Fasteners are a kind of Machine element that are used for fastening connection and are widely used. It is widely used in various industries, including machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments, and supplies, and is the most widely used mechanical foundation component.
Its characteristics include a variety of specifications, different performance uses, high degree of standardization, serialization, and generalization. Therefore, certain types of fasteners with existing national standards are also referred to as standard fasteners or simply as standard components.
1、 The parameters that need to be indicated for describing fasteners include: product name (standard), specification, material, strength grade, and surface treatment. For example: DIN912, M4-0.7x8, SCM435, grade 12.9, blackened.
1. Product name (standard): Note: For screws that do not have a standard and belong to non-standard parts, drawings need to be provided.
For example, DIN912, the Chinese name is: Hexagon socket head cap screw, which is the product name.
However, the most accurate approach still requires a naming standard, as GB70 is also the same product name; But there are many differences in size between the two standards.
The most influential standards in the world are: German Standard (DIN), International Standard (ISO), Chinese National Standard (GB), American Standard (ANSI), and Japanese Standard (JIS).
2. Specification, usually referred to as tooth pattern diameter * screw length.
The commonly used metric names for tooth pattern diameter include: M2, M3, M4, M5, M6, M8, M10, M12, etc;
Commonly used in the American system include: 4 # -40,6 # -32,8 # -32,10 # -24,1/4-20,5/16-18,3/8-16,1/2-13, etc.
The length of a screw refers to the effective length of the embedded object. For example, a countersunk screw is loaded with the total length, a half countersunk screw needs to add the length of half the head, while a cylindrical screw does not include the head size. For example:
For specifications, it is best to add pitch to the full name. For example, M4-0.7x8,4 refers to a tooth with an outer diameter of 4mm, 0.7 refers to a distance of 0.7mm between two tooth peaks, and 8 refers to an effective length of 8mm embedded in the loaded object.
Fundamentals of Fastener Products
1、 Functional aspects:
1. Screw torque requirements: The external hexagonal screw has a relatively larger torque, the internal hexagonal screw has a smaller torque, and the cross groove has a smaller torque (therefore, these types of screws are generally ordinary grade screws).
2. Hexagonal bolts are usually equipped with adjustable wrenches, wrenches, and open-ended wrenches. Adjustable wrenches have low assembly efficiency but are widely used. Suitable for various head bolts. The wrench has the highest efficiency, but it is not suitable for certain occasions. Only one ring wrench head can be used. Two types of hex head screws; An open-ended wrench is similar to a cross wrench, but it can be used with a long socket. The smaller the size of the hexagonal screw, the higher the angle requirement of the hexagonal bolt, otherwise the head will easily slide when subjected to (wrench) force. In order to save materials, Wenzhou people invented the hexagonal depression. The hexagonal screw of the pocket is light and lightweight, and the thickness of the head is thin, making it easy for force to slide and the head may be unscrewed.
3. The socket head screws shall be assembled with a Hex key. This has a high requirement for the inner hexagonal hole, as the wrench slips when the hole is larger and cannot be inserted when the wrench is smaller. The smaller the size of the hexagonal socket, the higher the requirements for the hole. For some large hex socket screws, as long as one of the opposite sides of the hex socket is qualified, they can be assembled normally with a wrench; For some very small hex socket screws, such as the M2 hex socket, if the wrench is inserted with a little force, the hex socket will slip, so a slightly larger side is not qualified. Therefore, the internal hexagonal screws of M2, M2.5, and M3 (especially tight set products) are prone to slipping during the assembly process.
4. Cross recessed screws are assembled with a screwdriver and do not require excessive force, so the strength is only 4.8 grade. Occasionally, high-strength screws are required, and only carburizing heat treatment is required.
