What's the Difference Between Bearings? Bearings
are used to help reduce friction.
Metal-upon-metal contact produces large amounts of friction. The friction adds to wear
and tear of the metal, producing grinding that slowly degrades the metal. Bearings
reduce friction by having the two surfaces roll over each other, reducing the amount of
friction produced. They consist of a smooth metal ball or roller that rolls against a
smooth inner and outer metal surface. The rollers or balls take the load, allowing the
device to spin.
The load acted upon a bearing is either a radial or thrust load. Depending on the
location of the bearing in the mechanism, it can see all of a radial or thrust load or a
combination of both. For example, the bearing in the wheel of your car supports a radial
and a thrust load. The weight of the car on the bearing produces a radial load while the
thrust load is produced as the car turns a corner. Here we will examine some types of
Ball bearings are most common type of bearing and can handle both radial and thrust
loads. Ball bearings are also known as deep-groove single-row or Conrad bearings. The
inner ring is typically fastened to the rotating shaft and the groove on the outer
diameter provides a circular ball raceway. The outer ring is mounted onto the bearing
housing. The ball bearings are housed in a race and when the load is applied, it is
transmitted from the outer race to the ball and from the ball to the inner race. The
raceway grooves have typical curvature radii of 51.5% to 53% of the ball diameter.
Smaller curvature raceways can cause high rolling friction due to the tight conformity
of the balls and raceways. Higher curvature raceways can shorten fatigue life from
increased stress in the smaller ball-race contract area.
1. Ball bearings, also known as Conrad bearings, are typically used in small load
The contact points between the ball and the outer race is very small due to the
spherical shape of the bearing. This also helps the ball spin very smoothly. Since the
contact point is so small, the flanged
can become overloaded at a specific point causing the ball bearing to
become deformed. This will ruin the bearing. Ball bearings are typically used in
applications where the load is relatively small.
2. The table above lists some general types of ball bearings and their typical load
Straight roller or cylindrical bearings run in cylindrical raceways and have low-
friction, high-radial load capacity, and high speed capability. Roller bearings
shaped stainless bearing
the point of contact between the bearing and the race is a line rather than a point.
Load is distributed over a larger area and allows the bearing to handle a greater load.
To minimize its tendency to skew, the roller’s length is not much greater than the
diameter of the roller.
3. Straight or cylindrical roller bearings can be found in applications like
conveyor-belt rollers, which are required to hold heavy radial loads.
Their usual design is free to float axially, and they have roller-guiding flanges on
both sides of one ring and none on the other side. This allows for the bearing to expand
due to thermal activity when used in combination with a ball miniature bearing
location at the opposite end. A thrust load can be supported in one direction if a
guiding flange is added on one of the opposing rings’ side. A second flange can be
added for two-directional thrust capacity.
Tapered Roller Bearings
4. Tapered roller bearings are designed to withstand a radial and thrust load, and
can be found in car hubs due to the amount of radial and thrust loads they can carry.
In a tapered roller bearing, the rings and the rollers are tapered in the shape of
truncated cones to simultaneously support axial and radial loads. The ratio of the loads
depends on the angle of the axes between the roller and bearing. The greater the angle
is the greater axial load can be supported. The contact angle for most tapered roller
bearings range is between 10 to 16 degrees. For higher thrust-load capacity, a 30-degree
contact angle is used.
5. Tapered bearings are mounted pairs since they handle radial loads better than a
single row of tapered small size
. For heavy-duty applications, two or four rows of tapered rollers are
combined in a single unit in large bearings.
Spherical Roller Bearings
Spherical roller bearings typically consist of two rows of barrel-shaped rollers
running in two raceways. One is on the inner ring and the other is on a continuous
spherical surface ground on the inner diameter of the outer ring. This allows the
bearing to operate with some misalignment. Spherical rollers have barrel profiles that
closely match the raceways profiles, hence making them robust and having a high load
capacity. They are mounted in pairs inside the large size bearing
housing and are faced in opposite directions.
This is done so that the load can be supported in either direction.
Needle Roller Bearings
Needle roller bearings use elongated cylindrical rolling elements with small
diameters. They are used in applications where radial space is limited. The diameter to
length ratio for the needles varies between 1-to-2.5 and 1-to-10. Due to their small
size, they cannot be guided accurately and generate high amounts of friction. They are
used at low speeds and oscillating motions as a result. Cages may be used to help guide
the needles and improve retention.
Designed to handle high thrust loads, roller-thrust bearings are typically found in
gearsets used for car transmissions between gears or between the housing and rotating
shafts. The angled teeth found in helical gears used in car transmissions produce a high
thrust load that is supported by the roller-thrust bearings. Roller-thrust bearings
slide within a roller-race contact to handle the surface-speed variation that comes as a
result of the varying diameter across the contact zone.
8. Ball-thrust bearings are designed to handle almost exclusively thrust loads in
low-speed, low-weight applications. An example of its use would be in bar stools where
they are used to support the seat.
Ball-thrust bearings are comprised of two grooved plates with a set of balls between
them. The ball-race contacts have a sliding action that is increased at high speeds by
the centrifugal force on the balls. Cylindrical roller thrust middle size bearings
limited to about 20% of the speed of its radial bearing counterpart and ball-thrust
bearings are limited to 30% of the speed of their counterpart.