1, to ensure that loading wedge load failed. Proof load and wedge products under tensile load load is assessment of critical projects in the mechanical properties of a class. And especially important for high-strength fasteners. Ensure loads are assessment provisions under the products ability to resist plastic deformation under tensile load, if the items do not meet requirements, due to preload and load functions, which may cause plastic deformation, thus reducing the pretension, the loose connection. Load test is a check bolt wedge product of tensile strength and bond strength, the indicator is not eligible in a larger work load, especially under impact load or partial load the support surfaces, broken or turned around, causing connection failures or even accidents.
2, hardness is not eligible. Hardness is assessment tight firmware mechanical performance of important index, for the performance grade products by used of material is different of, tight firmware selection Shi mechanical performance grade is important of according to, in installation and using in the to according to performance grade determine work load and installation torque, for specific of material, hardness should control in a reasonable of level, high of hardness may reduced products of resistance fatigue performance, some enterprise to improve products of strength, hardness control in high of level, caused part products exceeded.
3, decarburized layer standard. Decarburization is also a kind of project because carbon, surface hardness and strength greatly reduced serious impact on fastener contact strength and fatigue life of screw parts of the more prominent victims. The main reason causing decarburization is raw material carbon, material in the process of restructuring and decarbonization carbon and heat treatment.
4, size variance. Fasteners are common components, high interchangeability requirements, size variance will directly affect their interchangeability, influence connection strength, locking or even life. Caused size not qualified of main reasons a is process process control improper, to province material will part size control in lower near, production process in the no timely adjustment equipment, using super poor of workers mold: II is test poor, process test and factory test not strict, makes some not qualified batch clearance; three is in with measuring cannot regularly for measurement verification, even using over wear limit of gauges.

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