Another type of thrust bearing occasionally found in older units uses a plate rather than separate
bearing shoes. The plate is usually babbitt lined and has radial oil grooves machined in the plate
to give an appearance similar to segmented shoes. The plate may be attached directly to the
baseplate with bevels machined into the plate to help form the oil wedge. The plate also may be
made fairly flexible and set on a bed of springs. In this case, the plate flexes slightly to help
create the oil wedge.
2.2 Thrust Block
The rotating components of a thrust bearing are the thrust block and runner. In most cases the
thrust block and thrust runner are separate parts. The thrust block is usually a shrink fit onto the
shaft and the runner is bolted or doweled to the block. On umbrella units, the thrust block is
usually an integral part of the shaft, while the thrust runner is split into two pieces. The bottom
surface of the runner is highly polished to provide a mating surface for the bearing shoes. In
some instances, the outer diameter of the thrust runner is also polished to provide a bearing
surface for a guide bearing. The purpose of the separate runner is to provide a replaceable
component in the event it is damaged when a bearing fails.
There are a number of thrust block designs, but the most common is shown in figure 7. The
block is keyed to the shaft with an axial key and held onto the shaft with a split radial key. A
solid keeper is usually placed over the radial keys to hold them in place. When removing this
type of thrust block, the unit jacks are used to raise the generator rotor high enough to remove the
weight from the thrust block. Then, depending on the design of the jacks, the jacks are locked in
position, or blocks are installed to prevent the rotor from drifting down. The thrust block is then
heated quickly using large propane torches or large "rosebud" type oxyacetylene torches. When
the block is expanded sufficiently for removal, it will drop slightly, allowing the radial keys to be
removed. The block can then be lifted off of the shaft. To install the thrust block, it is heated to
a predetermined temperature and lowered over the shaft, again with the unit on the jacks. The
block is set on the thrust shoes, the rigging removed, and the radial keys and keeper installed.
With the block still hot, the jacks are released to allow the full weight of the unit to set the block
in place against the keys.
Another type of thrust block found on Reclamation units is shown in figure 8. Like the
previously described thrust block, an axial key is used between the block and the shaft, but with
this type, the block is held to the shaft using a series of radial clamping keys. The keys clamp the
block to a shoulder on the shaft. To remove this type of block, the unit is lifted and blocked on
the jacks, the clamping keys unbolted, and rigging to lift the block is attached. Before heating, a
slight amount of tension is placed on the rigging so that the block will pop up slightly when it is
loose. A crane scale should be used to prevent overloading the rigging. To install the block, it is
heated to a predetermined temperature and lowered onto the shaft until it sets on the ledge on the
shaft. The unit must be on jacks and high enough to allow the thrust block to reach the ledge.
The keys are then installed and the bolts torqued according to the manufacturers instructions.