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TOOL FOR TRIM BALANCING A ROTOR

IP.com Disclosure Number: IPCOM000240868D
Publication Date: 2015-Mar-06
Document File: 9 page(s) / 303K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention relates to a method of rebalancing a compressor rotor within a gas turbine engine. Specifically, the invention relates to a tool used for moving trapped balancing weights.

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TOOL FOR TRIM BALANCING A ROTOR

TECHNICAL FIELD

    The invention relates to a method of rebalancing a compressor rotor within a gas turbine engine. Specifically, the invention relates to a tool used for moving trapped balancing weights.

BACKGROUND

    Gas turbine engines typically include several rotor stages, each having a rotor disk carrying an array of airfoils (i.e., compressor or turbine blades), commonly known as a "bladed disk". An unbalanced rotor element can lead to excessive vibrations within the core of the engine. There is a certain tolerance for vibrations that, if exceeded, can cause problems within the engine. Thus, turbine rotors are balanced to prevent damage and excessive loading on bearings and supporting structures, as well as efficiency losses caused by loss of clearance between the airfoils and the surrounding structure (caused by, e.g., shroud rubs).

    Despite efforts to first balance their constituent components, turbine rotors still require dynamic balancing following assembly and then rebalancing after use due to wear on rotor parts over time or foreign object damage that can cause the rotor disk to become unbalanced. Typically, the engine must be disassembled, completely or partially, to permit rebalancing or trim balancing of the offending rotor element. The process to rebalance an engine often takes over 6 weeks to complete. With aircraft gas turbine engines, it is desirable to be able to quickly and easily trim balance the compressor rotor without removal of the engine from the aircraft.

    One method of achieving this is to use balancing weights that can be re-positioned to redistribute the mass of the rotor as needed and allow the system unbalance to be fine-tuned to


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meet precise requirements. One design uses two arcuate balancing weights trapped within a pocket formed between the first and second stage high pressure compressor rotors. Such weights are described in detail by US Publication 20100316496 A1. The weights lock into place within a cavity in the first stage rotor hub using anti-rotation bumps on the ends of the weight's two spring arms which settle inside corresponding anti-rotation scallops within the stage one bladed disk that are made to fit the bumps. This traps them between the cavity in the stage one bladed disk and an annular shaft connected to the second rotor stage. The weights can be moved by deflecting the spring arms which moves the bumps out of the scallops and allows for circumferential movement by the weight along the hub of the stage one bladed disk.

    An engine designed with this system of trapped spring balancing weights is capable of being trim balanced much quicker than other engines using other balancing methods. The balancing process can be made even quicker if there is a way to adjust the movable weights without having to disassemble the engine. One way to do this would be to make use of the borescope ports within the engine casing. A tool is needed that is capable o...