UC300 Series Insert Bearings are tabulated at a 30 mm bore: the row from the product table, the recommended shaft and housing tolerances under a rotating inner ring, the abutment the corner radius permits, and the notes that decide whether this bearing reaches its calculated life.
30 mm Bore Dimensional Row (JIS B 1558 / ISO 9628)
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) |
|---|---|---|---|
| UC306 | 30 | 72 | 42.9 |
What a UC300 Series Insert Bearings Does
A housed unit is a complete mounted bearing: an insert bearing with a wide inner ring, its housing, its seals and its grease, ready to bolt down. It clamps onto a commercial-tolerance shaft with setscrews or an eccentric collar, and the insert's spherical outer surface takes up the misalignment between two bolted feet — so a conveyor or a fan can be built without machining a bearing seat at all.
Primarily radial load, with a limited axial capacity in both directions. Treat the axial figure as a secondary rating, not as a thrust rating.
Speed at 30 mm Bore
No limiting speed is tabulated for this product. Where speed matters, the figure to work to is the one the bearing supplier states for the exact design, cage and lubricant supplied — not a family value.
Mounting a 30 mm Bore UC300 Series Insert Bearings
The insert bearing clamps onto the shaft with setscrews or an eccentric locking collar; the shaft needs only a commercial tolerance (h6 to h9), not a ground bearing seat. That is what makes a housed unit quick to install, and it is also its limitation: a setscrew grip transmits far less torque than an interference fit and can fret or creep on the shaft under reversing or heavily shocked load, where a keyed or interference-fitted arrangement should be used instead.
Lubrication & Relubrication
The unit is supplied greased and sealed, ready to run. Most housed units also carry a grease nipple: relubricate through it at the interval the duty calls for, with the shaft turning, until fresh grease shows at the seal. Speed, temperature and a wet or dusty environment all shorten the interval, and a unit run continuously in a washdown line needs a purge schedule rather than an annual one.
Sealed-for-life versions carry their whole service life of grease inside the seals and cannot be relubricated. That is the right choice where the bearing is inaccessible and the duty is mild; it is the wrong one where the temperature is high, the environment is wet, or the required life is longer than the grease life — and the grease, not the steel, is what ends it.
Where a 30 mm Bore UC300 Series Insert Bearings Is Used
At a 30 mm bore, uc300 series insert bearings are typically found in electric motors, pumps, gearbox layshafts, machine tool auxiliaries, agricultural machinery and general industrial drives — the volume range of the whole bearing industry.
Failure Modes and What They Look Like
- Subsurface fatigue (spalling) — a flake of raceway lifts out and the bearing gets noisy and rough. This is the failure the L10 life calculation predicts — if it arrives near the calculated life the bearing did its job, and if it arrives early the load, the fit or the lubrication was not what the calculation assumed.
- Inadequate lubrication — a polished, then discoloured, then torn raceway, running hot with a darkened grease. It is the most common cause of early failure by a wide margin, and the interval, not the grease, is usually what was wrong.
- Contamination — dents in the raceway with raised edges, then premature spalling from those dents. Wear particles, casting sand and washdown water all do it; sealing and filtration are what prevent it.
- False brinelling and fretting — evenly spaced dull marks at ball or roller pitch, produced by vibration while the shaft is stationary — a machine that travels on a truck, or a standby pump beside a running one. It is not caused by overload and cannot be cured by fitting a bigger bearing.
- Shaft fretting under the setscrews — a polished, reddish band on the shaft under the inner ring and a unit that loosens repeatedly. The setscrew grip was asked to hold against reversing torque that needs a key or an interference fit.
- Seal failure — grease escaping, then water and dirt getting in. A contact seal is a wearing part with a temperature limit of its own, and a washdown at 80 °C will get past a standard nitrile lip long before the bearing itself is in trouble.
Where NOT to Use a UC300 Series Insert Bearings
- Do not use a setscrew insert bearing under reversing or heavily shocked torque. The grip is a friction one; it frets and creeps, and the shaft ends up polished and undersized. Use a keyed shaft, an adapter sleeve unit, or a plummer block.
- Do not use the unit's self-alignment as a substitute for parallel feet. It takes up static misalignment between two seats; it does not survive a soft foot or a base that flexes under load.
- Do not specify a standard cast iron unit for a washdown line. The housing corrodes, the standard seals let water in, and the correct answer is a stainless or composite unit with the right seal package.
- Do not treat a sealed bearing as sealed for life in a wet or hot environment. A contact seal has a temperature and a pressure limit of its own, and once it is past them the grease leaves and the water arrives.
