Self-tapping screw structure

Each self-tapping screw is composed of three parts: the head, the rod and the end of the rod. Each self - tapping screw is composed of four elements: head shape, screw type, thread type, end form

1. Head shape

Heads come in all shapes and sizes. There are round head (semicircle head), flat head, round head flange (with pad), flat head flange (with pad), pan head, pan head flange (with pad), countersunk head, semi-sunk head, cylindrical head, spherical cylindrical head, horn head, hexagon head, hexagon flange head, hexagon flange and so on.

ASME B86.3 describes the standard head shapes and sizes of 13 self-tapping screws, and explains the head shapes.

(1) head of common self-tapping screw and self-cutting self-tapping screw. Among the 13 types of common self-tapping screws and self-cutting self-tapping screws, the following 5 types (countersunk head, semi-sunk head, pan head, hexagon head and hexagon flange head) are the most important, which together account for about 90% of the total amount of self-tapping screws. In application, one of the five types of heads should be considered first. The other five head types (clear root countersunk head, neat countersunk head, clear root semi-sunk head, neat semi-sunk head and spherical cylindrical head) are secondary and can be used as the second choice. The other three types of head (oblate, round and 100 countersunk) are not recommended for the new design because they can all be replaced by other heads with similar advantages. If pan head can replace flat head and round head, countersunk head instead of 100 countersunk head.

(2) head type of self-squeezing self-tapping screw

Self - tapping screws have the same head type as normal self - tapping screws and self - cutting self - tapping screws. However, in the selection of countersunk head, semi-countersunk head pan head, hexagon head and hexagon flange head in addition to the five commonly used head type other head, must be carefully considered. Self - extrusion self - tapping screw mainly to the above several types of head.

(3) self-drilling and self-tapping screws

Self - drilling self - tapping screw commonly used head is: countersunk head, half countersunk head, pan head and hexagon flange head. Because the drilling operation requires the end pressure is also required to support the head shape of the rotary, such as countersunk head, countersunk head and pan head cross groove or hexagon flange head flange, hexagon head is not. Although the us national standard recognizes only 13 types of head as standard head, many special head products are also available on the market.

As mentioned above, the self - tapping screw (dry wall screw) horn head. Other semi - round head flange, large flat head flange, high hexagon flange and a variety of after assembly lock screw design, can query the screw maker's data and introduction.

2. Plate twist mode

Screw-down mode refers to the way to twist the screw head when installing and fastening the screw. There are two basic modes: external screw-down and internal screw-down. External screw-down is greater than any form of internal screw-down (internal groove). External rotation: hexagon, hexagon flange hexagon flange, hexagon pattern, etc.; Internal wrench: one groove, cross groove H (Phillips), cross groove Z (Pozidriv), cross groove F (Frearson), square groove (Scrulox), compound groove, internal spline, inner hexagon (club groove), inner triangle, inner hexagon, inner 12 Angle, clutch groove, six blade groove, high torque cross groove, etc.

(1) external rotation: hexagon head and hexagon flange head are external rotation. For special orders, hexagon head and hexagon flange head products may be slotted (monochrome) or cross slotted.

(2) internal wrenching: internal wrenching includes slotting (one word groove), cross groove and square groove.

Slotting (slotted) is a form of grooving that is standard for all head types of slotted screws except for fine countersunk and fine semi-sunk heads. The ASME B18.6.3 standard specifies the slotted dimensions for each type of head. Slotted heads are most suitable for manual assembly, but not for semi-automatic or fully automatic assembly.

Slotting processing by groove or forging forming, these two methods can be processed into slot head, forging forming because of the need for edge crinkle, difficult to accurately measure the depth of the groove; And the more important is to reduce the contact, meshing area of the rotary. Forging grooves on the round head can keep the contact area of the spinner intact. However, the forming pressure often leads to the increase of the diameter of the head perpendicular to the groove and the decrease of the diameter of the head parallel to the groove. For some sizes and head shapes, it is difficult to keep the head diameter within the specified maximum/minimum limit, that is, to maintain the roundness of the head shape.

In order to meet the need of automatic assembly in large quantities, a new internal rotation structure of cross groove was developed. The main purpose of these structures is to allow the rotary head and tools to be easily accessible at high speed and to deliver high torque in a stable screwing groove. At present, most of the cross - groove structures are welcomed to some extent. ASME B18.6.3 identifies three types as standard structures. These three types are cross structures, marked as follows: type I non-phillips cross groove (Phillips for short :H type cross groove), type IA Pozidriv (Pozidriv for short :Z type cross groove, commonly known as: rice type groove). Type Ⅱ Buddha Luo Erxun cross slot (Frearson F type cross slot). The dimensions of these cross grooves are all listed in the ASME B18.6.3 standard

Ⅱ type is the cross slot first appeared, followed by type I, then the type 1 a (is actually a modified type I). Is currently the most widely used type 1 and type 1 a, Ⅱ demand at least

Tusk rollo Knox (Scrulox) four square groove type (also called Ⅲ), is very popular in Canada. In the United States, especially in the furniture manufacturing and shipbuilding industries are also widely used. Square groove can effectively deliver high torque, and the spinner does not slip or arch out. However, the square groove is not as suitable for high speed assembly as the cross groove.

Currently, some other grooves that can be used are hexagon socket, clutch groove, six blade groove, Supadriv(type IA improvement

Type), high torque grooves and quad-airfoil grooves (torg-set). The latter two are more widely used in high strength aviation fasteners. So far, except for the I type, IA and Ⅱ these other grooves have not an ASME included in formal standards. Their full size and performance data can be obtained from the person who originally issued or obtained the license.

3. Type of thread

There are a wide variety of threads, including self-tapping threads (wide-tooth threads), machine threads (normal threads), dry-wall screw threads, fiberboard screw threads, and other special threads. In addition, threads can be divided into single lead (single head), double lead (double head), multiple lead (multiple head) and high and low tooth double head threads.

4. End form

There are two terminal forms: cone end and cone end. But according to the needs of use, in the end of the rotary part, can be machined with cutting function of the groove, groove, cut or similar to the shape of the part of the drill. In some standards, the same cone end or flat end, there are different forms such as round head end.

It can be seen from the above introduction: since tapping screw head shape, screw type, thread type and end form, have a variety of changes. They can be combined with each other to produce many different products belonging to the category of self-tapping screws.