By Jerry McLain
All rotating equipment requires timely and effective lubrication to help reduce wear, minimize lubricant consumption, maximize efficiency, and curb unscheduled downtime. For many industrial plants the job can seem daunting. With potentially hundreds of individual lubrication points and potentially harsh operating conditions, industrial plants face their fair share of lubrication challenges.
There is no shortage in the number and types of lubrication applications in a plant (conveyor bearings, chain drives, gears, gearboxes, un-mounted bearings, electric motors, air compressors, fans and blowers, and many others) and no shortage of environmental influences (temperature extremes, dirt and dust, and moisture). All make the case for proper lubrication.
In addition, cracks are beginning to surface with traditional “manual” lubrication methods. Over- or under-greasing of bearings (leading to failure) always looms; lubrication intervals may be sporadic or ill-timed; contaminants can inadvertently be introduced; equipment reliability ultimately may be compromised; and, in some instances, points simply may be out of reach or otherwise impractical for maintenance staff to handle.
All this has paved the way for “centralized” lubrication systems engineered to provide consistent lubricant in the right amount at the right time in the right way. Such systems (in all their forms) feed lubricant from a central source to the points on a machine or machining system where friction occurs.
With centralized lubrication, every bearing receives the proper lubricant in an exact amount to minimize wear and promote longer service life. The problems associated with excessive lubrication can vanish; lubricant consumption can fall over time (in some applications by as much as 50% compared with inexact manual methods); and maintenance time, energy, and costs can diminish. (The only requirements: Refill the lubrication reservoir and occasionally inspect the connected lubrication points).
Regardless of their configuration and scope, centralized lubrication systems have demonstrated that they can add value in today’s (and tomorrow’s) industrial plants.
Centralized lubrication technology generally falls under two broad “umbrella” categories: total loss and circulating oil systems.
In total loss systems friction points are always supplied with fresh lubricant (oil, fluid grease, or grease) at specific intervals (time or machine-cycle dependent) during the lubricating cycle (such as pump run time). The lubricant is supplied in the proper quantity at friction points to allow for buildup of an adequate film of lubricant during the subsequent idle period. Over time, the forces of aging, evaporation, bleeding, and leaks will contribute to partial depletion of the lubricant at the friction point.
Circulating oil lubrication systems provide for the lubricant to flow back into the lubricant reservoir for reuse after passing through the friction points. In this way, the lubricant carries even more benefits as it transfers forces and damps vibrations; removes abrasion particles from friction points; stabilizes the temperature (cooling or heating) of friction points; prevents corrosion; and removes condensate and process water.
Within the total loss and circulating oil categories, primary types of installations include single-line, dual-line, and progressive feeder lubrication systems. Their profiles:
Single-Line. These total-loss lubrication systems supply machinery lubrication points with relatively small amounts of lubricant (oil or fluid grease up to NLGI grade 2) to cover precisely the amount consumed. As such, they operate intermittently as required. Lubricant can be delivered by manually, mechanically, hydraulically, or pneumatically operated piston pumps or by electrically driven gear pumps.
In single-line systems, lubricant is metered out by piston distributors installed in the tubing system. Exchangeable metering nipples on the distributors make it possible to supply every lube point with the requisite amount of lubricant per stroke or pump work cycle. Metered quantities can range from .01 to 1.5 ccm per lubrication pulse and lube point. The amount of lubricant to be fed to the lube points can also be influenced by the number of lubrication pulses.
The standard layout of a single-line total loss lubrication system incorporates a pump and spring-loaded piston distributor; main line (connecting to pump and distributor); and secondary line (connecting to distributor and lube point). Performing as a total loss lubrication system, an oil return line from the lube point to the oil reservoir is unnecessary.
Dual-Line. These systems can deliver oil or grease (up to NLGI grade 2) to as many as 1,000 lube points (and distribution points can be easily added or removed). They can be configured to run either as total loss or circulating oil versions.
Their layout consists of two main lines with their respective secondary lines and fittings; an electrically driven pump with reservoir; dual-line feeders; reversing valve; and control unit.
All the distributors of a system are pressurized at the same time, resulting in low pressure losses, and the “reset” of the delivery piston is simultaneously the second delivery stroke, which takes place at full pump pressure. This makes the dual-line versions especially suitable for extended systems and more viscous types of grease. Assemblies with or without compressive seals can be specified to accommodate light and heavy-duty operating conditions.
Progressive Feeder. Whether functioning as a total loss or circulating oil system, these are intended for intermittent delivery of lubricant (grease up to NLGI grade 2) and can handle up to several hundred lube points. They further offer the capability to provide central monitoring of all feeder outlets, if desired, at relatively low cost.
These installations use pneumatically, manually operated, or electrically driven piston pumps. Metered quantities of lubricant are fed progressively in predetermined ratios from master feeders to the lube points either directly or via a secondary downstream feeder. The lubricant does not leave the respective feeder until the preceding one has discharged its volume. If a lube point does not accept any lubricant, regardless of the reason, or if a secondary feeder is blocked, the entire lubrication cycle is interrupted, which can be used to emit a signal to alert operators to the problem.
GUIDELINES FOR SUCCESS
Decision-making for the most appropriate system will depend, in general, on the application and, in particular, on a range of other parameters, such as the operating conditions, (variations in the operating temperature and lubricant viscosity); accuracy requirements for lubricant quantities; system geometry (size, dimensions, and symmetry); and monitoring demands, among others.
When planning, installing, and subsequently implementing a centralized lubrication system, these guidelines can help maximize opportunities:
• Address process critical equipment first.
• Choose a system compatible with the operating environment.
• Determine the number of lube points.
• Choose the proper lubricant for the temperature, speed, and load conditions.
• Calculate appropriate dispense rates and quantities for the application.
• Choose pumps consistent with the type of actuation and capacity of the system.
• Consider monitoring systems that may be required.
• Train all operations, maintenance, and production personnel on lubrication basics and how they relate to the plant’s equipment reliability strategy.
Footnote: Care should be taken during the installation, startup, and maintenance of any centralized lubrication system. The designated system should receive the same attention as all other sophisticated equipment on a machine. Partnering early in the process with an experienced and knowledgeable expert can help fulfill the promise these systems can deliver.
Article published with permission from SKF. Jerry McLain is Business Development Manager-Lubrication for SKF USA Inc., 1510 Gehman Road, Kulpsville, PA 19443. Phone: 513-248-4335. His extensive experience includes assisting in the development and implementation of customized machinery and equipment lubrication programs for industry. E-mail: firstname.lastname@example.org Web site: www.skfusa.com