Types of Industrial Greases: Guide to Choosing the Right One

The Importance of Correct Industrial Grease Selection

In the industrial maintenance environment, choosing the right lubricant is as critical as selecting the mechanical component itself. An incorrect industrial grease not only reduces the service life of bearings but can also cause costly unplanned downtime. At Lubricalia, with over three decades of experience distributing lubricants in Madrid, we have observed that the most common error is not a lack of lubrication, but rather the chemical or thermal incompatibility of the chosen thickener.

Grease is, essentially, oil retained by a thickener. While the base oil defines lubricity and viscosity, it is the thickener that determines temperature resistance, mechanical stability, and compatibility with other lubricants. Below, we break down the most common types to facilitate their technical identification.

Lithium Greases and the NLGI Standard

Lithium-based greases (lithium 12-hydroxystearate soap) have been the industry standard for decades. They offer an excellent balance between water resistance, mechanical stability, and dropping point, typically ranging between 180°C and 190°C. They are ideal for general applications in electric motors and transmissions operating at moderate temperatures.

To classify the consistency of these greases, we use the NLGI (National Lubricating Grease Institute) scale. This standard ranges from 000 (very fluid) to 6 (solid block). Most industrial bearings operate optimally with an NLGI 2 consistency grease, which allows for proper circulation within the bearing without generating excessive rotational resistance or leakage due to centrifugation.

Lithium Complex for High Demands

When operating conditions become more severe, standard lithium greases may fail due to their thermal limits. This is where lithium complex comes in. By adding a complexing agent (such as organic acid salts), the dropping point is significantly raised, typically exceeding 260°C.

These greases maintain their structure and sealing capacity at temperatures where conventional ones would liquefy. They are the mandatory choice for ovens, dryers, and steel industry applications. Furthermore, they usually incorporate EP (Extreme Pressure) additives and high-performance antioxidants to withstand shock loads and long relubrication intervals.

Polyurea: The Solution for Electric Bearings

Greeses thickened with polyurea represent modern technology for high-speed and high-temperature applications, especially in electric motors. Unlike metallic soaps, polyurea contains no metals, which eliminates the risk of corrosion due to catalytic oxidation and offers superior oxidative stability.

Their dropping point usually exceeds 250°C, and they possess a significantly longer service life in bearings compared to lithium greases. However, there is a critical warning: polyurea greases are not compatible with lithium or bentonite greases. Mixing incompatible thickeners can cause a drastic softening of the mixture, leading to total grease loss from the bearing.

Special Cases and Assembly Pastes

For applications where temperature exceeds the limits of organic thickeners or where extreme protection against wear during assembly is required, special pastes and greases are used. A relevant technical example is the use of pastes with molybdenum disulfide or solid particles to prevent galling in forced fits.

Products like Castrol Molub Alloy Paste TA are specifically designed to protect metal surfaces under extreme loads and high temperatures during the assembly of critical components, ensuring that future disassembly is viable without damaging the parts.