AERZEN TurboRelying on air foil bearings
For the sophisticated bearings inside turbo blowers, AERZEN uses neither oil nor other lubricants, but air. Steffen Helmert, Product Manager Turbo Blowers, explains the reasons for this and why AERZEN does not use magnetic bearings.
ComPress: Mr. Helmert, how does air foil bearings work in AERZEN turbo blowers?
STEFFEN HELMERT: As an effective bearing without any mechanical friction at all, AERZEN uses compressed air in the two radial drive shaft bearings and the thrust bearing for absorbing the axial forces. The compressor principle is used in a simple way. Due to certain unbalance, when starting the turbo blower, the rapidly rotating shaft generates an eccentric circular motion in the air gap of the bearing. With the minimal distance to the bearing wall, the shaft increases the pressure in this area, and counterforce is generated in the form of an increase in pressure. This forces the shaft back in the opposite direction. Due to the rapidly increasing speed the shaft centres in the bearing itself and increases the pressure in the air gap to more than 30 bar. The prevailing force couples are so high that they keep the shaft permanently in the centre of the bearing, even during considerably varied and challenging operational conditions, and although takes place in free-floating manner without surface contact. The genius of this principle is that the air cushion forms by itself during operation - and, thus, without any further energy input.
ComPress: What are the features of a magnetic bearing that other manufacturers’ turbo blowers use?
HELMERT: Turbo blowers from other manufacturers work with magnetic bearings, which also aim to overcome the high speeds without any mechanical bearing. However, this requires electrical energy so that the coils arranged in a ring around the drive shaft can develop their magnetic forces during operation and, thus, allow the shaft to rotate free of mechanical friction. In particular, variable operational conditions put the highly complex regulation system of the magnetic bearings to the test. It can result in frequent safety shutdowns of the entire turbo blower due to technological reasons. To ensure that this system remains active for a certain time in the case of a system malfunction, emergency stop or power failure, turbo blowers with magnetic bearings must always be equipped with a temporary power accumulator. This serves to reduce the high operating speed before the shaft falls into the so-called mechanical emergency bearings.
ComPress: Nonetheless, critics observe that when the turbo blower is started, the driven shaft rests on the bearing and develops wear friction until the air cushion is formed. What do you say to that?
HELMERT: AERZEN is addressing this theoretically existing disadvantage with innovative air foil bearings. For this, we use a two-component coating as a maintenance-free friction partner. One of these materials is polytetrafluorethylene. PTFE is a thermoplastic, which, due to its very low coefficient of friction, is used as a non-stick coating. With PTFE, we virtually create a lubricating film without grease and oil. Because the compressor effect in the bearing compacts the air so densely that the layer between bearing ring and shaft is practically as hard as steel, AERZEN has designed a damping layer specifically for this application. This is a millimetre-thick sheet of metal - also known as spring foil - which is rolled in a wave-like manner to support the sliding layer of the bearing and at the same time absorb vibrations.
ComPress: What are the decisive advantages of AERZEN air foil bearings?
HELMERT: With the air foil bearing principle, no electrical, mechanical or pneumatic controls are necessary, even for dynamic load changes. The AERZEN bearing type still has reserves to support higher speeds than are usually possible with magnetic bearings. The long service life of more than 80,000 operating hours, the complete freedom from maintenance and the high level of functionality without any peripherals are other decisive advantages of the bearing solution used in AERZEN turbo blowers.
"With the air foil bearing principle, no electrical, mechanical or pneumatic controls are necessary, even for dynamic load changes."
Steffen Helmert,
Product Manager Turbo Blowers
