An over the bridge crane (OTBC) runs on a runway system that is elevated and tends to follow the span of the building. It has a hook motion of three axises along the length of a factory and provides three axes of hook motion (X, Y, and Z). The trolley of the OTBC is responsible for moving the item to either side. The hoist, the second part of the over the bridge crane, handles up and down movements. There are two types of over the bridge crane: the single girder and the double girder. There are differences between the two, but they are both elements that allow precise and exacting positioning of the hook, and also control the placement of the load. Without them, it would drop heavily and potentially get damaged.
There are differences between the two. There is often confusion about the durability of the double girder crane. The perception is that it is sturdier. The fact is (and this is verified by the CMAA (Crane Manufacturers Association of America), both double and single girder cranes are strong and durable. However, the single girder has powerful cross girders which the double girder does not have, and it also comes equipped with lateral bracing. This actually makes the single girder the stronger of the two.
Types of Over the Bridge Crane
The main difference between double and single girder cranes is their hook (which controls the height that your load can be lifted. This is the area that double girder cranes dominate. They have a lift height that is 18-36 inches higher than the single girder. The reason their lift is so much more effective is because they have a hoist which is added between the cross girders, whereas on the single girder crane the cross girders are underneath.
There are also Electric Overhead Cranes (EOT). These cranes, simply put, are exactly like non-electric cranes but are run by electronic devices. They are often built specifically for the customer, based on industry and location-based needs. Since each industry has its own set of requirements, they require different technologies. Some industries include: construction companies who have to move materials, production halls, assembly lines, storage areas, and even power stations use overhead cranes and hoists.
Duty Cycle | What is It?
Companies must first decide their lifting needs when it comes to design, specifically the capacity required. Then they need to determine the “duty cycle” they’ll be using for the hoist. This is based on the lifts per hour, and the length of each lift.
There are also rotary overhead cranes, which has an end of the bridge that is on a pivot that is fixed, and the other end is carried on an annular track. The circular area underneath is where the bridge travels. This kind of crane allows for longer reach and also removes strain on building walls, as compared to, say, the jib crane.
These are the different designs that are on offer when looking at overhead cranes. There are many companies that provide support and help industries design and access the cranes that are best for their purposes.