1. Field of the Invention
The invention relates generally to the field of rotating machines, such as motors and generators. More particularly, it relates to bearing assemblies used with such machines and devices useful when removing the bearing assemblies.
2. Description of Related Art
Rolling element bearings, also known as anti-friction bearings, are widely used on many types of rotating machinery and have a limited life span. That life span can be reduced by misuse and adverse operating conditions. Bearing removal is frequently required in the field as part of the rotating machinery's maintenance.
Traditionally, bearing assemblies have been designed such that the removal of the bearing requires the removal of the entire bearing bracket that houses the bearing and that is mounted to the frame of the rotating machine (e.g., a motor or a generator). FIGS. 1 and 2 show an example of such a prior art bearing assembly.
Bearing 10 was positioned, or housed, in bearing bracket 20. Inner race 12 of bearing 10 contacted shaft 30 of the rotating machine (the body of which is not shown). Outer race 14 of bearing 10 contacted machined cavity 22 of bearing bracket 20. Rolling elements 16 (balls in this case) were positioned between, and in direct contact with, the two races. An inner cap 28 was bolted to bearing bracket 20 with bolts 25 positioned through bolt holes 27. The bearing bracket had a machined rim 24 near its outer edge that fit with very little radial clearance into the machined frame of the rotating machine. That tight fit between the frame and bearing bracket 20 is commonly known as a spigot fit, and bearing bracket 20's rim 24, which fit tightly inside of the machined frame, is known as a spigot. Mounting bolts (not shown, but see FIG. 1, which shows mounting holes 32) secured bracket 20 to the frame of the rotating machine to ensure that spigot 26 remained in contact with the frame. During normal operation, the rotor weight was transmitted through the bearings to the bearing brackets (there is typically one at each end of the machine) and through each bracket's spigot to the frame of the rotating machine, which was supported by the site foundation.
Bearing 10 has been removed from rotating machines, such as motors and generators, using jacking bolts. Jacking holes 34 were positioned in bearing bracket 20. Jacking bolts are normal bolts that were screwed into jacking holes 34, which were located evenly around the outside of the bearing bracket such that they aligned with flat, solid steel surfaces on the frame of the rotating machine. As the jacking bolts were placed in jacking holes 34 and tightened, the bottom of the bolts came into contact with the steel surface of the frame. Gradual and even tightening of all the jacking bolts caused the jacking bolts to pull bearing bracket 20 out of the frame. Bearing 10 typically stayed in place on shaft 30 because inner cap 28 was first un-bolted from bearing bracket 20. Because 10 normally stayed in place on shaft 30, bearing bracket 20 could only be removed a short distance before it had to be supported to keep it from falling onto and possibly damaging shaft 30. The weight of bearing bracket 20 (potentially over 200 pounds for a 300 horsepower (HP) rotating machine) generally required a crane or other large lifting device to be used for bearing removal on 300 HP (and larger) motors.
To summarize, the following steps have been taken during removal of the bearing shown in FIGS. 1 and 2. The end of shaft 30 has been supported using any suitable mechanism, such as a crane or jacks. The mounting bolts positioned in mounting holes 32 that held bearing bracket 20 to the frame of the rotating machine have been removed, as have bolts 25 positioned in bolt holes 27 that held inner cap 28 to bearing bracket 20. Jacking bolts have been inserted into jacking holes 34. The jacking bolts have been tightened gradually and evenly until spigot 26 of bearing bracket 20 has been completely pulled out of the frame. The supported shaft end has been lowered down until the rotor core (not shown) surrounding shaft 30 contacts the stator core (not shown) surrounding the rotor core. The shaft support has been removed. A crane has been attached to bearing bracket 20 and removed bearing bracket 20. A traditional bearing puller has been used to remove bearing 20 from around shaft 30.
An advance was made with the creation of the bearing assembly shown in FIGS. 3 and 4. Bearing assembly 40 (sometimes called a bearing cartridge) is positioned in a bearing assembly opening 42 of bearing bracket 20. Bearing 10 is seated inside of bearing assembly 40 instead of directly in bearing bracket 20, as shown in FIG. 2. As a result, the end user only had to remove bearing assembly 40—not bearing bracket 20—in order to remove bearing 10. Bearing assembly 40 is considerably lighter than bearing bracket 20 and eliminates the need for a crane.
Bearing assembly 40 includes a cylindrical insert 44, an inner cap 28, an outer cap 46, and bearing 10. Insert 44 was machined on its inside to hold bearing 10 tightly and had a spigot fit with bearing bracket 20. Insert 44 also had mounting bolt holes 48 through which bolts were placed to secure insert 44 to bearing bracket 20. Insert 44 also had insert jacking holes 49 that allowed for removal of the bearing assembly from bearing bracket 20. Insert 44, outer cap 46, and inner cap 28 each had aligned openings (designated generally at 50) that allowed them to be bolted together with bolts 52. Outer cap 46 was a disk that bolted onto insert 44 and that had a small clearance fit with shaft 30 to hold the bearing grease inside of bearing assembly 40. Inner cap 28 also was a disk that had a small clearance fit with shaft 30 for grease retention, but also had two ring-shaped projections 51 and 53, positioned to align with inner race 12 and outer race 14, respectively, of bearing 10. Those projections allowed inner cap 28 to act as a bearing puller.
During bearing removal, the jacking bolts positioned in insert jacking holes 49 pulled bearing assembly 40 out of bearing bracket 20. Because inner cap 28 was bolted insert 44, ring-shaped projections 51 and 53 contacted bearing 10's inner race 12 and outer race 14, respectively, and pulled bearing 10 off of shaft 30 during removal. This eliminated the need for the end user to use a bearing puller. Also, the lighter weight of bearing assembly 40 (versus bearing bracket 20) and the presence of bearing 10 in bearing assembly 40 reduced the risk of the bearing assembly falling sizable distances and damaging the shaft as the bearing assembly was pulled off of the end of the shaft.
To summarize, the following steps have been taken to remove bearing assembly 40. The end of shaft 30 has been supported. The mounting bolts running through mounting bolt holes 48 have been removed. Those same bolts have then been used as jacking bolts, inserted into insert jacking holes 49 and tightened gradually and evenly until bearing assembly 40 was removed from bearing assembly opening 42 of bearing bracket 40. Shaft 30 was lowered until the rotor core (not shown) surrounding the shaft contacted the stator core (not shown) surrounding the rotor core. The shaft support was removed. The loose bearing assembly 40 was removed by sliding it off of the end of the shaft.
The inventors have discovered certain shortcomings associated with the removal of bearing assembly 40 shown in FIG. 4. While removing bearing assembly 40 from bearing assembly opening 42, a large friction force is induced between bearing 10 and shaft 30 tends to move shaft 30 in the same direction as bearing 10. This shaft motion or force is transferred to, and undertaken by, the bearing or coupling at the other end of the shaft. If that bearing (i.e., at the other end) is a rolling element bearing, the friction force between that bearing and the shaft will cause the entire rotor assembly to be moved in the direction of bearing 10. Alternatively, the load will be undertaken by the rolling elements of the bearing or the inner cap located at the other end of shaft 30.