There was a time when anyone working with soiled base metals could easily clean any surface. Over the past 60 years regulations discouraging or preventing the use of solvent degreasing/cleaning and cyanide-based processes has forced metal finisher to find alternatives for properly cleaning the base metals they need to process.
No one disputes that a good clean surface is an absolute prerequisite for proper metal finishing. The old adage “nothing sticks until it is clean” has never been truer for metal finishers.
Today, Alkaline cleaning is the primary method used on base metals prior to further processing. Cleaning employs physical (solution movement, work movement, ultrasonic) and chemical reactions to remove soils for base metal surfaces. Alkaline cleaners most often used today are chemical blends which consist of alkaline builder salts, surfactants, sequestering agents, emulsifiers and chelators. These components react with the soils and oils on the surface of base metals and form soap. Wetting agents either allow the soap formed to be soluble in water or float to the top to be removed in some way. Most often the cleaner lifts the oil from the surface being cleaned and holds the oil in solution. Most finishers prefer this approach since there is always the possibility that anything floating on the surface will redeposit when the parts being processed exit the tank. The oil emulsion is then easily rinsed away. Heat can greatly accelerate this emulsification process by lowering the oil viscosity and enhancing the wetter.
How to choose the right Akalinity builder
Alkalinity builders have to be chosen with the specific base metal to be cleaned. Caustic Soda and potassium hydroxide are highly alkaline materials and their high pH works great on steel parts. However, they can be far too aggressive on Aluminum or other light metals. They work well for saponifying fats and neutralize any acid soils generally found on ferrous metals.
Aluminum, zinc based die-castings and zinc alloys such still have to be cleaned but with milder alkaline products. Silicates offer alkalinity and exhibit good detergency. They have the ability to neutralize acid soils while not attacking soft metals. But they can form scale that is difficult to rinse.
Phosphates also are used as alkaline building agents and are of medium alkalinity. They are generally safe on soft metals. The major objection to phosphates comes when they are discharged to municipal waste treatment facilities. The phosphates break down and function as fertilizer for algae.
Determining factors in alkaline cleaner selection requires some investigation and consideration of factors like base metal (steel, zinc, aluminum, brass, copper) to be processed and nature of the oils to be removed. Be sure the alkalinity of the building blocks for the cleaner will not attack your base metal.
Questions to ask when choosing your alkaline cleaner:
- What is the nature of the oils you are removing- are they neet oils or synthetic water soluble products.
- What is the temperature your cleaner will operate—too hot and you can have rinsing issues, too low and you may not clean the parts properly?
- What is the pH that is acceptable for the product you need to clean?
- What is the hardness of the water you will have for bath make-up and rinsing?
- What is your capability for treating the building blocks for the cleaner (silicates, phosphates, chelators)?
- What impact will your discharged treated water have on your municipal treatment system (phosphates)?
- Is the soil you are removing complex fats or simple coolants or rust preventatives?
- Are you more comfortable working with a powdered product or a liquid product.
- What is your top priority—safety and convenience vs. cost?
- You also have to consider the equipment that will use the cleaner. Is it an immersion or spray application? Wetting agents that work great in a soak application will cause excessive forming when used in a spray application.
Call us at 317-875-0051 or contact us for more information about alkaline cleaners.
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