Mixed capacity bridge cranes are a great solution for companies looking to leverage their system capabilities and reduce bridge deadweight. This is because using a larger capacity runway and multiple smaller capacity bridge cranes can help leverage the system's capabilities, providing multiple lifting options within a single coverage area.
Mixed Capacity Bridge Cranes Explained
Using mixed capacity bridge cranes on the same runway not only expands your coverage area, but also provides maximum productivity using one complete system. Mixed capacity systems allow for multiple bridges to be used on one system without downgrading the bridge or using bridge buffers (see options below for more information on bridge buffers). Bridges are sized for a single rated load, while runways are sized for the combined weight of all loads. For example, a 2,000 pound runway can run two 1,000 pound bridges or four 500 pound bridges. This not only leverages system capabilities and provides more flexibility, but also reduces bridge deadweight. Workers can use multiple bridges side by side to transport freight without overloading the system. Mixed capacity bridges also weigh less than single bridge systems, making them very ergonomic and easy to move.
However, it is important to note that the sum of the capacities of the bridges cannot exceed the capacity of the runway without adding a buffer component. The capacity of the runway is defined as the live load that the system can lift. Workstation bridge cranes are designed with a 15% allowance for the weight of the hoist and trolley. This means that a 1,000-pound bridge crane includes up to 150 pounds of allowance to cover the combined weight of the hoist and trolley. Overloading can result in serious system failure, worker injury, or even death. If in doubt, consult your crane manufacturer or a qualified engineer for more information.
Mixed Capacity Bridge Cranes and Safety
If you are considering using multiple mixed capacity bridges with a single runway in your facility, there are a few numbers you should also take into account. First, the length of your runway is essentially unlimited, making it possible for you to cover the entire length of your facility. However, keeping the length of the bridge to a minimum is another good way to ensure your system is ergonomically designed.
Generally speaking, the less deadweight the operator needs to move, the better. Therefore, when it comes to bridge cranes, "less is more." Short bridge crane lengths are better suited for high-cycle production areas, while long bridge cranes are often used in low-cycle production or maintenance areas. Most engineers also recommend using a lower-capacity system to increase productivity. This is because when you buy too much "capacity," you also have to move extra bridge "deadweight," which reduces efficiency.
Other Options
While one runway can handle multiple mixed-capacity bridges, there are other viable options to consider-depending on your operations and the needs of your facility. Bridge buffers and intermediate terminals are two such options.
Bridge buffers
With a normal mixed-capacity system, mixed-capacity bridges can run the entire length of your runway without worrying about overloading. However, this means you must purchase a runway heavy enough to support the load of all your bridges at the same time. If cost is a factor, a bridge buffer system can ensure the system is used properly without overloading, and at a lower cost than a mixed-capacity system. Here's how they work.
With a bridge buffer system, bridges are sized for a single rated load, while the runway is sized for the heaviest single load. This means that the runway will use the same series of tracks as the largest bridge. This is different from a mixed-capacity system because the runway capacity is not determined by all of your bridges added together, but rather by the heaviest bridge running along your runway. This still allows you to install one runway system throughout your facility, providing greater flexibility and productivity. However, instead of purchasing extremely heavy runways, you can purchase runways rated for the heaviest single bridge. This is because movable bridge buffers separate the bridges.
Bridge buffers are suspended from two dollies on the runway to create a predetermined minimum distance that allows the bridges to operate with each other. Essentially, bridge buffers are designed to roll on the runway track between the bridges to maintain the distance between them and avoid overloading the capacity of the runway. Using bridge buffers not only ensures that workers do not accidentally overload the system; it also ensures that the two bridges do not contact each other, especially when loaded. While bridge buffers can be an excellent solution for keeping costs low and increasing system flexibility, they do have one drawback. Buffers utilize space and create a moving "dead zone" between bridges, therefore slightly limiting your reach. Whether to use a mixed capacity system or a bridge buffer system depends entirely on the needs of your operation and facility.
Intermediate Terminals
Intermediate terminals achieve the same goals as bridge buffers, but with a slightly different design. Similar to bridge buffers, bridges are sized for a single rated load, while runways are sized for the heaviest single load. This means that the runway is the same size as the largest bridge. The bridges are completely separated by internal stops or buffers. There are advantages to using intermediate stops because – like bridge buffers – they allow for the use of smaller runways. This makes them very cost-effective compared to regular mixed capacity systems. Intermediate terminators also create fewer "dead spots" in the system. However, they do limit the travel of each bridge on the runway, and they require additional support to eliminate potential overloading of the system. Intermediate terminators are installed at intervals to prevent more than one bridge from operating on certain sections of the runway. This means that each bridge is isolated as an independent span, minimizing the track capacity of the runway.
Improving the flexibility of your system can be very beneficial to productivity, but it does require careful consideration of system design. Whether you decide to use a regular mixed capacity bridge crane system, bridge buffers or intermediate terminator stops depends on your facility and the overall needs of your operation. Installing a proper bridge crane system can greatly improve productivity and safety in any environment, but installing the perfect system for your unique needs will ensure cost-effective results for you every time.
