Several major issues with high-strength fastener products

Several major issues with high-strength fastener products

With the development and progress of the industry, the demand for high-quality fasteners is also increasing, and the requirements for fasteners are also constantly increasing. High strength fasteners can meet everyone's needs. At present, the development prospects of high-strength fasteners are promising, but there are still some problems with domestically produced high-strength fasteners. As far as we know, there are mainly the following issues.

One. Ensure that the load and wedge load are not qualified. The guarantee load and wedge load are the A-level key points for evaluating the mechanical properties of products under tensile load. This is particularly important for high-strength fasteners. Guarantee load is the ability to evaluate the product's resistance to plastic deformation under specified tensile loads. If the indicators do not meet the requirements, the preload and working load may cause plastic deformation, thereby reducing the preload and loosening the connection. The wedge load test is used to test the tensile strength and head reinforcement bonding strength of bolt products. This index is not qualified. Under the action of large working loads, especially impact loads or local loads on the bearing surface, fracture or turning occurs, leading to connection failure and even safety accidents.

II. The hardness is not qualified. Hardness is also an important indicator for evaluating the mechanical properties of fasteners. For products with different performance levels, the materials used are different. The level of mechanical performance is an important basis for selecting fasteners. During installation and use, the working load and installation torque should be determined based on the performance level. For specific materials, the hardness should be controlled at a reasonable level. High hardness may reduce the hardness of products to improve their strength, and some companies control the hardness at a higher level, resulting in some products exceeding the standard.

III. The decarburization layer exceeds the standard. The decarburization layer is also a Class A project. Due to decarburization, the surface hardness and strength of the parts are greatly reduced, which seriously affects the surface contact strength and fatigue life of fasteners, especially the damage to threaded parts. The main reasons for decarbonization are raw material decarbonization, material transformation decarbonization, and product heat treatment decarbonization.

Four. The size exceeds the tolerance. Fasteners are universal parts with high interchangeability requirements. The size deviation will directly affect its interchangeability, and even affect its connection strength, anti loosening performance, or service life. The main reasons for unqualified dimensions are: firstly, improper process control. In order to save materials, some dimensions were controlled to approach the lower limit, and equipment was not adjusted in a timely manner during the production process, resulting in the use of out of tolerance tooling; The second is that the inspection is not qualified, and the process inspection and factory inspection are not strict, causing some unqualified batches to pass the inspection; The third reason is that the measuring tools in use cannot be regularly calibrated, and even exceed the wear limit when using abrasive tools.

The company's main products include high-strength bolts, high-strength nuts, steel structural bolts, steel structural nuts, grid sealing plates, grid bolts, etc.