Saturday, December 31, 2011

Methods of securing blades to disc and Rotors of drum and disc construction


Fig. 3-11 Methods of securing blades to disc.
Fig. 3-10 Rotors of drum and disc
construction.
23. The construction of the compressor centres around the rotor assembly and casings. The rotor shaft is supported in ball and roller bearings and coupled to the turbine shaft in a manner that allows for any slight variation of alignment. The cylindrical casing assembly may consist of a number of cylindrical casings with a bolted axial joint between each stage or the casing may be in two halves with a bolted centre line joint. One or other of these construction methods is required in order that the casing can be assembled around the rotor. Rotors

24. In compressor designs (fig. 3-10) the rotational speed is such that a disc is required to support the centrifugal blade load. Where a number of discs are fitted onto one shaft they may be coupled and secured together by a mechanical fixing but generally the discs are assembled and welded together, close to their periphery, thus forming an integral drum.
25. Typical methods of securing rotor blades to the disc are shown in fig. 3-11, fixing may be circumferential or axial to suit special requirements of the stage. In general the aim is to design a securing feature that imparts the lightest possible load on the supporting disc thus minimizing disc weight. Whilst most compressor designs have separate blades for manufacturing and maintainability requirements, it becomes more difficult on the smallest engines to design a practical fixing. However this may be overcome by producing blades integral with the disc; the so called ’blisk’.

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