
Good Morning,
In May 2011 I experienced a girth gear teeth failure on the joints on one of my Ball Mill and recently I just experienced the more or less the same failure on my other Ball Mill. See Mill Spec and Attched Pictures.
ROM SAG Mill
Mill Type
Grate discharge, dry grinding, ball mill.
Construction
The mill is constructed from a fabricated shell, bolted by
Means of flanges to cast steel ends with integral
trunnions which are supported on hydrodynamic white
Metal bearings.
Drive
The mill is driven by a high-speed electric motor via a
Gearbox, pinion and girth gear. The girth gear is fitted
The mill shell flange at the discharge end.
Process Data
Feed Description : Chrome Ore (80%) + Fine Anthracite (20%)
New Feed Rate : 85 tph
Ore Specific Gravity : 2.0 - 2.4 t/m³
Bond Work Index : 22 kWh/t max
Volumetric Loading : 35% of mill volume
Ball Charge : 30% of mill volume (nominal)
35% of mill volume (maximum)
Feed Size : 10 mm (80% passing)
Product Size : 45 μm (80% passing)
Circulating Load : 0%
Effective Grinding Length : 13543 mm
Inside Diameter : 4000 mm
Length - Flange to Flange : 14000 mm
Plate Thickness :50 mm
Plate Specification :SABS 1431 Grade 300WA
Flange Specification :ASTM-A516 Grade 60
Flange Configuration :Straight
Manholes :3
Head / Trunnion Specification Cast Steel to BS 3100 Grade A2
Main Bearing Size :Ø1700 mm x 810 mm wide
Mill Speed (rpm / % critical) :15.71 rpm / 73%
Motor Speed :994 rpm
Mill Motor Power :3000 kW
Feeder Type :Ø400 mm Bore Cast Pipe
Gearing
Gear Type :Cast Steel Single Helical
Pinion Type :Single Helical Integral to Shaft
Teeth (gear / pinion) : 194 / 21
Normal Module :30
Face Width :660 mm
Pressure Angle :25°
Hardness (gear / pinion) :290 - 330 BHN / 58 - 60 Rc
Helix Angle : 9° 3'
AGMA Service Factors : 1.5
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