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Turbine Gear high rpm BHD-VOITH Gear Repair
Model : TG 63s - 1250mm Diameter - hardness HrC 60. Works carried out Metalock Thailand

Initially 1 tooth fractured and local firm welded another tooth into position. Unit put back into service and failed immediately – this time 3 teeth broke off.  Scope of repairs - crack tested damaged area, followed up by a portable hardness test [scleroscope] of adjacent teeth, welded areas and HAZ [heat affected zone]. Large fluctuations of hardness required removal of the 4th tooth


Picture shows Drill Jig and initial test holes to gauge hardness /machinability at suitable depths. Main and starter gears flanges and couplings were removed


Drilled holes to depth – inconsistency in hardness due to welding required use of carbide and HSS drills at different intersections to establish a uniform depth [and hardness substrate]


Damaged section removed and cleaned up.  Dummy block made and fitted – blued in bottom to ensure good contact. 3 blocks in total made here. 1 block test dummy piece for profile and geometry. 1 block as used / fitted. 1 spare in case of gear cutting or heat treatment problems.  Half hole perforations visible are drilled out and temporary locks, dowels and unbrako’s installed for gear cutting.Block then removed for heat treatment, refitment, gear grinding etc as follows. Unable to heat treat section in gear as damage, embrittlement and softness would occur in adjacent teeth.


Gear being set up for machining Gear cutting finished, temporary locks etc, removed prior to heat treatment.


Section after Heat treatment [case hardening]. Section required fitment and reworking of butt face contact area as some movement - typical / expected and allowed for in heat treatment occurred. Piece being installed by Metalock / Masterlock method. Higher [harder] grade pads used in caulking process, high tensile MN555 Metalock keys used throughout. Some 50 taps, 12 carbide and 45 HSS / normal drills used on this small section – tools resharphened continuously.  Section fitted prior to secondary finish grinding.
 

Gears cleaned up and set onto jig to establish clearances, backlash and contact in line with other teeth. Section after grinding, hand finishing.