Several problems of high strength fastener products

With the development and progress of the industry, the demand quality of fasteners is higher and higher, and the requirements for fasteners are also constantly improving. High strength fasteners can meet the needs of everyone. At present, the development prospect of high-strength fasteners is good, but there are still some problems in domestic high-strength fasteners. As far as we know, there are mainly the following problems.
One. Guarantee load and wedge load are unqualified. Guarantee load and wedge load are the grade a key points to evaluate the mechanical properties of products under tensile load. This is particularly important for high strength fasteners. Guarantee load is to evaluate the ability of the product to resist plastic deformation under specified tensile load. If the index fails to meet the requirements, the preload and working load may cause plastic deformation, which will reduce the preload and make the connection loose. Wedge load test is to test the tensile strength and bond strength of bolt products. This index is not qualified. Under the action of large working load, especially under impact load or local load of bearing surface, fracture or turning occurs, which leads to connection failure and even safety accident.
Two. The hardness is unqualified. Hardness is also an important index to evaluate the mechanical properties of fasteners. For products with different performance levels, the materials used are different. Mechanical property level is an important basis for fastener selection. In the process of installation and use, the working load and installation torque should be determined according to 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 the strength of products. Some enterprises control the hardness at a higher level, resulting in some products exceeding the standard.

3. The decarburization layer exceeds the standard. Decarbonization 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 of threaded parts. The main reasons for decarbonization are raw material decarbonization, material transformation decarburization and product heat treatment decarburization.
4. Dimension out of tolerance. Fastener is a general part with high interchangeability. Dimension out of tolerance will directly affect its interchangeability, even its connection strength, loose resistance or service life. The main reasons for the unqualified size are as follows: first, improper process control, in order to save materials, the size of the control part is close to the lower limit, the equipment is not adjusted in time in the production process, and the out of tolerance tooling is used; second, the inspection is not qualified, and the process inspection and factory inspection are not strict, so that some unqualified batches pass the inspection; third, the measuring tools in use can not be regularly measured and verified, or even exceed the grinding Wear limit using abrasive tools.
The company's main business: high strength bolt, high strength nut, steel structure bolt, steel structure nut, grid sealing plate, grid bolt, etc.