More about Metal Cleaning
Soils
A metal can become contaminated with various soils from previous manufacturing operations, handling, or from the raw metal stock. Some examples of soils are:
Typical Soils
- Rust
- Scale
- Tarnish
- Oxides
- Drawing Compounds
- Machining Oils
- Stamping Oils
- Drawing Compounds
- Fingerprints
- Fluxes
- Inks & Dyes
- Smuts
- Chemical Residues
- Buffing Compounds
- Polishing Compounds
The various soils can be broken down into six categories. 1)Pigmented Drawing Compounds, 2) Unpigmented Oil and Grease, 3) Chips and Cutting Fluids, 4) Polishing and Buffing Compounds, 5) Rust and Scale and 6) Miscellaneous Surface Contaminates.
Pigmented Drawing Compounds
Pigmented drawing compounds are very difficult to remove from metal. Because of this, it is recommended that the pigmented compounds not be used when ever possible.Unpigmented Oil and Grease
Unpigmented drawing lubricants, rust-preventative oils, quenching and lubricating oils can be removed without much trouble using the appropriate cleaning process.Chips and Cutting Fluids
Chips and cutting fluids are usually relatively easy to remove either by immersion or steam cleaning. Once the metal is cleaned of the cutting fluids, the chips usually simply fall away. The only problem comes when the metal has become magnetized. Then removing the chips become more of a challenge.Polishing and Buffing Compounds
Removing polishing and buffing compounds can be difficult. For effective cleaning it is important to choose the proper cleaning method and make certain that cleaning is thorough.Rust and Scale
There are a number of methods, both chemically and mechanically, for removing rust and scale from metal. The method chosen should be made based upon a number of factors. The thickness of the rust or scale, the composition and condition of the metal, allowable metal loss and surface finish requirements are just a few of these considerations.Tests for Cleanliness
White Glove Test: The metal may be tested while wet or dry. A white glove, cotton swab or lens tissue is wiped over the surface of the metal and examined. If there are traces of black, gray or off-white residue, or traces of oil staining, then the metal is not sufficiently clean. This test is to show the presence of particulate and organic contaminations.Water Break Test: This simple test is performed by submerging the metal in clean water and examining it. If the metal retains a film of water across the surface without any signs of water-breaks, the metal is considered clean of hydrophobic contaminants such as oils, greases and water-insoluble organic compounds.
There are other more thorough or specific methods of testing for cleanliness of metal. These require more sophisticated testing equipment and methods, and are more costly to perform. The method of testing will largely depend upon the degree of cleanliness required and the application of the part being tested.
