Multiuse greases are required in a variety of different applications, many having different performance challenges. In specific applications, the grease may need to deliver enhanced levels of performance over the high-performance multiuse (HPM) core specification, such as increased high load carrying capacity (HL).
High load carrying capacity may be a requirement in many applications, such as heavily loaded wheel bearings on trailers, or heavy loaded bearings in industrial machinery.
Greases meeting the enhanced high load carrying capacity specification requirements will be awarded the HPM + HL certification mark. In order to meet this higher level of performance, a grease must first pass the HPM core specification.
To demonstrate an enhanced level of high load carrying capacity over the HPM core specification, there are an additional five test performance requirements.
Two performance test requirements demand more stringent limits than the HPM core specification. These are the four-ball wear test (ASTM D2266), which covers the determination of the wear preventive characteristics of greases in sliding hardened steel-on-steel applications, and also the four-ball extreme pressure test (ASTM D2596), with performance requirements increasing significantly from 250kg to 400kg weld point.
A new test to determine extreme pressure properties of lubricating greases (ASTM D5706) has been added to the specification, as well as the ASTM D7594 fretting wear scar test. The fretting wear scar test is used to determine antiwear properties of greases in order to prevent fretting wear, and is a test which is currently included in many European specifications, such as wind turbine greases.
Finally, a fretting wear loss test has been added (ASTM D4170), used to evaluate a grease’s ability to protect oscillating bearings from fretting wear. Despite issues surrounding the availability and technical specification of the bearings to run the test, this performance requirement remains part of the specification process, with provisional licensing being awarded until these technical points have been addressed.
Greases passing the enhanced performance category/categories allow grease marketers to use the approved certification mark on their products and in promotional materials, in line with NLGI’s terms of use.
Our View
The HPM + HL enhanced category provides the opportunity to market higher-performing multiuse greases for applications where enhanced levels of high load carrying capacity may be required above the HPM core specification.
In order to pass the more severe high load carrying capacity specification requirements, the grease lubricant requires careful re-formulation, such as higher-performing extreme pressure agents, anti-wear additives and copper passivators.
The availability of HPM certified greases provides a true upgrade in performance levels, delivering tangible benefits to all stakeholders in the supply chain.
For more information on the NLGI HPM grease specification, visit our NLGI High-performance Multiuse (HPM) Specification section or contact your Lubrizol representative.
