The 50 mm bore of the 21300 Series Spherical Roller Bearings is the 21310: 50 mm bore, 110 mm outside diameter, 27 mm wide. This page gives the dimensional row from the table, the shaft and housing fits that suit it, the internal clearance to expect and the mounting, lubrication and failure notes that go with the type.
50 mm Bore Dimensional Row (ISO 15 / GB/T 288 / DIN 635-2)
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) | Chamfer r min (mm) | Permissible misalignment (deg) |
|---|---|---|---|---|---|
| 21310 | 50 | 110 | 27 | 2 | 1 |
What a 21300 Series Spherical Roller Bearings Does
Two rows of barrel rollers share one spherical outer raceway. The result is the highest basic load rating available in a given envelope together with genuine self-alignment under both mounting error and shaft deflection, which is why it is the standard bearing of vibrating screens, crushers, conveyor pulleys, fans and gearbox output shafts.
Radial load, and axial load in both directions. The steep contact of the barrel rollers gives real thrust capacity, but the axial load must be kept within the manufacturer's stated ratio to the radial load — a spherical roller bearing loaded almost purely axially loses the load sharing between its two rows.
Speed at 50 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.
Shaft & Housing Fit for a 50 mm Seat
With the inner ring rotating under a load whose direction is fixed, the inner ring sees a circumferential load and must be an interference fit, or it will creep on the shaft and fret it. The outer ring sees a point load and takes a transition or clearance fit so that it can shift slowly and spread the wear — and so that one of the two bearings on the shaft is free to take up axial expansion.
| Shaft, light load (P ≤ 0.06 C) | j6 |
|---|---|
| Shaft, normal load (P = 0.06–0.12 C) | k5 or k6 |
| Housing — Axial displacement of the outer ring required | H7 |
| Housing — Normal load, outer ring may still shift | J7 |
| Housing — Normal to heavy load, quiet running, outer ring not displaceable | K7 |
ISO 286-2 tolerance grades, applied per the conventional bearing seat recommendations of ISO 1132-2 and DIN 5425-1, for a SOLID STEEL shaft in a cast iron or steel housing. A hollow shaft, a thin-walled housing or a light alloy housing needs a tighter fit than these, because the seat itself deflects.
Radial Internal Clearance at 50 mm Bore
Radial internal clearance is the total distance one ring can be moved relative to the other, across the bearing, before it is mounted. It is not a tolerance and not a quality grade: it is a quantity that gets USED UP on installation. An interference fit on the shaft expands the inner ring; a tight housing fit compresses the outer ring; and a shaft that runs hotter than its housing grows more than the housing does. All three subtract from the clearance the bearing was made with. C3 exists for that reason. Specify it when the shaft fit is heavier than normal, when the inner ring will run 10 °C or more above the outer, when a hollow or heated shaft is involved, or when the bearing sits on an adapter sleeve that is driven up hard. Specify CN — normal, and usually left out of the designation entirely — for the ordinary case of a moderate fit on a shaft close to housing temperature. The failure this prevents is specific and quick: fit a CN bearing with a heavy interference on a shaft that then runs hot, and the residual clearance goes negative. The bearing is now preloaded by its own installation, the rolling elements are squeezed, friction and temperature rise together, and the temperature rise tightens the fit further. It runs hot, then it runs blue, and the raceways spall long before the calculated life.
ISO 5753-1 tabulates clearance separately for each bearing type, and the numbers for this type are not the deep groove ball bearing numbers. Order the group — CN, C3 or C4 — and take the values from the table for this type.
Abutment Shoulder & Fillet Radius for 50 mm
The chamfer dimension r min for this size is 2 mm. That figure is a limit on YOUR machining, not just on the bearing: the fillet radius in the corner of the shaft or the housing must be smaller than the bearing's corner radius, or the ring seats on the fillet instead of on the shoulder face and is loaded on its corner.
| Chamfer dimension r min (from the table) | 2 mm |
|---|---|
| Maximum fillet radius on the shaft or housing | 2 mm |
| Shaft shoulder must exceed | 54 mm diameter |
| Housing shoulder bore must be under | 106 mm diameter |
The two shoulder figures are the geometric floor and ceiling: a shoulder outside them fouls the corner radius instead of bearing on the ring face. The practical values sit inside them — the shoulder must contact the ring face over a useful area without touching the seal, the cage or the opposite ring, and it must still leave room for a puller when the bearing is dismounted. Take the working da and Da from the abutment table for the bearing; the ring shoulder height they are built on is not a boundary dimension and is not in this table.
Mounting a 50 mm Bore 21300 Series Spherical Roller Bearings
The ring that carries the rotating load takes an interference fit; the ring under a stationary point load takes a transition or clearance fit so that it can creep slowly and spread the wear, and so that one ring is free to take up axial expansion. With a rotating shaft under a fixed load direction, that means an interference fit on the shaft and a looser fit in the housing. Press only against the ring being fitted — force driven through the rolling elements leaves brinell marks in the raceway before the bearing has run a revolution.
At a 50 mm bore the interference is small enough that a cold press or a light hydraulic press is normally enough; heating the bearing in an induction heater or an oil bath to 80–100 °C above the shaft is the alternative, and never above 120 °C for a standard-stabilized bearing. Keep the heated bearing pressed against the shoulder while it cools, because it shrinks axially as well as radially.
Lubrication & Relubrication
Oil is the usual lubricant here, because this type is used where the load, the speed or the heat generated is beyond what a grease charge can carry away. Oil bath, oil mist, circulating oil and jet lubrication all take heat out of the bearing as well as separating the surfaces, and the viscosity has to be selected at the OPERATING temperature — a viscosity chosen at 40 °C when the bearing runs at 90 °C is not the film thickness the calculation assumed.
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.
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.
- Loss of internal clearance — the whole raceway path is loaded, the bearing runs hot from installation and it discolours evenly. The fit was too heavy, the shaft ran hotter than the housing, or a CN bearing was fitted where C3 was needed.
- 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 21300 Series Spherical Roller Bearings
- Do not treat the self-alignment as unlimited. A spherical roller bearing accommodates a fraction of a degree to a couple of degrees depending on the series and the seal — beyond that the rollers run off the end of the raceway.
- Do not load one almost purely axially. The two rows share the load through the spherical raceway; a nearly pure thrust load unloads one row completely, and the unloaded row skids.
- Do not drive a tapered-bore bearing up its adapter sleeve by feel. The drive-up is measured — as clearance reduction or as axial travel — because too far removes the internal clearance the bearing needs to survive.
- 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.
Stepping Up or Down from 50 mm
Within the same series, the next bore up in this series is 55 mm and the next bore down is 45 mm. Changing bore changes the shaft, so it is the last thing to change: when the calculated life at 50 mm is short, the first move is to a heavier diameter series at the SAME bore — the 6300 envelope instead of the 6200, for instance — which raises the rating without touching the shaft. The second is to change type: a roller bearing carries far more radial load than a ball bearing of the same envelope.
