Why conveyors use housed units
A conveyor has many shafts: head and tail pulleys, snub and bend rollers, drive shafts and take-up pulleys. They are mounted on welded steel frames, not on precision-machined housings. The frame flexes, the bolts loosen and the shaft deflects under belt tension. A plain bearing pressed into a machined bore would be pushed out of line almost immediately. A housed unit solves this by combining an insert bearing with a spherical outside surface and a housing with a matching seat, so the bearing can rock a few degrees to follow the shaft.
The result is a unit that bolts straight onto the frame, takes up misalignment and can be changed in minutes. The pillow block bearing page covers the line, and the bearing housing page covers the housings themselves.
Anatomy of a housed unit
A housed unit has two components. The insert bearing is a deep groove ball bearing with a wide inner ring and a spherical outer surface, often with seals on both sides and a grease nipple or a plain relubrication port. The housing is usually cast iron or ductile iron, sometimes pressed steel, polymer or stainless steel, and it has a mounting pattern to suit the frame. The two are matched so that the insert can swivel in the housing until it is locked by the fit and the end load.
| Housing type | Typical code | Where it fits on a conveyor |
|---|---|---|
| Pillow block (P) | UCP | Base mounting on a frame, most shafts |
| Square flange (F) | UCF | Bolted to a vertical face with four bolts |
| Oval flange (FL) | UCFL | Face mounting with two bolts, compact frames |
| Take-up (T) | UCT | Adjustable tail pulley tensioning |
The nominal bore of the insert is the shaft diameter. Typical insert sizes, such as UC204 to UC212, appear in the size chart with nominal ISO dimensions; confirm them against the drawing and datasheet before ordering.
How the insert locks on the shaft
Insert bearings do not rely on a press fit. Three locking methods are common, and the choice depends on shaft quality, load and whether the shaft reverses.
- Set screws in the inner ring tighten onto the shaft. They are quick and widely used, but they can mark the shaft and may loosen under reversing load.
- Eccentric collar locks the inner ring with a cam on the ring side. It suits one direction of rotation and light to moderate load.
- Adapter or tapered sleeve clamps the ring around the shaft over a taper and suits larger shafts and heavier duty. Sleeve and nut sets are listed under bearing accessories.
Whichever method you choose, specify it on the order. A set-screw unit and an eccentric-collar unit look similar in a catalogue, but they are different parts and are not interchangeable on the frame.
Sealing for dust, water and washdown
Conveyor bearings usually fail because contamination gets past the seal, not because the load exceeded the rating. In grain, cement, coal, fertiliser or aggregate plants, dust packs into the seal lip and works inward. In food and beverage plants, high-pressure washdown forces water past standard lip seals and washes out the grease. The remedy is to match the sealing to the environment.
| Environment | Sealing approach | Note |
|---|---|---|
| Dry, light dust | Standard double lip seal | Relubricate on schedule |
| Heavy dust, abrasive | Multi-lip or labyrinth seal plus flinger | Purge old grease through the seal when relubricating |
| Washdown, damp | Stainless or coated unit with extra seals | Use a grease suitable for the process |
| Outdoor, rain | Seals plus housing end covers | Check drain and vent paths |
Sealing options and materials are detailed under bearing seals. Contamination damage is also treated in contamination damage in bearings.
Reading early warning signs
Conveyor teams that walk the line with a thermometer and a screwdriver catch most failures before a shaft seizes. A housing that is clearly hotter than its neighbours, a grinding or rattling sound, grease leaking in an unusual colour, or a seal that has been pushed out of its seat all point to trouble. A rusty brown smear around a seal suggests water entry, while black, gritty grease suggests abrasive dust. Housed units that loosen on the shaft often show a bright polished ring or a fretted shaft surface at the bore.
Two habits help. First, mark the shaft and the inner ring with a paint line, so that any slip shows as a break in the line. Second, check the mounting bolts and the frame flatness when a unit is replaced; a bent frame will kill the new unit in the same way as the old one. A recurring failure at one position is usually a mounting or sealing issue and should be fixed at the source, not handled with more spares.
Belt tracking also matters. A belt that runs to one side pushes an axial load into the end bearings, and that load is far above what an insert bearing is designed for. Correct the tracking before blaming the bearing.
Relubrication and spare planning
Many housed units carry a grease nipple. Greasing them little and often is better than greasing them heavily and rarely, and over-greasing sealed units can push seals out of position. A practical interval depends on speed, temperature and contamination, and the method is described in relubrication intervals. Record the grease type used, because mixing incompatible greases softens the fill and shortens life.
For MRO and plant teams, it helps to standardise on a few insert sizes and housing types, so one spare range covers many positions. Typical practice is to hold at least one spare per critical position and a few of the most common sizes. See the MRO and distributor page for stocking programmes.
Buying conveyor housed units through the desk
- State the shaft diameter, the housing type and the locking method.
- Specify the seal and the housing material for the environment.
- Name the grease and the relubrication port if you need one.
- Agree marking, carton labelling and rust protection, because housed units are heavy and ship in bulk.
- Ask for sample units for a fitting check on a real frame before the first volume order.
The desk shortlists partner plants for insert bearings and cast housings, which are often made in different places, and assembles the complete units. Reference MOQ and lead time ranges are on the MOQ and lead time page and are confirmed in writing for each program. Send the list through the quote form.