Needle Roller Inner Rings
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Needle Roller Inner Rings
What is a needle roller inner ring?
A needle roller inner ring is a hardened and precision-finished steel ring that fits onto a shaft and gives the needle rollers a raceway to run on. Many needle roller bearings are designed to run directly on a hardened shaft, but if the shaft is not hard enough or not finished accurately, an inner ring is fitted instead. It acts as a replaceable raceway, protecting the shaft from wear.
A standard inner ring has three main features:
- A bore, which fits onto the shaft
- An outer surface, which acts as the raceway for the needle rollers
- Chamfered edges on both end faces.
Inner rings are made to work with other needle roller components.
- They are used with drawn cup needle roller bearings, machined needle roller bearings without an inner ring, and needle roller and cage assemblies.
- The chamfers make it easier to slide the bearing onto the ring and help protect the lips of any seals during fitting.
Inner rings are made from hardened chrome steel (grade 52100), with the raceway finished to a very smooth surface. Some inner rings are made wider than the bearing, so the shaft can move axially, for example as it expands with heat, without the needles running off the raceway.
Why are needle roller inner rings essential?
They let needle roller bearings be used on shafts that cannot be hardened and ground, which saves the cost and time of heat-treating and grinding the shaft. If the raceway wears, only the inner ring needs replacing rather than the whole shaft. This makes servicing quicker and cheaper.
They also give designers more flexibility. A standard inner ring can turn a bearing without an inner ring into a complete bearing, and a wider ring can allow for axial movement. Their dimensions are standardised, so an inner ring of a given reference has the same bore, outer diameter, and width, regardless of which reputable manufacturer makes it.
Typical applications include:
- Gearboxes and transmissions
- Pumps and compressors
- Agricultural and construction machinery
- Engines and power tools
- Machine tools
- Printing and textile machines
- Pivot points and linkages
- Rollers and idlers
The main types of needle roller inner rings
- Standard inner rings (IR) - These are the most common type, with a finely machined raceway and chamfers on both end faces. They are made to close tolerances and suit most needle roller bearings.
- Inner rings with wider tolerances (LR) - These have a ground raceway, turned faces, and broken edges. They have wider tolerances than IR rings and suit applications where width tolerance and axial run-out are less critical.
- Inner rings with a lubrication hole - These have a hole through the ring so oil or grease can be fed from inside the shaft to the needles.
- Wide inner rings - These are wider than the bearing they run in, allowing the shaft to move axially without the needles running off the raceway.
- Inner rings for sealed bearings - These have a smooth outer surface and chamfers that protect seal lips, so they can be used with sealed needle roller bearings.
How to choose the right needle roller inner ring?
- Size and dimensions - The bore must suit the shaft, and the outer diameter must match the needle roller bearing or cage it will run in. Check the width suits the bearing and any axial movement needed.
- Matching bearing - The outer diameter of the inner ring must match the inside diameter of the needle roller bearing, often called the under-roller diameter. If it does not match, the bearing will be too tight or too loose.
- Tolerance - Choose an IR ring for accurate applications, or an LR ring where wider tolerances are acceptable.
- Lubrication - Choose a ring with a lubrication hole if oil or grease is fed through the shaft.
- Fit - The inner ring is usually an interference fit on a rotating shaft. Check the shaft tolerance suits the ring and the load.
Essential references and specialised ranges
How the numbering works:
The letters at the start identify the type:
IR = inner ring with finely machined raceway
LR = inner ring with ground raceway and wider tolerances
The numbers show the dimensions in mm:
Bore x outer diameter x width, so an IR 20x25x20 has a 20mm bore, a 25mm outer diameter, and is 20mm wide.
The outer diameter is the important one for matching the bearing. For example, an IR 20x25x20 would be used with a bearing that has a 25mm under-roller diameter, such as an HK 2516 or a K 25x29x13.
Suffixes:
IS1 = lubrication hole in the inner ring
XL = X-life series
Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.
FAQ - All you need to know about needle roller inner rings
When do I need an inner ring?
You need an inner ring if the shaft is not hardened and ground to a smooth enough finish for the needles to run on directly. If the shaft is already hardened and ground, the needles can run straight on it and no inner ring is needed.
What is the difference between IR and LR inner rings?
IR rings have a finely machined raceway and close tolerances, so they suit most applications. LR rings have a ground raceway, turned faces, and wider tolerances, so they suit applications where width tolerance and axial run-out are less critical.
How do I match an inner ring to a bearing?
Match the outer diameter of the inner ring to the under-roller diameter of the bearing. For drawn cup bearings such as HK, this is the first number in the bearing reference, so an HK 2516 needs an inner ring with a 25mm outer diameter.
Do inner rings need lubrication?
The inner ring is lubricated together with the bearing. Rings with a lubrication hole let oil or grease be fed through the shaft to the needles, which is useful where the bearing cannot easily be lubricated from outside.
Click here to learn how to maintain a bearing.
Can I replace a needle roller inner ring myself?
In many cases, yes. Inner rings are usually an interference fit, so they need to be pressed on or heated with an induction heater so they expand onto the shaft. Press only on the end face of the ring, and make sure it sits fully against the shaft shoulder. Old rings can be removed with a bearing puller or by carefully heating the ring.
How do I identify an inner ring I need to replace?
The reference is sometimes marked on the end face of the ring. If it is not marked, measure the bore, outer diameter, and width with callipers. Also note whether the ring has a lubrication hole, and check the reference of the bearing it runs in.
Click here to learn how to measure a bearing.
How can I tell if an inner ring is worn or damaged?
Warning signs include:
- Pitting, flaking, or spalling on the raceway
- Grooves or dents where the needles run
- Blue, brown, or straw-coloured marks from overheating
- Rust or corrosion on the raceway
- Play between the ring and the bearing
- Signs that the ring has been turning on the shaft
