Hoist Types: Trolley Hoist for Single Girder vs Double Girder Overhead Cranes

Overhead cranes are essential lifting equipment in modern industrial operations, ranging from manufacturing plants to warehouses, steel mills, and construction sites. One of the most critical components of an overhead crane is the hoist system. The hoist not only determines the lifting capacity of the crane but also influences efficiency, safety, and versatility. Among various hoist types, trolley hoists play a central role in both single girder and double girder overhead cranes. Understanding their differences, applications, and technical considerations is essential for selecting the right crane for specific industrial needs.

Understanding Trolley Hoists

A trolley hoist is the mechanism that moves the crane hook horizontally along the bridge of an overhead crane. It consists of a motorized trolley, the hoist unit, and the hook assembly. The hoist can lift, lower, and position heavy loads with precision. Depending on the crane design, the trolley hoist is mounted on either a single girder or double girder bridge crane.

The choice of trolley hoist impacts the crane’s lifting capacity, travel speed, maintenance requirements, and overall cost. Before diving into specific comparisons, it’s important to understand the basic crane types:

• Single Girder Overhead Crane: This crane has one main bridge beam (girder) running between the runway rails. The trolley hoist travels along this single girder. Single girder cranes are generally simpler, lighter, and cost-effective.

• Double Girder Overhead Crane: This crane uses two parallel girders to support the trolley hoist, which runs on rails mounted on top of the girders. Double girder cranes provide higher lifting capacities, longer spans, and greater structural stability.

Trolley Hoists in Single Girder Cranes

Single girder overhead cranes typically use underslung trolley hoists, which are mounted beneath the girder. The hoist travels along the bottom flange of the girder, keeping the load close to the beam. This configuration has several advantages:

1. Cost Efficiency: Single girder overhead cranes use less material and simpler hoist systems, making them more economical.

2. Compact Design: The underslung trolley allows for a lower headroom requirement, which is advantageous in factories with limited ceiling height.

3. Ease of Installation: With only one girder, the crane structure is lighter and easier to install, reducing installation time and cost.

4. Flexibility: Single girder cranes are suitable for moderate lifting capacities, generally up to 20 tons, making them ideal for light to medium-duty applications.

However, there are some limitations:

• Limited Lifting Capacity: Because the hoist runs on a single beam, it cannot handle extremely heavy loads.

• Shorter Lifespan for Hoist: The underslung configuration may cause more stress on the hoist components over time.

• Limited Span: Single girder cranes typically have a shorter maximum span compared to double girder cranes.

Applications of single girder trolley hoists include small workshops, warehouses, assembly lines, and maintenance operations. Industries that do not require extremely high lifting capacities often benefit from the cost savings and simpler design of single girder eot cranes.

Trolley Hoists in Double Girder Cranes

Double girder cranes use top-running or above-girder trolley hoists, which travel along rails mounted on the top of the two bridge girders. This design allows for heavier lifting capacities and longer spans. Key advantages include:

1. High Lifting Capacity: Double girder cranes can handle loads from 20 tons up to hundreds of tons, making them suitable for steel mills, shipyards, and heavy machinery manufacturing.

2. Longer Span Capability: With two girders, the bridge can span greater distances without compromising structural integrity.

3. Durability: The top-running trolley distributes the load more evenly across the structure, reducing wear and extending the crane’s service life.

4. Flexible Hoist Options: Double girder cranes can accommodate more advanced hoist systems, including electric wire rope hoists, heavy-duty chain hoists, and specialized lifting devices like spreader beams.

5. Enhanced Safety: The increased stability of the double girder design reduces sway and provides safer operation under heavy loads.

However, double girder cranes are more expensive due to the additional material, labor, and more complex hoist systems. They also require higher headroom, which may not be feasible in factories with limited vertical space.

Technical Comparison: Single vs Double Girder Trolley Hoists

The choice between single and double girder cranes depends heavily on operational needs. Single girder cranes are ideal for facilities with limited lifting demands and tight budgets. Double girder cranes excel in heavy-duty applications, long spans, and industrial environments where stability and durability are critical.

Key Considerations When Choosing Trolley Hoists

When selecting a trolley hoist for either single or double girder cranes, several factors must be considered:

1. Load Requirements: Determine the maximum load to be lifted and the frequency of lifting operations.

2. Crane Span and Headroom: Ensure the crane design fits the physical constraints of the facility.

3. Duty Cycle: Industrial cranes with high lifting frequency require more robust hoist mechanisms.

4. Operational Environment: Consider temperature, humidity, dust, and other environmental factors that may impact hoist performance.

5. Budget Constraints: Balance initial investment with long-term operating costs, including maintenance.

6. Future Expansion: Consider potential future load increases or changes in production requirements that may necessitate higher capacity heavy duty overhead cranes.

Applications of Trolley Hoists in Industry

• Single Girder Hoists: Small workshops, automotive assembly, warehouse material handling, light manufacturing.

• Double Girder Hoists: Steel production, shipbuilding, power plants, precast concrete plants, heavy machinery fabrication, container handling in ports.

By understanding the specific lifting and operational requirements, facility managers and engineers can make informed decisions on the hoist type that best meets their needs.

Conclusion

Trolley hoists are fundamental to the functionality of overhead cranes, and their configuration – single girder versus double girder – significantly affects performance, cost, and operational efficiency. Single girder cranes offer simplicity, compactness, and cost-effectiveness for light to medium-duty operations, while double girder cranes provide superior lifting capacity, stability, and adaptability for heavy-duty industrial applications.

Selecting the right trolley hoist involves a careful evaluation of lifting capacity, span, duty cycle, and environmental considerations. Ultimately, choosing the optimal crane and hoist combination ensures safe, efficient, and reliable material handling, supporting productivity and operational success in a wide range of industries.