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How to detect surface defects of casting

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How to detect surface defects of casting

Date:2018-03-02 Author: Click:

1. Magnetic particle detection

Magnetic particle detection is suitable for detecting surface defects and defects several millimeters deep below the surface. It requires dc (or ac) magnetization equipment and magnetic powder (or magnetic suspension) to detect the defects. The magnetization equipment is used to generate magnetic field on the inner and outer surface of the casting, and magnetic powder or magnetic suspension is used to display defects. When a magnetic field is generated within a certain range of the casting, the defect in the magnetized area will generate a leakage magnetic field. When magnetic powder or suspension is applied, the magnetic powder is absorbed, so that the defect can be shown. The defects of this show are basically crosscutting defects of the magnetic field lines in parallel to the magnetic field lines are defects showed not to come out, therefore, the operation need to change the direction of magnetization, in order to make sure to check out the direction of the unknown various defects.

Ii. Liquid penetration detection

Liquid penetration testing is used to check various opening defects on the surface of casting, such as surface cracks, surface pinholes and other defects that are difficult to be detected by the naked eye. Commonly used penetrant testing is shading detection, it is capable of high permeability colored (red) liquid (penetrant) soaking or spraying on the casting tables, penetrating agent into the open defect, a quick wipe surface infiltration liquid layer, and then will be easy to do agent (also called imaging agent) sprayed on the surface, the casting stay will remain in the open defect penetrant after coming in, according to agent is dyed, which can reflect the shape, size and distribution of defects. It should be pointed out that, the accuracy of the penetrant testing decreased with increasing surface roughness checked material, namely the light detection, the better the results, the surface grinding machine for grinding the surface of the highest detection accuracy, can even detect the intergranular crack. In addition to color detection, fluorescence penetration detection is also a common method for liquid penetration detection. It requires ultraviolet lamp for irradiation observation, and the detection sensitivity is higher than that of color detection.

Eddy current testing

Eddy current testing is applicable to defects generally not greater than 6 ~ 7MM below the surface. There are two methods for eddy current detection: placement coil method and through coil method. : when the specimen is placed near the coil of alternating current on, into the alternating magnetic field of the specimens can be induced in the specimen perpendicular to the direction of the magnetic field phase, the shape of vortex flow of current (eddy current), eddy current will produce a and motivation in the opposite direction from the magnetic field magnetic field, reduce part of the original magnetic field in coil, thus cause the coil impedance change. If the casting defects in the surface, the electrical characteristics of the eddy current distortion happens, to detect the presence of defects, the main disadvantage of eddy current testing is not intuitive display detected defect size and shape, normally only determine the defect on the surface of the position and depth, and it small openings on the workpiece surface defect detection sensitivity than penetrant testing.

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Phone: 18940018888

             13889888886

Telephone: 024-62908888

Email address: sjj8000@sohu.com

Address: no. 15, liaozhong commercial street, shenyang city

Fax: 024-87880508

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