In a tunnel boring machine (TBM), the main bearing is one of the most critical mechanical components, designed to withstand substantial loads while supporting the rotational movement of the cutterhead. To ensure stable and continuous TBM operation, protecting the main bearing against friction, wear, and the ingress of water, soil, and rock particles is an essential technical requirement.
TBM lubricating grease and main bearing sealing materials therefore play a vital role in protecting the drive system, maintaining operational performance, and minimizing the risk of tunnelling interruptions.
How do TBM main bearing lubrication and sealing systems work? Which technical properties should be considered when selecting suitable materials? This article explores their functions, key performance requirements, and important considerations for choosing effective lubrication and sealing solutions.
What is a TBM main bearing and what is its role in Tunnel Boring Machine?
In a tunnel boring machine (TBM), the main bearing is a critical component of the cutterhead drive system. It enables cutterhead rotation while accommodating the loads generated during excavation.
During TBM operation, the cutterhead continuously interacts with the surrounding ground, generating complex forces acting on the drive system. The main bearing supports rotational movement while accommodating and transmitting axial loads, radial loads, and overturning moments according to the machine’s design.
The TBM main bearing is also a high-value, mechanically complex assembly that requires stringent maintenance practices. Particularly in long-distance tunnelling projects or deep underground construction, accessing and repairing the main bearing can be extremely challenging, potentially causing significant disruption to project schedules.
Maintaining appropriate operating conditions for the main bearing is therefore not merely a matter of mechanical maintenance. It is also essential to ensuring the continuity and efficiency of mechanized tunnelling operations.
Functions of TBM main bearing lubrication and sealing
TBM main bearing systems typically operate under heavy loads, relatively low rotational speeds, and environmental conditions involving potential exposure to water, slurry, soil, and abrasive particles.
To protect this critical component, TBMs employ lubrication and sealing solutions specifically designed to suit the machine’s mechanical configuration.
Although closely related, lubrication and sealing perform distinct yet complementary functions in protecting the main bearing assembly and maintaining stable operating conditions.
1. Main bearing lubrication – Reducing friction and protecting contact surfaces
During operation, the bearing’s contact surfaces are continuously subjected to mechanical loads and relative movement. Inadequate lubrication can increase friction and wear, adversely affecting bearing performance and service life.
TBM main bearing lubricating grease is used in grease-lubricated systems to perform several essential functions:
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Friction and wear reduction: Forms and maintains a lubricating film between contact surfaces, helping minimize direct metal-to-metal contact within the permissible operating conditions.
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Mechanical load resistance: Helps protect heavily loaded contact surfaces, particularly under operating conditions requiring extreme-pressure performance.
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Corrosion protection: Helps protect metallic components against moisture and other corrosive influences.
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Stable operating conditions: Supports efficient drive system operation and reduces the risk of performance deterioration caused by insufficient lubrication.
Maintaining appropriate lubrication conditions is essential for protecting the TBM main bearing, minimizing adverse mechanical effects, and supporting consistent operational performance.
2. Main bearing sealing – Preventing water and contaminant ingress
In addition to lubrication, TBM main bearing sealing is essential for protecting the cutterhead drive system against harsh underground construction environments.
During excavation, the area in front of the cutterhead may be exposed to ground pressure, groundwater, and excavated material. If these substances penetrate the bearing system, they can contaminate the lubricant, accelerate wear, and adversely affect mechanical components.
Main bearing sealing systems typically combine mechanical sealing elements with specialized sealing materials to:
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Minimize the ingress of water, slurry, soil, and fine particles into the bearing assembly.
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Protect lubricants against contamination from the surrounding environment.
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Help maintain sealing performance under differential pressure and relative movement.
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Protect bearing components and support the operational stability of the drive system.
TBM main bearing sealing greases are generally formulated to provide suitable adhesion, resistance to washout, and a durable protective barrier within the sealing system.
Key technical factors when selecting TBM main bearing lubricating and sealing greases
In mechanized tunnelling, effective main bearing lubrication and sealing depend not only on material properties but also on operating conditions, equipment design, and grease delivery methods. Therefore, selecting suitable TBM lubricating grease and specialized main bearing sealing materials requires a comprehensive assessment of the actual technical requirements of each system.
1. Load-carrying capacity and wear protection
During tunnel excavation, variations in thrust force, cutterhead torque, and rotational speed can generate complex loading conditions within the main bearing assembly.
In particular, when a TBM operates under heavy or continuously fluctuating loads, protecting bearing contact surfaces becomes increasingly important.
For grease-lubricated systems, the selected material should provide suitable load-carrying capacity, friction reduction, and anti-wear performance.
Extreme Pressure (EP) and Anti-Wear (AW) additive systems can help maintain protection of bearing contact surfaces under demanding operating conditions.
2. Washout resistance and protection against contaminants
In TBM tunnelling environments, groundwater pressure, slurry, soil, and abrasive fine particles can present significant challenges to main bearing sealing systems.
If water or excavated material penetrates the sealing interfaces, lubricant contamination may occur, increasing the risk of corrosion and mechanical wear.
Therefore, TBM main bearing sealing grease should provide appropriate water resistance, minimize washout, and maintain an effective protective barrier under the relevant operating pressures.
These properties are important for helping prevent the ingress of external contaminants and protecting the bearing assembly.
3. Adhesion and material stability
During TBM operation, lubricating greases and sealing materials may be subjected to mechanical movement, shear forces, and fluctuations in temperature and pressure.
Suitable adhesion helps the material remain on the surfaces requiring protection, while mechanical stability supports the retention of its functional properties throughout operation.
If the material does not meet the required performance criteria, the grease may undergo changes in consistency, become unevenly distributed, or lose its ability to maintain a protective layer at the application point.
Therefore, rheological properties, mechanical stability, and the ability to remain in position should be evaluated against actual operating conditions.
4. Pumpability and grease distribution
For lubrication and sealing systems equipped with automatic grease delivery units, pumpability is a critical technical consideration. The material must have suitable rheological characteristics to be transported through pipelines, distribution valves, and grease delivery points according to the system design.
Grease with excessively high consistency, or grease unsuitable for the operating temperature, may increase pumping resistance and impair distribution performance. In addition to material characteristics, grease flow rate, delivery pressure, and distribution uniformity must also be controlled.
Even when a suitable product is selected, insufficient or improperly controlled grease supply can compromise lubrication and sealing performance. Consequently, material selection must be aligned with the operating capabilities of the grease delivery system and the parameters specified by the TBM manufacturer.
5. Equipment compatibility and maintenance requirements
Each tunnel boring machine has its own main bearing configuration, sealing design, grease delivery system, and operating conditions. The selected material must therefore be compatible with the relevant components, particularly seals, elastomeric materials, and distribution systems.
Using incompatible greases or mixing materials without prior verification may alter their functional properties and compromise equipment protection. Furthermore, proactive maintenance and condition monitoring are particularly important for critical mechanical components with limited accessibility and repair options, such as TBM main bearings. Monitoring grease delivery pressure, consumption rates, equipment condition, and any signs of abnormal operation should be performed in accordance with the machine manufacturer’s recommendations.
Overall, effective TBM main bearing lubrication and sealing require an integrated approach combining specialized materials, system design, operating conditions, and maintenance procedures. Selecting the right solution not only helps protect critical mechanical components but also supports the continuity and efficiency of tunnelling operations.
Selecting TBM main bearing lubrication and sealing solutions based on project requirements
To identify suitable lubrication and sealing solutions for the specific requirements of each tunnelling project, several additional factors should be considered.
1. Identify technical requirements and application scope
The first step is to clearly define the intended function of the material within the TBM system. This may include lubricating load-bearing components, protecting the main bearing sealing system, or serving other specialized mechanical applications.
Accurately identifying the application requirements from the outset helps guide the selection of the appropriate product category and prevents materials from being used outside their intended application scope.
2. Review technical documentation and application conditions
In addition to the product Technical Data Sheet (TDS), material evaluation should consider equipment documentation, project technical specifications, and relevant test data. For specialized applications, additional assessments or appropriate testing may be required before finalizing the material selection. This is particularly important when considering replacement materials for an existing operating system.
3. Collaborate with specialized solution providers
For TBM systems with demanding technical requirements, collaboration among contractors, operating teams, equipment manufacturers, and specialized material suppliers can support a more effective evaluation and selection process. Early technical coordination helps define application requirements, clarify operating conditions, and establish an appropriate material supply strategy aligned with the construction schedule.
Selecting the right solution involves more than identifying a product that meets technical specifications. It also requires ensuring that the material is applied for its intended purpose, within the correct system, and under conditions compatible with the project’s actual requirements.
MC Underground – Advanced TBM main bearing lubrication and sealing solutions from Germany
MC Underground (MCU) is part of the MC-Bauchemie Group, a global leader in construction chemicals with more than 60 years of experience, operating in over 50 countries and employing more than 3,500 people worldwide.
Focused on delivering specialised chemical systems and technologies tailored to the specific requirements of tunnelling and mining projects, MCU has developed a comprehensive portfolio of materials supporting various stages of TBM construction, including dedicated main bearing lubrication and sealing grease systems.
1. MC-Montan Support MB L1 – Multipurpose EP2 grease for TBM tunnelling machines
- Excellent lubricating properties and pumpability.
- Excellent sliding properties.
- Ensures material consistency.
View product: MC-Montan Support MB L1
2. MC-Montan Support MB L11 – Bio-based EP2 lubricating grease for TBM tunnelling machines
- Excellent lubricating properties and pumpability.
- High biodegradability.
- Based on renewable raw materials.
- Good water washout resistance.
- Good adhesion to metal surfaces.
View product: MC-Montan Support MB L11
3. MC-Montan Support MB S1 – Main bearing sealing grease for TBM tunnelling machines
- Excellent lubricating properties and pumpability.
- Excellent sliding properties.
- Good adhesion to metal surfaces.
View product: MC-Montan Support MB S1
4. Tailored solutions for individual project requirements
For TBM tunnelling, MCU offers a comprehensive portfolio of specialised chemical technologies and solutions, including:
- Soil Conditioning & Stabilisation
- Tail Sealants
- Annulus Backfill Grouting Systems
- Main Bearing Lubrication & Sealing Greases
- Admixtures for Precast Tunnel Lining Segments
- Specialised Injection Systems
What distinguishes MCU’s approach is not simply its product portfolio, but the integration of chemical technology with in-depth knowledge of ground conditions, TBM equipment and construction processes. This enables solutions to be selected and applied according to specific project requirements, rather than relying on a single standard approach for all tunnelling conditions.
With global technical expertise, practical project experience, and a comprehensive systems-based approach, MC Underground delivers reliable and effective solutions tailored to individual project requirements and the demanding conditions of underground construction worldwide.
Khám phá hệ giải pháp hóa chất & công nghệ TBM từ MC Underground
