Grease Formulators

Grease contains a thickener system that acts like a sponge, releasing oil when force is applied. The proper release of oil is essential for effective lubrication.

Consistency and Penetration (ASTM D-217): Grease consistency refers to its thickness or firmness. ASTM D 217 Cone Penetration Test measures the penetration of the grease under specific conditions. Unworked penetration assesses the grease’s consistency during storage, while worked penetration (60 strokes) determines the NLGI (National Lubricating Grease Institute) consistency grade.

Mechanical Stability: Consistency and mechanical stability are linked. If the grease consistency is too high, it might not release oil effectively, potentially causing bearing damage. If it’s too low, leakage might occur, leading to lubrication failure and bearing damage.

Prolonged Working: Grease’s behavior under prolonged use is assessed by penetration tests after various stroke counts (10k, 60k, 100k). These tests determine the grease’s stability and consistency during extended operation.

Roll Stability Test (ASTM D 1831): In rolling applications like bearings, the grease’s consistency and mechanical stability are evaluated using ASTM D 1831. This test is conducted at room temperature for two hours to mimic real-world conditions.

In addition to mechanical stability, it’s imperative to thoroughly assess the grease’s resistance to high temperatures and oxidation. The grease’s dropping point stands as a pivotal measure – indicating the precise temperature at which the grease transitions from a semi-solid to a liquid state, as determined by specific testing conditions.

For this assessment, industry standards ASTM D 2265 and ASTM D 566 are employed, delineating methods to ascertain the dropping point of the grease.

It’s essential to underscore that should the operational temperature exceed the grease’s dropping point, the grease will liquefy and escape the intended application. Consequently, it’s imperative that the grease’s dropping point substantially surpasses the expected operational temperature to prevent any inadvertent melting and runoff.

Due to moisture present in the air, metal parts are prone to get corroded. Lubricants are applied to protect these metals from rust and corrosion. Before applying any lubricant, it becomes necessary to determine its rust and corrosion-preventive properties.

EMCOR RUST Test (ASTM D6138 / IP 220): The EMCOR rust test is a dynamic corrosion test used to assess the rust-preventive properties of lubricating greases when exposed to water or seawater over a 7-day period. The test involves running ball bearings that are lubricated with the grease being evaluated. After the 7-day period, the outer rig of the ball bearing is examined, and a rating is assigned based on the extent of corrosion observed. This test is valuable because it simulates real-world conditions and helps determine how well the lubricant can protect metal surfaces from rust and corrosion when exposed to moisture.

Static Rust Test (ASTM D-1743): The static rust test is designed to evaluate the corrosion-preventive properties of greases when applied to tapered roller bearings. The lubricated bearings are subjected to wet conditions by exposing them to water and then stored at a temperature of 52°C (125.6°F) for a duration of 48 hours. This test assesses how well the grease can protect the bearings from corrosion when they are subjected to prolonged exposure to moisture and elevated temperature.

Both of these tests provide important insights into the ability of lubricants (specifically greases) to protect metal parts, such as ball bearings and tapered roller bearings, from rust and corrosion under different conditions. These tests are crucial in industries where metal components are exposed to moisture, as corrosion can lead to significant mechanical failures and reduced lifespan of equipment

Greases that are used in marine applications or areas where water contact is likely need to have strong water resistance properties to maintain their effectiveness.

Calcium-based greases are commonly preferred in such scenarios because they exhibit good water resistance. However, there might be situations where lithium-based greases or other types of greases are required due to specific performance characteristics. In these cases, additives can be introduced to enhance the water resistance properties of those greases.

The water resistance of a grease is often assessed using tests such as the Water Washout Test, which follows the ASTM D 1264 standard. In this test, ball bearings are lubricated with the grease under investigation. The bearings are then rotated at a specific speed (600 rpm in this case), while a controlled amount of water (5ml/s) is directed onto the bearings for a set duration (usually around 60 minutes). After the test, the amount of grease that has been washed out of the bearing is measured.

This test simulates real-world conditions where the grease could come into contact with water, and it provides a quantifiable measure of the grease’s ability to resist being washed away by water. Greases with higher water resistance will retain their lubricating properties better under wet conditions.

It’s worth noting that proper grease selection and testing are crucial for maintaining machinery and equipment in various environments, ensuring their longevity and performance. Different applications might require different grease properties, and understanding the specific needs of each application is essential for making informed choices.

The concept of grease adhesiveness pertains to its inherent propensity to maintain its cohesion with metal surfaces even when subjected to operational conditions. This fundamental property directly influences the performance of grease in real-world applications. The evaluation of grease adhesiveness is typically conducted through the application of the water spray-off method, as defined by the ASTM D 4049 standard.

The ASTM D 4049 standard employs the water spray-off method as a systematic approach to assess the capacity of grease to adhere resolutely to a metal substrate in the face of water spray. This method serves as a crucial benchmark for determining the robustness of grease adhesion, which is particularly relevant in scenarios where exposure to water or moist environments is anticipated. By simulating such conditions, this evaluation sheds light on the ability of grease to retain its protective and lubricating qualities even in challenging circumstances. In essence, the water spray-off test outlined in ASTM D 4049 provides valuable insights into the reliability and performance longevity of grease formulations under conditions of potential moisture exposure.

Greases play a crucial role in lubrication by reducing friction, preventing wear, and enhancing the performance and longevity of mechanical components. Evaluating the antiwear, extreme pressure (EP), and frictional properties of greases is essential for selecting the right lubricant for specific applications. The Four-Ball Machine is a widely used testing apparatus that simulates the contact conditions and tribological behaviour of lubricated surfaces under various loads, speeds, and temperatures.

Methodology: The Four-Ball Machine test involves placing three stationary balls in a triangular arrangement and a fourth rotating ball held against them with a predetermined load. The rotating ball’s RPM, load, and duration of testing can be varied to mimic different operating conditions. The grease sample is applied to the balls before initiating the test. The key parameters assessed in this test are:

Wear Scar Diameter (WSD) ASTM D-2265: The WSD measurement provides insights into the grease’s antiwear properties. A smaller WSD indicates better antiwear performance, as the lubricant effectively reduces the contact-induced material loss on the ball surfaces.

Weld Load ASTM D-2596: The weld load indicates the EP properties of the grease. It represents the load at which the lubricant film prevents direct metal-to-metal contact, thereby preventing excessive wear and surface damage. A higher weld load signifies better EP performance.

Friction Coefficient ASTM D-5183 : The friction coefficient quantifies the ease with which the lubricated surfaces slide against each other. A lower friction coefficient indicates reduced energy loss due to friction and improved energy efficiency.

Analysis: By analyzing the results from the Four-Ball Machine test, one can assess the performance of different greases under various operating conditions. The data helps in selecting greases that exhibit superior antiwear, EP, and frictional properties for specific machinery and applications.