The most adaptable and the most widely used type of power driven crane for indoor service is undoubtedly the three motion EOT crane. It serves a larger area of floor space within its own travelling restrictions than any other permanent type hoisting arrangement.
With a hoist that is fixed to a trolley, cranes raise and lower the loads. Along a bridge, the trolley travels back and forth. The bridge is travelling on a runway. Some cranes do not have a bridge, such as a jib crane, but they still have a hoist mounted to a trolley and can shift a load horizontally.
A bridge crane is described as a crane with at least one primarily horizontal girder, fixed or able to travel along tracks and fitted with at least one hoisting mechanism. There are four major types of top-running, under-running, single and double-girder overhead cranes. As the name implies, this type of EOT crane is provided with movement above the floor level. Hence it occupies no floor space and this can never interface with any movement of the work being carried out at the floor of the building.
Types of EOT Crane Motions or Movements:
The three motions of such crane are the hoisting motion and the cross travel motion. Each of the motions is provided by electric motors. A typical EOT crane movement consists of three distinct movements:
1. The hoist is the initial motion, and it is responsible for raising and lowering the material.
2. The second kind of hoist is the trolley (cross travel), which enables the hoist to be positioned exactly above the item to be placed during installation or carry.
3) The third kind of crane motion is gantry or bridge motion (long travel), which enables the whole crane to be moved across the working area.
The above characteristics have made this type of EOT crane suitable for medium and heavy workshop and warehouses. No engineering erection shop, machine shop, foundry, heavy stores is complete without an EOT crane.
In a steel plant, rolling mill, thermal power plant, hydraulic power plant, nuclear power plant, this type of crane is considered indispensable. In short in all industries, wherein heavy loads are to be handled, EOT crane find its application.
13 Guidelines to remember when designing the EOT Cranes
EOT cranes are designed in a variety of ways depending on their key operating guidelines, which include things like the type of motion of the crane structure, the weight and type of the load, the location of the crane, geometric features, functioning regimes, and the environment in which they operate. It is essential to choose the appropriate kind of EOT crane in order to simplify workflow and increase production. A variety of variables are taken into account, including the following:
1. What is the necessary capacity of the bridge?
2. How often will the crane be in use?
3. How long is the span?
4. How long does it take to go from one end of the runway to the other?
5. How high does the hoist have to go?
6. Will the bridge be supported by the structure, will it be self-supporting, or will it be both?
7. Do you want to build the bridge inside or outdoors?
8. What is the source of electricity for the crane? Is it all motorized push-pull, all manually geared, or a mix of the two?
9. How quick will it be if it is motorized? Is it better to have one or two speeds? What exactly are variable frequency drives?
10.What voltages are needed for this application?
11.What kind of control do you want? Is it better to use a pendant from the hoist, a separate track, or a remote control?
12.Do you have any unique characteristics? Cabs, pathways, horns, and lights, to name a few things.
13.Are there any relevant standards, codes, or local regulations?
The different types of EOT Cranes
Even though there are many different types of EOT cranes, with many of them being highly specialized, the vast majority of installations may be divided into four categories:
1. Single Girder Cranes
A single bridge girder is supported on two end trucks, and the crane is composed of this design. On the bottom flange of the bridge girder is a trolley hoist mechanism, which operates in the same manner as a crane.
2. Double Girder Bridge Cranes
This kind of crane is composed of two bridge girders that are supported by two end trucks on each side of the crane. The trolley is supported by tracks that run along the top of the bridge girders.
3. Gantry Cranes
These types of cranes are basically the same as conventional EOT cranes, with the exception that the bridge for transporting the trolleys is firmly mounted on two or more legs that travel on fixed rails or other runways. These “legs” do away with the need for a supporting runway and column system, instead running on a rail that is either embedded in or placed on top of the floor.
For certain applications, such as a manufacturing assembly line or a service line, a trolley hoist is all that is necessary. This kind of crane is constructed from I-beams, which are similar to those found in the ceiling constructions of many manufacturing facilities. The trolleys roll along the flat surface of the beam, supported by the horizontal bars at the bottom of the beam. It is similar to a single girder crane in that it does not have a movable bridge and the hoisting trolley operates on a fixed girder, with the exception that the crane does not have a moveable bridge.
EOT Crane Parts:
A EOT crane consists of two distinct parts
The Bridge consists of two main girders fixed at their ends and connected to another structural components called the end carriages. In the two end carriages are mounted the main runners or wheels (four or more) which provide the longitudinal motion to the main bridge along the length of the workshop.
The motion of the bridge is derived from an electric motor which is geared to a shaft running across the full span of the bridge and further geared to a wheel at each end. In some design separate motors may be fitted at each corner of the main bridge. The wheels run on two heavy rails fixed above the floor level along the length of the shop on two girders, called gantry girder.
The Crab consists of the hoisting machinery mounted on a frame, which is in turn mounted on at least four wheels and fitted with suitable machinery for traversing the crab to and fro across the main girders of the crane bridge. Needless to mention that the crab wheels run on two rail sections fixed on the top flange of the main bridge.
Thus the load hook has three separate motions, these being the hoisting, cross traverse of the crab, and longitudinal travel of the whole crane. Each motion is controlled independently of the other motions by separate controllers situated in a control cage or in a suitable position for controlling from the floor by pendent chains.
The essential parts of EOT Crane are:
Bridge– 2 No’s
End carriage– 2 No’s
Wheel of the bridge– At least 4 No’s
Crab (without auxiliary hoist)– 1 No’s
Hoisting machinery set– 1 No’s
Wheels of crab– At least 4 No’s
Bottom Block (without auxiliary hoist)– 1 No’s
Lifting hook– 1 No’s
Rail on the gantry girder for crane movement– 2 No’s
Rail on the bridge for crab movement– 2 No’s
Operators cabin– 1 No’s
1. The bridge
The bridge is the most important structural component of an EOT crane system. There are one or more load bearing beams or girders that span the breadth of the structure and support the roof. These may be manufactured steel box girders or rolled steel joists, depending on the application. During operation, the bridge carries the hoist trolley, which traverses the length of the girders to reach its destination.
The track and supporting structure on which the crane is mounted and used to operate. The runway girders are often regarded to be a component of the building structure and are constructed in accordance with that consideration.
3. Runway Rail
The rail on which the crane travels, which is supported by the runway beams.
4. End trucks
Located on each side of the bridge, the end trucks are responsible for housing the wheels on which the whole crane is transported. An assembly of structural members, wheels, bearings, axles and other components that supports the bridge girders or the trolley cross member is known as a girder support assembly. Powering the wheels and moving the crane into the desired position are two-speed or variable-speed electric drive motors, respectively.
When installed on drive motors, brakes are necessary to prevent uncontrolled loads from becoming hazardous. Brakes are typically powered by electricity and are placed on the drive motors. After reaching the end of their travel range, the electrical limit switches turn off the drive motors and prevent the crane from colliding with any structure on the building’s exterior.
The hoist framework is a device that includes the following components: a motor drive, a coupling and brakes; gears; an overhead drum; ropes; and a load block. It is intended to lift, hold, and reduce the maximum rated load. The hoist gear is attached to the trolley by means of a bracket.
6) Trolley or Crab (TC)
A ‘crab’ is the term used to describe the cross travel unit wherein the hook is lowered and lifted. A top-running trolley on a double-girder crane travels along rails that are attached to the crane bridge’s uppermost girder. An under-hung trolley on a single-girder crane runs on the bottom flange of the crane beam, with the driving units for the trolley being linked directly to the crane beam.
The trolley transports the electric wire rope hoist, which provides support for the load block and hook via a series of pulleys, to its final destination. The weight is moved up and down by a variable-speed alternating current motor on the hoist. Using limit switches, you can keep the load block from collapsing against the trolley.
When a moving crane or trolley approaches the limit of its allowed journey, or when two moving cranes or trolleys come into contact, an energy-absorbing device known as a bumper (buffer) is used to reduce the impact. This device is mounted to a bridge, trolley, or runway halt, among other places.
8. Remote Controls
The remote controls for an EOT crane are often housed in an operator cabin or remote panel, and they consist of a variety of push buttons and switches which thus activate relays and contactors placed on the crane’s mainframe. During operation, the drive motors and the hoist motor draw significant currents, necessitating the use of contactors with suitable current ratings to turn them on and off.
Variable frequency inverters are used to regulate the speed of motors in situations where precise placement is required. When a hazardous scenario arises, a master contactor is activated by the main switch and shuts off all power to the crane. Specialty cranes may also include additional features such as end stops, full length platforms on both girders, under bridge illumination and a closed cabin that is either glazed or air conditioned, as well as specific controls and other amenities.