NSK: The damaging effects of counterfeit rolling bearings
21 March 2017
Counterfeit rolling bearings are a growing industry issue. To the untrained eye, replica products are increasingly difficult to distinguish from genuine OEM bearings, which means that ever-more users are suffering from the consequences of using counterfeits. A case in point is highlighted at the Technical University of Dortmund (TU Dortmund), which was recently tasked with conducting research into enhancing the distillation process (the purification of liquids through repeated heating and cooling). The project was undertaken in close co-operation with a well-known Chinese university, which already had experience of the process. TU Dortmund's Chinese partners built the pilot plant for the project but, when it arrived in Germany, a number of unexpected problems soon became evident.-Image1.jpeg - Scrutinise the quality of individual bearing components to distinguish between original and counterfeit bearings
Distillation is deployed when the components of a liquid mixture can be successfully separated as a result of different boiling points. Purity increases in line with how often the process is repeated. In industrial production, however, spatial expansion of the columns can prove restrictive. Furthermore, throughput can be limited due to gravitational acceleration. For these reasons, an idea was put forward by TU Dortmund to research and further-develop a more flexible and space-saving distillation process, one which is already being used within eastern Asia's chemical industry.
Partnering with an established university in China, TU Dortmund wanted to build a pilot plant. It was agreed that this three-stage modular system (with a rotor diameter of about 90 cm) would be manufactured in China. Once built, the plant passed acceptance tests in China before being transferred and set-up in Dortmund. However, during the first system test runs, it became apparent that the trials were not successful. Less than 20 minutes into the first test, audible knocking sounds emanated from the drive train despite only running at half speed.
The drive system utilises a 5 kW motor with a V-belt connection to a central vertical shaft which has a maximum speed of 750 rpm. A ball bearing is used to provide support from below, with two tapered roller bearings performing a similar function from above. The bearings are also required to support some axial loads.
Initially, it was assumed that the knocking noise was a result of contact between moving parts. With this in mind, the rotors were disassembled, but the knocking persisted. Subsequently, the drive itself was disassembled, but still the cause of the knocking could not be determined. Finally, engineers at TU Dortmund removed the rolling bearings and contacted the manufacturer, NSK.
Based on the information provided, the possible cause was considered to be a design error and tension in the tapered roller bearings. Suitable adjustments were made, with greater clearance provided for the tapered roller bearings. However, once the drive had been reassembled, the next test run provided no significant improvement. What's more, a test run of the drive without the centrifuge resulted in a temperature increase at the shaft of 80°C after just 90 minutes. Due to thermal expansion, the shaft duly seized.
Faced with this baffling failure, emphasis shifted to the quality of the tapered roller bearings, type HR 30322J. Detailed images of the bearings were sent to NSK and all became clear: the bearings were counterfeit.
The counterfeiters had gone to great lengths with the appearance of the bearings; even the NSK logo looked deceptively authentic. In fact, the only way to distinguish between the original and counterfeit bearings was to scrutinise the quality of the individual bearing components.
Disappointed but relieved to have pinpointed the issue, TU Dortmund ordered replacement bearings from an NSK authorised distributor. As a result of superior materials and production processes, test runs demonstrated that bearing and shaft temperature remained below ambient, even after nine hours of continuous operation. In addition, the drive's cooling system was now able to function correctly, ensuring there were no more knocking sounds.
As a result of using counterfeit bearings, the project at TU Dortmund suffered delays. However, if the application had been safety-related, the consequences could have been far worse. In all cases, the message is clear: always order from reliable sources such as official distribution partners of the rolling bearing manufacturer.
NSK is a member of the World Bearing Association (WBA) and supports users in the identification of counterfeit rolling bearings.
For more information, please contact:
NSK UK Ltd
Tel: +44 1636 605123
Fax: +44 1636 602775