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#114 Cleanliness Testing Methods - 4

Category : Metal cleaning
February24, 2012
(8) Radioactive tracer test

It is said that by making artificial soiling, mixing in some radioactive isotopes (radioactive material) and measuring with a Geiger counter can yield sensitivity 1000 times of the spray pattern test and 100 times of the atomizer test. Since this test yields very high sensitivity, it is useful in comparing the cleanliness levels of various washing methods and detecting minute amounts of substances otherwise undetectable by other means. However, since the radioactive material is difficult to handle in actual process sites, it is not a generally applicable method.

(9) Rust test

There is a pinhole test for electroplated objects and this test is similar to that. A piece of filter paper soaked with potassium ferricyanide and sodium chloride are made to contact the surface of steel. The test utilizes Prussian blue precipitation caused by ferric salt ions reacting with the indicator on cleaned surface, and the sensitivity is said to be 1/10 of water wetting method.
Also, there is a rust method that uses a water solution containing 2% hydrogen peroxide and 0.008% salt where the solution is dripped on the metal surface and observed.

(10) Plating test

This is a method that uses electro plating. The plating adhesion is evaluated as well as salt water spray and wet box testing can also be used. The cleanliness evaluation by examining the plating adhesion condition utilizes the nature where plating adhesion is especially sensitive to inorganic soils such as oxidation films. Also, by applying high bright plating the evaluation can be performed. Incomplete degreasing before plating will cause loss of gloss and may leave residues and fingerprints that are clearly visible.
For surfaces treated with oil based grinding compounds, residual oils remain on the treated surfaces as thin films. These surfaces must be completely degreased and the method to evaluate the difficultness of this is to use a test sample shown in [Fig.1] and Fuff polishing >> alkali degrease >> bright nickel plate >> then evaluate. The plated surface incompletely degreased will show with lost glossiness with residues and fingerprints clearly visible.

[Fig.1] Test sample for plating test

The reason for the various sized holes on the plate is to make the level of degreasing by observing differences due to fuffing heat and buff compound residue adhesion.

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