19/11/2017
In-SITU RECONITIONING OF RAW MILL FAN SHAFT IN CEMENT PLANT
In a new brown field Clinkerisation unit 4500 tpd capacity havening 6 stage preheater, precalcinator,kiln ,VRMS, Polytrack cooler m/s Polysius Germany/ Thyssen krupp industries Ltd.supplied Raw mill cyclone Fan 7,40000CU-M/HR ,3300KW for the vertical Roller mill RM-54/27/460 OF 330 TPH in the raw material grinding circuit. The clinkerisation unit was commissioned in March 2009.I
RAW MILL CYCLONE FAN
The Fan had been operating at rated capacity &rpm with vibration level of 1.4 mm.sec DE& 1.3 mm/sec NDE bearings In the month of June 2012 the fan tripped two times due to high vibration during plan operation. The Fan was stopped & detailed visual inspection of Impeller, shaft, bearings coupling,7 drive motor had been carried out and also checked the Dynamic balancing of Impeller& no abnormality was observed.
Being a major critical process fan& to keep the plant running ,operated the Fan at lower 931 rpm, Maintaining thr vibration level 3 mm/sec well below the permissible tripping limit 7.1 mm/sec recommended by (O.E.M.) for the safety of the equipment &waiting for the opportunity for longer plant stoppage to have detailed inspection of the Fan system.
In the end of june 2012the kiln had to be stopped for 8 days to reduce the clinker production & inventory as per the marketing conditions. During this shutdown a detailed inspection of both the bearings was carried out and discovered that the inner race of the DE BEARING (22244W-33 CC/C-3) was loose on the Fan shaft due to inadequate interference fit between shaft and bearing.
Since the process fans in clinkerisation unit like preheater fan, calciner fan, Raw mill fan, RABH fan,cooler ESP fan & coal circulating fan handles hot gases,in the process the fan impeller& shaft is subjected to higher temperature, variable operating conditions resulting in to lenior expansion of the shaft.To take care of this expansion the shaft slides with bearing in the free end (NDE) bearing housing.
In case the this phenomena is not happening due to friction and operating conditions the shaft takes shape like banana due to increase in length and exsert pressure on the bearings resulting in to slippage of shaft in to inner race of the bearing due to poor interference fit.
The management had already initiated procurement action& placed an order with m/s venti oelde Germany (O.E.M.) for a spare Impeller shaft assembly as an insurance spare for this Fan, with expected delivery in may 2013.
Under the circumstance no alternative left except to adopt local cold repair procedure for this critical process fan to keep the plant running .
RECNDITIONING PROCEDURE ADOPTED
PHASE -1
➢ The Drive motor,Fan shaft half coupling removed& dismenteled the DE bearing from the shaft.
➢ Cleaned & measured the worn out shaft size 219 mm against standard
Shaft size 220 mm.
➢ Preperaed the worn out shaft area with Fine dot punch to get knurling type rough surface on the shft for better interference fit
➢ Loctite superior Metal putty-40025 apllied on the worn out surface uniformily, new bearing heated up to 100 c& pushed on the shaft.sppilover metal putty in sides cleaned & left for 4Hrs curing to get proper interference fit between bearing inner race & shaft.
➢ After reassembly of the components, Ht motor7 alignment, Dynamic balancing of impeller the fan was put back in to poperation and observed fan vibration at DE &NDE bearings in the range 2.5 – 4.0 mm/sec at 931 rpm.
PHASE-II
➢ Experienced that cold repair of the shaft with Loctite steel putty is just to get interim relief.
➢ Expected delivery of new impeller with shaft assembly shall be in may 2013.
➢ Operating Fan at lower rpm effecting the VRM operational effiency.
➢ Removal of fan assembly from casing ,transportation to Heavy Enginnering works for repair, Dismentling &repair Reassembly at workshop&at plnt site will take minimum 20 -25 days& during this period plant has to be stopped resulting in to heavy loos of production.
Under these prevailing circumstances it has become imperative to think out of box to find better in-situ shaft repair technique &methodology to complete the reconditioning job with minimum possible time frame.
M/S MPA Power Ltd. Gurgaon (expert in grinding of critical shafts in sta tionary condition, especially DG set crank shafts) and m/s Wave NDTservices Ltd india (providind services for preheating & stress relieving ) of the shaft were contacted and confirmed the deputation of their teams wtth machines at site for heat treatment and grinding of the shaft.
Finally the plant was stopped on 11th fef 2013 for 15 days for kiln ,cooler preheater refractory works and annual maintence jobs.The following preparatory works and activities were performed
The Raw mill cyclone Fan was stooped and isolated from the electric supply& work permit taken.
➢ 3300 KW Drive HT motor was dismantled from the base frame and removed the coupling halves.
➢ Dismantled drive end bearing and housing and removed top half of bearing housing at NDE side.
➢ Additional bearing support was provided with housing at the DE bearing shaft end.
➢ A drive arrangement with geared motor,vvvf drive was installed for rotatiof the Fan during the welding and machining process to avoid distortion and bend of the shaft.
➢ A Lathe machine compound slide with tool post was installed for in-situ machining of tha shaft.
➢ Worn out bearing seat area of the shaft was cleaned and undercut the shaft area by 1 mm to get a clean & uniform surface area for buildup.te
➢ Preheated the shaft area up to 200 c in controlled manner with heat tracing equipment.
➢ The worn out shaft area was builtup with Eutectic electrode CGS-680 3.15mm dia. Applied in a single layer at 0,180,and 270 positions,intermittently,the cleaning and peening procedure continued during welding.
➢ Three dial indicatoters were positioned by the side of the bearing seat area and shaft end to check &maintain the shaft distortion, bend and run out within permissible limits during welding procedure.
➢ Stress relieving procedure & cotrolled cooling was adopted for the shaft built up area.
➢ Engineers/ Technicians machined the shaft area with a lathe machine tool post, rotating the fan impeller shaft assembly with an auxiliary drive arrangement during machining operation.
➢ The shaft size was maintained to 221 mm agains the standard size of 220 mm, Keeping 1 mm tolerance for final grinding.
➢ Engineers then fixed the special Grinding machine to grind and polish the shaft IN-SITU,in stationary condition.The special feature of this Machine is that it revolves circumfrentially on the stationary shaft to grind the machined builtup area.
➢ Final shaft size was maintained 220 mm dia to achieve better interference fit between shaft and bearing during assembly.
➢ Dismenteled the auxiliary geared motor drive arrange ment &lathe machine tool post.
➢ All foundation bolts were checked for looseness and tightened.
➢ Reassembled all the Fan components ,bearings coupling,motor and aligned the fan and motor couplings.Achieved radial and axial run ou within was 0.05 mm.
➢ An inspection of the fan inlet cone ,inlet louver dampers was carried out and the impellerwas dynamically balanced.
➢ No load/load trials of the fan and motor were taken and vibration measurements were recorded at DE and NDE bearings.
➢ Finally the Raw mill cyclone fan was put back into operation on 26 th feb 2013.
Since then the Fan has been in operation at 990 rpm inoriginal normal conditions with vibration level of 1.20 mm/sec DE and 1.15 mm/sec at NDE bearings.
Conclusion=
In-situ reconditioning of the Raw mill cyclonr Fan shaft (to bring it into original condition) bt adopting buildup,heat treatment, maching and grinding with special machine on a stationary shaft had been a unique experience.
Based on the experience gained In-situ Fan shaft reconditioning methodology can be adopted in such a critical situation to avoid a Lengthy plant stoppage production loss.
