Bearing units: Materials, applications and types

Bearing units

The bearing in a bearing unit is designed based on the construction of a single-row ball bearing (for example, the 6200 series), but with the difference that the outer ring is rounded. This unique design allows bearing units to compensate for significant misalignments.
Bearing housings are manufactured from various materials, including cast iron, sheet metal, stainless steel, or plastic, and can take various forms - pillow block, flanged, or special.

Mounting the bearing unit onto a shaft is typically easy and efficient, with an eccentric locking collar or set screws most commonly used for securing. Thanks to this simplicity in installation, bearing units have become an essential component in many industrial sectors.

What a bearing unit consists of

A bearing unit is a complex mechanism consisting of several main components. Here is a brief overview of these components and their functions:

• Bearing: This is the key component of the bearing unit. The bearing can be ball, roller, plain, or another type, depending on the specific application. The bearing allows rotation or linear movement between two parts and reduces friction between them.
• Bearing housing: The bearing housing is usually made of steel, cast iron, or plastic and serves to protect the bearing. It holds the bearing in place and protects it from damage or contamination.
• Seals: Seals are an important part of the bearing unit. Their role is to protect the bearing from the ingress of dust, dirt, and other contaminants that could damage the bearing or shorten its lifespan. There are various types of seals, including contact and non-contact seals.
• Lubricant: Lubricant is also a key component of the bearing unit. It helps reduce friction and wear on the bearing and can also help protect the bearing from corrosion.
• Rings: Rings are used to secure and retain the bearing within the bearing housing. They can be fixed or clamping, depending on the design of the bearing unit.
• Fasteners: Fasteners such as screws, nuts, and washers are used to mount the bearing unit onto a machine or equipment.

Which materials are commonly used to manufacture bearings?

100Cr6 Steel

100Cr6 steel is a type of chrome steel widely used for bearing manufacture. This material is popular for its high hardness and wear resistance, allowing it to withstand the heavy loads and high speeds typical of many bearing applications.

Advantages of 100Cr6 steel:

• High hardness and wear resistance
• Good resistance to corrosive wear
• Reasonable price

Disadvantages of 100Cr6 steel:

• Lower resistance to corrosive substances than stainless steel
• Requires regular maintenance and lubrication for a long service life

AISI 440C / SUS440C Stainless Steel

Stainless steel, such as AISI 440C or SUS440C, is another popular material for manufacturing bearings. This material is highly resistant to corrosive substances, making it ideal for applications in harsh environments such as the chemical industry, food industry, or marine applications.

Advantages of AISI 440C / SUS440C stainless steel:

• High resistance to corrosive substances
• Long service life even with minimal maintenance
• Ability to operate at high and low temperatures

Disadvantages of AISI 440C / SUS440C stainless steel:

• Higher costs compared to 100Cr6 steel
• Less resistant to shock loads compared to some other steel types

When selecting a bearing material, it is important to consider the specific requirements and conditions of your application. While 100Cr6 steel may be suitable for standard applications, AISI 440C or SUS440C stainless steel may be a better choice for more demanding environments.
 

Overview of the most common bearing housing materials

• Grey cast iron (FC200, FG20, FG25)

Grey cast iron is a traditional and commonly used material for manufacturing bearing housings. It is known for its good wear resistance and ability to withstand significant loads. Anti-corrosion passivation and a protective coating increase its corrosion resistance and extend its lifespan.

• Ductile cast iron (FCD450)

This material is approximately 30% more durable and 40% lighter than grey cast iron, making it an excellent choice for applications where higher load resistance and lower weight are needed. Like grey cast iron, ductile cast iron is also treated with anti-corrosion passivation and a protective coating.

• Steel (SS400)

Steel bearing housings are ideal for applications with heavy loads, vibrations, and shock. SS400 steel is highly durable and provides excellent strength and rigidity, which increases bearing service life.

• Stainless steel (AISI 304 - X5CrNi 1810, SCS13)

Stainless steel is an excellent choice for applications in harsh environments where corrosion resistance is required. AISI 304, also known as X5CrNi 1810 or SCS13, is resistant to many chemicals and can withstand high temperatures.

• Galvanized cold-rolled sheet metal

Galvanized cold-rolled sheet metal is a lightweight and affordable material that provides good corrosion resistance. It is suitable for applications where lightness and economic efficiency are needed.

• PBT Thermoplastic

PBT thermoplastic (polybutylene terephthalate) is a modern material used for manufacturing bearing housings. It is resistant to many chemicals and offers excellent thermal and electrical insulation. Its main advantage is that it is very lightweight yet strong.
 

Bearing unit seals

Bearing units require adequate sealing to prevent the ingress of dust and dirt, which could cause premature wear or failure. There are several types of seals:

• Single-piece seal: This seal has a flexible plastic lip on a metal cap and is designed for normal operating conditions and medium to high speeds.
• Two-piece seal: This variant combines a single-piece seal with a robust metal cover with a lip, which improves sealing performance without reducing maximum speeds. It is suitable for medium to high speeds.
• Multi-lip seal: This seal (designated as L3, L4 for SNR, LL for NTN, T.. for RHP) is ideal for heavily contaminated environments. It provides excellent sealing performance for low to medium speeds.
• Silicone seals: These are designed for high temperatures up to 180°C.
• Non-contact labyrinth seals: These seals are also designed for high temperatures up to 200°C.

For additional protection against contaminants, sheet metal, stainless steel, plastic, or cast iron covers can be used. These covers can be either open or closed.

As for the lubrication of bearing units, they are already pre-lubricated during manufacture. In more difficult operating conditions, the bearings can be relubricated. Bearing units are typically supplied with a plugged relubrication hole covered by a plastic plug. A steel grease nipple is included with the units for potential relubrication. It is important to use a type of lubricant for relubrication that is identical or compatible with the original (most commonly a lithium base, NLGI2).
 

What to always keep in mind when selecting a bearing unit

Bearing units and housings are key components of many industrial and mechanical systems. Their selection and proper use can significantly affect the overall efficiency and lifespan of the equipment in which they are installed. When selecting, it is important to consider the bearing type, housing material, seal type, and the needs of the specific application.

Different types of bearing units, from pillow blocks to flanged, are suitable for different applications and conditions. The materials from which these units are made, such as steel, stainless steel, or cast iron, also have their advantages and limitations. Sealing of bearing units ensures that the bearing remains clean and well-lubricated, which is key to its long-term functionality.

With proper selection and use, bearing units and housings can significantly contribute to the success of any mechanical or industrial project. Therefore, it is important for technicians to be well-informed about the various options and best practices. We hope this article has provided useful information for those who are currently deciding on bearing units and housings.