HOIST & CRANE CLASSIFICATIONS—HOW TO SELECT THE RIGHT DUTY CLASS FOR YOUR OVERHEAD CRANE




Purchasing an overhead crane system is a massive step towards improving the efficiency of your business and the safety of your workers. You would not want to create dangerous conditions by overworking your crane or waste money by underutilizing the power of your new equipment, either. To get the most out of and preserve the longevity of your long-term investment, selecting the appropriate service classification for your specific application is critical. 

Why do we need crane classifications?

Variables that go into determining your crane’s components will vary according to the weight of lift load, loading cycles, frequency of use, required speed, length of the bridge span, existing conditions in the work environment, or architectural limitations. Ace Industries designs and engineers cranes custom to your environment.  However,  on some occasions, a crane built from a kit is an appropriate choice for the customer. Still, engineers keep system fatigue and component durability in mind for specific crane uses when designing a complete system. Mechanical, structural, and electrical components are selected to handle unique conditions for each type of application and condition. Therefore, this is why we need crane classifications.

An excellent place to start when purchasing an overhead crane is to answer these questions:

  • What is the intended use of the crane? 
  • How many average lifts and trolley & bridge movements will are made per/hour?
  • What is the average length of each movement?
  • What are the required speeds?
  • What is the estimated load of each lift?
  • How many work shift(s), current and future? 
  • What will the total operating hours be per day?
  • Are there any dangerous conditions in the environment or process?


What is a duty class and who creates these standards?

The Crane Manufacturers Association of America (CMAA) has established crane service classes so that the most appropriate crane for a particular installation may be specified in accordance with Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes-No. 70 or Specifications for Top Running and Under Running Single Girder Electric Overhead Cranes Utilizing Under Running Trolley Hoist-No. 74. The crane service classification is based on the load spectrum reflecting the actual service conditions as closely as possible.

The American Society of Mechanical Engineers (ASME) is a professional engineering society founded in 1888 that is widely known for establishing code standards for mechanical devices, and in this case, hoists.

 

Crane Classification is the category of crane class based on average load, the number of lifts, and the frequency of the lifts performed in a given period. 

 

Duty Rating is a classification given to a hoist indicating the amount of use and type of abuse it can withstand during a given time.

 

Hoist Classification is the category of hoist according to loading, duration, and application.



CMAA Crane Duty Classifications

Light Service— Class B
Moderate Service — Class C
Heavy Service — Class D
Severe Service — Class E
Continuous Severe Service
 — Class F

CLASS B (LIGHT SERVICE)

This service class covers cranes that may be used in repair shops, light assembly operations, service buildings, light warehousing, etc., where service requirements are light, and the speed is slow. Loads may vary from no load to occasional full-rated loads with two to five lifts per hour, averaging ten feet per lift.

 

CLASS C (MODERATE SERVICE)

This service class covers cranes that may be used in machine shops or paper mill machine rooms, etc., where service requirements are moderate. In this type of service, the crane will handle loads that average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet, not over 50 percent of the lifts at rated capacity.

 

CLASS D (HEAVY SERVICE)

This service class covers cranes that may be used in heavy machine shops, foundries, fabricating plants, steel warehouses, container yards, lumber mills, etc., and standard duty bucket and magnet operations where heavy duty production is required. In this type of service, loads approaching 50 percent of the rated capacity constantly handled during the work period. High speeds are desirable for this type of service, with 10 to 20 lifts per hour averaging 15 feet, not over 65 percent of the lifts at rated capacity.

 

CLASS E (SEVERE SERVICE)

This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead traveling cranes. It requires a crane capable of handling loads approaching the rated capacity throughout its life. Applications may include magnet, bucket, magnet/bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc., with 20 or more lifts per hour at or near the rated capacity.

 

CLASS F (CONTINUOUS SEVERE SERVICE)
This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead traveling cranes. It requires a crane capable of handling loads approaching the rated capacity throughout its life. Applications may include custom-designed specialty cranes essential to performing the critical work tasks affecting the entire production facility. These cranes must provide the highest reliability, with particular attention to ease of maintenance features.



ASME Hoist Duty Classifications

Light Use— Class H2
Moderate Cycle—Class H3 or H4
Heavy Cycle— Class H4

H2 LIGHT USE 
Light machine shop fabricating, service and maintenance, loads and utilization randomly distributed, rated loads infrequently handled.
Uniformly Distributed Work Periods (Operating Time Ratings at 65% Mean Load Factor)
Maximum On-Time Minimum per hour: 7.5 minutes (12.5%)
Maximum Number of Starts per hour: 75
Infrequent Work Periods (Operating Time Ratings at 65% Mean Load Factor)
Maximum on Time From Cold Start: 15 minutes
Maximum Number of Starts: 100


H3 STANDARD USE

General machine shop fabricating, assembly, storage, and warehousing, loads, and utilization randomly distributed.

Uniformly Distributed Work Periods (Operating Time Ratings at 65% Mean Load Factor)
Maximum On-Time Minimum per hour: 15 minutes (25%)
Maximum Number of Starts per hour: 150

Infrequent Work Periods (Operating Time Ratings at 65% Mean Load Factor)

Maximum on Time From Cold Start: 30 minutes

Maximum Number of Starts: 200

 

H4 HEAVY USE

High volume handling in steel warehouses, machine shops, fabricating plants and mills, foundries, manual or automatic cycling operations in heat treating and plating, loads at or near rated load frequently handled.

Uniformly Distributed Work Periods (Operating Time Ratings at 65% Mean Load Factor)
Maximum On-Time Minimum per hour: 30 minutes (50%)
Maximum Number of Starts per hour: 300

Infrequent Work Periods (Operating Time Ratings at 65% Mean Load Factor)

Maximum on Time From Cold Start: 30 minutes

Maximum Number of Starts: 300

 

Buying an overhead crane for your business would be challenging without guidance from a reputable and proven expert. Need help determining which crane duty class you’ll need for your new overhead crane purchase? Ace Industries has crane experts on hand to walk you through any questions you might have. Call (800) 733-2231 for more information.






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