine threads, and self-tapping threads are rarely used. In the wrenching method, in order to ensure the use of high-speed automatic assembly wrenches, slotting is generally not recommended. The cross-section of the screw of the self-extrusion self-tapping screw is triangular, so it is also called a triangular thread screw.
4. Self-Drilling and Self-Tapping Screws
In practical applications, self-tapping screws require prefabricated holes. Moreover, in order to make the prefabricated holes have a good effect in practical application, the size of these holes must be controlled within a fairly strict range.
In the early 1960s, self-drilling and self-tapping screws appeared. Since there is no need to machine prefabricated holes, a large part of the problem of reducing assembly costs is solved. In a nutshell, self-drilling and self-tapping screws realize the one-time operation of drilling, tapping, and tightening.
In Chinese, German and international standards, the threads of self-drilling self-tapping screws are self-tapping threads. The thread of the BSD self-drilling self-tapping screw in the American ASME and SAE standards is a self-tapping thread, while the CSD-type self-drilling self-tapping screw is a machine thread. Self-drilling self-tapping screws generally do not use “slotted” and “ordinary hexagon head”.
In addition to self-tapping screws, KENENG, as a fastener manufacturing factory, can also provide many other types of screws, as well as bolts, rivets, washers, and other fasteners. We hope you will contact us for a specific product quote.