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	Direction of Load			Ratio of Load/Bulk			Misalignment Capacity
	radial	axial	both	high	med	low	high	med	low
Thrust Ball		y			y				y
Deep Groove Ball	y		y		y			y
Cylindrical Roller	y		certain types		y				y
Needle Roller	y			y					y
Tapered Roller	y	y	y		y				y
Self-aligning Ball	y		y			y	y
Self-aligning Spherical Roller	y		y		y		y
Angular Contact Ball		y	y			y			y

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

If only radial forces act,

Fstatic = Fsrad

Where  Fstatic  = The combined, equivalent static bearing load Fsrad  = The static radial load Fsax  = The static axial load Xsrad  = The static radial factor (dimensionless) Xsax  = The static axial factor (dimensionless)

The basic static load rating coefficient, Co, can be obtained from: Co = So · Fstatic Where  Co  = The basic load rating So  = The static safety factor (dimensionless) Fstatic  = The combined, equivalent static bearing load

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 Loading Type Noise Irrelevant Normal Operation Quiet Operation ball roller ball roller ball roller Smooth Loading 0.5 1 1 1.5 2 3 Normal Loading 0.5 1 1 1.5 2 3.5 Shock Loading > 1.5 > 2.5 > 1.5 > 3 > 2 > 4 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. Fdyn = Xdrad · Fsrad + Xdax · Fsax Where  Fdyn  = Equivalent dynamic bearing load Fsrad  = Static radial load on bearing Fsax  = static axial load on bearing Xdrad  = radial dynamic factor (dimensionless) Xdax  = axial dynamic factor (dimensionless) 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: Where  L =  basic rated life (millions of revolutions) C =  basic dynamic load rating P =  equivalent dynamic bearing load m =  exponent in the life equation,  m = 3 for ball bearings  m = 3.3 for other bearings. Where  L =  basic rated life (millions of revolutions) C =  basic dynamic load rating P =  equivalent dynamic bearing load m =  exponent in the life equation,  m = 3 for ball bearings  m = 3.3 for other bearings. Machine Usage Type Life Required of Bearings (Hours) household appliances — intermittent use 300 - 3000 hand tools, construction equipment — short period use 3000 - 8000 lifts, cranes — high reliability for short periods 8000 - 12000 8h/day gears, motors — full day partial use 10000 - 25000 8h/day machine tools, fans — full day full use 20000 - 30000 continuous use 40000 - 50000 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 1 Both races are made in almost the same way. Since they are both rings of steel, the process starts with steel tubing of an appropriate size. Automatic machines similar to lathes use cutting tools to cut the basic shape of the race, leaving all of the dimensions slightly too large. The reason for leaving them too large is that the races must be heat treated before being finished, and the steel 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. 2 The rough cut races are put into a heat treating furnace at about 1,550 degrees Fahrenheit (843 degrees Celsius) for up to several hours (depending on the size of the parts), then dipped into an oil bath to cool them and make them very hard. This hardening also makes them brittle, so the next step is to temper them. This is done by heating them in a second oven to about 300 degrees Fahrenheit (148.8 degrees Celsius), and then letting them cool in air. This whole heat treatment process makes parts which are both hard and tough. 3 After the heat treatment process, the races are ready for finishing. However, the races are now too hard to cut with cutting tools, so the rest of the work must be done with grinding wheels. These are a lot like what you would find in any shop for sharpening drill bits and tools, except that several different kinds and shapes are needed to finish the races. Almost every place on the race is finished by grinding, which leaves a very smooth, accurate surface. The surfaces where the bearing fits into the machine must be very round, and the sides must be flat. The surface that the balls roll on is ground first, and then lapped. This means that a very fine abrasive slurry is used to polish the races for several hours to get almost a mirror finish. At this point, the races are finished, and ready to be put together with the balls. Balls 4 The balls are a little more difficult to make, even though their shape is very simple. Surprisingly, the balls start out as thick wire. This wire is fed from a roll into a machine that cuts off a short piece, and then smashes both ends in toward the middle. This process is called cold heading. Its name comes from the fact that the wire is not 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".