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 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.
The three motions of such crane are the hoisting motion and the cross travel motion. Each of the motions is provided by electric motors.
The above characteristics have made this type of 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.
EOT Crane Parts:
A EOT crane consists of two distinct parts
- 1. Bridge
- 2. Crab
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 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