Proper lubrication of rolling bearings in rotating machinery—pump systems included—is essential in realizing optimized performance and reliability. Whether grease or oil, lubricants serve to prevent wear and damage between a bearing’s rolling and sliding contact surfaces, reduce friction and heat generation, help protect against corrosion, and help keep out contaminants.
The right lubricant for an application should always be supplied in the right quantity at the right time. This may seem intuitive, but adhering consistently to this practice can be challenging, especially when bearings are lubricated manually.
Many manual-lubrication technologies—some quite advanced and user-friendly—have been developed to aid the process. But what if lubrication points are difficult to access? What if too much or too little lubricant is dispensed? What if the number of points requiring lubrication is especially high? Typically, there can be upwards of 7,500 individual lubrication points at a paper mill, 4,000 for a steel mill, 3,500 for a refinery, and 2,000 for a cement mill—all requiring service and vigilance over time.
Can your operation afford the costly downtime to make lubrication-related maintenance repairs that could have been avoided?
When manual lubrication turns out to be impractical or inconvenient, automatic lubricators and centralized lubrication systems provide a range of solutions.
As one of the many handheld tools appropriate for manually lubricating bearings, rechargeable battery–driven grease guns offer portability, consistent performance and user-friendly interfaces to maximize efficiency and accuracy. With such a tool, lubricant flow rates can be precisely adjusted and an integrated grease meter will dispense the proper amount of lubricant to prevent possible over- or under-greasing. A visual display further assists users by showing battery charge level, amount of grease dispensed and blocked lubrication points.
Where manual lubrication does not make sense, “hands-free” lubricating technologies offer viable alternatives, depending upon the size of a machine, type of required lubricant, and number of lubrication points, among other factors.
- Automatic lubricators. These inject the precise and correct amounts of contaminant-free grease at single or multiple lubrication points. They inherently minimize the risks of over- or under-lubricating and can supply lubricant 24/7 for periods up to a year as governed by a pre-set timer. These lubricators will easily control the amount of grease used in each application.
- Single-line systems. In this centralized configuration, a central pump station automatically delivers lubricant through a single supply line to a lubricant metering device. Each metering device serves one lubrication point and can be adjusted to deliver a precise amount of grease or oil. Such systems can service one machine, different zones on one machine, or several separate machines, and can allow for expansion.
A single-line system can pump long distances and operate within a wide temperature range. And even if one lubrication point becomes blocked, the system continues to operate. System components include pumps; devices for metering, control and monitoring; and accessories. The system components will differ in size and design, depending on the lubricant (oil or grease) required for the application.
- Dual-line systems. These centralized systems are designed for large machines with many lubrication points, long lines and harsh operating conditions. They use two main lines that are supplied alternately with grease or oil.Such systems are engineered to deliver lubricant to hundreds of points (and distribution points may be added or removed as necessary).
System layout consists of the two main lines and respective secondary lines and fittings, an electrically or pneumatically driven pump with a reservoir, dual-line feeders, solenoid valves, and pressure switches or transmitters for a main-line monitoring and control unit.
- Progressive systems. These dispense small measured amounts of lubricant at frequent and intermittent intervals while machines are operating. The grease or oil flow created by the system’s pump is proportioned by progressive metering devices and distributed to each lubrication point according to need.
Such centralized systems represent a relatively simple and inexpensive method of automating the lubrication process for machinery in service.
Progressive systems include a pump connected to at least one primary metering device. If needed, second-level metering devices can be connected to the outlets of the primary metering device to increase the number of lubricated points.
Deciding which type of lubricant to use and how the lubricant would best be dispensed will influence success or failure in service, complicated by the fact that no single “universal” lubricant exists to cover all application scenarios. Partnering with a knowledgeable specialist can help end users understand and implement the best lubrication practices to maximize operational productivity and reliability.
Grease or Oil?
In addition to guiding how and when lubricant can best be supplied, application parameters will similarly help in selecting grease or oil. Such parameters include the type of machine, bearing type and size, temperature, load conditions, speed range, operating conditions (such as vibration and horizontal/vertical orientation of the shaft), and external environment. Equipped with this knowledge, users can narrow the choices to arrive at the most appropriate lubricant type and formulation.
Grease. When feasible, grease for bearing lubrication is usually the preferred choice, because it is easy to apply, can be retained within a bearing’s housing, and improves sealing against solid or moisture contamination. The relative tradeoffs, which may not be significant for a particular application are that grease offers no cooling capability, increases friction and torque, limits bearing speed, cannot filter contamination and will be difficult to remove from a bearing if required.
Lubricating greases consist of mineral or synthetic base oil suspended in a thickener (with the oil accounting for at least 75 percent of the grease volume). Additives may also be introduced to impart characteristics such as protection against wear or corrosion- and friction-reducing properties. By varying base oil viscosities, thickeners and additives, greases can be developed with distinct characteristics to satisfy particular applications and operating conditions.
Oil. This category will usually be specified to lubricate rolling bearings when high speeds, high temperatures or lubricant life and cleanliness preclude the use of grease. If heat needs to be removed from the bearing, circulating oil, oil jet, oil mist, oil splash or air-oil lubrication methods should be used.
When application conditions permit, the advantages of oil include easy filling and draining, increased bearing speed limit, reduced heat generation, and the capability to filter contaminants. The tradeoffs are that oil systems are relatively expensive, often complex, and potentially require special sealing methods to prevent oil leakages.
Mineral oils represent the most common oil lubricants, and rust and oxidation inhibitors are typical additives. Synthetic oils will usually be considered for bearing lubrication in extreme cases, such as very low or very high operating temperatures, or when extended service life is required.