Process for degreasing and cleaning metal surfaces

Details Process for degreasing and cleaning metal surfaces Process for degreasing and cleaning metal surfaces

1994-05-05

1996-04-02

Andrews, Melvyn

Cleaning and liquid contact with solids

Processes

For metallic, siliceous, or calcareous basework, including...

134 10, 134 40, B08B 302

Patent

active

055036821

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for degreasing and cleaning metal surfaces using surfactant-containing water-based cleaning liquids in baths and/or by spray cleaning, optionally followed by rinsing of the degreased and cleaned surfaces. In spray cleaning, the cleaning liquid is normally recirculated.


STATEMENT OF RELATED ART

Metal parts, for example plates, have to be freed from surface residues after machining and before any subsequent surface treatment, for example electroplating. Apart from small metal particles, it is mainly fats and oils of natural or mineral origin, which have been used as drilling and cutting aids or as lubricants in preceding treatment steps, that have to be removed.
The surface is freed from the various soil types, above all from the fats and oils, typically in water-based cleaning baths which generally contain surface-active components, for example nonionic surfactants. Both dip cleaning and spray cleaning methods are applied. A review of the cleaning preparations typically used, also known as cleaners, can be found for example in J. Kresse et al., "Sauberung technischer Oberflachen" Title in English: Cleaning of Technical Surfaces!, Kontakt & Studium Vol. 264 (Expert Verlag).
The performance of the cleaning baths decreases with increasing degree of soiling. In addition, part of the cleaning liquid is removed by the parts to be cleaned. Beyond a certain bath soiling level, the necessary cleaning performance is no longer guaranteed. Bath servicing measures have to be taken to keep the cleaning performance of the bath at its original level. This is done on the one hand by replenishment of the cleaning preparation as a whole or individual components thereof and, on the other hand, by removal of the various soil types from the cleaning liquids. Typical processes for the removal of oils from the cleaning bath are carried out inter alia with skimmers, separators, oil separators, centrifuges, evaporators or by membrane techniques, for example microfiltration or ultrafiltration.
However, because the various bath soils and also the separators interact with the ingredients of the cleaning preparations, not only the soils, but also some of the cleaning components are also removed from the solution, so that the components in question have to be replenished to guarantee the required cleaning effect.
Monitoring the cleaning baths, i.e. measurement of the bath soiling level and the cleaning reserves still present, is crucially important to bath servicing measures. This is because, on the one hand, it is important to keep to the optimal time for replacing the bath. The optimal replacement time arrives when the soiled cleaning liquid fails to provide a satisfactory cleaning result in the next cleaning operation. On the other hand, only that quantity of cleaning preparation or components thereof which is required to obtain the desired cleaning effect should be replenished following the removal of soil from the bath. Overuse should be avoided.
The cleaning effect of the baths cannot be satisfactorily monitored by the methods in use at the present time. Conductivity and pH measurement or titration pick up only the inorganic components. Accordingly, these methods cannot be used for salt-containing cleaning preparations. Another disadvantage of these methods is that they do not include the surfactant system.
Besides the surfactants, determination of the COD (chemical oxygen demand) or TOC (total oxidizable carbon) value also encompasses all other organic bath constituents, for example oil-containing soils, so that this process can only be used in selected cases.
Chemical analysis of the cleaning baths or even the determination of individual surfactants and classes of surfactants, for example hydrocarbon measurement, the BIAS or MBAS method, requires the presence of trained personnel. In addition, the analyses are time-consuming and therefore expensive.
The determination of residual grease on the surface to be cleaned or on test specimens by burning the carbon-containing

REFERENCES:
patent: 3150518 (1964-09-01), Peterson
patent: 4276094 (1981-06-01), Gutnick et al.
patent: 5188135 (1993-02-01), Neumann et al.
patent: 5404606 (1995-04-01), Mueller-Kirschbaum et al.
Journal of Applied Science vol. 28, 1983, Schork, Ray "On-Line Measurement of Surface Tension and Density with Aplications to Emulsion Polymerization" pp. 407-430.
Kresse et al., "Sauberung technischer Oberflachen, Kontakt & studium", vol. 264, Expert Verlag 1988.

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