rotor balancing the importance of smooth running

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Tips for the operator

Have you ever driven a car witha wheel out of balance? Thefaster you drive the more younotice the vibrations that come

through the steering wheel. The vibra-tions not only affect your driving comfort,but over time will translate into wear inyour car’s steering and suspension. Aswell as the cost of replacing worn parts,these are both systems that closelyaffect your safety and need to be in topcondition.

Small cause – big effect The effects of imbalance in your car

wheel should be relatively small and easily detected. But since the forces and vibrations created by an imbalanceincrease with rotational speed, and midsized ABB turbochargers rotate at up to30,000 rpm (compared to about 800 fora car wheel at 130 kph /80 mph), we cansee that accurate balancing of your turbo-charger rotor is proportionately morecrucial.

In fact, in a turbocharger even just asmall deviation in the distribution of themass around the rotor creates significantforces. The TPL 67-C is a medium sized

turbocharger. In normal operation therotational speed of the rotor is about26,000 revolutions per minute. If youremoved only 10 g of material from oneblade tip, the imbalance created willcause a centrifugal force of 13,700 N.This is equivalent to a weight of 1400 kg – or a medium sized car! The mass of thebladed shaft, in comparison, is just 31 kg.

For these reasons rotor balancing hashigh priority during the turbochargermanufacturing process. Before deliveryevery rotor is balanced within very stringent limits. First, only the turbineshaft is balanced. Later, the completerotor assembly with compressor wheelattached is balanced again. A balancingreport is issued and stored as a referencein our database, along with the serialnumber of the turbocharger.

Factory balancing – the best start in life The balancing process itself is a skill

that requires not only know-how but a lotof experience as well. Nowadays, thebalancing machine readily locates whereand how big your imbalance is. The chal-lenge is how you use this information tocorrect the imbalance on the shaft.

Where to remove (grind off) some mate-rial? Or maybe a slight change to theassembly of the rotor is enough?

Proper balancing is guaranteed forevery rotor that leaves the ABB Turbo -charging factory. Balancing is, however,not a “for life” process. In operation, thebalance of the rotor may be affected byvarious influences. Fouling is one ofthese. In particular, the exhaust gasesfrom heavy fuel oil (HFO) contain solidparticles that can be deposited on coolersurfaces anywhere between the engineexhaust gas valve and the exhaust stack.And there is no law which states thatthese deposits have to be evenly distrib-uted!

Imbalance – part of turbocharger life In the turbocharger it is primarily the

nozzle ring and the turbine which areexposed to deposits of solid matter inthe exhaust gases. Fouling on the nozzlering influences the performance of theturbocharger by changing the aero-dynamic shape of the vanes ABB Turbo -charging so carefully designs and exe-cutes. Fouling on the turbine blade alsoaffects the shaft and as stated, deposits

Rotor balancingThe importance of smooth runningSmooth running is the “sine qua non” of high performance, high availability turbocharging. Fabian Wittmer explains how to achieve it through accurate rotor balancing.

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Tips for the operator

are never evenly distributed. Indeed, it isnot only the material deposited on theturbine that can affect balance. Thedeposited material can be removed ordisplaced just as unevenly by variousmechanisms – including turbine washing.

In addition, foreign objects in the gasflow may hit and damage turbine bladesor the compressor wheel. The solid parti-cles carried by the exhaust gases areabrasive, leading to uneven erosion ofrotor material. And, finally, to complicatematters even further, while fouling, ero-sion or mechanical damage can be de -tected by eye, some influences are noteven visible.

Hence – if you experience – or evensuspect – any of these conditions,checking and balancing of the rotor byan ABB Turbocharging Service Station isstrongly recommended.

What could happen? As with your car, persistent imbalance

will eventually cause wear and associatedexpense. A rotor that is out of balancemoves laterally within its bearings. Smallmovements and forces are damped bythe lubrication oil in the bearings and

their supporting components. A largerimbalance will increase the wear on your bearings and force you to change themmore frequently. You might also experi-ence the turbine or compressor wheelrubbing against adjacent components(e.g. casings) due to increased shaftmovements. In more severe cases ofimbalance, higher vibrations in the turbo -charger are noticeable. Or, in the worstcase, a complete bearing breakdown canoccur. Consequentially, the compressorwheel and the turbine blades also suffersignificant damage due to rubbing, andwill need replacing.

Reduced efficiency During the period prior to replace-

ment of worn blades, vanes and casings,turbocharger efficiency can be adverselyaffected due to aerodynamic and ther-modynamic inefficiencies. In this regard it is worth noting that on the latest turbo -chargers, a 1 % reduction in turbo -charger efficiency can result in anincrease in fuel consumption of over 1⁄3gram per kWh, translating into as muchas 30,000 dollars in additional fuel costsper year for a 10 MW engine.

Where to goOur ABB Turbocharging Service Sta-

tion network offers a rotor balancingservice with worldwide coverage. Everystation has qualified personnel andstate-of-the-art automated equipmentfor accurate balancing within very tighttolerances. In fact, when opening a newService Station, the balancing machine isone of the first tools to arrive and itscommissioning is one of the main signalsthat the station is open for business.

Make balancing a “must”Balancing the rotor is recommended

as part of every overhaul performed in an ABB Turbocharging Service Station.When servicing the turbocharger in thefield, balancing is recommended whenev-er time and distance to the next ABBTurbo charging Service Station permits.

Regular balancing throughout the life-time of a turbocharger is essential forsafe and long-lasting operation. It savesyou cost in the long run.

All ABB Turbocharging Service Stations have sophisticated balancing equipment.