In the realm of large-scale steel structure erection, precast concrete handling, and heavy machinery installation, efficient and safe material handling is paramount to project timelines and worksite safety. The Dongqi 75/20t Double Girder Overhead Crane (QD Type) is engineered specifically to meet the demanding challenges of such heavy-load construction environments. Integrating a robust structure, powerful lifting capacity, and flexible operation, this crane is designed to serve as a backbone piece of equipment in modern construction sites, precast yards, and industrial assembly halls.

Core Structure & Design Advantages

The fundamental strength of this model lies in its double girder bridge configuration. Compared to single girder designs, the two parallel main girders deliver superior structural integrity and rigidity. This design offers several direct benefits:

• Enhanced Stability & Safety: The double girder structure effectively distributes stress and minimizes deflection under full 75-ton load, ensuring smooth operation and significantly reducing load sway. This provides a stable foundation for precise positioning and installation tasks.
• Greater Hook Height: The hoist trolley travels on rails mounted on top of the main girders, optimally utilizing the space above the bridge. This results in a greater useful lifting height within the same building headroom, facilitating the handling of tall components.
• Superior Adaptability: The robust double girder platform reliably supports the heavy-duty main and auxiliary hoist system. It is also well-suited for large spans (customizable beyond 30 meters), ensuring comprehensive coverage of wide work areas.

Powerful Main & Auxiliary Hoist System

The “75/20t” capacity designation highlights the versatility of this crane for complex lifting operations.

• Main Hoist (75t): Undertakes the core heavy-lifting tasks, such as moving and installing large steel roof trusses, heavy columns, massive precast concrete beams, or heavy construction modules.
• Auxiliary Hoist (20t): Serving as an efficient complement to the main hoist, the auxiliary hoist typically features higher lifting speeds. It is used for frequent handling of lighter materials or works in tandem with the main hook for component turning and precise positioning. This configuration significantly boosts overall productivity, combining “heavy-duty precision lifting” with “lighter, faster material flow.”

Performance Features Tailored for Construction

1. Smooth Travel Mechanisms: The bridge and trolley travel drives often utilize integrated “three-in-one” units (combining motor, reducer, and brake) paired with frequency control systems. This ensures smooth acceleration, stepless speed variation, and accurate stopping, effectively controlling load swing for precise placement.
2. Comprehensive Safety Assurance: Safety systems are prioritized in the design. Standard features typically include:
   • Independent overload limiters for both the main and auxiliary hoists.
   • Hoisting limit switches and travel limit switches.
   • Emergency stop buttons.
   • End buffer stops and anti-collision systems (optional).
   • Key electrical components with suitable ingress protection ratings for dusty site conditions.
3. Flexible Control Options: Control modes can be selected based on site conditions and operator preference, including remote radio control, cabin control, or pendant station. Wireless remote control, in particular, offers the operator optimal visibility and mobility for safer and more intuitive operation in complex environments.
4. Robust Construction & Durability: Main structural components are manufactured from high-quality steel, employing rigorous welding procedures and stress relief treatment. Surfaces are shot-blasted and coated with high-performance anti-corrosion paint to withstand the challenging conditions of construction sites.

Typical Technical Parameters (Reference)

Item	Specification
Rated Capacity	Main Hoist: 75 Metric Tons
Duty Class	A5 (Heavy Duty) or A6 (Very Heavy Duty) as per FEM/ISO standards
Span (S)	Customizable to actual building dimensions (e.g., 22.5m, 25.5m, 28.5m, 31.5m, etc.)
Lifting Height	Customizable for Main/Auxiliary Hoist (Aux. hook is usually higher)
Hoisting Speed	Main Hoist: ~1.5-3.0 m/min
Bridge Travel Speed	~20-40 m/min (VF controlled)
Trolley Travel Speed	~10-20 m/min (VF controlled)
Power Supply	3-Phase, 380V/400V/415V, 50/60Hz

Primary Application Scenarios

• Steel Structure Erection: Handling and positioning columns, beams, and trusses for factories, power plants, stadiums, and other large structures.
• Precast Concrete Installation: Transporting and installing large precast wall panels, floor slabs, bridge segments, and utility tunnels.
• Heavy Machinery Installation: Positioning large mechanical equipment, generators, pressure vessels, etc., within buildings or industrial plants.
• Construction Material Yards: Systematic stacking and transfer of heavy materials in precast yards or on-site storage areas.
• Major Infrastructure Projects: Suitable for heavy-duty applications in bridge precast yards, port machinery assembly workshops, and similar environments.

Conclusion

The Dongqi 75/20t Double Girder Overhead Crane is more than just lifting equipment; it is an integrated solution designed to enhance the lifting capabilities of major construction projects. We understand what equipment reliability, safety, and efficiency mean for your operations. Therefore, we focus on providing professional consultation, customized design, meticulous manufacturing, and comprehensive after-sales support at every stage.

If you are seeking a reliable lifting solution for your next significant construction project, the technical team at Dongqi Crane is ready to provide detailed consultation and project-specific planning to ensure the equipment you receive is perfectly matched to your unique requirements and challenges.