Which Type of Overhead Crane Suits Your Needs?
Top Running or Under Running Cranes
Dependent on the type of building, comparative costs of the basic cranes are almost identical. Costs of runways and supports however, can vary tremendously.
Underhung cranes are almost universally used in capacities up to 3 tons and frequently up to 10 tons. If your building has been engineered to support from the roof girders, joists, etc., then the cost of runways and installation is relatively inexpensive, and underhung cranes can be used.
When the overhead beams cannot support the crane load, then a top running crane, operating from self supporting runways, is required. Headroom requirements for top running cranes are generally less than for underhung models; however, recessing the bridge girder on the underhung crane may give a similar headroom savings.
Single Girder or Double Girder Cranes
Single girder cranes are substantially less expensive to build, but are limited to shorter spans and lighter capacity applications. They are ideal for capacities up to 10 tons and spans to 60′. Longer spans and larger lifting capacities are available under certain circumstances. Intermittent duty service will allow capacities up to 15 tons and spans to 60′ which allows the economy of simple design and the use of the lower cost monorail style hoists.
Double girder cranes give the maximum stability for high speed cranes and are essential for long spans and large capacities and a must in heavier duty applications. Somewhat lower headroom clearances may be achieved with the double girder design; however, properly designed single girder cranes with low headroom hoists can offer the same or less space requirements at substantially lower cost.
Hand Push or Hand Geared Cranes
For very light capacity cranes of one or two ton capacities, hand push cranes can be furnished. They have either a hand or an electric hoist, and are without motor drives on the trolley and bridge crane wheels.
Hand geared drives are for cranes of heavier capacities up to 10 tons and suited for short runway applications of stand-by service (i.e., located over a specific piece of machinery for refined areas). These cranes will normally have a hand hoist or a slow speed lift electric hoist with a geared trolley and hand geared bridge.
Gantry Cranes – Great in the Right Application
Gantry cranes can offer a unique solution in answering a need for additional and supplementary crane coverage, off-setting costs of the building structure and in covering outside storage and fabrication areas.
Gantry cranes can be an inexpensive solution to overhead crane requirements when existing building structures cannot support a crane or when the cost of a self supporting crane runway structure is prohibitive.
The initial expense of a Gantry crane is somewhat greater than a conventional overhead crane of the same size, however, the larger cost is more than compensated by the elimination of the overhead structure and runways.
The major drawback to the use of a Gantry crane is the moving structure rolling along the floor, and the necessity of a clear floor space along the length of the runways. The in-floor tracks may prove bothersome to wheel carts and fork lift trucks operating across these areas.
Gantry cranes normally travel on small gauge ASCE railroad rail similar to the travel of the top-running crane. The rails can either be recessed into the floor or set directly on top of an adequate floor surface. Two specific types of Gantry cranes are commonly employed:
Single-Legged Gantry Cranes
These cranes are normally used to offer additional crane coverage in plants having large capacity and long span bridge cranes operating overhead. An additional rail system is mounted below the rail on the overhead bridge crane. One side of the Gantry crane rolls on a rail on the floor and the other side rolls on the supplementary overhead crane rail. This type of crane is used to cover long work areas where the swing area coverage of a jib crane would not be sufficient.
Double-Legged Gantry Cranes
These cranes are used on two parallel in-floor tracks and are excellently adapted for very heavy lifts, supplemental inside crane systems, and outside cranes.
Jib Cranes – A Lot of Work for the Money
Jib cranes are primarily used as supplementary light capacity lifting systems to service a single machine or manufacturing operation. They are available in a wide variety of styles and can be mounted on existing building columns, or on an independent, self supporting post located virtually anywhere a lifting task must be performed. Jib cranes are a rotation boom suspended on a fixed hinge point and can be designed to allow hook coverage with up to 20 ft. radius and 360 degrees around the center support point.
Jib cranes are normally available up to 5 ton capacity and are a relatively inexpensive structure compared to a full coverage overhead crane system.