The Basics of Alkaline Cleaning in the Electroplating Industries

The most important phase of metal working, fabricating and finishing is cleaning.  Alkaline cleaning is the mainstay of industrial cleaning and may employ both physical and chemical actions.  Cleaners are many in number and vary in type and formulation.  Alkaline cleaners are specifically formulated (proprietary) chemical blends which consist of alkaline builder salts, surfactants, sequestering agents, emulsifiers and chelators .  Wetting agents, soaps and synthetic detergents, allow oil to be removed by displacing the oil from the surface of the part being cleaned by creating an emulsion win which the oil droplets are easily dispersed in water.  Functionally the surfactant consists of two distinct parts. One part is soluble in oil and the other is soluble in water.  This combination allows the cleaner to lift the oil from the surface being cleaned and holds the oil in solution.  The resulting oil in water emulsion is then easily rinsed away.  Heat can greatly accelerate this emulsification process by reducing the oil viscosity and increasing the activity of the wetter.

Alkaline builders can vary considerably and must be chosen judiciously with respect to the metal substrate being cleaned.  For example Caustic Soda or Caustic Potash are highly alkaline materials and impart a high pH to the cleaning solution.  They are particularly effective in saponifying fats and oils and neutralize any acid soils.  They work synergistically with surface active agents to disperse and deflocculate soils.  However highly causticized cleaners are not safe on soft metals such as aluminum, zinc based die-castings and zinc alloys such as brass.  Silicates impart medium alkalinity and exhibit good detergency .  Furthermore while having the ability to neutralize acidi soils they inhibit alkaline attack on soft metals.  They do however tend to form scale at higher temperatures and can leave dried on films if not rinsed quickly after the alkaline process.  Phosphates also are used as alkaline building agents and are of medium alkalinity.  They exhibit good detergency and are generally safe on soft metals.  They further function to condition hard water.  However phosphatized cleaners are subject to environmental control depending upon local regulations.

Alkaline cleaners owe their detergency to the displacement of soils by surface active materials (surfactants) and alkaline builders to create emulsions that are easily rinsed away.  The correct blend of builders, surfactants and conditioners will provide the aqueous cleaner you need.

Determining factors in alkaline cleaner selection:

  • Determine the basis metal undergoing the cleaning process.  This is a most critical step to assure that the builders chosen will not attack the basis metal.  Remember that soft metals such as aluminum , zinc and zinc alloys will require a milder (lower pH) cleaning solution.
  • Choose a cleaner formulated to effectively remove the soils most commonly encountered on the basis metal.
  • Drawing and stamping compounds typically require higher heat to saponify the animal fat usually encountered with this type of soil.
  • Simple rust preventive oils and water soluble coolants are most easily removed with less aggressive (lower pH) containing products and lower temperatures.
  • Waxes, heavy oil rust preventives and heavy corrosion resistant compounds usually require a combination of an aggressive cleaning compound (higher pH), strong emulsifiers and dispersing agents along with higher temperatures in order to effective clean the metal substrate.
  • Choose a cleaner that is consistent with the method by which the parts will be processed: Immersion cleaners versus spray cleaners.  Formulations of these products differ significantly.
  • Decide if a liquid cleaner or powdered product is preferred.  Liquid product can be easily automated and are typically safer to handle.  Powdered products on the other hand are usually more economical.