What is the mileage of Indian trains
Millions of kilometers and not a bit "tired"
Innovative bearings can increase the traveling comfort on railways. In principle, wheelset bearings are among the most important parts of rail vehicles for safety.
They are highly stressed, have to meet a multitude of different requirements and should run millions of kilometers without any problems.
Since the wheel break in Eschede, innovations in the field of drives have received critical attention. The wheelset bearings are also among the highly stressed parts, but these days they hardly "tire". In Schweinfurt, a test stand is being tested at FAG Kugelfischer, which should enable the use of wheelset bearings even after 5 million km of mileage.
“We procured five wheelsets from the ICE 1 from Deutsche Bahn to test them on the new test stand. However, the railway was unable to provide us with defective wheelset bearings from the ICE 1: They have none, ”said Edgar Pröschel, Head of Development for the Railway Division at FAG Kugelfischer in Schweinfurt, happily. Every wheelset bearing is now removed after 1.5 million km, given new lubricant and thoroughly checked. It is no longer used after a mileage of over 5 million km. "This means that even bearings that are still completely flawless are thrown away as a precaution," says Pröschel. That could be different in the future if a test bench developed in Schweinfurt and the associated fault diagnosis using structure-borne noise prevail.
"Defective rolling bearings generate shock pulses when rolling over the damaged area," explains test field manager Dr. Thomas Lösche, and this structure-borne noise is to a certain extent a reflection of the error. "For processing and evaluating the vibration signals, we have developed the rolling bearing damage diagnosis, VibroCheck" ". Cracks or material fatigue on rolling surfaces and rolling elements can be identified at an early stage through vibration measurements on the bearing at 100 min-1. The greatest advantage: The analysis can be carried out in the assembled state, the housing and bearings no longer have to be separated from the wheelset for testing. The entire time-consuming dismantling of the bearing is unnecessary, the wheelset and the bearings are put to the test.
In addition to an exact measurement, the test system offers the advantage of much less time and effort. If the measurement results are flawless, there is no longer any reason to replace intact bearings. Actually, this is not a reason for joy for the manufacturer of such bearings. That is why test stands are now also to be sold to the railways.
Head of Development Pröschel is convinced that the demand for test stands will be high - for economic reasons. The Austrian Federal Railways had already looked at the test stand in Schweinfurt, the Deutsche Bahn had announced their visit and specific inquiries had already been received from Russia and India. Incidentally, FAG is trying to compensate for the decline in demand for bearings for rail vehicles that is associated with the ever increasing service life by opening up new markets, adds Dr. Raimund Abele, Head of FAG's Railway Division, added.
There is a long way to go from the ball mill, which the company founder Friedrich Fischer invented in 1883, to today's ball and roller bearings. In 1957, the average maintenance period for axle bearings on the Federal Railroad was only 130,000 km; by 1995 it had risen to 1.5 million km. The steels used, but also the lubricants, have been continuously improved. Above all, their purity could be increased. It has also been possible to almost completely exclude inclusions in the structure, especially of aluminum oxide, reports Pröschel. All wheelset bearings are now also tested with ultrasound due to a European standard.
No longer the steel, but the lubricant is meanwhile "the weakest load-bearing element". Roller cages made of polyamide instead of the brass used in the past have closed a gap here. They show very good emergency running properties: while a bearing with a brass cage runs hot after 20 minutes if the lubrication fails, tests with polyamide cages have shown that the temperature only rises above 150 ° C after 5.5 hours. In the meantime, the “warm” warehouse would have long since been detected by one of the hot-runner and parking brake detection systems installed on the routes, and the vehicle would have been taken out of service.
For a future ICE generation, reported Pröschel, new types of inner bearings are being developed, the temperature of which cannot easily be detected from the outside. However, sensors would be integrated into these bearings, which, in addition to other functions, also constantly monitor the temperature and trigger an alarm in the driver's cab in the event of excessive heating.
"Our goal is", says head of research Dr. Klaus Baalmann, to enable "a complete, onboard condition monitoring" with diagnosable wheelset bearings. "Even today, in addition to temperature and speed, accelerations in all three spatial axes - longitudinal, vertical and axial - can be measured and monitored while driving. The documented values can also be used as basic data for needs-based maintenance.
One day, according to the development engineer’s vision, the wheelset bearings will become the key to an “intelligent wheelset” that will ultimately even offer passengers a higher level of comfort. That is when “mechatronic” components, such as active spring systems, are integrated into the drives. The signals from the sensors could then ensure a smooth, shock-free ride via the suspension. Wheelset bearings with integrated sensors are available from FAG ready for installation.
RALF ROMAN ROSSBERG
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