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Powder Welded Turbomachine Rotor

IP.com Disclosure Number: IPCOM000146866D
Published in the IP.com Journal: Volume 7 Issue 3A (2007-03-25)
Included in the Prior Art Database: 2007-Mar-25
Document File: 4 page(s) / 377K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Rotors for high-speed turbomachinery such as steam turbines, gas turbines, gas compressors or turbogenerators are often formed from sections to ensure that defects, which cause catastrophic failure, are not hidden within large cast or forged shafts. If such components are not anchored securely, they can move in service causing excessive vibration and requiring maintenance, which severely disrupts the business of the user. Up to the current time several methods have been used to address this problem. For rotors, which are bolted together from component parts (usually discs), the discs have couplings machined into them (so-called Hirth or Curvic teeth) to maintain a rigid lock when tightened. It is not unknown even then for subsequent movement to occur. The advantage of mechanical locking is that forces can be carried by disc material, which has not been denatured metallurgically by the welding process. Alternatively sophisticated welding processes are used. These require specialist equipment and expensive production sequences (especially Electron Beam Welding) to avoid heat distortion and damage to the rotor material and/or an out-of-balance result at the end of manufacture. Even then such problems are not unknown due to the limited number of welding points, which such production routes can practically afford.

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Powder Welded Turbomachine Rotor

Idea: Peter Senior, GB-Lincoln

Rotors for high-speed turbomachinery such as steam turbines, gas turbines, gas compressors or turbogenerators are often formed from sections to ensure that defects, which cause catastrophic failure, are not hidden within large cast or forged shafts. If such components are not anchored securely, they can move in service causing excessive vibration and requiring maintenance, which severely disrupts the business of the user.

Up to the current time several methods have been used to address this problem. For rotors, which are bolted together from component parts (usually discs), the discs have couplings machined into them (so-called Hirth or Curvic teeth) to maintain a rigid lock when tightened. It is not unknown even then for subsequent movement to occur. The advantage of mechanical locking is that forces can be carried by disc material, which has not been denatured metallurgically by the welding process.

Alternatively sophisticated welding processes are used. These require specialist equipment and expensive production sequences (especially Electron Beam Welding) to avoid heat distortion and damage to the rotor material and/or an out-of-balance result at the end of manufacture. Even then such problems are not unknown due to the limited number of welding points, which such production routes can practically afford.

The novel idea proposes the use of finely divided ferrous and aluminum powder as the welding heat source, trapped in grooves between mating discs, which are clamped together in any well-known way. Such powders are know to react very rapidly once burning, which can be initiated with any common method of heat ignition such as fuses, sparks, induction heating, etc. The composition of the powder for this application must be tailored specifically to match the disc materials, particularly their expansion coefficient, to avoid residual tension. Furthermore, since the welding may take place in closed cavities, the powder may also have to contain its own oxidant.

The proposal is that such powder pockets should be ignited around the circumference and along the length of the rotor so that the welding takes place simultaneously at all points avoiding asymmetric heat distortion. The high reaction temperature of the powder welding process also minimizes heat damage to the substrate discs, but it has been used before for successful welding large broken machine beds made from cast iron, which are often difficult to weld without metallurgical micro- damage.

The pockets can be circumferential grooves about the axis of the rotor itself, or rings or any other shape disposed in groups around the circumference, provided only that they maintain the rotor symmetry. It would also be possible to lay the powder in longitudinal grooves along the length of rotor bolts so t...