Magnetic bearing technology is becoming more and more important as an alternative to conventional bearing supports, and is used when the technical requirements can no longer be fulfilled by other bearing types. This especially applies to medium and large industrial machinery with very high rotational speeds and shaft weights of up to several tons. Typical application fields for magnetic bearings of this size include electric motors, gas and steam turbines, compressors, and chillers. Electromagnetic bearing supports are based on the principle of a shaft that is levitated by means of a magnetic field and can be made to rotate with practically no friction. Sensors are used to measure any deviations by the shaft from its reference position. Regulation is carried out by the electronic control system and power electronics, which return the shaft to its nominal position. The back-up bearings serve as a safety mechanism for the machine if, for example, a power failure occurs and causes the shaft to drop.

Standardized complete unit
With the FAG Active Magnetic Bearing, Schaeffler has developed a standardized, cross-system complete unit comprising magnetic and back-up bearings as well as the relevant services. A special feature is that Schaeffler uses rolling bearings as back-up bearings. Schaeffler's rolling back-up bearings are also available for shaft diameters greater than 200 mm and can be used again after a shaft drop has occurred. They are the result of many years of experience and expertise in the area of high-precision spindle bearings. Existing magnetic bearing systems for shaft diameters greater than 200 mm mostly use a plain bearing as a back-up bearing, which requires replacement or complicated repair work following a magnetic bearing failure.

At the same time, the use of electronic control systems and power electronics from Siemens, which have been proven and on the market for many years, allows easy integration into the machine architecture. This represents an important milestone that has been reached in the standardization of magnetic bearing technology. Machine operators thus receive an overall system that is optimized in every respect: The use of rolling back-up bearings, the proven electronic control systems and power electronics, and the high level of replacement parts availability reduce outlay and costs, and increase performance, reliability, and efficiency. The objective is to develop and provide a comprehensive modular system with which both four and five-axis systems can be implemented from a single source.

Reduced lifecycle costs
In terms of lifecycle costs, Schaeffler's system featuring rolling back-up bearings offers multiple advantages in comparison with systems that use plain back-up bearings. Rolling back-up bearings not only have significantly less wear, they can also ensure emergency operation at reduced speed in the event of a magnetic bearing failure.

In addition, the FAG ProCheck condition monitoring system and Schaeffler's system behavior and analysis expertise allow statements and recommendations to be made regarding the further operation of the system. This means that downtimes are reduced and damage to bearings and machinery prevented in the event of the shaft dropping into the back-up bearings. Schaeffler thus offers a cost-effective complete system that is capable of fulfilling the highest requirements.

As a solution provider for magnetic and back-up bearing applications, Schaeffler offers all relevant services ranging from initial operation through to electronic and mechanical monitoring, in addition to the development and manufacture of the magnetic and back-up bearing systems themselves. Schaeffler customers have a global network of experts at their disposal for this purpose.

Systems expertise from one source
With the FAG Active Magnetic Bearing system solution, Schaeffler has succeeded in developing a convincing complete system that fulfills the increasingly high requirements of even large machinery in terms of reliability and robustness. A significant leap forward in terms of performance and efficiency has been made thanks to the bundling of expertise from the core technologies of back-up and active magnetic bearings together with system analysis and the use of standardized electronic control systems and power electronics.

Both the magnetic and back-up bearings are developed and the overall system designed and manufactured at Schaeffler. The specialists use a calculation model developed in-house to simulate application-specific scenarios in which the machine's shaft drops into the back-up bearings, which allows them to make statements regarding possible system behavior. These simulations are validated on the basis of tests.

Finally, the systems are tested in the field in cooperation with the customer. Schaeffler is already collaborating with customers on various development projects of this type, including bearing supports for large electric motors and compressors.

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