Machinery Lubrication

Machinery Lubrication November December 2015

Machinery Lubrication magazine published by Noria Corporation

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2 | November - December 2015 | FROM THE FIELD V i s c o s i t y I AVOIDING ndustry rides on a film of oil. The oil's viscosity bears the load and defines the extent of clearance achieved between working surfaces. Some- times that clearance is thick and bountiful, and other times it is deflated or extinct. Without viscosity, most machines would rapidly self-destruct with mechanical fric- tion and wear. There is also a well-known penalty and reliability risk from too much viscosity. Like most things, the selection of a lubricant's viscosity must be optimized to enable needed protection and disable the danger from excessive viscosity. For instance, too much viscosity can cause churning losses and exces - sive heat generation from molecular friction. It can also impede lubricant movement and flow to lubricant-hungry surfaces. One of the most famous disadvantages of too much viscosity is high energy consumption. In recent years, we've seen automaker-specified viscosity being lowered in crankcase service from 5W40 to 5W30, and now in some cases to 5W20. These changes are all for the sake of energy conser- vation. Of course, the primary driver for energy conservation is not to save money on fuel or electricity but rather to reduce the consumption of fossil fuels, which emit harmful gases (carbon dioxide, nitric oxides, hydrocarbons, etc.) into the atmosphere as a byproduct of combustion. While any effort to decrease energy consumption and protect the environment is a noble cause, you should be wise to how excessive viscosity trimming can backfire. Under ideal conditions, lowering viscosity in an engine may result in no harm. However, in worst-case scenarios, danger- ously collapsed oil films can accelerate wear and lead to premature failure. Such scenarios in a car engine may occur due to low coolant levels, heavy loads (pulling a trailer), hot ambient temperatures, low oil levels, driving on dirt roads (high particle ingestion), short-trip driving patterns, water contamination and fuel dilution. Excessive wear in the combustion chamber region (rings, cylinder wall, valves and cams/followers) caused by aggressively low viscosity and worst-case scenarios will result in the loss of combustion efficiency, higher fuel consumption and harmful gases being released out the tailpipe. Too low viscosity can also lead to exces- sive volatilization and oil consumption in engines, both of which have a negative environmental impact. Low viscosity equates to small molecules that are more prone to vaporization at high temperatures along the piston ring belt, cylinder wall and exhaust valves. VISCOSITY STARVATION IN WORST-CASE SCENARIOS Lubrication engineers consider numerous factors when matching viscosity selection to the needs of the machine. Speed is an important factor, as is load. Both define the viscosity needed to produce hydrodynamic and elastohydrodynamic oil films. These oil films build a clearance between working surfaces to mitigate fric- tion and wear from mechanical contact. Some machines operate at varying speeds. Without speed, oil films are not producible. This is why it's often said that each time you start your car or truck, you are causing mechanical wear equivalent to AS I SEE IT Jim Fi t ch | Nori a Corpor at ioN the Pitfalls of Viscosity-starved MACHINES

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