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What Is a Two-Bolt Flange Bearing?

UN two-bolt flange bearing (often called a 2-bolt flange bearing unit ou 2-bolt flanged bearing) is a mounted bearing assembly designed to support a rotating shaft while being bolted to a flat surface. The “two-bolt flange” refers to the mounting flange with two bolt holes, allowing quick, secure alignment on machine frames, side plates, conveyor structures, guards, and panels.

Most two-bolt flange bearing units consist of:

• UN housing (flange body) with two mounting holes

• UN bearing insert (typically a ball bearing)

• UN locking method to fix the insert to the shaft (set screw, eccentric collar, or clamp style)

• Optional seals and covers to protect against contamination and washdown

This design is popular because it offers a strong, compact mounting method while simplifying maintenance and replacement.

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Why Two-Bolt Flange Bearings Are Used So Often

Two-bolt flange units are widely chosen because they combine mechanical stability avec simple mounting:

Fast mounting and repeatable alignment

The two-bolt pattern makes installation straightforward on flat plates and machine sidewalls. It’s also easy to reposition during line modifications.

Good radial load support

Two-bolt flange units handle typical radial loads seen in conveyors, packaging machines, processing equipment, and rotating assemblies.

Service-friendly design

When maintenance is required, many units allow the insert to be changed without redesigning the machine.

Flexible sealing options

From light dust protection to aggressive washdown, sealing levels can be matched to the environment.

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Common Applications for Two-Bolt Flanged Bearing Units

Two-bolt flange bearings are used wherever a shaft needs stable support on a vertical or angled surface, including:

• Convoyeurs (belt, modular, roller, and hygienic conveyors)

• Machines d'emballage (cartoners, case packers, flow wrappers)

• Équipement de transformation des aliments (washdown zones, wet areas, splashing zones)

• Beverage lines (filling, rinsing, capping, labeling systems)

• Pharmaceutical and biotech equipment (cleanable assemblies, controlled environments)

• Material handling and automation (guides, rollers, actuators, transfer systems)

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Two-Bolt Flange Housing Materials and Why They Matter

Choosing the right housing material is critical for reliability and compliance.

Stainless steel housings

Ideal for hygienic and corrosion-prone environments:

• Washdown and chemical exposure

• Food, beverage, dairy, meat, seafood, ready-meals

• Pharmaceutical and biotech production

Cast iron housings

Common in general industrial environments:

• Dry areas, moderate loads

• Lower cost, strong mechanical stiffness
  Not recommended for harsh washdown unless properly protected and compatible with cleaning chemicals.

Composite (polymer) housings

Often used where corrosion resistance and weight reduction matter:

• Wet environments

• Good chemical resistance (depends on polymer)

• Useful in many washdown applications, especially when paired with sealed inserts

Bearing Insert Options: Stainless vs Standard, Sealed vs Open

The insert is the heart of the unit.

Stainless steel bearing inserts

Best where corrosion resistance is required. Common in hygienic processing and outdoor systems.

Standard steel inserts

Used in dry, controlled environments. Typically lower cost, widely available.

Sealing levels

• Contact seals help block water spray and fine contamination

• Non-contact seals reduce friction and heat but offer less protection

• Multi-lip seal systems provide stronger protection in wet/washdown zones

If your equipment is exposed to frequent cleaning or splashing, prioritize high-quality sealing and a housing designed to reduce crevices.

Locking Methods: Set Screw, Eccentric Collar, or Clamp

Two-bolt flange bearing inserts typically lock to the shaft in one of these ways:

Set screw locking

• Simple and widely used

• Best for moderate loads and standard speeds

• Shaft surface quality matters for holding strength

Eccentric collar locking

• Stronger locking for vibration and reversing loads

• Common in conveyors and general machinery

Clamp (concentric) locking

• Even clamping around the shaft

• Good concentricity and often better for higher speeds and precision applications

• Popular where vibration, alignment accuracy, or hygienic cleaning routines demand reliability

How to Choose the Right Two-Bolt Flange Bearing Unit

Use this selection checklist:

1) Environment and cleaning method

• Dry production area vs splash zone vs full washdown

• Chemicals used (alkaline/acid foams, sanitizers)

• Temperature range and thermal cycling

2) Load and speed requirements

• Radial load (common) and any axial load present

• Shock loads from starts/stops or product impacts

• Shaft speed and duty cycle

3) Shaft size and fit

• Correct bore diameter

• Shaft tolerance and surface finish

• Keyway presence (if used)

4) Sealing and ingress protection expectations

If your goal is high resistance to water and contamination, choose:

• Robust seal system

• Housing design that avoids “dirt shelves” and crevices

• Corrosion-resistant materials

5) Maintenance strategy

• Greaseable vs maintenance-free (sealed-for-life)

• Re-lubrication intervals and access points

• Replace insert only vs replace complete unit

Installation Best Practices for Long Bearing Life

Correct installation prevents premature wear and failures.

Align before tightening

Misalignment is a top cause of bearing problems. Ensure the flange sits flat and the shaft rotates freely before final tightening.

Use correct bolt torque

Over-tightening can distort housings or mounting plates. Under-tightening can cause movement and vibration. Follow manufacturer torque guidance for mounting bolts and locking mechanism.

Confirm shaft locking method is properly engaged

Set screw and collar systems must be correctly positioned. Clamp styles should be evenly tightened to specification.

Avoid contamination during assembly

Keep the insert and sealing surfaces clean. In hygienic environments, use clean tools and prevent residue build-up around the housing.

Maintenance and Troubleshooting Tips

Signs your two-bolt flange bearing needs attention

• Increased noise or vibration

• Rising operating temperature

• Shaft play or visible misalignment

• Grease leakage or water ingress signs

• Corrosion staining on housing or insert

Good routine practices

• Inspect seals and covers regularly

• Confirm mounting bolts remain secure

• Use the correct grease type (if greaseable) and avoid over-greasing

• Review washdown direction and spray pressure—direct high-pressure spray at seals can shorten life even on sealed units

Hygienic Design Considerations (Food, Beverage, Pharma)

In hygiene-critical production, selection is not just about load—it’s about cleanability and risk reduction.

Look for designs that support:

• Smooth surfaces and minimal crevices

• Crevice-minimized seal geometry

• Corrosion-resistant materials suitable for your cleaning regime

• Optional protective end caps (where appropriate)

• Documented material suitability and traceability when required

A two-bolt flange unit that survives washdown but traps residue is not truly hygienic—aim for both durability and cleanability.

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FAQ: Two-Bolt Flange Bearings

What’s the difference between a two-bolt and four-bolt flange bearing?

UN two-bolt flange is usually more compact and easier to mount on narrow frames. A four-bolt flange can offer more mounting stability for heavier loads or larger shafts.

Can two-bolt flange bearings be used in washdown areas?

Yes—if you select appropriate materials (often stainless or composite) and robust sealing designed for wet environments.

Are two-bolt flange bearings self-aligning?

Many bearing inserts allow a degree of self-alignment within the housing. This helps compensate for minor mounting inaccuracies, but it’s not a substitute for good installation and alignment.

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