Finishers' Think Tank: Identifying Specific Oily Soils

It’s not uncommon to be hit with a vexing cleaning problem. Oily soils on parts can at times provide a real challenge. Unfortunately these soils may be the result of a mixture of these materials, rather than one simple, uncomplexed, oily soil. Backtracking with the fabricator helps. They may submit, on request, technical data bulletins and MSDS that can identify or shed light on the unknown oils. Suppliers of cleaner blends may also have practical experience to tackle the specific cleaning problem. It may be the case that identifying the soil or soils may need to be undertaken, in order to develop a solution to the cleaning problem. Should this be the challenge, and then perhaps the following sequence may be helpful.

 

The oil or oils in doubt may encompass: drawing, sulfurized, quench, chlorinated paraffin, machining, types. The suggested evaluation steps that follow must be conducted using proper lab safety procedures and properly operating equipment, including technique and protective clothing. Handle chemical reagents properly. 

 

 

 

 

 

 

 

 

Note: Sulfurized oils are commonly black or brown. This test in Step #5 is reliable, unless the sulfur is chemically-bonded in a complex way in the oil.

 

 

 

 

Once the unknown soils have been identified, selecting an effective soak cleaner is easier. Suppliers provide a wide range of cleaners, blended specifically to remove many different types of soils. Surfactants and wetting agents have been developed with balanced alkalis, conditioning agents, solvents and dispersants, to address the most challenging cleaning issues. That is why there is not one universal cleaner. The metal forming and fabrication industries utilize more synthetic “green” oils in their processing operations, such as soy derivatives. These, in turn, may simplify cleaning demands.

 

 

When a candidate cleaner has been selected, it is of practical importance to aggressively prescreen it. Doing so improves confidence that cleaning will be a snap. I suggest adding the oil or mixture of oils to the cleaner prepared per recommended operating parameters (concentration, temperature). Gradually add the soil to the cleaner with good mixing.  Stop mixing and let the solution settle. Observe for any floating oils (lack of emulsification). Continue adding the soil by percentage increments until emulsification no longer occurs. Now, add the cleaner concentrate at 10 - 20% of the initial make-up. Mix well. Stop mixing and confirm that emulsification of the soil has been restored. Repeat this test as required. To this artificially-aged cleaner bath, immerse a previously cleaned steel panel for a few minutes, rinse in cold running water for 30 seconds, and observe for water breaks. If there are no water breaks, continue by immersing the panel in either 5% hydrochloric or sulfuric acid for 30 seconds. Rinse again in cold running water for 30 seconds. Again, observe for water breaks. If there are none, then the cleaner, artificially-aged with soils, appears to be a good selection for the cleaning challenge. Still not satisfied? Then why not coat a stamping grade steel panel with the oily soil or its mixture. Next bake the soils into the surface. Now, repeat the above-described cleaning test. This second test, if passed, should afford a high level of confidence that the selected cleaning will be effective.