This is the first post in a series of posts on CMAA, HMI, and FEM classifications and duty cycles. We will be covering each type of classification in a biweekly post. We will also be doing a comparison of these classifications as a separate post so you can determine which overhead crane and hoist best suits your application. If you have any questions throughout the series, please feel free to contact us.
Today we’re going to talk about crane service classes and duty cycles. The Crane Manufacturers Association of America (CMAA) has established these crane service classes to assist in determining the appropriate crane type for the environment it will be used. CMAA classifications are based on the crane’s number of lift cycles and average load intensity. Basically, how high and how much weight the crane needs to lift and how often the crane needs to do those things in an hour. It is important to choose the right crane classification to ensure safety and longevity of the system as a whole.
To determine which classification is the best fit in your facility, you need to know two main things: how often you will be lifting materials and how much the material weighs. From there, you can select the appropriate crane classification. Crane classifications according to the CMMA service classes are below.
Class A (Standby or Infrequent Service) - This service class includes cranes that are used at slow speeds for precise operations, such as installation and maintenance. These cranes have long periods of idle time between lifts and maximum capacity lifts may be required for installation and infrequent maintenance. Examples are installation and maintenance cranes in turbine rooms, transformer stations, and public utilities.
Class B (Light Service) – This service class includes cranes where the speed is slow and service requirements are light. Loads will vary from no load at all to occasional full capacity. Duty cycle is two to five lifts per hours, at an average of ten feet per lift. Example applications include repair shops, light warehouse, and light assembly operations.
Class C (Moderate Service) – Most cranes fall into this service class. The service class includes cranes that are generally handling loads that average fifty percent of the rated capacity. These cranes have duty cycles of five to ten lifts per hours, averaging fifteen feet per lift. Not over 50% of the lifts are at rated capacity. Example applications include general machine shops, fabrication shops, and moderate assembly shops.
Class D (Heavy Service) – This service class includes cranes that are used in heavy service applications. Loads at fifty percent of the rated capacity are handled constantly during the crane’s working period. In general, high speeds are desired and the duty cycle is ten to twenty lifts per hour, averaging fifteen feet per lift. Not over 65% of the lifts are at rated capacity. Example applications include foundries, steel warehouses, heavy machine shops, and lumber mills.
Class E (Severe Service) – This service class includes cranes that handle loads that approach the rated capacity throughout the crane’s lifetime. The duty cycle is 20 or more lifts per hour at or near rated capacity, at any height per lift. Because of this, the maintenance for these cranes is more frequent. Example applications include cement plants, scrap yards, lumber mills, and container handling. Check out our recent Class E crane installation here.
Class F (Continuous Severe Service) – This service class includes cranes that are capable of handling loads that approach the rated capacity continuously and under severe service conditions throughout the lifetime of the crane. These are cranes with the highest reliability and maintenance frequency. Example applications are custom designed cranes that perform a specific function constantly. You may see these cranes in some industrial type settings, but most cranes do not need to meet such a high service rating.
Please note that the duty classification of a crane has nothing to do with the capacity of the crane. When we build a Class B 10 ton overhead crane, it is an entirely different set of components than when we build a Class E 10 ton overhead crane. In general, the class E crane is going to have heavier duty rated motors, end trucks and more steel.
The easiest analogy to help understand the class ratings of overhead cranes is to compare a Ford F150 truck to a Ford F350 truck. If you planned to haul a pallet of bricks once to pave your walkway, the F150 could handle that task. However, if you are a professional brick layer that will be hauling multiple pallets of bricks per day, you would likely opt for the heavier duty F350.
If you have any questions about which class of crane you should use in your application, please don't hesitate to contact us.
Look for our next post in the series coming soon!