Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1399684
ML www.machinerylubrication.com | July - August 2021 | 19 ML Lubricant Degradation & Deposit Formation ere are many sources of lubricant degradation that often lead to deposits. Some of these include: • Oxidation • ermal Degradation • Micro-Dieseling • Spark Discharge • Extreme Temperature Zones • Combustion • Ultraviolet Degradation • Contamination • Incompatible Lube Or Other Liquid • Dirt And Hard Particles • Water • Gas • Additive Reaction By-Products Once a fluid has undergone degrada- tion or been exposed to contamination or initiation failure, there are several factors to determine the lubricant's propensity to develop deposits. e formulation can play a large role in this. Engine crank- case formulations contain dispersants to suspend or solubilize soot and other degradation products in the fluid. e base stock of the lubricant also contributes to its solvency and the fluid's deposit control abilities. Mineral oils have lower solvency, and synthetic API Group V fluids have higher solvency. In addition to lubricant formulation, two other variables that determine deposit formation are temperature and pressure. ese factors are particularly relevant when the degradation products are soluble and easily transition in and out of a solution. Lower temperatures will decrease a fluid's solvency, causing some types of degrada- tion by-products to precipitate, forming deposits. Pressure can also drive these contaminants out of solution, explaining one of the reasons why it is common to see deposits in journal and thrust bearings. Deposit Classification Bins ere are many mechanisms that degrade lubricants and an even higher number of different chemistries found in lubricant deposits. e virtually limitless number of deposit chemistries can, however, be classi- fied by their physical characteristics and the source of their formation. Sorting deposits into classification bins is beneficial to better understand the source of the deposits and determine appropriate remediation efforts. is article suggests some nomenclature and definitions for these Deposit Classification Bins, as shown in Fig 2. ese bins can first be defined as Level 1 in broad terms based on their chemistry, as illustrated in Fig. 3. Deposit Water Organic Lubricant Non-organic Figure 3: Level 1 Deposit Classification Bins Better understanding the composition of the deposit allows further classifications based on the deposit formation source. e most basic chemistry difference is whether the deposit is organic or non-organic. Non-organic deposits can be defined as those deposits that are insoluble in highly polar organic solvents and contain no carbon-hy- drogen spectral features. Organic deposits can be defined as material that contains carbon-hydrogen bonds (CH2 and CH3), is primarily insol- uble in hydrocarbon solvents (which makes it a deposit) and is often soluble in polar organic solvents. Water content is also found in many deposits. Although water is potential sediment itself, more often it is part of the deposit. It often determines the consistency and tenacity of a deposit. It is common to find moisture in deposits when they are first generated, allowing the deposits to be easily wiped off. ese types of deposits are often referred to as Determine Root Cause Deposit Lubricant Separation Process Compare Results Characterize & Classify Elemental Spectroscopy FTIR XRF FTIR Figure 1: Root Cause Determination Process Deposit Water Lubricant Non-organic Formulation Derived Formulation Derived Thermoplastic Inorganics Thermal Decomposition Soot Oxidatively Derived Coke Contaminant Derived Coal Biological Organic Figure 2: Deposits Classifications