Magnetic Particle Testing - Tecsud

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Test piece ASTM centrifuge tube with stand Ref. No. 135 015 The exact portion of magnetic powders suspended in oil or water can be determined with the centrifuge tube. If the concentration is correctly mixed, a certain number of graduation marks must be obtained after a settling time of 30 minutes. <strong>Magnetic</strong> particle suspensions already circulating in pump circuits should no longer be checked with the centrifuge tube, because dirt paricles deteriorate the result. Reference test piece type 1 with reference photo Ref. No. 135 012 acc. to. pr. EN ISO 9934-2 appendix B (MTU No. 3) When using magnetic paricle suspensions it is of overall importance to check the indication efficiency of the test material. Hydromechanical stresses in pump circuits, separated particles, too weak or too concentrated test material mixture could affect the operational efficiency. The test material is simply sprayed on the test piece to see whether is still efficient.
Why is a defect indicated? When a ferromagnetic material is magnetized, magnetic flux will flow within the magnetically conducting medium. When the flux lines meet an area of low magnetic conductivity, i.e. a surface crack, the associated high magnetic resistance changes the flux distribution. The field lines in the sound magnetic strayflux material are diverted, a small proportion passing through the material defect, but the majority are diverted out of the surface to form a bridge over the defect. The field lines diverted out of the surface are termed ”magnetic strayflux” and form the basis of magnetic powder techniques. With these techniques the magnetic strayflux is identified by applying fine iron powder or iron-oxide powder to the workpiece surface. The magnetic strayflux lines are moving in a basically non-conducting medium, and are therefore exposed to a relatively high magnetic resistance. To reduce this magnetic resistance the stray fields attract all the nearest freely-moveable iron particles which combine to form a magnetic bridge over the defect. The combination in the shape of a powder pattern can be easily identified as a defective area. Physical basic conditions What can be tested? All ferromagnetic materials with a permeability of µ > 100. The range of ferromagnetic materials includes: • All types of steel and their alloys with the exception of austenitic steels • Cast iron What can be detected? All surface and near surface crack-type defects which, due to their position and size, proportionally influence the magnetic field, providing that the crack width-depth-length dimensions are in the ratio > 1 – 10 – 50. Indication sensitivity to near-surface defects and inclusions rapidly reduces as their depth increases. When can a defect be detected? Optimum crack detection occurs when the magnetic field lines are at right-angles to the defect. The angle between the field direction and the expected defect position should not, however, be greater than 30°.
Page 1 and 2: Magnetic Particle Testing Ferroflux
Page 3: Test materials Concentrates for wet
Page 7 and 8: UV-LED- Portable light UV-Lights mi
Page 9 and 10: Pumps and Spraying Devices for magn
Page 11: Magnetic field strength measuring i

Magnetic Particle Testing - Tecsud

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