What is an Overhead Crane? 5 Factors to consider when choosing a ...

WHAT IS AN OVERHEAD CRANE?

An overhead crane is a significant concept in the industrial and construction sectors. Known by various names such as overhead cranes, hoist cranes, electric cranes, or manual cranes, they facilitate production, construction, and transportation processes. So, what is an overhead crane? This article will help you understand overhead cranes’ structure, operation, and common applications.

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What is an Overhead Crane?

According to Wikipedia. an overhead crane is a type of material handling equipment used to lift, lower, and move loads within a workshop or factory. This equipment is known for its convenience and high productivity in loading and unloading goods, with lifting capacities ranging from 1 to 500 tons. Electric motors primarily operate overhead cranes, making them widely used in industrial manufacturing plants and industries that require handling heavy loads.

An overhead crane has two main movements: the horizontal movement of the crane trolley along the workshop’s height and the vertical movement of the hoist (hook) to lift and lower the load. The crane trolley, which carries the hoist, can be a single girder beam, double girder beam, box girder, or suspension girder. The hoist is the part responsible for lifting and lowering the load and can be a chain hoist or wire rope hoist.

Types of Overhead Cranes

There are various types of overhead cranes, depending on criteria such as functionality, drive mechanism, beam structure, and usage. Here are some common types of overhead cranes:

•  By Functionality: There are two main types—general-purpose overhead cranes and specialized overhead cranes. General-purpose overhead cranes are typically used for loading, unloading, moving, installing, and repairing machinery. Specialized overhead cranes are used in specific industries such as metallurgy, hydroelectric power, explosives, etc. Specialized cranes come with unique attachments and heavy-duty working modes.

• By Drive Mechanism: Two types are manually operated overhead cranes and electrically operated overhead cranes. Manually operated overhead cranes use human-powered mechanisms like hand-cranked winches or hand-operated chain hoists. Electrically operated overhead cranes use electric motors or electric wire rope hoists.

• By Beam Structure: There are three types—single girder overhead crane, double girder overhead crane, and suspension overhead crane. Single girder overhead cranes have one main girder for suspending the hoist, usually an I-beam or box beam. Double girder overhead cranes have two main girders for hoist suspension, typically box girders or truss girders. Suspension overhead cranes do not have a main girder and instead have auxiliary beams suspended on overhead rails in the workshop.

• By Usage Scope: There are various types based on lifting purposes, such as port cranes, metallurgical cranes, hydroelectric cranes, explosive handling cranes, etc. These types often come with special attachments like grab buckets, electromagnets, etc.

Main Applications of Overhead Cranes for Factories:

• Mechanical manufacturing plants
• Processing plants
• Shipbuilding yards, hydroelectric, and thermal power plants
• Precast concrete pile plants
• Steel plants
• Warehouses

Factors to Consider When Choosing an Overhead Crane:

The choice of an overhead crane depends on several key factors, including:

Lifting Capacity: For loads under 25 tons, a single girder overhead crane is suitable.

Span: Single-girder overhead cranes are advantageous for spans under 25m, while double-girder overhead cranes are preferable for larger spans.

Equipment Layout:

• Lift Height: Single girder overhead cranes may limit lift height. For optimal lift height requirements, double girder overhead cranes are preferable.
• Distance from rail to beam end: In cases of limited space, a single girder overhead crane may be chosen. If ample space is available, a double girder overhead crane can be selected.
• Working range of the hook: Double girder overhead cranes offer an optimal working range for the hook compared to single girder overhead cranes.

Equipment Operation and Working Speeds:

• Light to medium-duty operation: Single girder overhead crane
• Heavy-duty operation, high working speeds, and demanding environments: Double girder overhead crane

Overhead Crane Operating Modes:

According to Vietnamese lifting equipment standards (TCVN -) and FEM1.001, overhead cranes are categorized into eight operating modes from A1 to A8. These modes vary based on the type and purpose of the crane. The classification is as follows:

No.Type and Function of Overhead CraneCrane Group1Manually operated overhead craneA1, A2,A32Overhead crane for construction and installationA4,A53Overhead crane for disassembly, assembly, and repair of power plants, in machine repair shopsA44Overhead crane for transporting materials in warehousesA55Overhead crane in workshopA56Overhead crane for use in demolition plants, landfillsA6,A7,A87Overhead crane for use in minesA88Overhead crane for unloading castings, opening furnace bottoms, and charging raw materials for metallurgical furnaceA89Overhead crane for use in steel forging shopA6,A7,A810Overhead crane for loading and unloading goods, transporting containers in portA6,A7,A811Overhead crane in portA6,A7,A812Overhead crane in shipyardA513Overhead crane for constructionA414Overhead crane for railwaysA4

Group 1: Light-duty overhead cranes, infrequent use: A3, A4

Group 2: Medium-duty overhead cranes: A5

Group 3: Heavy-duty overhead cranes: A6

Group 4: Very heavy-duty, continuous operation overhead cranes: A7, A8

Structure of Single Girder Overhead Crane

=>>> READ MORE: SINGLE-GIRDER OVERHEAD CRANE

A single girder overhead crane consists of:

• Main girder: Box or I-beam type, 01 girder
• End beam (end girder): Combination type, 02 end girders
• Moving wheels: Made of S45C, 42CrMnO4, heat-treated 38~42HRC, using self-aligning bearings
• Hoist, electric winch
• Crane travel motor
• Control system: Inverter, contactor, automatic switch
• Deep groove cable
• Remote control or pendant control box

Structure of Double Girder Overhead Crane

=>>> READ MORE: DOUBLE-GIRDER OVERHEAD CRANE

A double girder overhead crane consists of:

• Main girder: Box girder type, 02 girders
• End beam (end girder): Combination type, 02 end girders
• Operator platform, railing
• Moving wheels: Made of S45C, 42CrMnO4, heat-treated 38~42HRC, using self-aligning bearings
• Hoist, electric winch
• Crane travel motor
• Control system: Inverter, contactor, automatic switch
• Deep groove cable
• Remote control or pendant control box

Control Options for Overhead Cranes:

Overhead cranes have various control options:

• Cabin control mounted on the main girder
• Remote control
• Hand-held pendant control box for moving along the girder or moving independently of the girder.

Each control option has its advantages and disadvantages. However, remote control is the most cost-effective option.

Safety Features:

Safety is crucial in the use of overhead cranes for plant operations to prevent accidents and ensure a secure working environment. To ensure safe crane operation, the overhead crane must have the following minimum safety warning devices:

• Overload warning
• Limitation of lifting range: Two levels – level one control cutoff, level two dynamic cutoff
• Limitation of trolley travel range: Two levels – level one control cutoff and high speed, level two dynamic cutoff or slow speed.
• Limitation of crane travel range: Two levels – level one control cutoff and high speed, level two dynamic cutoff or slow speed.
• Bumpers at the end of travel distance: Rubber type with steel stops.
• Horn, warning lights during crane movement
• Starting bell.
• Load display board
• Load sway control (Anti-sway).
• Anti-collision device for cables
• Cable guidance

Notes on Usage and Maintenance

Like any other equipment, overhead cranes require regular maintenance to ensure safety and continuous operation, prolonging the crane’s lifespan.

Key considerations include:

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• Check the condition of gearbox oil, grease bearings, and wire rope lubrication.
• Inspect the condition of wire ropes for timely replacement and removal.
• Examine the condition of contactors, automatic switches, fuses, and circuit breakers.
• Verify the condition of travel paths.
• Check the condition of overload indicators.

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Maintenance Schedule:

Overhead crane maintenance is categorized into three types:

• Daily Maintenance: Before starting the work shift, operators should perform a preliminary check of the equipment and obstacles on the crane and rail.
• Monthly Maintenance: Check the equipment condition and replenish lubrication.
• Annual Scheduled Maintenance: Detailed inspection of each component, providing a comprehensive report for replacement, supplementation, or user warnings.

If you are interested in the overhead crane products, gantry cranes, hoists, and other lifting equipment offered by VINALIFT, please contact us. We will provide quick and accurate advice and quotations.

A Guest Post from the Members of the Electrification and Controls Manufacturers Association (ECMA).

Overhead cranes are essential equipment for many industries, including manufacturing and logistics. But in order for cranes to lift and move heavy loads within a facility, they need power. There are three primary crane electrification options: conductor bars, festoon systems, and cable reels. Each offers both advantages and disadvantages, making them ideally suited for different types of overhead cranes and applications.

Helping overhead crane owners and prospective buyers better understand their crane electrification options are the members of the Electrification and Controls Manufacturers Association (ECMA). The group publishes the American National Standard (ANSI) ECMA 35: Electrification Systems for Electric Overhead Traveling Cranes. This standard details minimum requirements and guidelines for both alternating current (AC) and direct current (DC) electrification systems used to power overhead electric cranes, monorails, gantry traveling cranes, and workstation cranes.

“All three types of crane electrification options — conductor bars, festoons, and cable reels — serve the same purpose,” explained Ben Hiebenthal, Mechanical Engineer III and Platform Lead of Rotary Motion Products at ECMA member Conductix-Wampfler. “They all provide power to the crane and its components. They each are simply different modes, or ways, to deliver electricity to the moving overhead equipment.”

The different form factors exist to accommodate different application limitations, Hiebenthal continued. “Often, what dictates the choice of which crane electrification option to use is the available space that surrounds the equipment. Each has different space requirements and, in many instances, a combination of two or more options is the optimal solution,” he said.

For that reason, Hiebenthal advises operations considering a new overhead crane to review ECMA 35. He also recommends engaging a crane electrification supplier early in the design process.

“Electrification is often an afterthought when a facility is planning a new crane purchase,” he said. “For the most cost-effective solution, an electrification supplier can advise about the amount of space required around the machinery to adequately support the power supply. They can also help to guide the selection of conductor bars, festoons, and/or cable reels individually or in combination to best suit the application.”

Crane Electrification via Conductor Bars

Conductor bar systems are a popular method for electrifying overhead cranes and their hoists. These systems generally consist of four linear bars (three live, one ground), collectors, and all mechanical components for installation. The collectors travel along the length of the bars as the crane moves to supply power to the crane and its components. Protective guarding options and grounding systems keep personnel safe from unintended contact.

“Inside a building, conductor bars are commonly mounted near the ceiling along the entire runway,” he said. “They’re also frequently mounted on a bridge to power the trolley’s movement back and forth across the crane.”

Conductor bars offer several advantages for overhead crane electrification. First, they provide a continuous power source to the crane, which eliminates the need for frequent stops and starts. This results in smoother and more efficient crane movements, as well as reduced wear and tear on the equipment.

Another benefit of conductor bars is easy customization. Options include different amperage ratings, voltage levels, and insulation options, depending on application requirements. “Some even permit transmission of data signals over the same bar used to transmit power,” Hiebenthal noted. “That can reduce the number of conductor bars needed on the crane.”

Additionally, conductor bars can be mounted for bottom or side collector entry to accommodate different crane designs and layouts. That makes them ideal for facilities with low ceiling heights. “While their sliding collector shoes do need adequate space to stack up at one end of the crane, they generally take up less space than festoons and cable reels,” he added.

Like all crane components, conductor bars require maintenance and inspection. Over time, the sliding contacts or collectors can wear down or become dirty, affecting their electrical conductivity. Regular cleaning and inspection of the conductor bars are necessary to ensure optimal performance and prevent downtime.

Powering Overhead Cranes with Festoon Cable Systems

Festoon systems are another frequently used overhead crane electrification option. A festoon system consists of a series of power cables suspended along the crane runway or bridge managed by trolleys. The cables drape between each trolley; as the crane moves, so do the trolleys, which extend the cables, feeding out the slack. When the crane or bridge returns to its starting position, the trolleys retract and stack back up — accordion style — to compress the loops of cable.

Festoons are flexible and easily customized in terms of length and the number of cables needed to support the crane’s movement through a work area. They are also relatively easy to install and maintain. They do, however, require more storage space for the trolleys and cables, said Hiebenthal.

“The longer the travel distance of the runway or bridge, the longer that collection of cables will be and the more space you’ll need to store them,” he said. “Additionally, in a low headroom area, a festoon system can be problematic if the loops are hanging into a work cell under a jib crane, for example.”

Festoon systems, like all crane components, require routine maintenance and inspection. The cables, because of their continuous extension and retraction, are more susceptible to wear. Likewise, depending on the environment, they can be more prone to damage.

Cable Reels Unspool and Retract as Overhead Crane Moves

Cable reel systems are another common option for overhead crane electrification. These systems consist of a cable wound onto a spool and connected to a power source. As the crane moves along the runway or bridge, the cable unspools from the reel and provides electrical power to the crane. As the crane returns, the reel system automatically retracts the cable either with a spring or motor and winds it back onto the spool.

One of the main advantages of cable reel systems is their ability to provide a continuous power source to the crane. Cable reel systems are also relatively easy to install and maintain. As long as there is adequate space to house the spool, mounting for this system can be above, below, or alongside the crane.

“The downside to a cable reel system is that they typically only manage one cable,” Hiebenthal noted. “In some special circumstances, it may be possible to wind two cables on the same spool, but that can limit the diameter of the cable. So if a system needs multiple cables, a cable reel system is probably not the best choice.”

Further, an exceptionally long travel distance for either the runway or bridge will require an exceptionally large reel system. That may not be practical, space efficient, or cost effective, he explained.

As with conductor bars and festoons, cable reel systems also require routine maintenance and inspection. The cables can be more susceptible to wear and damage, depending on the operating environment. Additionally, there is a chance that the cable could become tangled on the reel if the system is not designed and managed properly.

Where to Get More Information

Want to learn more about overhead crane electrification options, including conductor bars, festoons, and cable reels?

Ask the members of the Electrification and Controls Manufacturers Association (ECMA), the industry’s leading suppliers of electrification and controlling devices. They supply solutions worldwide and in virtually every major manufacturing and distribution sector. ECMA members manufacture and distribute equipment that controls, services, and enhances productivity and safety in industrial handling, including remote controls, anti-collision devices, weighing solutions, brakes, resistors, cabling, drives, motors, festooning, and more.

For more Electric Overhead Crane(vi)information, please contact us. We will provide professional answers.