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Because grease is so poorly understood, there are many myths surrounding grease quality. Some examples include: “black grease is better,” “sticky grease is better,” “red grease is the best,” “greases with different thickener types are always incompatible,” “good greases don’t bleed oil,” and “multi-purpose greases are all the same.”
Let’s take a closer look at that last myth. The truth is that multi-purpose greases can be made with different thickeners, different base oil viscosities and different additive combinations. Due to the possible combinations, this pretty much ensures that there is a range of performance in multi-purpose greases. There has not been an industry specification for “multi-purpose” grease to standardize performance. Until now.
Machinery Lubrication: Who is NLGI, and why did NLGI develop this new certification?
NLGI: NLGI (formerly the National Lubricating Grease Institute) was incorporated in 1933 and is a not-for-profit trade association, primarily composed of companies who manufacture and market all types of lubricating grease, companies who serve them with equipment, supplies, and services, as well as research and educational groups and companies whose interests are primarily technical. Another category for membership is “Consumer,” which is for organizations that are users of lubricating grease. The Institute works continuously to strengthen its association by rendering service to the end-user of grease, as well as those on the manufacturing and supply side.
The objectives of NLGI are to disseminate information that can lead to the development of better lubricating greases for the consumer and to provide better grease lubrication engineering service to the industry.
NLGI endeavors to promote these objectives in several ways, including funding lubricating grease research, promoting improved laboratory and field tests and lubricating grease manufacturing improvements. Technical discussion forums between consumers, producers and educators are provided, and dissemination of technical data relevant to improved manufacturing techniques, new products, new uses, and new application and testing methods is fostered. Part of NLGI’s mission is to provide resources that are relevant to the global grease end-user (consumer) community.
Figure 1. The HPM specification and
four performance enhancement categories.
In the 2015-2016 timeframe, one key priority set by NLGI’s board was to “modernize and update the GC-LB program.” Since grease technology and applications have evolved since 1989, and the original target for GC-LB was chassis and wheel bearing applications, NLGI’s board prioritized the modernization of the GC-LB program. Early in the process of collecting input to modernize the GC-LB program, feedback clearly stated the need for a new grease specification with higher performance and broader utility in the marketplace. The result focused on this High-Performance Multiuse (HPM) grease specification, which provides a benchmark for grease used in a variety of bearings and applications that require similar lubricating properties.
Machinery Lubrication: What type of applications are a good fit for an HPM certified grease?
NLGI: While the NLGI HPM grease specifications are designed to ensure a high level of performance for many different applications (multiuse), they are not suitable for all applications. We consider that multiuse applications may include the following:
Thus, HPM grease is a good choice for many applications which require “more than just a multi-purpose grease,” but not where a “specialty grease” is required.
It is important to remember is that the HPM specification should not be used as a shortcut to grease selection. Each application should be evaluated for its requirements based on speed, load, temperature and operating environment. These parameters will affect the choice of base oil viscosity, consistency, thickener type and additive needs. An HPM-certified grease may or may not meet these requirements. We recommend that you consult an application engineer from your grease supplier to find out if an HPM grease is right for your application.
Machinery Lubrication: How were the limits chosen for the HPM specifications?
NLGI: A team of grease experts representing large and small manufacturers, additive suppliers, original equipment manufacturers (OEMs) and an expert consultant collaboratively created the HPM specification. The limits chosen for the tests in the HPM specifications were selected in several ways. When the original drafts of the specifications were developed, limits were selected based on defining a high level of performance using the decades of experience from global experts in grease lubrication.
Then, during an extensive interview process conducted with grease manufacturers, marketers, end-users, GC-LB certification holders and OEMs, the specification team received feedback which led to the philosophy that emerged pertaining to limit-setting: “challenging, but achievable.”
In some cases, the specification steering committee members identified applicable products for the HPM program and then ran tests to validate the proposed limits.
The final specification defines a level of performance where HPM greases may have a significant impact on the operational success of a manufacturing plant.
Machinery Lubrication: What if my application calls for better water resistance or higher load carrying capability or some other area?
NLGI: Since greases in some applications experience more challenging conditions (e.g., low temperature or exposure to water or corrosive liquids), different sub-categories with additional performance requirements are defined as part of the overall specification. In these sub-categories, a grease must meet the performance of the core HPM grease specification plus the additional testing related to (a) water resistance (+WR), and/or (b) high load-carrying capacity (+HL), and/or (c) saltwater corrosion resistance (+CR), and/or (d) low-temperature performance (+LT) (Figure 1).
Machinery Lubrication: How will the end-user ensure that greases of different chemistries certifying to the HPM specifications will be compatible in real application situations?
NLGI: Since the HPM and HPM+ specifications are performance specifications, there are no formulation or grease chemistry requirements to meet the specifications. Because the specifications are “chemistry neutral,” there is a possibility for different HPM-certified greases to be incompatible, even if the greases are from the same supplier.
By definition, two lubricating greases are incompatible when a mixture of the products has physical or performance properties that are inferior to those of the individual greases. When two greases are incompatible, some mixtures will soften, leading to leakage through seals and away from lubricated surfaces. Some mixtures will cause the thickener to release the oil, and the separated oil may run from the bearing housing. Less often, mixtures may harden and cause lubricant starvation and poor grease mobility. Grease incompatibility can lead to lubrication and equipment failure and is, therefore, an important issue.
Figure 2 Examples of HPM certification marks.
Operators and end-users may not always be aware of the risks involved when considering a change of grease in an application. This is true regardless of whether the grease(s) involved are HPM greases or any other greases. Therefore, it is incumbent upon the grease user to ensure compatibility if changing greases. Generally, grease suppliers can provide compatibility information if asked. The use of publicly available grease compatibility charts is not recommended, as these generalize compatibility based solely on thickener types, whereas incompatibility can be the result of incompatible base oils or additives. It is always the safest choice to have the specific greases evaluated via laboratory testing.
If NLGI were to include some sort of compatibility requirement in the HPM specifications, it would likely lead to the exclusion of some types of grease thickener technologies, which goes against the HPM specification design principles. And since grease compatibility predictions should not be based on generic thickener-based compatibility charts, specific grease pairs should be tested. Given the wide variety of chemistries utilized in grease products, there is no way to include such a compatibility requirement in the HPM specifications.
Machinery Lubrication: Where can I find HPM certified greases?
NLGI: With the launch of the program to grease manufacturers in late 2020, NLGI is now receiving applications for certification. Grease from the manufacturer is submitted to a third party, the Center for Quality Assurance (CQA), for lab testing to verify that the grease meets the strict performance levels set in the HPM specification. Greases certified by the program will bear the HPM trademark showing approval to the core and any sub-category endorsements, as shown in Figure 2.
Marketers and manufacturers who market their HPM certified greases must display the HPM trademark on their containers and will be listed on the NLGI website at High-Performance Multiuse (HPM) Grease Certification (nlgi.org).