Typical magnetization method for welded joints---yoke method and contact method
Typical magnetization method of yoke method
Typical magnetization method of contact method
1. Characteristics of magnetization method: The magnetization is clamped to the part by a fixed electromagnetic yoke for overall magnetization, or the two magnetic poles of the portable electromagnetic yoke are used to contact the surface of the workpiece for local magnetization. Used to find discontinuities perpendicular to the line connecting the two poles.
2. Scope of application: Monolithic magnetization Suitable for lengthwise parts with a cross-section of the part smaller than the cross-section of the pole. Local magnetization is suitable for the detection of large parts.
The following points should be noted when using the yoke method:
(1). The magnetic pole of the yoke must be in good contact with the workpiece, especially the rotating magnetic field and the crossed magnetic field, otherwise the detection is invalid.
(2). The yoke must meet the lifting force requirements, and the detection sensitivity should be verified by the A-type sensitivity test piece before and after the test.
(3). The pole pitch of the yoke should be controlled between 75mm and 200mm.
(4). Make at least two approximately perpendicular magnetizations for each magnetized region.
(5). The electromagnetic yoke should be used to detect the T-shape and the angle type. The electromagnetic yoke with movable joint should be used to ensure the contact between the magnetic pole and the workpiece surface by adjusting the angle of the movable joint of the electromagnetic yoke.
Contact method characteristics
The surface of the part is contacted with the struts and electromagnetically polarized to form a circumferential magnetic field. Used to find discontinuities parallel to the line connecting the two contacts.
3. Application range:
Suitable for local inspection of welded parts and large castings, forgings and plates
The welded joint and the groove are mainly tested by the yoke method and the contact method.
Pay attention to the following points when using the contact method:
(1). It is necessary to maintain good contact between the contact and the workpiece, reduce heat generation at the contact point and prevent sparking and local overheating. If a copper contact is used, when an electric spark is generated, there is a possibility that copper is generated at the contact point of the contact and the workpiece and microcracks are generated, thereby causing damage to the workpiece. It is therefore recommended to use contacts or gaskets of steel, aluminum or copper mesh instead of solid copper.
(2). The contact should be firmly pressed against the surface of the workpiece to be inspected first, and then energized, so that the circumferential magnetic field is superimposed on the workpiece along the periphery of the electrode and between the two contacts, which is sufficient for local magnetic particle detection.
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