What is an Overhead Crane?

An overhead crane, also known as a bridge crane, is a type of material handling equipment used to lift, lower, and move heavy loads horizontally within a facility. It consists of a hoist, a bridge, and a runway system. The hoist is the lifting mechanism, while the bridge spans the width of the workspace and moves along the runway, which is typically mounted on the building’s structure or support columns.

Overhead cranes are available in various sizes, types, shapes, and configurations and come with a range of components and accessories. They are utilized for tasks such as loading and unloading, moving materials, lifting dies from stamping machines, and feeding raw materials.

Ⅱ. What Are The Types of Overhead Cranes?

Overhead cranes come in various types, each designed for specific applications and environments. Here are the most common types:

a. Single Girder Overhead Crane

Description: Features a single bridge girder supported by two end trucks. The hoist and trolley are mounted on the bottom flange of the girder.

Applications: Ideal for light to moderate lifting tasks in workshops, warehouses, and manufacturing facilities.

Advantages: Cost-effective, lightweight, and easy to install.

b. Double Girder Overhead Crane

Description: Consists of two bridge girders supported by end trucks. The hoist and trolley are mounted on a rail system between the girders.

Applications: Suitable for heavy-duty lifting in industries like steel, automotive, and aerospace.

Advantages: Higher lifting capacity, greater hook height, and better durability.

c. Gantry Crane

Description: Similar to an overhead crane but supported by legs that move on wheels or rails along the ground instead of being mounted on a building structure.

Applications: Commonly used in outdoor settings like shipyards, construction sites, and rail yards.

Advantages: Portability and flexibility for outdoor use.

d. Monorail Crane

Description: Features a single rail system with a hoist that moves along a fixed path.

Applications: Used in assembly lines, paint shops, and material handling systems.

Advantages: Ideal for repetitive tasks and linear movement.

e. Jib Crane

Description: Consists of a horizontal arm (jib) mounted to a wall or floor-mounted pillar. The hoist moves along the jib.

Applications: Suitable for small work areas like workshops and loading docks.

Advantages: Compact design and precise load positioning.

f. Top-Running vs. Under-Running Cranes

Top-Running: The crane moves on rails mounted on top of the runway beams. Offers higher lifting capacity and hook height.

Under-Running: The crane moves on rails suspended from the bottom flange of the runway beams. Ideal for facilities with limited headroom.

Ⅲ. How Are Overhead Cranes Used?

Transporting bulky, heavy, and cumbersome loads along the aisles and floor of a manufacturing facility can be both dangerous and time-consuming. Installing an overhead crane to utilize the factory's overhead space enhances efficiency, cost-effectiveness, and safety. It allows for easy lifting, lowering, and movement of loads through unused vertical space, saving both time and energy.

Specially trained operators use various control devices to manage the crane’s movements. When considering movement options, it’s crucial to assess the available space and the feasibility of installing an overhead crane.

1. Warehousing

The first industry that often requires an overhead crane is warehousing, where supplies, equipment, and materials are frequently moved, positioned, and prepared. A key advantage of using an overhead crane in warehousing is its ability to efficiently transport large items from storage to the shipping dock.

2. Assembly

Industries that assemble large equipment need a method for lifting and relocating incomplete assemblies during production. Forklifts, AGVs, and other material-handling equipment often fall short in terms of safety and efficiency, making an overhead crane essential. It facilitates the smooth movement of assemblies as a natural part of the production process.

3. Transportation

The parameters applicable to warehousing also apply to transportation, where heavy, bulky products must be loaded onto planes, trains, and trucks. Overhead cranes efficiently position large materials for transport, including in situations like overseas shipping, where they lower massive containers and goods into ship holds.

4. Equipment Repair

When the repair of a punch press or other factory equipment is required, overhead cranes assist in facilitating the repair by gradually moving and positioning pieces for easy access. Gantry and bridge cranes can remove heavy equipment from their permanent location to a repair shop and then return them. Overhead cranes make it easier to lift machines up and over other equipment to be placed at a repair station.

Ⅳ. How Do Overhead Cranes Work?

Overhead cranes operate using a combination of mechanical, electrical, and hydraulic systems. Here’s a step-by-step breakdown of how they work:

Power Supply: The crane is powered by electricity, typically through a conductor bar or festoon system.

Control System: Operators use a pendant control, remote control, or cabin to direct the crane’s movements.

Hoisting: The hoist, equipped with a hook or other lifting attachment, raises or lowers the load using a motorized drum and wire rope or chain.

Trolley Movement: The trolley moves the hoist horizontally along the bridge girder.

Bridge Travel: The entire bridge moves along the runway beams to transport the load across the workspace.

Load Handling: The crane positions the load precisely at the desired location.

Modern overhead cranes often feature advanced technologies like variable frequency drives (VFDs) for smooth operation, load sensors for safety, and automated controls for increased efficiency.

Ⅴ. Overhead Crane Construction

Choosing and constructing an overhead crane requires considering several factors beyond just the load or materials involved. Since overhead cranes are tailored to specific conditions and configurations, it is crucial to thoroughly understand how the crane will integrate into the operation and meet the operational needs.

It is extremely important to plan and prepare carefully for the installation of an overhead crane. Manufacturers work closely with their clients to ensure that what is planned and installed exactly meets the needs of the customer.

1. Span

The span is the distance between the runway rails, which is one of the more costly aspects of the construction process. A longer and wider span determines the amount of material required to construct the girders, which increases the cranes' weight and cost.

2. Load Capacity

The determination of a crane‘s capacity is the maximum load that may be applied to the crane under the required working conditions. When figuring the load capacity, the first condition is the size and weight of the material to be lifted. Once the load capacity is determined, the type of hook and hoist can be decided.

In cases where the crane will have a large span and capacity and must endure severe circumstances, a double girder design may be necessary. For extra strength, double girders are made of welded reinforced steel.

3. Runway

The installation of the runway can be a challenge depending on the type of structure where the overhead crane will be installed. This does not apply to gantry models that have supporting legs, while buildings have runways placed along the upper part of the walls. The first determination is the length of the runway, which determines the speed and movement of the trolley and hoist up and down the runway.

4. Building Structure

When a crane is being placed in a new building, the runways are planned as a part of the construction and are included in the blueprints. In this case, the contractor has to pay close attention to crane tolerances since they are more restrictive than typical construction codes.

Adding an overhead crane to an existing structure can be expensive since several steps have to be taken in the fabrication, design, and installation process. To ensure proper performance and safety, it is usually necessary to add extra support to the existing structure.

Ⅵ. Precautions for Operating Overhead Cranes

Operating an overhead crane requires skill, training, and adherence to safety protocols. Here are some essential precautions:

a. Proper Training

Ensure operators are trained and certified to use the specific type of crane. Provide refresher courses to keep skills up to date.

b. Pre-Operation Inspection

Check the crane for any signs of wear, damage, or malfunction. Inspect the hoist, wire rope, hooks, and controls before use.

c. Load Capacity

Never exceed the crane’s rated load capacity.

Use load charts to determine safe lifting limits.

d. Clear Communication

Use hand signals, radios, or other communication methods to coordinate with ground personnel.

Ensure everyone involved in the operation is aware of their roles.

e. Avoid Sudden Movements

Operate the crane smoothly to prevent swinging or dropping the load. Use VFDs for controlled acceleration and deceleration.

f. Maintain Clear Pathways

Ensure the workspace is free of obstacles and personnel during crane operation.

Use barriers or warning signs to keep unauthorized personnel away.

g. Regular Maintenance

Schedule routine maintenance to keep the crane in optimal condition. Replace worn or damaged parts promptly.

h. Emergency Procedures

Familiarize operators with emergency stop procedures. Conduct regular drills to prepare for potential accidents.

Ⅶ. Conclusion

Overhead cranes are vital tools in modern industry, offering unmatched efficiency and safety for heavy lifting tasks. By understanding the different types of cranes, their applications, and how they work, businesses can choose the right equipment for their needs. Additionally, adhering to safety precautions and proper maintenance practices ensures the longevity and safe operation of these powerful machines. Whether in a factory, warehouse, or construction site, overhead cranes continue to play a crucial role in driving productivity and innovation.