With the development and progress, the demanding qual […]
With the development and progress, the demanding quality of its industry is getting higher and higher. Therefore, the demand for bolts is also increasing. High-strength bolts can meet everyone's needs. At present, the development prospect of high-strength bolts is good, but at present, some bolt factory in China also have many problems when making this product.
First, the size is out of tolerance. Bolts are general-purpose parts with high interchangeability requirements. The excessive size difference will directly affect interchangeability, even affect connection strength, anti-loosening performance or service life. One of the main reasons for unqualified size is improper process control. In order to save materials, some sizes are controlled near the lower limit, equipment is not timely adjusted in the production process, and excessive tool is used. The other is ineffective inspection, lax process inspection, and ex-factory inspection, resulting in some unqualified batches passing customs. The third is that measuring tools of use cannot be calibrated regularly, and even gauges exceeding the wear limit can be used.
Second, the hardness is unqualified. Hardness is also an important indicator to assess the mechanical properties of bolts. The materials used for the products of each performance grade are different. The mechanical performance grade is an important basis of the selection of bolts. During installation and use, the working load and installation torques should be determined according to the performance grade. For specific materials, the hardness should be controlled at a reasonable level. High hardness may reduce the fatigue resistance of the products. In order to improve the strength of the products, some enterprises control the hardness at a higher level, resulting in some products exceeding the standard.