Mounted Bearings

Mounted Bearings – How to Choose: Pillow Block, Flange, or Take-Up?

Quick Answer: Mounted bearings are pre-assembled units combining a bearing insert with a housing, ready to bolt onto your equipment frame. Choose pillow block for flat base mounting, flange for vertical surfaces, or take-up for conveyor tensioning. Locking options include set screw (economy), eccentric collar (quick positioning), and adapter sleeve (heavy-duty reliability). Select housing material based on your environment – grey cast iron for general use, stainless steel for washdown, or ductile iron for heavy loads.

Ever had a bearing fail because the housing couldnt handle the load direction? Or spent hours aligning a shaft because the mounting surface wasnt perfectly flat? These are everyday challenges in industrial maintenance.

Mounted bearings solve these problems. They combine the bearing, housing, and sealing into a single, ready-to-bolt unit. You dont need to machine precision bearing seats or press-fit bearings. You just bolt the housing to your frame, slide the shaft in, lock it, and youre done.

This guide covers what mounted bearings are, how the main housing types compare, and how to pick the right one for your application. Whether youre an engineer, a maintenance professional, or a procurement specialist, youll find practical selection criteria and real-world decision frameworks.

What Are Mounted Bearings?

A mounted bearing – also called a mounted bearing unit or housed bearing unit – is a complete assembly consisting of a bearing insert pre-fitted into a housing. The housing supports the bearing inside and transmits loads from the shaft to the surrounding machine structure.

Unlike standard bearings that must be pressed into a precision-machined housing bore, mounted bearings bolt directly onto equipment frames. The surrounding structure does not need to be a casing that provides precision-machined bearing seats. You can design a machine structure with beams and frames welded, riveted, or bolted together without the need for high precision.

The bearing insert is typically a wide inner ring ball bearing with a spherical outer diameter that provides self-aligning capability. This allows the bearing to compensate for shaft deflection and mounting inaccuracies. Each unit is pre-lubricated and sealed, ready for immediate installation.

Core Components

A mounted bearing unit consists of three core elements:

• The Bearing Insert – A deep groove ball bearing, typically with C3 or greater internal clearance to accommodate thermal expansion and minor misalignments. The extended inner ring provides the surface for the locking device. For heavy-duty applications, spherical roller bearing inserts are available, offering higher load capacity and inherent misalignment accommodation.
• The Housing – The structural component that supports the bearing and provides the mounting interface. Available in pillow block, flange, take-up, and hanger configurations. Common housing materials include grey cast iron, ductile iron, pressed steel, stainless steel, and thermoplastic.
• The Sealing System – Effective sealing is critical for protecting the bearing from contaminants and retaining lubricant. Modern insert bearings feature multi-labyrinth seals, rubber contact seals (e.g., NBR, FKM), or a combination of both.

Housing Types – Which One to Choose?

The choice of housing affects mounting convenience, load orientation, and maintenance accessibility. There are four main housing types for mounted bearings: pillow block, flange, take-up, and hanger.

Pillow Block Bearings (Plummer Blocks)

Pillow blocks are the most commonly used type of mounted units. They sit on a flat foundation and are bolted down from above, supporting shafts parallel to the mounting surface.

When to choose a pillow block: You have a flat mounting base (machine bed, conveyor stringer, welded frame); you want easy shaft height control via shims or machined pads; you expect moderate frame misalignment; you need fast swap-out on long conveyor lines. Pillow blocks often excel on long bases where radial loads dominate – conveyors, fan shafts, general line shafts.

P is the standard pillow block configuration; PA features concealed mounting holes or narrow lightweight design; PH provides increased mounting height.

Flange Mounted Bearings

Flange units are face-mounted: the housing bolts to a vertical or perpendicular surface – end plates, bulkheads, machine sidewalls. The shaft axis is perpendicular to the bearing mounting surface. Available in various flange shapes (round, square, diamond) and bolt configurations. Two-bolt flanges are diamond shaped; three-bolt flanges have three mounting holes arranged radially at 120 degrees or on a triangular flange; four-bolt flanged bearings typically have round or square housings.

When to choose a flange unit: Your structure is a wall or plate rather than a base; you need compact mounting where base space is restricted; you want better control of shaft position relative to a wall or guard. Flange units can be ideal when the housing must react loads close to a plate or end wall – end-of-shaft support, compact assemblies, motors/gearbox-adjacent mounting.

F is the standard square 4-bolt flange; FA is adjustable rhombic flange; FB is 3-bolt flange; FC is boss circular flange; FL is diamond 3-bolt flange; FS is boss square flange.

Take-up Bearings

Take-up bearings feature a sliding base that moves within a frame. Designed to maintain belt or chain tension in conveyor systems. The unit slides along guide rails within a slotted frame, enabling precise tension control. Essential for conveyor systems where tension must be maintained over time.

Hanger Bearings

Hanger units are overhead-mounted housings that suspend the shaft from above. Specifically designed for screw conveyor applications, supporting the rotating shaft while allowing bulk material to pass underneath. The housing typically features a cast iron split housing design.

Quick Selection Reference

Locking Mechanisms Compared

The connection to the shaft can be done by set screws, a locking collar, or by an adapter sleeve. Except for the adapter sleeve, the other locking methods do not require the knowledge and tools that you typically need to mount a rolling bearing.

Set Screw Locking – One or two set screws in the extended inner ring are tightened against the shaft using a hex key. Fast and economical, but creates point-load indentations on the shaft. Suitable for moderate speeds and steady loads. Common in lighter-duty applications. The most common and economical method incorporates two set screws set 90 degrees apart.

Eccentric Locking Collar – A collar with an eccentric cam tightens against the shaft when rotated. Provides a secure, vibration-resistant lock without damaging the shaft. Provides more uniform clamping than set screws. Suitable for quick axial positioning and constant rotation applications. Can be used instead of screws when a stronger connection is needed to prevent slippage or fretting.

Adapter Sleeve Locking – A tapered sleeve is driven between the shaft and the bearing bore using a lock nut. Provides 360-degree concentric clamping force without shaft damage. Recommended for reversing loads, heavy vibration, shafts without shoulders, and applications where shaft fretting corrosion must be prevented. Offers better balance at speed and reduced shaft damage. Concentric locking should be selected when shaft centerline shift is a concern, as it improves the strength of the connection and increases reliability.

Locking Mechanism Quick Reference

Series Classifications and Naming

Understanding the naming convention helps identify the correct replacement unit. Complete mounted bearing unit codes combine the insert series designation with the housing suffix.

Take UCP210 as an example:

• UC = Insert series (set screw locking)
• P = Housing type (pillow block)
• 210 = Bore size code (50mm bore), with “2” indicating 200 series

The full designation tells you both the bearing series and the housing style in one code. This standardized naming is recognised globally and cross-referenced across brands.

200 Series (Standard Duty) – Standard load capacity mounted bearing units for general industrial applications including conveyors, fans, and agricultural equipment. Suitable for moderate loads and speeds. Available across all housing types and insert series. The “2” in the bore size code indicates 200 series construction with standard section dimensions and standard radial internal clearance.

300 Series (Heavy Duty) – Enhanced load capacity and robust construction mounted bearing units for demanding applications with higher loads, vibration, and reversing conditions. Suitable for heavy industrial and mining applications. Available across all housing types and insert series. The “3” in the bore size code indicates 300 series construction with heavier section dimensions and enhanced radial internal clearance for thermal expansion accommodation.

Series Classification Table

How to Select the Right Mounted Bearing

When selecting mounted bearing solutions for your application, ultimately you want to be certain of achieving the required level of equipment performance and robustness at the lowest possible cost. Here’s a practical framework:

Selection Cheatsheet

• Start with the mounting surface – Flat base means pillow block; vertical wall means flange; tensioning requirement points to take-up; overhead shaft suggests hanger.
• Consider the load direction – Pillow blocks excel with radial loads on long bases. Flange units are ideal when loads must be reacted close to a plate or end wall.
• Evaluate the environment – Washdown conditions require stainless steel or thermoplastic housings. Dusty environments need enhanced sealing.
• Check shaft diameter – Select the correct bore size and ensure proper shaft fit. Recommended shaft tolerance classes are h6 to h9.
• Assess vibration and reversing loads – High vibration favours adapter sleeve locking for 360-degree clamping.

Environment-Attributes Matrix

Six Selection Criteria

When specifying a mounted bearing, evaluate these factors:

• Housing style – Pillow block for flat base mounting; flange for vertical/face mounting; take-up for tension adjustment; hanger for overhead/screw conveyor applications.
• Shaft diameter – Select the correct bore size to ensure proper shaft fit. Recommended shaft tolerance classes are h6 to h9.
• Load magnitude and direction – Consider radial, axial, and combined loads.
• Operating environment – Dust, moisture, chemicals, and temperature extremes dictate housing material and seal type.
• Misalignment tolerance – Most mounted bearings use insert designs intended to tolerate small misalignment. The spherical outer diameter of the insert provides self-aligning capability.
• Maintenance strategy – Units are pre-lubricated and sealed for reduced maintenance. Some designs offer relubrication capability via grease fittings.

Why Choose Mounted Bearings?

Mounted bearings deliver tangible benefits across the design, installation, and operational phases:

Simplified Design and Procurement – Engineers can specify a single, standardized part number, eliminating the need to separately source a bearing, housing, seals, and locking device. This simplifies BOM management and reduces procurement complexity.

Reduced Installation Time and Cost – No need for complex housing machining, precise shoulder turning on shafts, or delicate assembly of separate components. Alignment is simplified as the housing self-aligns during mounting. This drastically cuts labor costs and accelerates machine build times.

Enhanced Performance and Reliability – Factory-preassembled units ensure optimal internal bearing setting and correct seal installation. High-quality housings provide stable support, dissipate heat, and protect against environmental factors. The robust locking mechanisms prevent creep and fretting corrosion on the shaft.

Flexibility – Available in multiple housing styles, materials, and bearing types to suit diverse applications.

Misalignment Compensation – Most mounted bearing solutions compensate for alignment errors either by adjusting the bearing in the housing or by using self-aligning rolling bearings.

When Not to Use Mounted Bearings

Mounted bearings are not the best option when your machine requires high precision in the positioning of your shaft relative to other components, or when your machine design requires a casing that encloses the bearing seats. An electric motor is a typical example of this type of casing. When you select rolling bearings for such applications, it is better to use standard bearing selection processes for ball and roller bearings.

Shaft Fit and Housing Setup

Insert bearings are designed for slip-fit mounting onto shafts, not interference fits. These bearings are designed to locate the shaft axially; they do not permit relative axial movement between the shaft and housing. The distance between bearing positions should therefore be short to avoid excessive induced axial loads as a result of thermal expansion of the shaft.

Shaft fit is typically slip-fit with locking; verify OEM guidance. Ensure the spherical seat can align freely.

Temperature Limits

The permissible operating temperature for NBR seals is -30 degree C to +100 degree C. Temperatures up to 120 degree C can be tolerated for brief periods. For higher temperatures, specialty seals (e.g., FKM) or high-temperature bearing variants are available.

Common Industry Applications

Mounted bearings are found throughout industrial machinery:

• Automotive – Assembly line conveyors, powertrain test rigs, suspension component manufacturing, and material handling systems where reliable shaft support is required.
• Agricultural Machinery – Combine harvesters, balers, tillage equipment, and sprayers. Demanding environments require enhanced sealing and corrosion-resistant housings.
• Material Handling and Conveyors – Belt conveyors, roller conveyors, bucket elevators, and palletisers. Pillow block and take-up units are standard for tension adjustment and shaft support.
• Food Processing – Stainless-steel housings and food-grade lubricants are used in wash-down areas. Bearings must resist corrosion and frequent cleaning cycles.
• Mining and Aggregate – Crushers, screens, and heavy-duty conveyors. Ductile-iron housings and robust sealing handle high loads and abrasive contaminants.
• Pumps and Fans – Industrial pumps, HVAC fans, and blowers. Reliable operation and low maintenance are key selection factors.

Interchangeability and Standards

Most mounted bearings follow international standards (ISO, AFBMA) for external dimensions and housing bolt hole patterns. This ensures that a bearing from one manufacturer can be replaced with an equivalent from another without modifying the equipment.

The UC, UK, SA, SB, UE, and UEL series designations are widely recognised and cross-referenced across brands. When ordering a replacement, match both the insert series and the housing style.

Conclusion

Mounted bearings offer a versatile, cost-effective solution for shaft support across countless applications. Their key advantages – simplified machine design, easy installation, misalignment compensation, pre-lubrication, and standardised dimensions – make them a practical choice for engineers and maintenance professionals alike.

When selecting a mounted bearing, focus on three decisions:

• Housing type – pillow block for flat base mounting; flange for vertical/face mounting; take-up for tension adjustment; hanger for screw conveyor applications
• Locking mechanism – set screw for economy and quick MRO replacement; eccentric collar for quick axial positioning; adapter sleeve for heavy-duty reliability, reversing loads, and high-speed operation
• Housing material – grey cast iron for general industrial; stainless steel or thermoplastic for washdown/food processing; ductile iron for heavy-duty and high-impact applications

Start with your mounting surface and load requirements. Work through the selection framework above. You’ll find a solution that fits your machinery and your maintenance schedule.

Key Takeaways

• Mounted bearings are pre-assembled, ready-to-bolt units that eliminate the need for precision-machined bearing seats
• Three main housing types: pillow block (flat base), flange (vertical face), and take-up (tension adjustment)
• Three locking mechanisms: set screw (economy), eccentric collar (quick positioning), and adapter sleeve (heavy-duty reliability)
• Choose housing material based on your operating environment – stainless steel for washdown, ductile iron for heavy loads
• Standardized dimensions ensure global interchangeability across brands
• Mounted bearings are not suitable for applications requiring high precision shaft positioning, such as electric motors