Generally refers to pointed, coarse teeth, texture hard wood screws, but also for aluminum alloys, plastic. A special self-tapping screw used for threading a metal hole is called a tap.
Self-tapping screws are used for non-metallic or softer metals, not to use low holes and tapping;
Self-tapping screws
Self tapping screws are pointed so that they can "self-tapping"; ordinary screws are flat and uniform in thickness.
The self-tapping screw is said to be: The drilled hole is a hole that does not require tapping. The screw used is different from the general one. The head is pointed and the pitch is relatively large. It is similar to the tapping without tapping. It can be screwed directly into without tapping. Metals and plastics usually use this method.
It can be on the material being consolidated, by its own thread, will be "attack - drill, squeeze, press" the corresponding body of the corresponding thread, so that they closely cooperate with each other.
Self-tapping screws are screws with drills, drilled, tapped, fixed, locked by special electric tools.
Self-tapping screws
Tightly completed. Self-tapping screws are mainly used for the connection and fixation of some thin plate parts, such as the connection of color steel plate and color steel plate, and the connection of color steel plate and purlins, wall beams, etc. The penetrating ability is generally not more than 6mm and the maximum is not more than 12mm. Self-tapping screws are often exposed outdoors, and they have strong corrosion resistance. Their rubber seals can ensure that the screws do not leak water and have good corrosion resistance.
Self-tapping screws are usually described by three parameters: the diameter of the screw, the number of threads per inch of length, and the length of the screw. There are two kinds of screw diameters, grade 10 and grade 12, and their corresponding screw diameters are 4.87mm and 5.43mm respectively; the number of threads per inch has three levels of 14, 16, 24, and the number of threads per inch of length is more. The stronger the drill capacity.
1 EvolutionSelf-tapping screws have been commercialized since 1914. The first design - mainly from wood screws - was carburizing steel cone-tailed A-type thread forming screws. The main application was to use the joints of metal sheets on ducts of air-conditioning systems. Therefore, it is also called tin screw. After more than 80 years of development, it can be divided into four periods - thread forming, thread cutting, thread rolling and drilling.
Thread forming tapping screws(Thread Forming Tapping Screws) ─ directly developed from tinned screws, thread tapping screws must be pre-drilled, then screw into the hole, strong extrusion with the female thread, and the original position in the female thread The material will be squeezed between the male threads. This is referred to as a thread forming tapping screw. It is only applicable to thin and malleable materials and has therefore evolved; Thread Cutting Tapping Screws - on threads The tail end cuts one or more cutting edges to enable the female thread to be cut in a screw-like manner using the screw tails and teeth during the pre-drilling. It can be used on thick plates and is relatively hard. Or materials that are not easily crumbable, such as
Thread rolled into self-tapping screws(Thread Rolling Tapping Screws) - Taper Screw Taping Screws, also known as Type TT (Type Tai is still patented) is based on the principle of forming screw tapping, thread rolling tapping screws with specially designed thread and tail The end of the screw can be rolled under the intermittent pressure to match with the female thread. At the same time, the material around the hole can more easily fill the space of tapping screw thread and the bottom of the teeth, because the friction force is higher than the thread forming tapping screw Smaller, so it can be used on thicker materials, the torque required for rotation is better controlled, and the combined strength is higher. The thread rolls into a self-tapping screw whose engineering standard defines the tapping screw over the forming or cutting material in the material, heat treatment, The definition of strength is higher and more explicit, making the thread rolling into self-tapping screws become a true “structural†fastener.
Drilling tail tapping screws(Self Drilling Tapping Screws) - also known as Tec, in the assembly process of all self-tapping screws, the most costly is the preparation of pre-drilling. The use of self-tapping screws, drilling must first. And the aperture must be limited. There is no need for pre-drilling and it can save costs in some respects. This is the drilling, tapping and screwing of self-tapping screws for one-time operation. The surface hardness and the hardness of the heart of the self-tapping screws are slightly higher than that of the self-tapping screws. This is because there is one more drill hole for the drill screw, and the drill screw is still required to pass through the test to test that the screw can drill and tap the thread within the specified time. The above is the design of the four main tapping screws. And the development process, there are two kinds of screws designed for special threads, the first is; High - Low Tapping Screws - used in plastic or other low-density materials. Double thread design, high thread (larger outer diameter of teeth) with a flatter and sharper thread pattern with a 30 degree thread angle. Low thread (smaller outer diameter of teeth) with a thread angle of 60 degrees, height only high Half of the thread. The combined design of the high and low threads reduces the rotational torque, improves the pull-out strength, and greatly reduces the risk of breakage of the combined workpiece. Another is used in the drywall (Drywall) assembly applications in the construction industry. With this Self-tapping screws with thread design are especially suitable for plastics, part boards and wood.
Double thread self-drilling trumpet head tapping screw(Twin Lead Self Drilling Point Tapping Screws) ─ It can be easily screwed into the drywall during assembly, drills a hole in the steel bar, and taps the female thread. The receiving end of the horn can be screwed in. It will not damage the wallpaper or plaster surface. Most of the self-tapping screws are for commercial use. For example, when the self-tapping screws are provided with a combination screw (SEMS), they can provide a more compact service. The screws, for example, have special designer for thread thickness. Then focus on the anti-loose after assembly.
2 Engineering standardsSelf-tapping screws have the following standards in terms of dimensions, mechanical properties and performance:
ANSI/ASME B18.6.4─Thread Forming And Thread Cutting Tapping Screws And Metallic Drive Screws (Inch Series)
SAE J933─Mechanical and Quality Requirements For Tapping Screws
SAE J81─Thread Rolling Screws
SAE J1237─Metric Thread Rolling Screws
SAE J78─Steel Self-Drilling Tapping Screws
FIP 1000─Tapping Screws Performance Specifications
DIN 7500─Thread Rolling Screws For ISO Metric Screws Thread
DIN 7504─Self-Drilling Tapping Screws Dimensions, Requirements And Testing
ISO 2702─Heat-Treated Steel Tapping Mechanical Properties
JIS B1055─Mechanical Properties For Heat-Treated Steel and Stainless Tapping Screws
3. Thread typeStandard self-tapping screws recognize characters, including symbols representing the thread and the tail shape. Self-tapping screws have one or two characters that represent threads to represent mechanical threads or wide threads (SPACED). If the character with identification "B" stands for Wide thread screws. No "B" stands for mechanical thread. The end of the line represents the character used to distinguish the tapping screws for thread forming, cutting, rolling or self drilling.
The mechanical thread has the same thread angle of 60 degrees as the Anglo-American uniform thread, and the same thread pitch as the fine thread. If the screw is lost or needed after disassembling, the standard thread fastener can be used instead.
The wide thread has a 60 degree thread angle but its pitch is wider, and because of its wide pitch, its thread is steeper and its thread lead is larger than the mechanical thread. There is also a thread specially designed for plastics. Its thread angle is 48 degrees, commonly known as PT tooth screws.
Thread forming tapping screws A, AB, B, BP, C, etc. have gradually been replaced by thread rolling tapping screws, so they are not recommended for new designs. AB, B, BP differ only in the tail shape, AB has a threaded taper, B has a blunt tail, BP has an unthreaded taper, the center of the spigot enters the pre-drilled hole and begins to form the thread. The thread cutting tapping screw has BF, BP, D, F, G And T and other forms, BF, BP is a wide thread, the rest is a mechanical thread.
The distinguishing characters differ in their cutting tails. Each cutting tail has a shape that can collect waste material under cutting. If a tapping screw is screwed into a blind hole (a hole that does not penetrate), its debris will remain and be sealed at the bottom of the hole. However, if it breaks into the through hole, the scrap will fall on the other side of the workpiece. Therefore, when selecting this type of tapping screw, it must be taken into consideration that the waste may cause contamination, fall into the running part or make the electronic substrate unable to Working.
All threads rolled into self-tapping screws are mechanical threads. Same as Anglo-American uniform thread coarse teeth, refer to SAE J81. For metric thread, refer to SAE J1237 and DIN 7500 regulations.
Drilling tail tapping screws have two types of cutting wide thread BSD and mechanical thread CSD. There are special thread types, including high and low double thread, and various attack drilling tails are also applicable. Because drilling tail and thread properties, drilling screws Not suitable for blind hole operations. When assembling the self-drilling screw, the drill tail must penetrate the workpiece completely to cut or shape the thread, so there will usually be some debris. If thread-type thread is used, it will not be broken. Therefore, practical considerations must be taken into account. There are provisions for SAE J78 and DIN 7504 (wide thread) for BSD and CSD tail screws.
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