When you choose mounted bearing solutions for your application, your main goal is to ensure good performance and reliability. You also want to keep costs low.
There are multiple factors to evaluate when selecting a mounted bearing. This guide will help ensure your choice meets the required operating conditions and performance standards.
Operational Requirements and Working Conditions
The first and most important step in choosing a mounted bearing is to identify your key needs. Write them down for your application. This ensures that the chosen solution can reliably meet both performance and operational demands.
Determine Required Performance
Service life: Estimate how long the mounted bearing is expected to operate under normal conditions without failure. This includes considering maintenance intervals and expected operational load cycles.
Speed capability: Evaluate the maximum rotational speeds the bearing will experience, as well as acceleration and deceleration rates. Mounted bearings have specific limits depending on their type, material, and lubrication.
Environmental tolerance: Consider extreme conditions such as high or low temperatures, humidity, or exposure to contaminants. Certain mounted bearings are designed to withstand harsh conditions, while others are optimized for standard environments.
Assess Operating Conditions
Load characteristics: Note the size, direction, and type of loads. These can be radial, axial, or combined. Understanding load patterns is crucial for choosing the correct bearing design.
Operating intervals: Note speed variations, temperature fluctuations, and duty cycles. This ensures that the bearing can maintain its performance consistently throughout the operating range.
Assumptions and typical scenarios: Write any expected changes in operation. This includes occasional overloads or environmental changes. Doing this helps avoid choosing a bearing that might fail in unexpected conditions.
Bearing Arrangement and Mounted Bearing Type
A bearing arrangement helps support and position a shaft. It does this in both radial and axial directions compared to nearby parts.
In most designs, two bearing supports are used to accurately locate the shaft. The support on the left handles both radial and axial loads. The support on the right only handles radial load.
The main benefit of the non-locating support is that it can handle axial shaft movement. This movement can happen because of thermal expansion during operation or from manufacturing differences between the two supports.
If this movement were restricted, additional axial loads could be introduced 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
They offer a distinctive advantage in applications where installing the bearing onto the shaft is challenging:
The housing, bearing, and seal parts are all split. This design lets the unit be put together directly around the shaft.
Available bearing options include cylindrical, spherical, and tapered roller bearings.
Housing Type
A pillow block, a flanged housing, or a take-up housing can all satisfy your application requirements.
Locating or Non-locating Support
Across roller bearing units, housings, and split units, there are product variants designed for either locating or non-locating support. In contrast, when ball bearing units are used, the non-locating support must be accommodated by the surrounding structure.
Compensation of Misalignment
First, identify the type of misalignment that may occur in your application. Then verify the misalignment capability of the selected product. Most mounted bearing solutions are designed to tolerate misalignment, with the exception of designs that use cylindrical or tapered roller bearings.
Mounted Bearing Size
Two key parameters define the bearing size required for your application:
The shaft diameter
The magnitude of the load to be supported
The steps below outline how to determine the appropriate size.
Choose a Suitable Mounted Bearing that Matches Your Shaft Diameter
For integrated bearing units, simply choose the complete unit.
If you are assembling a housing and bearing, first select a self-aligning bearing. You can choose a spherical roller bearing or a CARB toroidal bearing. Then, check that a matching housing size is available.
Verify the Load Carrying Capacity of the Selected Mounted Bearing
The basic rating life L10 is a reliable and practical method for selecting a bearing size. Evaluate the calculated L10 life against the expected service life for the specific bearing application.
A mounted bearing must handle static loads. It should not cause permanent damage or deformation to the rolling elements or raceways.
If the basic rating life is less than the needed service life, a stronger bearing is required. This is also true if the static safety factor is not enough.
The basic rating life is one of many indicators. It helps estimate the actual service life of your application. Factors such as sealing and lubrication also play a critical role.
Guideline values of specification life for different machine types | |
Machine type | Specification life |
Operating hours | |
Household machines, agricultural machines, instruments, technical equipment for medical use | 300-3 000 |
Machines used for short periods or intermittently: electric hand tools, lifting tackle in workshops, construction equipment and machines | 3000 -8 000 |
Machines used for short periods or intermittently where high operational reliability is required: lifts (elevators), cranes for packaged goods or slings of drums, etc. | 8 000-12 000 |
Machines for use 8 hours a day, but not always fully utilized: gear drives for general purposes, electric motors for industrial use, rotary crushers | 10 000-25 000 |
Machines for use 8 hours a day and fully utilized: machine tools, woodworking machines, machines for the engineering industry, cranes for bulk materials, ventilator fans, conveyor belts, printing equipment, separators and centrifuges | 20 000-30 000 |
Machines for continuous 24-hour use: rolling mill gear units, medium-sized electrical machinery, compressors, mine hoists, pumps, textile machinery | 40 000-50 000 |
Wind energy machinery, this includes main shaft, yaw, pitching gearbox, generator bearings | 30 000-100 000 |
Water works machinery, rotary furnaces, cable stranding machines, propulsion machinery for ocean-going vessels | 60 000-100 000 |
Large electric machines, power generation plant, mine pumps, mine ventilator fans, tunnel shaft bearings for ocean-going vessels | 100 000-200 000 |
Confirm that the Selected Mounted Bearing Operates within Its Allowable Speed Range.
When choosing ball or roller bearing units, consider the maximum speed values in the technical data. Also, think about how shaft tolerances may affect the allowable speed.
For housings with bearings or split bearing units, consider any speed limits set by the chosen seal.
Mounted Bearing Lubrication
Mounted bearings require proper lubrication to ensure reliable operation. The lubricant helps reduce friction and wear. It protects bearing surfaces from corrosion. In some cases, it also helps with heat dissipation.
Grease lubrication is often used for mounted bearings. However, oil lubrication can also be used when bearings are in housings.
Ball and Roller Bearing Units
These units are delivered pre-greased with a high-quality, multi-purpose lubricant. For application-specific designs, a lubricant tailored to the intended operating conditions is used.
Ball and roller bearing units can be re-lubricated as needed. The bearing inserts have lubrication holes in the outer ring. The housings are generally equipped with grease fittings, except for some application-specific ball bearing unit housings.
When re-lubricating, it is essential to check the new grease. Ensure it is fully compatible with the original grease fill.
Housings with Bearings
Mounted bearing solutions that combine a housing and bearing can be configured for either grease or oil lubrication.
For oil-lubricated applications, the housing and seal design must be selected to ensure compatibility with oil lubrication.
Split Bearing Units
Split bearing units usually use grease for lubrication.
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
Grey cast iron is the most widely used material for bearing housings. When selecting a housing, it is important to evaluate which material option best suits your specific application requirements.
Ball bearing units are available with housings made from different materials. These materials include cast iron and black composite. Other options are blue food-grade composite, spheroidal graphite cast iron, pressed steel, and stainless steel.
Most roller bearing units, bearing housings with bearings, and split bearing units are made from grey cast iron. This material is commonly used because it is reliable and durable. In addition, certain rolling bearing housings are available in spheroidal graphite cast iron or cast steel.
Corrosion Protection
All housings are supplied with effective corrosion protection as a standard feature.
Pressed steel housings are protected by a zinc coating, while housings manufactured from cast materials are finished with paint.
The standard paint system ensures suitability for operating environments classified as corrosivity category C2 in accordance with ISO 12944-2.
Load Carrying Ability
To achieve full load-carrying capacity, the housing must be securely fastened to its support structure. This should be done using suitable mounting bolts tightened to the specified torque.
In ball bearing units, the housing is usually designed to carry at least the same load as the bearing inside it. An exception is pressed steel housings. For pressed steel designs, the housing strength should be verified against the actual operating loads of the application.
This applies to roller bearing units, bearing housings with bearings, and split bearing units. The load capacity depends on the load direction. It is also affected by the housing material. When split housings are used, the bolts joining the housing sections must also be checked to ensure adequate strength and correct tightening torque.
Support Surface
The support surface must meet the specified flatness and surface roughness tolerances.
Following these requirements helps prevent distortion of the housing seating area. This applies when mounting bolts are tightened or when operating loads are applied.
Proper surface conditions help reduce vibration. They also improve heat transfer from the bearing, through the housing, to the surrounding structure.
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.
How Maintenance, Mounting and Dismounting
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?
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.
Conclusion
Choosing the right mounted bearing ensures your equipment runs smoothly and lasts longer. By considering factors like bearing type, size, housing, seals, and maintenance needs, you can make an informed choice. This allows you to select a solution that fits your application.
A proper selection process helps reduce wear, prevent downtime, and improve overall performance. Lily Bearing offers a wide range of mounted bearings and guidance to help you make the best choice.
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