Double girder overhead cranes are among the most robust and widely used lifting solutions in heavy industry. Their strength, durability, and ability to handle large capacities make them indispensable for sectors such as steel production, power plants, shipyards, mining, and logistics. Behind every double girder overhead crane is a careful process of engineering design and precise manufacturing, ensuring the crane meets both functional requirements and international safety standards.
In this article, we will explore in detail how double girder overhead cranes are designed and manufactured, from the initial planning to final assembly and testing.
1. Understanding the Role of Double Girder Overhead Cranes
A double girder overhead crane is characterized by two parallel girders that span across the crane runway. The hoist and trolley are mounted on rails above the girders, allowing for higher lifting heights compared to single girder designs. This configuration provides enhanced stability, larger load capacity, and greater flexibility for heavy-duty applications.Because these cranes handle critical tasks—such as lifting turbines, molten metal, or ship components—their design and manufacturing process must meet stringent reliability and safety standards.
2. The Design Process
a) Requirement Analysis
The design process begins with analyzing customer requirements. Engineers work closely with clients to understand:
- Lifting capacity (commonly 10 tons to over 500 tons)
- Span length (distance between crane runways)
- Lifting height (clearance above the floor)
- Work duty classification (light, medium, heavy, or extra-heavy duty based on usage frequency)
- Environment conditions (temperature, humidity, explosion risk, or corrosive atmosphere)
This information defines the foundation for the crane’s structural and mechanical design.
b) Structural Design
The crane girders, end trucks, and supporting frame are designed with advanced software (like CAD and FEA analysis). Engineers evaluate load distribution, stress points, and deflection limits. The design must balance strength, rigidity, and weight efficiency.
- Girders: Double girders are typically box-shaped or welded plate girders to provide higher load-bearing capacity.
- End Carriages: These connect the girders to the wheels and runway rails, ensuring smooth travel.
- Runway Beams: Designed to support the entire crane, these must be matched with the crane’s load and frequency of operation.
c) Mechanical and Electrical System Design
- Hoisting Mechanism: The hoist and trolley design includes drum, rope, gearbox, and motor selection.
- Travel Mechanism: Motors and gearboxes for crane and trolley movement are chosen for energy efficiency and durability.
- Control System: Modern cranes use advanced PLC, variable frequency drives (VFD), and sometimes remote or automated controls for precision.
- Safety Features: Limit switches, overload sensors, emergency brakes, and anti-sway systems are integrated.
d) Compliance and Standards
Designs must comply with international standards such as FEM, ISO, CMAA, and DIN. These regulations guide aspects like load ratings, fatigue resistance, and safety protocols.
3. The Manufacturing Process
Once the design is approved, manufacturing begins. This process combines heavy steel fabrication, precision machining, and quality control.
a) Material Procurement
High-strength steel plates and structural sections are sourced, often standardized according to international material grades. Special coatings or alloys may be used for environments with high corrosion risk.
b) Girder Fabrication
- Cutting and Shaping: Steel plates are cut using CNC plasma or laser cutting machines.
- Welding: Automatic submerged arc welding (SAW) is commonly used to produce strong and uniform welds for box girders.
- Stress Relief: After welding, components may undergo stress-relief treatment to eliminate internal stresses.
- Machining: Key areas, such as rail seats and connections, are machined precisely for proper alignment.
c) End Carriage and Trolley Fabrication
The end trucks are fabricated from steel sections and fitted with wheels, bearings, and drive mechanisms. The trolley frame is also assembled and prepared to house the hoist.
d) Hoisting Mechanism Manufacturing
The hoisting unit is manufactured separately, consisting of:
- Drum and Wire Rope: Designed to handle the rated load without excessive wear.
- Gearbox: Precision-engineered gears reduce speed and multiply torque.
- Motor: Electric motors are tested for performance, often paired with VFDs.
- Braking System: Electro-hydraulic or electromagnetic brakes ensure reliable stopping.
e) Electrical Assembly
Electrical panels, control wiring, and sensors are installed. Modern cranes often feature smart monitoring systems that provide real-time load data and diagnostic alerts.
f) Surface Treatment
Steel structures are sandblasted, primed, and painted to resist corrosion. For offshore or chemical environments, special epoxy or galvanization treatments may be applied.
4. Assembly and Testing
a) Workshop Assembly
The crane components are pre-assembled in the double girder overhead crane manufacturer workshop to ensure proper alignment. This includes mounting girders on end trucks, installing the trolley, and testing the hoist.
b) Load Testing
Every crane undergoes rigorous testing before delivery:
- No-load Test: Verifies smooth operation without load.
- Static Load Test: Crane holds a load 1.25 times its rated capacity to check structural integrity.
- Dynamic Load Test: Crane lifts and moves a load 1.1 times its capacity to ensure mechanical systems work under real conditions.
c) Disassembly for Shipping
After testing, the crane is disassembled into transportable parts and shipped to the installation site.
5. Installation and Commissioning
At the customer’s facility, the crane is reassembled under the guidance of the manufacturer’s engineers. Runway alignment, electrical connections, and control calibration are finalized. Once installed, the crane undergoes another round of on-site testing before being handed over for use.
6. Continuous Innovation in Design and Manufacturing
Overhead crane manufacturers are constantly innovating to improve performance and efficiency:
- Lightweight but stronger materials reduce energy consumption.
- Intelligent monitoring systems provide predictive maintenance insights.
- Automation and remote operation enhance workplace safety.
- Green manufacturing practices reduce the environmental footprint.
These advancements ensure double girder overhead cranes remain competitive in a rapidly evolving industrial world.
Conclusion
Designing and manufacturing a double girder overhead crane is a complex but highly engineered process. From requirement analysis and structural design to precision manufacturing, rigorous testing, and final commissioning, each step ensures that the crane is reliable, safe, and efficient.
For industries that depend on heavy lifting, selecting an eot crane manufacturer with proven expertise in both design and production is essential. By combining advanced technology, strict quality standards, and customer-specific solutions, double girder overhead cranes continue to support the backbone of global industry.
