Working principle of self-tapping screws

Update:08-06-2020
Summary:

The self-tapping screw is a screw with a drill bit. It […]

The self-tapping screw is a screw with a drill bit. It is completed with a special electric tool for drilling, tapping, fixing and locking at one time. But the general screw must have the processed screw hole to screw in.

Self-tapping screw structure
Each self-tapping screw is composed of three parts: the head, the shank and the end of the shank. The composition of each self-tapping screw has four major elements: head shape, wrenching method, thread type, and end form.

1 Head shape

Various head shapes. There are round head (semi-round head), flat round head, round head flange (with pad), flat round head flange (with pad), pan head, pan head flange (with pad), countersunk head, semi countersunk head, Cylindrical head, spherical cylindrical head, trumpet head, hexagon head, hexagon flange head, hexagon flange (with pad) head, etc.

2 wrenching method

The wrenching method refers to the method of twisting the head of the screw when installing and tightening the screw. The basic methods include two kinds of external wrenching and internal wrenching. In general, the torque allowed by an external wrench is greater than any form of internal wrench (inner groove). Outer wrench: Hexagon, Hexagon flange face, Hexagon flange, Hexagonal flower shape, etc.; Inner wrench: Slotted groove, cross groove H type, cross groove Z type, cross groove F type, square groove, composite groove, inner flower Key, inner hexagon flower shape, inner triangle, inner hexagon, inner 12 angle, clutch groove, six-blade groove, high torque cross groove, etc.

3 Thread types

There are many kinds of threads, including self-tapping threads (wide-thread threads), machine threads (common threads), drywall nail threads, fiberboard nail threads, and some other special threads. In addition, the thread can be divided into single lead (single head), double lead (double head), multi lead (multi head) and high and low tooth double head thread.

4-terminal form

There are two types of end forms: cone end and flat end. However, according to the needs of use, grooves, grooves, cuts or parts similar to the shape of a drill can be processed at the screw-in part of the end. In some standards, the same is the tapered end or flat end, there are also different forms such as round head end.

Self-tapping screw type

According to the development and evolution of self-tapping screws, we believe that there are the following types of self-tapping screws:

1 ordinary self-tapping screws

The thread is "self-tapping thread", also known as "wide thread". The surface is mostly electroplated.

2 cut self-tapping screws

The Chinese standard is called "self-tapping screw scraping end", the thread is self-tapping thread or machine thread, and the cross groove is also "H" type. There are several types of self-cutting self-tapping screws: cross recessed pan head self-cutting self-tapping screws, and cross recessed countersunk head self-cutting self-tapping screws. Cross recessed countersunk head self-cutting self-tapping screws, hexagon head self-cutting self-tapping screws.

3Self-tapping self-tapping screws (self-tapping locking screws)

The thread of self-extruded self-tapping screws is generally machine thread, and self-tapping threads are rarely used. In the wrenching mode, in order to ensure the use of high-speed automatic assembly wrenches, slotting is generally not recommended. The screw cross section of the self-extruded self-tapping screw is triangular. So it is also called triangle screw.

4 self-tapping screws (self-drilling screws)

The thread of self-drilling self-tapping screws, Chinese, German and international standards are self-tapping threads. In the American ASME and SAE standards, BSD self-drilling self-tapping screws are self-tapping threads, and CSD self-drilling self-tapping screws are machine threads. Self-drilling self-tapping screws are not recommended to use "slotted" and "common hexagon head".

5 Metal drive screw (metal strong attack screw)

The thread of the metal drive screw is multi-start and has a special thread with a certain helix angle. Only the American standard has metal drive screws, but not my country and German standards.

6 Wallboard self-tapping screws (dry wall screws)

The white tapping screws for the wallboard are trumpet head, cross groove (H type), special thread with 60° tooth angle, and the surface is mostly phosphated (phosphated).

7 Fiberboard nails

The cross groove is Z-shaped, and the surface treatment is mostly electroplating. There are several types of fiberboard nails: countersunk head, double countersunk head fiberboard nails, pan head, pan head flange (with pad) fiberboard nail, semi countersunk head, semi countersunk head flange (with pad) fiberboard nail.

8 combination self-tapping screws

Common white tapping screws, self-cutting white tapping screws, self-drilling self-tapping screws, etc. combined with flat washers and elastic washers (including spring washers and elastic lock washers) are self-tapping screws.

9 Other self-tapping screw types

High- and low-tap double-lead self-tapping screws, thick and fine teeth (different pitch) thread self-tapping screws, self-tapping screws with threads coated with sealing material (fall-resistant), various compound groove self-tapping screws, other special design Self-tapping screws, etc.

In short, there are many types of self-tapping screws. With the development of production and the progress of technology, new materials, new structures and new thread forms, new types of self-tapping screws will continue to appear.