With the development and progress, the quality of its i […]
With the development and progress, the quality of its industry requirements is getting higher and higher, so the requirements for fasteners are constantly increasing at the same time, and high-strength fasteners can meet everyone's needs.
1. Guarantee radius, wedge load is unqualified. Ensuring thickness and wedge load is the key item of category A for evaluating the mechanical performance of the product under the action of the tensile screw. It is especially important for high-strength fasteners. If the plastic deformation resistance of the product under the thread is not up to the requirements, due to the action of the pre-tightening force and the working screw, plastic deformation may occur, thereby reducing the pre-tightening force and loosening the connection. The tensile strength and the bonding strength of the head bar are unqualified, and the work decomposition of the fracture, especially under the action of the impact bias or the supporting surface, will break or turn around, causing the connection to fail, and even safety accident.
2. The hardness is unqualified. Hardness is also an important index for evaluating the mechanical performance of fasteners. The materials used in products of various performance levels are different. The mechanical performance level is an important basis when replacing the fasteners. The performance level must be followed during installation and use. Pressure and installation budget. 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 fastener, especially the damage to the thread height. The primary 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 higher interchangeability. Oversized dimensions will directly affect their interchangeability, and even affect the connection strength, anti-loose performance or life span. The cause of the unqualified size itself is the improper process control. In order to save materials, some sizes 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 poor inspection, processing inspection and factory inspection. Strictness has allowed some unqualified batches to pass; third, the measuring tools cannot be regularly checked and even used gauges that exceed the wear limit.