The shank structure of the bolt refers to the unthreaded polished rod portion, which is divided according to its diameter, and is mainly a large diameter rod, a medium diameter rod, a stepped rod, and a large rod. Large-diameter rods are also called standard rods. Their nominal diameter is equal to the nominal diameter of the thread. There are two types of diameter public service. One type is loose service. It is mainly used for tensile bolts, such as h12 and h14; the other type is compact. In service, it is mainly used for shear bolts, such as f9, f7, f6; the medium diameter rod is also called a thin rod, its nominal diameter is approximately equal to the middle of the thread, its service band is h12, or no special rules are imposed. For tensile bolts; stepped rods, also known as waisted rods, whose rod diameter is smaller or equivalent to the diameter of the thread, chiefly for bolts requiring reduced stiffness may require bolts with reduced thread stress gathering; Also known as a reinforcement rod, the rod diameter is larger than the diameter of the thread and can form an interference fit with the mounting hole and can also be used for structural repairs.
Bolt detection is divided into two types: manual and machine. Labor is the most primitive and consistent method of detection. In order to reduce the outflow of defective products as much as possible, general production companies conduct inspections of products that are packaged or shipped by visual means to eliminate bad products (poor dental injuries, mixed materials, rust, etc.).
Another method is automatic detection of the machine, mainly magnetic particle inspection.
Magnetic particle flaw detection is the use of the interaction between leakage magnetic field and magnetic powder at the defect of the bolt, and the difference between magnetic permeability and steel permeability of possible defects (such as cracks, slag inclusions, mixed materials, etc.) of the bolt. These data are not connected after magnetization. The magnetic field at the site will change abruptly, forming part of the magnetic flux leaking at the surface of the workpiece to generate a leakage magnetic field, and then attracting the magnetic powder to constitute a pile of magnetic powder at the defect—a magnetic mark. Under the appropriate light conditions, the position and shape of the defect will appear. The accumulation of these magnetic powders has been investigated and explained, and the intention to remove defective products has been achieved.