Many companies fail to realize the importance of lubrication and the application of its five basic "rights" in achieving world-class machinery reliability. This article examines each of these concepts in detail, along with a summary of best practices including procedures in the selection of the optimal lubricant supplier.
1. Right type
As a first step in the lubrication of equipment, refer to the OEM manual, and contact the OEM if you have any questions. With old equipment, the manual may be outdated and better lubricants may be available. When in doubt, utilize your lubricant supplier along with the OEM.
The two major classes of lubricants are oil and grease. The selection of the type is based on the application. Greases are used extensively in the lubrication of small bearings. As rule of thumb, use oil where possible, because it can be cooled and filtered-this is not possible for many applications where grease is the better choice. The following are applications for grease:
Greases are composed mainly of oil dispersed in a thickener with additives. Typical grease is ~ 85% oil. It is the oil in the grease that does the lubricating. The NLGI classifies greases according to consistency with the following grades increasing in hardness: 000, 00, 0, 1, 2, 3, 4, 5, 6.
The most common NLGI grade is #2. At high speeds, #3 may be used and at low temperatures and in centralized systems, #0 or #1 is used.
Most large equipment is oil-lubricated and selection of the right type is critical to reliability. Two major factors in selection of an oil-based lubricant are the correct viscosity and additives in the formulation. For a more complete discussion of viscosity, refer to the article "Basic Principles Of Viscosity And Proper Selection Techniques," published in this magazine last year. For a more complete discussion of the additive types, refer to one of the installments appearing in another recent series in this magazine, "All Lubricants Are Not Created Equally (Basic Concepts In Formulation Of Finished Lubricants)."
OEMs will recommend the correct ISO viscosity grade for their equipment, based on the operating temperature. Table I classifies kinematic oil viscosity in centistokes for industrial lubricants, based on the ISO grade that is the midpoint of a viscosity range +/-10%.
Since grease is made up primarily of oil-which does the lubricating- the correct viscosity must be selected in the grease formulation. Table II provides guidelines on the selection of the correct viscosity in grease. Once the correct viscosity has been determined, the correct lubricant type based on additive composition needs to be selected. Lubricant formulations consist of a base stock and additives. Most base stocks are mineral oils from refining of crude oil. Table III summarizes lubricant composition in various lubricant types.
2. Right quality
Once the right type of lubricant has been selected, it is important to select a high-quality lubricant. Quality is both the ability of the lubricant to meet OEM specifications, based on performance on ASTM tests, and the cleanliness of the fl uid in which is delivered. You can have the highest quality lubricant, but if it is not handled properly during delivery or storage, it will not perform the way you expect it to.
Product data sheets provide useful information on lubricants and their behavior on ASTM tests, which, in turn, provides insight on their performance on equipment. The best test for a lubricant is how it has performed in YOUR plant, but there are some situations where a lubricant is selected only on specification tests. In 2005, a series of articles was published in this magazine on turbine, hydraulic and gear oil specification tests. Refer to these articles for an in-depth coverage of lubricant specification tests and how they can help in the selection of the right quality lubricant.
The following list is a summary of the best practices for maximizing lubricant quality:
3. Right amount Grease lubrication...
More is not better. Too much lubricant in a system can be as destructive as not enough.as evidenced by the over-greasing of electric motors, which is a major failure mode. Use the formula in Fig. 1 to help grease rolling element bearings with the correct amount.
The calculation in Fig. 1 will give you the number of ounces to add to a bearing during greasing. This is especially important with electric motors, as there seems to be a tendency to over-grease. In order to add the correct amount, grease guns need to be calibrated on their delivery of number of shots/ounce. This can be done by using a postage scale to weigh out one ounce of grease. An easier method is to count the number of shots required to fill a 35mm film canister; thatfs approximately one ounce of grease. Once your grease guns have been calibrated, try to use the same grease gun type for a given application. Some newer guns will indicate the amount that is being added.
Centralized oil systems add the right amount at the right time. This section focuses on having the correct level in oil baths and splash-lubricated gearboxes. Many small pumps are lubricated by oiler baths, as illustrated in Fig. 2. The correct level for a bottle oiler bath should be at the middle of the lowest ball.
Large pumps and process steam turbines that have journal bearings are often
lubricated with the use of slinger rings, as illustrated in Fig. 3.
The oil level with slinger rings should be set at 1/8"to 3/8" from the bottom inside edge of the ring. The faster the speed the lower the level should be.
Splash-lubricated gearboxes are very common where both gears and bearings are lubricated. Enough oil needs to be splashed up for cooling and lubrication. Too high an oil level will cause churning that over heats the oil; too low a level will not provide proper oil cooling and lubrication for bearings and gear teeth. Spur helical, bevel and spiral bevel gears are lubricated with the gears dipping into the oil at twice the tooth depth. The OEM will provide information on the correct oil level
Worm gears consist of a steel worm and a bronze wheel with the worm being either above or below the wheel. Fig. 4 shows a worm below the wheel, where the oil level is normally set just below the worm center line. With the worm above the wheel, as illustrated in Fig. 5, the oil depth ranges from just above the wheel tooth depth to the center line of the wheel. The oil level is dictated by the speed. The higher the speed the lower the oil level to minimize churning.
4. Right place
Once we have selected the right type lubricant and the quantity to add, we need to apply it at the proper location. Adding the wrong oil to a lubrication point is not uncommon. This situation will usually go undetected until a problem occurs. With an oil analysis program, early-stage detection is more likely, thus helping to avoid possible equipment damage.
All lubrication points should be properly labeled as to the lubricant to be added. Lubricant manufacturers provide lube tags for proper identifi cation of the proper lubricant to be used at the lube point. A typical tag is illustrated in Fig. 6.
It is a good practice to use separate containers for different lubricant types. Mixing lubricants with different additive packages is not recommended. Normally, each lubricant supplier color-codes its tags by lubricant types. In Fig. 6, all of the supplier's hydraulic oils would have red tags, but they would display different ISO numbers, such as ISO 46 and 68. Containers also should be properly tagged, as should the drums or totes from which the oil is transferred to the container. This will minimize the addition of the wrong oil.
The following summarizes best practices for the addition of lubricant at the right place:
5. Right time
Once we have established our program with the right type, quality, amount and place, we need to establish proper lubrication intervals. Grease frequencies can be determined by using charts, but the following easy calculation also can be used:
The frequency of changing lubricants depends upon the type of system and size of the reservoir. Initial guidance can be obtained from the OEM and should be adjusted based on the environmental conditions
Small reservoirs (under 50 gallons) in non-circulated systems are often changed on a certain frequency based on OEM recommendations and experience. As an example, small ANSI centrifugal pumps in plants typically hold less than two quarts of oil. Interestingly, one plant may change the oil in such pumps every quarter, while another, using the same type of pumps, will change it every two years.
Environmental conditions dictate oil change frequency. The plant changing its pump oils on a quarterly basis probably has diffi cult conditions leading to water ingression and contamination problems, while the plant changing biannually has much more favorable conditions. Such factors also apply to splashlubricated gearboxes and bath-lubricated systems. To determine the correct change frequency for similar equipment under similar conditions, statistically evaluate the condition of the oil through oil analysis tests. This can provide useful information on establishing change frequency.
Change frequency for large systems (over 50 gallons) should be established with oil analysis condition monitoring tests. Two major failure mechanisms for lubricants are contamination (particles/water) and oxidation. Routine visual monitoring of the oil is crucial. Oils that are becoming darker indicate possible oxidation and should be further evaluated. Oils that appear to be hazy or have suspended solids in them indicate excessive contamination and also should be further evaluated.
Oxidation, one of the primary reasons lubricants fail, is temperature-dependent. For every increase in temperature of 18 F degrees, the oxidation rate doubles, which in turn, cuts oil life in half. This is noticeable at temperatures over 140 F. When oils oxidize, they produce sludge, varnish and acids, all of which can cause equipment damage. One very useful test is to monitor the increase in the acid number of a lubricant through oil analysis and to set condemning limits for the oil. Refer to "Proactive Maintenance Practices Through Condition Monitoring Of Used Oils," an article published in this magazine in 2005. Excessive water contamination can be determined with a Karl Fisher test and particle counts that measure the cleanliness of the oil. Both of these procedures are an integral part of an oil analysis program.
The following summarizes best practices in determining oil change frequencies:
Establishing a world-class lubrication program through application of the fi ve rights of lubrication will pay dividends. In the long run, enhanced equipment reliability will result in major bottom-line savings. Establishing the right program requires real planning and work-and the lubricant supplier and OEM should be utilized when needed. The fi rst step is to recognize and promote the importance of a well-designed lubrication program to management. The next step-and the most diffi cult one-is to effectively implement that program.