A critical task for maintenance professionals revolves around lubricating rotating machinery. Timely, effective lubrication reduces component wear, minimizes lubricant consumption and sustains equipment performance and reliability. With the goal to deliver the proper lubricant precisely when and where needed, workers more often than not will have their hands full. Manual user-friendly lubrication tools (such as grease guns, packers, pumps and meters) provide a big assist, but some applications present even bigger challenges, especially when time and labor are at a premium.
[pullquote]In some cases, handling the sheer number of lubrication points — sometimes hard-to-access — can consume countless hours. As examples, there can be upwards of 7,500 individual lubrication points in a paper mill, 5,500 in an automotive assembly plant, 4,000 in a steel mill, 3,500 in a refinery, 2,000 in a cement mill and 1,500 in a plastics plant. Each requires service and vigilance, while adding to the potential risk and problems associated with over- or under-lubricating, ill-timed or sporadic application and the introduction of harmful contaminants.
Technology has responded with an array of automatic lubricators and centralized lubrication systems engineered to provide reliable time- and labor-saving alternatives to manual lubrication.
Set and forget automatic lubricators
Figure 1. Single-point lubricators allow users to “set and forget” for a predetermined period, typically one to 12 months.
Automatic single- or multipoint lubricators offer around-the-clock lubrication service with minimal maintenance staff involvement. Single-point automatic lubricators for bearings (Figure 1) typically feature flexible time-setting periods ranging from one to 12 months and enable users to “fit and forget” about the lubrication procedure until some predetermined date. Transparent one-piece lubricant containers (usually polyamide) allow visual inspection of the dispense rate and the container material reduces gas diffusion. Hermetic sealing safeguards against ingress of dirt or foreign matter. Such lubricators can be filled before they reach the plant and ready-to-use, supplied with the proper grease, which removes guesswork, mistakes and effort.
Multipoint automatic lubricators for bearings and machinery can be configured for as many as 20 lubrication points. These flexible systems benefit from electronically-controlled programming options and alarm functions to signal when feed lines are blocked or cartridges or containers are empty. Advanced versions use a high-pressure pump and progressive feeder to dispense the same amount of lubricant for each designated lubrication point.
Automatic lubricators can be complemented with additional technologies to make life easier for maintenance staff. For example, relubrication calculation software accurately determines correct interval settings. After entering the criteria and specified grease, the program pinpoints the correct settings for optimized lubrication and timing.
Another device automatically adjusts oil lubrication levels inside a bearing housing, gearbox, crankcase or similar oil-bath application. These oil levelers adjust the level in real time (eliminating potential equipment downtime) and compensate for leakage.
Centralized systems can service any machine
Figure 2. Circulating systems offer the opportunity to remove wear particles and contaminants.
Any standard or specialized machine can be serviced by a centralized lubrication system. Applications encompass equipment used in automotive, machine tool, metals, printing, paper, food and beverage, mining, chemical, plastics, hydrocarbon processing, refinery and wind energy, among many others.
With centralized lubrication, every bearing receives the proper dose of lubricant. 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 manual requirements are to refill the lubrication reservoir and occasionally inspect the connected lubrication points.
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 lubricating cycle (such as pump run time). The lubricant is supplied in the proper quantity to buildup an adequate lubricant film during the subsequent idle period.
In circulating-oil lubrication systems (Figure 2), the lubricant flows back to a reservoir for reuse after passing through the friction points. In this way, the lubricant, without human intervention, removes abrasion particles from friction points, stabilizes the friction point temperature (cooling or heating), prevents corrosion, and removes condensate and process water.
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Figure 3. A single-line, total-loss system operates only as required to replenish consumed lubricant.
With either approach, installation configurations include single-line parallel, dual-line and single-line series progressive feeder systems. Single-line parallel lubrication systems supply 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 (Figure 3) has a pump and a positive-displacement metering device, often described as an injector piston distributor; main line (connecting to the pump and distributor); pressure switch for main line monitoring; and secondary line (connecting to the distributor and lube point). It functions as a total-loss lubrication system and has no oil return line from the lube point to the oil reservoir.
The piston distributors installed in the tubing system meter the lubricant by controlling the stroke of an internal piston. 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 range from 0.01 cc to 1.5 cc per lubrication pulse and lube point.
Dual-line systems deliver oil or grease (up to NLGI grade 2) to as many as 1,000 user-specified lube points (Figure 4). They can be configured to run either as total-loss or circulating-oil systems. 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 a control unit.
Figure 4. Dual-line centralized systems can be configured to feed as many as 1,000 points in either recirculating or total-loss mode.
In a parallel system, the distributors are pressurized simultaneously, resulting in low pressure losses. The delivery piston resets itself under full pump pressure as opposed to the spring pressure used in a single-line parallel system. This makes the dual-line versions especially suitable for extended systems and more viscous grease. Assemblies with or without elastomeric seals can be specified to accommodate light and heavy-duty operating conditions.
Single-line series progressive systems are for either a total-loss or circulating-oil system. They’re intended for intermittent lubricant delivery (grease up to NLGI grade 2) and handle several hundred lube points. The series nature allows central monitoring of feeder outlets at relatively low cost.
Metered quantities of lubricant are fed progressively in predetermined ratios. The lubricant can be delivered directly from a single feeder to as many as 20 points or via master feeders or a zone valve to secondary downstream series-progressive feeders. The lubricant doesn’t leave the respective feeder until the preceding outlet has discharged its prescribed volume. If a lube point doesn’t accept lubricant for any reason, the entire lubrication cycle is interrupted. This makes the cycle switch mounted on one feeder delivery piston emit a signal to alert maintenance workers to the problem.
Tips for success
Determining the most appropriate centralized system depends, in general, on the application and, in particular, a range of other variables, 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 planning a centralized lubrication system, these guidelines can help the cause and keep problems at bay:
- Determine the number of lube points.
- Determine the type and amount of lubricant required per lube point and the subsequent volume required per minute or per cycle for system operation.
- Select the distributors in accordance with the metering range, lubricant type, monitoring desired/required and installation requirements. A distinction must be made between oil-only distributors and those also suitable for various grease consistencies.
- Choose pumps consistent with the type of actuation, lubricant and system capacity.
- Determine the type of control for automatic systems (time- or load-dependent) and any monitoring system that might be required.
- When installing a system, lay out the main lines and distributors to enable air in the system to escape on its own via the lube points.
- Check the resistance in the main line, particularly regarding the relief process in single-line parallel systems, when especially large and widely branched systems are involved, and when high-viscosity oils are used or low temperatures are expected.
You can expect reliable lubricant coverage (especially important for machines with dozens or more 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 via different sizes of pumps and lubricant reservoirs. Such systems additionally help you realize:
- Decreased lubricant consumption and environmental contamination
- Increased machine uptime and reliability
- Lower machine life-cycle/operating costs
- Decreased energy consumption through proper friction management
Along the way, automatic lubrication systems deliver opportunities to better deploy maintenance staff and hand off many of the lubrication responsibilities to enabling technology.
Brian Richards in technical sales support manager-lubrication for SKF USA Inc. Contact him at [email protected].