Tapered roller bearing capable of sustained operation without lubricant replenishment

A tapered roller bearing has a porous rib ring against which the large ends of its wrought steel tapered rollers bear so that the ring prevents the rollers from being expelled. The rib ring is formed from porous powdered steel that has been compacted to a density of about 70% to 85% of theoretical and then sintered and machined. Thereafter, the machined rib ring is etched to expose the pores at the surface against which the large ends of the rollers bear. Finally, the rib ring is impregnated with oil. Should the bearing lose its normal supply of lubrication, the critical region of contact between the abutment face on the rib ring and the large ends of the rollers will nevertheless be adequately lubricated for a reasonable time by lubricant which escapes from the pores of the rib ring. The cage of the bearing may be piloted by the rib ring and by a ring-like cup insert that is formed in the same manner as the rib ring.

BACKGROUND OF THE INVENTION 
This invention relates in general to antifriction bearings and, more 
particularly, to a tapered roller bearing that is capable of sustained 
operation in the absence of its normal supply of lubrication. 
Tapered roller bearings offer many advantages which other types or 
combinations of bearings do not. For example, a pair of tapered roller 
bearings will carry extremely heavy radial and thrust loading, and the 
individual bearings may be adjusted against one another to control radial 
and axial play. Due to their large load carrying capacity in both radial 
and axial directions, it is often possible to replace a combination of 
three other bearings with only two tapered roller bearings and still 
achieve the desired bearing life. 
Due to the tapered configuration of the rollers radial loads on the rollers 
create an axial force component which tends to expel the rollers from the 
annular space between the two races, that is, from between the cup and 
cone. This expulsion force is resisted by means of a thrust rib on one of 
the races, usually the cone. Thus, as the cup and cone rotate relative to 
each other the large diameter end faces of the tapered rollers experience 
rolling and sliding contact against the thrust rib. Unless a film of 
lubricant is maintained between the roller end faces and the thrust rib, 
the bearing will overheat and sustain damage. 
In some machinery it is important to have safety features which will enable 
the machinery to operate even though its lubricating system is disabled. 
This is particularly true of helicopters. 
SUMMARY OF THE INVENTION 
One of the principle objects of the present invention is to provide a 
tapered roller bearing that will remain operable for a reasonable time 
after the loss of normal lubrication. Another object is to provide a 
bearing of the type stated that may be operated at high angular velocities 
while carrying heavy loads. A further object is to provide a bearing of 
the type stated that affords adequate time to recognize the disruption of 
lubrication to it and also adequate time to shut down machinery into which 
it is incorporated so that the machinery is not damaged. An additional 
object is to provide a bearing of the type stated that is simple in 
construction and relatively easy to manufacture. These and other objects 
and advantages will become apparent hereinafter. 
The present invention is embodied in a tapered roller bearing having a rib 
ring along which the rollers run, with the ring having pores that are 
exposed at the surface against which the large ends of the rollers bear, 
so that the rib ring will absorb a lubricant and release it to lubricate 
the roller ends when the bearing loses its normal supply of lubrication. 
The invention also consists in the parts and in the arrangements and 
combinations of parts hereinafter described and claimed.

DETAILED DESCRIPTION 
Referring now to the drawing, a single row tapered roller bearing A has an 
axis X of rotation and is designed to carry both radial loads and thrust 
loads and to do this for a reasonably long time after the normal supply of 
lubrication to the bearing A is terminated. The bearing A includes several 
basic components, namely, a cone 2, a cup 4 that surrounds the cone 2, a 
complement of tapered rollers 6 arranged in a single row between the cone 
2 and cup 4, a cage 8 for maintaining the correct spacing between the 
rollers 6, and a rib ring 10 that serves as an abutment for preventing the 
rollers 6 from being expelled from the space between the cone 2 and cup 4. 
Preferably the cone 2 and cup 4 are formed from a high quality wrought 
bearing steel of the type commonly used in bearings. The cone 2 has a 
tapered raceway 12 which at its small end runs out to a cone front face 14 
and at its large end runs out to a cone back face 16. Both of the cone end 
faces 14 and 16 are perpendicular to the axis X. The cup 4, likewise, has 
a tapered raceway 18 which at its large end runs out to a cup front face 
20. Its small end is located adjacent to a rabbet 21 which opens out of 
the end of the cup 4. The rabbet 21 contains an insert 22 having two 
exposed surfaces, one being a cylindrical surface 23 that is presented 
inwardly toward the axis X of rotation and merges with the large end of 
the tapered raceway 18. The other exposed surface is along and indeed 
forms part of the cup back face 24. Again both end faces 20 and 24 are 
squared off with respect to the axis X. Thrust loading and reaction loads 
derived from radial loads are transmitted through the cone back face 16 
and cup back face 24. The raceways 12 and 18 are on apex, meaning that if 
each is extended to an apex, those apexes will be located at a common 
point along the axis X of rotation. 
The tapered rollers 6 occupy the space between the cone 2 and cup 4 and 
along their tapered side faces contact the two raceways 12 and 18, there 
being line contact between each roller 6 and the raceways 12 and 18. Since 
the raceways are on apex, rolling contact will occur between the roller 
bodies and the raceways 12 and 18 when the cup 4 rotates relative to the 
cone 2 or vice-versa. The rollers 6 are axially positioned by the rib ring 
10 against which the large diameter ends of the rollers 6 bear. In this 
regard, the large diameter ends of the rollers 6 are somewhat spherical, 
for that configuration maintains the rollers 6 in the proper orientation 
between the raceways 12 and 18. Like the cone 2 and cup 4, the rollers 6 
are preferably formed from wrought steel of a high quality bearing grade. 
The cage 8 tapers to conform generally with the angular disposition of the 
rollers 6 and has pockets in which the rollers 6 are received. At each of 
its ends, the cage 8 turns outwardly to provide end rings 36. The large 
diameter end ring 36 is located in close proximity to the inside face of 
the rib ring 10 while the small diameter end ring 36 is located in close 
proximity to the cylindrical surface 23 on the insert 22 of the cup 4. 
Indeed, the rib ring 10 and insert 22 serve to position the cage 8 in the 
radial direction so that the cage 8 is in effect piloted. The cage 8 is 
preferably made of steel. 
The rib ring 10 fits against the front face 20 of the cup 4 and projects 
inwardly beyond the large end of the cup raceway 18 so as to prevent the 
rollers 6 from moving axially out of the annular space between the cone 2 
and cup 4. In the actual operation of the bearing A the cup 4 and rib ring 
10 are clamped together so that the force exerted on the rib ring 10 by 
the rollers 6 does not separate the ring 10 from the cup 4. The rib ring 
10 is of unitary construction and includes a cylindrical outer surface 26 
which is the same diameter as the outer surface of the cup 4. It also has 
an end face 28 which is squared off with respect to the axis X, and it is 
along this face that the ring 10 abuts against the front face 20 of the 
cup 4. The end face 28 merges into a roller abutment face 30 which is 
generally perpendicular to the cup raceway 18 and hence oblique to the 
axis X of rotation. The abutment face 30 extends inwardly to a cylindrical 
inner face 32 which serves as a guide for the large end of the cage 8. 
Finally the ring 10 has a front face 34 which is parallel to the end face 
28 and extends between the outer and inner cylindrical surfaces 26 and 32. 
Unlike the cone 2, the cup 4, and the tapered rollers 6, the rib ring 10 is 
formed from a porous alloy steel that has been impregnated with a liquid 
lubricant. Moreover, the pores of the steel are exposed at least along the 
roller abutment face 30, and the cylindrical inner face 32 as well. The 
pores hold the liquid lubricant. The insert 22 is formed from the same 
porous alloy steel that has likewise been impregnated with a liquid 
lubricant, and its pores are exposed at least along th cylindrical surface 
23. 
During operation of the bearing A the cone 2 rotates within the cup 4 or 
the cup 4 revolves around the cone 2. In either case, the tapered rollers 
6 roll along the two raceways 12 and 18, there being rolling contact, that 
is no significant sliding, between the tapered bodies of the rollers 6 and 
the raceways 12 and 18. The large diameter end faces of the rollers 6 bear 
against the abutment face 30 of the rib ring 10, and thus the ring 10 
positions the rollers 6 in the axial direction. In this regard, any radial 
load that is applied to the bearing A will be transmitted through the 
rollers 6, and by reason of the tapered geometry, this load is translated 
into a radial component and an axial component at the rollers 6, with the 
axial component being directed toward the large ends of the raceways 12 
and 18. Indeed, the axial component constitutes an expulsion force which 
would drive the rollers 6 out of the bearing A were it not for the 
obstruction caused by the abutment face 30 of the rib ring 10. In contrast 
to the rolling contact between the rollers 6 and the raceways 12 and 18, 
the contact between the large end faces of the rollers 6 and the abutment 
face 30 is combined sliding and rolling. Since the cage 8 is piloted by 
the rib ring 10 and the cup insert 22, sliding contact exists between the 
end rings 36 on the cage 8 and the cylindrical surface 23 of the cup 
insert 22 and the cylindrical face 32 of the rib ring 10. 
Normally, a liquid lubricant is introduced into the bearing A at the small 
ends of the raceways 12 and 18 and is pumped through the bearing A by the 
natural pumping action of the rollers 6. This lubricant forms a thin, low 
friction, film along the surfaces at which rolling and sliding contact 
exist in the bearing A--namely along the raceways 12 and 18, along the 
abutment face 30, and along the cylindrical surfaces 23 and 32. 
Should the bearing A lose its normal supply of lubrication, the lubricant 
retained within the pores of the rib ring 10 will emerge from the pores of 
the rib ring 10 at the abutment face 30 and for a reasonable time will 
supply sufficient lubrication to prevent excessive friction from 
developing between the large ends of the rollers 6 and the abutment face 
30. Indeed, even at high speeds and under heavy radial and thrust loads 
the bearing A will operate for at least 30 minutes without failure. This 
provides adequate time to recognize the loss of the normal supply of 
lubricant and to shut down the machinery containing the bearing A without 
damaging that machinery. 
Not only does the rib ring 10 supply lubrication to the large ends of the 
rcllers 6, but it also supplies lubrication to the large and small end 
rings 36 of the cage 8. This prevents excessive friction from developing 
between the large end ring 36 and the cylindrical inner face 32 of the rib 
ring 10 and from likewise developing between the small end ring 36 and 
cylindrical surface 23 of the cup insert 22. Having adequate lubrication 
in these regions is also important, for it is along the surface 23 and 
face 32 that the cage 8 is piloted. Without adequate lubrication, the cage 
8 could weld to the rib ring 10 and insert 22. 
Perhaps the best procedure for manufacturing the rib ring 10 is to compress 
a suitable powdered metal, such as a powdered high strength, high 
temperature, bearing steel, into a ring form that roughly approximates the 
rib ring 10, but is slightly larger in cross-section. The compression 
should be sufficient to compact the powder to a density of between 70% and 
85% of the maximum possible or theoretical density, which would be the 
density of comparable wrought steel. The metal powder contains a lubricant 
so that the powder flows with relative ease within the die in which the 
compaction takes place. This results in a ring form of uniform density. 
Once the ring form is acquired, it is heated to between 1350.degree. F. 
and 1500.degree. F. to eliminate the lubricant that is within the 
compacted metal powder. 
Next the ring form is sintered by heating it still further within a vacuum 
or in a reducing atmosphere to between 2000.degree. F. and 2200.degree. F. 
for at least 20 minutes. It is then cooled to about 1000.degree. F. in a 
vacuum and then to room temperature in nitrogen gas. 
Thereafter, the sintered ring form is heat treated by heating and 
quenching, and the temperature to which it is heated and the composition 
of the quenching medium are to a large measure determined by the metal of 
the ring form. 
Either before or after the heat treatment, and preferably after, the 
sintered ring form is machined to bring it to the proper configuration and 
dimensions. This machining may be along all of the faces 26, 28, 30, 32, 
and 34, and most certainly should be along the abutment face 30 against 
which the tapered rollers 6 bear, along the end face 28 at which the rib 
ring 10 is fitted against the cup 4, and along the cylindrical inner face 
32 which pilots the cage 8. The machining may involve both turning and 
grinding, and certainly grinding. Both of these machine operations tend to 
obliterate the pores at the machined surface. In other words, the turning 
and grinding tend to smear over and cover the pores, producing a thin 
metal surface layer which is commonly referred to as the "Beilby layer". 
The Beilby layer inhibits the absorbtion of a lubricant by the rib ring 10, 
and much worse prevents the lubricant from being released at the critical 
abutment face 30 once it has been absorbed. To overcome this problem, the 
Beilby layer is removed by immersing the machined ring form in a suitable 
etchant. In the alternative, the Beilby layer may be removed by 
mechanically etching the ring form along the surfaces 30 and 32, and this 
may be achieved by subjecting the ring form to ionized gas molecules. 
Once the ring form is removed from the etchant, the etchant remaining on it 
is neutralized. After cleaning the ring form, it is impregnated with 
lubricant by immersing it within a suitable liquid lubricant which has 
been warmed to about 300.degree. F. to reduce its viscosity. This produces 
the rib ring 10 for the bearing A. 
The insert 22 is formed in essentially the same manner, it being etched at 
least along its inwardly presented cylindrical surface 23. It is inserted 
into the rabbet 21 of the cup 4 and welded in place. 
Suitable material for the rib ring 10 and insert 22 are powders of high 
quality steel such as M2, CBS1000M and 46100. CBS1000M is the trademark of 
The Timken Company, Canton, Ohio. Irrespective of the material from which 
the rib ring 10 is formed, that material should be porous, and the pores 
should hold a liquid lubricant and be exposed at a surface where the 
material is free to bear against another machined surface, such as a 
ground surface on wrought bearing steel. Moreover, the material should be 
capable of bearing against the wrought bearing steel with a force that 
translates into a contact stress of at least 40,000 lb/in.sup.2. When the 
impregnated material along the surface at which its pores are exposed 
bears against a ground surface on wrought bearing steel, the coefficient 
of friction at the contacting surfaces should not exceed about 0.10 in the 
absence of all lubrication other than the lubricant derived from the pores 
of the impregnated material. Finally, the impregnated material when 
against a ground surface on wrought bearing steel should be capable of 
enduring for at least 30 minutes a pressure-velocity multiple of 
22.times.10.sup.6, where, pressure is measured in lb/in.sup.2 and velocity 
in ft/min. The pressure is of course the contact stress, while the 
velocity is the relative lineal velocity between the impregnated material 
and the wrought bearing steel at the surfaces along which they are in 
contact. Where these surfaces are circular, the lineal velocity is 
measured along the outer diameter, that is at the location of the maximum 
velocity, although in the case of a relatively narrow rib ring or thrust 
rib for a tapered roller bearing, it is acceptable to measure the lineal 
velocity at the rib pitch circle, which is generally speaking the median 
diameter of the face against which the large end faces of the rollers 
bear. In other words, the impregnated material and the wrought bearing 
steel, when operated under conditions at which pressure multiplied by the 
velocity is 22.times.10.sup.6, should continue to operate for at least 30 
minutes without any significant damage to either the impregnated material 
or the wrought bearing steel. 
The tool steel alloy known as M2 has essentially the following composition 
by weight. 
______________________________________ 
C .85% Mo 5.0% 
Mn .30% W 6.3% 
Si .30% V 1.85% 
Cr 4.15% Fe balance 
______________________________________ 
To convert M2 powder into a rib ring 10 or insert 22, the powder is first 
blended with a lubricant, such as the one sold under the trademark 
Acrawax. The lubricant should amount to about 0.5% to about 1.5% by weight 
of the powder. The blend of M2 powder and lubricant is then compacted in a 
die to provide a ring form having the general shape of the desired rib 
ring or insert. The density of this ring form should be between about 70% 
and 85% of theoretical density, and should preferably be about 75% of 
theoretical. Next the compacted ring form is heated to 1350.degree. F. to 
1500.degree. F. in a vacuum and maintained at that temperature for 30 to 
60 minutes to eliminate the lubricant used in the compacting step. 
Thereafter the ring form is heated to at least 2000.degree. F. in a vacuum 
and maintained at that temperature for 15 to 45 minutes to sinter the ring 
form. At the end of this time it is cooled to about 900.degree. F. in a 
vacuum and then to room temperature in nitrogen gas. 
Next, the sintered ring form is heat treated by preheating it to about 
1450.degree. F. in a vacuum and maintaining it at that temperature for 
about 30 minutes. Then its temperature is raised to about 2175.degree. F. 
and held there, while still in a vacuum, for about 5 minutes. It is then 
quenched in nitrogen gas maintained at room temperature. 
Following the quench, the ring form is tempered by heating it within a 
vacuum to about 1000.degree. F. and holding it at that temperature for 
about 2 hours. This procedure is repeated so that the ring form is 
tempered twice. After the tempering the particle hardness of the ring form 
exceeds Rc 60, and the microstructure of the ring form consists of 
tempered martensite with M.sub.6 C carbides, but no retained austenite. 
Its porosity remains about 25%. 
Next the ring form is machined by grinding it wet in soluble oil coolant to 
provide finish grinds on all of its surfaces. Then it is ultrasonically 
cleaned in a solvent. Thereafter the machined ring form is etched by 
immersing it in an acid etch for several minutes. The etch removes the 
Beilby layer and exposes the pores of the sintered alloy. After the etch, 
the ring form is immersed in a basic solution to neutralize the etchant, 
and this solution should be agitated at an ultrasonic frequency. Then the 
ring form is cleaned by immersing in a solvent which is likewise agitated 
ultrasonically. Thereafter the ring form is heated to remove the cleaning 
solution. 
Finally, the ring form is impregnated with a lubricant, this being achieved 
by immersing it in a low viscosity lubricant for 2 hours, the lubricant 
being maintained at about 300.degree. F. This completes the rib ring 10 or 
insert 22. 
A lubricant impregnated block manufactured from M2 steel in accordance with 
the foregoing procedure such that it had a ground and etched surface was 
subjected to a dynamic load applied through a ground surface on another 
block of hardened wrought steel, the load being dynamic in the sense that 
sliding contact existed between the ground surfaces of the lubricant 
impregnated block and the wrought steel block. Indeed, the relative 
velocity between the two blocks amounted to 550 ft/min, while the initial 
Hertzian contact stress was 40,000 lbs/in.sup.2. Without any lubrication, 
other than that derived from the pores of the lubricant impregnated block, 
the coefficient of friction between the two blocks was 0.05. The dynamic 
load, which existed at a pressure-velocity multiple of 22.times.10.sup.6, 
was sustained for in excess of 30 minutes. This indicates that the bearing 
A operating under a similar dynamic load at the abutment face 30 of its 
rib ring 10 would remain operable for at least 30 minutes after 
interruption of its normal supply of lubricant. 
The steel known as 46100 has essentially the following composition by 
weight: 
______________________________________ 
C 1.00% Ni 2.0% 
Mn .25% Mo 0.5% 
Fe balance 
______________________________________ 
To manufacture the rib ring 10 or insert 22 from 46100 metal powder it is 
first blended with a lubricant, such as Acrawax lubricant, to lubricate 
the powder. Next it is compacted to a density of about 75% theoretical to 
produce a ring form. Thereafter the ring form is heated to 1350.degree. to 
1500.degree. F. for 30 to 60 minutes in a vacuum to remove the lubricant. 
Then, the ring form is sintered in a vacuum at 2000.degree. F. for 15 to 
45 minutes. It is next cooled to about 900.degree. F. in a vacuum and 
thereafter to room temperature in nitrogen gas. 
The sintered ring form is thereupon heat treated by elevating its 
temperature to about 1500.degree. F. for 15 to 45 minutes in an 
endothermic atmosphere having 0.25% CO.sub.2 by volume and then quenching 
it in oil. Next it is tempered by heating it to about 360.degree. F. for 
about one hour and allowing it to cool to ambient temperature. At this 
point its particle hardness exceeds Rc 60 and it contains essentially 80% 
tempered martensite and 20% of austenite, and it has about 25% porosity, 
or in other words is 75% of theoretical density. 
Next, the 46100 ring form is machined in the same manner as the M2 ring 
form and is etched for several minutes to remove the Beilby layer. The 
ring form is thereafter neutralized, cleaned, heated, and impregnated with 
lubricant in the manner previously described, whereupon it becomes the rib 
ring 10 or insert 22. 
An impregnated block formed from 46100 steel in accordance with the 
foregoing procedure was subjected to the same dynamic test as the M2 
block. It sustained an initial Hertzian contact stress of 40,000 
lbs/in.sup.2 at 550 ft/min applied by a wrought steel block--or in other 
words a pressure-velocity multiple of 22.times.10.sup.6 --and the 
impregnated block endured that condition for over 30 minutes without any 
lubrication other than that derived from the pores of the block. The 
coefficient of friction between the two blocks amounted to 0.10. 
The steel known as CBS1000M forms the subject of U.S. Pat. No. 3,954,517 
and in its preferred composition has essentially the following composition 
by weight: 
______________________________________ 
C .30%-.85% Cr 1.05% 
Mn .50% Ni 3.0% 
Si .50% Mo 4.5% 
V .35% 
Fe balance 
______________________________________ 
It is converted into a ring form and thereafter into a rib ring 10 or 
insert 22 using substantially the same procedure as 46100 powdered metal 
is converted into a rib ring 10 or insert 22. 
A block of CBS1000M steel formed in accordance with the procedure for 
making the 46100 rib ring 10 and impregnated with oil was run against a 
block of wrought bearing steel and withstood an initial Hertzian stress of 
40,000 lbs/in.sup.2 at 550 ft/min, that is a pressure-velocity multiple of 
22.times.10.sup.6, for over 30 minutes without any additional lubrication. 
The coefficient of friction between the two blocks was 0.07. 
In lieu of positioning a porous rib ring 10 at the front face of the cup 4, 
it may be placed at the back face of the cone 2 or it may take the form of 
an insert fitted to the cone. In either case it will have a slightly 
different configuration and will project outwardly from the large end of 
the cone raceway 12. Also, the insert 22, instead of being confined to a 
rabbet 21, may extend across the entire back face of the cup 4 much like 
the rib ring 10 at the opposite end of the cup 4. In that case the cup 4 
would not contain a rabbet 21. Similarly, a modified insert may be 
installed in the cone at the small end of the cone raceway or it may take 
the form of a separate ring at the small end of the cone, that is against 
the cone front face. 
M2, 46100 and CBS1000M steels are ideally suited for use in manufacturing 
the porous rib ring 10, for each of these steels when powdered and 
converted into a compacted and sintered rib ring 10 that is impregnated 
with oil will sustain a contact stress of 40,000 lbs/in.sup.2 and a 
pressure-velocity multiple of 22.times.10.sup.6 for at least 30 minutes in 
the absence of any additional lubrication when run against a smooth 
surface on wrought steel of bearing quality. When calculating this 
multiple, pressure is measured in lbs/in.sup.2 and velocity in ft/min. 
Moreover, the coefficient of friction between the impregnated steel and 
the wrought bearing steel with no lubrication present other than that 
derived from the pores of the impregnated steel does not exceed 0.10. 
Certain other porous steels will suffice as well. These steels, however, 
should have properties which include high hardness, good wear resistance, 
high strength and preferably high temperature resistance and must also 
withstand a contact stress of 40,000 lbs/in.sup.2 and pressure-velocity 
multiple of 22.times.10.sup.6 and produce a coefficient of friction no 
greater than 0.10. 
Instead of forming the rib ring 10 from powdered metal, the tapered rollers 
may be formed from powdered metal and the rib ring from wrought steel. In 
that case, the pores would be exposed at the large end faces of the 
rollers to release the lubricant onto the abutment face of the thrust rib. 
Other than that, essentially the same steps and materials are used to 
manufacture the powdered metal rollers as have been described in 
connection with the manufacture of the powdered metal rib ring 10. Also, 
both the rib ring and the rollers may be formed from powdered steel in 
accordance with the procedures previously described. 
This invention is intended to cover all changes and modifications of the 
example of the invention herein chosen for purposes of the disclosure 
which do not constitute departures from the spirit and scope of the 
invention.