Design Scheme for Hoisting Mechanism of 900t Gantry Crane

I. Design Overview

The 900t gantry crane is key equipment for beam prefabrication plants in railway passenger dedicated lines, primarily used for lifting, transporting, and loading 20m, 24m, and 32m double-track full-span box girders. This design addresses the specific requirements of precast beam construction, integrating advanced crane technology from domestic and international sources to propose a complete solution for the hoisting mechanism.

Based on the application scenario, the 900t gantry crane can be categorized into two types: double-gantry structure and single-main-girder structure. The double-gantry structure facilitates longitudinal passage of beam transport vehicles without being constrained by their length during loading; whereas the single-main-girder structure utilizes a rigid leg and a flexible leg for support, featuring a compact design. This design references the MGHZ900t beam handler, which has a rated lifting capacity of 900t (excluding spreader self-weight), a total machine weight of 480t, an inner clear span of 40m, and a lifting height of 9.8m.

II. Hoisting Mechanism Composition and Working Principle

As the core system of the gantry crane, the hoisting mechanism mainly consists of the following key components:

1. Driving Device: Utilizes high-power motor sets to provide the power source for the hoisting mechanism. Based on the design experience of the MDGE900t beam handler, motor power needs to be determined according to the actual load calculation, typically requiring drive capability in the hundreds of kilowatts range.
2. Transmission Device: Includes components such as reducers and couplings. The reducer converts the high-speed rotation of the motor into low-speed, high-torque output suitable for the drum operation.
3. Winch System: Comprises the drum, wire rope, and pulley block. The drum diameter and rope capacity must be precisely calculated based on the lifting height and wire rope diameter.
4. Load Handling Device: Cranes of the 900t class typically use specialized spreaders; a balanced beam structure can ensure stability during box girder lifting.
5. Braking System: Equipped with a main brake and a safety brake to ensure reliable stopping and load holding of the hoisting mechanism.
6. Safety Devices: Include hoisting height limiters, overload limiters, and three-wrap protection, etc.

During operation, the motor drives the reducer via the coupling, the output shaft of the reducer drives the drum to rotate, and the lifting and lowering motion of the spreader is achieved through the wire rope and pulley block. The entire system employs closed-loop control, enabling positioning accuracy within millimeters.

III. Key Parameter Calculation and Selection

1. Motor Power Calculation

Motor power P can be calculated based on the hoisting weight, hoisting speed, and mechanism efficiency:

P = (Q × v) / (6120 × η)

Where:

• Q: Hoisting load (including spreader weight), taken as 950t (900t + 50t spreader)
• v: Hoisting speed, according to railway box girder installation requirements, typically 0.5-1 m/min
• η: Total mechanism efficiency, taken as 0.85

Calculating with a hoisting speed of 0.8 m/min:
P = (950 × 1000 × 0.8) / (6120 × 0.85) ≈ 146 kW

Considering starting inertia and other factors, a 2 × 160 kW motor set is actually selected.

2. Wire Rope Selection Calculation

The breaking force S of the wire rope shall satisfy:
S ≥ n × S_max

Where:

• n: Safety factor, taken as 6
• S_max: Maximum static working tension in the wire rope

Based on the pulley block multiplicity m=12, the tension in a single wire rope is:
S_max = (950 × 1000 × 9.8) / (2 × 12 × 1000) ≈ 388 kN

Therefore, the wire rope breaking force S ≥ 6 × 388 = 2328 kN

Select a 40mm diameter wire rope with a nominal tensile strength of 1870 MPa and an independent wire rope core.

3. Drum Design

Drum diameter D ≥ 20d = 20 × 40 = 800 mm, take D = 1000 mm

The drum length L depends on the wire rope working length and the number of winding layers. For a lifting height H=9.8m and pulley block multiplicity m=12:
Wire rope working length = m × H = 12 × 9.8 = 117.6 m
Considering safety wraps, etc., the total rope length is about 130 m.
Using a twin drum, the rope capacity per side is 65 m, wound in 2 layers:
L = 65 / (π × 1.0 × 2) ≈ 10.34 m
Take L = 11 m.

4. Reducer Selection

Total transmission ratio i of the hoisting mechanism:
i = (n_m × π × D) / (v × m)

Where:

• n_m: Motor rated speed, taken as 1500 rpm
• v: Hoisting speed, 0.8 m/min
• D: Drum diameter, 1.0 m
• m: Pulley block multiplicity, 12

i = (1500 × π × 1.0) / (0.8 × 12) ≈ 490

Select a two-stage planetary gear reducer with a transmission ratio of 500:1.

IV. Structural Design and Finite Element Analysis

1. Main Girder Structural Design

The main girder of the 900t gantry crane can adopt a double-main-girder or single-main-girder structure. Referencing the MGHZ900t beam handler, when using a single-main-girder design, the following must be met:

• Mid-span camber not less than 0.7L/1000 (L is the span)
• Maximum camber controlled within the middle L/10 region of the span.

Main girder cross-section dimensions are determined based on load calculations:

• Section height h ≈ (1/14~1/18)L, take h=3m (for a 40m span)
• Flange width b ≈ (1/50~1/60)h, take b=1.2m.

2. Leg Structure Design

A combination of rigid leg and flexible leg design is adopted:

• Rigid leg: Rigidly connected to the main girder, bearing most horizontal and vertical loads.
• Flexible leg: Allows free expansion and contraction of the main girder due to temperature changes.

The leg cross-section is typically designed as a box structure with high bending and torsional stiffness. Based on the experience of the MDGE900t beam handler, the leg height must accommodate the required lifting height of 9.8m.

3. Finite Element Analysis

Finite element software like ABAQUS is used to establish a detailed 3D model of the main girder, analyzing stress distribution and deformation under different load combinations. Main analysis conditions include:

1. Rated Load Condition: Main girder bear 900t uniform load.
2. Dynamic Load Condition: Considering a 1.1 dynamic load factor.
3. Wind Load Condition: Calculated according to the maximum wind pressure in working state.
4. Seismic Condition: Analyzed based on site seismic parameters.

The analysis results are used to optimize the main girder cross-section dimensions and stiffener layout, ensuring the maximum stress does not exceed the allowable value and deformation meets usage requirements.

V. Hydraulic and Control System Design

1. Hydraulic System

The main functions of the hoisting mechanism’s hydraulic system include:

• Lifting and steering of the gantry travel mechanism (enabling 90° steering).
• Leg leveling.
• Brake control.

The hydraulic system uses load-sensing variable pumps and proportional valves to match flow and pressure with the load, improving energy efficiency.

2. Electrical Control System

The control system adopts a PLC + frequency converter scheme to achieve the following functions:

• Hoisting mechanism speed regulation (0-100% stepless speed variation).
• Synchronous control (when dual motors are driving).
• Safety monitoring (load limiting, height limiting, wind speed monitoring, etc.).

Referencing the overall lifting construction method for the 900-ton gantry crane, the control system can achieve computer remote control and full-process program control with live monitoring.

VI. Safety Devices and Protective Measures

The hoisting mechanism of the 900t gantry crane must be equipped with comprehensive safety protection devices:

1. Overload Limiter: Automatically cuts off the hoisting power when the load exceeds 105% of the rated lifting capacity.
2. Hoisting Height Limiter: Prevents the spreader from topping out.
3. Three-Wrap Protection Device: Ensures at least three wraps of wire rope remain on the drum.
4. Emergency Stop Device: Quickly cuts off power in emergency situations.
5. Wind Speed Alarm: Issues an alarm when the wind speed exceeds the working limit.
6. Dual Braking System: Service brake + safety brake, ensuring braking reliability.

VII. Manufacturing and Installation Requirements

1. Manufacturing Requirements

• Welds of metal structures require ultrasonic testing, complying with JB/T10559 standard.
• Materials for main load-bearing components must have quality certificates and be re-inspected if necessary.
• All exposed machined surfaces must have anti-rust measures.

2. Installation Requirements

Referencing the overall lifting construction method for the 900-ton gantry crane, attention during installation is needed for:

1. Track installation accuracy: Track gauge deviation ≤ ±5mm, track straightness ≤ 2mm/m.
2. Structure assembly sequence: Legs first, then main girder, finally the hoisting mechanism.
3. Hydraulic system pipelines must be thoroughly cleaned before connection.
4. Electrical system wiring should meet lightning protection requirements (grounding resistance ≤ 4Ω).

VIII. Maintenance and Servicing

To ensure long-term reliable operation of the 900t gantry crane hoisting mechanism, a regular maintenance system should be established:

1. Daily Inspection: Wire rope wear, brake performance, structural deformation, etc.
2. Monthly Maintenance: Lubricate all rotating parts, check for hydraulic system leaks.
3. Annual Overhaul: Replace wearing parts, inspect metal structures for cracks, recalibrate safety devices.

Pay special attention to wire rope maintenance, regularly checking for broken wires, wear, and corrosion. The rope must be replaced immediately when the number of broken wires reaches the discard criteria.

IX. Design Innovations

This hoisting mechanism design for the 900t gantry crane features the following innovations:

1. Dual-Motor Synchronous Drive Technology: Uses a 2 × 160 kW motor set, achieving precise synchronous control via PLC.
2. Modular Design: The hoisting mechanism can be lifted as a whole, facilitating transport and on-site assembly.
3. Intelligent Monitoring System: Integrates a sensor network to monitor load, stress, vibration, and other parameters in real-time.
4. Energy-Saving Design: A regenerative braking system can convert lowering kinetic energy into electrical energy fed back to the grid.

X. Conclusion

This design scheme proposes a complete solution for the hoisting mechanism of the 900t gantry crane, specifically addressing the requirements of railway passenger dedicated line precast beam construction. Through precise parameter calculation, finite element structural analysis, and advanced control system design, the safety, reliability, and advancement of the hoisting mechanism are ensured. This design incorporates mature experience from domestic and international crane design and introduces several innovations, enabling it to meet the high standards required for large-scale lifting equipment in modern beam prefabrication plants.

In practical application, it is recommended to further optimize details based on specific construction conditions and strictly adhere to relevant standards for manufacturing, installation, and acceptance to ensure the equipment performance meets design expectations.