The main contaminants of cutting fluid are metal powder, grit fines, floating oil, free water, as well as microorganisms and their colonies, especially Mucorales fungi.
Solid powder in cutting fluid originates from workpieces and cutting tools, with the primary hazards being accelerated tool wear and impaired machining quality.
Floating oil refers to oil leaking into the cutting fluid system from the machine tool’s transmission and hydraulic systems due to poor sealing, plus anti-rust oil on the surface of processed materials. The hazards of floating oil include causing swelling and deformation of certain materials in the cutting fluid system, disrupting the emulsification balance of emulsion and leading to its destabilization. Moreover, floating oil usually floats on the surface of the emulsion, blocking the contact between the emulsion and air, which results in oxygen deficiency in the emulsion, rapid reproduction of anaerobic bacteria, and accelerated spoilage and deterioration of the emulsion.
Cutting Fluid Maintenance Work
Detect the concentration of cutting fluid with a refractometer daily and adjust it in a timely manner; a proper concentration ensures the stability of the cutting fluid.
Inspect the floating oil concentration and solid powder content (in PPM), and adjust the floating oil concentration by turning on the oil skimmer as needed.
On-site Communication
Nick: Since the current detection of aluminum powder content has reached the upper limit of the measuring range, the actual content can be determined by testing after dilution, and the aluminum powder content from the stretching machine can also be measured. Is there any leakage in the valves of the emulsion filtration system?
Ben: There is a lot of foam today. The waste emulsion skimmed by the oil skimmer contains a large amount of water but a small amount of aluminum powder.
Jack: A preliminary qualitative analysis of the delivered emulsion was conducted today. Preliminary qualitative results: When 20ml of the emulsion was filtered through a 5μm membrane, particles larger than 5μm were retained, covering 30-40% of the membrane surface area (black aluminum powder); particles ranging from 2.5μm to 4.9μm covered 80-90% of the surface area.
Ben: Is this result generally acceptable or unsatisfactory?
Jack: The membrane with particles ≥5μm needs to be dried and measured tomorrow. The black substance identified in the qualitative analysis is a mixture of black oil and aluminum powder, so microscopic testing is required after dehydration!
…………………………one week later………………………………………….
Nick: Has there been any progress on installing the additional oil skimmer we discussed yesterday? According to current statistics, the customer is still replacing cutting tools frequently, so we need to consider further improving the emulsion.
Ben: The oil skimmer for the intermediate coating tank has been installed, and the substance skimmed from the tank is quite concentrated. The installation of the oil skimmer for the sewage tank has also been improved.
Nick: Test the content of aluminum powder and tramp oil. Ben: It was tested at 100 yesterday, and the emulsion has become much whiter. The tramp oil content has been controlled at 1.3%.
Nick: Did you provide the standard values for aluminum powder content and emulsion? Are these standards reasonable?
Jack: In accordance with industry standards, the effective concentration of the emulsion is 4.1% as shown in the table, which is acceptable; a slightly higher effective concentration is beneficial for machining.
Summary
Tramp oil is removed by the oil skimmer, and the fine cutting chips wrapped in the tramp oil are also removed together. Regular operation of the oil skimmer can maintain the balance of the entire emulsion system, including the concentrations of emulsion and tramp oil, as well as the content of fine particles (in PPM). This thus avoids the aforementioned problems caused by excessive tramp oil concentration and particle content.
