IN-SITU RECONDITIONING OF RAW MILL FAN SHAFT
An Innovative Approach
Jaiprakash Associates Limited. India
Complete Specifications:-
Description
Reconditioning Procedure Adopted
Phase-I
The Drive motor, Fan shaft half coupling removed & dismantled the DE bearing from the shaft.
Cleaned & measured the worn-out shaft size 219mm against standard shaft size 220mm dia.
Prepared the worn-out shaft area with Fine dot punch to get knurling type rough surface on the shaft for better interference fit.
Loctite superior Metal Putty-40025 applied on the worn out surface uniformly, new bearing heated up to 1000c & pushed on the shaft. Spillover Metal Putty in sides cleaned & Left for 4 Hrs curing to get proper interference fit between bearing inner race & shaft.
After reassembly of the components, HT motor & alignment, dynamic balancing of impeller the fan was put back into operation and observed fan vibration at DE & NDE bearings in the range 2.5 – 4.00mm/sec. at 931RPM.
Since there was no alternative we restricted the Fan RPM 911 to run at lower vibration level 2.5 to 3.5mm/sec. for the safety of equipment against permissible limits H1- 4.5 & H2 - 7.1mm/sec.
The fan performance was just satisfactory whereas the VRM feed reduced by 10 TPH due to lower fan RPM and air flow in the mill system.
To make up this short fall transferred Raw Meal from K#4 unit-I Blending & Storage silos with pneumatic transport system to K#5 unit-II blending silo to maintain same clinker production level.
Page 2 of 3
Phase-II
In January 2013, observed changed erratic vibration behavior of the fan and noticed blackish colour of the DE bearing oil indicating wear of the steel putty applied on the worn out shaft bearing area.
Planned 48 hrs. stoppage of the Raw Mill fan after having sufficient raw meal storage in blending silo to keep the Kiln in operation during the period & adopted the same repair methodology with steel putty.
Experienced that cold repair of the shaft with loctite steel putty is just to give interim relief.
Expected delivery of new Impeller with shaft assembly shall be in May 2013 from OEM M/s Venti Oelde Germany.
Operating fan at lower RPM affecting the VRM operating efficiency.
Removal of fan assembly from casing transportation to Heavy Engineering work (HEW) Jaypee Rewa (located 300 KM distance). Repair of the worn out shaft & reassembly at Plant site will take minimum 20-25 days & during this period plant has to be stopped, resulting into heavy production loss.
Under these prevailing circumstances, it has become imperative to think out of box to find better technique & methodology for shaft repair & reliability.
Raw Mill fan stopped isolated from electric supply & work permit taken. Dismantled drive HT motor (3300KW) from base frame & coupling half from the fan shaft. Provided additional bearing support with housing at the fan shaft end. Dismantled drive end bearing, bearing housing. Cleaned the worn out shaft bearing seat area.
Plant stopped on 11.02.13 for Kiln, Cooler, Preheater refractory works & maintenance jobs for 15 days. The following activities were performed during the In-Situ Repair of the Fan Shaft.
Drive arrangement with Geared Motor made for rotation of fan during welding and machining process to avoid distortion & bend of the shaft.
Installed Lathe machine compound slide with tool post for In-Situ machining of the shaft.
Installed special pneumatically operated grinding machine on the shaft & undercut worn out shaft area by 1mm with the machine to get clean & uniform surface for buildup.
Preheated worn out shaft area up to 200˚C in controlled manner with heat tracing equipment
Buildup worn out area with Eutectic electrode CGS-680, 3.15mm dia. applied single layer at 0˚, 180˚, 90˚ & 270˚ positions intermittently. Cleaning & penning Procedure continued during welding.
3 nos. dial indicators positioned by the side of bearing seat area & shaft end to check & maintain the shaft distortion, bend, run out within permissible limits during welding procedure.
Stress relieving procedure adopted for the worn out shaft buildup area & followed by controlled cooling.
Machined the shaft worn out build up area with Lathe Machine tool rotating the Fan Impeller shaft assembly with auxiliary drive arrangement during machining operation.
Maintained the shaft to 221 mm against standard shaft size of 220 mm dia, Keeping 1 mm tolerance for final grinding
Machined the shaft worn out build up area with Lathe Machine tool rotating the Fan Impeller shaft assembly with auxiliary drive arrangement during machining operation.
Page 3 of 3
Maintained the shaft to 221 mm against standard shaft size of 220 mm dia, Keeping 1 mm tolerance for final grinding
Fixed the special grinding machine for In-Situ grinding & polishing the shaft in stationary condition.
The special feature of this machine is that it revolves circumferentially on the stationary shaft for grinding the machined build up area. Completed the grinding & final finishing operation and maintained the final shaft size 220+0.05 mm dia to achieve interference fit between shaft & bearing during assembly.
Dismantled the auxiliary drive & machining arrangement. All foundation bolts were checked for looseness & tightened. Reassembled the coupling, drive HT motor 3300 KW & aligned fan and motor shaft coupling, achieved radial & axial run out within 0.05mm. Inspected the fan, inlet cone & inlet louver dampers, dynamically balanced the impeller.
No load/load trial of fan & motor taken & recorded vibrations at DE & NDE and motor bearings.
Finally the Raw Mill cyclone Fan has been put back in operation with Kiln/VRM for Raw material grinding on 26.02.2013
Since then the fan has been in operation at 980 RPM in original normal condition with vibration level 1.20 mm/sec DE & 1.15 mm/sec at NDE bearing, operating raw mill at Rated production level.

We claim
1) That this innovative methodology for “In Situ-Reconditioning of Raw Mill cyclone fan shaft” (to bring it into original condition) adopting build up heat treatment machining, grinding with special grinding machine on stationary shaft has been a unique experience at Dalla Cement Factory (A Unit of Jaiprakash Associates Limited).
2) That the fan is running in normal condition & operating parameters with minimum vibration level 1.20mm/sec. & 1.15mm/sec.
3) That based on the experience gained this innovative, In-Situ Fan shaft reconditioning methodology can be adopted in such critical situation to avoid long stoppage of the plant.