Bearing and stub shaft assembly

A bearing and stub shaft assembly for a belt conveyor or the like provides a non-rotatable connection between the stub shaft and the inner race of a bearing supporting one end of a cylindrical roller. An inner surface of a central cup in the inner race and the deformed elliptical outer surface of a hollow end of the stub shaft interfit to give a simple, non-rotational connection. At the same time, a cylindrical coil spring captured within the end of the stub shaft as it is deformed is compressed within the central cup to provide a preload to the bearing.

This invention relates to bearings in general and specifically to an 
improved bearing and stub shaft assembly for a belt conveyor or the like. 
BACKGROUND OF THE INVENTION 
Belt conveyors are in common use in various industrial, mining and 
agricultural operations. They generally consist of a belt supported all 
along its length by a series of conveyor idlers. Each conveyor idler 
consists of a frame on which is mounted one or more freely rotatable 
cylindrical rollers on which the belt runs. Generally, two or more stub 
shafts are fixed to the frame. Each end of each cylindrical roller is 
supported on a stub shaft by a bearing having rolling bearing elements, 
generally bearing balls. The bearing balls are in turn held between an 
outer race fixed to the end of the roller and an inner race connected to 
the stub shaft. It is necessary that the connection between the inner race 
and stub shaft be non-rotational. Often, this connection is provided by an 
inner race having a splined bore and a solid stub shaft with grooves cut 
into the end thereof. The grooves and splines interfit with a small amount 
of radial and axial play, and give a non-rotatational connection, but 
require expensive machining. 
The belt may be subjected to heavy, varying loads and varying speeds, as 
will the bearing elements. It would be desirable, therefore, to provide a 
preload to the bearing to help assure that the load is shared equally 
among all the bearing elements. A conveyor disclosed in the U.S. Pat. No. 
1,362,910 to Zoeller et al shows a bearing assembly with a compression 
spring loaded against the outer race of a bearing. However, the spring is 
primarily designed to compensate for wear on the races and to create a 
braking effect on the roller when the load is removed. This structure is 
also somewhat complex, requiring an axially slidable outer race and a 
retaining ring. 
SUMMARY OF THE INVENTION 
The present invention provides an improved bearing and stub shaft assembly 
for a belt conveyor that provides both a non-rotational connection between 
the inner race and the stub shaft and a preload means for the rolling 
bearing elements. 
A belt conveyor includes at least one belt supporting cylindrical roller 
with at least one end of the roller supported on a stub shaft fixed to a 
frame. The end of the roller is supported on the stub shaft by a bearing 
including a complement of bearing balls held between an outer race fixed 
to the end of the roller and an inner race connected to the stub shaft. 
The bearing and stub shaft assembly of the invention provides both a 
non-rotational connection between the inner race and stub shaft as well as 
a preload means for the bearing balls. A central cup is formed in the 
inner race and has a generally elliptical inner surface. The stub shaft 
has a hollow cylindrical end with a wall thickness thin enough to allow it 
to be deformed. Deformation of the hollow end of the stub shaft gives it 
an elliptical outer surface that is generally complementary to the 
elliptical inner surface of the central cup in the inner race. These 
complementary elliptical inner and outer surfaces allow the inner race to 
be connected to the stub shaft by inserting the deformed stub shaft end 
within the central cup. The complementary surfaces interfit with a 
clearance sufficiently small that rotation therebetween is prevented. 
Thus, a non-rotational connection between the inner race and stub shaft is 
achieved with a simple and easily produced structure. 
In addition, a cylindrical coil spring sized to fit closely within the 
hollow end of the stub shaft is inserted therewithin before deformation 
with an end of the spring projecting out. When the hollow end of the stub 
shaft is deformed to create the elliptical outer surface described, the 
coil spring is gripped within the deformed end of the stub shaft. 
Therefore, when the end of the stub shaft is inserted within the central 
cup of the inner race as described, the coil spring is simultaneously 
compressed within the central cup. The force of the compressed spring on 
the central cup and inner race serves to preload the bearing balls to 
evenly distribute the load thereon. 
Other benefits may be easily achieved by modifying the structure. The stub 
shaft may be fixed to the frame so that the major axis of the elliptical 
outer surface of the deformed end of the stub shaft is substantially 
horizontal. When the belt carries a load, which is in turn transmitted to 
the cylindrical roller and to the inner race, substantially the entire 
respective upper halves of the interfitting surfaces will be engaged, 
giving the maximum load supporting contact. In addition, the clearance 
between the interfitting surfaces may be made sufficiently large to allow 
a certain amount of relative tilting between the axis of the stub shaft 
and the axis of the central cup of the inner race, while still preventing 
relative rotation. Thus, the stub shaft and inner race can self-align to 
an extent to compensate for misalignment in other parts of the conveyor 
structure. 
It is, therefore, an object of the invention to provide an improved bearing 
and stub shaft assembly for a belt conveyor with a cylindrical roller 
supported by a rolling element bearing with an inner bearing race 
connected to the stub shaft by interfitting an elliptical inner surface of 
a central cup in the inner race with an elliptical outer surface of a 
deformed hollow end of the stub shaft with sufficiently small clearance to 
prevent rotation therebetween, while a cylindrical coil spring received in 
the cylindrical hollow end of the stub shaft before deformation is gripped 
therewithin by the deformation and compressed within the central cup of 
the inner race when the deformed stub shaft end is inserted therewithin to 
also provide a preload to the bearing elements. 
It is a further object of the invention to provide an improved bearing and 
stub shaft assembly of the type described in which the major axis of the 
elliptical outer surface of the deformed stub shaft end is oriented 
substantially horizontally to provide a maximum load supporting contact 
between the interfitting elliptical surfaces of the inner race central cup 
and deformed stub shaft end when the belt of the conveyor carries a load. 
It is yet another object of the invention to provide an improved bearing 
and stub shaft assembly of the type described in which the clearance 
between the interfitting elliptical surfaces of the central cup of the 
inner race and the deformed stub shaft end is also made sufficiently large 
to allow self-aligning tilting between the axis of the stub shaft end and 
the central cup of the inner race.

Referring first to FIG. 8, a belt conveyor generally includes a series of 
conveyor idlers 10, which in turn include a cylindrical roller 12 
rotatably mounted to a fixed frame, one member of which is designated at 
14. Cylindrical roller 12, one end of which is shown, is mounted to frame 
member 14 by the bearing and stub shaft assembly of the invention, 
designated generally at 16, and described in further detail below. 
Cylindrical roller 12 may rest beneath and support a loaded conveyor belt, 
not shown, or an unloaded belt may run beneath roller 12 on the return 
portion of the belt's path of travel. The load seen by cylindrical roller 
12, when the belt is loaded, and in turn by the bearing and stub shaft 
assembly 16, may be quite heavy, and may also vary considerably, as may 
the belt speed. 
Still referring to FIG. 8, the end of roller 12 shown is supported on a 
stub shaft designated generally at 18 by a rolling element bearing 
designated generally at 20. Stub shaft 18 is fixed to the frame member 14 
by any suitable means, not shown. Bearing 20 includes outer race 22, an 
inner race designated generally at 24 and a complement of rolling bearing 
elements held therebetween, in this case bearing balls 26. Bearing balls 
26 are circumferentially spaced by a conventional separator 28 with a 
suitable lubricant, not shown, retained by a conventional seal 30. As 
shown, outer race 22 is an integral stamping welded or otherwise attached 
within the end of cylindrical roller 12, although other types of bearing 
races may be used within the scope of the invention. 
Referring next to FIGS. 1 and 2, inner race 24 includes a central cup 
formed therein, designated generally at 32, which has a base 34 and a 
generally elliptical inner surface 36, best seen in FIG. 2. Central cup 32 
opens outwardly across a chamfer 38. Since outer race 22 rotates with 
cylindrical roller 12, it is necessary to establish a non-rotational 
connection between inner race 24 and stub shaft 18. In addition, because 
of the type of forces and loading experienced by bearing 20, it is 
desirable, if possible, to apply a preload to bearing balls 26. These and 
other objects are achieved by the remaining structure of bearing and stub 
shaft assembly 16, described below. 
Referring next to FIG. 3, stub shaft 18 includes at least one cylindrical 
hollow end designated generally at 40. As disclosed, stub shaft 18 is 
entirely hollow, although this would not be strictly necessary. The wall 
thickness of cylindrical hollow end 40 is thin enough that it may be 
deformed, as described further below. A cylindrical coil spring, 
designated generally at 42, is sized to fit within undeformed hollow stub 
shaft end 40 with an end 44 thereof projecting out, as seen in FIG. 4. 
This fit is substantially close, as may be best seen in Figure 5. 
Referring next to FIG. 6, hollow stub shaft end 40 is deformed by any 
suitable means to give a generally elliptical outer surface 46, the shape 
of which may be best seen in FIG. 7. The entire purpose for this 
deformation will be described below, but it will be understood that that 
part of coil spring 42 within hollow stub shaft end 40 will be likewise 
elliptically deformed and gripped by this deformation. Thus, spring end 44 
will be rigidly axially held relative to stub shaft 18. 
Referring next to FIGS. 8 and 9, the connection of inner race 24 to stub 
shaft 18 may be seen. Spring end 44 and deformed hollow stub shaft end 40 
are moved axially past chamfer 38 and into central cup 32, compressing 
spring end 44 against cup base 34 a desired amount. Stub shaft 18 is then 
fixed to frame member 14. The compression of spring end 44 provides a 
preload to bearing balls 26, thereby distributing any load they experience 
more evenly. This is advantageous regardless of the load on the belt, 
because of wear equalization on balls 26. Furthermore, this preload helps 
to cushion any axial play or run out of roller 12 relative to stub shaft 
18 that might result from misalignment of outer race 22. 
Referring next to FIG. 9, the elliptical outer surface 46 of deformed 
hollow stub shaft end 40 is sized and shaped to be substantially 
complementary to the elliptical inner surface 36 of cup 32 so that the two 
surfaces interfit with a clearance C. Stated specifically, the ellipse of 
the outer surface 46 has essentially the same major axis, but is of a 
smaller degree, than the ellipse of the inner surface 36. In the 
embodiment disclosed, this clearance C is on the order of 30 to 40 
thousands of an inch, and is exaggerated in FIG. 9 for purposes of 
illustration. The smallness of clearance C and the complementary sizing of 
the inner and outer surfaces 36 and 46 assures that one will not turn 
within the other, and inner race 24 will therefore be non-rotatably 
connected to stub shaft 18. 
While the inner race 24--stub shaft 18 connection will be non-rotatable for 
any orientation of stub shaft 18, fixing stub shaft 18 to frame member 14 
so as to orient the major axis of elliptical outer surface 46 
substantially horizontally, as shown, gives an additional advantage. In 
the case where cylindrical roller 12 is supporting a loaded belt, which 
load is transmitted through roller 12 to inner race 24, elliptical outer 
surface 46 will interfit within elliptical inner surface 36, under the 
influence of the load carrying belt, with substantially the entire 
respective upper halves of both surfaces engaged. This gives the maximum 
load supporting contact between the two surfaces. The clearance C appears 
between the respective lower halves of the surfaces 46 and 36, as seen in 
FIG. 9. 
Furthermore, the clearance C may also be made sufficiently large, 
regardless of the orientation, to allow an angular offset or tilting 
between the axes of central cup 32 and hollow stub shaft end 40. This 
self-alignment between stub shaft 18 and inner race 24 can compensate for 
misalignments in other parts of the structure, such as outer race 22. 
Clearly, clearance C could be made larger without losing the 
non-rotational connection between stub shaft 18 and inner race 24. 
However, as a practical matter, only a very few degrees of self-aligning 
motion is necessary, and the clearance C should be kept as small as 
practicable. 
Therefore, it will be seen that the structure of the invention gives a 
benefit of a non-rotatable connection and a preload with simple and easily 
assembled structure, as well as additional benefits of good load 
supporting contact and a degree of self-alignment. It will be understood 
that the invention is capable of being embodied in structures other than 
those disclosed, and is not intended to be so limited.