Understanding the difference and choosing the right lubricant

What is the difference between oil and grease?

Oil and grease are common terms that we often hear, but their differences may not be clear to everyone. Unless they work in the field of lubrication. It's important to know when to use oil or grease, as each has its own advantages and applications. In this article, we explore the differences between oil and grease, how grease is made, considerations for choosing the right lubricant, and when to use oil instead of grease.

Oil and grease: what sets them apart?

While both oil and grease serve as lubricants, they differ in their physical properties and applications. Here's a simple breakdown:

Composition: Greases are essentially oils with a thickening agent added to them.
Physical state: At room temperature, greases are typically solid, while oils are usually liquid.
Transformation: All oils can be converted into greases, but not all greases originate from oils.
Applications: Greases are primarily used in machinery, tools, and equipment, whereas oils have a wider range of non-industrial uses.

The making of grease: a closer look

Grease is formed by incorporating oil into a fibrous network, acting like a sponge. This fibrous network, referred to as the thickener, is responsible for creating a structure with spaces where oil particles are contained. The lubricating properties of grease stem from the oil within this network, while other qualities depend on the type and quality of the thickener.

The network containing the oil provides other qualities, such as:

Consistency: The thickness or viscosity of the grease.
Dropping point: The temperature at which the oil begins to separate from the thickener.
Water resistance: The ability of grease to remain intact under water and high-pressure hose spray.
Base oil viscosity: The stickiness of the oil used in the grease formulation.
Load carrying ability: The capacity of grease to withstand pressure while maintaining performance.
Shear stability: How well the grease retains its consistency during repeated and rapid movements.
Compatibility: Ensuring that different greases used in the same location do not compromise each other's properties.
Pumpability: The ease with which grease can be transported using a pump.
Oil separation: A certain amount of oil must separate from the grease for effective lubrication.

Food-grade lubricants: safety in sensitive environments

Certain greases need to be food-safe or food-grade to ensure they do not pose any harm if they accidentally come into contact with items meant for consumption. However, being labeled as "Food Safe" doesn't imply that the grease can be used for cooking. It simply means that it adheres to specific safety regulations. Interflon offers various food-safe lubricants. For more information read our article about food-grade lubricants.

The NLGI: a dedicated institution for grease

The National Lubricating Grease Institute (NLGI) is an institution entirely focused on the world of grease. They provide a scale for consistency, rating greases from 000 (fluid) to 6 (very hard). Choosing the appropriate grease consistency depends on the specific application. Very fluid greases can be used in low-speed applications where there is no danger of leakage. Harder greases can be used in high-speed applications.

When to use grease instead of oil?

The decision to use grease over oil largely depends on the application at hand. Grease is often preferred in the following scenarios:

Where leakage and drippage is present
In hard-to-reach places where lubricant circulation is impractical
Where sealing is required in a high-contaminant environment (e.g. water and particles)
To protect metal surfaces from rust and corrosion
To lubricate machines that are operated intermittently
To suspend solid additives during slow-speed, high-load sliding conditions
For use in sealed-for-life applications such as electric motors
To lubricate under extreme or special operating conditions
To lubricate badly worn machines
Where noise reduction is important

When to choose oils instead of greases?

Oils have cooling properties and can transfer heat away from an application, making them ideal for applications where heat generation is a concern. Additionally, oils penetrate tight spaces more easily than grease, making them suitable for delicate mechanisms. In general, oils are used when greases are impractical to apply.

Conclusion

Understanding the difference between oil and grease is crucial for selecting the right lubricant for your applications. Grease, with its thicker consistency and specific properties, is often preferred for machinery and specialized environments. On the other hand, oils offer cooling capabilities and are suitable when greases may be impractical. By considering the unique characteristics of each lubricant, you can make informed choices and optimize performance in your applications.