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#113 Cleanliness Testing Methods - 3

Category : Metal cleaning
February17, 2012
(6) Fluorescence Test

This test uses fluorescent dye mixed into the soiling. After cleaning, the remaining soil is exposed to a fluorescent light and visually inspected or photographed. The light reflection strength of oil containing the fluorescent dye is proportion to the amount of the oil. Completely clean surface will show as black for the lack of oil (dye) and soiled surface will show the amount of remaining oil by the reflection amount.
Therefore, this test will not soiling containing no dye and cannot be applied to detect normal soiling. Rather, it is useful for evaluating cleaning solution degradation levels and compatibility of cleaning process.

Generally, a luminographic photography system shown in Fig.1 to evaluate. This equipment can detect remaining oil of 0.004mg/cm2 where it was 0.113mg/sm2 before the wash.

[Fig.1] Luminograph System

(7) Contact angle test

When 0.05mL of water is dropped on a clean metal surface, the droplet will form almost perfectly circle with a flat wave shaped edge, but the droplet will be small and with a non-wave formed edge if there is a thin film of oil on the surface. The droplet will not be circular if a significant amount of oil soiling exists.
It is said that this method can detect a difference of metal surfaces that are completely clean versus a surface with 0.01% oil dissolved in a solution.

By utilizing this principle, soiling can be quantified by measuring the contact angle ([Fig.2]) with a drop of water on a cleaned surface.

[Fig.2] Contact angle θ

[Table 1] shows the amount of oil in the solution versus the contact angles.

[Table 1] Soiling within solution versus contact angle
Concentration of oil in solution
(%)
Contact angle
(degrees)
0.00 61
0.005 63
0.01 66
0.1 74
0.5 78

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