Lifting loads in factory applications is as old as the Industrial Revolution, but today’s manufacturers face problems unimagined by pioneers such as Henry Ford or George Westinghouse.

Modern operations are optimized to extract every dollar of value from every square foot of plant floor area and with increasing automation; the need for higher throughput is accelerating. Moving loads by overhead bridge, gantry or jib cranes is a proven method for both in-process production articles and for tooling, but most manufacturing engineers have little understanding of how to optimize their lifting systems.

Which Crane Type is Best for Your Application?

In manufacturing operations, overhead cranes and jib cranes are most commonly used, with large overhead units frequently built as part of the plant facility during construction. Bridge units offer heavy lift capability over a wide area, frequently the entire production floor, while jib cranes are used for localized, lower capacity lifting in typical manufacturing use. Selecting the right crane for a manufacturing application requires more information than simply the weight of the load to be lifted.

American Crane, located in Douglassville, Pennsylvania, maintains a large database of downloadable resources and describes how the Hoist Manufacturer’s Institute and the Crane Manufacturer’s Association of America specifications define the industry standard classification system for cranes commonly used in manufacturing:

CMAA Class C: This is a moderate service classification for loads which average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet, not over 50 percent of the lift at rated capacity. Manufacturing operations, tool rooms, machine shops and maintenance facilities frequently use Class C equipment.

CMAA Class D: Class D cranes are heavier service units used in foundries, heavy fabrication shops, shipyards, steelyards and similar heavy production environments. Loads approaching 50 percent of the rated capacity are handled constantly in this service. For production use, speed is more important than for Class C uses, typically 10 to 20 lifts per hour averaging 15 feet, not over 65 percent of rated capacity.

For heavy loads, traditional designs use open deck machinery, which is straightforward to engineer using heavy bearings, shafting and drive units. Smaller loads were typically handled by more economical packaged hoists, but improvements in technology have allowed packaged units to handle heavier payloads – enough to move some applications into Class D service.

The Hoist Manufacturing Institute lists several classifications from multiple standards organizations around the world. In North America, a popular system has been established by the ANSI and ASME, Classes H2 through H4.

Medium duty H2 and H3 hoists are common in service and machine shop applications, while heavy duty H4 equipment is migrating into big Class D territory, which can add failure risk in some applications. While it’s easy to specify an overrated unit for moderate loads, operating at the upper end of a hoist’s rating for big loads requires careful planning to match the equipment to the dual target of high efficiency and low cost.

For lowest cost and profitability, packaged hoist solutions are frequently the best answer – if they meet the needed service class.

Matching the Right Hoist to the Task with the Norheim Hoist Line

American Crane CEO and President, Oddvar Norheim. (Image courtesy of American Crane.)

American Crane & Equipment Corporation recently launched a new hoist line that addresses the issue of matching the right hoist to the task. Named for American Crane’s president, Oddvar Norheim, the Norheim Hoist Line consists of six basic hoist types with extensive, customizable options to suit specific industrial requirements.

These options include single, double and two part double-reeved versions, operating on top running, dual rail underhung or monorail trolleys. The line is built in compliance with OSHA requirements and CMAA Specifications 70 and 74.

This Norheim Type 16 version is designed as a double reeved, top running trolley. Capacity is 15 – 50 tons. Many versions are available in multiple ratings and configurations. (Image courtesy of American Crane.)

The Norheim line was developed by combining CAD design and simulation tools to optimize bearings, gear trains and motors, taking advantage of variable frequency AC drive systems. Variable frequency drives are common in modern industrial equipment where loads and speeds vary, but they’re especially efficient in hoist applications because they allow fine speed control with consistent torque. The drives accomplish this by starting with a lower frequency and voltage, preventing the very fast current ramp-up common to direct online starting. Both frequency and voltage are ramped together to accelerate the motor.

This has several benefits, but a major advantage for hoist applications is torque. With variable frequency drives, it’s possible for an AC motor to develop 150 percent of its rated torque while drawing half its rated current when operating at low speeds. The same process works to slow the motor smoothly, and even allows a braking effect if needed.

The benefits for hoist applications include:

Smooth acceleration and deceleration
Lower peak current loading
Reduced energy consumption
Reduced wear on mechanical components
Little or no shock loading when “jogging” the load
Enhanced user control and safety

Variable speed AC drives on electric motors have been used successfully as discrete components for years, but until recently cost and size constraints limited their application in packaged hoists. American Crane’s Norheim Line integrates the drive electronics into the units as complete assemblies. No special electrical service is required, and issues such as bearing damage due to shaft currents are avoided by shielding and grounding designed specifically for the hoist assembly.

From a user perspective, however, this drive technology is ideal for applications where speed must be combined with precision. An example is press tooling, where the need to split a die shoe weighing several tons is a balance between precision, minimum downtime and the need to avoid shock loading to protect hardened tool steels. If desired, Norheim hoists can be specified with conventional contactor controls in dual speed configurations of up to 20 horsepower.

Norheim hoists can be delivered in top running or monorail trolley versions in standard or low profile and single or double reeved. Custom solutions are also available. (Image courtesy of American Crane.)

How to Maximize Efficiency

Many engineering professionals responsible for manufacturing production come from a mechanical engineering background. However, most have no idea how to specify the correct hoist for maximum efficiency. That’s understandable, when we consider the complexity of hoist standards and testing.

Consider the ANSI/ASME HST-4 standard, widely used in the industry. Average operating time per day, load spectrum, starts per hour, operating periods and desired equipment life are all factors that need to be considered when choosing a hoist in the correct service class. European standards assume a 10-year service life, which is a good baseline for comparing service classes for the US ANSI/ASME standard. Assuming 250 working days per year, the average operating time per day to achieve the ten-year life expectancy can be as little as 30 minutes/day for service class H1 units, or as much as 8 hours for an H5 hoist. That’s a wide range, and it’s only one factor to consider.

This American Crane fabricated custom grapple saves time in production. Its weight must be factored into the service classification equation. (Image courtesy of American Crane.)

Load spectrum is another issue. Load spectrum is a mathematical model of the range of loads a hoist will lift in service, including occasional full load conditions. This is an important consideration in manufacturing applications, especially where large permanent “below the hook” lifting devices are used to cradle the load. Even a simple spreader beam is a dead load that the hoist supports between lifts; load spectrum calculations take this into consideration, as well as occasional heavy lifts in an otherwise light duty application.

Starts per hour and average operating time per day are also important, although advanced AC drives, such as those used in the Norheim hoists, reduce the significance of starts compared to run time per hour.

Do these tough standards exclude packaged hoists from performing bigger jobs? Not necessarily. The Norheim line meets HMI H4 standards, and can be ordered with CMAA Class A, B, D, E and F ratings up to 160-ton capacity. Custom designs are also available.

Why Not Just Over-Engineer My Hoist?

What does all this mean to a manufacturer? The calculations performed by crane and hoist manufacturers such as American Crane might surprise even an experienced mechanical engineer. A lightly loaded unit used continually in a production environment such as a mid-sized metal service center might need a higher service class than a company that needs heavy lift capability three or four times per shift.

It’s not just a paper problem. A machine tool manufacturer, for example, typically moves a heavy base casting between multiple work cells. From raw casting to loading dock, a unit might move a dozen times, with each workstation assembling to labor cost targets that require minute-by-minute monitoring of assembly time. A slow hoist that adds even two or three extra minutes per movement has a cascade effect on productivity that can add significant cost to a production line.

It’s not uncommon for a manufacturer to install expensive automation solutions to shave a minute or two from an assembly task, then end up giving that advantage away between work stations. A standard engineering approach, selecting the maximum expected load and adding a safety factor, can lead to choices that compromise safety or result in expensive, needlessly slow production.

There are many factors to consider when specifying a hoist system; where should a manufacturing engineering manager start? Consult experts like American Crane, and be ready to talk about your production process, productivity goals and cost targets. Packaged hoists such as the new Norheim Line can offer a significant cost advantage, both in acquisition and running costs.

Every minute of line time on the production floor is valuable, and choosing the right crane and hoist system can make the difference between lost productivity and a smooth-running operation.

American Crane offers a comprehensive free guide to choosing the right crane, courtesy of the CMAA, here. Also, for more information about American Crane’s new Norheim Hoist Line, click here.

American Crane has sponsored this post. All opinions are mine. –James Anderton