Self-tapping screws are generally fingertip, coarse teeth, and hard wood screws, as well as aluminum alloy and plastic. A special self-tapping screw for opening metal holes is called a tap.Self-tapping screws are used for non-metallic or softer metals without the need for bottom holes and tapping.
Self-tapping screw is a kind of screw with a drill bit, which is constructed by a special electric tool, drilling, tapping, fixing and locking are completed at once. Self-tapping screws are mainly used for the connection and fixing of some thin plate parts, such as the connection of color steel plate and color steel plate, the connection of color steel plate and purlin, wall beam, etc., and its penetration capacity is generally not more than 6mm, and the maximum is not more than 12mm.Self-tapping screws are often exposed to the outdoors and have strong corrosion resistance; The rubber sealing ring can ensure that the screw does not seep water and has good corrosion resistance. Self-tapping screws are usually described by three parameters: screw diameter series, number of threads per inch length and screw length.There are 10 and 12 screw diameter classes, and the corresponding screw diameters are 4.87mm and 5.43mm respectively. The number of threads per inch length has 14, 16, 24 three levels, the more the number of threads per inch length, the stronger its self-drilling ability.
From beginning to end, the self-tapping screw is composed of three parts: the head, the rod and the end of the rod. The composition of each self-tapping screw has four major elements: head shape, screw mode, thread type and end type.
Self-tapping screw surface treatment: Most self-tapping screws are coated with zinc plating or zinc phosphate. Cadmium plating is rarely used because of its high cost and toxicity, and nickel or chromium plating can be selected if appearance is important.In order to penetrate the iron plate, the self-tapping screws shall not be disposed of without carburizing. High hardness and high carbon content will occur after carburizing treatment, and hydrogen embrittlement will occur when electroplating or pickling is done in this situation. The method advocated by the code to eliminate hydrogen embrittlement is :a). Baking within 1 hour after electroplating or pickling treatment.b). Temperature 375 ~ 425 oF(190 ~ 220 oC). Time at least 4 hours.
Although there are many types of self-tapping screws, they all have the following main characteristics: (1) They are generally made of carburized steel (accounting for 99 percent of the total product). It can also be made of stainless steel or non-ferrous metals. (2) The product must be heat treated. Carbon steel self-tapping screws must be carburized, stainless steel self-tapping screws must be solid solution hardening treatment. In order to make the self-tapping screw to meet the requirements of the standard mechanical properties and performance.(3) The product surface hardness is high, the core toughness is good.This is a major feature of the performance requirements of self-tapping screws. If the surface hardness is low, it cannot be screwed into the matrix; Such as the core toughness is poor, a twist will be broken, can not be used.
(4) The surface of the product needs surface protection treatment, generally electroplating treatment. The surface of some products needs to be treated with phosphate (phosphating). For example: wall panel tapping screws are mostly phosphating. (5) Production by cold heading process. It is recommended to use high-speed cold heading machine and high-speed wire rolling machine or high-speed planetary wire rolling machine to ensure product quality. The head of the self-tapping screw produced in this way is well formed and the thread quality is high.
