High Strength Fastener Product Quality Analysis

In the past ten years, China's fastener industry has undergone a period of structural adjustment. The structure of enterprises and products has undergone tremendous changes. The number of high-strength fastener manufacturers has increased, and the market competition has become fierce, prompting companies to improve product quality and develop new products. Products, the use of new technologies, new processes, new equipment, new materials, reduce production costs to occupy the market, the overall quality of the industry has improved, China has become a major fastener manufacturing country. From the quality inspection results of high-strength fastener products, the qualified rate of spot checks has been at a level of 60% to 80% for many years. The problems reflected are relatively concentrated. The level of fastener products in China needs to be improved and the quality is not optimistic. There is still a big gap between becoming a strong manufacturing country for fasteners.

The main problems found in spot checks are:

(1) Guaranteed load, failed wedge load. The guaranteed load and the wedge load are the key items for evaluating the mechanical properties of the product under tension loading (Type A), which is particularly important for high-strength fasteners. The guaranteed load is the ability of the product to resist plastic deformation under the specified tensile load. If the index of the item fails to meet the requirements, plastic deformation may occur due to the effects of preload and working load, thus reducing the pre-tightening force and loosening the connection. . The wedge load test is to evaluate the tensile strength of the bolted product and the strength of the head bar. The index of the project is unqualified. When the working load is large or the support surface is subjected to eccentric loading, it will break or turn, causing the connection to fail. There was even a security incident.

(2) The hardness is not qualified. Hardness is also an important indicator for evaluating the mechanical properties of fasteners. The materials used for each performance grade product are different. When the fasteners are selected, the mechanical performance grade is an important basis, and the working load must be determined according to the performance level during installation and use. And installation torque, for specific materials, hardness should be controlled at a reasonable level, high hardness may reduce the product's fatigue resistance, some companies in order to improve product strength, hardness control at a higher level, resulting in some products exceeded

(3) The decarburized layer exceeded the standard. The decarburization layer is also a type A project. Due to decarburization, the surface hardness and strength of the components are greatly reduced, which seriously affects the surface contact strength and fatigue life of the fasteners, especially the damage to the threaded parts. The main causes of decarburization are decarburization of raw materials and decarburization during heat treatment of products.

(4) The size is poor. Fasteners are universal components and require high interchangeability. Exceeding the size of the fasteners will directly affect its interchangeability, and even affect the connection strength, anti-loosening performance or life. One of the main reasons for the unqualified dimension is improper control of the process. In order to save part of the material, the size is controlled near the lower limit. During the production process, equipment is not adjusted in time, and an over-weaver tool is used. The second is poor inspection, process inspection and factory inspection. Lax, so that some unqualified batches clearance; Third, in the use of measuring instruments can not be regularly measured and even exceeded the wear limit of the gauge.

At present, the fastener sales market is still relatively confusing. Some distribution units only care about the immediate interests and do not pay attention to the quality of products. They simply rely on the reduction of product prices to compete for the market, and even sell counterfeit and shoddy products. This has become a breeding ground for poor performance products.

Standard Parts Overview

Standard parts are also known in the market as fasteners. It is used as a kind of mechanical parts for fastening and connection, and it is widely used. The characteristics of fasteners: variety of specifications, performance and use are different, and the degree of standardization, serialization and generalization is extremely high. Therefore, it is also known as a standard fastener for a type of fastener that already has a national (industry) standard, or simply a standard part.

The specific requirements for each specific fastener product's specifications, dimensions, tolerances, weights, performance, surface conditions, marking methods, and inspection, marking, and packaging items are specified separately in several national (industry) standards. For example, there are English, German and American systems.

Fasteners are the most widely used mechanical basic parts. With China's accession to the WTO in 2001 and entering the ranks of major countries in international trade. Fast fastener products that are exported to fasteners in many countries in the world and countries in the world are also pouring into the Chinese market. Fasteners, as one of the products with a large volume of imports and exports in China, are in line with international standards. They are of great significance to the promotion of China's fastener companies to the world and the promotion of the full participation of fastener companies in international cooperation and competition. Strategic significance.

Fasteners are the general term for a type of mechanical part used when two or more parts (or components) are fastened together to form a whole, and are also called standard parts in the market.

Standard parts include the following 12 types of parts:

1. Bolt: A type of fastener consisting of a head and a threaded rod (cylindrical body with external threads), which is required to cooperate with a nut and is used to fasten two parts with through holes. This type of connection is called a bolted 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: A type of fastener without a head that is only threaded at both ends. When connected, one end must be screwed into the part with the internally threaded hole and the other end through the part with the through hole, and then the nut is screwed on even if the two parts are fastened together in one piece. This type of connection is called a stud connection and it is also a detachable connection. It is mainly used for occasions when one of the connected parts has a large thickness, requires a compact structure, or is frequently used for bolting because of frequent disassembly.

3. Screw: It is also a type of fastener composed of two parts of the head and the screw. It can be divided into three categories according to the purpose: machine screws, set screws and special purpose screws. The machine screw is mainly used for a part with a tight threaded hole, and a fastening connection with a part with a through hole, and does not require a nut to fit (this type of connection is called a screw connection and is also a detachable connection; it can also be Fits with a nut for fastening connections between two parts with through holes.) Set screws are used to fix the relative position between two parts. Special-purpose screws such as eyebolts are used for lifting parts.

4. Nuts: With internal threaded holes, the shape is generally flat hexagonal, cylindrical or flat cylindrical, with bolts, studs or machine screws, used to fasten two parts, so that It becomes a whole. Such as the butterfly nut.

5. Self-tapping screws: Similar to machine screws, but the thread on the screw is a special thread for tapping screws. It is used to fasten and connect two thin metal components into a single piece. Small holes need to be made in advance on the components. Because the screws have a high hardness, they can be screwed directly into the holes of the component and make the components In response to the formation of internal threads. This type of connection is also a detachable connection.

6. Wood screws: similar to machine screws, but the thread on the screw is a special wood screw with a rib that can be screwed directly into a wooden member (or part) for the metal (or non-metal) with a through hole The parts are fastened together with a wooden member. This connection is also a detachable connection.

7. Gasket: A type of fastener that is oblate in shape. Placed between the supporting surface of the bolt, screw or nut and the surface of the connecting part, play the role of increasing the contact surface area of ​​the connected parts, reducing the pressure per unit area and protecting the surface of the connected parts from being damaged; another type of elastic gasket, Can also play a role in preventing the nut from loosening.

8. Retaining ring: It is installed in the shaft groove or hole groove of the machine and equipment and plays the role of blocking the left and right movement of the part on the shaft or hole.

9. Pin: mainly used for positioning of parts, and some can also be used to connect parts, fix parts, transmit power or lock other fasteners.

10. Rivet: A type of fastener consisting of a head and a shank that is used to fasten parts (or components) that connect two through-holes to make it a unitary piece. This type of connection is called rivet connection, or simply riveting. Generic and non-detachable connection. Because the two parts that are connected together must be separated, the rivet on the part must be destroyed.

11. Assemblies and couplings: Assemblies are a type of fasteners that are supplied in combination, such as the combination of a machine screw (or bolt, self-provided screw) with a flat washer (or spring washer, lock washer); Sub-finger A type of fastener that supplies a special combination of bolts, nuts, and washers, such as high-strength large hex head bolts for steel structures.

12. Weld nails: Because of the different types of fasteners made up of light energy and nail heads (or no nail heads), they are fixedly attached to a part (or component) by welding so that they can be connected to other parts.