HPM + WR
Multiuse Grease. Focusing On The New HPM + Water Resistance Specification.
In this article we take a look at the water resistance enhanced category of the new NLGI high-performance multiuse grease specification.
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 water resistance (WR).
Water resistance is required in many applications that undergo a large amount of exposure to water, such as a boat trailer’s wheel bearings, or a truck’s exposed fifth wheel.
Greases meeting the enhanced water resistance specification requirements will be awarded the HPM + WR certification mark. In order to meet this higher level of performance, a grease must first pass the HPM core specification, discussed in an earlier article in the series (see link at the end of this article to learn more).
To demonstrate an enhanced level of water resistance over the HPM core specification, there are an additional three test performance requirements.
The water washout test (ASTM D1264) is the same as used in the HPM core specification, but with more restrictive limits. The test evaluates the resistance of a grease to washout by water from a bearing, when tested at 79°C (175°F). While concerns the GC-LB limits (15.0 wt%) were too wide and have been addressed in the HPM core specification (10.0 wt%), even more severe limits (5.0 wt%) are required to meet the enhanced HPM+WR specification.
It is known that water contamination can affect the structural stability of some greases in service. The test added to address this potential issue is the wet roll stability test (ASTM D8022), which determines the roll stability of lubricating grease in the presence of 10.0 wt% added water.
A water spray off test (ASTM D4049) has also been added to the enhanced water resistance specification. This test method is very relevant to the steel industry and paper industry, and is used to evaluate the ability of a grease to adhere to a metal surface when subjected to direct water spray. Test limits with a maximum of 40% spray off require the grease to have greater performance levels than many everyday greases (which may be around 90% spray off); though the limit stops short of a specialty grease which may provide less than 20% water spray off.
The HPM + WR enhanced category provides the opportunity to market higher performing multiuse greases for applications which require enhanced levels of water resistance, above the HPM core specification.
In order to pass the more severe water resistance specification requirements, the grease lubricant requires careful re-formulation, such as the use of a higher-performing water resistant polymer.
The availability of HPM certified greases provides a true upgrade in performance levels, delivering tangible benefits to all stakeholders in the supply chain.
HPM® is a registered trademark for NLGI. To learn more, visit www.NLGI.org.