Equipment 101: Overhead handling equipment basics
With straight rails that result in easy installation, under-hung bridge cranes can handle up to 15 tons and their spanning capabilities can eliminate the need for additional supporting structures.
December 01, 2011 - MMH Editorial
Up, up and safely on its way. Sometimes the best way to transport product through a warehouse or manufacturing facility is to lift it up then move it along. Handling materials overhead can increase productivity, enhance safety, improve ergonomics and maximize available floor space.
There are many types of overhead materials handling equipment, but they all share the same goal of safely lifting product and moving it efficiently and ergonomically from one point to another without damage to the product or the facility—or injury to the worker.
The right equipment for the job depends on the process, the product being moved, the task being performed and the desired rate of throughput. “There is a range of solutions in overhead handling,” says Jeff McNeil, marketing manager at Gorbel. Different configurations and technology mean there are a lot of choices in overhead handling equipment, he says, and an operation’s final equipment selections are usually based on performance and cost.
Overhead handling solutions can range from simple, manual hoists to fully automated systems with movements directed by software. Regardless of the complexity, the equipment, especially the equipment in the middle where people are working together with technology, should shoulder the bulk of the work. This equipment report looks at the primary overhead handling equipment: cranes, hoists and monorails.
Today’s overhead cranes enable the movement of product above the floor, especially when handling materials manually or by lift truck isn’t practical, productive or safe. Instead of being limited to available aisle space and moving materials by a lift truck or other floor traveling systems, overhead cranes allow you to cover a broad area of the manufacturing plant and move products through the manufacturing or storage process using all of the free space overhead, explains John Paxton, president of Demag Cranes & Components.
Cranes can be manual or power driven, depending on the application and the size of the load that’s being moved. For example, workstation cranes and jib cranes are used to improve ergonomics in small areas, while bridge and gantry cranes handle the heavy lifting tasks over longer distances.
While there are a variety of crane styles, all include three basic components: bridge, trolley and hoist.
The bridge, which can be stationary or mobile, is made of rails and can carry one or more trolleys.
The trolley is the unit that travels side to side and carries the hoist.
The hoist is the lifting device that hooks onto and manipulates the load.
Cranes are also available in various load capacities, from workstation cranes that enable operators in a work cell to safely manipulate light loads (typically below 2 tons) to very large overhead cranes capable of transporting loads weighing as much as 500 tons.
While many cranes are pre-engineered solutions, which are produced from standard hoist and drive components, Paxton explains that the cranes with lifting capacities above 50 tons are usually engineered solutions with controls specifically designed for the manufacturing process that the cranes support.
On a smaller scale, free-standing workstation cranes enable operators in a work cell to safely and accurately maneuver light loads. These free-standing units improve ergonomic handling of product in a limited area, like production environments.
Some of the newest workstation cranes are intelligent devices that combine manual and servo-driven operations. The manual function allows workers to move at their own pace as they walk to a bin, select a part, and guide the crane to a machining center process.
The servo-driven function controls the positioning of the part on the machine, preventing damage to both by slowing down for part placement and release.
Gantry cranes are comprised of two uprights connected by an I-beam that serves as the bridge for the trolley. Gantry cranes can be manual or powered. In a powered gantry crane, the uprights run on a track at floor level; in a lighter-duty crane, the uprights are on wheels and can be manually positioned and repositioned around a facility. With load capacities of up to 5 tons and spans of up to 30 feet, gantry cranes are most commonly used in maintenance operations. They are a cost-effective solution for applications that require infrequent duty.
Jib cranes are also used for spot handling. These cranes include a single bridge that rotates to cover a circular area. Because the crane rotates, loads are easy to position. Jib cranes are often used in conjunction with an overhead crane to improve throughput in areas with more traffic and production than a single crane can handle.
Free-standing jib cranes are bolted to the floor and require a strong enough foundation to support the load without the crane tipping over. Because they are free-standing, they offer 360-degree rotation.
Articulating-arm jib cranes are simply jib cranes equipped with a pivoting two-piece arm. This gives the operator more precise control in positioning the load.
When it comes to muscle, overhead cranes have the most lifting capacity. Bridge and gantry cranes do the heavy lifting over long distances.
Bridge cranes are ceiling-mounted and allow loads to move in six directions: up and down, forward and backward, and side to side. They are typically part of a building’s structure and installed when the facility is being built.
Always powered, bridge cranes consist of a trolley that runs across a bridge (which can have one or two girders). The bridge moves across a bay along a runway. The largest capacity units—known as top-running, double-girder cranes—mount the bridge on top of the runway and have two girders for the bridge. With capacities of up to 600 tons, a top running crane gives you the maximum headroom of any crane. Alternately, under-hung cranes, which are ideal for loads of 15 tons or less, have a trolley that runs on the bottom of the support I-beams.
In addition to top-running cranes, there are under-hung cranes where the trolley runs on the bottom of the support I-beams and can get loads closer to the wall. While distance is no impediment for this type of crane, an under-hung crane cannot lift a load as high as a top-running crane system and is meant for loads of 15 tons or less.