There are six (6) different classifications for overhead cranes, specified by the Crane Manufacturers Association of America (CMAA). There are six (6) different classifications for overhead cranes, specified by the Crane Manufacturers Association of America (CMAA). Each overhead crane classification takes the following criteria into consideration:
How frequently will the crane be used?
How quickly can the crane transfer materials or equipment? How many lifts per hour can the crane perform?
Will the crane need to be serviced regularly?
How far does the crane need to move material in your facility?
What is the average rated load of the materials that your crane will be moving? How often will the crane be lifting fully-rated loads?
What type of environment will the crane be operating?
Different Types of Overhead Crane Classifications
If you can answer or define each of the criteria above, it will be much easier to determine the type of overhead crane that works best for your business or industry. Below we’ll identify and define the six types of overhead crane classes and provide types of businesses or industries that match up the best with each overhead crane classification.
CRANE CLASS A (STANDBY OR INFREQUENT SERVICE)
This service class covers cranes where precise handling of equipment at slow speeds with long idle periods between lifts are required. Capacity loads may be handled for the initial installation of equipment and for infrequent maintenance. Typical examples are cranes used in powerhouses, public utilities, turbine rooms, motor rooms, and transformer stations. This is the lightest crane as far as the duty cycle is concerned.
CRANE CLASS B (LIGHT SERVICE)
This service class covers cranes where service requirements are light and the speed is slow. Loads may vary from no load to occasional full-rated loads with 2 to 5 lifts per hour, averaging 10 feet per lift. Typical examples are cranes in repair shops, light assembly operations, service buildings, light warehousing, etc.
CRANE CLASS C (MODERATE SERVICE)
This service covers cranes where service requirements are deemed moderate, handling loads which average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet, with not over 50 percent of the lifts at rated capacity. Typical examples are cranes used in machine shops, paper mill machine rooms, etc.
CRANE CLASS D (HEAVY SERVICE)
In this type of service, loads approaching 50 percent of the rated capacity will be handled constantly during the work period. High speeds are desirable for this type of service with 10 to 20 lifts per hour averaging 15 feet, with not over 65 percent of the lifts at rated capacity. Typical examples are cranes 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.
CRANE CLASS E (SEVERE SERVICE)
This type of service requires a crane capable of handling loads approaching the rated capacity throughout its life with 20 or more lifts per hour at or near the rated capacity. Typical examples are magnet, bucket, magnet/bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc.
CRANE CLASS F (CONTINUOUS SEVERE SERVICE)
In this type of service, the crane must be capable of handling loads, approaching rated capacity continuously under severe service conditions throughout its life. Typical examples are custom-designed specialty cranes essential to performing the critical work tasks affecting the total production facility, providing the highest reliability with special attention to ease of maintenance features.
Components of an Overhead Crane System
In order to get a better understanding of some terms we’ll be using later when we describe the different types of overhead cranes, we’ll discuss the different parts and components of a crane, and how they can affect performance and design.
The lifted load is supported using a hook which connects to the hoist.
The hoist is what makes the lift and holds, raises, or lowers the load using wire rope or chain. Hoists can be powered manually (by hand), with electricity, or with compressed air (pneumatic).
The trolley supports the hoist and moves horizontally along the crane bridge, to poisiton the hoist and hook, prior to picking up or lowering a load. Trolleys can be configued in and Under Running or Top Running design.
A load-bearing beam that runs the width of the building. This is the primary structural component that connects the runways and moves the hoist forward and backward using a trolley. A bridge can be comprised of one or two beams that run the width of the building. This is the primary structural component that connects the runways and moves the hoist forward and backward using a trolley.
What the bridge crane travels on to move the crane up and down the bays. These are typically part of the building structure, as beams, and there are two (2) per overhead bridge crane system.
Runway Rail or Tracks
Rail supported by the runway on which the crane travels. Top-running cranes typically run on ASCE/railroad rails. Gantry cranes can also utilize a rail or track system installed in the floor to move the bridge back and forth.
Located on either side of the bridge, the end trucks move the bridge up and down the runway utilizing a series of wheels that ride on the rail. Each end truck can have a configuration of 2, 4, or 8 wheels based on the crane's capacity.
Bumpers are designed to absorb the crane's energy and reduce impact—bringing the crane to rest in a controlled manner and minimizing forces where the crane or trolley reaches the end of its travel. Bumpers can be attached to the bridge, trolley, or runway stop.
Controls are typically mounted in a panel on the crane or hoist and the pendant or remote radio console allows the operator to run the crane. The controls operate the drive and hoist motors, and can control the Variable Frequency Drives (VFDs) to control hoist speed for precise load positioning.
Insulated conductor bars or festoon systems (flat cables) bring power to the crane from the building.
If you put a little bit of thought and consideration into how often you will be using an overhead crane, how hard your overhead crane will have to work, and the type of environment that your crane will be working in, you can get a pretty good sense of what type of crane class will be best for your business or facility.