A casting surface and near surface defect detection

1.1 Liquid penetrant testing
Liquid penetrant testing is used to check all openings on the surface of the casting defects, such as surface cracks, pinholes and other surface defects difficult to find the naked eye. Penetration testing is commonly used color test, which is colored with a high permeability (usually red) liquid (penetrant) soaked or sprayed in the casting surface, penetrating into the open defects inside, quickly wipe the surface of liquid penetration layer, then the display easy to dry agent (also known as imaging agents) sprayed on the surface of the casting, to be defective will be left in the open suck out the penetrant, the show was staining agent, which may reflect defects in shape, size and distribution. It should be noted that the penetration test accuracy was seized with an increase in surface roughness decreased, the more light that is detected the better the surface, the surface finish grinding the highest detection accuracy, or even detect intergranular cracks. In addition to color detection, fluorescent penetrant testing is commonly used in liquid penetrant testing method, it needs to configure the UV light irradiation observed higher detection sensitivity than color.
1.2 Eddy Current Testing
Surface eddy current inspection for the following general not more than 6 ~ 7MM deep defects. Sub-coil eddy current testing method and placed through the coil method two kinds. : When the specimen is placed in an alternating current through a coil near, the specimen into the alternating magnetic field can give birth in the sense of the specimen in the magnetic field perpendicular to the direction and motivation, and was vortex-like flow of current (eddy current), vortex will produce a magnetic field in the opposite direction with the magnetic field excitation, the coil part of the original magnetic field reduction, causing the coil impedance change. If the casting surface defects, the electrical characteristics of eddy current distortion will occur, to detect the presence of defects, the main disadvantage of eddy current testing can not detect defects in visual display size and shape, generally only determine the location and depth of surface defects which In addition it has a small opening on the surface defect detection sensitivity as penetration testing.
1.3 Magnetic Particle Testing
Magnetic particle testing for detection of surface defects and surface defects in the following few millimeters deep, it needs to DC (or AC) magnetic devices and magnetic (or magnetic liquid) in order to test operation. External magnetic device used in the casting surface magnetic field, magnetic or magnetic fluid is used to show defects. When casting a range of magnetic field, the magnetic defects within the region will produce leakage magnetic field, when sprinkled with powder or suspension, the powder was suck, so you can show a defect to. This shows that the defects are basically cross-section of magnetic field lines of the defects, parallel to the magnetic field lines for the long-type defects are not showing up, this operation requires changing the magnetization direction in order to ensure to check out the various defects in the direction of the unknown .