NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING PGDIE-42
Industrial Engineering
Assignment on Product Design & Manufacture
UNDER THE GUIDANCE OF:-
Dr. KVSS NARAYAN RAO
PROFESSOR,NITIE-Mumbai
Presented By: -
Pradeep Kumar Dubey
PGDIE 42
Roll NO. 62
Pramod C Nair
PGDIE 42
DESIGN OF BALL BEARINGS:-
Ball
bearings are used primarily to support rotating shafts in mechanical equipment.
They can be found in everything from personal computers to passenger cars. They
are of simple design and can be precision made in mass production quantities.
They can support heavy loads over a wide speed range and do it virtually
friction free. They come in many different sizes and shapes, are relatively
inexpensive, and require little or no maintenance.
DESCRIPTION
A ball bearing consists of an inner ring
(IR), an outer ring (OR), a complement of balls, and a separator to contain the
balls. The outer diameter of the inner ring (IROD) and the inner diameter of
the outer ring (ORID) have a groove in which the balls roll on. This groove is
commonly called the pathway. The raised surfaces on each side of the
pathway are called the shoulders. The balls are held equally spaced
around the annulus of the bearing by the separator. The basic dimensions of the
bearing are the bore (B), outside diameter (OD), and the width (W).
THEORY OF OPERATION
In
most applications, there are two ball bearings supporting a rotating shaft. The
ball bearing inner ring is a press fit on the shaft so there is no relative
movement between the two while the shaft is rotating. The outer ring is a close
push fit in the housing for assembly reasons and also to allow slight axial
movement to accommodate manufacturing tolerances and differential thermal
expansion between the shaft and housing.
DIFFERENT BEARING MATERIALS
BALL BEARING LIFE
B10
life is a calculated number of hours that 90% of bearings are expected to
achieve in their lifetime under a specified load and speed without failure. The
B10 ball bearing life formula follows:
L10=3000(C/P)10/3(500/S)
L10 is
the bearing B10 life in hours. C is the capacity of the bearing and is found in
industry catalogs; it is the number of pounds that the bearing can support for
3,000 hours of operation at 500 rpm. The factors in determining bearing
capacity include steel cleanliness and quality, ball diameter, number of balls,
and inner ring pathway curvature. Ball diameter is the biggest single
contributor to bearing capacity. P is the equivalent radial load in pounds
which takes into account both radial and thrust loads and is also found in
industry catalogs. S is the application speed in revolutions per minute (rpm).
It can be seen that because of the 10/3 power exponent, bearing life is
especially dependent on load and not as dependent as speed which has no
exponent. Should a bearing operate under a number of different loads and
speeds, the following equation is used:
L10=1/[(t1/L1)+(t2/L2)+(t3/L3)+etc]
L10 is
the bearing B10 life in hours. t is the percent of time spent at each different
life (L) level. Bearing life calculations are necessary to determine if
predicted values meet actual design requirements.
WHEN
TO SELECT A CERTAIN TYPE OF BEARING
Rearing Type
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Direction of Load
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Ratio of Load/Bulk
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Misalignment Capacity
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radial
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axial
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both
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high
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med
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low
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high
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med
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low
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Thrust Ball
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y
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y
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y
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Deep Groove Ball
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y
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y
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y
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y
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Cylindrical Roller
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y
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certain types
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|
y
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|
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y
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Needle Roller
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y
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|
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y
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|
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y
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Tapered Roller
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y
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y
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y
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y
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|
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y
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Self-aligning Ball
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y
|
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y
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y
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y
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Self-aligning Spherical Roller
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y
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y
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y
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y
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Angular Contact Ball
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y
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y
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y
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y
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Static Load Specification:
The axial and radial forces acting on
the stationary rotary bearing determine the Basic Static Load Rating listed in
bearing catalogs. When there are both axial and radial loads on a bearing, the
combined static load can be found as follows.
Fstatic = Xsrad · Fsrad + Xsax · Fsax
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If only radial forces act,
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Fstatic = Fsrad
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The basic static load rating
coefficient, Co, can be obtained from:
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Values of So depend upon the
requirements for low-noise operation and the type of bearing, as shown in the
following table.
Static Safety Factor (So) Guidelines
Dynamic Load Specification:
The dynamic load specification of a rotary bearing is dependent on both the dynamic and static forces acting upon the bearing. Therefore, please first calculate the Static Load Specification as outlined above. Axial and radial static forces multiplied by dynamic factors combine to form the equivalent dynamic bearing load, which is calculated as follows.
When Fsax =
0 or is relatively small up to Fsax/Fdyn =
e (The values of Fsrad, Fsax, and e are given in the Rotary Bearing Data) then
Fdyn = Fsrad
Since we have calculated the
equivalent dynamic bearing load we can now compute the bearing dynamic load
rating, which is used to select the bearing. Catalog dynamic load rating values
should be chosen higher than the computed value for safety.
The catalog-listed dynamic load
ratings are dependent upon both the equivalent dynamic load and the required
bearing life. The ISO equation for the basic rating life is:
The Manufacturing of a Ball
Bearing
Ball bearings are at the heart of almost every product with a
rotating shaft.
Our machining capabilities include ultra precision machining, mass
production technologies and our own vertical integration systems.
Dies and Tools
Pressed Parts
The pressed parts productions include outer rings, inner rings,
retainers, shields and snap rings.
The Manufacturing Process
There are four major parts to a standard ball bearing: the outer
race, the rolling balls, the inner race, and the cage.
Races
Surprisingly, the rolling balls start out as thick steel wire.
Then, in a cold heading process, the wire is cut into small pieces smashed
between two steel dies. The result is a ball that looks like the planet Saturn,
with a ring around its middle called "flash."
usually warps during this process. They can be machined back to
their finished size after heat treating.
Balls
The bulge around the middle of the rolling balls is removed in a
machining proess. The balls are placed in rough grooves between two cast iron
discs. One disc rotates while the other one is stationary; the friction removes
the flash. From here, the balls are heat treated, ground, and lapped, which
leaves the balls with a very smooth finish.
heated before being smashed, and that the original use for the
process was to put the heads on nails (which is still how that is done). At any
rate, the balls now look like the planet Saturn, with a ring around the middle
called "flash."
Quality Control
Bearing making is a very precise business. Tests are run on
samples of the steel coming to the factory to make sure that it has the right
amounts of the alloy metals in it. Hardness and toughness tests are also done
at several stages of the heat treating process. There are also many inspections
along the way to make sure that sizes and shapes are correct. The surface of
the balls and where they roll on the races must be exceptionally smooth. The
balls can't be out of round more than 25 millionths of an inch, even for an
inexpensive bearing. High-speed or precision bearings are allowed only
five-millionths of an inch.
Modifications
for its Mass Production
1.Total
control and product compliance: Manufacturing engineers
work with machine tool builders and gage producers to develop new equipments or
introduce improvements to existing equipments.
2.
Continual
unit gaging and inspection: by machine operators and Quality control
stations throughout the line.
3.
Assembly
under Clean Room conditions: to assure
contamination-free products
4.
Bearing
Testing Equipment: Starting and Running Torque Testers. They provide direct read-out
of torque measurements, also provide information on bearing geometry and
cleanliness.
5.
Lubricants:
developed a line of speciality lubricants for use in specific critical
applications.
Packaging
The same rigid cleanliness standards are observed in the packaging
section as are specified for the inspection, lubricating and testing sections
of the clean room.
Packs are formed from strips of transparent, heat sealable
polyester backed polyethylene film. To prevent damage during shipment, the
boxes containing the pack strips are enclosed in sturdy corrugated shipping
cartons along with filler material to prevent shifting and to strengthen the
package.
Ball
Bearing Handling Manual
It contains detailed step-by-step approach to ball bearing
cleaning and installation. Some
environmental guidelines, servicing procedures are also covered.
The Future
Ball bearings will be used for many years to come, because they
are very simple and have become very inexpensive to manufacture. Some companies
experimented with making balls in space on the space shuttle. In space, molten
blobs of steel can be spit out into the air, and the zero gravity lets them
float in the air. The blobs automatically make perfect spheres while they cool
and harden. However, space travel is still expensive, so a lot of polishing can
be done on the ground for the cost of one "space ball".
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