Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/680544
www.machinerylubrication.com | May - June 2016 | 55 and give the oil time to cool down before being reintroduced to the delivery system. Another is dispersing contami- nants within the sump. A high oil level in the crankcase can lead to oil churning. Depending on the severity, this increased agitation can result in foaming problems. Churned motor oil produces increased oil temperatures, which causes oil oxida- tion and lower oil pressures. Aerated oils become spongy and harder to pump, which can lead to starvation within the engine. A low oil level in the crankcase can also result in lubricant starvation if it is low enough. However, just being one quart of oil low can make a difference in the life of the engine and the oil. With less oil in the sump, the same oil must now make more passes through the system without a cooldown and release period. The frictional zones within the engine that generate heat are exposed to higher temperature oil, which will start to oxidize faster. Also, being low a quart of oil changes the amount of addi- tives in the system and how they are depleted. While being one quart low won't lead to an immediate failure, it has a huge impact on engine longevity. Gearboxes When discussing gearbox oil delivery systems, there are two primary types: circulating systems and splash- or bath-lubricated systems. Circulating systems deliver oil to the bearings and gears inside the housing by use of a pump. These systems usually consist of a pump, filter, oil cooler and piping to supply fresh oil to internal components. With splash- or bath-lubricated systems, the internal components of the gearbox are partially submerged, allowing the lubricant to be picked up to create a lubricating film. Although each of these systems operates using different principles, they have the same goal: supply lubricant to the internal components to reduce friction. When maintaining circulating systems, being low on oil generally isn't as devastating to the internal compo- nents as it is to the lubricant. You just don't want too high or too low of an oil level. I have found that when running an oil cooler in line with the flow of fluid, you can get away with a lower oil level without damaging the equipment and the oil. However, if the oil level gets too low in the system, the pump may start to suck air and decrease the amount of oil delivered to the internal components. In splash- and bath-lubricated systems, a precise oil level is very important. If the level is too high, the oil can aerate and may not deliver a substantial oil film. Frequently, foaming issues result if the oil level is too high in a splash-/bath-lubricated gearbox. If the oil level is too low, lubricant is starved from component surfaces and rapid wear is generated, causing machine failure. This is probably one of the costliest failures due to metal-on- metal friction, which can lead to shaft, housing and other machine damage. It's crucial when installing or maintaining splash- or bath-lubricated gearboxes to set the oil level correctly. Failure to do so can be the difference between getting one hour or 10 years of operation. Pumps Maintaining a correct oil level is also critical to the operation of oil-lubricated pumps. I've been in many plants that employ constant-level oilers. When asked why they use this type of device, the response is usually because it came with the pump or to check the oil level. However, constant-level oilers should not be used to determine the oil level. Think of it like a dog's water bowl with a 2-liter bottle for a reserve. The constant- level oiler supplies oil when the level decreases in the sump, just like the reserve of water refills the bowl when your dog takes a drink. While the water level in the dog's bowl doesn't matter as long as there's some water in the bowl, the oil level in your pump does matter. The majority of pumps set the oil level halfway up the lowest roller on the bearing. This supplies adequate lubri- cant film to the bearings while reducing energy consumption and oil churning. Damages Not only does the machine suffer if there is an inaccurate oil level, but so does the lubricant. When oil levels are too low, rapid machine damage occurs. There may be an increase in friction due to boundary conditions from a shortage of lubricant film or viscosity changes created by increased oil temperatures. This metal-to- metal contact is adhesive wear that leads to smearing (material transfer), spalling, pitting and seizing. If oil levels are low for long periods of time, higher equipment rebuild costs may result. High oil levels usually affect the lubri- cant properties. Some machine damage may also take place if the level is not corrected. When the oil level is high for long periods of time, the equipment can Checking a level indicator might seem like a small task, but it is critically important for the reliability of your machinery.