Choosing the right mounted bearing for your grain conveyor or elevator
If you're replacing a bearing on a grain conveyor, bucket elevator, or auger, you've probably run into two common types: pillow block bearings and flange block bearings. Both do the same basic job — supporting a rotating shaft — but they mount differently, and choosing the wrong one can mean redrilling holes or reworking your frame.
Here's a practical breakdown of how these two bearing types differ and how to pick the right one for your system.
What Is a Pillow Block Bearing?
A pillow block bearing has a housing that sits on top of a flat surface, with mounting bolts running vertically down through the base. The bearing itself sits above the mounting surface, supported by two or four bolts depending on the design.
This style works well when you're mounting onto a flat horizontal surface, such as a conveyor frame or support bracket, and there's enough clearance underneath for the housing.
Common pillow block configurations include:
- 2-bolt pillow block — lighter duty, used where loads are moderate
- 4-bolt pillow block — heavier duty, often with a self-aligning spherical insert to tolerate minor shaft misalignment
Pillow block bearings are common on grain conveyors, bucket elevators, augers, and other agricultural machinery where the shaft runs parallel to a flat frame.
What Is a Flange Block Bearing?
A flange block bearing has a flat, plate-style housing that bolts directly to a vertical or perpendicular surface, such as the side wall of a housing or frame. The bolt holes run through the face of the flange rather than down through a base.
This makes flange block bearings the better choice when your mounting surface is vertical, or when space constraints don't allow for a pillow block's raised housing.
Like pillow blocks, flange block bearings come in a few common configurations:
- 4-bolt flange block — rigid mount, requires precise shaft alignment
- Spherical 4-bolt flange block — self-aligning insert for minor misalignment tolerance
Pillow Block vs. Flange Block: Key Differences
| Feature | Pillow Block | Flange Block |
|---|---|---|
| Mounting surface | Flat, horizontal | Vertical or perpendicular |
| Bolt orientation | Vertical, through the base | Through the face of the flange |
| Typical use | Open frame conveyors, elevator legs | Housings, side walls, enclosed frames |
| Clearance needed | More — housing sits above the surface | Less — mounts flush against a wall |
| Alignment options | Rigid or self-aligning spherical | Rigid or self-aligning spherical |
The biggest factor in choosing between them usually isn't load capacity — it's simply which way your mounting surface faces. If you're replacing an existing bearing, the easiest approach is to match what's already there, since the housing style is dictated by how your equipment was originally built.
Rigid vs. Self-Aligning (Spherical) Inserts
Both pillow block and flange block bearings are available with two insert styles:
- Rigid mount — requires precise shaft alignment during installation. Less forgiving, but a solid choice when your shaft and housing are already well-aligned.
- Self-aligning (spherical) — the bearing insert can pivot slightly inside the housing, tolerating minor misalignment between the shaft and the mounting surface. This reduces stress on the bearing and extends service life, especially in equipment that sees vibration or slight frame movement over time.
If you've had repeated bearing failures on the same shaft, misalignment is a common culprit — switching to a self-aligning spherical bearing can sometimes solve a problem that keeps coming back.
How to Choose the Right Bearing
When selecting a replacement bearing, work through these questions in order:
- What's your mounting surface? Flat and horizontal points to pillow block. Vertical or perpendicular points to flange block.
- What's your bore/shaft size? Measure the shaft diameter carefully — this determines which bearing size you need, regardless of housing style.
- Is alignment a known issue? If your shaft and housing aren't perfectly aligned, or if you've seen premature wear, choose a self-aligning spherical insert over a rigid one.
- What's the load and duty cycle? Heavier, continuous-duty applications generally call for 4-bolt designs over 2-bolt.
Final Thoughts
Pillow block and flange block bearings solve the same problem — supporting a rotating shaft — but they're built for different mounting situations. Matching the housing style to your equipment's frame, and choosing rigid or self-aligning based on your alignment tolerance, will help you avoid premature wear and unnecessary downtime.
If you're not sure which bearing fits your system, our grain conveyor bearings collection includes pillow block and flange block options in multiple bore sizes, or you can contact our team for help identifying the right part.
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