This guide contains everything you need to know about overhead cranes.
You will learn about:
- What is an overhead crane?
- How overhead cranes operate
- How overhead cranes are used
- Industries that use overhead cranes
- And much more…
Chapter One – What is an Overhead Crane?
An overhead crane is a type of heavy duty machinery that is capable of moving extremely heavy loads and equipment from one location to another in a safe and precise manner using the overhead space of a manufacturing facility. Due to the nature of the work they perform, they are precision configured and designed to fit a specific form of loading application.
Overhead cranes come in a variety of sizes, types, shapes, and configurations with components and accessories that can be easily changed to improve their capacity and performance. They are used for loading and unloading, moving materials, lifting dies from stamping machines, or feeding raw materials.
The two main reasons for installing an overhead crane are efficiency and safety. Overhead cranes can work several times faster than floor or land based devices. In hazardous, dangerous, and severe conditions such as where there are heated metals, chemicals, or toxic materials, overhead cranes can safely move materials without endangering workers.
Chapter Two – How Overhead Cranes Work
When it is necessary to move bulky materials or extremely heavy loads through a manufacturing facility, it is more convenient and efficient to use an overhead crane instead of struggling to navigate aisles and floor space. Overhead cranes lift, lower, and move horizontally along a rail or beam and are capable of safely lifting extremely heavy loads. The travel and speed of the crane is controlled by an operator using a pendant station or wireless control.
Overhead cranes cover a rectangular area and are able to move loads from side to side as well as forward and backward. Though not every overhead crane is the same, they do have certain standard features such as a hoist, trolley, beams, girders, and control systems.
How Overhead Cranes Work
The bridge of an overhead crane runs longitudinally along tracks laid on runway beams over the rectangular working area. Bridges are made of steel girders that are connected to runways at either end of the girders.
Lifting Trolley –
The lifting trolley contains the lifting mechanism that has a brake, motor, reducer, drum, and set of pulleys. The motor drives a drum that rotates through the reducer to drive the wire rope or chain that raises and lowers the load.
Driving Mechanism –
There are two parts to the driving mechanism of a crane. There is the long transmission that drives the wheels on both sides, while a separate motor drives each set of wheels individually.
Power Supply –
The power supply is a complex subject since there are so many different types of power systems with different connections for each type of system. The three common types are conductor bar, festoon system, and cable reels.
The majority of overhead cranes depend on electricity for their power supply though there are versions that run on pneumatic power versions. The cable festoons, conductor bars, or reel cables transfer power to the crane runway and bridge crane control. This power feed is used to power the trolley and hoist.
Conductor Bar – A conductor bar system is installed on the crane’s runway or monorail. They can be used on runways with more than one bridge. Power is supplied through a sliding shoe collector system, which is safer than other methods.
- Festoon System – A festoon system can be track, I beam, or square rail mounted. They use flat or round cables on a trolley that moves along the track. The cable hangs below the track and expands or retracts depending on the position of the trolley.
- Cable Reel – Spring loaded or motorized cable reels are used to release, retrieve, and store the conductor cable. This method is used for mainline power along a runway or monorail.
The height at which the crane is installed has a bearing on the type of motor and the capacity of the crane. The lift height for an overhead crane is the distance from the floor to the saddle of the hook, which is a crucial measurement since it ensures there is enough lift room as well as area to reposition the load.
Another important factor is the C dimension, the maximum height to which the hook can be lifted. The C dimension is the measurement from the trolley wheels to the hook saddle.
Each part of an overhead crane's movements is controlled by software and electronics that are designed to work in unison for safety and ease of operation. Overhead crane controls give the operator full control of the load at all times. The most basic form of controls have a start and stop button, while more advanced controls have joysticks and tablets to program a wider range of motions and movements. Programmed into the controls are the limitations of the crane, which determines what it can do and where it can move. Control systems provide usage data, diagnostics, and methods for controlling possible errors in operation.
The two main types of hoists for an overhead crane are chain and wire. A chain hoist is held in place by a chain holder and is designed for lifting loads of less than ten tons. They provide true vertical lift and rise straight up without any lateral drift.
Wire rope hoists wrap around the load and are capable of lifting ten tons or more. They allow for more options and greater flexibility. Unlike chain hoists, wire rope hoists are susceptible to lateral movement.
Overhead Crane Terms –
- Axial Load – total vertical force on the supporting structure in a jib crane
- Box Section - rectangular cross section where girders, trucks, or other members meet
- Drag Brake – locking system that does not require force to provide braking
- Explosion Proof – made of explosion preventing materials
- Height Under Boom (HUB) – distance from the floor to the underside of the boom
- Lifting Capacity – the maximum lifting load for a crane
- Lifting Speed – speed at which the lifting mechanism lifts the load
- Running Speed – speed of the crane mechanism and trolley
- Span – the distance between the centerline of the wheels at each end of the main beam
- Two Blocking – when the load suspended from the hook is jammed against the crane
- Web Plate – the plate that connects the upper and lower flanges of a girder to the web plate.
- Wheel Load – the weight in pounds a single crane wheel will experience
- Work Duty – is determined by the load rate, which can be light, medium, heavy, or extra heavy
Chapter Three – Uses for Overhead Cranes
Moving bulky, heavy, and cumbersome loads down the aisles and floor of a manufacturing facility can be dangerous and time consuming. By making use of the overhead space of a factory by installing an overhead crane, applications can be performed more efficiently, cost effectively, and safer. Loads can be easily lifted, lowered, and moved through the unused space to save time and energy.
Specially trained operators control the movement of the crane through a variety of control devices. When examining movement options, it is important to review the space available and the practicality of installing an overhead crane.
Uses for Overhead Cranes
The first industry that comes to mind when determining the need for an overhead crane is warehousing where supplies, equipment, and materials are constantly moved, positioned, and prepared. A major benefit of an overhead crane in warehousing is the movement of large items from storage to the shipping dock in a timely manner.
Industries that assemble large equipment require a means for lifting and moving incomplete assemblies from one location to another for completion. Forklifts, AGVs, and other forms of material handling are not adequate or safe, which makes the use of an overhead crane a necessity. Assemblies can be moved easily as a natural part of the production process.
The parameters that apply to warehousing are also true for transportation where heavy bulky products have to be loaded onto planes, trains and trucks. Overhead cranes can easily position large materials to be placed for transport. This can be especially true for overseas shipping where huge containers and materials have to be lowered into the holds of ships.
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.
Chapter Four – Types of Overhead Cranes
When the decision to install an overhead crane has been made, the next step is to select the type of overhead crane that suits your circumstances. Overhead cranes come in a wide variety of configurations, sizes, shapes, and designs. Each type is specific to fit the standards for a particular application.
The varied selection can make choosing the proper crane difficult. The choice of the right crane and its specifications can radically improve productivity and efficiency as well as streamlining workflow.
Types of Overhead Cranes
Bridge Crane –
A bridge crane has two runways built into either side of a building and attached to the superstructure. The runways are connected by a bridge by end trucks that run on wheels on the runway. The bridge can be configured as either a single or double with a trolley running on each. The trolley and hoist are underhung and run along the bottom of the bridge.
Gantry Crane –
A gantry crane is very similar to a bridge crane with a single difference. A bridge crane has its runways attached to the super structure of a building. A gantry crane sets on four legs that support and move it. The bridge, trolley, and hoist are connected to the legs. The legs move along rails to position the bridge for loading, lifting, and moving. The rails for the legs are mounted on the floor, ground, or foundation much like a railway track.
The brief video below from Konecranes is an example of how gantry cranes are constructed.
Monorail Crane –
Unlike gantry and bridge cranes, monorail cranes do not have a bridge or girders. The trolley connects to an I beam that is built into the ceiling and travels along the flat surface at the bottom of the beam. Material runs in a straight line along the beam being carried by the hoist and moved by the trolley. The unique value of a monorail overhead crane is its ability to have curves, branches, and switches to change its elevation and direction.
Jib Crane –
A jib crane is another variation of overhead cranes that does not use a bridge, runway, or any form of track system. They can be placed and mounted in several different positions from being connected to a wall to standing alone. Jib cranes are space saving, economical, and perfect for moving assemblies. They can be designed to rotate in a complete circle or have a limited range of rotation. Jib cranes, even small ones, can lift and move several tons.
Top and Bottom Running Crane –
Top running or bottom running crane configurations refers to where the wheels run along the girders of the bridge. With top running cranes, the bridge runs along the top of the runway beams. In the case of bottom running, or underhung cranes, the beam bridge is supported on the bottom of the runway beams. The crane wheels run along the lower flange of the girders.
Top running cranes have a higher capacity and ability to lift heavier loads. Underhung cranes are normally used for lighter loads, have a lower capacity, and are supported by roof or ceiling structures.
Automated Crane –
The control of an overhead crane can be fully automated where the operator programs the activities of the crane and it completes each operation without manual interference or be semi-automated where certain functions are controlled by the operator. The key to a fully automated system is the type of software programmed into the crane. This type of system is ideal for demanding and hazardous conditions where there is a possibility of harm to the operator. A second benefit of an automated system is relieving the operator of the tedious monotony of repetitive motion.
Automated systems, by removing the operator, make fewer errors or mistakes and complete operations efficiently and flawlessly. Duty cycles can include lifting, positioning, stacking, and storing that can be repeated multiple times during any time frame from eight hours up to twenty four hours.
Workstation Crane –
Workstation cranes are a form of bridge crane that is designed for light to heavy production. They can have a lifting capacity of up to two tons and come in a configuration to fit the workspace. Since workstation cranes are smaller and more compact than larger cranes, they can be easily installed underneath jib or other forms of overhead cranes to produce a more efficient work cell.
The important factor regarding workstation cranes is ergonomics and removing the need to lift heavy materials or items. A major benefit of workstation cranes is the improvement in worker morale, quality, productivity, and safety.
Grab Overhead Cranes –
The design of a grab overhead crane can be bridge, gantry, and folding arm. It is equipped with a bucket, orange peel, or clam shell. This type of crane is used for handling bulk materials and has a single or double girder design. Grab cranes are used in mines, ports, and station yards to load logs, minerals, coal, sand, and gravel.
Chapter Five – Industries that Use Overhead Cranes
A key factor in any production operation is the supply change that brings needed raw materials and components to assembly operations. In many cases, these processes can be performed by forklifts, pallet jacks, and AGVs. For larger bulky materials, a more precise approach is necessary for the safety of workers and the efficiency of the operation. It is in these situations that overhead cranes become a necessity.
Unlike other industrial equipment, overhead cranes, regardless of their size, have to be configured and designed to fit the operation. A crane that may be applicable for auto production may not be able to perform shipping operations. This can also be said of cranes that are used in steel production.
Since their introduction, during the first industrial revolution, overhead cranes have become an essential part of innumerable production operations due to their safety, savings of time, and ease of operation.
Industries that Use Overhead Cranes
Auto Industry –
Overhead cranes for the auto industry serve several functions from material handling and the supply chain to lifting and transport applications. In press plant operations, overhead cranes move and store dies and tools as well as keep lines supplied. In assembly plants, workers rely on overhead cranes as a means of making their function more efficient and avoiding the need to lift materials.
Every operation of an automotive production plant relies on overhead cranes for their time savings and convenience. Their use improves production and avoids unnecessary delays due to interruption in the supply chain.
The first qualification for cranes for the steel industry is their ability to perform in harsh conditions at elevated temperatures with high grade dust and severe vibrations. Ladle cranes are reinforced and stabilized for handling the ladle safely and efficiently. Double girder overhead cranes are used for the delivery of components such as molds for casting and supplying casting parts.
The steel industry makes extensive use of overhead cranes for safety purposes and efficiency. Aside from ladle handling cranes, there are tundish, slab, scrap, billet or ingot, coil, and foundry cranes to name a few.
The plastic industry uses different molding methods such as extrusion, injection molding, and rotation molding. Regardless of the process, the frequent changing of molds is a necessity to keep up production and meet customer demands. The dies used require careful handling and precision placement. The types of cranes used for these processes are capable of millimetric accuracy when placing a die.
Much like the steel industry, shipbuilding makes extensive use of overhead cranes due to the nature of the materials required to build a ship. The three types of cranes that are used the most by the industry are jib, gantry, and overhead. Depending on the type of material to be moved, either a chain or wire rope hoist will be used.
The main function of overhead cranes in ship building is material handling during the assembly process. An overhead crane is used for each of the steps of shipbuilding, which are processing, assembly, fieldwork, launch, rigging, and delivery. The overhead cranes for shipbuilding are specifically designed to fit the space requirements and include steel plate hooks and various types of chain hoists with electric motors.
Biomass overhead cranes are designed to handle waste, refuse, garbage, slag, sludge, and straw bales. A different type of crane is used for each type of waste. Much like other industries, the biomass industry uses jib, gantry, and overhead cranes with chain and wire rope hoists.
There are various considerations that have to be made when deciding to purchase a biomass crane, which include truck delivery times, tonnage, density of the biomass, and the size and dimensions of the storage area. Biomass hoists include either a bucket, orange peel, or clam shell device for grabbing the load.
Gas and Petroleum –
Due to the volatility of gas and petroleum, overhead cranes must be designed to avoid the risk of igniting the material. They are made of explosion proof materials that are spark resistant. A challenge of the oil and petroleum industry is designing cranes for offshore drilling sites. Originally, the industry used land based designs that were adapted to fit the unique conditions.
Since offshore platforms have special conditions such as waves pitching a boat during loading and unloading, cranes are designed to handle the load as well as accounting for the distance of the load from the crane. Another key factor is the mounting structure and other pertinent environmental conditions.
Food and Drink –
The main qualification for material handling in the food and drink industry is cleanliness and sanitation. For food processing, overhead cranes are used to move rail mounted containers for production or storage. The main reason overhead cranes are used in food production is for efficiency, though there is a challenge to keeping the cranes sufficiently sanitary.
Controlled environments are essential in the food industry. To meet the requirements and high standards, producers work to develop lifting equipment that is custom designed to fit the conditions.
The semiconductor industry has a variety of heavy components that require reliable lifting solutions that are hygienic and do not contaminate the assembly. Overhead cranes must be precise, accurate, clean, and efficient to meet the quality standards of the industry.
For an overhead crane to be accepted by the semiconductor industry, it must meet the standards for a cleanroom. Unlike other material handling solutions, cleanrooms are strictly monitored in regard to the particulate content of the dust in the room. This adds a special challenge for producing overhead cranes for the semiconductor industry.
The rugged nature of the mining industry places a great deal of demand on the types of overhead cranes that can meet the conditions. The mining industry depends on overhead cranes for repairs and service on underground mining equipment. The corrosive environment of mining operations leads to rapid deterioration of equipment.
Cranes for mining are heavy duty equipment designed to carry several tons of equipment and material. They are made of heat, dust, and moisture resistant metals. In the face of the harsh conditions, overhead cranes must be able to perform efficiently and constantly.
The paper industry requires heavy duty cranes that are able to handle materials with great precision and gently since paper rolls can easily be damaged by the slightest impact. Paper is produced in extremely heavy giant rolls that require sanitary and careful handling.
For the protection of workers, cranes for the paper industry have automated control systems, which can be used for pulp production and paper manufacturing. The speed of the crane has to be closely regulated for proper handling of materials as well as being equipped with slings for loading and unloading of paper scrolls.
Chapter Six – Overhead Crane Construction
The construction and choice of an overhead crane involves the investigation of several factors beyond what needs to be lifted or the type of materials being loaded. Since overhead cranes are designed, shaped, configured, and engineered to fit predetermined conditions, it is important to have a complete understanding of how the crane will fit into the operation.
It is extremely important to carefully plan and prepare for the installation of an overhead crane. Manufacturers work closely with their clients to ensure what is planned and installed exactly meets the needs of the customer.
Overhead Crane Construction
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.
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, capacity, and must endure severe circumstances, a double girder design may be necessary. For extra strength, double girders are made of welded reinforced steel.
Overhead cranes have six classifications established by the Crane Manufacturer Association of America (CMAA). The determination of a crane’s classification uses these criteria:
- Frequency of use
- Speed of material transfer
- Number of lifts per hour
- Maintenance cycle
- Average load
- Number of full capacity lifts
- Work environment
Work Environment –
The severity, number of obstructions, and danger of the work environment is a major determining factor regarding overhead crane construction. Heat, chemicals, fumes, steam, dust, or moisture require special construction materials to prevent the deterioration of the crane. Various coatings may also be needed for protection and to ensure proper crane operation.
Operations that have the potential of explosions such as wastewater processing, fertilizer plants, and oil and gas processing necessitate explosion proof qualifications, which means the crane must not generate sparks. This type of crane operates using a pneumatic air powered system or a specially designed explosion proof electrical system.
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 the 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.
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.
Chapter Seven – Overhead Crane Construction
The nature of overhead cranes and the dangers involved in their use is the concern of several regulating agencies, which includes the National Electrical Manufacturers Association (NEMA), the Occupational Safety and Health Administration (OSHA), the American National Standards Institute (ANSI), and Crane Manufacturers Association of America (CMAA).
Each of these organizations have a different approach to the operation and use of overhead cranes. What is the concern of all groups is the safety of workers and materials. The operation of an overhead crane falls into the category of heavy industrial equipment, which requires that it be operated and used by trained staff.
Overhead Crane Regulations –
Crane Manufacturers Association of America (CMAA) –
The CMAA is a voluntary membership organization where affiliated producers adhere to mutually agreed manufacturing standards for overhead cranes. They provide training, guidance, and classifications for overhead cranes. They classify cranes according to their per hour use and number of times they are at full capacity. The A to F classification system is:
Class A refers to installation and maintenance cranes that operate at slow speeds, have long periods of idleness, and infrequently have capacity loads. Class F covers the top of the line bridge, gantry, multiple girder, electric overhead, and monorail cranes that constantly handle full capacity loads.
Occupational Safety and Health Administration –
OSHA standards regarding crane operation are under classification 1910.179 titled Overhead and Gantry Cranes. The over 300 standards cover every aspect of crane operation from the type of clothing and fire prevention equipment to methods for avoiding the dropping of loads.
OSHA load handling requirements address the following:
- Size of load
- Attaching the load
- Moving the load
- Hoist limit switch
National Electrical Manufacturers Association (NEMA) –
The NEMA publishes ratings for construction, testing, and performance guidelines for industrial control systems for crane and hoist controllers under standard ICS 8-2019.
American National Standard Institute (ANSI) –
Much like OSHA, the ANSI has a wide range of requirements and standards regarding load capacity, ropes, inspection guidelines, and every aspect of the construction and maintenance of an overhead crane. Included in their documentation are diagrams and designs regarding proper use and manufacturing of overhead cranes.
- An overhead crane is a form of heavy duty machinery that is capable of moving extremely heavy loads and equipment from one location to another in a safe and precise manner using the overhead space of a manufacturing facility.
- Overhead cranes come in a variety of sizes, types, shapes, and configurations with components and accessories that can be easily changed to improve their capacity and performance.
- When it is necessary to move bulky materials or extremely heavy loads through a manufacturing facility, it is more convenient and efficient to use an overhead crane instead of struggling to navigate aisles and floor space.
- By making use of the overhead space of a factory by installing an overhead crane work can be more efficient, cost effective, and safer.
- Overhead cranes come in a wide variety of configurations, sizes, shapes, and designs. Each type is specifically engineered to fit the set of standards for a particular application.