In this article, we lay out the basics of FEM and ASME duty service ratings, CSA certifications, and how to identify the right duty service rating for your hoist and crane application.
Picture this: Two people are in the market for a new lawn mower. The first person owns a landscaping business. The second person has a small patch of grass they will mow once a week.
These lawn mowers have very different duty cycles, or expected average workload and daily operating time. The first person will need a heavy-duty lawn mower that can handle a high duty cycle so that it can safely perform a high volume of repetitive workloads without overheating or needing excessive maintenance. The second person should choose a low-duty push mower because the investment into heavy-duty equipment is not economical for a small patch of grass.
The stakes are much higher when it comes to investing in a crane or hoist. That’s why cranes and hoists are engineered to meet specific, standardized duty service classifications. The greater a crane’s workload, the higher its duty cycle and the greater its potential to experience abnormal wear and require unexpected maintenance if not properly sized.
Service conditions have an important influence on the performance of a hoist’s wearing parts, such as bearings, ropes, sheaves, electrical equipment, brake linings and wheels. Careful consideration of the crane service classifications will enable the user to evaluate their application and obtain a hoist and crane designed for optimum performance and minimum maintenance coupled with the best value.
DUTY CLASSIFICATION TYPES
When a crane manufacturer calculates the duty cycle for your application, they do so using FEM, ASME and CMAA classification systems. FEM classifications are primarily employed in Europe and are the standard for hoist, trolley and bridge duty motion. In North America, crane builders use ASME classifications to provide duty cycle standards for the hoist and CMAA standards for the duty cycle of the trolley and bridge. Each of the following standards are intended to be a guide to manufactures, purchasers or users when defining duty cycles.
FEM Standards
FEM Standards are created by the European Material Handling Society and apply to the mechanical function of hoists, trolleys and bridges with typical metric capacities. According to the FEM 9.511 standard, hoist-duty services application is determined by 1) load spectrum and 2) daily operating time.
The FEM classification best suited to your application is determined by first identifying the appropriate load spectrum. Cranes are split into four categories by load spectrum: light, medium, heavy and very heavy.
After load spectrum is determined, the expected daily operating time of the equipment is calculated using the following equation:
H = average hoisting height (m)
N = hoisting cycles per hour
T = daily working time (hrs.)
V = hoisting speed (m/min)
Once both load spectrum and daily operating time are identified, the chart below identifies the appropriate classification. For example, when R&M equipment is used exactly to the appropriate duty cycle, it consumes 10 percent of its Safe Working Period annually, which translates to a 10-year equipment lifecycle. This equation also serves as a starting point for calculating the Safe Working Period of your equipment.
ASME Standards
ASME standards are developed by the American Society of Mechanical Engineers and approved by the American National Standards Institute (ANSI). While FEM covers the mechanical standards of hoist, trolley and bridge motion, ASME covers the mechanics of the hoist only. ASME hoist duty ratings (H3, H4, etc.) apply to hoists marked with typical U.S. capacities (for example, 1 ton = 2000 lbs. = 907 kg) and do not apply to hoists marked with typical metric capacities (for example, 1 metric ton = 1,000 kg = 2,200 lbs.) for R&M equipment.
The ASME hoist-crane duty classification is determined by three main factors:
1. Max no. of starts per hour, defined as the maximum number of motor starts per hour uniformly distributed over a given work period.
2. Max on-time minutes per hour, which equals the maximum number of minutes per hour of run time.
3. Mean effective load, a theoretical single load value that has the same effect on the equipment as various loads applied to the equipment over a period of time.
Typical applications for ASME standards are:
H1 = Idle one to six months, used for installation and/or maintenance
H2 = Light maintenance, fabrication; capacity loads infrequently handled; randomly distributed loads; low running time
H3 = General machining; randomly distributed loads; total running time ≤ 25 percent of work period
H4 = High volume handling of heavy loads near rated capacity; steel warehousing, machining, foundries; total running time ≤ 50 percent of work period
H5 = Bulk material handling with attachments; approaching continuous operation
Defining the correct ASME standard for an application requires referencing the ASME publication catalog ASME HST-4 (latest edition) for electric wire rope hoists and B30.16 for overhead, underhung and stationary hoists.
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