Duty Cycle is Everything to the Expert

Crane Duty Cycle

I once read that the amateur military historian argue strategy, while the professionals argue logistics. In other words, to use another saying, "the devil is in the details."

When is comes to talking about cranes, most "amateurs" just say capacity and span or 10 ton/30 ft span and think their done. The real "pros" know, they've just started. Like almost any piece of electro-mechanical piece of machinery, Duty Cycle means everything. Duty Cycle dictates brake size, wire size, horsepower, gearbox size, etc. Without considering Duty Cycle, it implies that your Kubota lawn tractor from Home Depot would be just fine for cutting the grass at Augusta National Golf Course.

Even though your Kubota does a fine job on your one acre lot, it would have a very short life working, eight hours a day, seven days a week, and the same goes for cranes.

The following is a part of the Crane Manufacturers of American, Duty Cycle Classifications.

Class A ( Standby or Infrequent service)

This service class covers cranes which is in installations such as public utilities, turbine rooms, power houses, motor rooms and transformer stations where precision handling of equipment at slow speeds with long, idle periods are required. Capacity loads may be handled for initial installation of equipment and for periodic maintenance shutdowns.

Class B (Light Service)

This service covers cranes which may be used in  light assembly operations, service buildings, repair shops, light warehousing, etc. where service requirements are light and travel/lift speeds are slow. Loads may vary from no load to occasional 100% full rated loads with two to five lifts per hour, averaging ten feet.

Class C (Moderate Service)

(this is by far the most commonly crane sold)

This is for cranes which may be used in machine shops or paper mill machine rooms, etc., where service requirements are light to moderate. Cranes will handle 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 full rated capacity.

Class D (Heavy Service)

(most "mis-represented" classification by sellers)

This service covers cranes 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 (Severe Service)

(could be compared to a AIST class crane)

This type of service requires a crane capable of handling loads approaching a 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 twenty or more lifts per hour at or near the rated capacity.

Class F (Continuous Severe Service)

(could also be compared to a AIST class crane)

This service rating requires a crane capable of handling loads approaching rated capacity in constant service under severe service conditions. This may include custom designed specialty cranes essential to performing the critical work tasks affecting the 24/7 production facility. These cranes must provide mission critical reliability with special attention to ease of maintenance features.

 

This is a good starting point to understanding the differences between the crane classifications. To give you an idea of the importance of getting it right, I once had a customer need both a Class C and Class F crane of the same capacity and span. The Class C crane was $30K and the Class F crane was over $350K. The exact same capacity and exact same span!!!

The bottom line, is that Duty Cycle should not be a footnote but rather a headline in the conversation about choosing the right crane.