Talking about several major problems of high-strength bolt fastener products

Talking about several major problems of high-strength bolt fastener products

With the development and progress, the quality of its industry requirements is getting higher and higher, so the requirements for fasteners are also increasing. High-strength fasteners can meet everyone's needs. At present, the development of high-strength fasteners The prospects are good, but there are still some problems with domestic high-strength fasteners. According to our understanding, there are mainly the following major problems.

1. Guaranteed load, wedge load is unqualified. Guaranteed load and wedge load are the key items for assessing the mechanical properties of the product under tensile load. Class A. It is especially important for high-strength fasteners. Guaranteed load is to assess the ability of the product to resist plastic deformation under the specified tensile load. If this index does not meet the requirements, plastic deformation may occur due to the pre-tightening force and working load, 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 a large working load, especially an impact load, or when the supporting surface is subjected to an eccentric load, fracture or Turn around, causing the connection to fail, or even a safety accident. (Guide: Strength grade of stainless steel bolts and types of stainless steel bolts)

2. The hardness is unqualified. Hardness is also an important indicator 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 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 reasons for decarburization are 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 size tolerances will directly affect their interchangeability, and even affect the connection strength, anti-loose performance or life. The main reason for the unqualified size is the 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 ineffective inspection, the process inspection and the factory inspection are not strict, which makes some unqualified batches pass the Measuring tools cannot be regularly checked, and even gauges that exceed the wear limit are used.

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