7300C Series Angular Contact Ball Bearings are tabulated at a 15 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.
15 mm Bore Dimensional Row (ISO 15 / DIN 628-1 / GB/T 292)
| Designation | Bore d (mm) | Outer diameter D (mm) | Width B (mm) | Chamfer r min (mm) | Contact angle a (deg) |
|---|---|---|---|---|---|
| 7302C | 15 | 42 | 13 | 1 | 15 |
What a 7300C Series Angular Contact Ball Bearings Does
The raceways are ground so that load passes between them at a contact angle to the radial plane — typically 15°, 25°, 30° or 40°. The bearing therefore carries radial and axial load together, and the steeper the angle the more axial load it takes. A single row acts in one axial direction only and has to be opposed by a second bearing.
Combined radial and axial load, with the axial component taken in one direction only. A single bearing therefore has to be opposed — by a second bearing of the same type mounted face to face or back to back, or by a bearing that locates in the other direction.
Speed at 15 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 15 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) | h5 |
|---|---|
| Shaft, normal load (P = 0.06–0.12 C) | j5 |
| 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 15 mm Bore
This type is specified by PRELOAD, not by a clearance group. The rings are set against one another on assembly — by a ground spacer, by a matched set, or by drawing a nut up to a measured endplay — and the resulting axial setting decides the stiffness, the running accuracy and the heat generated. Ordering a "C3" version of this bearing asks the wrong question: the equivalent decision here is light, medium or heavy preload, or a specified endplay.
Abutment Shoulder & Fillet Radius for 15 mm
The chamfer dimension r min for this size is 1 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) | 1 mm |
|---|---|
| Maximum fillet radius on the shaft or housing | 1 mm |
| Shaft shoulder must exceed | 17 mm diameter |
| Housing shoulder bore must be under | 40 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 15 mm Bore 7300C Series Angular Contact Ball 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 15 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
Grease is the normal lubricant for this type: it stays where it is put, helps to keep contamination out, and needs no circulation system. Fill roughly 30% to 50% of the free space in the bearing arrangement — a bearing packed full runs hot, because the excess grease is churned rather than used. The relubrication interval is not a fixed figure; it falls with speed, with temperature and with load, and it halves for roughly every 15 °C of temperature rise above about 70 °C. Where speed, temperature or the required interval put grease out of reach, change to oil.
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 15 mm Bore 7300C Series Angular Contact Ball Bearings Is Used
At a 15 mm bore, 7300c series angular contact ball 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.
- Skidding under light load — smeared, matte patches on the raceway. A ball or thrust bearing that is not loaded enough to make its rolling elements roll lets them slide instead, and the film breaks down where they scuff.
- 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 7300C Series Angular Contact Ball Bearings
- Do not mount a single row angular contact bearing on its own. It takes axial load in one direction only and must be opposed, or it will be pulled apart axially by the very load it was fitted to carry.
- Do not order this bearing by a clearance group. It is set by preload or by a measured endplay on assembly, and "C3" is not an answer this type has.
- Do not fit a four-point contact bearing as a radial bearing. Its split inner ring and single row of balls are there to take thrust in a short axial space; carrying significant radial load is what a companion bearing is for.
- 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.
