Bolt inspection is broadly categorized into two methods: manual and automated. The manual method is the most traditional and widely utilized approach for consistency verification. To minimize the release of defective products, manufacturing personnel typically conduct visual inspections of products prior to packaging or shipment, aiming to identify and segregate defective items (defects may include thread damage, material mixing errors, rust, etc.).
The alternative method is fully automated machine inspection, primarily utilizing magnetic particle testing. This technique leverages the interaction between magnetic particles and the magnetic flux leakage fields generated at bolt defects. It exploits the difference in magnetic permeability between potential defects-such as cracks, slag inclusions, or material mixing errors-and the surrounding steel substrate. When the bolt is magnetized, the magnetic field at these material discontinuities becomes distorted; this distortion causes a portion of the magnetic flux to leak out onto the workpiece surface, thereby attracting magnetic particles. This attraction results in an accumulation of particles at the defect site-known as a "magnetic indication"-which, under appropriate lighting conditions, reveals the precise location and geometry of the defect. By observing and interpreting these particle accumulations, the objective of identifying and eliminating defective products is successfully achieved.