Overhead cranes cover a rectangular area, moving a load side to side and backward and forward. The lifting device, called a hoist is mounted on a trolley for horizontal movement across a
bridge beam connected to one or more horizontal girders which are supported at either end by end trucks. The end trucks are attached at right angles to the girders and move on fixed runways. The horizontal travel of
push type cranes is powered manually by the operator; alternately, an
electric overhead crane is powered by electricity. Still other cranes can be air-powered (pneumatic).
Cranes come in a variety of styles and are used with a number of attachments to facilitate load lift, including:
- Single girder crane - Utilizes a single bridge beam attached to the two runways and end trucks. This bridge beam or single girder supports a
lifting mechanism or hoist that runs on the bottom flange of the bridge beam; also referred to as an under running crane or
- Double girder crane – These cranes utilize two bridge beams set atop the runway end trucks. They typically incorporate a top running trolley hoist
which moves along the top of the two bridge beams on its own set of wheels for increased headroom under the crane; also called a top running crane.
- Box girder crane - Utilizes a four-sided box configuration in fabricating the bridge girder. This enhances the crane’s load capacity and accommodates wider bridge
distances. Generally, they are utilized in pairs with the hoisting mechanism operating on rails attached to the top of each box girder.
- Truss girder crane – A crane designed with structurally reinforced bridge girders for greater span and loading capabilities.
- I-beam crane - Utilizes standard I-beam as the bridge girder and may also employ I-beams as the runway beams.
- Straddle crane - Configured to straddle a load and often on wheels, these cranes are typically used in lumber yards or to move large containers at sea ports.
- Tower crane – Handles very large, heavy loads at construction sites and for the loading and unloading of shipping containers.
- Stacker crane – Cranes that use a load handling device other than a hoist, such as a rotating ridged or telescoping mast suspended from the bridge trolley and
equipped with single or double forks or a gripping lifter.
End effectors or below the hook equipment: A variety of different, application-specific, attachments can be added to the overhead crane’s hoist
to handle the lifting or positioning of different loads. These include:
- C hook A device that enables the lifting of a coil by through the insertion of a hook into the coil’s inner diameter.
A motorized hook rotator powers the rotation of the hook attached to the bottom block of a hoist for additional load control.
- Gripping lifters use either friction or
indentation-causing pressure to hold a load.
Tong grabs or clamps utilize a scissor-type action to grip a load.
Coil grabs grasp the outer diameter of a coil via tongs or gripping mechanisms to lift or turn it.
- Mechanical lifters are composed of two or more rigid parts that move in tandem when manually actuated to secure the load.
- Vacuum lifters utilize an electric-powered extraction pump and sealed pads to create a vacuum to attach the lifter to an object.
- Sheet lifters use two claws to grab a load of sheet metal or wood by wrapping around the edges. A lip on the lower portion of the claws prevents the sheet
from falling out of the lifter.
- Pallet lifters use forks to lift pallets from underneath.
- Lifting beams made from solid or fabricated metal, or from wood, are suspended from a hoist/crane to provide multiple load lifting points for better security and control of the load’s movement. A spreader beam uses two or more hooks to spread the load over more than one lifting point.
- Magnets lift, carry or release flat or round ferrous objects with or without an electrical power supply.
- Slings or strap hoists made of nylon, polyester, wire rope or chain lift materials that are too large and bulky to be transported any other way, such as steel coils or sheets.
- Drum turners turn over drums for filling and emptying.