Fasteners are a type of mechanical parts used for fastening connections, and they are widely used. The characteristics of fasteners: a wide variety of specifications, different performance and uses, and a high degree of standardization, serialization, and generalization. Therefore, some people call a type of fasteners that have national (industry) standards as standard fasteners, or standard parts for short. Since the specifications, dimensions, tolerances, weight, performance, surface conditions, marking methods of each specific fastener product, as well as the specific requirements for acceptance inspection, marking and packaging, are separately stipulated in several national (industry) standards , Such as the British system, the German system and the American system.
Fasteners are the most widely used mechanical basic parts. With my country's accession to the WTO in 2001, it has entered the ranks of major international trading nations. my country's fastener products are exported to various countries in the world, and fastener products from all over the world are also pouring into the Chinese market. Fasteners, as one of the products with a large import and export volume in my country, are in line with international standards. It is of great significance to promote Chinese fastener companies to the world and to promote fastener companies to participate in international cooperation and competition in an all-round way. Strategic significance.
Fasteners are a general term for a type of mechanical parts used when two or more parts (or components) are fastened and connected into a whole. Also called standard parts on the market. It usually includes the following 12 types of parts:
1. Bolt: A type of fastener consisting of two parts, a head and a screw (cylinder with external thread). It needs to be matched with a nut to fasten and connect two parts with through holes. This type of connection is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.
2. Stud: There is no head, only a type of fastener with threads on both ends. When connecting, one end of it must be screwed into the part with internal threaded hole, the other end must pass through the part with through hole, and then the nut is screwed on, even if the two parts are tightly connected as a whole. This type of connection is called a stud connection, which is also a detachable connection. It is mainly used where one of the connected parts has a large thickness, requires a compact structure, or is not suitable for bolt connection due to frequent disassembly.
3. Screw: It is also a type of fastener composed of two parts: head and screw. According to the purpose, it can be divided into three categories: machine screws, set screws and special purpose screws. Machine screws are mainly used for a tightening connection between a part with a threaded hole and a part with a through hole, without the need for a nut to fit (this connection form is called a screw connection, which is also a detachable connection; Cooperate with the nut, used for the fastening connection between two parts with through holes.) The set screw is mainly used to fix the relative position between the two parts. Special purpose screws such as eyebolts are used for lifting parts.
4. Nut: with internal threaded hole, the shape is generally flat hexagonal column, there are also flat square column or flat cylinder, with bolts, studs or machine screws, used to fasten the connection of two parts, so that It becomes a whole.
5. Self-tapping screws: similar to machine screws, but the thread on the screw is a special self-tapping screw thread. It is used to fasten and connect two thin metal components into one piece. Small holes need to be made in the component in advance. Because this kind of screw has high hardness, it can be directly screwed into the hole of the component. Form a responsive internal thread. This type of connection is also a detachable connection.
6. Wood screw: It is also similar to machine screw, but the thread on the screw is a special wood screw with ribs, which can be directly screwed into the wooden component (or part) to use a metal (or non-metal) with a through hole. The parts are firmly connected to a wooden component. This connection is also a detachable connection.
7. Washer: A type of fastener with an oblate ring shape. It is placed between the supporting surface of bolts, screws or nuts and the surface of the connected parts, which increases the contact surface area of the connected parts, reduces the pressure per unit area and protects the surface of the connected parts from damage; another type of elastic washer, It can also play a role in preventing the nut from loosening.
8. Retaining ring: for installing in the shaft groove or hole groove of the machine, it plays a role in preventing the parts on the shaft or hole from moving left and right.
9. Pin: Mainly used for parts positioning, and some can also be used for connecting parts, fixing parts, transmitting power or locking other fasteners.
10. Rivet: A type of fastener composed of two parts, a head and a nail shaft, used to fasten and connect two parts (or components) with through holes to make them into a whole. This type of connection is called rivet connection, or riveting for short. Belong to and non-detachable connection. Because to separate the two parts connected together, the rivets on the parts must be broken.
11. Assemblies and connection pairs: Assemblies refer to a type of fastener supplied in combination, such as a combination of machine screws (or bolts, self-supplied screws) and flat washers (or spring washers, lock washers); connection; The secondary refers to a type of fastener supplied by a combination of a certain special bolt, nut and washer, such as a high-strength large hexagonal head bolt connection pair for steel structures.
12. Welding nails: Because of the heterogeneous fasteners composed of light energy and nail heads (or no nail heads), they are fixedly connected to a part (or component) by welding so as to be connected with other parts.
Each fastener product must involve some standards in several aspects:
1) Standards for the size of fastener products: specify the content of the basic size of the product; for the threaded product, it also includes the basic size of the thread, thread end, shoulder distance, undercut and chamfer, and the end of external threaded parts Dimensions and other aspects.
2) Standards on technical conditions of fastener products. Specifically, it includes the following standards:
a) Standards for fastener product tolerances: specify product size tolerances and geometric tolerances.
b) Mechanical performance standards of fastener products: specify the marking method of product mechanical performance levels and the content of mechanical performance items and requirements; some fastener products will change this content to product material performance or work performance Aspect content.
c) Standards for surface defects of fastener products: specify the types and specific requirements of product surface defects.
d) Surface treatment standards of fastener products: specify the types of product surface treatments and specific requirements.
e) Fastener product testing standards: specify the content of the above-mentioned various performance requirements testing.
3) Fastener product acceptance inspection, marking and packaging standards: specify the qualified quality level and sampling plan of the random inspection items during the factory acceptance of the product, as well as the content of the product marking method and packaging requirements.
4) Standards on the marking method of fastener products: specify the complete marking method and simplified marking method of the product.
5) Other standards of fasteners: such as the standard of fastener terminology, the standard of fastener product weight, etc.
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