Machinery Lubrication

Machinery Lubrication July - August 2018

Machinery Lubrication magazine published by Noria Corporation

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44 | July - August 2018 | www . When it comes to issues of viscosity and viscosity index, there are several questions that must be answered in order to properly set limits and alarms for oil analysis and oil change-out param- eters. One of the first things to determine is the proper viscosity to be used in the compressor. is usually requires some research in maintenance manuals as well as under- standing which components are being lubricated by the oil. Within a compressor, there may be gearing, bearings, slides, seals and countless other components that will stress the lubricant in different ways and require a different viscosity. For simplicity, let's assume that all internal parts need a viscosity of 5.5 centistokes and that the working temperature is 100 degrees C. If you are using an ISO 32 oil with a viscosity index of 108, you will hit that viscosity at 100 degrees C. If the temperature increases, the oil will thin and you won't have the same lubricating film needed to fully separate the machine surfaces. If a synthetic base oil or a different base oil with a higher viscosity index is used, the viscosity will be "What is an acceptable tolerance level for the viscosity index of a compressor oil (32 viscosity synthetic oil) for a screw compressor?" "Can GL-5 gear oil be used in an application where manual transmission f luid is recommended?" e American Petroleum Institute (API) GL rating system is intended for gear oil specifications. While a manual transmission does in fact have gears, it may also contain other components such as synchronizers. e gears and synchronizers have seemingly conflicting requirements. In general, the higher the GL rating, the higher the extreme pressure (EP) protection provided. is is great for reliability and wear reduction in hardened gear sets, but it can spell disaster for synchronizers. EP additives are often made of a sulfur/phosphorus compound that will adhere to metal surfaces through polar attraction. Once they have coated a metal surface, these additives need only to be introduced to heat and/or pressure (from a collapsing lubricant film) to spring into action and start doing their job. In a hard- ened gear set, this adds a great deal of wear protection as well as life and reliability to the component. However, because of the mech- anism in which these EP additives work, when they are introduced to softer yellow metals, the results can be disastrous. ey attach in the same manner (metal-wetting polar attrac- tion), and when heat and/or pressure is introduced, the additives will chem- ically attack the softer yellow metals. is aggressive attack can prematurely wear out synchronizers. GL-4 products typically use about half the sulfur/phosphorus additives of their GL-5 counter- parts. is means they provide less protection for the gear set but do not damage synchronizers quite as severely. When a GL-5 gear oil is used in a manual transmission that contains synchronizers, you can expect to find two to four times as much copper in the used oil analysis report as compared to a GL-4 oil. Eventually, the synchronizers will wear to the point that they no longer make contact with the other half of the cone, bottoming out before stop- ping the opposing gear. So while an API GL-5 gear oil can be utilized in an application where manual transmission fluid is recom- mended, there will be a tradeoff. You can anticipate excellent protection for the gears but also a reduction in synchronizer life if these components are made of softer material. Generally, you should heed the recommendations made by the manu- facturer. Issues such as those outlined above are considered during the components' design phase. Manufac- turers usually have all the information required to make educated decisions, which are then incorporated into their recommendations. ASK THE EXPERTS

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