Workhorse hoists

From steel plants to assembly work cells, hoists lift, lower and position loads weighing several tons as easily as they handle a few pounds.

By Gary Forger, Editorial Director -- Modern Materials Handling, 3/1/2003

Think of a hoist and the first image that usually comes to mind is one with a heavy load such as a large coil of steel. But that isn't always the case. Hoists are just as adept at lifting and lowering relatively light loads, even less than 20 pounds, and positioning them at a work cell or elsewhere.
In fact, hoists now play an even greater role in workplace handling as managers become more aware of the ergonomics of moving loads.

Where workers were once expected to move much heavier loads, 25 pounds is now considered to be the high end of what is acceptable practice. And as hoists are more widely used for these lighter loads, they have a positive impact on workers' compensation claims.

When paired with other handling equipment such as overhead cranes, hoists literally bring another dimension to materials handling. That additional equipment allows loads to move horizontally between pickup and deposit points as the hoist moves the load vertically. In other words, hoists have greater range than sometimes thought.

The trick, of course, is matching the right hoist to the application. Considerations to take into account include the size of the load, lifting distance and desired speed. Then it's a matter of matching those parameters to hoist specifications. Important ones include; the frequency of hoist use, power source, type of motor, controls, chain or wire rope, and mounting options.

All hoists are categorized by duty classes from H1 for infrequent use to H5 for use 60 to 100 percent of the work period (see table below). It is important to match this class to the application to ensure a proper balance between cost efficiency and work efficiency of the hoist. In fact, it is just as important as matching the load capacity of the unit to the tasks at hand.

Then there's the matter of the power source. The options are manual and powered.

There are two types of manual hoists - ratchet lever and hand chain. With the former, the operator performs short lever strokes with a hand ratchet that manually moves a wire rope with a hook that is attached to the load. Hand ratchet hoists are typically used for rigging or installing machinery as well as other activities that require infrequent use.

Hand chain hoists are usually used to lift loads of several tons to a maximum height of 20 feet. The operator pulls on the chain that runs through the hoist's internal gearing, which eases the lifting process and ensures the chain does not slip back. Hand chain hoists are best suited to infrequent or light use. 

For most other applications, powered hoists are preferred. They handle loads in a wide range of duty service classes, and offer excellent ergonomics for lifting and lowering loads.

Both electric- and air-powered models are available. Although widely used, electric hoists are not always preferred. Air power is the answer when a spark from an electric motor could endanger operators. In addition, pneumatic hoists may be the choice if a pressurized air system is already installed in the facility. Both types position loads with equal precision.

Motors on powered hoists have single, double or variable speeds. The motor selected has the most impact on how smoothly the load is moved, and the precision of positioning the load. Generally, single- and double-speed motors have less flexibility. However, flexibility is not always required as much as the simplicity of operation possible with single- and double-speed motors.

As a rule of thumb, single-speed motors run at 10 to 26 feet a minute. A creep speed that helps with positioning is added with double speed. Variable speed typically offers the greatest load positioning precision and smoothness of movement.

To control the speed of a hoist, either an attached pendant or remote control can be used. The pendant is hard-wired to the hoist and consists of a series of push buttons that control hoist movements. Depending on the length of the wire, the pendant requires the operator to be relatively close to the load as it moves. Under certain circumstances, this can be a safety issue. These include the possibility that the operator might
trip when walking along with a load being moved by an overhead crane. Furthermore, operators sometimes must wend their way around obstacles on the floor, making their movement awkward at best. As a result, some companies prefer not to have their operators use pendants.

That's where remote controls come into the picture. Using radio or infrared signals, these control boxes allow the operator to be any distance desired from the moving load. About 98% of these units are radio frequency today. Unlike infrared signals, radio frequency does not require a line of sight to send the signal, giving operators still greater flexibility in where they are positioned doing load movement.

Just as with manual hoists, powered ones use either a chain or wire rope to lift and lower the load. Chain is used primarily to lift lighter loads with less frequency and provides greater service life than wire rope. During operation, the chain is either allowed to trail on the floor or is stored in a container.

Wire rope hoists wrap unused rope around a grooved drum on the unit. The lifting distance required will determine the length of chain or wire rope required.

One final consideration is the mounting of the hoist. Options here include a fixed point, a trolley that runs along an I-beam, and an overhead crane. While the first one limits load travel to up and down, the other two allow the hoist to move the load horizontally between locations. Packaged hoists are for use with fixed or I-beam mountings. Engineered hoists are for overhead cranes.

Whatever the final selection made, hoists not only make the work easier but safer and more ergonomic.

Click on the icon to read how Brannon Steel retrofit its hoists for new efficiency.