Customer approval in powertrain technology depends specifically and to a great extent on the reliability and robustness of the facilities and in particular on their individual components. These include the gearbox and gear wheels of the specialist transmission manufacturer, C u. W Keller GmbH & Co.KG (KELLER). The high customer requirements can be met by the custom made gearbox manufacturer Keller with its experience in the design and manufacture of gear wheels and gearbox that spans more than 100 years.
In the past, individual parts as well as gear units for steel manufacturing and mining comprised the key components of sales planning. In addition to the traditional gearing applications for sugar presses and rubber kneaders, gear units for marine applications were added to the list 17 years ago. Today, KELLER has also become a supplier of gearboxes especially for dredging operations.
Following the decision by the Chinese dredging and shipping company Tianjin Dredging Corporation (TDC) to build the Tian Kun, one of the largest dredging vessels for the Chinese market in terms of its performance and technology, KELLER was commissioned to build, not least for its extensive experience in dredging operations, not only three pump gearboxes but also the most essential part of the drive train, the so-called cutter-head gearbox.
In addition to gearing systems for two inboard pumps and an underwater pump, this project also involved a cutter-head gearbox with a nominal engine power of 5,000 kW.
As KELLER has thus far served mainly European customers in the dredging field and because the awareness level of KELLER was less pronounced in China, TDC had initially to be convinced of the expertise and competencies of KELLER. Over the last 10 years, KELLER said it has delivered about 75 percent of all large cutter-head gearboxes in Europe.
It all started in 2006 with a relatively small cutter-head gear unit – small from today’s perspective – for the JOKRA with an output of 1,000 kW for the Dutch dredging company Boskalis.
After the JOKRA, further ship owners and shipyards followed very quickly with requests. For example, in 2015 KELLER was assigned with the building and delivery of the first 7,000 kW gearbox.
At that stage it was the 25th cutter-head gearbox for KELLER in the 1,000 kW and larger class. With such a list of references, it did not prove difficult to quickly convince the next customer, TDC.
The thumbs-up was actually only given after the gearing specification was discussed. A great many issues, which influenced the drive construction, had to be thought through. Such as the issue of how deep the gearbox would work under water, which design collaterals would be required, how the gearbox would be connected to the cutter head shaft, which electric control would be considered, etc.
The actual design layout of the gearbox only got underway after these parameters had been sorted out.
Here, it became clear quickly that the specification factors for the 5,000 kW gearbox to be developed were comparable with those high level safety and application specifications of the 7,000 kW cutter-head gearing system delivered in 2015.
In addition to the classic bearing, shaft and interlocking calculation, comprehensive research was also carried out on the deformation and stress behavior of the gear-casing structure using FEM. This was conducted with the aim of optimizing the casing structure due to the immense and additional changing loads that occur during the dredging process. KELLER’s years of experience in the deformation behavior and the stiffness ratios of the conductor structures on which the cutter-head drive is installed carried its weight in this consideration. The deformation behavior not only affects the structural load but also impacts the smooth operation of gears and bearings significantly. Thus, these findings were also taken into account in the determination of the tooth-contact-stress levels in the tooth engagement.
To this end, KELLER, as long-standing member of the Research Association for Drive Technology in Germany (FVA), uses the RIKOR program of FVA, which enjoys a firm standing and recognition over the years in such construction processes.
The optimized gears have a final weight of 180,000 kg and rank among the largest gearboxes that KELLER had built in its 115 years of existence.
A project team consisting of a dozen engineers was entrusted with the tasks and questions concerning development, manufacture and assembly, as well as the ensuing logistics. KELLER excels in the manufacturing of large gear wheels and its expertise in the impact of heat treatment on the quality of the component parts in particular is just one of its core competencies.
During the design and manufacturing phase, project meetings took place regularly during which all internal processes including the special required transportation were discussed. By doing this, the required quality as well as the tight time schedule could be maintained at all times.
An essential component of the quality control was conveyed to the final test run. Drive and gear mechanisms were put through their paces. Support images of the gear toothing were taken and these were then compared with the calculations; the noises and vibrations were measured and the transmission tightness verified. In addition, the bearing temperatures were recorded over a period of several hours.
After the final inspection, as well as the final acceptance by the customer, the seaworthy packing of the complete powertrain was carried out, followed by shipment to the harbor in Bonn, Germany. The powertrain was then transported via Rotterdam, Netherlands on its long sea route and was delivered punctually in China.