The Maintenance of Rotor Assemblies
9Pages

1 The Maintenance of Rotor Assemblies from Strategic Rotating Machines - On Site – The Way Forward – Vic Ryan Product Manager IRD® Balancing ABSTRACT Throughout the more enterprising countries of the world, the benefits to industry of undertaking on site, the complete servicing and repair of strategic rotating machines have long been recognised and applied with considerable reward. The higher the capacity of the machines and the more strategic their nature of operation to production demands, the greater are the benefits to be realised in terms of reduced overall costs and machine downtime. The most difficult maintenance procedures to undertake on site are always seen as the final machining and balancing of rotor assemblies, particularly the higher capacity and more precise “Flexible” rotors from machines such as turbines, compressors, electrical motors and generators. This led to the development of a range of special purpose, fully transportable balancing machine systems with turning capability, and the special techniques for applying them to best effect in the field. This paper covers experiences gained and developments to date on the design and application of these “Transportable Maintenance Facilities” and provides a discussion document on how this growth business can best be adapted to the needs of industry world wide.

2 Introduction Throughout industry, it is accepted that the most time-efficient and cost-effective means of maintaining fixed plant, is to undertake as much as possible, if not all of the work, on site; the growing trend being to promote complete on site maintenance. This applies mainly to rotating machines that are critical to production processes, such as: turbines, generators, compressors, pumps, fans and motors and, in particular, to the electrical power generation industry. The higher the capacity of the machines and the more strategic the nature of operation, the greater are the...

3 balance rotors should there be any undue changes in mass concentricity as a result of induced load and/or running temperature changes. Transportable Maintenance Facility Recognising the benefits to be achieved by overcoming the problems associated with having to ship rotor assemblies away from site for repairs and balancing, has led to many joint ventures between original equipment manufacturers, service organisations, end users and balancing machine/machine tool manufacturers. Having full maintenance facilities permanently located at all production sites has always been discounted as not...

4 7. The system must be very adaptable for use as a complete work station for all types of field service applications, not only for balancing. Such as: „h General turning/grinding operations, when used in conjunction with a transportable machining attachment; „h Rotor inspection and Non Destructive Testing; „h Re-blading of bladed rotors; „h Geometric tolerance measurements; „h General electrical and mechanical repairs. Basic System Design Many years of application experience has shown that the requirements of a truly transportable maintenance facility can only be met if it is designed...

5 „h The constraints introduced by the need to maintain the high mass / stiffness constants, severely limit the overall system versatility, and the ability to adapt to differing service application demands and environmental situations, which are essential requirements of a fully transportable service facility. Soft Bearing Balancing Machines, in contrast, are ideally suited as the basis for the truly transportable service facility, particularly machines whose design incorporates high sensitivity, minimal stiffness pendulum suspensions and universal, self-aligning, flat surfaced rotor...

6 - Although having been designed specifically for low speed balancing, the self-centring pendulum suspensions and self-aligning rollers, in either free or locked up mode, provide a very good pair of “steadies” for supporting all types of rotor assemblies during various maintenance and testing operations. In fact, the versatility and application of the overall machine system is limited only by the ingenuity of the operating personnel concerned. Rotor Types For balancing purposes, there are essentially two types of rotors: “Rigid Rotors” and “Flexible Rotors”. A Rigid Rotor is that which,...

7 body of a paper roll is manufactured from a single component, running it up to speed is the only sure means of determining the points of unbalance or deflection. Fortunately, paper rolls generally operate at comparatively low speeds which are within the scope of a transportable balancing machine. When newly manufactured rotors are first put into service, many undergo some degree of plastic deformation. In most cases, this is only to a small extent that has no significant effect on the overall balance condition. However, some rotors, electrical rotors in particular, can undergo marked...

8 Rotors that cannot be balanced in component form, such as those from large generators, are balanced in stages, at incremental speeds up to and including their maximum service speeds. The procedure includes overspeed, testing and making balance weight corrections in three or more transverse planes to offset any tendency for the rotor to bend when running within the influence of its critical speeds. Service Balancing of Flexible Rotors Although the low speed balancing of flexible rotors using transportable machines is practised with considerable success by many service organisations world...

9 is also very important. An example is ensuring that blades used for re-blading turbine wheels are moment weighed and diametrically matched when being installed. Even in the unlikely event of the exact cause of unbalance being unknown, or where it may be distributed along the length of the rotor, the amount will be comparatively small, and applying what is known as the “Static / Couple Derivation” balancing technique will usually give very satisfactory results. Static/Couple Balancing Most elastic rotors operate above their first critical speeds (flexural modes) and below, but sometimes...