Cylindrical roller bearings
Cylindrical roller bearings are a type of rolling-element bearing that uses cylinders as rolling bodies, guided between an inner ring and an outer ring. They are designed to support high radial loads due to the linear geometry of the contact between the rollers and the raceways, and can operate at moderate and high speeds. The radial load capacity is typically higher than that of a deep groove ball bearing of equivalent dimensions.
The cylindrical rollers rotate about their own axes and roll on the raceways of the inner and outer rings. The line contact distributes the load over a larger area compared to the point contact of ball bearings, which reduces contact pressure and allows greater radial forces to be supported. The cage keeps the rollers separated to prevent friction between them and ensure uniform load distribution. Some designs allow free axial displacement of the ring relative to the rollers (types NU, N) to absorb thermal expansion of the shaft, while others include flanges to guide the bearing in one axial direction (NJ, NUP).
Characteristics
Section titled “Characteristics”Cylindrical roller bearings are characterized by very high radial load capacity, low friction, suitability for high speeds, and separability. The rings are separable, which facilitates assembly and disassembly. They do not support axial loads or only do so in one direction and with limited values, depending on the flange design. Radial stiffness is high, and they are suitable for applications with long shafts where axial freedom of movement is required in one of the supports.
Standard dimensions
Section titled “Standard dimensions”The main dimensions of cylindrical roller bearings are governed by the dimensional series defined in ISO 15, DIN 616, and ANSI/ABMA 20 standards. The most common series are 10, 02, 03, 22, 23, etc. The following table provides indicative dimensions for the most common sizes. Actual values may vary by manufacturer and specific flange design.
| Inner diameter (d) | Outer diameter (D) | Width (B) |
|---|---|---|
| 20 mm / 0.7874 in | 47 mm / 1.8504 in | 14 mm / 0.5512 in |
| 25 mm / 0.9843 in | 52 mm / 2.0472 in | 15 mm / 0.5906 in |
| 30 mm / 1.1811 in | 62 mm / 2.4409 in | 16 mm / 0.6299 in |
| 35 mm / 1.3780 in | 72 mm / 2.8346 in | 17 mm / 0.6693 in |
| 40 mm / 1.5748 in | 80 mm / 3.1496 in | 18 mm / 0.7087 in |
| 45 mm / 1.7717 in | 85 mm / 3.3465 in | 19 mm / 0.7480 in |
| 50 mm / 1.9685 in | 90 mm / 3.5433 in | 20 mm / 0.7874 in |
| 60 mm / 2.3622 in | 110 mm / 4.3307 in | 22 mm / 0.8661 in |
There are special executions with the same inner and outer diameter but greater width (series 23, for example), as well as light (10, 02), medium (03) and heavy (22, 23) series. The complete designation includes prefixes such as NU, N, NJ, NUP, which indicate the flange configuration.
Load capacities
Section titled “Load capacities”Load capacity values depend on the manufacturer, the number and size of the rollers, and the material. The following table shows indicative capacities for cylindrical roller bearings of series 02 with brass or steel cage, under proper lubrication conditions. Basic dynamic load rating (C) and basic static load rating (C0) are given.
| Inner diameter (d) | C (dynamic) | C0 (static) |
|---|---|---|
| 20 mm / 0.7874 in | 6240 N / 1403 lbf | 4840 N / 1088 lbf |
| 25 mm / 0.9843 in | 8190 N / 1841 lbf | 6550 N / 1473 lbf |
| 30 mm / 1.1811 in | 10600 N / 2383 lbf | 8800 N / 1978 lbf |
| 35 mm / 1.3780 in | 12900 N / 2900 lbf | 11000 N / 2473 lbf |
| 40 mm / 1.5748 in | 16000 N / 3596 lbf | 14000 N / 3147 lbf |
| 45 mm / 1.7717 in | 18600 N / 4181 lbf | 16600 N / 3732 lbf |
| 50 mm / 1.9685 in | 20400 N / 4586 lbf | 18600 N / 4181 lbf |
| 60 mm / 2.3622 in | 30000 N / 6744 lbf | 28000 N / 6295 lbf |
Permissible axial loads are limited; typically they do not exceed 10-20 % of the radial load capacity, and are only allowed in combination with sufficient radial load to prevent sliding.
Materials
Section titled “Materials”The rings and rollers are mostly manufactured from bearing steel AISI 52100 (chromium-carbon steel, similar to 100Cr6) fully hardened, with surface hardness of 58-64 HRC. The cage can be made of pressed steel (for light series), machined brass (general purpose and high speeds), or glass-fiber reinforced polyamide (for applications with moderate temperatures and low load). For corrosive or high-temperature conditions, stainless steel (AISI 440C) or special coating executions are available.
Applications
Section titled “Applications”Cylindrical roller bearings are used in gearboxes, electric motors, machine tools, compressors, pumps, industrial fans, rolling mills, conveyor rollers, gear reducers, wind turbines, and all types of machinery where intense radial loads predominate and high rotational precision is required. They are especially useful as a floating bearing on long shafts, where the inner ring can move axially to compensate for expansion.
Mounting and maintenance
Section titled “Mounting and maintenance”- Hot mounting: For interference fits on the shaft, heat the inner ring to 80-120 °C / 176-248 °F using an induction heater. Avoid local overheating.
- Alignment: The permissible angular misalignment is very low (typically < 4 arc-minutes for standard series); incorrect alignment causes edge loading and premature failure.
- Lubrication: Grease or oil is recommended depending on speed and temperature. For high speeds, use oil with adequate viscosity; the grease quantity should not exceed 30-50 % of the free volume.
- Disassembly: Since the rings are separable, the inner or outer ring is removed individually. Use pullers that act on the ring to be removed, never apply force through the rollers.
- Radial clearance: Select the appropriate internal radial clearance (normal, C3, C4) according to fitting conditions and service temperature.
Selection criteria
Section titled “Selection criteria”The selection of a cylindrical roller bearing depends on:
- Magnitude and type of load: predominantly radial. If axial load exists, verify flange capacity.
- Rotational speed: for high speeds, prefer series with smaller diameter rollers and brass cages.
- Need for axial displacement: NU or N designs allow free displacement; NJ and NUP fix the shaft in one or both directions.
- Mounting conditions: consider the fitting method and shaft and housing tolerances.
- Service temperature: select appropriate internal clearance and cage material.
- Required stiffness: most cylindrical bearings offer high radial stiffness; for ultra-precision applications, opt for specific series with reduced tolerances.
Selection tables by application
Section titled “Selection tables by application”The following table suggests series and types of cylindrical roller bearings for typical applications, along with indicative inner diameter and speed values.
| Application | Recommended type | Typical inner diameter (d) | Approximate limiting speed (rpm) |
|---|---|---|---|
| Electric motor (floating bearing) | NU10 or NU2 | 30-60 mm / 1.2-2.4 in | 5000-8000 rpm |
| Industrial gearbox | NJ2 or NUP2 | 40-100 mm / 1.6-3.9 in | 2000-4000 rpm |
| Conveyor roller | N or NU3 (heavy series) | 50-120 mm / 2.0-4.7 in | 500-1500 rpm |
| Machine tool spindle | NN30 (double row, super precision) | 60-150 mm / 2.4-5.9 in | 3000-10000 rpm |
| Screw compressor | NU2 or NJ2 | 25-80 mm / 1.0-3.1 in | 4000-9000 rpm |
| Rolling mill (roll neck) | Four-row (FC, FCD) | 100-400 mm / 3.9-15.7 in | 100-500 rpm |
The indicated speeds are approximate and depend on the lubrication method, load, and temperature. For each specific case, the manufacturer’s n x dm speed factor should be verified.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the typical service life of a cylindrical roller bearing?
Section titled “What is the typical service life of a cylindrical roller bearing?”The L10 nominal life for a medium-size cylindrical roller bearing (e.g., inner diameter 40 mm / 1.6 in) is approximately 20,000 hours under a load equivalent to 10 % of the dynamic capacity, with proper lubrication and correct alignment.
How much misalignment can it absorb without damage?
Section titled “How much misalignment can it absorb without damage?”The permissible angular error for standard cylindrical roller bearings is less than 4 arc-minutes (0.066 degrees), although some designs with profiled rollers can tolerate up to 10 arc-minutes without significant life reduction.
What maximum working temperature can it withstand?
Section titled “What maximum working temperature can it withstand?”A standard cylindrical roller bearing in dimensionally stabilized 100Cr6 steel can operate continuously up to 150 °C / 302 °F. With special heat treatment (higher tempering temperature) and a metal cage, 200 °C / 392 °F can be reached, and with high-temperature steels up to 300 °C / 572 °F.
How much axial load can an NJ type bearing support?
Section titled “How much axial load can an NJ type bearing support?”The permissible axial load for a medium NJ (diameter 50 mm / 1.97 in) typically does not exceed 15-20 % of the radial dynamic load capacity, i.e., on the order of 3000-4000 N / 675-900 lbf, and always in the presence of sufficient radial load to keep the rollers in uniform contact.
How is the correct internal radial clearance determined?
Section titled “How is the correct internal radial clearance determined?”The internal radial clearance must be selected based on the fit of the ring on the shaft and in the housing. For an interference fit of 0.02 mm / 0.0008 in on the shaft and a service temperature of 70 °C / 158 °F, clearance C3 is recommended, which for a 40 mm / 1.57 in diameter corresponds to a radial clearance range of 25 to 51 µm / 0.00098 to 0.00201 in.
What is the minimum recommended interference for the shaft fit?
Section titled “What is the minimum recommended interference for the shaft fit?”For a steel shaft and a bearing with inner diameter 50 mm / 1.97 in subjected to a rotating load relative to the shaft, an interference between 0.005 mm and 0.030 mm / 0.0002-0.0012 in is recommended, depending on the load magnitude and ring thickness.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/iso-threads-d_752.html
- mcmaster.com: https://www.mcmaster.com/products/cylindrical-roller-bearings