With the development and progress, the industry need […]
With the development and progress, the industry needs more and more high - quality, so the fastener requirements are constantly improve, high strength fasteners can meet the needs of the people, at present, the high strength fasteners good development prospects, but the domestic high strength fasteners still exist some problems, according to the understanding, there are the following big problem.
1, Ensure the load, wedge load is not qualified. It is important to ensure the load and wedge load to evaluate the mechanical performance of the product under tension load. Ensure the load is the assessment of the resistance to plastic deformation under tensile load under the provisions of the product, if the index is not up to the requirements, the pretightening force and work load, may produce plastic deformation, thereby reducing the preload, the loose connection. Wedge load test is a kind of bolt tensile strength assessment products and head binding strength, the index is not qualified, in greater work load, especially the bias load impact or support surface by, or turn fault, causing the connection failure, even the occurrence of safety accidents.
2, Hardness unqualified. The mechanical properties of hardness is an important indicator of assessment of fasteners, is different for each performance level of products used in the selection of materials, fasteners, mechanical performance level is an important basis in the installation and use in accordance with the level of performance to determine the working load and installation torque for a specific material, the hardness should be controlled in a reasonable level, high hardness may reduce the fatigue resistance of products, some enterprises in order to improve product strength, hardness control at a high level, resulting in some of the products exceed the standard.
3, Decarburization layer exceeded. The decarburization layer is also a class a project. Because of 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 for the thread parts. The main causes of decarburization are decarburization of raw materials, decarburization in the process of material reform and decarburization during the process of heat treatment.
4, The size of ultra poor. The fastener is general parts, interchangeability requirements for high dimension deviation will directly affect the interchangeability, and even affect the joint strength, anti loose performance or life. The main cause is the improper size up a process control, in order to save material will be part of size control in the lower limit near the production process is not timely adjustment the use of equipment, tooling tolerance: two inspection is ineffective, process inspection and factory inspection is not strict, so that some unqualified batch pass; three is the verification in measuring not regularly, even more than the amount of wear limit gauge.http://www.lwhardware.com/