Crane And Hoist Duty Cycle Classification

Date: 05/26/2020

Previous Blog: Improving Safety with Data

 

What is Duty Cycle and Why Does It Matter?

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 builder 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.

FEM Classification Chart

 

After load spectrum is determined, the expected daily operating time of the equipment is calculated using the following equation:

Expected Daily Operating Time Calculation

  • 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.

Safe Working Period Chart

 

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-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.

 

Comparison Of FEM And ASME Hoist Duty Service Classifications

There are three important differences to note between FEM and ASME duty classifications. First, FEM is one of the most stringent classification systems, meaning if your crane is covered by FEM, it is held to one of the highest standards. Second, FEM and ASME cover different parts of a crane. FEM covers the mechanical standards of hoist, trolley and bridge motion, while ASME covers the hoist only and relies on CMAA specifications for the bridge and trolley motions. Finally, ASME takes the number of starts/stops per hour into account.

Conversion between FEM and ASME is possible using the following conversion charts:

FEM and ASME conversion chart

 

CSA C/US Certification For Electronic Cranes And Hoists

CSA International is a Nationally Recognized Testing Laboratory (NRTL) accredited by the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA) to test and certify products. All CSA requirements for overhead cranes, gantry cranes, monorails, hoists, and jib cranes are found in CSA B167-16.

Certification from CSA International indicates that a trolley or bridge conforms to a range of electrical safety compliance measures and are subject to periodic follow-up inspections to verify conformance. CSA certification is an important factor because it ensures protection against electric shock and fire hazard. CSA Certification is required in Canada.

 

Determining Hoist Duty Service Rating

The longevity and duty rating of your equipment is one of the top five questions you should ask your crane builder before moving forward with a purchase. Duty service classifications are highly technical and specific. If you’re in the market for a new crane or hoist, it’s worthwhile to consult with experienced professionals about duty ratings.

At R&M Materials Handling, our customers often rely on us to find the crane best suited for their application. Our online Crane Designer tool can even provide instant recommendations and helpful information, based on your specific lifting needs. Contact one of our application experts online before making any duty cycle decisions or give us a call at 937-328-5100.