2h Hex Nut Manufacturers introduces the use strategy of fasteners:
1. Load, wedge load is unqualified. Load and wedge load are to assess the mechanical properties of the product under tensile load. Load is to assess the plastic deformation resistance of the product under the specified tensile load. If this index does not meet the requirements, due to the effect of pre-tightening force and working load, Plastic deformation may occur, thereby reducing the pre-tightening force and loosening the connection. The wedge load test is to assess the physical tensile strength of the bolt product and the bonding strength of the head rod. This index is unqualified. Under the action of large working load, especially impact load, or the supporting surface is subjected to eccentric load, fracture, or Turn around, causing the connection to fail, or even a safety accident.
2. The hardness is unqualified. Hardness is also an important indicator for assessing the mechanical properties of fasteners. The materials used in products of various performance levels are different. The mechanical performance level is an important basis for the selection of fasteners. The working load should be determined according to the performance level during installation and use. And the installation torque, for specific materials, the hardness should be controlled at a reasonable level. High hardness may reduce the fatigue resistance of the product. In order to improve the strength of the product, the hardness is controlled at a higher level, causing some products to exceed the standard.
3. The decarburization layer exceeds the standard. The decarburization layer is also a category 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 the fasteners, especially the harm to the threaded parts. The main cause of decarburization is decarburization of raw materials, decarburization in the process of material reforming, and decarburization in the process of product heat treatment.
4. The size is out of tolerance. Fasteners are general-purpose parts and require high interchangeability, and the size tolerance will directly affect their interchangeability and even affect the connection strength, anti-loose performance, or life. The main reason for the unqualified size is improper process control. In order to save materials, some dimensions are controlled near the lower limit, the equipment is not adjusted in time during the production process, and the out-of-tolerance tool and die are used: the second is the poor inspection, the process inspection, and the factory inspection are not strict so that some unqualified batches pass the customs; the third is Measuring tools cannot be regularly checked, and even gauges that exceed the wear limit are used.