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		Surface Treatment
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Surface Treatment

Washing Techniques

The choice of technique is dictated by a few main considerations, such as:

Type of surface and shape of the pieces
Type of polluting material to be removed
Level of cleaning required

Type of surface and shape of the parts
Different types of materials (gold, steel, brass, alluminum, zinc, plastics in general, Teflon, polyurethane, etc.) must be treated differently (especially if using water based detergents – when compatible), therefore it is necessary to carefully take into consideration the chemo-physical parameters of the materials to be treated (heat sensitivity, resistance to warping, risk of corrosion), the structure of the parts (presence of dead holes, grooves, layers, etc.), the texture of the surface (shiny, porous, etc.) and if the parts can sustain being joggled during the washing cycle. It is important to keep in mind that the cleaning process will be much easier and thorough if the parts going through the process are the same or at least of the same kind.

Type of polluting materials
The following table classifies the different impurities that can be found on surfaces subdivided in organic and inorganic contaminating materials.

INORGANIC CONTAMINANTS
Group	Example	Chemo Physical Characteristics	Origin
Metals	scales, base metal shavings	Not soluble in water or organic solvents; soluble in acids and more infrequently in alkaloids	Mechanical productions
Non - metals	Graphite	Not soluble in water, organic solvents, acids or alkaloids; can only be destroyed with energetic oxidants	Graphite based lubricants or metal grains
Metal oxidants and hydroxides	Al(OH)3, Fe2O3	Not soluble or barely soluble in water with decomposition; soluble in acids	Base metal components
Sulphurs, phosphides, silicides	CuS, FeP, ecc.	Partially soluble in water with decomposition, soluble in acid	Base metal components
Salts	FeCl3, Fe2(SO4)3, NaCl	Generally soluble in water,accelerating corrosion	Pickling residues

ORGANIC POLLUTING MATERIALS
Group	Example	Chemo Physical Characteristics	Origin
Hydrocarbons	Paraffin	Not soluble in water or mineral oils;soluble in organic solvents	Lubricants,anticorrosive oils and greases, etc.
Inferior aliphatic acids	Lactic acid, butyric acid	They reinforce corrosion due to salts, are not water soluble but can be dissolved in solvents	Human perspiration
Fatty acids and their glycerides	Oleic acid, stearic acid, oxidising products	They prevent the adhesion of the linings,(coatings), not soluble in water and slightly soluble in solvents; they are soluble in alkaline solutions.	Cleaning paste residues and oils in general
Amorphous carbon	Carbonisation of organic matter	Extremely adherent, can be dispersed in water or solvent	Miscellaneous

For the different kinds of products used in the degreasing process, below is a listing of the polluting materials and which products are best used for their removal.

PRODOCTS USED	POLLUTING MATERIAL
Water	Salts; residue from materials used to process water soluble metals
Acids	Metal oxides (rust) salts (limestone [calcareous]); a great number of metals
Alkali	Some metal oxidants (amphoteric); some metals (amphoteric);natural saponifiable fats; some polymer paints
Complex Agents	Metal oxides; metal salts
Surface -active agents	Synthetic oils and greases (emulsions)
Solvents	Natural and synthetic oils and fats; some paints and plastics

Level of cleaning required

In relation to the specific requests and to the different operations that must be performed after the washing cycle (assembly, processing, temporary warehousing, gluing, galvanization, thermal treatments, painting, etc.), because there is no specific method to determine the degree of cleaning achieved, only the user, based on personal experience, can decide the actual cleanliness of the parts.