1. Unqualified hardness. Hardness is also an important […]
1. Unqualified hardness. Hardness is also an important index for evaluating the mechanical performance of fasteners. The materials used for 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 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, some companies control the hardness at a higher level, causing some products to exceed the standard.
2. The decarburization layer exceeds the standard. The decarburization layer is the main assessment item for the quality of fasteners. Decarburization greatly reduces the surface hardness and strength of the parts, which seriously affects the surface contact strength and fatigue life of the fasteners. The damage to the threaded parts is more prominent. The main cause of carbon is improper heat treatment process control or backward heat treatment equipment, which causes surface carbon loss.
3. The size and thread are unqualified. Fasteners are general-purpose parts and require high interchangeability. Oversize will directly affect their interchangeability, and even affect the connection strength, anti-loose performance or life. Thread is an important indicator for evaluating the effective fastening force of fasteners. The main reason for the unqualified thread is the failure of effective quality control on the size of the material during the drawing process, and the blind reduction of the screw diameter in pursuit of profit is not ruled out. Unqualified threads will reduce the connection strength, which is often one of the major hidden dangers that cause some accidents.