What is casting surface and near surface defect detection?

Casting surface and near surface defect detection:

1.Liquid penetrant testing

Liquid penetrant testing is used to check a variety of openings on the surface of the casting manufacturers defects such as surface cracks, pinholes and other surface defects difficult to find the naked eye. Penetration testing is commonly used color detection, it is colored with a high penetration ability (usually red) liquid (penetrant) soaked or sprayed on the surface of the casting, penetrating defects penetrate into the opening inside, wipe the surface quickly permeate layer, easy to dry and then a display agent (also called imaging agent) sprayed onto the casting surface defects to be remaining in the opening of the penetrant sucked out, the display of agent to be dyed in the investment casting, which can reflect the shape of the defect, the size and distribution. It should be noted that the accuracy of penetration test material was seized with increased surface roughness is reduced, the more light that is detected, the better the surface, grinding, polishing the surface detection of the highest accuracy, even intergranular cracks can be detected. In addition to coloring test, the fluorescent penetrant testing is also commonly used liquid penetrant testing method, which you need to configure the UV light irradiation was observed, high detection sensitivity than coloring.

2. Eddy Current Testing

Eddy current testing for the examination of the surface is generally not less than 6 ~ 7MM deep defects. Eddy current testing of coil placement through the coil method and the method of two kinds. When the test piece is placed in an alternating current through a coil close to the test piece into an alternating magnetic field is induced in the test piece perpendicular to the direction of the excitation field, a swirl-like flow of a current (eddy current), eddy current will and generating a magnetic excitation field in the opposite direction, the coil portion of the original magnetic field reduced, thereby causing the coil impedance change. If the cast steel productssurface defects, the electrical characteristics of the eddy current distortion occurs, thereby detecting the presence of defects, the main disadvantage of eddy current testing can not be detected visually show the size and shape of the defect, the defect can only determine the general location in the pump casting and depth of the surface at In addition it has small openings on the surface defect detection sensitivity as penetration testing.

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