Since 1914, self-tapping screws have been commercialized. The first design - mainly derived from wood screws - is a carburizable steel tapered tail A-shaped thread forming screw. At that time, the main purpose was to join the iron sheets on the ducts of the air conditioning system, so they were also called iron sheet screws. After more than 80 years of development, the industry can be divided into four periods - thread forming, thread cutting, thread rolling and self-drilling.
Thread Forming Tapping Screws (Thread Forming Tapping Screws) are directly developed from sheet metal screws. When using thread forming self-tapping screws, you must pre-drill the holes, then screw the screws into the holes and squeeze them hard. When the female thread is removed, the material originally on the female thread will be squeezed between the male threads. This is called a thread-forming self-tapping screw. It can only be applied to thin and plastic materials, so thread cutting self-tapping screws have been developed;
Thread Cutting Tapping Screws - one or more threads are cut at the end of the thread. The cutting opening of the Tao enables the screw tail and teeth to be used to cut matching female threads in a similar way to a screw tap when screwing into the pre-drilled hole. It can be used on thick plates, relatively hard or fragile materials that are difficult to shape.
Thread Rolling Tapping Screws - Triangular thread self-tapping screws, also known as special types (large models are still patented at this stage), are developed based on the principle of forming screw tapping. , Thread-rolled self-tapping screws have specially designed threads and tail ends so that the screws can roll themselves into matching female threads under intermittent pressure. At the same time, the material around the hole can more easily fill the space between the thread and the bottom of the self-tapping screw. Since its friction force is smaller than that of the thread-forming self-tapping screw, it can be used on thicker materials, and the torque required for rotation is greater. Easy to control, and stronger when combined. The engineering standard definition of thread-rolled self-tapping screws is higher and clearer than that of formed or cut self-tapping screws in terms of material, heat treatment, and strength, making thread-rolled self-tapping screws a true "structural" fastener.
Self Drilling Tapping Screws (also known as Tec), among all assembly processes, the most cost-consuming is the preparation of pre-drilling holes. To use self-tapping screws, you must drill holes first. And the pore size must also be limited. Eliminating the need for pre-drilling can result in some cost savings. This is a drill tail self-tapping screw that integrates drilling, tapping and tightening in one operation. The surface hardness and core hardness of drill screws are a little higher than that of ordinary self-tapping screws. This is because drill screws have an extra drilling operation. In addition, drill screws still need to undergo a penetration test to test whether the screws can be used within a specified time. Drill and tap the inside.
The above is the design and development process of the four main self-tapping screws. There are also two screws with special thread design. The first one is; high-low thread self-tapping screws (high-low tapping screws)- Used on plastic or other low density materials. Double thread design, high thread (larger outer diameter of tooth) has a flatter and sharper thread angle of 30 degrees. Low threads (smaller outer diameter of thread) have a thread angle of 60 degrees, and the thread height is only half of that of high threads. The combined design of high and low threads reduces the rotational torque, improves the pull-out strength, and greatly reduces the risk of rupture of the combined workpiece. It is also used in the assembly of drywall (drywall) in the construction industry. , self-tapping screws with this kind of thread design are particularly suitable for plastics, parts boards and wood.