2.3.6.3
Rotors
Rotors shall be steel, and of one-piece construction, with an asymmetric
profile to minimize leakage losses, and ensure high efficiency. Rotors
shall be treated for corrosion resistance. It rotors are welded to the
shaft, the assembly shall be stress relieved and heat treated for proper
strength. Rotors shall be dynamically balanced to ensure vibration-free
operation.
2.3.6.4
Gears
Gears shall be of alloy steel, AGMA 390.03A Quality Number 12 or better for
both bull and pinion gears. Gears shall be hardened to 275 Brinell for
bull gear and 320 Brinell for pinion, unless otherwise approved. Gears
shall be ground to the required contours, checked for proper contact during
assembly at the factory, and shall not require a break-in period in the
field for proper operation. All gears shall be pressure lubricated.
a.
Timing gears shall be provided on the rotor shafts to maintain the
rotors in correct relative position. The compressor design shall
allow the timing gears to absorb no more than 10 percent of the
total input power at full load.
2.3.6.5
Seals
Separate air and oil shaft seals shall be provided to confine air in the
casing and prevent contamination of the air stream by lubricating oil.
Shaft seals shall be the restrictive ring type. The seal rings shall be
stainless steel, brass, or carbon, and retainers shall be made of stainless
steel. Provide an air space vented to the atmosphere between the air and
oil seals. Seals shall be suitable for all operating conditions including
suction throttling, start-up, and shutdown.
2.3.6.6
Thrust Bearings
Thrust bearings shall be anti-friction ball or roller type or hydrodynamic
(fluid film) type. Anti-friction bearings shall have an L-10 life of
80,000 hours in accordance with ABMA 9 or ABMA 11. Axial rotor thrusts due
to air compression shall be absorbed by main thrust bearings or transferred
to auxiliary thrust bearings by a load balancing arrangement. Hydrodynamic
thrust bearings shall be Kingsbury type or other approved type and shall be
adequate to accommodate all operating conditions. Speed increaser bull
gear thrust bearings shall be sized for equal thrust in both directions and
shall be adequate for any axial loads transmitted through the driver
coupling.
2.3.6.7
Radial Bearings
Radial bearings shall be anti-friction roller or ball type or hydrodynamic
type. Anti-friction bearings shall have an L-10 life of 40,000 hours in
accordance with ABMA 9 or ABMA 11. Hydrodynamic bearings shall be
precision bored sleeve or pad type, designed for easy replacement by a
split design or axially removable arrangement. High speed hydrodynamic
pinion bearings shall be anti-oil whip, tilting pad type. Hydrodynamic
bearing design shall provide low vibration and sufficient damping at rated
speed and all operating modes, including rated capacity and unloading down
to 20 percent of unloaded power.
SECTION 15215N
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