Hot-dip galvanized hexagonal bolts are divided into ordinary and reamed holes. According to the head shape: there are hexagonal head, round head, square head, countersunk head, etc. The hexagonal head is the most commonly used. Hot-dip galvanized bolts generally use countersunk heads where connection is required.
It is a non-standard part, the shape is U-shaped, so it is called U-shaped bolt. The hot-dip galvanized bolt has threads on both ends and can be combined with a nut. It is mainly used to fix tubular objects such as water pipes or sheet objects such as car leaf springs. The object is like a person riding on a horse, so it is also called a riding bolt.
For connecting bolts for steel structures, unless otherwise specified, hot-dip galvanized bolts are generally ordinary crude grade C bolts. ①The bolts of grade A and B bolts are processed by lathes, with smooth surface and accurate size. The material performance grade of hot-dip galvanized hexagonal bolts is 8.8 grade. The production and installation are complicated, the price is high, and it is rarely used; ②The grade C bolts are not used. The processed round steel is not accurate enough in size, and its material performance grade is 4.6 or 4.8. Large deformation during shear connection, but easy installation and low production cost, it is mostly used for tensile connection or temporary fixation during installation.
The magnetic particle inspection of hot-dip galvanized bolts uses the interaction between the leakage magnetic field at the bolt defect and the magnetic powder, and aims at the difference between the magnetic permeability of the bolts (such as cracks, slag inclusions, mixing, etc.) and the magnetic permeability of the steel after magnetization. The magnetic field at the discontinuity of these materials will be turbulent, forming part of the magnetic flux leakage, and the surface of the workpiece will generate a leakage magnetic field, thereby attracting the accumulation of magnetic powder at the defect formation of the magnetic powder—magnetic marks. The hot-dip galvanized bolts are under appropriate lighting conditions. The defect position and shape are revealed, and the accumulation of these magnetic powders is observed and explained, and the purpose of rejecting defective products has been achieved.