It’s hard to imagine a machine operating without grease in it, as the majority of dynamic machine operations run on bearings, which need grease for lubrication. Historically, the utilization of grease to lubricate a wheel and axle occurred just after the discovery of the wheel.
The first universal greases were crude forms of lime mixed with vegetable oils. These classes of grease continued to be used for almost all kinds of applications requiring lubrication until the industrial revolution.
However, in the last few decades, remarkable progress has been made in terms of machine design. This has affected operating parameters and thus the requirements for lubricating greases. As operating parameters like speed, load, temperature, etc., vary significantly based upon the equipment, it is practically impossible for a single grease to handle all the diversified applications.
Consequently, a large number of lubricating greases have been developed, resulting in thousands of greases on the market. The concept of one universal lubricating grease covering all types of applications no longer holds true. Also, from a selection and suitability standpoint, the vast array of available greases can make choosing the right grease a confusing process.
Lubricating greases basically are composed of a thickener (10 to 15 percent), base oil (80 to 90 percent) and performance additives (5 to 10 percent). The total global market size of lubricating greases is about 2.38 billion pounds and consists of lithium/lithium complex, calcium, sodium, aluminum/aluminum complex, calcium sulfonate, clay based, polyurea, etc.
By far the most popular greases worldwide are lithium-based greases with a market share of more than 75 percent. While various kinds of greases may be required in a particular plant, there have always been efforts to rationalize and minimize the number of greases from a purchasing and logistics standpoint. This likely has led to the development of multi-purpose greases.
In simple terms, a multi-purpose grease can be defined as a grease combining the properties of two or more specialized greases that can be applied in more than one application. For example, lithium grease can be applied both in chassis and wheel bearing applications of transport vehicles. Traditionally, calcium greases were used for chassis, and sodium-based greases were utilized for wheel bearings.
Calcium-based greases have been rated high for water resistance but poor for elevated temperatures. On the other hand, sodium-based greases better cover high temperatures but are not as good in regards to water resistance. When lithium greases emerged in the marketplace, they were found to be superior to calcium and sodium greases, and soon became the most popular multi-purpose greases in industry.
In modern machinery design and construction, machines operate under more severe conditions with the expectation of increased productivity and less downtime. This has made it difficult for lithium greases to satisfactorily fulfill these requirements. The National Lubricating Grease Institute (NLGI) GC-LB specification, which is the most closely followed in the transport sector, also requires greases beyond just lithium 12-hydroxy greases.
Table 1. Comparison of fully formulated greases
These stringent requirements can be met by more efficient high-performance greases like lithium-complex, calcium-sulfonate, aluminum-complex, polyurea and clay-based greases. However, because of their compatibility with most widely used lithium greases, lithium-complex and calcium-sulfonate greases appear to be the best candidates of these high-performance multi-purpose greases.
Lithium-complex greases generally possess good stability, high-temperature characteristics and water-resistance properties. Other performance requirements like extreme pressure, anti-wear, rust and corrosion can further be improved by adding suitable additives. These greases also meet the NLGI’s GC-LB specification requirements.
Calcium sulfonate, by virtue of its thickener property, provides excellent water-resistance properties and does not break down even in the presence of water. However, limitations with calcium-sulfonate greases are their inferior pumpability and cost. Each option has its strengths, but your choice should focus on finding the grease that helps maintain or even extend the life of your assets without breaking the bank. In this way, you can lower total costs while helping your assets perform to their highest potential.
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by Jeremiah "JB" Bacon, S.T.L.E. CLS
Multipurpose grease can cover many applications making it desirable for reducing inventories and associated costs, and simplifying a lubrication program. In general, most multipurpose greases are lithium thickened and have Antiwear (AW) and/or Extreme Pressure (EP) additives and base oils with viscosities ranging from SAE 30 to SAE 50.
But multipurpose greases cannot handle all applications in the typical industrial facility. To understand grease, we must look at grease make-up. Grease is essentially made up of three things; base stock or stocks, a thickener and additives.
When considering grease, general factors to consider include;
Also consider the environmental conditions of the application. Ambient temperature ranges and location of the application are necessary to assess the conditions in which the grease must perform. Wet environments and dusty conditions require more frequent regreasing to help keep these contaminates out of the components. Also consider the operating temperature of the application and relubrication logistics to determine the best product to use and best method for applying the grease. Remote or difficult to access locations make the case for automatic lubricators. From a base oil type and viscosity standpoint, extreme temperature ranges must be factored into the decision on which grease to choose.
Grease thickeners are vast in number and some have unique properties and benefits. Some thickener types can add performance characteristics to the grease. For example, water resistance can be improved when aluminum complex or calcium complex thickeners are used. There is a heat advantage that some thickeners have over others. Thickener Compatibility is of major concern. There are Thickener Compatibility Charts available to consider, but the best approach is to consult with your supplier to see if they have run compatibility tests against different thickener types. If not, grease compatibility testing can be run for a few hundred dollars to ensure against compatibility issues.
Base stocks used in greases are typically mineral oil, synthetic blends or full synthetic stocks. Polyalphaolefin (PAO) synthetic oils are used frequently, as these are compatible with mineral base oils. Other synthetic fluids used in grease manufacture include esters, silicone fluids, Perfluoropolyethers, and other synthetics and synthetic blends. Again, compatibility of
the base stock(s) used in different greases isn’t assured. Check the grease manufactures data to see if it states the base oil type. If there is doubt, contact the supplier for more information on the type of base fluid used in the candidate grease. Check it for compatibility with the base fluid used in the grease that is currently in service. Remember that the Viscosity of the base fluid used in the grease should be matched as close as possible to the requirements for Speed, Load and Temperature of the application.
Additives included in greases are typically antioxidants, rust and corrosion inhibitors, and antiwear or extreme pressure (EP) additives. Special additives may be required to increase performance. Adhesive and solid lubricants like Molybdenum Disulfide (Moly) are added to grease to provide extra protection when conditions are extreme or regreasing is difficult to accomplish.
National Lubricating Grease Institute (NLGI) Grades are a measure of grease consistency. That is to say it measures the greases firmness or softness via the ASTM D 217, “Cone Penetration of Lubricating Grease” test. There are nine different NLGI “grades” including 000, 00, 0, 1, 2, 3, 4, 5 and 6. We are all familiar with “EP 2” grease. This tells us two things, EP 2 grease is a NLGI Grade 2 and it is fortified with Extreme Pressure (EP) additives. This tells us nothing else about the thickener type, base oil type or viscosity of the base oil. The correct NLGI grade is an important consideration because not all grease applications are the same. Some grease applications require softer grease so it can be pumped easily through small distribution lines and valves. While other grease applications like bearings mounted on vertical shafts require firmer grease so the grease stays put.
With all these factors to consider, no wonder there is confusion regarding grease. Most industrial facilities should be able to use a handful of greases that will lubricate their facility in its entirety. There should be a grease specific for:
Additionally, one or two specialty greases may be required for extreme applications.
Greases and grease dispensing equipment should be color coded and labeled so as not to cross contaminate products. Work with your supplier to know and understand the greases being used at your facility. When you're choosing grease, practice due diligence and choose the right grease for the application.
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