Common problems of high-strength screws

Update:09-10-2021
Summary:

With the development and progress, the industry has hig […]

With the development and progress, the industry has higher and higher requirements for high-strength screws, and the requirements for high-strength screws are also increasing. High-strength and high-strength screws can meet everyone's needs. At present, the development prospects of high-strength and high-strength screws are good, but there are still some problems with domestic high-strength and high-strength screws. It is understood that there are the following main problems.

 

1. Make sure that the load and wedge load do not meet the standard. Guaranteed load and wedge load are the key A items to evaluate the mechanical properties of the product under tensile load. It is especially important for high-strength and high-strength screws. The guaranteed load is used to evaluate the plastic deformation resistance of the product under the specified tensile load. If the 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 an assessment of the tensile strength of the bolt product and the connection strength of the head rod. This index does not meet the standard. Under the action of large load, especially under the action of impact load, or when the supporting surface is subjected to local load, the phenomenon of fracture or U-turn will occur, resulting in connection failure and even safety accidents.

 

 

2. The hardness is unqualified. Hardness is also an important index to evaluate the mechanical properties of high-strength screws. The materials used in each performance grade product are different. When selecting high-strength screws, the level of mechanical properties is an important basis. During installation and use, the working load and installation torque should be determined according to the performance level. For certain materials, the hardness should be controlled at a reasonable level, and high hardness can reduce the fatigue resistance of the product. In order to improve the strength of products, some companies have controlled their hardness at a high level, which has caused some products to exceed the standard.

 

3. The decarburization layer exceeds the standard. The decarburization layer is also a type 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 high-strength screws, especially the damage of threaded parts. The reason is decarburization of raw materials, decarburization of material modification and product heat treatment decarburization.

 

4. The size is too bad. High-strength screw is a general-purpose component, and its interchangeability requirements are high, and its size difference will directly affect its interchangeability, and even affect its connection strength, anti-loose performance or service life. The main reason for the unqualified size is improper process control. In order to save the material control part, the size is close to the lower limit, the equipment is not adjusted in time during the production process, and the out-of-tolerance mold is used. Qualified approval; third, the dose cannot be measured and verified regularly, and even the gauge that exceeds the wear limit is used.