The shaft expands, the outer ring slides within the housing, and somewhere in this movement, the problem begins: fretting corrosion on the mating surface, rough running, and vibrations that travel throughout the entire machine. What initially looks like normal wear is often a consequence of the design principle. This is because wherever shafts expand axially due to temperature changes, this movement must be accommodated by the bearing arrangement. In the classic fixed-floating bearing arrangement, it is precisely the floating bearing that takes on this task—though not without side effects.

This is neither a defect nor an installation error. The problem lies in the operating principle itself. This is because the necessary length compensation is achieved by the outer ring sliding within the housing. Under unfavorable operating conditions, it is precisely this relative movement that can cause friction, wear, and vibrations.

The question, therefore, was not how to improve the floating bearing, but whether axial length compensation could be addressed in a fundamentally different way. In the 1990s, SKF took this as an opportunity to fundamentally rethink the floating bearing. With the CARB toroidal roller bearing, SKF developed a new bearing geometry in which axial length compensation takes place within the bearing, eliminating the need for sliding between the outer ring and the housing. Schaeffler later followed suit with the TORB version.

Here, we’ll take a look at how both types of bearings solve this problem, what advantages toroidal roller bearings offer over conventional loose bearings, and how they differ.

The silent problem of any fixed-loose storage system
The classic floating bearing allows axial movement by enabling the outer ring to slide within the housing. In practice, this very sliding generates friction, stick-slip effects, fretting corrosion, and vibrations.

These effects quickly intensify in the case of long machines, high temperatures, or harsh environmental conditions. The result is unplanned downtime and shorter maintenance intervals—not because the design is flawed, but because the system itself forces this movement.

So the key question was: Can this gliding be eliminated?

A bearing that combines two properties
This is exactly where the toroidal roller bearing comes in. What makes it unique is that it meets two requirements simultaneously: it supports high radial loads and compensates for axial length changes in the shaft within the bearing. In this way, it performs the function of a non-locating bearing without the outer ring having to slide in the housing.

The rollers are long and slightly rounded, and the raceways are toroidal—that is, curved in a saddle shape.

This allows the rollers to align themselves so that the load is distributed evenly along their entire length. This works even when the inner and outer rings are misaligned or tilted relative to each other.

The result is a bearing that combines the angular adjustability of a self-aligning roller bearing with the axial displacement capability of a cylindrical roller bearing: angular misalignment of up to approximately 0.5 degrees and axial displacement of approximately ±10 percent of the bearing width are internally compensated without the outer ring coming into contact with the housing.

However, it’s also important to note what this bearing cannot do: It is a purely radial bearing. It does not absorb axial loads, nor should any be applied to it. That task is handled by the fixed bearing—more on that in a moment.

CARB: SKF’s Innovation, Decades Ahead of the Curve
SKF introduced the CARB toroidal roller bearing to the market in the 1990s and has consistently refined the design ever since. Today, CARB is one of the established solutions for applications in which thermal linear expansion, shaft deflection, and high radial loads must be reliably controlled. The product range includes 13 ISO size series as well as versions with cylindrical and tapered bores. In addition, there are cages made of plastic, sheet steel, or brass, as well as full-roller and sealed variants. All CARB bearings belong to the SKF Explorer class, which we already explored in the article before last.

How SKF changed the industry: The history of spherical ball and spherical roller bearings

Specific examples demonstrate that the design principle delivers on its promises in practice.

In large industrial fans, vibrations occur as soon as the conventional floating bearing in the housing fails to slide smoothly. In documented applications, replacing it with a CARB bearing significantly reduced vibrations without requiring any changes to the rest of the bearing assembly.

The difference is even more evident in continuous casting lines. There, abrasive particles, corrosive chemicals, extreme temperatures, and heavy load spikes all act on the bearing simultaneously. Under these conditions, in one documented application, bearing service life was doubled after switching to CARB.

Such improvements not only extend the service life of individual bearings; they also lengthen maintenance intervals, reduce unplanned downtime, and increase plant availability.

TORB: Schaeffler’s Response with a Clear Industry Focus
With the TORB toroidal roller bearing, Schaeffler also developed a solution based on the same operating principle. The key parameters are largely identical: up to 0.5 degrees of angular adjustability, an axial displacement of approximately ±10 percent of the bearing width, and a temperature resistance of up to 200 degrees Celsius.

The fact that Schaeffler has adopted the approach pioneered by SKF speaks to the effectiveness of the concept. At Schaeffler, the X-life design stands for increased load-carrying capacity and extended service life.

Unlike SKF, Schaeffler positions the TORB specifically for applications in the paper industry. That is precisely where the bearing demonstrates its strengths. Hardly any other application poses so many challenges at once: Long, steam-heated drying cylinders undergo thermal expansion, angular misalignment occurs due to deflection, and operations must run for months without unplanned downtime.

TORB can accommodate axial thermal expansion of up to 15 millimeters in these cylinders without introducing additional axial forces into the bearing system.

Why Self-Aligning Roller Bearings and Toroidal Roller Bearings Work So Well Together
Toroidal roller bearings replace the floating bearing, but they never replace the entire bearing system. Both manufacturers recommend a self-aligning roller bearing as the fixed bearing, and this pairing is no coincidence.

Spherical roller bearings can accommodate angular misalignment, while the toroidal roller bearing additionally accommodates axial expansion. Together, this results in a bearing system that accommodates misalignment, shaft deflection, and thermal length changes without generating forced forces that stress the bearings, shaft, or housing.

The division of responsibilities is clear: The pendulum roller bearing guides the shaft axially and absorbs axial forces. The toroidal roller bearing carries only radial loads and allows for longitudinal compensation.

Anyone planning to use this combination should keep one point in mind: axial displacement and angular misalignment reduce the radial operating clearance. Structural clearance is required on both sides of the toroidal roller bearing, and the remaining clearance should be checked before commissioning.

Conclusion
Toroidal roller bearings resolve a design-related trade-off inherent in traditional fixed-floating bearing arrangements. Instead of allowing axial length compensation through sliding mating surfaces, the movement occurs within the bearing itself. This significantly reduces friction, fretting corrosion, and constraint forces.

CARB and TORB are based on the same technical principle. SKF currently offers the broader product range, which has been refined over many years. With TORB, Schaeffler clearly focuses on applications in the paper industry. Which bearing is the better choice, therefore, depends less on the operating principle than on the specific application.