Multipurpose Does Not Mean All-Purpose

Wes Cash, Noria Corporation

The term “consolidation” is very popular - especially when it comes to reducing the number of lubricants in an industrial facility. The thought is we can mitigate risks of accidentally using the wrong fluid by reducing the total number in storage. It's also possible to enhance our purchasing power by purchasing more of a specific lubricant than many obscure ones. Even more appealing is reducing the inventory levels of unique, one-off lubricants that may only be used in a very specific application. This process is underway at countless plants across the planet at any moment, some headed by a task force of plant personnel, others with the aid of outside consultants and lubricant suppliers. While consolidation efforts are necessary to save money and reduce accidents, grease is often the focus of overzealous consolidation.

Most facilities look intimately at each oil-filled component to ensure the selected lubricant can meet the demands of the equipment and still be properly lubricated. Meanwhile, greased components are rarely scrutinized, and grease consolidation is done heavy-handedly, often resulting in sub-optimum lubrication for many critical components. While a plant may be satisfied with an overall oil product reduction from 25 down to 15, we often find the same plant is not satisfied with grease consolidation until only two to five greases remain. Oils are uniquely formulated to handle certain stresses in operation from either the machine or the environment, so too are greases. It is generally understood that a machine operating in harsh environments may get a more premium formulated oil or even a synthetic option. We take that same machine and look at greases in use, and they are often a mismatch for those situations.

Some of this issue comes from grease’s dubious reputation as many do not know what it is made of or even how it operates. We know that greases are formulated with specific applications in mind and are made from the same base oil and additives as lubricating oils, but many purchasers fall prey to the allure of the “multipurpose” grease. Once that label is applied to a grease product, some take it as a seal of approval for the grease to used virtually everywhere.

This could not be further from the truth.

To understand how the term “multipurpose” was introduced and why it is so prevalent in grease nomenclature, we need to understand how greases are specified and tested. The de facto authority in grease is the National Lubricating Grease Institute (NLGI), a membership group comprised of lubricant manufacturers, researchers, consultants and end-users. This group is a working group that helps create standards as well as share technical information among its members. As such, the NLGI was instrumental in the creation of a grease standard for automotive greases known as ASTM D 4950, which outlined the performance characteristics and specifications for greases used for chassis and wheel bearing applications.

These greases were denoted by a series of letters that corresponded with their degree of service. The prefix “L” was chosen for chassis applications, while “G” was chosen for wheel bearings. These were further characterized by a second letter that coincides with the severity of service. For chassis, LA means light-duty, LB for severe duty and then a similar scale for wheel bearings of GA through GC. There are a series of performance criteria that must be met by the grease in order to achieve these ratings, but early on, it became apparent that a single grease might be able to perform well in both applications and thus pass the specification and testing for both chassis and wheel bearings. Hence these greases became marketed and known as “multipurpose” grease and bore the dual certification GC-LB. This nomenclature stuck, and now if you simply do an internet search for multipurpose grease, you will be awash in results from multiple outlets wanting you to purchase their product. It’s important to note that the term “multipurpose” does not have a formalized definition, so this is largely marketing and a common term used to define a grease that may work in multiple applications.

We think back to our consolidation task force that is sitting in a conference room pouring over lubricant technical data sheets and machine manuals to determine the best lubricant to use in their machine, and they come across a grease that is listed as multipurpose. This is viewed as a godsend as it falls in line with what we are hoping to do - find a lubricant that will perform well in multiple applications without sacrificing the health of the machine. Looking at the equipment manuals, all they recommend is to use an NLGI 2 Lithium grease, so surely this multipurpose grease will work fine. Unfortunately, without an industry standard, these greases can vary widely in their performance as well as their chemical and physical properties.

“Multipurpose” has become such a normal descriptor for grease that it has further confounded the issue of over-consolidation. Looking through just three different lubricant manufacturers’ product catalogs yielded over a dozen products using the term “multipurpose” in the description of the grease. When compared to each other, there were a variety of different thickeners used, a wide range of base oils and varying additive loads. Many were lithium or lithium complex thickened greases, but some were aluminum complex and even polyurea. The base oil viscosity ranged from the low end of an ISO 100 all the way up to an ISO 460. Some had solid additives such as molybdenum, while others were more formulated to resist water-washing. So, selecting a grease based solely on a marketing term could have disastrous effects on our equipment.

Simply looking at the viscosities of the greases is enough to be concerned about. What is typical in an industrial plant is for the same lubricant to be used in most greased bearings regardless of load, speed or environment. This means the overhung fan operating at over 1,000 RPM will be getting the same grease as the conveyor bearing operating at 100 RPM. Selecting a multipurpose grease will undoubtedly lead to a less-than-optimum lubricating film in many cases. So, we need to become more diligent in specifying what grease to use in each application. While this may require the use of more greases onsite, the equipment will be more reliable and operate with a higher degree of efficiency. Often, greases are over-consolidated because of a people problem, not a lubricant problem. There are ways to avoid the cross-contamination of greases, and most of them center around the training of your lubrication team. We also need to have a more technical specification for the greases we are going to use, rather than generic terms that allow purchasing to drift away from our original product.

Writing a grease specification should consider all the unique aspects of the grease to ensure if our supplier changes, we can still get the same level of performance from the next lubricant. Some items to consider in your grease spec for each piece of equipment are:

  • NLGI Grade
  • Thickener Type
  • Base Oil Type
  • Base Oil Viscosity
  • Dropping Point
  • Water-Wash Resistance
  • EP Characteristics
  • Oxidation Stability
  • Pumpability
  • Rust Protection

Other properties unique to the application should be considered in addition to this list.

The NLGI is also working on expanding the specification and getting a standard in place that can begin to address the deficiencies in this area. The new standard will attempt to break down this category into more distinct grease formulations to handle more stressful applications such as high water, load, saltwater and prolonged life. These future classifications will be more granular and allow for a tighter tolerance than what is currently the market norm.

While there are options available to reduce the number of greases in use, careful thought and consideration should be employed to avoid the over-consolidation and subsequent sub-optimum lubrication for these grease-lubricated components. After all, not all greases are the same, regardless of what the description may lead you to believe.

New NLGI Certifications Eliminate Confusion

The NLGI (National Lubricating Grease Institute) has seen the need for updated grease specifications and are currently building these specifications, complete with performance testing criteria. While the traditional wheel bearing and chasis certifications will persist, new certifications will be created in order to further segment greases, breaking down the “one-size-fits-all” approach. High-Performance Multiuse Grease (HPM) is the first of these new certifications. It serves as a core specification and has additional performance tags to further designate a specific grease application. These tags include water resistance (HPM+WR), salt-water corrosion resistance (HPM+CR), high load (HPM+HL), and low temperature (HPM+LT). There is no limit to the tags a grease may have, so it is possible for a formulation to achieve multiple tags based upon its performance in testing. This is certainly a great step forward and helps to ensure that the lubricant selected is correct for the application, bringing grease certifications into the modern age. For more information on these certifications, specifications, and testing you can visit the NLGI website here: https://www.nlgi.org/about-us/high-performance-multiuse-grease/

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About the Author

Wes Cash is the director of technical services for Noria Corporation. He serves as a senior technical consultant for Lubrication Program Development projects and as a senior instructor for ...