aluminum bronze, C95500 should be used. If the heel-to-toe sealing surfaces require
repair, these surfaces should be built up with the same or similar material as
originally used unless there is galling or other problems that indicate a change in
material is needed.
In performing weld repairs to the wicket gates, the following general procedures should be
followed. In preparation for welding, the surface to be welded should be machined to sound
material at least 0.125 inch deeper than the final dimension. Where an overlay of a
dissimilar material is being used, such as bronze or stainless steel over mild steel, enough
material should be removed to allow at least three weld passes to be made. This will ensure
that the metal at the finished surface will be undiluted by the parent material and therefore
possess the desired properties. After the welding is complete, the gates should be finish
machined to the manufacturer's drawing dimensions. It is important that the finish
machining be completed after all the welding is complete to allow for the correction of any
distortion that may occur from the heat of welding.
4.4 Facing plates and wicket gate bushings
The top and bottom facing plates' surfaces should be checked for wear and galling. The
headcover should be installed without the wicket gates. All of the headcover's mounting
bolts should be installed and tightened to full torque to check the facing plates for level and
parallel. While the plates should be level, it is more important that they be parallel to each
other and perpendicular to the wicket gate bushings to prevent binding of the wicket gates.
Parallelism can be checked by measuring the vertical distance between the plates with an
inside micrometer. The plates can be checked for level using a precision level or a laser
device with horizontal sweep capability. If the plates are not parallel and/or not level, the
method of correction will depend on the amount the plates are off and the amount of excess
material available to machine.
The easiest method of repair is to install a boring bar and machine the surfaces level
and parallel, but this can only be done if there is sufficient material. If this is done,
the top and bottom surfaces of the wicket gates will have to be built up to maintain
the design clearances between the gates and the plates. If there is not sufficient
material for machining the plates true and if the unit is designed for replaceable
plates, new plates will have to be installed. Building up the replaceable plates by
welding is not recommended as their relatively thin cross section can allow a great
deal of distortion from welding.
Removing the old plates normally requires locating the retaining bolts, usually twist-
off bolts that have been welded in place, and drilling them out. The new facing
plates should have sufficient thickness to allow for machining to compensate for any
unlevelness in the plates. The retaining boltholes can be drilled and counterbored
according to the manufacturer's drawing, but if a drawing is not available or if there
is any doubt as to