During the tunneling process of a shield machine, the cutter head requires a continuous supply of various media-such as slurry, foam, hydraulic oil, and sealing grease-to maintain flushing, cooling, lubrication, and sealing functions. Given that the cutter head is constantly rotating through 360 degrees, how can these diverse media be reliably conveyed from the stationary end to the rotating end? The answer lies in the large-bore, multi-passage rotary joint.
I. Structural Positioning: The Critical Connection Component Behind the Cutter Head
This rotary joint is typically installed at the center or rear of the main drive gearbox; its rotating section is rigidly coupled to the cutter head drive flange. As the cutter head rotates, the independent internal passages within the joint rotate synchronously, conveying different media separately without cross-contamination or leakage. The number of passages can be customized to meet the specific functional requirements of the shield machine, with 6 to 12 passages being the most common configuration.
II. Large Bore: Prioritizing Flow Rate Over "Speed"
For large-scale shield machines (e.g., those with diameters exceeding 12 meters), the volume of media required for cutter head flushing and cooling is substantial. The primary objective of the large-bore design-where the central bore diameter can reach DN300 or even larger-is to minimize flow resistance and ensure an adequate flow rate. This guarantees that slurry and foam are delivered promptly to the cutter head's cutting face, thereby preventing the formation of mud cakes and averting cutter overheating.
III. Multi-Segment Design: Driven by Engineering Constraints, Enabling Maintenance Convenience
Rotary joints used in shield machines feature an elongated profile (reaching lengths of 3 to 5 meters); consequently, a single-piece, monolithic structure presents practical challenges regarding machining equipment travel limits and oversized transport restrictions. Therefore, engineering practice has widely adopted a multi-segment, modular design approach: the entire assembly is divided into several independent segments, each housing embedded sealing components and bearing supports. These segments are then joined together using precision spigot-and-recess locating mechanisms and flange connections.
The core advantages conferred by this design include:
- Feasibility in Machining and Transport: The length of each individual segment is kept within the operational limits of standard machine tools and conventional transport dimensions.
- On-Site Serviceability: In the event of a seal failure or bearing damage in a specific segment, only that particular segment needs to be dismantled and replaced; there is no need to hoist and remove the entire rotary joint assembly, thereby significantly reducing downtime.
- Flexible Expandability: When the functional requirements necessitate an increase or decrease in the number of passages, the configuration can be adjusted simply by modifying the combination of segments.
Conclusion
The integration of large-bore, multi-passage rotary joints with a multi-segment design is both an inevitable outcome of the increasing scale and complexity of shield tunneling machines, and a successful response by the rotary joint industry to the demands of extreme operating conditions. For equipment manufacturers, understanding the technical logic behind this design holds far greater value than merely knowing that such a product exists.