Boosting dredger system reliability
15 January 2020
The global dredging industry needs confidence in its assets. That led one major equipment provider to specify customised Stromag shaft couplings on a new product platform
The fortunes of the dredging sector are closely tied to many of the most significant trends faced by society today. The evolution of global trade is driving cargo carriers to boost efficiency by using ever-larger ships, which is encouraging ports around the world to expand their facilities. There’s also the energy revolution, especially the rapid recent growth in offshore wind turbine installations that require significant seabed works to prepare the seabed for foundations and cables. Then there are demographic changes, like population growth and, especially, urbanisation, which lead to land reclamation projects.
Each of these activities, and many others besides, require the use of specialist dredging vessels. Dredging is at least a $5.5 billion industry, according to trade body the International Association of Dredging Companies (IADC). The industry’s dynamics mean that reliability is critical for dredging companies. Their work usually has to slot into tightly planned project schedules, and delays caused by unexpected breakdowns can incur huge costs for project owners, not to mention loss of revenue and the risk of financial penalties for dredgers.
It’s no surprise, therefore, that the owners and maintainers of dredging vessels take equipment performance and reliability very seriously. They need the confidence that their vessels and the equipment on board will offer the highest possible levels of uptime and availability. That’s why, when a major manufacturer of dredging systems needed a reliable coupling solution with a small footprint for use on a new dredging vessel platform, it turned to Stromag, a brand of Altra Industrial Motion Corp.
The supplier’s system features a 1200 HP diesel engine that drives a complex, custom-designed, eight-pad gearbox with primary output to a two-speed clutch that drives the system’s main pump, as well as hydraulic pump pads to operate a crane and auxiliaries.
The coupling arrangement between the engine and gearbox was critical to the performance and reliability of the application. In use, the system experienced high levels of torsional vibration; if not properly managed, this vibration could accelerate wear, and potentially lead to early failure of key components. It was essential, therefore, that the supplier found a coupling technology that was capable of handling the high power, torque and vibration levels involved while also protecting other mechanical elements from excessive vibrations and shock loads.
To compound the challenge, the space envelope available for the coupling was severely constrained, as the chosen solution would need to fit into the supplier’s existing gearbox bell housing.
After reviewing the customer’s requirements in detail, the Stromag engineering team designed a hybrid Periflex CR (PCR) shaft coupling to meet the challenging dredging rig application requirements. The modified PCR coupling used a rubber element from a similar Stromag model PCS coupling and a bolt-on adaptor hub with a splined bore. The flexible ring used in this coupling design is key to its effectiveness, since it transmits torque while absorbing torsional impacts.
The Stromag Periflex shaft coupling is a highly flexible rubber-fabric coupling, particularly suitable for connecting two shafts in diesel engine and electric drives. Due to the special design of the shaft tyre, the Periflex shaft coupling is able to absorb extremely large displacements in every direction with low restoring forces, without noticeable wear and tear. As standard, the tyre can be radially mounted and dismantled using a separation joint without moving the connected machines. The Periflex shaft coupling transmits the torque absolutely free of backlash. It is suitable for absorbing torque shocks and dampens vibrations. The standard Periflex CR series covers the torque range from 480 to 14,800 Nm.
To ensure that it’s proposed solution would be able to handle the expected operating conditions, the Stromag team conducted extensive torsional vibration analysis (TVA) on a model of the complete transmission system and its nine driven components.
As this case demonstrates, Stromag supports its products with in-depth application expertise, assisting customers in the specification, selection and integration of the most appropriate coupling technology for their needs. Where necessary, this work can encompass customer-specific adaptions, modifications or even completely bespoke designs.
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