Bearing Inner Rings.

What are Bearing Inner Rings?

Bearing inner rings, also called bearing rings or inner raceway rings, are precision-ground steel sleeves that provide the inner running surface for a needle roller bearing. In a rolling bearing, the inner ring is the part nearest the shaft and its outer face is the hardened raceway the rolling elements run against. A needle roller bearing inner ring supplies exactly that surface as a separate component, pressed onto a shaft to turn a plain shaft into a true raceway. This differs from the inner ring of a ball bearing, which is normally built into the complete bearing rather than sold on its own. 

The category exists because needle roller bearings are often designed to run straight on the shaft, though not every shaft can be hardened and ground to cope with that duty.

How Bearing Inner Rings Work

A bearing inner ring works as a hardened, ground raceway that presses onto the shaft with an interference fit and rotates with it. The needle rollers of the surrounding bearing run directly on the ring's outer surface, so the load and wear fall on a purpose-made bearing ring rather than on the shaft. That allows softer or smaller-diameter shafts to be used without compromising the life of the needle bearing, since the raceway is no longer limited by the shaft material.

Take a compact gearbox where a needle roller bearing supports a layshaft to save the space a full bearing would take. If that shaft is made from a grade that cannot be hardened to a proper raceway finish, the rollers would soon score and wear it and the assembly would lose accuracy. Pressing a needle roller bearing inner ring onto the shaft solves it in one step: the rollers now run on a hardened, ground surface rated for the job, the shaft can stay a cheaper or lighter material and the bearing reaches its full rated life. It is a small component that lets the designer separate the choice of shaft from the demands of the raceway.

Materials Bearing Inner Rings Are Made From

A bearing inner ring is only as effective as its raceway, so there’s one material that’s ideal for the job.

• Steel - (AISI 52100): A chrome bearing steel that hardens to a ground surface hard enough to take the concentrated line contact of needle rollers head-on.

The rings are supplied with no additional coating or plating, so selection comes down to matching the ring's three dimensions to your shaft and to the needle roller bearing it pairs with.

Sizes and Types of Bearing Inner Rings Available

Accu's bearing inner rings run to 37 sizes in the IR series, covering a broad spread of shaft and bearing combinations in small and mid-scale assemblies, matched to standard needle roller bearing envelopes.

• Inside diameters: from 5 mm to 17 mm
• Outside diameters: from 8 mm to 20 mm
• Widths: from 10 mm to 23 mm

Each ring is identified by an IR code that reads as inside diameter, outside diameter and width, for example IR12X16X20, so the part number states the exact envelope at a glance. 

FAQs

Q: What is the inner ring and outer ring of a bearing?

A: A typical rolling bearing has two rings with the rolling elements running between them. The outer ring forms the outer raceway and usually seats in the housing, while the inner ring forms the inner raceway and fits onto the shaft. The balls or rollers roll along both surfaces, carrying the load while allowing free rotation. In a sealed ball bearing the inner ring and outer ring are supplied together as one unit, so a ball bearing inner ring is not sold separately. 

A needle roller bearing is different: its outer raceway is often a drawn cup or machined ring and its inner raceway can be either the shaft itself or a separate bearing inner ring pressed onto it, which is where these components come in.

Q: How do you fit a needle roller bearing inner ring?

A: A bearing inner ring is fitted with an interference fit, so it is pressed onto the shaft rather than slid on by hand. The bore is sized slightly smaller than the shaft, which grips the ring firmly and makes it rotate with the shaft in service. Fitting is usually done with an arbor press or a bearing fitting tool that pushes squarely on the ring face, and warming the ring gently can ease it home on tighter fits. The aim is a square, fully seated ring with no damage to the ground outer surface, since that raceway is where the needle rollers run.

Q: Can a bearing inner ring be reused?

A: In most cases, a bearing inner ring is treated as a replacement part rather than a reusable one. Because it is held by an interference fit, removing it tends to mark or distort the ring, and any scoring on the hardened raceway shortens the life of the needle rollers that run against it. Where a ring has to come off for maintenance, it is good practice to inspect the raceway for wear, brinelling or discolouration and fit a new ring if there is any doubt, given how small the component is against the cost of a worn bearing.

Q: What are the four types of bearings?

A: Bearings are commonly grouped into four broad families: ball bearings, roller bearings, thrust bearings and plain or journal bearings. 

• Ball bearings: use spherical elements for general radial and light axial loads
• Roller bearings, including needle roller bearings: use cylindrical elements to carry heavier radial loads in a compact cross-section 
• Thrust bearings: take axial load acting along the shaft
• Plain bearings: rely on a sliding surface rather than rolling elements. 

Bearing inner rings sit within the roller bearing family, supplying the inner raceway that lets a needle roller bearing run on a shaft that could not otherwise serve as one.

Bespoke Bearing Inner Rings Manufacture.

High precision, bespoke manufacture of Bearing Inner Rings to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.