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Bainite
hardening Through hardening heat treatment method of
bearing rings which gives extreme toughness.
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Ball
bearings Bearings that have balls as rolling elements.
May contain one or more rows of balls. They have very low
friction and can operate at high speed. Used at moderate
loads. The picture shows a deep groove ball
bearing.
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Ball bearings versus roller
bearings The main difference in the performance of
these two bearing types is that ball bearings have lower
friction than roller bearings, while roller bearings have
higher load carrying capacity.
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Ball screws Ball
screws have one or more circuits of balls interspaced between
a screw shaft and nut. As the screw or nut is rotated, the
balls roll in helical grooves formed by the threads.Each
circuit has a return device that recirculates the balls to
form a closed path. The high efficiency screws offer an
opportunity to displace loads by transforming rotary motion
into linear motion. The balls transfer the load under very low
friction, whereas the Acme sliding screw typically consists of
a steel shaft with trapezoidal thread and a bronze
nut.Replacing sliding friction with rolling friction increases
the efficiency of the screw from ~30% to ~90%. See also http://linearmotion.skf.com/
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Balls Of all
components mass-produced within industry, the precision
demands placed on balls for ball bearings are probably the
most rigorous. For example the surface roughness of the ball
has a tolerance of 0.01 micron (= 0.00001mm).
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Basic dynamic load
rating When calculating bearing life, the basic dynamic
load rating C is used. It expresses the bearing load, which
will give a life according to ISO (L10) of one million
revolutions. See also Basic rating life.
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Basic rating
life The bearing life calculated with the most simple
of ISO equations.
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Basic static load
rating When the bearing is stationary or makes slow
oscillating movements or is subjected to heavy shock loads
under rotation, the bearing size should be selected on the
basis of the basic static load rating C0. This is the load
that corresponds to a certain stress level, according to ISO,
at the centre of the most heavily loaded rolling
element.
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Bearing Wherever
there is rotation, there is a need for some form of bearing.
The function of a bearing is to minimise the friction between
moving machine parts and to carry a load. The majority of
bearings nowadays are rolling bearings consisting of an inner
ring, an outer ring, a number of rolling elements (balls or
rollers) and a cage. Most bearings are made of steel, but
other materials are also used, such as ceramics. In addition
to rolling bearings, SKF produces spherical plain bearings,
with different sliding contact surface combinations e.g.
steel-on-steel or maintenance-free with special sliding layers
and also magnetic bearings where friction is eliminated
because the moving parts are separated by a magnetic
field. The SKF standard product range comprises more than
5,000 variants covering all the principal bearing
types.
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Bearing
accessories Sleeves, nuts, spanners and washers for
locking, sealing and spacing are called bearing
accessories.
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Bearing
components The bearing components are the inner and
outer ring, the rolling elements and the cage.
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Bearing failure
analysis SKF has the means for calculating the life of
a bearing with considerable accuracy. If for various reasons
however, a bearing does not attain its calculated life (see
Bearing-failure), the failed bearing should be examined to
find the cause of the damage. Corrective action can then be
taken to prevent any recurrence.
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Bearing failure
due to electric current Passage of electric current
across the rings and rolling elements damages the contact
surfaces and the lubricant. A process similar to electric arc
welding, with very high localised temperatures occurring,
causes this damage. In the picture, the ball on the left
has a dull surface due to multiple micro craters from passage
of current. For comparison, an undamaged ball is shown on the
right.
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Bearing failure Only
a fraction of all bearings in use fail, and the main reasons
are: - Poor lubrication - Contamination - Faulty
mounting - Careless handling - Fatigue The picture
shows flaking due to faulty mounting. The mounting force has
passed through the balls and made indentations in the raceway,
causing flaking.
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Bearing
fatigue Fatigue cracks in the raceways can originate
from sub-surface stress raisers like slag inclusions or from
an indentation in the surface. As the rolling elements pass
over the cracks, fragments of material break away and this is
known as flaking. The flaking increases over time and
eventually leads to bearing failure. The pictures show the
gradual development of flaking.
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Bearing housing The
structure in which a rolling bearing is mounted for protection
and support. Often made of cast iron or plastic and used in
many different applications, such as fans, papermaking
machines etc. A wide range of standard bearing housings
simplifies bearing arrangements.
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Bearing internal
clearance The total distance that one bearing ring can
be moved relative to the other in either the axial or radial
direction. In the figure, the left shows radial clearance and
the right, axial clearance.
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Bearing life Bearing
basic rating life is defined as the number of revolutions a
bearing is capable of enduring before the first signs of
flaking occur on one of the rings or rolling elements.But
there are also other ways to define bearing life: - Service
life = Real life in operation - Specification life =
Specified e.g. by the electric motor manufacturer
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Bearing basic
rating life L10 = Millions of revolutions or operating
hours at a given speed
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Bearing steel The
steel from which rolling bearings are produced is vital to
bearing quality, and SKF's Ovako Steel produces the cleanest
steel in the world. The steel must be suitable for
hardening, and have good fatigue strength and wear resistance.
Precise analysis and freedom from inclusions are factors
critical to the operational life of the bearing, and the
structural and dimensional stability of the bearing components
must be satisfactory at the operating temperatures which can
be expected. See also http://www.ovako.com/
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Bearing
units Products in which the bearing has been integrated
with other components in a single unit. The bearing is often
greased for its entire lifetime. The picture shows a hub
bearing unit for cars.
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Bearing precision
classes Rolling bearings are precision products, but
sometimes even higher than normal precision is required e.g.
in machine tool spindles. For such applications, several
higher precision tolerance classes are available according to
SK17, ISO or ABEC specifications. (ABEC = Annular Bearing
Engineers Committee).
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Examples of higher
precision tolerance classes of equal value:
SKF |
ISO |
ABEC |
PA9A |
ISO 2 |
ABEC 9 |
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BEAST BEAring
Simulation Tool, developed by SKF, is a very advanced
computer-based 3D tool used to simulate different types of
bearings. It replaces expensive and time consuming laboratory
tests and is regarded as a virtual test rig.
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Bogie-monitoring system
(BoMo) SKF and Sécheron have jointly developed a highly
sophisticated bogie-monitoring system, BoMo. The axleboxes are
equipped with compact and integrated multifunction sensors.
The sensors for instance, monitor wheel condition and risk of
derailment, and generate warning signals.
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BoMo See
Bogie-monitoring system.
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Brake-by-wire SKF
and Brembo have jointly developed an electromechanical brake
calliper which incorporates SKF actuators.The braking-system
control is mounted on the Guida (see By-Wire Technology) and
activated by squeezing handgrips. The mechanical design of the
driver's braking controls incorporates progressive resistance
and a small but clearly discernible free-play at the beginning
of the movement. This provides the driver with a tactile
indication that the brakes are starting to operate. Each brake
is controlled as an individual sub-system under an overall
control arrangement for the complete vehicle braking
system.
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Prototype SKF and Brembo Brake-by wire calliper
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Brembo S.p.A Italian
brake manufacturer collaborating with SKF in brake-by-wire
development.
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Bushings SKF now has
an extensive range of bushings comprising many different types
- from traditional solid bronze to maintenance-free SKF
Filament Wound bushings. A wide stock assortment ensures
prompt delivery.
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By-wire
technology In by-wire systems, direct mechanical
control of a machine is replaced by electronic control. The
drive-by-wire system follows the fly-by-wire concepts used
successfully by the aerospace industry. In conventional
control, the movements the driver makes with the steering
wheel are transmitted mechanically to the front wheels. In a
by-wire system, the driver's physical movement on the steering
wheel is sensed and converted into a digital electronic signal
that is transmitted to a smart electro-mechanical actuation
unit that controls the wheels. The same principle can be
applied to the braking and gearbox systems. This is aircraft
technology applied on automotive applications. See also
Drive-by-wire. |
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Guida - drivers control - with the brake-by-wire
calliper, steering actuator and clutch
actuator. |