Most lubrication basics are fairly well-understood in this day and age, and there are plenty of resources of documentation regarding lubricating systems and analysis. But there's still one lubricant that remains a mystery to many - grease. Grease itself is a poor lubricant. The oil and additives held in place by the grease soap fibers are the elements that actually perform the lubrication in a system. 

Areas such as manufacturing environments, OEM formulations, correct sampling methods, and compatibilities give us a better understanding of the functionality and necessity of grease analysis in lubricated equipment. 

Grease Manufacturing Causing Complications

The manufacturing process for grease requires high temperatures and pressures, and accurate applications, which cause complications during manufacturing. The tests designed to qualify grease from the manufacturing environment were designed decades ago, mainly to ensure quality. However, they were not specifically designed to encompass qualifying grease for use in the field.

Not All Greases Are Compatible

To make the scenario more complicated, most OEM's specify three parameters: National Lubricating Grease Institute (NLGI) grade, soap type, and (sometimes) a base oil viscosity requirement. Grease manufacturers have identified formulations. While these three parameters may be identical, the actual formulations could be significantly different. Not all greases are compatible - even greases of the same soap composition may be incompatible with each other. In extreme cases, this can result in a complete loss of lubrication in the component, and, ultimately, equipment failure.

Grease Sampling vs. Oil Sampling

Collecting an accurate, representative sample of your grease - to send in for analysis that provides a valuable maintenance recommendation - can be challenging; it's not as simple as oil sampling. Poor sampling techniques and processes can give you limited information, or a false sense of security when there could, in fact, be a catastrophic problem.

The sampling processes of grease lubrication and oil lubrication are different. Grease is designed to release the lubricating oil charge with the soap holding it into the area where the lubrication is required. As a result, the grease in the compartment will most likely be extremely non-homogeneous. Collecting a grease sample from the incorrect location (for example, the outer surface of your component) may not be representative of the grease next to the area being lubricated. Sending in an incorrect, non-representative sample can mean receiving incorrect analysis results and maintenance recommendations. 

To help collect a representative grease sample, some fluid analysis laboratories provide customers with cost-effective, easy-to-use sampling devices and other materials used to extract grease from the system. These sampler devices are included in each type of sample kit. They come with shipping tubes and labels for easy sampling and submitting to the laboratory.

Why Test?

It all comes down to cost. Grease is significantly more expensive than an equivalent lubricant. Accurate grease analysis is a major value add when it comes to maintenance, given that grease-lubricated systems are designed to last extensively longer than oil-lubricated systems. This means there's a financial gain from gathering effective and actionable maintenance recommendations from the results of your grease analysis.

Grease Testing and Analysis

Grease testing and analysis provides valuable insight into grease performance and integrity, including reliability-centered areas like wear, consistency, contamination, and oxidation.

Performing the maintenance actions recommended after grease is analyzed will result in: Minimized unplanned repairs; Decreased downtime; Extended machine life.

The following laboratory tests analyze properties within grease to target potential problems that could cause equipment failure.

• Die extrusion| Measures the grease's consistency by applying different loads on the sample and extruding the grease through a die, and measuring the resistance
• FTIR| Identifies contaminants and oxidations levels by looking at the absorbance of different functional groups in the spectra
• Colorimetry testing| Finds changes in appearance that are caused by overheating, aging and contamination
• ICP-OES| Evaluates grease for wear metals, additive elements, and contaminants
• Linear sweep voltammetry| Measures antioxidant content and estimates life expectancy of the antioxidant package in the grease
• FdM+| Identifies ferromagnetic materials in the grease to determine wear concentration by passing the sample through a magnetic field, and measuring the disturbances of that field from the entrained magnetic particles

Unfortunately, grease as a lubricating agent will continue to be a mystery for the foreseeable future. Accurate grease sampling, coupled with laboratory analysis can help alleviate the confusion, provide insights into what is going on in the system and help protect your grease investment. The results from testing your grease can give you an inside look into your system, the grease-lubrication properties to stop problems from occurring, and extend the health of your system.

David Swanson is Director of Technical Services for POLARIS Laboratories, an independent fluid analysis laboratory specializing in oil, grease coolant, and diesel fuel analysis. David has more than 25 years of analytical laboratory, industrial processes and management experience, including quality control, laboratory analysis and leadership roles for petrochemical and industrial chemical companies. He leads the science, quality and maintenance teams at POLARIS, and also oversees the laboratory processes, ensuring our science operations are compliant and functioning under the highest quality standards. He is the ISO 17025 Quality Manager for the company.

POLARIS Laboratories | polarislabs.com