Do you know what is footstep bearing and about their types? If you don’t know the answer don’t worry, let us learn about a comprehensive overview about footstep bearing definition along with their parts and constructions, types, applications & uses, advantages & disadvantages etc.
What is Footstep bearing?
Footstep bearing is typically a type of thrust bearing which is used to support a vertical shaft under axial load. In footstep bearing the end of the shaft will rest always within the bearing surface. Footstep bearings are also called as pivot bearings and axial load bearings.
Now let’s discuss about the parts of a footstep bearing.
Parts of a footstep bearing
Footstep bearing is constructed using the following parts.
- Base Block
- Bearing Disc
- Collar Bush
- Snug Plate
Base block or body of a footstep bearing acts as an external case which holds all other parts within itself including rotating shaft. It is a simple cylindrical hollow body with an opening on the top side. As already mentioned, all other parts such as snug pin, bearing disc, collar bush and including shaft is assembled in base block. It also has embossed holes at the base which helps in joining purposes like fastening or riveting with other machine parts. Base blocks are mostly made up of cast iron.
Pin plays a major role in footstep bearing by preventing the rotational motion of disc placed inside the base block. There is a dedicated space for pin inside the base block and discs. The pin will be arranged in a vertical manner where half of the pin will fit in base block and the remaining will fit by the disc. Pins are mostly made up of general purpose martensitic stainless steels that contain 11.5% chromium.
The bearing discs are circular in shape and placed inside the base block. The rational motion of the disc is arrested by the locking pin. The shaft will be placed over the disc. Usually steel and bronze bearing discs are used in footstep bearing. In some cases, the top face of the bearing disc will be concave instead of flat surface.
The Collar bush is fitted in the base block which helps in supporting the shaft position and manages the radial thrust coming from the shaft. The main function of collar bush is to guide the shaft. Collar bush is made up of gunmetal. The collar bush has a groove which acts as a space between shaft and collar for oil lubrication. The rotation of bush is prevented by snug.
Snug is a small metal part in footstep bearing, which helps to lock collar bush from rotation motion of shaft. It is placed on the top of base block and screwed along with it.
Functions & Working of Footstep Bearing
Footstep bearings or pivot bearing supports a vertically loaded shaft where axial load acts on the bearing surface. Based on the bearing surfaces of disc it may classified into different types. The shaft should be always metal, if not at least the end of shaft should be fitted with metal.
In footstep bearing, the high velocity of rubbing surface results in high wear since they are proportional to each other, and this also increases the radius of the bearing. In simple words, if radius of the bearing increases, wear also increases. This always results in uneven distribution of pressure over the bearing surface. So to avoid high end wear, shafts are counterbored at the end or a pile of bearing discs made up of steel and bronze are used.
Types of Footsteps bearing
Now let’s see the classification and types of footstep bearing.
Based on pivot surface, Footstep bearings are classified into three types, they are
- Flat Pivot Bearing
- Conical Pivot Bearing
- Truncated Pivot Bearing
Note: Do you know what is meant by Pivot in Footstep bearing?
The bearing surface of discs placed at the end of the shaft which supports the axial load thrust is called pivot.
- Flat Pivot Bearing: Pivot surface is flat.
- Conical Pivot Bearing: Pivot surface is conical in shape.
- Truncated Pivot Bearing: Pivot surface is trapezoidal or truncated cone in shape.
Flat Pivot bearing is the commonly used footstep bearing type in a wide range of applications.
Application & Uses of Footstep bearing
- Used in many machines that has vertical shaft to support axial thrust
- Used in marine applications like shafts with slow speed and less load.
- Used in shafts of steam turbines
Advantages of Footstep bearing
- Simple and compact design.
- Easy for maintenance.
- Easy to assemble and dismantle.
- Bearing design has a design to lubricate because collar bush has a cub like shape for oil lubrication.
Limitations & disadvantages of Footstep bearing
- Even though there is a way for oil lubrication, still wear and tear occurs in shaft and internal components of bearing.
- In some cases, ball and roller thrust bearings are used to transmit power when thrusts are large.
- It can be used only at the end of the shaft.
- Footstep bearings are not used for high-speed shafts
- Even though it has a design for oil lubrication, it is difficult to lubricate because oil always spills outside due to centrifugal force of the shaft.