Centralized systems can deliver proper lubrication

Many small problems can arise from improper or lack of lubrication. Proper lubrication is critical in helping to reduce component wear, minimize lubricant consumption, and sustain the performance and reliability of machinery.

By Brian Richards, SKF America January 10, 2011

The lubrication of rolling bearings and connected points on machinery can present an array of challenges on the plant floor. The number of lubrication points across industries can be daunting with typically upwards of 7,500 individual lubrication points for a paper mill, 5,500 for an automotive assembly plant, 4,000 for a steel mill, 3,500 for a refinery, 2,000 for a cement mill, and 1,500 for a plastics plant.

It is small wonder that problems can arise in meeting the needs, especially when handling manually. Points may become over- or under-lubricated and the application of lubricant may be sporadic or ill-timed. Ultimately, improper lubrication can result in unscheduled machinery downtime, lost production, and premature failure of equipment.

Proper lubrication – using the right lubricant at the right time with the right lubrication system at the right lubrication point – is critical in helping to reduce component wear, minimize lubricant consumption, and sustain the performance and reliability of machinery. Various enabling lubrication-related technologies have been introduced in the marketplace over the years, ranging from manual tools (such as grease guns, packers, pumps, or meters) to more sophisticated (and more precise) automatic and centralized lubrication systems.

In particular, centralized lubrication systems have emerged as viable and practical solutions by feeding lubricant from a central source to the points on a machine or machining system where friction occurs without imposing undue demands on maintenance personnel. With these systems in place, maintenance is simply limited to refilling the system’s lubrication reservoir and periodically inspecting the connected lubrication points, thereby allowing the maintenance staff to perform other skill-related tasks.

Problems and solutions

Consider these examples demonstrating how centralized lubrication systems can solve real-world application challenges:

Problem: Grease-lubricated bearings for fan and blower applications in manufacturing plants often will be housed in hard-to-access locations, which can make manual lubrication difficult and potentially unsafe. And, in those applications where high speeds and/or high temperatures preclude the use of grease, supplying the right amount of lubricant can especially turn problematic.

Solution: Centralized grease lubrication units have been developed to deliver grease to multiple points consistently and properly without manual intervention. For oil-lubricated applications, centralized circulating oil systems can supply a continuous flow of cooled and filtered oil directly to bearings. A metered pump flow (matched to bearing and housing size) helps prevent oil leaks and the excessive heat generation associated with conventional oversized pumping systems.

Problem: Lubrication systems for filling and packaging conveyors in the food and beverage industry traditionally have relied upon a combination spray of water and soap. The troubling issues: Precise metering of the quantity of lubricant sprayed on the conveyor belt surfaces and guides is virtually impossible (and often will be higher than the required amount) and the use of water can lead to bacteriological growth, foaming, corrosion, slippery (and unsafe) floors, and damaged packages.

Solution: Centralized dry lubrication systems can be engineered to replace classic wet lubrication systems by using a PTFE-based oil lubricant (instead of water) and air. The dry system automatically and precisely delivers the proper quantity of lubricant at the appropriate friction point (conveyor belt, surface, or guides) from a central unit, which feeds multiple lubrication points and eliminates all the problems flowing from the use of water.

Problem: Oil-mist lubrication for high-speed rolling bearings in machine tool spindles, especially in the automotive, aerospace, steel and metal industries, consumes excessive amounts of lubricant and further raises plant environmental and safety concerns from the dispersed oil mist.

Solution: Centralized oil-air lubrication systems can resolve these issues. They supply small and exactly metered quantities of lubrication to each friction point and consume about 90% less lubricant than oil-mist systems (accruing savings in the process). An oil-air system delivers the lubricant directly to each bearing using compressed air to carry the oil. The relatively small amount of lubricating oil is projected to bearings via a nozzle or directed passage and no mist develops. Other system advantages: The compressed air helps cool the bearing (allowing the bearings to run at lower temperatures and higher speeds) and produces positive pressure within the bearing arrangement to offer protection from external contaminants.

All types of standard and specialized machines can be serviced by centralized lubrication systems. Applying the principle of centralized lubrication, every bearing and friction point receives the exact amount of the proper lubricant to minimize wear and promote longer service life. Problems associated with excessive lubrication can vanish; lubricant consumption can fall over time (in some applications by as much as 50% compared with less exact manual methods); and maintenance time, energy, and costs can diminish.

Lubrication systems

Centralized lubrication technology generally falls under two “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 designated lubricating cycle. The lubricant is supplied in the proper quantity at friction points to allow for buildup of an adequate film of lubricant.

Circulating oil lubrication systems enable the lubricant to flow back into a lubricant reservoir for reuse after passing through the friction points. In this way, the lubricant carries even more benefits as it removes abrasion particles from friction points, stabilizes the temperature (cooling or heating) of friction points, prevents corrosion, and removes condensate and process water without any assistance from maintenance staff.

Within the total loss and circulating oil categories, installation configurations include single-line parallel, dual-line, and single-line series progressive feeder systems.

Single-Line Parallel: This configuration can be used for both total loss and circulating oil systems. The total-loss lubrication systems supply machinery lubrication points with relatively small amounts of lubricant (oil or eliminated “fluid” grease up to NLGI grade 2) to cover precisely the amount consumed. As such, they operate intermittently as required.

The standard layout of a single-line total loss lubrication system incorporates a pump and a positive displacement metering device, often described as an injector piston distributor; main line (connecting to pump and distributor); pressure switch for main line monitoring; 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 not utilized.

The piston distributors installed in the tubing system effectively meter the lubricant by controlling the stroke of an internal piston to determine the exact volume being dispensed. 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-ccm to 1.5-ccm per lubrication pulse and lube point.

A single-line parallel lubrication system incorporates a pump to supply an array of metering devices, often described as an orifice, adjustable orifice, needle valve, or some other type of device used to control oil flow to a particular point within a system of multiple lubrication points. The standard layout of a parallel lubrication system includes a pump supplying via a main header line (connecting to pump and metering device); pressure switch for main line monitoring; and secondary line (connecting to metering device and lube point). Performing as a circulating oil lubrication system, an oil return line from the lube point returns oil to the reservoir.

Dual-Line: These parallel-type systems can deliver oil or grease (up to NLGI grade 2) to as many as 1,000 lube points. 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, pressure switches for main line monitoring, and control unit.

In a parallel system all the distributors of a system are pressurized at the same time. The “reset” of the delivery piston is provided by full pump pressure as opposed to spring pressure in a single line parallel system. This makes the dual-line versions especially suitable for extended systems and more viscous types of grease. Assemblies with or without elastomeric seals can be specified to accommodate light and heavy-duty operating conditions.

Single-Line Series Progressive: These can be utilized as the metering device in either a total loss or circulating oil system. They are intended for intermittent delivery of lubricant (grease up to NLGI grade 2) and can handle up to several hundred lube points. Due to their series nature, they further offer the capability to provide central monitoring of all feeder outlets, if desired, at relatively low cost.

Metered quantities of lubricant are fed progressively in predetermined ratios, based on the spool diameter in the feeder. The lubricant can be delivered directly from a single feeder with systems under 20 points or via master feeders or zone valve to secondary downstream series progressive feeders. The lubricant does not leave the respective feeder until the preceding outlet has discharged its prescribed volume. If a lube point does not accept any lubricant, regardless of the reason, or if a feeder is blocked, the entire lubrication cycle is interrupted, which allows a cycle switch mounted on one feeder delivery piston in the system to emit a signal to alert maintenance workers to the problem.

Select the best system

Selecting the most appropriate centralized 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, installation criteria, system geometry (size, dimensions, and symmetry), and monitoring demands, among others.

When systems are properly designed and implemented, users can expect reliable lubricant coverage at all lubrication points, optimal lubrication intervals and dynamic lubrication, enhanced oversight (supported by available integrated control units and fill-level monitoring), and lubricant consumption-specific setup and adjustment of maintenance intervals related to the different sizes of pumps and lubricant reservoirs. An experienced supplier of lubricants and systems can help guide throughout the decision-making process.

Brian Richards in Technical Sales Support Manager-Lubrication for SKF USA Inc. You can email him at Brian.G.Richards(at)skf.com, or go to the website at www.skfusa.com