HPM + LT
Multiuse Grease. Focusing On The New HPM + Low Temperature Specification.
In this article we take a look at the low temperature 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 low temperature performance (LT).
The HPM low temperature enhanced category has been developed primarily for multiuse grease requirements in colder climatic conditions, such as the northern parts of the U.S. and Canada.
Greases meeting the enhanced low temperature specification requirements will be awarded the HPM + LT 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 low temperature performance over the HPM core specification, there are an additional three test performance requirements.
Firstly, new performance limits are required in the same low temperature, low torque test (ASTM D1478) contained within the HPM core specification. This test measures the extent to which a grease delays the rotation of a slow-speed ball bearing by measuring starting and running torques. In order to pass the enhanced low temperature specification, greases must successfully pass this test at a reduced temperature of -30°C, as opposed to -20°C for the HPM core specification.
Secondly, to measure the flow of grease, the U.S. steel mobility test (LT 37) is incorporated as part of the HPM + LT specification, a test which measures flow through a capillary under pressure at a temperature of -20°C.
The final test is a low temperature flow pressure test (DIN 51805), with the test requiring satisfactory yield strength of the grease, the point at which the grease will start to flow, at a temperature of -30°C.
The HPM + LT enhanced category provides the opportunity to market higher-performing multiuse greases for applications which require enhanced levels of low temperature performance, above the HPM core specification.
In order to pass the more severe low temperature performance specification requirements, the grease lubricant requires careful re-formulation, such as higher-performing low temperature performance polymers.
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.