There are multiple items you need to consider in terms of a grease’s performance properties other than price. In fact, picking the most expensive or the least expensive grease could be financially disastrous, because the properties of that grease might not meet the specific needs of your equipment. This is why it is important to understand the make-up of a lubricating grease.
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Price is always important, but using price as the single factor should only happen after you have compared the products for their chemical and physical similarities and dissimilarities — in other words, what greases have the characteristics for the equipment needs. Then price, and possibly the manufacturer, become the deciding factors.
The anatomy of a liquid lubricant (such as, motor oil) blends a base oil with additives. Additives can enhance the properties of the base oil or impart new characteristics that the base oil lacked. Combining the base oil and additives creates a liquid lubricant with specific qualities and properties.
A grease adds an additional component by suspending that liquid lubricant (base oil plus additives) into a sponge-like thickener. Close-up, grease is honeycombed throughout, allowing space to temporarily trap the base oil and the additives within those pores. When a load is placed on a layer of grease, a small percentage of the liquid lubricant is pushed out to coat and protect the interactive metal surfaces. The excess lubricant that is not needed at the time is absorbed back within the grease’s structure, similar to how a sponge absorbs excess water.
The anatomy of a grease consists of three main categories: a base oil, a thickener, and additives, which can collectively represent dozens of chemicals blended together to create the properties needed. The main ingredient of any grease is a base oil refined from petroleum, but laboratory-produced synthetics and plant-based oils can also be used. Remember, the base oil trapped in the grease provides the lubrication that prevents metal-to-metal contact.
The second ingredient in grease is the thickener that traps and retains the base oil and additives. Manufacturers use metals mixed with synthetic fatty acid soaps or non-soap compounds to create the semi-solid condition of grease.
Manufacturers select the compounds used to thicken a grease based on their ability to hold the base oil and additives within the soap, maintain its consistency at high temperatures, and to remain in place without leaking out of the joint or bearing, while allowing grease applications at ambient temperatures during maintenance.
Lithium, or lithium complex thickeners, are commonly used as thickeners. Manufacturers often prefer lithium complex thickeners, because they provide a grease with higher temperature resistance and suspend and hold the base oil and additives better than other metal soaps.
Three of the more important additives are: graphite, molybdenum (moly), and polytetrafluorethylene Teflon (PTFE). Grease impregnated with these solid suspension additives provide additional protection against friction, wear, and fusion of metal surfaces. This is another advantage that grease has over liquid lubricants — grease can hold these materials in suspension, while they would settle out or be removed by a filter (like an engine oil filter) in a liquid lubricant.
Moly and graphite are sacrificial additives that work when the base oil is no longer able to lubricate moving parts (when the lubricant film collapses). New grease will help protect moving components in a machine (for example, gear boxes, joints, and bearings). However, it is possible there may come a point when the grease no longer remains in place. Grease can move when the stress of the equipment is significantly increased, the temperature is severely elevated, or the base oil viscosity becomes too thin that the lubrication film between the parts collapses. When this protective film collapses, moly and graphite will help form a temporary solid suspension film between the moving metal parts. This is why these sacrificial additives are important.
Equipment (like tractors, planters, mowers, sprayers, backhoes, bulldozers, and other heavy equipment) can challenge how well a grease performs. There are many rotating parts and oscillation joints on these types of equipment. Often, users operate this equipment in both cold weather during the winter and extreme high temperatures during the summer. These changing conditions can exacerbate heavy shock loads on the equipment you are trying to protect. Conditions can vary from dusty to muddy on any given day. And yet, the grease you selected is expected to work in such diverse mechanical and environmental conditions. These extreme conditions bring us back to the importance of the constituents of a specific grease.
Grease is one of the more complex lubricants you can buy, because each grease has its own set of chemical characteristics and physical properties based on what ingredients were used to formulate the product. Manufacturers can change from one thickener to another, modify the base oil, or add a laundry list of additives to get a new set of properties.
This is why grease manufacturers off›er several types of grease in order to meet the specific needs of equipment. Lubricant manufacturers want to test grease formulations to ensure that the base oils, thickeners, and additives are working well together, meet the intended goals for the lubricant product, meet equipment requirements, and are not antagonistic under varying conditions.
Grease containers may look the same, but the contents can be very different. Two tubes of grease may appear identical, except the endcaps might differ in color. The manufacturer uses the same tube for two grades of grease, but use different cap colors. The month and year of manufacture is also shown for inventory control purposes.
Why This Test Matters: A higher consistency grease will remain in place better under a heavy load, but it is harder to pump and push through a grease fitting or line at colder temperatures. A grease with a lower consistency is easy to pump, but doesn’t stay where it is needed as well under heavy loads or slower speeds.
The shear stability test (also called the roll stability test) measures consistency after mechanical shearing. For this test, it’s useful to revisit the analogy of a thickener being a sponge that holds the liquid lubricant.
A grease that is repeatedly called upon to lubricate a bearing or joint is like physically chopping the sponge-like matrix as it is being worked. This test is like the cone penetration test, but the grease has been worked 10,000 or 100,000 times through the grease worker to determine if mechanical shearing changes the thickener’s consistency. The NLGI table is then used to reclassify the grease after it has been worked.
Why This Test Matters: What is important to know at the end of the day is that the grease can change its consistency after it has been used. It could or might be expected that a “worked grease” may drop one NLGI category as it is mechanically sheared over time.
The dropping point test measures resistance to high temperatures by determining the melting point of the thickener. Testers find the melting point by putting a small sample of grease into a cup that has a hole in the bottom. The cup is then heated to the point that the first drops of grease leak out of the hole. The test helps manufacturers determine whether the product has been properly blended to reach a certain dropping point.
Why This Test Matters: This test has little value to end users. Simply put, most greases (including those using lithium complex thickeners) can have dropping points between 300°F and 500°F. If you have a piece of equipment that operates near those temperatures, you will have more problems to worry about than the grease’s dropping point, considering that most equipment usually operates at less than 150°F. If the grease is getting hot enough that it converts to liquid, check the equipment for possible failures.
The oil separation test and wheel bearing leakage test measure how thickeners hold the liquid lubricant. Testers place grease into an apparatus that spins at a certain speed, time, temperature, and pressure. The test measures how much of the liquid lubricant under a centrifugal force actually separates out of the grease thickener. It is normally measured in percent loss by weight.
Why This Test Matters: It is important to know that the liquid lubricant will migrate out at a constant, but slow, rate.
But you don’t want a grease to bleed out too quickly under high pressures and/or under extreme temperature swings. Additionally, the lubricant has to remain in place without leaking out of the seals or thrown away from the desired bearing surface that you want to lubricate and protect. The results of this test are especially important for determining the lubrication intervals. For instance, an equipment manufacturer might indicate a bearing or joint only be greased at six-month intervals or after a certain number of hours of use. But if the liquid lubricant is gone after two months (or less hours than suggested), waiting for the recommended interval would lead to metal-on-meal contact as the grease has already “played out.”
The U.S. Steel mobility test and ventimeter test measure the impact of cold temperatures on pumpability. Testers cool a tube of grease down to a specific temperature. Then, they apply a specific amount of pressure to the grease gun for 5 minutes while collecting the grease in a cup. Testers then weigh the grease in the cup. By continually lowering the temperature, manufacturers can determine the lowest temperature a grease can be pumped.
Why This Test Matters: We want to know the lowest temperature that the grease can practically be pumped or pushed through a grease gun, fittings, and into bearings. If the grease is not delivered to the desired surface, equipment will fail.
The 4-ball weld test measures wear protection under heavy loads. The test measures how much load a grease can take before it is pushed out, causing the bearings in the experiment to seize and weld together by friction and heat. Three balls are locked within a device and the grease applied to the cup. A fourth ball is placed in a chuck that rotates over the bottom three bearings to form a pyramid.
During the test, downward pressure is applied from the top ball onto the bottom three until the lubricant film fails under the load. It is at this point that ingredients like moly, graphite, and other extreme pressure and anti-wear additives are activated. However, the continuous downward pressure will cause these additives to fail, too. Eventually, increasing the load will weld the four balls to one another.
Testers calculate the weld load in kilograms, which means the higher the number, the more weight the grease can carry before major wear starts to degrade the parts.
Why This Test Matters: This is a real-world test that shows how the grease protects under extreme pressures and loads. The greater the weld load, the higher the pressure the lubricant will continue to work and prevent metal-to-metal contact.
The 4-ball wear scar test and Falex continuous load test measure wear protection under heavy loads. This test uses the same apparatus as the 4-ball wear test. But instead of running until the failure or seizing point, this test will take the balls out of the test rig to measure the scars made under certain pressures.
It measures how much of the metal is wearing out under certain pressures. Testers remove the bearings and evaluate the length of the scars and the depth of the gouging under a microscope. They repeat this process over a number of different pressures up to the weld point.
Why This Test Matters: We want to be able to compare the performance properties of a grease and its liquid lubricant at higher pressures. For instance, if we need a grease to perform at a high load and slow speed, we want to make sure the product has a high score in these two categories.
The water washout test and water spray off› measure a grease’s resistance to water. Testers apply grease around a bearing at temperatures of 100°F or 175°F. Testers apply a steady stream of water across the rotating bearing. After a set amount of time, testers remove the remaining grease, dry the grease, and weigh it. Testers subtract the weight of the grease remaining at the end of the test from the weight at the beginning of the test to determine how much grease was washed o›ff, which is reported as a percentage loss.
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Why This Test Matters: It is important to select the proper grease if there is ever a possibility that your equipment may be submerged in water — for example, the wheel bearings on a boat trailer.
With these two measurements, you can use the following formula to calculate how much grease you need for that assembly unit:
0.114 x assembly unit diameter x assembly unit width = quantity of grease (in ounces) needed
The bearing pictured on this page has a diameter of 1.2 inches and a width of 0.572 inches. Using the formula:
0.114 x 1.2 x 0.572 = 0.07 ounces of grease needed
The last step to determine how much grease to apply to a bearing or fitting is to compare the output of the gun to the amount needed in the assembly. The formula showed us that this specific bearing needs 0.07 ounces. The grease gun puts out 0.027 ounces per squeeze, so it takes about three squeezes to put in the right amount of grease (0.07 ÷ 0.027 = 2.59 — or about 3). Write this down for future reference.
Application Frequency
There are many factors involved in answering how often a bearing or bushing needs to be greased. Timing often depends on these variables:
• Size — the larger the component, the more frequently it needs to be greased
• Speed — the faster the operating speed, the more frequently it needs to be greased
• Temperature — the hotter the operating temperature is, the more frequently it needs to be greased
• Contaminants — the more dust and dirt in the operating environment there is, the more frequently it needs to be greased
• Moisture — the more water in the operating environment there is, the more frequently it needs to be greased
• Vibration — the more vibration in the operating environment there is, the more frequently it needs to be greased
Engineers will consider these and other variables to estimate how frequently a fitting needs to be greased and list it in the operator’s manual. However, the manufacturer recommendations are based on the average use for a piece of equipment. It is up to you to determine if you are working the equipment under extreme weather conditions (as you might find, for example, in Texas, Montana, Arizona, or Alaska). If you are working your equipment in more extreme conditions, then you will need to shorten the intervals between the recommended greasing times.
Clean grease fittings and the surrounding area before applying new lubricant. Do not let the act of lubrication introduce additional dirt and debris into the machine. Wipe off excess grease after application to avoid dirt and debris from adhering to the outside surface.
Pumping grease in a fitting when the equipment is “cold” can sometimes destroy seals prematurely.
After the rest period, see if any grease came out of the seal. If it didn’t, then apply the remainder of the grease. If you notice grease being pushed out, then stop greasing. Make a note in your records for the next time that bearing needs greased. Your last step is to clean the area around the fitting and wipe o› any excess grease. Excess grease will only allow more dirt and grime to be collected around the area.
Document Applications
It is always a good practice to have a checklist to follow and document what you do. Your records might provide valuable clues if the equipment fails down the road. Your records might indicate that you were not lubricating enough, too much, or using the wrong grease. It’s a way of determining the root cause of problems so you do not repeat them later. Documentation also becomes important if any questions are raised related to the warranty. In discussions with the manufacturer, be ready to answer these questions:
• Did you grease them?
• What type of grease did you use?
• How often did you grease them?
Most people don’t understand that manufacturers want to determine if any measures were being taken or if something was being done that caused any failures. By understanding your case, manufacturers also can educate others not to do things that might cause premature failures. At the end of the day, manufacturers may have to change the protocols they list in their operating manuals to prevent the problem from reoccurring.
We have seen an explosion in the use of pressure washers in cleaning machinery. Always consider the impact of power washing on bearing longevity. In most cases, the pressures from power washing equipment exceed even compressed air. Using a high-pressure system to clean equipment can generate 1,000-3,000 PSI; whereas, air pressure rarely exceeds 125 PSI.
Under these pressures, it is easy to wash the grease out of bearings. Remember two points when you use a high-pressure washer to clean equipment.
First, never direct high-pressure wash water toward a bearing parallel to the shaft on which its mounted. In other words, wash a machine down its sides, not into its sides.
Second, remember that high-pressure water can breach even sealed bearings. Such breaches shorten bearing life by introducing water and contaminants into the bearing, corroding the contact surfaces or creating surface roughness.
As the tube says, store grease tubes with the plastic cap up (left). Failure to do so can result in an oily mess (right).
It is in your best interest to use the types of grease that equipment manufacturers recommend to help keep the warranty intact. Once the warranty period ends, you may want to switch over to another type of grease that meets the original specifications.
However, mixing greases can create unintended problems. Manufacturers design each grease product with a specific application in mind. If you mix one grease with another that is incompatible, it can cause more harm than good.
It is best to assume that if you switch from one grease to another, it will lead to compatibility problems. In most cases, your assumption will be the correct one. If you want to switch to another grease, be sure to call the manufacturer of the grease you want to purchase and ask them: first, if their product is compatible with the one you are currently using, and second, recommended for the equipment application or manufacturer.
Major grease manufacturers and distributors have their own sales representatives who routinely answer questions about compatibility. The representatives will know what is and what is not compatible with their products. Although they want to sell you a product, representatives do not want to be on the hook for recommending an incompatible grease. This is why it is important to develop a relationship with a grease expert, because their knowledge will help you eliminate making mistakes and causing additional or unwanted problems.
Calling someone a “grease-monkey” is often considered derogatory, implying that it does not take any skill to put grease into a fitting. But nothing can be further from the truth. This publication demonstrates that selecting and using the correct grease for each application is, if anything, a highly technical science that requires skilled decision-making.
Selecting the right grease for the right situation isn’t as simple as choosing rye versus wheat bread. Technology has changed not only the design of much of the equipment we use, it has also changed the formulation of greases.
Greases, just like oils, have come a long way since the times of Henry Ford. No longer do we have to use the vice and hammer method to determine if a grease is tacky enough to stay where you want it.
The vice and hammer method required users to place grease on a vice and smack it with a hammer. If all the grease shot out and none was left on the vice or hammer, then it probably wasn’t a very good grease. But if some stayed on the vice and on the head of the hammer, it would probably hold up under extreme conditions.
Micro Lube is a leading and diversified maintenance company associated with several manufacturers of supreme quality filtration and lubrication products.
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