Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1399684
20 | July - August 2021 | www . machinerylubrication.com LUBRICANT SELECTION Formulation Derived Thermoplastic Thermal Decomposition Oxidatively Derived Contaminant Derived Biological Derived Organic Formulation Derived Inorganics - metallic and non-meallic Soot Coke Coal Non-Organic sludge; however, they don't necessarily contain the chemistry to make them actual sludge. Over time, these deposits may dehydrate and cure onto metal surfaces, becoming difficult to remove mechanically. ese deposits are often referred to as varnish. In contrast, sludge deposits have been shown to be those containing metal salts of carboxylic acids. When these deposits are dried, they become powders. ey physically differ from varnish in that they are always soft deposits. ese deposits are classified as oxidatively derived-organic deposits with inorganic parts. Deposits that fall into the Lubricant Bin are those components that are part of the oil formulation. Occa- sionally, one may find an additive component that has come out of a solution from the lubricant and deposited itself in the system. Improper blending or additive incompatibility is a prime cause of this type of deposit. Incompatibilities between two lubricant formulations can also cause one or more of the additive formulations to come out of the solution to form a deposit. Further categorization of the deposits into Level 2 Clas- sification set of Bins is also possible, allowing one to group by the sources of deposit formation. Figure 4: Level 2 - Organic Deposit Classifications Figure 5: Level 2 - Classifications of Non-Organic Deposits Organic Deposits Organic deposits are often soluble in the in-service lubricant, allowing them to transition in and out of the solution depending upon the environ- ment. ese deposits are often referred to as "soft contaminants." Organic deposits can be further divided into- formulation derived, thermoplastic, thermal decomposition, oxidatively derived and contaminant derived sub-categories. is Level 2 Classifi- cation is illustrated in Fig. 4. Formulation Derived Many additive components may contribute to deposits either after they have reacted or due to dropping out of the solution in an unreacted state. It is common to see reaction products from sacrificial additive components in deposits. In Rust and Oxidation lubricants, it is common to find reacted primary antioxidant species in deposits, which produce organic deposits. Thermoplastic Some high-temperature degrada- tion processes produce high molecular weight molecules that create deposits which act like thermoplastics. ese deposits are typically solid at room temperature, however, they become liquid and flow at elevated temperatures (typically at or below fluid operating temperatures). It is common to see this type of deposit from fluids that have failed due to spark discharge. Thermal Decomposition Hydroca rbon molecu les will typically crack at temperatures above 300°C. ere are two actions that can happen. e first is when small, cleaved-off moleculesl volatize from the fluid. is portion of the reaction is not a deposit former. e second is molecular condensation. As the small molecules are split off, the remaining portion of the molecule will condense. is condensation is in the absence of air, so dehydrogenation will be part of its decomposition. As a final product, the formation of coke will be observed, however, there are numerous deposit chemistries observed before the coke is formed. Oxidatively Derived Oxidatively derived deposits are among the most common classification found in lubricant deposits because oxidation is one of the primary lubri- cant failure modes. These deposits usually have a higher molecular weight than the lubricant, which contributes to their inability to stay in solution. Many incorrectly assume that most deposits fit into this category. Contaminant Derived Organic contaminants can ingress into the lubricant system, initiating a reaction. is reaction can be with the current formulation or it can be incompatible with the fluid, resulting in an organic contaminant deposit. is has been observed with some types of gas contaminants that may react with the in-service lubricant to create unique, organic deposits. Ammonia gas ingression, for example, has been found to react with Oxidation Derived degradation products to create deposits consisting of primary amides. Other gases have been known to produce their own signature deposits. Biologically Derived Deposits that are derived from biological growth include plant mate- rials such as sugar, cotton and proteins are considered biologically derived. These are often from fermentation processes. Microbial growth can also cause deposits classified in this bin. Although these deposits are organic in nature, they are typically found with the non-organic deposits during isolation. Non-Organic Deposits Non-Organic deposits are also defined as a Level 2 Deposit Classi- fication Bin. e Non-Organic Bin includes wear metals and dirt. In the non-organic classification, one finds the categories of coal and plant life. ese two do contain some carbon-hydrogen functionality; however, they behave