How does Pillow Block Bearing work? | Types of Pillow Block Bearings

What is Pillow Block Bearing?

The pillow block bearing is also known as a plummer block. A pillow block bearing is a base that supports the rotating shafts by using compatible bearings and different accessories. This type of bearing contains a mounting block (pillow block). The bearing is installed inside the mounting block.

The pillow block bearings are most commonly used in low-torque applications. The slots or bores in the bearing base or feet of the bearing allow for easy assembly and adjustment.

Pillow block bearing

The pillow block bearing housing has the following two types:

  1. Solid housing: It is a single-piece housing
  2. Split housing: It is divided into two pieces

The pillow block bearing has different types, such as tapered, roller, and ball bearings.

Types of Pillow Block Bearings

Pillow block bearing contains a bearing and housing. The pillow blocks have the following major types:

  1. Plain Bearing
  2. Ball Bearing
  3. Roller Bearing
  4. Needle-roller Bearing
  5. Hydrodynamic Bearing

1) Plain Bearing

Plain bearings most commonly use in linear applications to limit motion, guide and reduce friction. These bearings utilize a sliding motion instead of the rolling motion used in needle bearings, roller bearings, and ball bearings.

Different types of materials (such as plastic, graphite metal, or bronze) are used for the construction of the plain bearing. Metallic plain block bearings should be appropriately lubricated to decrease friction and wear.

2) Ball Bearing

The ball bearing contains a ball. These types of pillow block bearings are used in rotary applications to offer low-friction and smooth motion. The ball bearing has a cage, balls, outer and inner rings. These bearings also have a ball separator instead of a cage.

Read More: Working and types of Ball Bearings

3) Roller Bearing

The roller bearing contains a roller instead of a ball as a rolling element. These bearings also use in rotary applications to reduce friction and offer smooth motion. The structure of this bearing contains inner and outer races, rollers, and a roller separator or cage.

The roller bearings have the following three types:

i) Tapered-roller Bearing

These bearings have tapered rollers that run on conical raceways. The tapered roller bearings have the ability to support both axial and radial load.

Due to the large contact area of the tapered roller bearing, it can carry a higher load than a ball bearing. It contains rollers, a cage, an outer race (cup), and an inner race (cone). When used at low to medium speeds, these bearings can carry high radial and axial loads.

ii) Spherical-roller Bearing

It is a double row, self-aligning, combination of axial and radial bearings. The rolling elements of the spherical-roller bearing have a spherical or crowned design. These bearings are best suitable for heavy loads and loads that need shock resistance, but their speed ability is limited.

iii) Cylindrical-roller Bearing

These bearings have moderate axial load carrying capacity and high radial load-carrying capacity. These bearings have crowned or end-relieved designs to reduce stress concentration. They permit high speed and reduce friction.

4) Needle-roller Bearing

They use needle rollers as a rolling element. These bearings have a very similar design to cylindrical roller bearings. However, the needle roller bearing has a smaller diameter-to-length ratio than the cylindrical roller bearing.

By regulating the circumferential clearance between the needles or rollers, the rolling element remains parallel to the shaft axis. These bearings are designed to support radial loads that require a low profile.

5) Hydrodynamic Bearing

These are oil film bearings. They depend on the air or oil film to produce a clearance gap between the stationary and rotatory elements.

They have low load carry ability, long service life, and maintain high rigidity. However, they have a complex design and high cost than standard rolling bearings.

Pillow Block Bearing Specifications

The pillow block bearing has the following specifications:

  1. Shaft Height: The height of the backing or shaft is calculated by determining the distance from the shaft center to the pillow block bearing
  2. Shaft Diameter: The diameter of the shaft must match the corresponding hole size in the bearing unit. A well-sized bearing can easily slide on the shaft and be secured with a locking device.
  3. Shaft size: Maximum shaft diameter or hole diameter of the attached bearing.
  4. Maximum Load: The maximum load-carrying ability of a bearing is the ability that a bearing can support a combination of axial and radial loads, or the maximum allowable radial load of a bearing that can support only one radial load. The rated load depends on the speed of the shaft.
  5. Maximum speed: The maximum permissible shaft speed at which the bearing is intended to operate.

Material Selection for Pillow Block Bearing

1) Housing Material

The main function of the housing is to protect the internal parts of the bearing from damage due to external material. Following are the most common materials used for the construction of the pillow block bearing housing:

  1. i) Aluminum: Aluminum has high resilience, fatigue strength, and thermal conductivity. It has a high load-carrying ability.
  2. ii) Cast iron: It is an iron-based material that contains significant traces of silicon and carbon. Cast iron is a natural composite material. The features of the cast iron depend on its microstructure (metastable and stable phases produced during solidification or successive heat treatment).

iii) Stamped steel: Stamped steel is mild carbon steel that is stamped instead of machined. These bearings have low cost than the cast or machined pillow block bearings. These bearings are ideal for light load carrying applications.

Iv) Plastic: Plastic represents synthetic, organic, or processed materials, most of which are high molecular weight thermoplastic or thermoset polymers. The most famous plastic materials include Teflon, nylon/polyamide, and Acetal.

V) Stainless steel: It has high corrosion and chemical resistance ability. It also has a relatively high-pressure rating.

2) Bearing Material

The bearing is a most important part of the system. The bearing material highly affects the performance of the system. The following materials are most commonly used for the construction of bearing:

i) Steel: The steel has approximately 7% carbon. Carbon is a most important element of the alloying constituent. It differs from cast iron in that it is ductile under specific conditions and has low ductility and low carbon content.

ii) Stainless steel: It is a corrosion and chemical resistant material. It has a relatively high-pressure rating.

iii) Sintered metal: It is also known as a powdered metal bearing. The sintered metal bearings have a low cost and simple design. They also have self-lubricating abilities. These bronze and copper alloys can impregnate with PTFE, graphite, or oil.

iv) Graphite-metal alloy: The graphite metal alloy has a bearing surface made of metal and molten graphite. It has a self-lubricating ability.

How to install Pillow Block Bearing?

The installation of the pillow block bearing is very easy and simple:

1) Check and Clean the Shaft
  1. Firstly, properly inspect the shaft and ensure that it is straight, round, clean, and isn’t undersized, according to the instructions of the manufacturer.
  2. You should use a scotch bright or sandpaper to remove the shaft rust.
  3. Use oil to expel the contamination.
2) Position the Bearings on the Shaft

Now properly place the bearing on the shaft. If you want to tap the bearing in its place, then use a mild steel tube, block of hardwood, or a hammer against the inner race. Avoid hitting or applying pressure to the seal or body.

3) Lightly Bolt the Housing to the Mounting Structure

Lightly screw the casing to the mounting frame to lock the shaft. Now, connect the housing mounting bolt slots with high-strength spring washers or high-strength flat washers. This will prevent it from loosening.

4) Align the Final Mounting Position

Before tightening the bolts, align the bearing unit with a rubber mallet or by hand to determine the final installation position.

5) Securely Bolt the Housing to the Mounting Structure

After aligning the bearing, tightly secure both units to the mounting frame.

6) Ensure the Axial motion of the Shaft

Now confirm the axial motion of the shaft through the bearing hole to ensure proper alignment. If it can’t move axially, loose the housing and re-adjust the shaft.

7) Tighten Both Collar Set Screws

Now follow the manufacturer’s instructions, tight both collar set screws, and rotate the shaft.

FAQ Section

What is difference between pillow block and Plummer block bearing?

The pillow blocks and Plummer blocks use the same type of bearings but they use for different applications.  These bearings also have the same design. Pillow blocks use to carry light loads while Plummer blocks use to transmit high power and carry heavy loads.

What does a pillow block allow a bearing to do?

Pillow Block Bearings have mounting brackets that house the bearings. These bearings are employed for light-load, low-torque applications. In this configuration, the bearing housing bolts to the base and secures in its place, but the inner race and bearing shaft can rotate freely.

What are the types of the pillow block bearings?

The pillow block bearings have the following major types:

  1. Plain Bearing
  2. Hydrodynamic Bearing
  3. Ball Bearing
  4. Needle-roller Bearing
  5. Roller Bearing
Read More
  1. Different types of Bearings
  2. Types of Ball Bearings
  3. Working of Thrust Bearing

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