Screening Eddy currents

When comparing the magnetic particle- and penetrant inspection with other visual methods it appears that our viewing eonditions are not so bad, compared with other methods. In radio-graphie the contrast on the film is mueh lower. In ultrasonies and eddy current the presentation times on the screen is shorter and the contrast is lower. 

After that, the residue is carried by conveyor belt to an air classifier. A stream of air is blown through the classifier, which has a zig-zag 20 shape. Low density materials such as plastic, paper, and some organic substances rise to the top of the classifier. Higher density materials such as glass and non-ferrous metals fall to the bottom and are discarded. These could be further separated out using a range of processes. For example, an eddy current mechanism 25 could screen out aluminium waste. Froth flotation techniques could recover glass. 

The phenomenon of perfect diamagnetism is not implied by perfect conductivity (i.e., (7 = oo) alone, even though perfect conductivity does imply a somewhat related property If a perfect conductor, initially in zero magnetic field, is moved into a region of nonzero field (or if a field is turned on), then Faraday s law of induction gives rise to eddy currents that cancel the magnetic field in the interior. It turns out that a perfect conductor when placed in a magnetic field cannot produce a permanent eddy current screen the field will penetrate about 1 cm in an hour. 

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