Analysis of Transmission Systems in Field Bridges (RTG & RMG)
Rubber-tired gantry cranes (RTGs) and rail-mounted gantry cranes (RMGs) are the backbone of container logistics at terminals such as Felixstowe and the Port of London. Unlike quay cranes (STSs), RTGs rely on pneumatic tires for their travel mechanism, which presents complex kinematic challenges that standard off-the-shelf drive shafts often cannot address.
The Kinematics of RTG Gantry Travel & Steering
The RTG operates by shuttling through stack blocks, a task that requires not just linear motion but complex maneuvering capabilities, including 90-degree steering for lane changing and, in some advanced models, spin-turn capabilities. This mobility imposes specific stress vectors on the driveline.
- Drive Architecture: A typical UK-spec RTG features an 8-wheel or 16-wheel structure. The electric motors are mounted either vertically or horizontally on the bogie frame, driving the wheel hubs through heavy-duty reduction gearboxes.
- The Steering Paradox: When an RTG executes a 90-degree turn, the wheel bogie rotates around a vertical axis. If the drive motor is fixed to the sill beam while the wheel rotates, the connecting drive shaft must accommodate extreme angular displacement.Engineering Solution: Modern designs favored by OEMs (and supported by our retrofit program) integrate the motor and gearbox directly onto the bogie, rotating in unison with the wheel. However, a short coupled arbore cardanic is still essential between the motor output and gearbox input to isolate vibration and correct inevitable misalignment.
- Suspension Compensation & Tyre Deflection: Pneumatic tyres compress under the variable load of 40ft containers. Furthermore, uneven ground conditions in older yards (common in legacy UK ports) cause the bogie to pitch. The drive shaft connecting the motor to the wheel hub must possess sufficient telescopic stroke (plunge) and articulation capabilities—typically maintaining efficiency at angles between 5° and 15°—to absorb these road-induced excitations without transmitting shock loads to the gearbox bearings.
Diesel Genset Connection: Torsional Vibration Damping
Most UK tire-mounted steam generator sets (RTGs) use diesel generator sets (Gensets) as their main or auxiliary power source. If poorly designed, the connection between the diesel engine flywheel and the alternator can become a critical point of failure.
Provocare: Uneven torque output from the diesel engine generates periodic torsional vibrations. A rigid connection here would have disastrous consequences. The drive shaft must act as a torsional damper.
Soluția noastră: We employ a two-stage damping system. On the engine side, a highly flexible coupling (compliant with Centa Flex standards) absorbs ignition frequency spikes. This coupling connects to a short universal joint leading to the alternator. For space-constrained applications, we offer shafts with internal rubber elements specially tuned to suppress harmonics that can cause fatigue in the alternator bearings.
👷 Engineer’s Log: The Felixstowe Salt Spray Issue
Data: November 12, 2024
Locaţie: Terminal 2, Suffolk
Problemă: A fleet of 12 RTGs experienced premature spline seizure on the gantry travel shafts. Despite regular greasing, the North Sea salt spray had penetrated the standard seals, causing corrosion welding of the slip assembly.
Analiză: The OEM shafts utilized a standard metal-on-metal spline with a felt seal, which is inadequate for the high-salinity humidity of East Anglia winters.
Rectification: We replaced the fleet’s existing shafts with marine-grade shafts. These shafts feature Rilsan® coated splines (reducing friction and preventing oxidation) and a reverse sliding yoke design to prevent water accumulation. We also upgraded the seals to double-lip Viton seals. Six months after installation, maintenance reports showed no seizures and a 40% reduction in vibration levels.
Technical Specification Matrix: Port Machinery Series
The following data represents our standard production capabilities for RTG/RMG applications. Custom engineering is available for non-standard bogie designs.
| ID-ul parametrului | Specificații tehnice | Valoare / Standard |
|---|---|---|
| 01 | Cuplu nominal (Tn) | 2,500 Nm – 85,000 Nm |
| 02 | Cuplu de oboseală (Tfat) | 1,5 x Tn |
| 03 | Unghiul maxim de articulație | 25° (Short Duration), 15° (Continuous) |
| 04 | Intervalul diametrului flanșei | 120mm – 435mm |
| 05 | Flange Connection Standard | DIN 15451 / SAE 1900 / KV / XS |
| 06 | Material spline | 34CrNiMo6 + Rilsan Coating |
| 07 | Materialul tubului | Oțel Domex de înaltă rezistență |
| 08 | Cross Kit (Spider) Material | 20CrMnTi (Carburized 60-62 HRC) |
| 09 | Bearing Life (B10) | > 5,000 Operational Hours (Heavy Duty Cycle) |
| 10 | Telescopic Stroke (Plunge) | +80mm / -40mm (Standard L=800mm) |
| 11 | Grad de echilibrare | G6.3 @ 2000 RPM (ISO 1940-1) |
| 12 | Temperatura de funcționare | -30°C până la +80°C |
| 13 | Specificații de vopsea | C5-M Marine Grade (3 Layers Epoxy) |
| 14 | Tipul de etanșare | Double-Lip Viton (Salt Spray Resistant) |
| 15 | Punct de lubrifiere | Centralized Nipple (Spider) + Spline |
| 16 | Rigiditate torsională | 180 – 450 kNm/rad |
| 17 | Viteză critică | Dependent on Length (Calculated per order) |
| 18 | Axial Force under Torque | < 12% of Transmitted Force |
| 19 | Diametrul tubului | 76mm – 180mm |
| 20 | Grosimea peretelui tubului | 4mm – 12mm Seamless |
| 21 | Materialul jugului | Oțel forjat 42CrMo4 |
| 22 | Retaining Ring Standard | DIN 471 / DIN 472 |
| 23 | Hardware Grade | 10.9 or 12.9 Dacromet Coated Bolts |
| 24 | Ciclul de întreținere | 500 Hours (Grease) / 2000 Hours (Visual) |
| 25 | Garanție | 24 Months or 4,000 Working Hours |
| 26 | Certificare | UKCA, CE, DNV-GL (Optional) |
| 27 | Mass (Weight) | 18kg – 250kg |
| 28 | Moment de inerție | 0.02 – 1.5 kg·m² |
(Disclaimer: All manufacturer names, symbols, and descriptions are used for reference purposes only and it is not implied that any part listed is the product of these manufacturers. UK pto-drive-shafts.com Co.,Ltd and UK PTO-DRIVE-SHAFTS are independent manufacturers.)
Operational Resilience in British Conditions
The UK’s maritime environment poses unique challenges. From the high humidity of the Solent to the freezing winds of the Scottish east coast ports, material selection is not a luxury—it is a necessity for compliance with PUWER (Provision and Use of Work Equipment Regulations 1998).
Southampton & Solent
Provocare: High salinity and rapid temperature cycles.
Soluţie: We supply the local maintenance teams with “sealed-for-life” center bearings for RMG cranes to reduce the need for technicians to access hazardous areas during wet conditions.
Liverpool & Mersey
Provocare: Heavy wind loads affecting gantry stability.
Soluţie: Our high-angle shafts allow for greater chassis flex without binding, ensuring the cranes can operate safely in wind speeds up to 20m/s.
Scottish Ports (Aberdeen/Grangemouth)
Provocare: North Sea Oil & Gas support heavy loads.
Soluţie: We provide reinforced “Super-Short” designs for heavy-lift mobile harbor cranes used in offshore module loading.
Integrated Power Transmission: The Gearbox Nexus
A drive shaft is only as effective as the gearbox it powers. In the ecosystem of an RTG or RMG, the interaction between the high-speed input shaft and the reduction gearbox is where efficiency is defined. We manufacture and supply a comprehensive range of industrial gearboxes designed to pair perfectly with our arbore cardanics.
Planetary Wheel Drives for Gantry Travel
For the gantry travel mechanism, we recommend our EP-Planetary Series. These compact, high-torque-density units are designed to fit within the wheel hub assembly.
Why Match Gearbox and Shaft?
Mismatched stiffness between the driveshaft and the gearbox input pinion can lead to resonance. Our EP-Planetary gearboxes feature a reinforced input bearing housing specifically calculated to handle the radial loads and bending moments exerted by the cardan shaft during high-angle articulation (e.g., during steering maneuvers).
- Capacitate de cuplu: Up to 120,000 Nm.
- Ratio: 40:1 to 150:1 (Multi-stage planetary).
- Brake: Integrated hydraulic or electromagnetic fail-safe parking brakes.
Helical-Bevel Units for Hoist Mechanisms
For the main hoist, reliability is paramount. Our K-series spiral bevel gearboxes achieve an efficiency of up to 96%, effectively reducing the heat load on the electrical compartment. Combined with our balanced high-speed composite drive shaft, noise levels in the operator’s compartment are significantly reduced, meeting the noise exposure limits set by the UK Health and Safety Executive (HSE).
Customized Lubrication for the UK Climate
Standard gearboxes often ship with mineral oil suitable for Central Europe. For our UK clients, we pre-fill gearboxes with synthetic polyalphaolefin (PAO) based lubricants with a wider viscosity index. This ensures that a crane in Grangemouth can start up instantly at -5°C on a Monday morning without inducing high starting torque on the drive shaft and motor.
The “Complete Driveline” Warranty
When you source both the Cardan Shaft and the Gearbox from us, we bridge the warranty gap. Usually, a shaft failure blamed on the gearbox (or vice versa) leads to supplier disputes. By integrating the supply chain, we offer a 3-Year System Warranty covering the interface between the flange and the input shaft.
See our full catalog for compatible replacements for Brevini, Bonfiglioli, and Reggiana Riduttori planetary drives. (Names for reference only).
Strategic Spares & Consumables
To maintain uptime, every port maintenance workshop should stock critical interface components. We supply:
Universal Joint Kits (U-Joints)
Featuring our “Triple-Guard” seal technology. Available in sizes from 57mm to 200mm cup diameter.
Flange Yokes (Quick Release)
For rapid change-outs during short maintenance windows (e.g., lunch breaks). Cross-serrated flanges for high-torque friction grip.
Center Support Bearings
Self-aligning bearings with varying rubber hardness (Shore A 45-70) to tune vibration isolation frequencies.
