GUIDE TO OVERHEAD CRANES
This information is intended to give a general understanding of the terminology used in the overhead crane industry. The following explanation of terms will assist you when communicating with our service advisor. Our service crew will then be well informed and your requirements can be fulfilled in the most efficient manner. On this website, you will find an easy to use Request for Quotation form which can be email to our office. If you have any questions regarding any of the products or services we provide, please contact us.
CRANE COMPONENTS
Bridge - The main travelling structure of the crane which spans the width of the bay. The bridge consists of two end trucks and one or two bridge girders depending on the Equipment Type.
End trucks - Located on either side of the span, the end trucks house the
wheels on which the entire crane travels. These wheels ride on the runway beam allowing access to the entire length of the bay.
Bridge Girder(s) - The principal horizontal beam of the crane bridge which supports the trolley and is supported by the endtrucks.
Trolley Hoist - The unit consisting of both the hoist and the trolley
frame. In situations where more than one hoist is required on one crane, both hoists can be supplied on a single trolley or on separate trolleys.
Trolley - The trolley carries the hoist across the bay along the bridge girder(s) traversing the span.
Hoist - The hoist is mounted to the trolley and performs the actual lifting function via a hook or lifting attachment. There are two basic types of hoist. The first is the Wire Rope Hoist which is very durable and will provide long term, reliable usage. The other type of hoist is the Chain Hoist. These hoists are used for lower capacity, lighter duty applications and for projects in which cost is a primary deciding factor.
BASIC TERMINOLOGY
Capacity - The maximum weight the crane will be required to lift.
Span - The horizontal distance between the rails of the runway on which the crane is to travel.
Lift or Hook Height - The required distance from the floor to the crane hook. This dimension is critical in most applications as it determines the height of the runway from the floor and is dependent on the clear inside height of the building.
Bridge, Trolley and Lift Speeds - The rate at which the bridge or trolley travels, or at which the hoist lifts, usually in feet per minute or FPM. You may specify either Single Speed or Two Speed travel/lift or a specific rate of speed, (i.e. 120 & 30 FPM bridge travel). Another option as far a motion speeds are concerned is a Variable Frequency Drive. See the Control section for more information.
EQUIPMENT TYPES
This section specifies the kind of equipment you require.Overhead cranes come in four basic configurations;
Top Running (T/R) - The crane bridge travels on top of rails mounted on a runway beam supported by either the building columns or columns specifically engineered for the crane.
Under Running (U/R) - The crane bridge travels on the bottom flange of the runway beam which is usually supported by the roof structure.
Single Girder (S/G) - The crane consists of two end trucks, a single bridge girder and the trolley hoist unit. The trolley runs on the bottom flange of the bridge girder.
Double Girder (D/G) - The crane consists of two end trucks, two bridge girders and the trolley hoist unit. The trolley runs on rails on top of the bridge girders.
A variation on these types of overhead crane are Gantry Cranes. These cranes are essentially the same as the regular overhead cranes, however, the bridge girder(s) are connected to “legs” on either side of the span. These “legs” eliminate the supporting runway and column system and connect to end trucks which run on a rail either embedded in, or laid on top of, the floor.
For some applications only a Trolley Hoist is required. For instance, in the case of a monorail system a Trolley Hoist unit similar to the one used on single girder cranes is mounted on a beam which might be used to service an assembly line within the clients facility. Other clients may have an existing single or double girder crane bridge and may just want to replace the hoisting unit. In most of these situations, capacity permitting, we can provide either a Wire Rope or Chain Hoist.
Another solution which may fit your needs is a Jib Crane. A Jib Crane basically consists of a boom which is supported as a cantilever on a column. A Trolley Hoist travels along the boom which can rotate.
CONTROL
Pendant - The pendant gives the operator precise control over the motions of the crane. There are many configurations of pendant depending on the functions of the equipment being controlled. Each pushbutton on the pendent controls an operating function of the crane.
The pendant may be suspended from the Trolley Hoist, requiring the operator to walk with and beside the load, or on a separate sliding track system allowing the operator to move independently of the load.
VFD - A pendant can also be used in conjunction with a Variable Frequency Drive. A VFD is used to vary the frequency of the motors controlling the motions allowing for smooth acceleration and deceleration. The buttons on the pendant operate a VFD unit in much the same way as Two Speed control. The first step is held to maintain the current speed while the second step is used for acceleration. Deceleration is achieved by releasing the button entirely. Pressing the button back to the first step will maintain the new slower speed. It should be noted that the deceleration is not achieved through uncontrolled coasting but through a programable dynamic braking system. The control provided by a VFD allows for a high level of customization.
Radio Control - The radio control performs exactly like the pendant but operates using a radio frequency. The radio control incorporates numerous safety features and allows the operator a greater range of operator motion than a pendant.
Power Supply - The electrical service available in the building for which the crane is being designed (i.e. 575 Volt, 3 phase, 60 Hertz).
Enclosures - The enclosures house all of the electrical components on the crane and are rated by the National Electrical Manufacturers Association (NEMA) or the Canadian Electrical Manufacturers Association as to the level of protection they provide from the conditions in the surrounding environment. There are three basic levels of protection.
CEMA/NEMA 1 - Provides protection against accidental contact with, and electrical shock from, enclosed equipment.
CEMA/NEMA 12 - Provides indoor protection against falling dirt, dust, oil and water.
CEMA/NEMA 4 - Provides indoor protection in hosed down, very wet or outdoor environments, as well as falling dirt, dust, oil and water.
RUNWAY
The rails, beams and columns on which the crane operates. The rail, on which the endtrucks run, is fastened to the runway beam. This beam is then supported on columns (Top Running) or from the roof structure (Under Running). The existing building columns can be used or new ones can be supplied with the system. New columns can either be completely Free Standing or Tied Back to the existing building structure for additional lateral support. When designing a runway system that is utilizing existing building columns, it is important to provide the center to center spacing between the columns. Conductors supply power to the crane and are mounted on the runway beam.
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