GB2457060A

GB2457060A - Rotor with balance mass

Info

Publication number: GB2457060A
Application number: GB0801799A
Authority: GB
Inventors: John Michael Harrison; Frank Anthony Hewitt
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2008-02-01
Filing date: 2008-02-01
Publication date: 2009-08-05
Also published as: GB0801799D0

Abstract

A rotor 22 comprises a balance land 24 and balance mass 30. The balance land 24 and balance mass 30 are adapted to permit radial positioning of the balance mass 30 relative to the balance land 24. The balance land 24 and the balance mass 30 have co-operating engagement features 60 which locate the balance mass 30 at a chosen radial position in the balance land 24, and the engagement features 60 are moveable relative to one another to permit adjustment of the radial position of the balance mass 30. The balance mass 30 may be located within a passage 32 in the balance land 24. The engagement features 60 may comprise screw threads, and locking means 70 may be provided to prevent radial movement of the balance mass 30. The rotor 22 may be part of a piece of turbo-machinery such as a compressor.

Description

ROTOR WITH BALANCE MASS

The invention relates to a rotor with a balance mass.

In particular it relates to a rotor with a balance land and a radially positionable balance mass.

Individual components of high speed rotating assemblies (for example a compressor or turbine rotor for a gas turbine engine) are balanced to a high degree of accuracy during manufacture. However, when the rotor is assembled in the engine, it frequently requires a final balancing operation to bring the engine assembly within desired balance limits. Once assembled into a casing it is difficult, and in some cases impossible, to make any adjustment to the balance state of the rotor. For example, in nested multi-shaft engines access to the internal shafts is extremely limited. The final balancing operation is often referred to as "trim balancing" and the normal means for performing this operation is to remove material from a balance land provided on the rotor.

Alternatively trim balancing may be achieved by attaching balancing weights by means of nuts and bolts at one or more radial planes within the assembly.

However, where the removal of material, or the attachment or adjustment of balance weights, involves some dismantling of the engine, the balancing process can become a time consuming and inconvenient process.

The rotatable components will also need balancing if a rotor blade is repaired or replaced because wear or damage, for example Foreign Object Damage (FOD), during service. As repair and overhaul tends to happen after the engine has been delivered to a customer, the requirement to dis-assemble the engine to balance the rotors will be a major inconvenience and may result in further damage and delay if the engine is not re-assembled correctly.

Hence a rotor having a balance means which can fix balance masses used in position and allow for controlled incremental movement of the balance mass to balance the rotor is highly desirable.

According to a first aspect of the present invention, there is provided a rotor comprising a balance land and balance mass, the balance land and balance mass adapted to permit radial positioning of the balance mass relative to the balance land, characterised in that the balance land and the balance mass have co-operating engagement features which locate the balance mass at a chosen radial position in the balance land, and the engagement features are moveable relative to one another to permit adjustment of the radial position of the balance mass.

Thus imbalance in a rotor can be countered by altering the radial position of the balance mass.

According to a second aspect of the present invention, there is provided turbo machinery comprising a rotor according to the first aspect of the present invention, wherein a casing is provided around the rotor with an aperture substantially axially aligned with the balance land and balance mass.

Hence the balance mass can be accessed, and its radial position adjusted, while the turbo machinery is assembled. In other words, it is not required to dismantle the turbo machinery in order to balance the rotor.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a cross sectional view of a section of turbo machinery comprising a rotor according to the present invention; and Figure 2 shows a sectional view of the rotor on line A-A shown in Figure 1.

Figure 1 shows a secflon of a compressor 10 for turbo machinery 12. A static vane 14 spans the distance between an outer annular wall 16 and an inner annular wall 18 to define a flow path 20 upstream and downstream of the vane 14. A rotatable hollow shaft 22, or rotor" is surrounded and spaced apart from the inner wall 18, and carries rotor blades (not shown) which are provided upstream and downstream of the static vane 14 in the flow path 20. A balance land 24 is provided on the rotor 22 as a thickened region or ring 26, where the balance land/ring 24 is concentric with the rotor axis 28 and extends radially inwards from an inner surface 29 of the rotor 22.

A sectional view of the rotor on line A-A in Figure 1 is shown in Figure 2. A balance mass 30 is located in a passage 32 provided in the balance land 24. The passage 32 extends in a substantially radial direction, is closed at its radially inner most end 34 and open at its radially outermost end 36, and, as shown in Figure 2, is at a twelve o'clock position on the rotor 22. Passages 40,42 and balance masses 44,46, as shown in Figure 2, are provided at a four o'clock and eight o'clock position respectively. An aperture 48 in the inner casing 18, and an aperture 49 in the outer casing 16 are substantially axially aligned with radially outermost end 36 of each passage 32,40,42, and hence with each passage 32,40,42 in the balance land 24, and each balance mass 30,44,46.

Each passage 32,40,42 in the balance land 24 is provided with engagement features 50,52,54 respectively which interlock with co-operating engagement features 60,62,64 on each balance mass 30,44,46. The respective engagement features locate the balance masses 30,44,46 within the balance land 24, with each balance mass 30,44,46 being at a chosen radial position within their respective passages 32,40,42. The engagement features co-operate to maintain the balance masses 30,44,46 in a chosen position relative to the balance land 24. The engagement features also permit adjustment of the radial position of each balance mass 30,44,46 in the balance land 24.

In one embodiment the engagement features 50,52,54,60,62,64 take the form of a screw thread on each balance mass 30,42,44, with a co-operating thread on the wall of the passage 32,40,42 in the balance land 24. Thus frictional contact between the co-operating threads will maintain the balance masses 30,42,44 at a chosen radial position. The screw threads can also slide relative to one another so that the radial position of the masses 30,42,44 within the balance land 24 can be adjusted.

A locking means 70 is provided on the radially outer end of each balance mass 30,42,44 configurable between a locked position to prevent radial adjustment of each balance mass 30,42,44 and an unlocked position to permit radial adjustment of each balance mass 30,42,44 within the balance land 24. The locking means 70 may take the form of a lock nut which tightens down on its respective balance mass 30,42,44, where the lock nut travels on the same thread provided in its respective passage 32,40,42 as its respective balance mass 30,42,44.

During a balancing operation the balance masses 30,42,44 are individually adjusted to alter the mass centre of the rotor 22 and hence compensate for any unbalance within the rotor 22. For example, if the unbalance is at the location 80 as shown in Figure 2, the balance masses 30,42,44 may each have a different radial distance from their outermost ends 36 in order to compensate for the imbalance 80. The position of each balance mass 30,42,44 in Figure 2 is diagrammatic and not intended to show the actual required relative positions of the balance masses 30,42,44.

When the rotor 22 is assembled inside the turbo machinery 12, access to the balance masses 30,42,44 is via the apertures 48,49 in the inner 18 and outer casings 16 respectively. The rotor 22 is rotated to bring each passage 32,40,42 in turn into alignment with the apertures 48,49 An operator can then use a tool (not shown) to configure the locking means 70 to an unlocked position and then turn each balance mass so that it moves radially inwards or outwards along its respective passage as required. The locking means 70 is then configured to a locked position to prevent further radial adjustment of the balance mass. The rotor 22 is then rotated to the next balance mass position and the process is repeated until all the balance masses are in the desired radial position.

While three balance masses and passages are shown in the figures and described above, any number may be provided. Likewise, while the principal intention of the apparatus described is to balance a rotor, it may also be used to introduce a desired amount of imbalance into the rotor, for example for unbalance testing.

Claims

1 A rotor comprising a balance land and balance mass, the balance land and balance mass adapted to permit radial positioning of the balance mass relative to the balance land, characterised in that the balance land and the balance mass have co-operating engagement features which locate the balance mass at a chosen radial position in the balance land, and the engagement features are moveable relative to one another to permit adjustment of the radial position of the balance mass.

2 A rotor as claimed in claim 1 wherein the balance mass is located in a passage provided in the balance land.

3 A rotor as claimed in claim 2 wherein the engagement features comprise a screw thread on the balance mass configured to co-operate with a screw thread provided on the wall of the passage.

4 A rotor as claimed in claim 3 wherein the engagement features further comprise a locking means configurable between a locked position to prevent radial adjustment of the balance mass and an unlocked position to permit radial adjustment of the balance mass.

A rotor as claimed in any one of the preceding claims wherein the balance land comprises a ring arranged concentric with the rotor axis.

6 A rotor as claimed in any one of claims 1 to 5 wherein the rotor is hollow and the balance land extends radially inwards from an inner surface of the rotor.

7 Turbomachinery comprising a rotor as claimed in any one of the preceding claims, wherein a casing is provided around the rotor with an aperture substantially axially aligned with the balance land and balance mass.

8 A rotor substantially as here inbefore described and/or with reference to the accompanying drawings.

9 Turbomachinery substantially as hereinbefore described and/or with reference to the accompanying drawings.