While still used in many applications, the primary choice for turbo machinery applications used to be a gear coupling. With the advances in turbo machinery technology, increased power and speed led to problems meeting balance requirements and ensuring extended service life with these designs. Today, new applications will almost always use a non-lubricated disc or diaphragm coupling which is a non-wearing mechanically flexible design and offers improved dynamic stability.
A review of previous applications and direct customer feedback identified the trend of leveraging smaller form factors and higher speeds to increase equipment efficiency. Higher speeds are achieved using smaller package overall, requiring the use of smaller bearings and long slender shafts. These changes result in an increased sensitivity to rotor dynamic issues, which can be mitigated using smaller, lighter couplings. Our solution from this feedback was the Kop-Flex® High Performance Disc 2.0 coupling. Starting with a simple component and validated model of the new design was built step by step, through a combination of Finite Element Analysis and physical testing.
Launched in 2016, the Kop-Flex® High Performance Disc 2.0 (HPD2.0) was designed for highly engineered equipment. To achieve the best weight and power density possible, a more compact coupling was developed, and aligned with the torque requirements of our customer’s applications. The HPD2.0 coupling was an evolutionary design built on the foundation of 30+ years of providing disc couplings for turbo machinery applications. Optimization of the stress distribution through the disc pack and improvement of the coupling geometry, reduces reaction loads and decreases imbalance forces on connected equipment.
While the flexible elements of a turbo machinery coupling are typically designed to be the weakest link, additional safety features can be added to further protect the connected equipment and nearby personnel. Given the engineered-to-order nature of couplings for API 671 applications, there are many features which can be added to ensure safe and reliable performance. One example would be an interlocking flange, which in the event of a disc pack failure, allows the coupling to continue to transmit torque so the equipment can be shut down safely.
Advances in Finite Element Analysis (FEA) have changed how our couplings are designed. In addition to the many types of loading a coupling is subjected to while in service, 26 million degrees of freedom and 12,000 surfaces from the stacked pack of thin discs are required to achieve an accurate model. During the development of the Kop-Flex® High Performance Disc 2.0 coupling, FEA testing was performed in parallel with physical tests; starting with the simplest component, complexity was increased step by step to arrive at the final full coupling model. By the end of development, 112 physical tests at five locations around the world had been performed, along with 113 FEA runs requiring almost 500 days of solve time.
We predict the trend of increasing efficiency requirements and speeds will continue as our customers continue to push the rotor dynamics limits of their equipment. The Kop-Flex® High Performance Disc 2.0 coupling was optimized for these high-speed applications and achieves up to a 30% weight reduction over our previous design. Combining our newest design with lightweight titanium components would allow the turbo machinery performance to be advanced even further.