OF ROTORS)
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7. COUPLINGS & ALIGNMENTS OF ROTORS
7.1. GENERAL DESCRIPTION
The coupling on turbine shaft are generally rigid coupling but in case of L.P.
rotor sometime the coupling head are shrunk fit and remachined. The basic function of any coupling is to connect two or more shaft together to form a shaft assembly. The number of shaft mainly depend upon the rating of the machine.
A very high accuracy is required during manufacturing of these rotor shaft at works. The axial runout on the coupling face may not exceed 0.02 mm.
and an additional check is also made at works/site to ensure that the geometry of the entire coupling surface does not deviate by more then the 0.02 mm.
except the concavity on the coupling face which is permitted upto 0.03/0.04 mm.
The radial and axial alignment of the various shafts are to be completed before their coupling and alignments are to be done in such a way that the entire shaft assembly follow the continuous deflection curve given over the drgs. for a particular machine. The coupling checks determines both the radial and axial position of the two adjacent coupling flanges relative to one another.
The radial measurement are performed on the circumference of the couplings and the axial measurement are performed on outer most diameter of the coupling. During coupling of the two shafts it should be ensured that the no stresses are exerted as a results of the coupling each other shaft.
After completion of the alignment and coupling of the shaft the casings are aligned radially and axially. Here equal importance is given to the radial & axial
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During the alignment of two coupling both are to be turned in same direction and by the same amount when the measurement are taken to avoid the influence of the axial & radial runout present in the shaft caused due to the machining.
7.2. PROCEDURE
7.2.1. Before placement of module/rotor in position check and record the coupling hole and journal dia of the shaft.
7.2.2. Check coupling faces for the concavity/convexity with the help of a thin rectangular straight edge before placement of module/rotor in position.
7.2.3. Check spigot and recess of the coupling and ensure their fitting before placement in position.
7.2.4. Place the module/rotor in position and check the radial runout of journal and axial runout of the coupling faces independently of each shaft. During checking of radial and axial runout of the shaft place H.P. rotor on both of its bearing and IP/LP rotor one end on its bearing and another end on the lifting tackle. The radial and axial face runout on the shaft should be within 0.02 mm accuracy. Any variation may not be permitted here and matter may be referred to the designer's.
7.2.5. The HP,IP & LP rotor are aligned together and then their couplings are made. After fully completion of HP/IP & IP/LP coupling with tightening of their final bolts the complete shaft is cleared for Generator rotor alignment.
7.2.6. During initial alignment of HP/IP & IP/LP rotor the radial checks are generally done with the help of depth micrometer and axial gap are measured with the slip gauges. After completion of the radial alignment the rotor are inserted in their spigot even with some minor variation in their axial gap values.
STEAM TURBINE effective spigot are not existing in two couplings i.e. in case of LP - Gen coupling the radial dial reading are also taken.
7.2.8. Avoid rotation of two shaft in their spigot. If necessary these may be rotated after taking out from their spigot.
7.2.9. During alignment of shafts the adjustment of shims in bearing torus may be fully avoided. The margin of + 0.30 mm. in height &
left/right direction may be kept for emergency works only. Any
7.2.10.The final packers of the pedestal and base plates are fitted before the grouting of the pedestal itself and here no adjustment is necessary during erection of the machine. But during overhauling of the machine the adjustment may be carried out in these packers for correction of catenary of the machine.
7.2.11.During alignment of rotor make HP/IP and IP/LP coupling gap parallel. After completion of final alignment no adjustment of packers and keys etc are permitted on pedestals and bearing the final alignment of HP/IP & IP/LP rotors should be checked after fitting of all the final keys and packers of the pedestals.
7.2.12.After alignment couple the HP-IP & IP-LP rotors on temporary bolts. Record coupled runout of the rotor and ensure that the coupled runout is not more then 0.03 mm. in any where in the journal as well as in coupling area. Before coupling of rotor on temporary bolts record their spigot clearances by actually moving the rotor radially.
7.2.13.During erection IP-LP swing check on IP front and HP-IP swing check on HP front are to be recorded on temporary bolts. These reading are to be ensured within the design limit.
7.2.14.Before alignment/coupling position the two shaft adjustment to each other depending upon the higher and lower point of the shaft with respect to their axial face measurement values.
Bharat Heavy Electricals Limited reaming/honing at site as this may cause serious problem at a later date during overhauling of the unit.
7.2.17.As for as possible ream/hone all the coupling bolts holes to same size. In exceptional cases only the variation in hole sizes are permitted. Each hole during honing should be checked for bananas shape with the help of a parallel ground straight pin of 0.02/0.03 undersize. No banana shape is permitted in any of the hole. The hole should be made to 0.005 mm accuracy.
7.2.18.All the coupling bolts are to be machined and ground by 0.02/0.03 mm undersize then the hole dia. These bolts are to be fitted with thumb pressure only and no additional force is recommended while fitting these bolts.
7.2.19.A very thin layer of molykote may be applied on all the exceptional cases the 180o opposite bolts may be made of equal weight.
7.2.21.During tightening of coupling at any stage first tighten four bolts on 90o location. Always tighten bolts in proper sequence with 180o opposite bolts. These bolts are to be elongated to the value given over drgs.
7.2.22.During tightening of coupling the radial runout on journal and coupling may be checked at various stages during tightening of
STEAM TURBINE 500 MW
ERECTION
CRITICAL ACTIVITIES (COUPLINGS & ALIGNMENTS
OF ROTORS)
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on coupling and journal of the shaft.
7.2.23.After final tightening of LP-IP and HP-IP coupling the swing check value on HP front rotor is to be rechecked. In case of variation in value a proper correction is to be made with consultation of designer's. The indifferent or unsequential tightening for achieving the swing check value or coupled runout value may be fully avoided. this may cause unnecessary stresses on the coupling.
7.2.24.After completing the coupling work the casing radial and axial alignment may be done.
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