Fastener

　　Fasteners, also known as standard parts in the market, are mechanical elements that can mechanically hold two or more components together or bond together. It is characterized by a wide variety of specifications, different performance and use, and a high degree of standardization, serialization and generalization. Fasteners are the most widely used mechanical base parts and are in high demand. Fasteners can also be used to keep containers (e.g., bags, boxes) closed, possibly by keeping the opening of the element tight and placing a lid on the container. There are also specially designed elements like bread clips, which do not permanently seal the container, and the user can still open the container without destroying the fastener. Fasteners, fasteners are a type of mechanical parts that are used for fastening and connection and are widely used, and a wide range of fasteners can be seen in a wide range of machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments and supplies.

Basic introduction

concept

A general term for a kind of mechanical parts used when fastening two or more parts (or components) to form a whole.

application

Fasteners are a kind of mechanical parts which are widely used for fastening connection. All kinds of fasteners can be seen on all kinds of machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, meters and supplies. It is characterized by a wide variety of specifications, different performances and uses, and a high degree of standardization, serialization and generalization. Therefore, some people call a class of fasteners with existing national standards standard fasteners, or standard parts for short. Fasteners are the most widely used mechanical basic parts. With China's accession to WTO in 2001, it has stepped into the ranks of major international trade countries. China's fastener products are exported to all countries in the world in large quantities, and fastener products from all countries in the world are constantly flooding into the Chinese market. As one of the products with a large import and export volume in China, it is of great practical and strategic significance for Chinese fastener enterprises to go global and participate in international cooperation and competition. Due to the specification, size, tolerance, weight, performance, surface condition, marking method of each specific fastener product

component

It usually includes the following 12 types of parts:

1. Bolt: A type of fastener consisting of a head and a screw (a cylinder with external threads), which needs to be matched with a nut and used to fasten and connect two parts with through holes. This kind 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 detachable.

2. Stud: a kind of fastener with no head and only external threads at both ends. When connecting, one end of it must be screwed into the part with internal thread hole, and the other end passes through the part with through hole, and then the nut is screwed on, even if the two parts are firmly connected into a whole. This connection is called stud connection, which is also a detachable connection. It is mainly used in situations 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 kind of fastener composed of head and screw, which can be divided into three categories according to its use: machine screw, set screw and special purpose screw. The machine is mainly used for the fastening connection between a part with a tight threaded hole and a part with a through hole, without nut fit (this connection form is called screw connection, which also belongs to detachable connection; It can also be matched with nuts for fastening connection between two parts with through holes. ) Set screws are mainly used to fix the relative position between two parts. Special purpose screws, such as eyebolts, are used for hoisting parts.

4. Nut: with internal threaded hole, the shape is generally flat hexagonal column, but also flat square column or flat cylinder. It is matched with bolts, studs or machine screws to fasten and connect two parts to make them a whole.

5. Self-tapping screw: similar to machine screw, but the thread on the screw is a special thread for self-tapping screw. It is used for fastening and connecting two thin metal components to form a whole. Small holes need to be made in the components in advance. Because of its high hardness, this kind of screw can be directly screwed into the holes of the components, so that corresponding internal threads are formed in the components. This 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 thread for wood screw, which can be directly screwed into a wooden component (or part) to firmly connect a metal (or nonmetal) part with a through hole with a wooden component. This connection is also a detachable connection.

7. Washer: a kind of fastener with oblate ring shape. It is placed between the supporting surface of bolts, screws or nuts and the surface of connected parts, and plays a role in increasing the contact surface area of connected parts, reducing the pressure per unit area and protecting the surface of connected parts from being damaged; Another kind of elastic washer can also prevent the nut from loosening.

8. Retaining ring: it is installed in the shaft groove or hole groove of machinery and equipment, and plays a role in preventing the parts on the shaft or hole from moving left and right.

9. Pin: mainly used for positioning parts, and some can also be used for connecting parts, fixing parts, transmitting power or locking other fasteners.

10. Rivet: a kind of fastener consisting of head and shank, which is used to fasten and connect two parts (or components) with through holes to make them a whole. This connection is called rivet connection, or riveting for short. It is non-detachable. Because to separate the two connected parts, the rivets on the parts must be broken.

11. Assemblies and connecting pairs: Assemblies refer to a kind of fasteners supplied in combination, for example, some machine screws (or bolts, self-supplied screws) are supplied in combination with flat washers (or spring washers, locking washers); Connection pair refers to a kind of fastener which is supplied by combining a special bolt, nut and washer, such as high-strength large hexagon head bolt connection pair for steel structure.

12. Welding nail: because of the heterogeneous fastener composed of light energy and nail head (or no nail head), it is fixedly connected to a part (or component) by welding method, so as to connect with other parts.

13. wire thread insert: wire thread insert is a new type of threaded connection element, which is refined from high-strength and high-precision corrosion-resistant diamond wire. Such as a spring, which is installed in a specific screw hole of the base, and its inner surface forms a standard thread. When it is matched with a screw (bolt), it can obviously improve the strength and wear resistance of the thread connection; Especially on low-strength materials such as aluminum, magnesium, cast iron and plastic. The locking type is to add one or several locking rings on the basis of the ordinary type. It is suggested that wire thread insert be embedded in the threads of low-strength engineering materials such as aluminum, magnesium alloy, cast iron, glass fiber reinforced plastic, plastic, etc., which can form standard M and MJ threads, have the functions of continuous strength, impact resistance and wear resistance, and can disperse stress to protect the base threads, thus greatly prolonging the service life of the base. At the same time, the stress condition of the thread is improved, the elastic connection is formed, the pitch and half angle error between the inner thread and the outer thread are eliminated, the load on the thread is evenly distributed, the base thread is protected from being damaged, and the service life is prolonged.

Lock up

Fasteners include bolts, studs, screws, nuts, washers and pins. Locking or biting often occurs on fasteners made of stainless steel, aluminum alloy and titanium alloy. These metal alloys have anti-corrosion properties, and when the surface is damaged, a thin oxide layer will be formed on the metal surface to prevent further corrosion. When the stainless steel fastener is locked, the pressure and heat generated between the teeth lines will destroy this oxide layer, which will block or shear the metal threads, and then cause adhesion. When this phenomenon continues to occur, the stainless steel fasteners will be completely locked, and can no longer be removed or locked. Usually, this series of blocking-shearing-sticking-locking actions takes place in just a few seconds, so a correct understanding of the use of such fasteners can prevent this phenomenon. Before use, confirm whether the mechanical properties of the product can meet the use requirements, such as the tensile strength of the screw and the guaranteed load of the nut. The length of the screw should be selected appropriately, and it shall be subject to 1-2 pitches of the nut exposed after tightening. It is recommended to use butter, molybdenum disulfide, mica, graphite or talcum powder for lubrication. Generally, wax dipping is used for lubrication and anti-locking. A, the speed and strength of screwing in should be appropriate, not too fast or too large. Torque wrenches or socket wrenches should be used as much as possible, and adjustable wrench or electric wrenches should be avoided. If the speed is too fast, the temperature will rise rapidly, resulting in locking.