Deciding Overhead Crane Duty Cycle Ratings

Overview:

• Determined by severity and repetition of use, not capacity.
• Can mean $100,000 difference in price of otherwise similar crane.
• Hard to explain, easy to fool customers and buyers.

The duty cycle of your overhead crane is very important. It can make a possible $100,000 difference in price of the crane. It’s determined by severity factors and repetition factors. It’s classified in a number of ways by a number of different manufacturer’s organizations, and the classifications can easily be twisted or bent into white lies that can mean a significant but un-needed jump in price or a perceived bargain that is really an undersized overhead crane.

The severity factors of overhead crane duty cycle include atmosphere, at-capacity lifts, distance lifted and shifts used. Atmospheric conditions such as fine grit or dust or combustive/caustic gases should be noted in your request for competitive proposals. When the overhead crane lifts loads at or near capacity more than fifty percent of the time, it should be noted in the request for competitive proposals. Also, note the amount of shifts used – sometimes a warranty or durability calculation is made on shifts. When a crane runs 3 shifts/year, that is technically three times the amount of work and wear on the overhead crane.

The main repetitive factor is starts per hour. This does not just include cycles per hour. A cycle is one productive step – in other words, it would be considered a cycle for the overhead crane to lift a steel coil from a truck and move it to a storage area or processing machine. Typically in that cycle, the up button is pressed two or three times. Each press of the up button is considered a start.

Many potential buyers approach us with the dilemma of not knowing the information. This writer understands time is valuable, and a supervisor spending an entire shift in the shop counting starts may seem wasteful or overly watchful. This is a case of do the best you can. A day spent in the shop making counts of starts, observing how many loads are at or near capacity, and noticing how long the overhead crane stays on between starts will be exceptionally beneficial! If a day in the shop is just not possible, provide a detailed explanation of what the crane does if possible. Also, note the duty cycle, typically expressed between “A” and “F”, and/or the hoist rating, typically expressed by the letter “H” followed by a number one through six.

      A few particular bits of info are useful. A standard crane under thirty tons is not made at less than a “C” class duty. Most cranes are “C” class duty. A manufacturer claiming to have an “electrical class D” is not providing a structural class D, and is not providing an uprated hoist. If a class D crane is called for, make sure the hoist and structural elements of the crane meet class D as well.