Magnetism Fundamentals Quiz

Magnetism and Magnetic Field Fundamentals

• Magnetic field lines in a bar magnet form closed loops from pole to pole without crossing, with decreased density as they move from higher to lower permeability areas

• Directional flow of magnetic field lines occurs from the south pole to the north pole within a material and vice versa in air

• Flux density, measured in Gauss, represents the number of flux lines per unit area and is denoted by "B" on the hysteresis curve

• Material classifications include paramagnetic, ferromagnetic, and diamagnetic materials, each exhibiting different magnetic properties

• Terms like demagnetization, induction, residual magnetism, and retentivity are essential in understanding magnetism in materials

• Hysteresis curve, permeability, reluctance, saturation, and coercive force are key aspects of a material's reaction to a magnetizing force

• Magnetic fields around a bar magnet are made up of continuous, curved lines linking the north and south poles

• Magnetic poles, though not actually flowing, exhibit directional properties and create attraction or repulsion

• Magnetic attraction and flux leakage are influenced by the presence of discontinuities and the orientation of flux lines

• Longitudinal and circular magnetization methods affect the orientation and detection of discontinuities in a component

• Different types of magnetizing currents, such as direct current, alternating current, and half-wave rectified single-phase AC, have varying penetration and particle mobility characteristics

• Understanding the magnetizing methods and the orientation of magnetic fields is crucial for effective magnetic particle testing.Magnetization Methods for Non-Destructive Testing

• For product magnetization, the recommended magnetizing current is 100-125 amperes per inch of product spacing.

• The spacing between the products should be limited to approximately 200mm for effective magnetization.

• In yoke magnetization, the intensity of the magnetic field is assessed by testing the lifting capacity of the yoke with the legs and the spacing to be used for the inspection.

• For AC yokes, they must be capable of lifting 4.

Magnetic Testing Training Material Summary

• Black lights with a wavelength of 3.6x10-4 mm and intensity not less than 800 µW/cm2 are recommended for magnetic testing.
• Techniques for magnetic testing include selection of current type, particles, method of application, sequence, direction of field, sensitivity level, and equipment.
• Direct current is preferred for deeper penetration, while alternating current is more sensitive to surface defects.
• Dry particles are more sensitive to subsurface defects, while wet particles are more sensitive to very fine surface defects.
• Residual method and continuous method are two sequences for applying magnetic particles during testing.
• The direction of the magnetic field is decided based on the shape and orientation of the defect in relation to the part's principal axes.
• Sensitivity in magnetic testing depends on factors such as particle type, magnetizing current, and sequence.
• The equipment used for magnetic testing depends on the size, shape, and number of parts to be tested.
• Test surface preparation involves removing dirt, rust, loose scale, and oil or grease from the test area.
• The magnetic field should be verified before testing by using production or fabricated test parts with discontinuities or magnetic field indicators.
• Magnetic field indicators, like the "pie gage," are used to indicate field strength and direction at the surface in the area of the part under test.
• The effective area of coverage, overlap of effective areas, yoke placement for weld examination, and application of magnetic particles are crucial steps in magnetic testing.