A mounted bearing combines a bearing with a housing that attaches to a machine frame or support structure. Common configurations include pillow block, flange, and take-up units. Depending on the design, the assembly may also include seals, shaft locking components, and lubrication fittings.
Selecting the right mounted bearing requires more than matching the bore to the shaft diameter. The complete assembly must satisfy load, speed, axial location, environmental, installation, and maintenance requirements.
This guide explains how to evaluate these factors step by step, verify the limits of the selected components, and prepare a complete specification before ordering.
Operational Requirements and Working Conditions
Step 1: Define Operating Requirements
Start by documenting the application conditions. These inputs provide the basis for selecting the bearing, housing, seals, lubrication, and shaft locking method.
Loads: Determine the radial and axial loads acting at each bearing support. Include belt or chain forces, overhung loads, shock loads, and changes in load direction. Do not assume that two supports share the load equally.
Speed and motion: Record normal and maximum speeds, start-stop frequency, acceleration, reversing operation, and any oscillating movement.
Duty cycle: Specify operating hours per day, continuous or intermittent operation, and periods spent under different loads and speeds.
Temperature: Identify ambient temperature, expected bearing operating temperature, and heat transferred from nearby equipment.
Environment: Describe exposure to dust, water, washdown, chemicals, humidity, and corrosion.
Shaft and installation: Record shaft dimensions, available mounting space, support spacing, and access for installation and maintenance.
Reliability: Define the required operating life, acceptable downtime, inspection schedule, and maintenance strategy.
Where operating data are uncertain, document the assumptions and identify which conditions require confirmation before final selection.
Bearing Arrangement and Mounted Bearing Type
A bearing arrangement must support the shaft radially and provide the required axial location.
In a common locating/non-locating arrangement, one support locates the shaft axially and carries the applicable axial loads. The other support carries radial load while allowing the axial displacement required by thermal expansion or dimensional variation.
The locating support may be positioned at either end, depending on the machine design. At the non-locating support, axial movement must be accommodated by a suitable bearing design, an approved sliding interface, or a purpose-designed expansion arrangement.
Check the required displacement against the available travel. Restricting thermal expansion can introduce unintended axial forces into the bearing system.
For shaft designs that rely on two bearing supports, the following bearing arrangement options are commonly used:
Ball and Roller Bearing Units (Mounted Bearings)
These units are valued for their straightforward design and ease of use:
Each bearing support needs only a few parts. Usually, it requires just one bearing unit and some mounting bolts.
They are delivered pre-lubricated and ready for immediate installation.
Installation on plain, commercial-grade shafts is simple, using convenient locking methods such as set screws.
Housings with Bearings
These solutions offer greater adaptability to specific performance needs and operating environments:
Multiple bearing types and size options are available.
A broad range of housing seal designs can be selected.
Both grease and oil lubrication systems are supported.
They are compatible with plain, commercial-grade shafts as well as stepped shaft configurations.
Split Bearing Units
Fully split bearing units allow the bearing and associated split components to be assembled around an existing shaft. They can simplify replacement where removing couplings, drive components, or the shaft itself would be difficult.
A split bearing unit should not be confused with a split housing containing a non-split bearing. A split housing provides access for inspection and maintenance, but it does not make the bearing itself separable around the shaft.
Confirm which components are split and check the available bearing types, load ratings, sealing options, and locating or non-locating configurations for the selected product.
Housing Type
A pillow block, a flanged housing, or a take-up housing can all satisfy your application requirements.
Locating or Non-locating Support
Select locating and non-locating configurations according to the required axial load path and shaft movement. Do not assume that a bearing unit provides axial freedom simply because it can accommodate angular misalignment.
For mounted ball bearing units, verify whether the selected design provides expansion capability. If it does not, the required axial displacement must be accommodated elsewhere in the arrangement.
Misalignment Accommodation
Distinguish between initial installation misalignment and misalignment that changes during operation because of shaft deflection or structural movement.
Many insert ball bearing units can accommodate initial angular misalignment through a spherical outer-ring seating surface. This does not automatically make them suitable for continuous dynamic misalignment.
Check the permissible misalignment of the complete assembly, including the bearing, housing, seals, and covers. Where shaft deflection is significant, select a bearing arrangement specifically suited to that condition.
Mounted Bearing Size
Select the Bore Size and Bearing Configuration
Use the shaft diameter to identify candidate bore sizes, then verify whether each candidate satisfies the application requirements. Bore size alone does not establish load capacity, speed capability, or suitability for the environment.
For a complete mounted bearing unit, check the insert bearing, housing dimensions, shaft locking method, seals, and mounting interface together.
For a separately selected bearing and housing, confirm dimensional and functional compatibility. Common split plummer block arrangements may use self-aligning ball bearings, spherical roller bearings, or CARB toroidal roller bearings. Other housing designs may accommodate different bearing types.
Include any required adapter sleeves, locating rings, seals, end covers, and fastening components in the selection.
Verify Dynamic Rating Life and Static Load Capacity
For constant load and speed, the basic rating life in operating hours can be calculated as:
L10h = [10^6 / (60 × n)] × (C / P)^p
where:
L10h = basic rating life, in operating hours
C = basic dynamic load rating
P = equivalent dynamic bearing load
n = rotational speed, in r/min
p = 3 for ball bearings or 10/3 for roller bearings
Use consistent units for C and P. Determine P using the calculation method and load factors applicable to the selected bearing; it is not necessarily equal to the radial load.
The basic rating life corresponds to a fatigue life that 90% of a sufficiently large group of apparently identical bearings can be expected to attain or exceed under identical operating conditions. It is not a guarantee of individual bearing life or complete mounted-unit service life.
Where loads or speeds vary, use a suitable duty-cycle calculation. Lubrication, contamination, mounting, and other operating conditions must also be evaluated.
Check static load capacity separately using:
s0 = C0 / P0
where s0 is the static safety factor, C0 is the basic static load rating, and P0 is the equivalent static bearing load. Select the required safety factor using the manufacturer's guidance for the actual operating conditions.
Finally, verify housing strength, mounting bolts, and shaft locking capacity separately. A satisfactory bearing life calculation does not confirm the capacity of these components.
Set the Required Life Target
Define the required rating life from the machine's operating schedule, reliability requirements, maintenance strategy, and consequences of failure.
Published life ranges for machine categories may support preliminary selection, but they should not replace application-specific requirements. State whether a quoted target refers to calculated bearing fatigue life, grease life, maintenance interval, or expected equipment service life.
Verify the Allowable Operating Speed
Check the permissible speed of the complete mounted bearing configuration. The limiting factor may be the bearing, seals, lubricant, shaft tolerance, locking method, or thermal conditions.
Use the product data for the actual configuration rather than the speed rating of the bearing alone. Confirm whether the published limit requires particular shaft tolerances, loading conditions, or lubrication.
For sustained operation near the permissible limit, review heat generation and dissipation with the supplier. Recheck speed suitability whenever the seal, lubricant, or locking arrangement changes.
Select Lubrication and Relubrication Requirements
Choose the lubricant according to bearing load, speed, operating temperature, contamination, and seal compatibility. Grease is widely used in mounted bearing applications, while suitable housing arrangements may also support oil lubrication.
Many complete units are supplied pre-greased, but the supplied lubricant and filling quantity must be suitable for the application.
Identify whether the selected product is relubricatable or designed for operation without relubrication. For relubricatable units, confirm the grease specification, quantity, interval, delivery route, and provision for excess grease to escape where required.
Before changing grease, verify compatibility with the existing lubricant and follow the supplier's changeover instructions. Avoid overgreasing, which can increase operating temperature and affect seal performance.
For oil lubrication, verify that the housing, seals, oil level or circulation system, and leakage control are suitable for the intended arrangement.
Housing Design
Housing Type
The most widely used design is the pillow (plummer) block housing, which can be secured using either two or four mounting bolts. Pillow block ball bearing units are also offered with threaded mounting holes to accommodate attachment bolts.
Flanged housings are available in several configurations, including round, oval, square, and triangular designs. In the case of ball bearing units, a three-bolt bracket-type flange is also an option.
Another common category is take-up housings. These are generally installed in take-up frames, and their designs differ depending on how the adjustment screw is arranged.
Housing Material and Corrosion Protection
Select housing material according to load, shock, temperature, corrosion exposure, and cleaning requirements.
Grey cast iron is common in general industrial applications. Depending on the product range and operating conditions, alternatives may include ductile iron, cast steel, pressed steel, stainless steel, or composite materials.
Check the corrosion protection specified for the actual product. A painted or plated housing should not automatically be treated as suitable for washdown, chemical exposure, or outdoor service.
Quote a coating system or corrosion classification only when it is documented for the selected housing. Also evaluate the bearing insert, locking components, fasteners, seals, and covers, since housing protection alone does not establish the corrosion resistance of the complete unit.
Housing Strength and Mounting Surface
Verify the permissible housing load for the actual load direction and mounting orientation. Do not assume that the bearing's dynamic load rating represents the allowable load of the complete mounted assembly.
Check the housing, mounting bolts, threaded connections, supporting structure, and—where applicable—split-housing cap bolts. Use the specified bolt grades and tightening torques.
The mounting surface must meet the product requirements for flatness, stiffness, and surface finish. An uneven or flexible support can distort the housing when bolts are tightened and can affect bearing alignment and load distribution.
Correct foundation and alignment problems before operation. Do not rely on bolt tightening to pull a distorted housing or supporting structure into position.
Shaft Locking Method
Mounted bearings or bearings in a housing can be fixed to the shaft in different ways. Several locking options are available. At a minimum, the following criteria should be taken into account when making your selection.
Shaft Design
Plain shafts are a cost-effective option and can use commercial-grade shafts with tolerances of h9 or better. All mounted bearings and housings are compatible with plain shafts.
Stepped shafts require machining but provide more precise shaft positioning and improved axial load capacity.
The typical method for securing bearings on stepped shafts uses a cylindrical bearing seat. An interference fit is created between the shaft and the bearing inner ring. A lock nut is then used to secure the bearing axially.
Easy Mounting
Bearings can be installed more easily when a small clearance exists between the shaft and the bearing’s inner ring.
Locking options that use this clearance include set screws for ball bearing units and set screws in a locking collar for roller bearing units. Another option is an eccentric locking collar, which is available for ball bearing units.
However, this small clearance can create a slight misalignment between the shaft and inner ring axes. This misalignment may reduce the mounted bearing’s maximum speed or induce vibration.
Additionally, accommodating the applied load with this setup may require stricter shaft tolerances.
Speed and Vibration
To maximize the speed performance of a mounted bearing and minimize vibration, a concentric locking method should be chosen.
This ensures that the axes of the shaft and the bearing’s inner ring are aligned.
Concentric locking can be achieved using a tapered sleeve between the shaft and bearing. This option is available for ball bearing units or housings with bearings.
Alternatively, SKF ConCentra locking technology can be used, which is available for both ball and roller bearing units. A third option is a cylindrical bearing seat, suitable for housings with bearings or split bearing units.
Maximum Axial Load of the Locking Mechanism
The allowable axial load can differ depending on the locking method used.
Sealing
Effective sealing can greatly extend the service life of a bearing. It does this by retaining lubricant and preventing the entry of contaminants. Ball and roller bearing units come equipped with seals.
For shaft end locations, using an end cover is recommended to enhance sealing. End covers also safeguard the exposed shaft end and help prevent accidents.
When choosing a mounted bearing solution, take into account the sealing differences among the various product types:
Ball Bearing Units
The seal is an integral component of the bearing within the unit. Several types of contact seals are offered. The most common for industrial use are standard seals and standard seals with extra flingers. Other options include multi-seal designs and 5-lip seals.
Roller Bearing Units
The seal is built into the unit as an essential component. Common options include a lip seal, a labyrinth seal, or a radial shaft seal.
Housings with Bearings
Housings feature seal grooves that can accommodate different types of seals.
Certain seals have specific requirements for the shaft’s sealing surface, so ensure these are met or consider using wear sleeves.
When choosing a seal, it is important to evaluate its sealing effectiveness. You should also consider its impact on allowable speed and shaft misalignment.
Split Bearing Units
Split bearing units feature housing grooves that allow for the installation of seals. The standard range includes felt seals, lip seals, labyrinth seals, and radial shaft seals.
Mounting, Maintenance, and Dismounting Considerations
When designing your equipment, take into account how maintenance could affect your requirements. Also consider how installation and removal processes might impact them.
It may be necessary to disassemble the equipment to replace components during its operational life. This need is not limited to the end of its service life.
Mounting
The mounting process defines certain constraints, including available space, installation sequence, and the potential need for lifting equipment. Ensure these constraints align with the requirements of your mounted bearing solution. Key considerations include:
Which tools are needed, and can you reach the areas where they must be used?
Is a lifting device necessary?
Are lubrication steps required, and if so, when and how should they be applied?
What protective measures are needed to prevent contamination during installation?
Post-Installation Checks
Before starting the machine, verify alignment, fastener tightening, shaft locking, lubrication, seal installation, and freedom for the required axial movement.
Carry out a controlled trial run according to the equipment and bearing supplier's instructions. Monitor temperature, vibration, noise, and leakage, and establish baseline readings for future inspections.
Investigate abnormal conditions before returning the equipment to normal service.
Maintenance
Typical maintenance considerations include:
Relubrication: Ensure the product is equipped with a grease fitting if relubrication is required. Using automatic lubricators can help streamline maintenance tasks.
Condition Monitoring: Monitoring the condition of machinery during operation can be advantageous. Mounted bearings and housings can be fitted with sensors to facilitate this.
Dismounting and Disposal
The same factors to consider during mounting also apply when dismounting. The disposal process is generally the same for all mounted bearing products. It involves metal components, rubber parts, and lubricants. All of these must be disposed of in compliance with environmental regulations.
Final Mounted Bearing Selection Checklist
Before ordering, record and verify:
Bearing unit designation, bore size, and housing configuration
Shaft dimensions, tolerances, and mounting interface
Radial and axial loads at each support, including peak loads
Operating speed range and duty cycle
Required rating life and static safety factor
Locating and non-locating functions, including available axial travel
Permissible misalignment of the complete assembly
Shaft locking method, axial holding capacity, and installation torque
Seal arrangement and environmental suitability
Lubricant specification and relubrication requirements
Housing load limits, fasteners, and supporting-surface requirements
Installation, inspection, and replacement access
Confirm that all checks refer to the same final configuration. Changes to seals, locking components, lubrication, or mounting conditions may require parts of the selection to be reviewed again.
Conclusion
Mounted bearing selection requires verification of the complete assembly: the bearing, housing, shaft connection, seals, lubrication, and mounting structure. Matching the bore size is only the starting point.
A documented selection process helps identify capacity limits, accommodate shaft movement, and establish practical installation and maintenance requirements.
For a mounted bearing inquiry, provide LILY Bearing with your shaft dimensions, support loads, speed range, operating environment, required life, and installation constraints. Include drawings and details of the locating/non-locating arrangement where available so that the proposed configuration can be reviewed against your application.
About the Author
