This article does not deal with the materials of self tapping screws, but only introduces the standards and some characteristics of self tapping screws.
During the installation of self tapping screw, the torque of its rotation into the base is the most important technical condition, which involves a series of requirements such as the diameter of the base bottom hole, and the thread length test of the self tapping screw. The friction force and locking torque produced during the installation are different for different bottom hole sizes and different thread lengths. As the self tapping screw is continuously screwed into the base, its torque parameters are constantly changing, When the self tapping screw is rotated to the optimal position, its torque should be the maximum value. Generally, if we use an ordinary screwdriver to screw, we should take it as the benchmark. However, because everyone's strength is different, we'd better use electric tools with torque adjustment for operation.
The self tapping screw also has a breaking torque, which is the torque parameter when the self tapping screw is directly rotated to fracture. For comparison of these two different torque parameters, the smaller the screw in torque is, the better the effect will be. The larger the final breaking torque is, the better the effect will be. The farther the difference between these two data is, which indicates that the better the performance and final installation effect of the self tapping screw.
The number of self tapping screws is relatively large. Why? Since self tapping screws are used in batches, the bottom holes on many plastic parts are dense. Because the installation of a self tapping screw or several self tapping screws cannot ensure its looseness prevention, after all, the self tapping screws are only locked by the friction between the thread and the matrix, and the locking mode of the bolts and nuts is still a little different from that of the normal ones. Therefore, when using self tapping screws in a matrix, Usually, it is not just one or several, but one by one. In order to ensure uniform stress, the specification categories of self tapping screws are usually reduced in the design, and only the self tapping screw standards of the same specification are used as far as possible, which can also ensure the flatness of an overall structure, reasonable space layout and ensure the installation accuracy.
The main difference between machine screws of self tapping screws lies in the design of threads. The distance between threads of self tapping screws is large, and the height of threads is higher than that of machine screws. In the case of the same bottom hole, if the machine screws are rotated in, the plastic matrix will crack, while the self tapping screws will not. This is because the threads of self tapping screws are sharp, and they can directly drill into the matrix without expansion. The installation of self tapping screws is also more convenient than machine screws. Machine screws need to be matched with nuts. The installation time is also more than that of self tapping screws, and the cost is also high. The self tapping screw can be directly rotated into place with a tool, which usually takes only ten seconds.
The thread tail of machine screws is basically a standard, but there are three different standards for self tapping screws. One is our most common pointed tail tapping screw. According to the head standard, its corresponding national standards can be expressed in GB/T845 and GB/T846. Another kind of self tapping screw has a flat tail. We only need to add the word "flat tail" to the standard. The last kind of self tapping screw is tail cutting, which uses a milling cutter to cut a slot at the tail of the thread. Select different self tapping screw standards according to different use environments.
