Principle of Magnetic Particle Inspection

Magnetic particle inspection is a method of detecting surface and subsurface defects in materials using magnetic flux. The method of magnetic particle inspection is specifically divided into dry magnetic particle, wet magnetic particle, and surface-applied magnetic methods.

For the magnetic particle inspection of railway wagon wheels, the dry magnetic particle inspection method is generally adopted. This method involves uniformly dispersing iron powder on the surface of the railway freight car wheel by applying a direct current or alternating current magnetic field to the tested workpiece, forming a thin film. When the magnetic field acts on the defective part, a magnetic flux impedance change occurs at the defect, resulting in a magnetic sliding phenomenon. The magnetic particles are attracted to the surface of the defect through the defect, forming black or purple magnetic particle traces, thus achieving defect detection.

Key Points of Magnetic Particle Inspection Technique

1. Selection of Components

The magnetic particles used in dry magnetic particle inspection are fine particle magnetic powders that are easy to adsorb and detect. Magnetic particles used in magnetic particle inspection can be classified into various types based on factors such as color, composition, and particle size. Generally, mineral oil, cellulose, and metal carbonates are used as the base for magnetic particles. Magnetic particles must meet the following requirements:

(1) Fine particles that do not affect the accuracy of defect detection.

(2) Clearly visible color to create a noticeable contrast with the inspected workpiece.

(3) Magnetic properties to adhere to the surface of defects on the inspected workpiece under the action of a magnetic field.

2. Generation and Detection of Magnetic Field

For the magnetic particle inspection of railway wagon wheels, an appropriate magnetic field intensity and direction should be used. Generally, the magnetic field intensity used for inspection is between 0.2-0.6T. It should be noted that a higher magnetic field intensity may cause a "pile-up effect" of magnetic particles, leading to inaccurate inspection results.

For magnetic field detection, the detected magnetic field strength should be calibrated using a magnetometer when the magnetostrictive method is applied. The magnetometer should have high measurement accuracy and resolution. The magnetometer should select a suitable range of probes according to the requirements of different magnetic field sizes and directions for measurement.

3. Control of Environmental Conditions

Dry magnetic particle inspection has high detection sensitivity and accuracy. However, the influence of environmental factors must also be taken seriously. Inspections should be conducted in enclosed, clean environments. During detection, vibrations, wind, sunlight, and air drafts should be avoided.

Advantages and Disadvantages of Magnetic Particle Inspection

Advantages:

Magnetic particle inspection has the characteristics of high inspection sensitivity, large detection depth, high detection efficiency, and clear inspection conclusions.

Disadvantages:

Dry magnetic particle inspection has high requirements for the environment and cannot be conducted in harsh environments such as wind, sand, water accumulation, and dust. In addition, dry magnetic particle testing requires grounding, consideration of grounding methods, and strict adherence to safety operating procedures to avoid injury to personnel.

Application of Magnetic Particle Inspection in Railway wagon Wheels

During the operation of railway freight car wheels, various factors such as load, wear, and vibration may cause surface or internal defects such as cracks, fissures, and damage. To ensure the safe operation of railway freight cars, regular inspections of wheels are required to promptly eliminate defects.

Magnetic particle inspection can detect surface and internal defects in car wheels, including fissures, fatigue, and cracks. In practical applications, common issues with railway freight car wheels can be improved and optimized, effectively increasing the service life and safety of railway freight cars.

Based on magnetic particle inspection technology, effective non-destructive testing systems and equipment can be developed to improve the detection efficiency and accuracy of wheels. Furthermore, a deeper and more comprehensive understanding of wheel wear in railway freight car wheels will play an important role in promoting wheel maintenance, safe operation, and management.