Duty Cycle

Duty cycle CMAA Classifications (HMMI similar classifications using H1 –H5)

Class A (Standby or Infrequent Service – irregular occasional use followed by long idle periods & which rarely hoist the rated load, and normally loads of about 1/3 of the rated load.)

This service class covers cranes which may be used in installations such as powerhouses, public utilities turbine rooms, motor rooms and transformer stations where precise handling of equipment at slow speeds with long, idle periods between lifts are required. Capacity loads may be handled for initial installation of equipment and for infrequent maintenance.

Class “A” applications (very limited use)

  • Power house & utilities
  • Hoists idle from 1 to 6 month periods
  • Low use maintenance
  • Pumping stations

Class B (Light Service – irregular occasional use followed by long idle periods & cranes which rarely hoist the rated load, and normally loads of about 1/3 of the rated load.)

This service covers cranes which 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 “B” applications

Class C (Moderate Service – regular use in intermittent operation & cranes which rarely hoist the rated load, and normal load of about 1/3 of the rated load.)

This service covers cranes which 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 which 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 “C” Applications (Loads Randomly Distributed):

  • General Machine Shop
  • Fabricating
  • Assembly
  • Storage
  • Warehousing

Class D (Heavy Service – regular used in continuous operation, and crane cranes which hoist the rated load fairly frequently and normally, loads between 1/3 and 2/3 of the rated load.)

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 “D” Applications (High Volume Handling):

  • Steel Warehouses
  • Machine shops
  • Fabricating Plants and Mills
  • Foundries
  • Heat treating and Plating
  • Rebar fabrication

Class E (Severe Service)

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 “E” Applications

  • Cement plants

Class F (Continuous Severe Service)

This type of service requires a crane capable of handling loads approaching rated capacity continuously under severe service conditions throughout its life. Applications may include custom designed specialty cranes essential to performing the critical work tasks affecting the total production facility. These cranes must provide the highest reliability with special attention to ease of maintenance features.

Class “F” Applications

  • Steel mills

Parameters to determine duty cycle:

  • Load distribution – proportions of full and partial loads handled
  • Operational time – running time of the hoist per hour
  • Work distribution – work distributed over a given time – effects electrical more than mechanical
  • Starts and stops – effects motors, contactors, drives, brakes, etc.

 


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