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Alkaline-cleaning,Methods, Mechanisms, Means.SOLUTIONS with Effective, Practical Advice
Alkaline-cleaning is needed for removal of oils, greases and soils from fabricated items before they are electroplated, conversion coated or finished by other processes. Any oily product on the metal surface to be treated would interfere with finishing processing causing defects. Several types of physical application of the cleaning media are available. Among them soak immersion, spray cleaning, electrolytic processing, steam-gun soil removal, rotary spray washers with or without rotary brushes, and manual application combined with mechanical, continuous work movement. The selection of the most useful and economic Alkaline cleaning processing depends on the dimensions of the workpieces, on the volume of work to be done in a given time, and on the requirements of further processing. Electrolytic cleaning provides the cleanest surfaces. Spray methods are used for large parts or for low volumes, either following a soak period or without it. The selection of Alkaline-cleaning is also conditioned by the type and stickiness of the soil and by the mechanisms of its removal. Large installations with conveyors generally permit the most economic equipment utilization, if the expense of their building is justified by the amount of work to be done in limited time. Soils are basically oily, semisolid or solid, these last ones with various particles dimensions and degrees of adherence to the substrate. They are removed from the metallic surface by one or more of the following mechanisms, namely saponification, emulsification, dispersion, flocculation or aggregation and film shrinkage. The basic Alkaline-cleaning processes employ either soak, spray or electrolytic cleaning, either singly or in combination and are performed, each for a determinate time at a preferred temperature, and are followed by cold water rinse, hot rinse and hot air drying. There is no universal Alkaline-cleaning agent effective for all types of soil, because the requirements for different cleaning jobs are too diverse and incompatible. Different formulations are therefore proposed with different degrees of effectiveness in every single case.
The Alkaline-cleaning action is attributed to the main components of the formulations, that are mainly sodium carbonates, phosphates, silicates and hydroxide that provide alkalinity, measured as pH values preferably between 7 and 13, and other favorable effects. Saponification reactions require high alkalinity, provided by considerable dissociation or ionization of the salts making up the cleaner. Alkalinity is continually lost to saponification, neutralization and drag-out but is preserved by buffers which are added to give long life to cleaners at constant pH. As water is the major ingredient of any Alkaline-cleaning solution, its hardness, or proportion of calcium carbonate present, must be softened, or kept under control, mainly by measured additions of selected phosphates. Surface active or wetting agents are added to cleaning compounds to lower surface tension and to increase the cleaning action. Agitation, keeping the solutions at their best action temperature, and scheduled maintenance through measurements of solution drift and corrective additions, are essential to assure continuing Alkaline-cleaning effectiveness. Various formulations are suggested in manuals and handbooks for different materials and soiling conditions: experience will help in determining those which prove their usefulness under the variable condition of any industrial facility. As with all other industrial processing ingredients, laws and regulations in effect at every location must be studied and taken care for, especially regarding the neutralization procedures requested before discharging large quantities of spent liquids to be disposed of. Keeping accurate accounting of the actual costs incurred in any given operation helps to provide essential information relative to the current performance and may be vital for taking decisions bearing on the soundness of the enterprise.
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