Vibration in Turbine Engines
Vibration in Turbine Engines
(OP)
I work for a turbine engine overhaul center. It is known that there are variety of reasons that cause vibration in turbine engines. The main reason is unbalance in rotating parts.In balancing procedures sometimes the unbalance value differs in subsequent runs.In general these differences are small so that they dont effect the residual unbalance value. however I experienced a 2 g.in unbalance value change in two subsequent run despite of nothing changed in the rotor and arbor.The unbalance tolerance was 1.5 g.in in either correction plane.The balancing machine is a hard-bearing horizontal dynamic one. The arbor is a well balanced nut-tightened arbor.Does anybody know the reason for this difference?





RE: Vibration in Turbine Engines
RE: Vibration in Turbine Engines
I have a very good experience from some things to care for:
1. Spray or add electrolythically and grind clean all radial clearances to minimum play inside the allowed according to manual or ask manufacturer (watch that you follow manual and if applicable FAA paperwork).
2. Measure the actual runout (dial gauge) when you balance the disk to zero unbalance. (If possible both sides, min. one side). (It is always some amount. Record how much and the direction!!).
3. Build the final rotor so that each disk has opposed or unbalances distributed in a spiralized fashion.
4. Check the actual mounted runout disk by disk and compensate for it when adding next disk as much as possible. Keep a careful record of the full rotor.
5. In cases where you are allowed: Make the fit almost zero and heat the rotor part to
somce 50K temp above room temp before the mounting.
6. When finally trim balancing the full rotor, always remove the static unbalance along the centre (spread any grinding well, smothly), and remove dynamic unbalance at the ends.
If in doubt what I mean, ask. Best regards, Arne
RE: Vibration in Turbine Engines
I have had the same problem in the past and it is caused by a very small bowing of the rotor. You need to keep the rotor turning all of the time on a such a sensitive rotor as this. What I did (on an IRD balancing machine) was to slow roll the rotor for about a day before carrying out the balancing procedure. On large rotors you may have to slow roll for a couple of days to get rid of any bow caused by the rotor sagging.
The main thing is not to let the rotor sit for a long time suspended between 2 bearing supports - you wouldn't do it on a steam turbine after a stop - you would keep it turning to avoid a thermally induced bow. If you have to have the rotor sitting for a long time on the supports, install a small drive to slow roll the thing.
ron.frend@predicon.net