How Does Bearing Speed Affect Grease Selection?

Not all bearing grease works the same way. A grease that works well in a slow-moving bearing may cause problems in a high-speed one. But why does bearing speed matter so much?

Increasing the bearing speed also increases friction and heat. The right grease reduces friction, controls heat, prevents wear and protects the internal parts of the bearing. Using the wrong grease can cause excessive drag, higher temperature, and reduced bearing life.

Selecting the right grease is about more than speed. Other factors are load, operating temperature, contamination, bearing type, seals and grease viscosity. Knowing these factors can help you select the right grease and keep your bearings running smoothly for longer. Fubex Lubricants provides quality bearing grease for a wide range of industrial applications. Free delivery, great prices and easy returns. Need help choosing the right grease? Call us at +971 50 544 9614 — our friendly team is ready to help! 

Awais I., Sales Director, says, ‘‘Understanding how bearing speed affects grease selection can help prevent overheating, reduce bearing wear, avoid costly repairs, and keep equipment running reliably for longer.’’ 

Understanding High-Speed Bearing Applications 

One common question during site visits is, “Why do high-speed bearings get hotter?” The main reason is the connection between the bearing speed and the grease being used. When a bearing runs at high speed, it creates more friction and heat. If the grease is not suitable for the application, it can make the problem worse and shorten the bearing’s service life.

For example, an industrial facility had an overhanging fan driven by a belt-connected motor running at 1,750 RPM. The fan bearings were running on grease that was too thick for the job. This caused more friction and the temperature of the bearings increased which reduced the service life. This instance illustrates the importance of selecting a grease appropriate for high speed applications.

Choosing a High-Speed Grease

Many industrial machines have bearings that run at very high speeds. These bearings need the right grease because different greases behave differently when exposed to high speeds.

Using the wrong grease increases friction, heat and drag. This can damage the bearing and shorten its lifespan over time. Using grease that is designed for high speed applications can help to alleviate these issues and keep the bearing running smoothly.

High-Speed Applications

During plant inspections, one common question is why some bearings run hotter than others. In many cases, the bearings that run at higher speeds also produce more heat.

For example, an industrial fan was connected to a large electric motor with a 1-to-1 belt drive. The motor ran at 1,750 revolutions per minute (rpm), so the fan bearings were also running at about the same speed.

The grease in the bearings was too thick for the application. This created more friction and heat which decreased the life of the bearing. Select greases having properties suitable for the bearing speed and operating conditions. 

This will help to reduce heat and increase bearing life. High speed applications are not limited to fans. Some grease-lubricated bearing pumps are capable of speeds above 2000 rpm. Also possible is high speed for blowers , agitators , mixers .

Using a general-purpose grease without considering the bearing’s speed and working conditions can lead to problems. Before choosing a grease, it is important to understand the bearing’s speed factor and select a lubricant that can handle the application.

Matching Grease Properties to Bearing Operating Conditions

Choosing the right grease for a bearing depends on factors such as speed, load, temperature, and working conditions. The main grease properties to consider include:

• Base Oil Viscosity: It affects the thickness of the oil film. Lower viscosity is usually better for high-speed bearings, while higher viscosity is more suitable for heavy loads.
• Thickener Type: The thickener helps the grease keep its structure. It also affects how well the grease releases oil and handles heat. For example, lithium complex grease works across a wide temperature range, while polyurea grease is often used in high-speed electric motors.
• Mechanical Stability: This shows how well the grease keeps its structure under pressure, movement, and vibration. Good mechanical stability is important for bearings that run at high speeds or in vibrating equipment.
• Oxidation Resistance: This helps the grease last longer, especially when bearings operate at high temperatures. Grease with good oxidation resistance is less likely to break down over time.

Key Lubricant Selection Factors

There are many factors that determine the proper grease to use. The best grease for a bearing depends on speed, load, temperature and the working environment.

Base Oil Viscosity

A heavily loaded bearing at lower speeds will normally require a higher viscosity base oil. Low viscosity is usually required for high-speed bearings to reduce friction and heat.

Thickener Type

Thickeners have different heat resistance, water resistance, shear stability and compatibility. Select a thickener appropriate to the bearing operating conditions.

NLGI Grade

The NLGI grade shows how thick or soft the grease is. It also affects how easily the grease can move through a lubrication system and how well it stays in place.

Load and EP Protection

Heavy-loaded bearings may require EP (extreme pressure) protection grease. EP grease protects bearing surfaces from wear at high pressure.

Operating Temperature

High temperatures can cause the base oil to break down and damage the thickener. This can cause the grease to separate, harden, or leak out. Always use a grease capable of withstanding the bearing’s operating temperature.

Water Resistance

Bearings exposed to water, moisture or frequent washdowns should be greased with a good water-resistant grease. This helps keep the grease from washing out and keeps the bearing from corroding.

Compatibility

Not all greases are compatible with one another. Mixing incompatible greases will change the consistency of the greases and will reduce their ability to protect the bearing. Always check grease compatibility before changing products.

Re-Greasing Interval

The right re-greasing interval depends on factors such as bearing speed, size, load, temperature, operating hours, and environment. Following the recommended interval helps keep the bearing properly lubricated and extend its service life.

Common Bearing Grease Selection Mistakes

Even experienced technicians can make mistakes when choosing or using grease. These mistakes can reduce bearing life and cause performance problems.

• Using High-viscosity Grease in High-Speed Bearings: Thick grease can create more friction, which can increase churning and heat.
• Running Grease beyond its Temperature Limit: Too much heat can cause the grease to oxidize, harden, and lose its effectiveness.
• Mixing Incompatible Greases: Different types of grease may not work well together. Mixing them can cause separation, hardening, or leakage.
• Using the Wrong Amount of Grease: Too much grease can increase friction and heat, while too little grease may leave the bearing without enough lubrication.

These mistakes often happen when the same grease practices are used out of habit instead of considering the bearing’s actual operating conditions.

Factors Affecting Bearing Lubrication

There are many factors that affect the efficiency of bearing lubrication. These things will help you to choose the right lubricant and also to use the bearing correctly.

• Speed: High speed bearings create more friction and heat. The lubricant needs to have the proper viscosity to handle the speed without creating excessive drag or heat. 
• Extreme temperatures can cause lubricants to break down or evaporate. At low temperatures the lubricant can thicken up, increasing drag and making the bearing harder to start. 
• Load: As the load increases, the pressure in the lubricant film increases. You need a lubricant that has the right viscosity to maintain a good film between the moving parts.
• Contamination: Dirt, dust and other particles can damage bearing surfaces and reduce the effectiveness of the lubricant. This helps keep the lubricant clean and protects the bearing.
• Viscosity: A measurement of how well a lubricant will flow. The proper lubricant film maintains sufficient viscosity when the bearing load and temperature change.
• Type of lubricant: Oils, greases, and solid lubricants have different properties. The best choice depends on the bearing, operating conditions, and application.

Low Speeds

Low speed bearings are usually subjected to heavy loads. At these speeds the oil might not be able to develop a complete protective film between the rolling surfaces. This can increase the risk of contact wear and metal-to-metal contact. 

For bearings where NDM is less than 20,000 mm/min (rpm × mean bearing diameter), the grease should offer additional boundary lubrication protection. Bearing protection may be achieved by using greases that contain solid lubricants such as molybdenum disulfide (moly) or graphite. Calcium sulfonate greases can also offer good protection under these conditions.

High-viscosity base oils can support heavy loads, but viscosity alone isn’t enough. The grease also needs to have the right additives and thickener properties to protect the bearing at low speeds and high loads.

Can You Mix Different Bearing Greases?

Two greases are not necessarily compatible just because they have the same NLGI grade, look similar or are both intended for industrial bearings. Different base oils, thickeners and additives will be in different greases. These ingredients may not go well together. This can alter the consistency of the grease, reduce its stability, cause leakage or interfere with the proper distribution of the grease inside the bearing.

If you do not know which grease is already in the bearing, first check the equipment or bearing manufacturer’s lubricant specifications. This will help you to find a suitable replacement. If you have to change the grease, you may have to purge or remove the old grease before putting in the new. Which way is right depends on what kind of bearing and lube system you are using.

Final Takeaways

Choosing the right grease starts with understanding the bearing’s speed and working conditions. High-speed bearings need grease that controls friction and heat, while low-speed bearings may need stronger protection against heavy loads and wear. 

Using the right grease for the bearing prevents overheating, cuts down on wear and lengthens the bearing’s life. Fubex Lubricants provides quality lubrication solutions for reliable bearing performance. 

FAQs

Q1: How do you choose the right bearing grease?

Choose a bearing grease based on the bearing’s speed, load, and operating temperature. Also, check the grease’s viscosity, thickener type, and NLGI grade to make sure they match the bearing’s working conditions.

Q2: What are the most common greasing mistakes?

The most common greasing mistakes are overgreasing, using the wrong lubricant, and greasing on a fixed schedule without checking the condition of the equipment. Such errors lead to overheating, to poor lubrication and to excessive wear of the bearings.