What is a duty cycle of a lifting crane

What is a duty cycle of a lifting crane?

Beyond “crane lifting capacity”, there is one additional factor to consider, “Duty Cycle”. What Does Duty Cycle Really Mean?

In the lifting crane world the terms “heavy” and “heavy duty” are often confused. A lifting crane is designed to lift, what it’s designed to lift, therefore it’s not “heavy”. Even if a lifting crane is a 500 ton lifting crane, if it only makes one pick per week, it’s cannot possibly be considered “heavy duty”. Heavy duty usage is a factor measured by the amount of work performed, and one pick a week is not much work.

overhead crane 

Service Class Description Duty Cycle Definitions

The CMAA has established a duty cycle rating system that ranges from a Class “A”-Standby Service to a Class “F”-Continuous Duty, to measure the amount of work to be performed by the lifting crane. It consist of a somewhat confusing combination of primarily two factors,

• Average percentage of full capacity lifted
• The number of starts/hour

According to Crane Manufacturers Association of America, the description service class and definitions of duty cycle of lifting cranes are as following:

Class A

Description: Standby or Infrequent Service
Duty cycle definition: This class normally includes installation and maintenance lifting crane s. This equipment usually operates at slow speeds for precise handling with long idle periods between lifts. Maximum capacity lifts are sometimes required.

Class B

Description: Light Service
Duty cycle definition: This class of lifting crane is used in repair shops, light assembly operations, service buildings, light warehousing, etc. Service requirement is light and speeds are slow. Loads vary from none to occasional full capacity. Lifts per hour would range from 2 to 5, and average 10 feet per lift.

Class C

Description: Moderate Service
Duty cycle definition: In terms of numbers, most lifting crane s are built to meet Class C service requirements. This service covers lifting crane s that may be used in machine shops or paper mill machine rooms. In this type of service, the lifting crane will handle loads that average 50% of the rated capacity with 5 to 10 lifts per hour averaging 15 feet. Not over 50% of the loads at rated capacity.

Class D

Description: Heavy Service
Duty cycle definition: This service covers lifting crane s which 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 will be handled constantly during the working 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

Description: Severe Service
Duty cycle definition: This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead traveling lifting crane s and requires a lifting crane capable of handling loads approaching rated capacity throughout its life. Applications may include magnet, bucket, magnet/bucket combination lifting crane s 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

Description: Continuous Severe Service
Duty cycle definition: This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead traveling lifting crane s and requires a lifting crane capable of handling loads approaching rated capacity throughout its life. Applications may include custom designed specialty lifting crane s essential to performing the critical work tasks affecting the total production facility. These lifting crane s must provide the highest reliability, with special attention to ease of maintenance features.
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