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Industrial Cylindrical Bearings
Two-direction locating bearings may be
self-contained or have a two-piece inner ring. They have a lower roller
complement and lower roller capacity, but a much higher load capacity. They are
rather complex bearings.
Full-complement Bearings use two snap rings in the non
locating race to retain the rollers. They have a high load capacity, their
disadvantage is low speed. The speed limitation results from the high rubbing
velocity between adjacent rollers and limits the bearing to low-speed or
oscillatory applications.
Double-row Bearings are used where alignment between shaft and
housing is very good and high loads are to be handled at moderate speeds. The
bearings are nonlocating. Another class of double-row bearings is the journal
roller bearing, which has two non locating races.
Physical Characteristics
Although the rolling elements in cylindrical roller bearings
are called "cylindrical," they are not true cylinders. True cylinders
would produce stress concentrations at the ends of the roller-race contact,
resulting in high wear and high sensitivity to misalignment. Instead, rollers
are usually crowned or end relieved.
Earthquake-Proof Buildings
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The new San Francisco International Airport uses many advanced building
technologies to help it withstand earthquakes. One of these
technologies involves giant ball bearings.
- The 267 columns that support the weight of the airport each ride on a
5-foot-diameter (1.5-meter) steel ball bearing. The ball rests in a
concave base that is connected to the ground. In the event of an
earthquake, the ground can move 20 inches (51 cm) in any direction. The
columns that rest on the balls move somewhat less than this as they
roll around in their bases, which helps isolate the building from the
motion of the ground. When the earthquake is over, gravity pulls the
columns back to the center of their bases.
Cylindrical roller bearings use rollers for rolling elements,
and therefore have a high load capacity. The rollers are guided by ribs
on either the inner or outer ring, therefore these bearings are also
suitable for high speed applications. The inner and outer rings can be
separated to facilitate assembly, and both can be fit with shaft or
housing tightly.
If there are no ribs, either the inner or the outer ring can move
freely in the axial direction. Cylindrical roller bearings are
therefore ideal to be used as so-called "free side bearings" that
absorb shaft expansion.
Cylindrical roller bearings have high radial capacity and low friction,
which permits operation at high speed. A certain amount of thrust loads
may be carried. The cylindrical rollers are either end relieved or
crowned to avoid stress concentrations at the ends of the roller-race
contact.
They are suitable for high-speed applications and made in precision
grades. Cylindrical roller bearings are generally lubricated with oil
that serves as a coolant. To avoid the bearings kid, a common problem
in cylindrical bearings an out-of-round raceway or two preloaded hollow
rollers may be used.Non locating Bearings have a separable outer ring or the inner
ring that allow considerable axial movement of the shaft. They are used
with an axially locating bearing such as ball bearings. Non locating
bearings have high radial and load capacity, high stiffness, and the
highest speed capability.
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