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"One of our customers recently found some waxy material in an enclosed gearbox after using a synthetic gear oil for approximately 61 hours. My initial thought was that this could possibly be the residue from a rust-preventive fluid. However, this gearbox has been used for a period of time. Is it possible that this is seal material or a sealant? If not, what could be causing this waxy residue and how can it be prevented?"
Waxy residuals are not as prevalent as sludge or solid sediment but can be generated by several sources depending on the fluids used, the contaminants present in the gearbox and the operating temperatures.
A common source is present in some mineral oils. When operating at low temperatures (0 to 30 degrees F), waxes existing in these lubricants may precipitate. Water contamination can also intensify this effect.
Other precipitations may be produced by a variety of causes such as cross-contamination of different lubricants (including synthetics), the use of assembly oils, employing certain types of additives or even contaminants from the environment.
In order to determine the root cause of the waxy material, you may wish to analyze it using Fourier transform infrared (FTIR) or X-ray fluorescence (XRF) spectroscopy and identify its properties. This information along with the machine’s maintenance/operation history can help you pinpoint the origin. Also, you can filter the oil for patch tests and observe it under a microscope.
Regardless of the waxy material’s origin, there are ways to help prevent it. You should try to minimize cross-contamination among lubricants, assembly oils and additives used in the machine. Take steps to control contaminants in the oil that come from the environment or production processes. Before using an additive or assembly oil, or switching to a synthetic lubricant, ask the lubricant supplier about the potential effects of mixing different products. Also, be sure to limit lubricant contamination with water or process emulsions.
In addition, if the equipment must work at low temperatures, verify that the lubricant formulation is appropriate for these operating conditions.
Most likely the waxy residue did not come from a sealant. When a seal or gasket is incompatible with a lubricant, the typical effects are gasket swelling or shrinking but not the generation of wax products.
For more information on inadvertent mixing of fluids and oils, read the following article at MachineryLubrication.com: https://www.machinerylubrication.com/Read/283/testing-lubricants-companibility.