The first tank on an anodize line is usually an alkaline soak cleaner, which are long lasting, and very effective in cleaning a wide variety of soils.
Mark JozefowiczA good alkaline soak cleaner should not foam excessively, nor should it significantly etch the surface of the aluminum. Since some mild etching of the aluminum surface will usually occur, the cleaner must be able to hold the dissolved aluminum in solution. The last thing you need is for the dissolved aluminum to fall out of the bath and form a sludge on the bottom of the tank or a scale on the heating coils.
Soils can vary widely in our business but those that are common include stamping and machining oils, lubricants, greases, buffing compounds, scale, dirt, flux, and graphite. A good cleaner is formulated to remove as many of these soils as possible. Its detergency is a result of a synergistic relationship between the alkali and the surfactant components.
The first part of the cleaner - the alkali - may include carbonates, phosphates, and borates. In addition to their detergency effect, these components provide a stable pH of around 9 or 10. The second part of a cleaner - the surfactant - is a key ingredient to good performance. Surfactants come in many varieties, and they all have their own individual characteristics. Other ingredients are added to inhibit attack on the aluminum and to reduce sludge.
Powders and Liquids Alkaline Soak Cleaners
Alkaline soak cleaners can be purchased in two forms: powders and liquids. For handling purposes, powdered cleaners tend to be overly rich in alkali and lean in surfactant. The surfactant may or may not be a strong emulsifier. Compositions containing strong emulsifiers (Anodal Cleaner PMP) produce cleaners which hold the soils in suspension even when the agitation is turned off. Formulations that contain weak emulsifiers (Anodal Cleaner NFO & NFB) create baths which allow oils to split out of the bath when the agitation is turned off. This allows the anodizer to skim off the oil and make additions of the surfactant package over the side of the tank. By operating the cleaner in this way, its life is extended, and the value of the product is maximized.
Liquid versions of alkaline soak cleaners are not limited to the amount of surfactant that can be added to the formulation. Compared to powder cleaners, four or five times as much surfactant can be included in the product. Because of this, liquid cleaners like Anodal Cleaner BMC New are formulated with true emulsifying surfactants. Unlike their powdered counter-parts, soils generally do not split out of solution when the air is turned off. These products can be pumped directly into the tank, with no waiting for the material to dissolve.
Another, cleaner used by our industry is the acid cleaner. Acid cleaners do not have the detergency or the soil holding capacity of alkaline cleaners, but they are terrific at removing oxides, scale, and chlorinated paraffin oils. If an acid cleaner is used, it is normally used as a back-up to an alkaline soak cleaner. Using one in this way ensures highly effective cleaning of even the most stubborn soils. After acid cleaning, the surface of the aluminum is considered “activated”, meaning it is free from any film, and pure base metal is presented to the next operation. Anodal Acid Cleaner 3 is based on phosphoric acid blended with surfactant emulsifiers and sequestration compounds. This cleaner bites into the aluminum surface as it cleans and as a result, the parts will have a slightly frosty appearance when they are pulled from the tank.
The amount of time that a load sits in an acid cleaner is generally a fraction of the time it would be allowed to sit in an alkaline cleaner. Alkaline cleaning usually takes a minimum of 10 minutes, whereas acid cleaning usually takes about 2 minutes. All cleaners should be used with agitation and they are most effective when they are run at a temperature of around 140 to 160 degrees Fahrenheit.
Simple Acid/Base Titrations
Cleaners are analyzed by means of simple acid/base titrations. This analysis tells you how much available alkali, or acid is in the bath, but not necessarily how well the cleaner is actually working. To determine how well the cleaner is working, regular on-line visual assessments should be performed. The most common method is to look for water breaks on the surface of your parts. What is a water break? Imagine a car after it has been waxed. When it rains, the water will bead up and run off the surface. If this happens on the part, it has not been cleaned well enough. Another method that is used to assess cleanliness is to take a clean white rag and gently wipe the clean wet surface. If you spot soil on the rag, the part is obviously not clean. If your parts aren’t being cleaned and your titration tells you that there is the correct amount of cleaner in the tank, than it is time to consider dumping and re-charging the bath.
Thorough cleaning of parts is an important first step to producing a consistent high quality surface finish. When parts aren’t cleaned properly, production problems start cropping up. These problems could be related to oil being dragged into down-stream tanks, or a higher occurrence of part defects. The kinds of defects that can be associated with inadequate cleaning include white spots, pitting, and an uneven surface appearance
Recommendations, notices or instructions as to handling, use, storage or disposal of this product, including its use alone or in combination with other products, or as to any apparatus or process for its use are based upon information believed to be reliable. No liability is taken with respect to any such recommendations or instructions. Sole and exclusive warranty is that products comply with published chemical and physical specifications as provided on the certificate of analysis. No other warranties, either express or implied are given.
Mark Jozefowicz is Vice President of Technical Services at Reliant Aluminum. Visit http://www.reliantaluminumproducts.com
