Bridge Crane and Hoist Duty Cycles

 

Bridge Crane and Hoist Duty Cycles

Shared with the kind permission of the author, Richard Wehrmeister (Advanced Overhead Crane)

For quite some time I have been an advocate of having all manufacturer’s adding the duty cycle designation to both the hoist and the bridge crane nameplate. My reasoning for this is it allows the bridge crane inspector to analyze the actual duty cycle as operated to the manufacturer’s designed duty cycle. It is not unusual to find equipment that is being used beyond the manufacturers designed duty cycle.

Situations that have come up:
• Equipment was sold for one application and over time the application changed to a more strenuous duty cycle.
• Equipment sold did not meet the application requirements from the start.

To give a couple of examples:

• A number of years back we sold a class C crane with a class H3 hoist. The crane was going to be used in a testing lab. The crane/hoist was only being used 3-4 times a day under capacity load. We were trying to save the customers a few dollars with the H3 hoist. Big mistake, after a couple of years the lab was gone and the crane/hoist became a production crane/hoist. While the crane is working trouble free for the operation the H3 hoist would not hold up. In other words the hoist had on going problems with both the mechanical load brake and the hoist motor brake up until we change out the hoist to a H4 classification.

• Not long ago we were asked for a second opinion involving a hoist. When looking at the hoist from the floor, I remarked that it looked like a brand new hoist with the gear cover off. The customer said that the hoist was a few weeks old. I started to question the customer about the application and I noticed a very large lifting magnet sitting at the other end of the shop and looking back up at the hoist I saw a cord reel. Of course my question to the owner was how often did they use the magnet and did they leave the magnet hanging on the hook during a normal shift. This magnet was about the size of a scrap yard magnet and for those of you familiar, they are very heavy. Once I received my answer I told him that the hoist would not work in this application unless he wanted to rebuild the mechanical load brake every few weeks. He was upset and of course I asked him if he addressed the hoist application with the supplier before ordering the hoist. Note: The lifting magnet far exceeded the maximum weight requirements allowed by the manufacturer for a below the hook device on this particular hoist.

The duty service classifications for hoists are listed In ASME HST Performance Standards. ASME lists five duty classifications H1, H2, H3, H4 and H5.

The duty classifications for bridge cranes are listed In CMAA 70 and 74. CMAA lists six duty classifications A, B, C, D, E and F.

Both ASME and CMAA define each classification according to loading groups and the service conditions as close as possible, taking into account the speed, load and quantity of lifts in a time frame.

Getting back to my first paragraph I believe this is a topic that both ASME and CMAA should address when Regulations and Specifications become due for rewrite. A simple change to a name plate is a very small cost when we’re only talking about adding a couple digits to a name plate however the only way these changes can get done is to get more crane inspectors, manufacturers and associations involved in advocating change.