17
bushings, the inner diameter will have to be slightly larger than required to
compensate for the reduction in diameter that occurs when the bushings are pressed
in place.
compensate for the reduction in diameter that occurs when the bushings are pressed
in place.
The bearing plates on the operating ring should be checked for excessive wear and
replaced if necessary. The grease grooves of the originals should be duplicated on
the new bearing plates.
replaced if necessary. The grease grooves of the originals should be duplicated on
the new bearing plates.
4.5
Packing box and shaft sleeve
Many times the packing box will be severely corroded. If the metal loss is significant
in the packing box bore, the packing will have to be overcompressed in order to fill
the bore. This will lead to shortened packing life and excessive wear of the shaft
packing sleeve. If the packing box is still structurally sound, the interior bore of the
box can be built up with a properly applied epoxy coating. If the corrosion has
reached the point that the box has been weakened significantly, some other method
of repair or complete replacement may be required. Once the surfaces have been
repaired, the packing box should be painted
in the packing box bore, the packing will have to be overcompressed in order to fill
the bore. This will lead to shortened packing life and excessive wear of the shaft
packing sleeve. If the packing box is still structurally sound, the interior bore of the
box can be built up with a properly applied epoxy coating. If the corrosion has
reached the point that the box has been weakened significantly, some other method
of repair or complete replacement may be required. Once the surfaces have been
repaired, the packing box should be painted
.
The turbine shaft packing sleeve is usually constructed in two pieces so that it can be
replaced when worn. In some cases, the sleeve can be built up by welding and
machined back to the drawing dimensions. Welding on the packing sleeve must be
accomplished with a minimum amount of heat input to prevent inducing stress and
distorting the sleeve. Another alternative is to flame spray the sleeve with a wear-
resistant material and machine it back to original dimensions. The coating used in
flame spraying must be chosen carefully and the proper procedure followed to
ensure proper bonding to the parent material.
replaced when worn. In some cases, the sleeve can be built up by welding and
machined back to the drawing dimensions. Welding on the packing sleeve must be
accomplished with a minimum amount of heat input to prevent inducing stress and
distorting the sleeve. Another alternative is to flame spray the sleeve with a wear-
resistant material and machine it back to original dimensions. The coating used in
flame spraying must be chosen carefully and the proper procedure followed to
ensure proper bonding to the parent material.
4.6
Servomotors
In some instances, due to contaminants in the oil or misalignment, the servomotors
for the wicket gates will require repair. The most common types of damage are
scoring in the cylinder and scoring on the piston rods. Scored cylinders must be
bored out and honed to remove the scoring. New piston rings then must be
fabricated to match the new inner diameter of the cylinder. To restore the piston to
cylinder clearance, bronze sleeves or bands of phenolic material can be installed on
the piston.
for the wicket gates will require repair. The most common types of damage are
scoring in the cylinder and scoring on the piston rods. Scored cylinders must be
bored out and honed to remove the scoring. New piston rings then must be
fabricated to match the new inner diameter of the cylinder. To restore the piston to
cylinder clearance, bronze sleeves or bands of phenolic material can be installed on
the piston.
The first step in repairing scoring on the piston rod is to turn down the rod by
machining to remove the scoring. The rod must then be built up to allow grinding to
the final diameter. If mildly scored, electroplating with industrial hard chromium
may be used to restore the rod diameter. If the scoring was deep, it may be
necessary to build the rod up by welding or other means to restore it to its original
diameter.
machining to remove the scoring. The rod must then be built up to allow grinding to
the final diameter. If mildly scored, electroplating with industrial hard chromium
may be used to restore the rod diameter. If the scoring was deep, it may be
necessary to build the rod up by welding or other means to restore it to its original
diameter.