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.
This is an old industry, says Bret Lussow, business development sales manager for Harrington Hoists. “This is not a high-tech industry such as computers or cell phones. However, this old industry is adapting the latest technology, making hoists more reliable and safer than ever before.”
A hoist can be a key part of a crane system. But these mechanical devices can also stand alone for vertical lifting jobs, raising and lowering loads, like individual work-in-process.
Hoists can be divided into three categories based on power source:
electric (including wire rope and chain hoists),
and manual (including hand chain and ratchet lever hoists).
Lately there have been improvements in the areas of material, construction and safety, explains Lussow.
Electric hoists, which are the most common type, are using more efficient motors that reduce amperage draw. Electric hoists range in lift capacities of 250 pounds, which can be purchased off-the-shelf, to several hundred tons, which are usually custom engineered.
All electric hoists are rated by duty cycle. The rating determines how long the hoist’s electric motor can run before it needs to cool. Meaning, an electric hoist with a 25% duty cycle can be used continuously for 25% of an hour, or 15 minutes, before it needs to cool.
Electric hoists are available with single-speed, double-speed or variable-speed electric motors. While single-speed motors are the least expensive, double- and variable-speed motors offer some advantages. For example, an operator can begin lifting a load at a slow speed then ease into a higher lifting speed. This reduces shock on the system and extends the life of the hoist. Operators can also slow the hoist at the end of a lift, allowing for more precise and gentle positioning of the load.
Because they are hard-wired to a power source, electric hoists have a dedicated location in a facility. Electric hoists are also available in wire rope and chain designs, which, according to Lussow, have seen improvements to the strength of wire rope or chain used as the lifting medium.
Wire rope hoists, which are used to lift very heavy loads, are controlled by an operator who presses a button to start the motor. The motor drives a set of gears, which then turns a grooved drum.
The wire rope winds around the drum as it turns and lifts the load. These hoists can reach capacities of hundred of tons, but the majority are 5-ton and 10-ton models and used for such jobs as assembling automotive equipment.
Chain hoists are also manually activated. An operator starts the electric motor that turns a set of gears, which then turns a lift wheel. Pockets in the lift wheel engage the links of the chain that raise the load as the chain rides over the wheel. The chain coming off the wheel either hangs or is collected in a container below the hoist. Chain hoists range in capacity from 250 pounds up to about 20 tons. They are slower than their wire rope hoist counterparts, smaller and more maneuverable.
Air driven, or pneumatic, hoists don’t have electric motors, don’t require electricity and don’t overheat. What they do have is the ability to facilitate highly repetitive assembly line applications because they can be used continuously and don’t need the cooling time that electric hoists require.
“Speed, speed, speed. It’s all about increased production,” says Lussow. “These hoists are ideal for mass production, production lines and foundries,” he adds.
The majority of air-driven hoists use chain as the lifting medium. They function much like electric chain hoists, but they are not hard-wired to an electrical system.
Slower, manual hoists are small and mobile, and usually used for maintenance and other non-repetitive tasks. Manual lifting devices like hand chain and rachet lever hoists are simple lifting technology that are very affordable and very effective, says Gorbel’s McNeil.
Hand chain hoists have two chains: one chain attached to the load and a pull chain. As the operator pulls the pull chain, the hoist’s internal gears raise and lower the lift chain and provide the mechanical advantage for easing the lifting process. For example, lifting a 1-ton load with a hand chain hoist requires just 54 pounds of effort. While these hoists can lift 70-ton loads, the majority of the market is in the 1- to 5-ton range.
Rachet lever hoists can use either wire rope or chain. They work like hand chain hoists, but use a lever rather than a pull chain to rotate the sprocket that activates the lifting mechanism. With capacity ranges from 500 pounds to 9 tons, rachet lever hoists are best suited for low-lift applications, usually less than 5 feet. These hoists can lift vertically and pull horizontally, and are commonly used for pulling rather than lifting.
Monorails consist of a single rail, or I-beam, from which a hoist or hook hangs. Together, the monorail system components allow loads to move both horizontally and vertically.
The basic concept of the monorail system has not changed much over the years, but what has changed are its applications. In addition to heavy-duty cycles, monorails are being used more and more for medium- and light-duty cycles in warehousing and a variety of manufacturing applications.
With load weight capacities of up to 30,000 pounds, electrified monorail is durable and flexible. Each carrier unit has its own drive unit and can run at variable speeds in different areas, traveling at up to 600 feet per minute. Product transported by monorail is powered by a bus bar, or power rail, inside the I-beam.
Monorail can be an expensive solution, and should be seen primarily as a high-speed, long-distance transportation system. “The cost of automation equipment is going down, but it’s still relatively expensive compared to more simple solutions like manual cranes and hoists,” says Gorbel’s McNeil.