Segmented Bearings: When a Component Is Too Large  

Summary

Segmented bearings are used when transporting or installing non-segmented bearings is not possible due to their size. Instead of a solid bearing unit, the main components, especially the rings, are manufactured as individual segments, transported separately and assembled only at the point of use. Typical applications include tunnel boring machines, mining equipment, cranes and offshore installations. Segmented bearings enable very large bearing diameters but require increased design, manufacturing and assembly effort.

Close‑up view of a precision‑machined segmented roller bearing showing modular raceway segments and cylindrical rolling elements

Most of our bearings are manufactured from seamless rolled rings. These rings are made from a single piece of steel that is heated, pressed, pierced and rolled into shape by our production staff. Together with other components, these rings form a complete bearing.This seamless manufacturing process means that the components must be transported and installed in one piece and at full size. In certain applications, however, this is difficult or even impossible.

What happens when infrastructure constraints such as narrow roads and tunnels prevent the transport of large components?

Case 1: If roads are too narrow to transport large bearings, the components must either be transported with considerable logistical effort or supplied in segmented form.

In most countries, the transport of large and heavy components on public roads is subject to strict legal regulations and approval procedures. A frequently cited example is Japan, where special permits are already required for transports involving widths of just 2.5 metres. Even though we transport our bearings in a tilted position to allow for larger diameters within the permitted transport envelope, the overall logistical effort increases significantly as the bearing size grows. Planning becomes more complex, transport routes must be carefully selected, and additional coordination with authorities is often required.

For XXL applications, such as tunnel boring machines, the limitations are often no longer just regulatory but physical in nature. Roads, bridges and underpasses frequently reach their absolute dimensional limits, regardless of permits or transport approvals. In these applications, we supply some of the largest bearings in our portfolio, with outer diameters of nearly ten metres.

This situation ultimately raises a fundamental and unavoidable question: how can machine components of this size be transported on public roads that were never designed to accommodate such extraordinary dimensions?

Case 2: In mining, the geometry of narrow and deep shafts prevents the transport of large, single‑piece machine components. As a result, segmented components are used.

Raw materials such as coal are often located very deep underground. Depths of 1,000 meters or more are not uncommon. To reach the coal seams, at least two shafts are typically drilled. First, a vertical access shaft is drilled using specialised drilling machines. One of its initial tasks is to lower a tunnel boring machine that drills a horizontal shaft. In this horizontal shaft, the production machinery reaches the seam and mining operations can begin.

Due to its depth, the vertical shaft is often very long and therefore drilled as narrowly as possible. Relatively small machines are used for this purpose. This reduces excavation volume, saves time, simplifies ground support and is overall more cost‑efficient.

The horizontal shaft, by contrast, is usually shorter than the vertical one, but significantly wider so that the mining machinery can operate within it. Consequently, the tunnel boring machine used for the horizontal shaft is larger than the one used for the vertical shaft.

This leads to a claustrophobic question: how can a tunnel boring machine be transported through a kilometer‑long shaft that was drilled by a much smaller machine?

The solution

In both cases, machines and large components are delivered in individual parts and assembled only at the installation site. For us, this means supplying so‑called segmented bearings. Segmented bearings are bearings whose main components are divided into multiple segments in order to facilitate transport, handling and installation.

Which bearing components are manufactured as individual parts or segments?

The main components of a segmented bearing are supplied as individual parts: rings, cages, and seals (in some cases). Other components, such as rolling elements, are always installed individually.

How are segmented rings manufactured?

There are two basic manufacturing methods for segmented rings.

The most common method for tunnel boring machine bearings is to manufacture the ring in one piece first, just as with a standard bearing. Only afterwards is the ring precisely divided into segments using wire electrical discharge machining (EDM). Wire EDM is a non‑contact cutting process in which electrically conductive material is precisely removed by spark erosion. In simplified terms, a heated wire splits the ring into individual segments. The segments then undergo further manufacturing steps.

The second method involves manufacturing the ring as segments from the very beginning. The larger the bearing, the more likely this method is to be used, as the limits of ring‑rolling machines are eventually reached.

The preliminary work is carried out by our suppliers. Similar to raw steel, we receive a rough, unfinished steel segment. This raw segment already has the correct rectangular cross‑section, curvature and dimensions, allowing us to machine the exact contours. Our production staff then carry out further steps such as hardening, drilling and gear cutting.

How are cages manufactured for segmented bearings?

Cages for segmented bearings are always manufactured from multiple individual parts. Often, the basic structure of a segmented cage is cut from steel plates. The sliding surfaces are then added to the cage body.

How are seals manufactured for segmented bearings?

Seals generally consist of a continuous strand that is cut to the exact required length and then reconnected by our employees. Depending on the material and its flexibility, the seal may be reconnected at our manufacturing site or later at the point of use.

How are the segments assembled on site?

Assembly is typically carried out by a customer team working together with one of our service engineers. The service engineer supports the assembly crew and uses measurements to ensure that the bearing and the surrounding structure form a properly functioning unit.

A typical process looks like this: The technicians unpack all bearing segments and components and clean them thoroughly. At the same time, our service engineer checks the flatness of the mounting surface. If it is within the specified tolerances, assembly can continue; if not, any unevenness must be compensated.

The technicians then install mounting blocks on the mounting surface. These supports are also checked to ensure they are all at the same height, as the bearing is assembled on them segment by segment. In some cases, a special compensation compound is applied at the contact points between the first ring segments. The individual ring segments are then placed onto the mounting blocks. Our service engineer then measures the form and position tolerances of the assembled ring.

Once all measurements are within tolerance, the cage segments, rolling elements, seals, and remaining ring segments are installed. Throughout the process, the components are repeatedly sealed, partially lubricated, and checked by additional measurements. The result is a fully assembled segmented bearing at the installation site, ready to be integrated into the surrounding structure.

What are the disadvantages of segmented bearings?

Oil-lubricated segmented bearings require additional encapsulation, involve greater installation effort, and are generally more expensive than non-segmented bearings due to their more complex design.

Regarding the encapsulation: segmented bearings should be equipped with encapsulation, as they are not 100% leak-proof and would leak lubricant without them. Alternatively, the lubricant can be collected and returned to the raceway system via a circulating oil lubrication system.

This creates additional design work for our customers or the machine manufacturers. The manufacturer must design this enclosure and integrate it into their machine.

There is no standard solution here. What the solutions have in common, however, is that they keep the lubricant within the raceway.

Another disadvantage of segmented bearings: Due to their design, the requirements are higher, so segmented bearings are generally more expensive.

What types of bearings can be manufactured in segments?

At Rothe Erde, we typically manufacture segmented three-row roller bearings for tunnel boring machines. The same applies to cranes, though in this case we also produce ball bearings. For Floating Production Storage and Offloading Units (FPSOs), segmented four-row roller bearings are our standard. However, depending on the application requirements, we are always open to evaluating other designs.

Conclusion:

Segmented bearings are a design solution for applications where large, non-segmented bearings cannot be used due to transport or installation constraints. They allow for very large bearing diameters but require greater design and logistical effort. Their advantages are particularly evident in extreme applications such as tunnel construction, mining, and offshore technology.