Price only becomes a point of measure when you know exactly what you are buying, and saying both quotes use a 10 ton capacity hoist and have a 50 foot span is not enough!
It is a rare occasion that an inquiry for a new crane system even addresses the crane duty cycle. Let me assure you, this is one of the three most important questions to be answered (if not the single most important).
Let me give you an actual example. I once was asked to provide two 10 ton cranes to operate on a single runway. The first crane was a bridge crane used to feed the charging system in a foundry. The crane ran at full capacity, 24/7 and had a magnet. If the crane went down, several hundred people went home and they had to “drop the furnace” (purge it of all hot metal). It was cab controlled with an optional radio control. The crane cost a little over $300,000 and was rated as a class E crane. Compare this to a maintenance crane, pendant operated, same capacity, same span. The crane was used for maintenance once a year. It cost $35,000, but it was a low end Class C crane. Two cranes with the same capacity, the same span, the same lift height and almost 10x difference in price!!!
So here’s the CMAA classification system:
CMAA Crane Service Classes
CMAA has established crane service classes so that the most economical crane for a particular installation may be specified in accordance with Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes-No. 70 or Specifications for Top Running and Under Running Single Girder Electric Overhead Cranes Utilizing Under Running Trolley Hoist-No. 74. The crane service classification is based on the load spectrum reflecting the actual service conditions as closely as possible. The CMAA
Crane Service Classes are as follows:
CLASS A (STANDBY OR INFREQUENT SERVICE)
This service class covers cranes which may be used in installations such as power houses, 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 B (LIGHT SERVICE)
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 C (MODERATE SERVICE)
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 lift at rated capacity.
CLASS D (HEAVY SERVICE)
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)
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)
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.
This information has been presented for reference purposes only. For more information regarding load spectrum, mean effective load factors, load classes, load cycles and how these relate to the determination of crane service classes, please refer to Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes-No. 70 or Specifications for Top Running and Under Running Single Girder Electric Overhead Cranes Utilizing Under Running Trolley Hoist-No. 74. These documents are available for purchase online at http://www.mhia.org/bookstore or through the Literature Department at 704-676-1190.
WARNING!!!
After you digest this, you’re not done yet. Next week I will list the dozen specific issues that you MUST include to protect yourself in a buyers spec to “hold your suppliers feet to the fire”. It’s not enough to say, I want it class D. You need to let your suppliers know that you are aware of what a “D” means and you will be checking them.
