What Are Pillow Block Bearings?

Pillow block bearings are vital elements across diverse machinery. These mounted bearing units support rotating shafts and keep them stable for seamless operation.

This blog post explores what pillow block bearings are, their components, types, materials, applications, sealing, lubrication, and how to select the best one.

Understanding Pillow Block Bearings

A Pillow block bearing is a pre-assembled housing with a machined mounting surface. It is commonly used in mechanical power transmission systems to support shafts and couplings.

The shaft runs parallel to the mounting surface, while the mounting screws are typically positioned perpendicular to it.

It has a bearing insert inside a pillow-shaped casing or block. This insert can accommodate various bearing types, including:  

Rolling element bearings, such as:

• ball bearings
• spherical roller bearings
• cylindrical roller bearings
• tapered roller bearings

or plain bearings (like sleeve bearings or bushings), depending on the application's specific load and speed requirements.

The block is designed to be securely bolted to a foundation or machine frame.

Components of a Pillow Block Bearing

• Bearing Insert
• Housing or Block
• Seals and Shields: Built into the bearing insert or housing. They keep contaminants out of the bearing and hold lubrication inside.
• Locking Mechanism: Used to firmly secure the bearing insert to the shaft.
• Grease Fitting/Nipple (Optional): Allowing for easy re-lubrication to extend the bearing's lifespan.

Fig 1 Components of a Pillow Block Bearing

Structural Features

The spherical outer ring of the bearing insert perfectly mates with a corresponding spherical bore in the housing.

In this design, pillow block bearings can compensate for minor misalignments between the shaft and the mounting surface.

Fig 2 Self-alignment of Pillow Block Bearings

Pillow Block Bearings vs. Plummer Block Bearings

While often confused, pillow and plummer blocks differ significantly in supply and typical use.

Both securely mount a bearing to allow inner ring rotation while bolting to a foundation.

Pillow Block Bearing Types

Pillow block bearings come in various forms, each suited for specific application requirements. Here's a breakdown by common categories:

1. By Housing Shape

The housing's design often dictates the unit's primary application and mounting orientation.

Standard Pillow Block Bearings

These are the most representative and common type. The housing is made for the whole assembly to be mounted vertically on the equipment. It uses its mounting holes to securely support shafts.

Fig 3 Standard Pillow Block Bearing

Models: Often starting with UCP, UKP, NKP+H, or NAP;

They are widely used in scenarios requiring vertical shaft support, such as:

• general industrial equipment
• conveyor belts
• agricultural machinery
• automotive systems
• construction machinery

Short/Tapped Base Pillow Block Bearings

With a narrower width than standard designs and built-in mounting holes at the base, they are well-suited for applications with limited space.

Fig 4 Tapped Base Pillow Block Bearing

• Models: starting with UCPA (e.g., PA200, PA200A, PG200 series).

High Center Pillow Block Bearings

These designs have a higher center than standard units. This makes them suitable for uses where the shaft is much above the mounting surface.

Fig 6 High Center Pillow Block Bearing

• Models: starting with UCPH

Pressed Steel Pillow Block Bearings

• The housing is typically stamped from high-quality carbon structural steel plates.
• They are designed for situations where the mounting surface is parallel to the shaft, typically involving medium to low speeds and light loads.

2. By Locking Way

Pillow block bearings use different ways to attach the bearing insert to the rotating shaft. They often use a locking collar or connect directly to the shaft.

Set Screw Locking Pillow Block Bearings

They are secured to the shaft using set screws that tighten against the shaft.

Eccentric Collar Pillow Block Bearings

An eccentric collar is tightened onto the shaft, which in turn secures the bearing.

Concentric Collar Pillow Block Bearings

A concentric collar is clamped onto the shaft, offering a more balanced hold.

Adapter Sleeve Pillow Block Bearings

An adapter sleeve is used to mount the bearing onto a stepped or plain shaft, allowing for easier mounting and dismounting.

3. Other Types

Split Pillow Block Bearings

Unlike single-piece solid housings, split pillow blocks are divided into two halves (a cap and a base).

• This design makes it easier to install and remove bearings. This is especially helpful for large shafts or when the shaft is hard to take off.
• Applications: Commonly used in heavy industrial applications like conveyors, paper mills, and power generation where maintenance and inspection access are crucial.

Common Materials of Pillow Block Bearings

The performance and durability of pillow block bearings rely heavily on the materials used. This includes both the insert and the housing.

Bearing Insert Material

• AISI 52100 Steel: This is the most common material for bearing inserts. This steel has great hardness, wear resistance, and strength against fatigue.
• Stainless Steel: Options like 440C, 304, and 316 Stainless Steel are used for their resistance to corrosion. They particularly work well in places with moisture or certain chemicals.
• Ceramic: High-performance ceramic bearings offer superior hardness and wear resistance. They can operate at extremely high temperatures and speeds, often in corrosive environments.

Housing Material

Cast Iron (e.g., HT200 Gray Cast Iron): Extremely common because of its strength, vibration dampening properties, and cost-effectiveness.

• Cast Steel: Offers higher strength and ductility than cast iron housing, suitable for more demanding applications.
• Stainless Steel: Provides excellent corrosion resistance, vital for washdown or corrosive environments.
• Zinc Alloy: Lighter and offers good corrosion resistance, often used for lighter-duty applications.
• Aluminum Alloy: Lightweight and corrosion-resistant, suitable for applications where weight is a concern.
• Thermoplastic (e.g., PBT Thermoplastic, Polyethylene Plastic): Lightweight, corrosion-resistant, and often used in food processing or medical industries where cleanliness and chemical resistance are paramount.

Advantages of Pillow Block Bearings

• Ease of Installation
• Accommodate Both radial and axial loads
• Self-Alignment
• Quieter Operation
• Robustness and Extended Lifespan
• Optimized Performance & Cost-Effective
• Less Frequent Servicing

What are Pillow Block Bearings Mainly Used For?

Pillow block bearings are incredibly versatile and found in a vast array of equipment and industries. They are specially used in agriculture and food processing sectors.

Agricultural Machinery

Pillow block bearings are the workhorses of the agricultural sector. They help equipment perform reliably in harsh conditions with dirt, dust, moisture, and heavy loads.

They are essential for supporting rotating shafts in almost every piece of farm machinery. This helps ensure reliable performance in the field.

Specific Equipment such as:

• Planters
• Harvesters
• Cultivators
• Tractors
• Balers
• conveyors in grain elevators
• fertilizer spreaders

Food Processing Machinery

In the food processing industry, pillow block bearings are important for keeping equipment clean and running smoothly. They can handle frequent washdowns and a wide range of temperatures.

Their design often uses food-grade, corrosion-resistant materials like stainless steel or thermoplastics. They also include special seals to meet strict sanitation standards and follow regulations from agencies like the FDA.

Specific Equipment such as:

• Conveyor systems for sorting/packaging
• Mixers
• Ovens
• bottling lines
• cleaning equipment

Sealing of Pillow Block Bearings

Effective sealing is paramount for the lifespan of pillow block bearings.  

Here are some common seal types.

• Lip Seals: Contact seals with a flexible lip that presses against a rotating shaft to form a barrier. They provide good protection against contaminants but generate some friction and heat.

• V-ring Seals: Self-centering rubber seals that accommodate shaft movement. Easy to install without special tools, perfect for vibrating equipment.

• Felt Seals or Strips: Non-contact seals made from compressed felt. They provide basic protection against dust and light contamination, commonly used in low-speed or legacy applications.

• Grease Purged Seals: Sealing systems designed to maintain a constant grease flow that pushes out contaminants. Ideal for harsh environments, ensuring consistent lubrication and cleanliness.
• Labyrinth Seals: Non-contact metal seals that use intricate channels to deflect particles, ideal for high-speed rotating equipment.

• Taconite Heavy-Duty Seals: Ultra-durable multi-layer seals specifically engineered to withstand severe abrasive conditions in mining and heavy industry.

The choice of seal type (e.g., lip seals & labyrinth seals) significantly impacts the bearing's ability to withstand contaminants and retain lubrication.

Do Pillow Block Bearings Require Lubrication?

The need for lubrication in pillow block bearings depends largely on their design type and operating conditions.

Maintenance-Free Types

Maintenance-Free Units are factory-sealed and pre-lubricated. They use effective seals to prevent grease leakage and block the ingress of impurities, dust, and water.

They are well-suited for most indoor and standard operating conditions.

Re-greasable Types

While maintenance-free bearings suffice for standard indoor use, re-greasable types are essential for specific, more demanding applications:

• High Temperatures: When operating temperatures go above 100°C (210°F), or for units that can handle up to 200°C (392°F).
• High Contamination: In environments with significant dust and impurities where space doesn't allow for external protective covers for the shaft assembly.
• Frequent Liquid Exposure: When bearings are regularly exposed to water or other liquids, and external protective covers are not feasible.
• High Humidity/Intermittent Operation: In humid environments where bearings operate intermittently, increasing the risk of condensation and corrosion.
• Heavy Loads/Low Speeds: For heavy-load applications where Cr/Pr (dynamic load rating / actual load) is less than 10, or speeds are below 10 rpm, or for oscillating movements.
• High Speed/Low Noise Requirements: In high-speed applications where minimal noise is critical (e.g., fans, air conditioners).

Key Considerations When Choosing a Pillow Block Bearing

Selecting the right pillow block bearing involves evaluating several critical factors to ensure optimal performance and longevity.

Housing Shape

The shape of the housing dictates its mounting orientation and suitability for specific space constraints or shaft positions.

Dimensions

Precise dimensions are crucial for a proper fit and optimal performance.

• Inner Diameter (Bore Size): This determines the shaft size the bearing can accommodate. Note that the bearing's internal diameter is often designed to be slightly larger than the shaft's diameter (e.g., 0.025 mm / 0.001 inch) to ensure a secure interference fit.
• Overall Mounting Dimensions: Including housing width, base length, overall housing height, shaft center height, mounting hole distance, mounting hole size, and mounting bolt diameter.

Duty-Related Factors

"Duty" means how well a bearing can handle steady loads and working conditions over time. It's judged based on how the equipment will be used and the loads it’s expected to carry.

• Light Duty: Suitable for light load operations, such as small equipment or low-speed applications.
• Medium Duty: Designed to handle moderate loads, commonly found in general industrial machinery.
• Heavy Duty: Made for applications with heavy loads or high pressure, such as in mining or steel plant equipment that handles intense work.

Load Capacity

Load is a critical consideration as it directly influences the bearing's material, size, type, and expected service life.

Bearing Selection Based on Basic Dynamic Load Rating

The formula for bearing life is:

L₁₀=(C_r/P_r)³

Where:

           L10: Basic Rating Life (in millions of revolutions)

           C_r: Basic Dynamic Radial Load Rating

           P_r: Equivalent Dynamic Radial Load

You must select a bearing with a dynamic load rating greater than the expected operating load. A safety factor (typically 1.2 times the expected load) is commonly applied to ensure sufficient capacity.

Environmental Factors

The operating environment plays a huge role in material and design choices.

High & Low Temperatures

• High-Temperature Environments: Often require stainless steel or ceramic bearings, along with specialized lubricants that maintain viscosity at elevated temperatures.
• Low-Temperature Environments: Demand materials that retain their integrity and do not become brittle in cold conditions.

Humid Environments 

• Corrosion Resistance: Stainless steel bearings or those with corrosion-resistant coatings are essential.
• Sealing: Sealed bearings (e.g., those with specific IP ratings for marine environments) are crucial to prevent moisture ingress.

Chemical Exposure

• Corrosive Environments: Require stainless steel and special coatings for chemical resistance.
• Food Processing/Pharmaceutical: Bearings must be FDA-approved, non-toxic, and resistant to chemical cleaning agents.

Contamination (Dust, Dirt, Debris)

• Abrasive Environments (e.g., mining, cement plants, construction): Often necessitate highly effective sealing solutions like labyrinth seals or metal shields to prevent abrasive particle ingress.
• Agricultural Machinery: Bearings and seals must specifically prevent dust and debris from entering. This can help extend bearing life in harsh field conditions.

Vibration and Shock Loads

• High Vibration: Bearings with self-aligning capabilities are beneficial.
• Heavy Machinery: Requires bearings with high load capacity and designs resistant to impact.

FAQ

Can you list some pillow block bearing manufacturers and brands?

Well-known manufacturers and brands of pillow block bearings include SKF, Timken, and Rexnord. Other brands are Dodge, Sealmaster, Link-Belt, NSK, NTN, and FAG.

How to tell if a pillow block bearing is bad?

A failing pillow block bearing is typically indicated by abnormal noise, excessive vibration, overheating, lubricant leakage, or visible damage.

Conclusion

Pillow block bearings are fundamental to industrial motion. Understanding their types, materials, and maintenance, alongside informed selection and diligent care, is crucial for significantly extending equipment life and minimizing costly downtime. For expert guidance on optimizing your machinery's performance with the right pillow block bearings, contact LILY Bearing today.