07 – Bearings and Bushings

07 – Bearings and Bushings

The intent of this presentation is to present enough information to provide the reader with a fundamental knowledge of bearings and bushings used within Michelin and to better understand basic system and equipment operations.

General Information Bearings and Their Categories Generalities A bearing is a mechanical device and it is important to know its various components.

KEY 1) Inner race ) Side of inner race. 2) Inner race chamfer. 8) Side of outer race. 3) Inner race track. 9) Cylindrical roller. 4) Outer race track. 10) Cylindrical roller track 5) Outer race ) Outer race. 6) Ball ) Cage

Categories of bearings When in operation, a shaft is subjected to axial and radial forces which tend to push it away from its axis center. Bearings are positioned to resist to these forces and maintain the shaft in proper equilibrium. Manufacturers have grouped bearings under two headings, on the basis of the forces being encountered: radial bearings and axial bearings. Radial bearings Radial bearings are made with balls or rollers, depending on the how the bearings are used. They are designed to withstand forces that are perpendicular to the axis of the shaft.

Axial bearings Axial bearings, also known as thrust bearings, have either balls or rollers, but both are designed to withstand axial forces, which push or pull along the axis. The following chart shows different Bearing Identification Codes

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In the precision and play (clearance) suffixes, "P" refers to the tolerances of each bearing component and "C" refers to the precision of radial play between the rolling element and the race (track).

Internal Clearance The internal clearance has a direct impact on the tightness of the bearing around the shaft. Therefore, one must replace a bearing by another of the same type with the same dimensions and clearance. Does NOT apply to Conical Bore bearings on adapter sleeves This chart is an example of differences between the various clearance codes. It explains the precision variance pertaining to the radial clearance for an identical bearing, but with a different degree of precision. The normal clearance is the standard manufacturing clearance.

Conversion of values into the imperial system To convert into inches the values shown in microns (SI), simply divided the microns by 25.4. 1 thousandth of an inch = 25.4 microns and 1 micron ‑ mm Major Rules of Bearing Maintenance Bearing components have highly‑precise surface finish and shape; therefore they are extremely sensitive to external forces. This is why it is imperative that they always be handled with utmost care. Storing Bearings must remain in their original packing material until installation time. The packing material must be removed only on the installation site and just prior to installation. Bearings must be stored in a dry place, away from the cold. Otherwise, they could gum up and corrode. They must always be stored flat. NOTE: Do not store bearings in any area that also contains corrosive chemicals, such as acid, ammonia or bleaching lime.

Rules pertaining to the handling of bearings work with clean and approved tools in a clean environment handle bearings with clean and dry hands or with clean canvas gloves work on a metal table or a table covered with metal carefully handle a used bearing as a new one, until it is clear that the bearing is defective use clean solvents put the bearing on a clean surface protect removed bearings against humidity and dirt if necessary, wipe the bearing with a clean, lint‑free cloth keep the bearing in waxed paper when it is not being used clean the shaft or the housing before installing the bearing install new bearings right from its packing material; do not wash a bearing that comes out of a sealed container use only clean lubricating material on a bearing and keep lubricant containers closed when they are not being used

Inspection Once a bearing has been removed, inspect it. First, it needs to be cleaned in a non‑flammable solvent, then dried carefully with a clean, lint‑free cloth or with low‑pressure compressed air (for safety reasons, make sure that no components of the bearing are set in motion). Examine the rings and the rolling components to look for possible deterioration.

Bearings that are protected by joints or flanges must never be cleaned. For obvious reasons, they cannot be inspected. To make sure that the rolling noise is normal, spin the outer ring. A bearing that has not suffered deterioration, is free of imprints, cracks and flaking, and its rotation is regular, without excessive radial play can be reinstalled without danger.

Single Row Ball Bearing vs. a Plain Bushing Generalities Advantages of a bearing: 1. Reduces friction 2. Axial space requirements are small 3. Reduced maintenance 4. Ease of replacement 5. Prevents wear on the shaft and housing Disadvantages of a bearing: 1. Requires more radial space 2. Less loading over the same I.D. bushing NOTE: When using bearings over bushings, we give up heavy loading for higher RPM’s

Pre-Lubricated Sintered Bronze Bushings (“Oilite”) This Oilite bushing is manufactured using metallurgical powder techniques in order to have a porous material. It takes on the form of a metallic sponge, all the pores of which communicate with each other and the surface. This porosity accounts for 30% of the volume of the part; and it is impregnated with a hydrocarbon oil. Manufacturing of the bushing Powder agglomeration: The powders are cold compressed in a mold (copper powders, tin powders, iron powders, etc.). Sintering: The parts are baked. Calibration: This is to compensate for the deformation caused during the sintering process. Impregnation: Oil is forced into the pores in a vacuum.

Fits: Tolerance on the housing: H7 Tolerance on the shaft: f7 or g6

Putting bushings in place Use a perfectly cylindrical polished mandrel. (Once the operation has been completed, give the tools back to the crib having greased them)

Material supplied by the tool crib for installing a bushing with a press Put washer 1 on mandrel 2 Slide the bushing onto the mandrel Push into the part using the press Remember the Fits are: Tolerance on the housing: H7 Tolerance on the shaft: f7 or g6 2 1

Removal of a mandrel Mount the extractor upon the fitted assembly. Turn the screw until the mandrel is completely removed. Utilization of these bushings: Low rotational speed High radial load No axial movement No alternating movement Note: These bushings should be mounted with a mandrel only, and should never be reamed to size, due to the fact that reaming will shear the sintered bronze spheres and the burrs will tend to clog the lubrication passages.

Teflon Impregnated Bronze Bushings (DU Bushing) Definition Different plastics are used for bushings; among these, is polytetrafluorethylene (called P.T.F.E. or Teflon), the most widely used. This type of bushing has the advantage of combining the excellent frictional properties of P.T.F.E. It is not a self-lubricating friction material, for it runs without lubricant. However, no difficulty is caused by the presence of a lubricant which can even often be a positive additive. Composition This bushing is composed of three layers: A support made of sheet steel, tinned to protect it from corrosion. An intermediary layer of sintered bronze mixed with P.T.F.E. and fine lead powder A surface layer which is a mixture of Teflon and a fine lead powder, approximately 25 µ meters thick.

Different parts Parts made of this combination of materials may be: rolled bushings thrust washers flat strips Fits Tolerance on the housing: J7 or H6 Tolerance on the shaft: h6 or h8

Mandrel DU Bushing After using the mandrel carefully grease it and return it to the tool crib. Fitting of a DU bushing using a press Lightly grease the outside of the DU bushing Chamfer the housing Press bushing into housing Note: These bushings are used to meet the following conditions: Reduced speed Heavy load Longitudinal movement Alternating movement The bore of these bushings must not be burnished or modified in any other way.

Installation techniques

Removal of bearings Great care must be taken when removing a bearing that will be used again. Preliminaries Before undertaking the removal of a bearing, the shaft and the bearing housing must be thoroughly cleaned. It also matters that reference points be noted regarding the position of the installed bearing (taking measurements with a ruler, for instance). It is also important to take down the number of the bearing so as to replace it, if necessary, by an identical one, or by an equivalent bearing approved by the company.

Tools There are three major families of tools used in removing a bearing: mechanical extractors or hydraulic rings; mechanical or hydraulic presses; hammer and proper support (bushes and pipes). Removal tools Removal Tools Extractors Extractors are tools which help remove bearing through a pulling action.

Mechanical extractors Mechanical extractors use the shaft as a support and their screw to pull away the bearing. Examples of mechanical extractors

Hydraulic extractor The hydraulic extractor is the most powerful extraction system for bearings. Some models can apply a number of tons of pressure. It works by gripping the bearing and then applying pressure on the shaft. NOTE: It is very important to leave the nut on the shaft, but it does need to be loosened by a couple of turns.

Presses Presses are used when one can use the bearing as a support and apply pressure against the shaft to separate it from the bearing. They are usually mounted on a workbench and the pressure is applied mechanically (rack) or hydraulically.

Hammer and supports When neither an extractor nor a press will do the job, the bearing can be removed with a hammer. The figure below shows two methods of removal with a hammer. It shows that the impact of the hammer is distributed over the entire surface of the bearing. Please note that the hammer does not strike the shaft directly, but a piece of soft metal is placed against it. Examples of hammer use These diagrams show that: when the bearing is installed on a shaft, support is taken on the inner ring when the bearing is lodged in a housing, support is taken on the outer ring NOTE: If the bearing held both in a housing and on a ring, one should, if possible, support simultaneously the inner and outer rings. If this cannot be done, try to support the tighter of the two rings.

Basic technique Removing a bearing is not a complicated operation. The only difficult thing is to avoid damaging it, so that it can be used again. As shown before, the bearing is equipped with an inner ring and an outer ring. Usually, pressure is exerted on only one of the two rings during removal. Therefore, the pressure is applied on the ring where the support is the greatest. Ring support

Installation of bearings In order for a bearing to work properly and last as long as it is intended to last, correct installation methods and the observance of work area cleanliness are of paramount importance. Preliminaries It is important to inspect carefully all components that pertain to the installation; to verify that the shape and dimension of the shaft face and of the housing are exact, since damage may have occurred during removal; to clean the shaft and shoulder; to examine the gaskets and to replace those that are worn or damaged. Tools Special tools have been devised to install bearings.

Various installation bushings There are a variety of installation bushings, depending on the type of bearing. If you do not have the specific bushing that is required to install a particular bearing, it is preferable that one be made. It could prove useful when installing other bearings of the same kind.

Hydraulic presses There are a number of models of hydraulic presses: some are designed specifically for bearing installation, while others have a more widespread use. Annular‑piston presses When a large swivel‑joint roller bearing has to be installed, it is preferable, when adjusting the tightness, to use an annular‑piston press rather than a spanner wrench and a locknut. The work performed with such a press is faster, safer and more precise.

Installation nuts Locknuts equipped with a lock clip as well as lock washers are required installation accessories. The locknut is used to tighten the bearing during the adjustment operation, while the lock washer is used to maintain the tightened locknut in position. Typical designations: KM 4 Nut + MB 4 Washer (metric) KM Nut MB Washer

Tight adjustment on the shaft When a bearing has to be tightly fitted onto the shaft, it is advisable to put a little bit of low-viscosity oil on the shaft face, so as to avoid damaging the shaft during installation. Small bearings can be installed with an installation bushing or a tube. The tube must be clean and have flat and parallel surfaces, as well as right angle ends. Position the tool against the inner ring and strike evenly all around with an ordinary hammer (not one made of lead or other soft metals, because small fragments could chip off). NOTE: Make sure that the bearing is not in an oblique (cocked) position relative to the shaft.

If a mechanical or hydraulic press is available, it can be used for installing small or medium bearings. Bearings are easier to install if they are heated to a temperature of 80 to 120°C (170 to 250°F). Make sure that the temperature does not exceed 120°C. The most appropriate heating method is to use an oil bath. The oil must be clean and have a flash point greater than 250°C. The bearing must not touch the bottom of the container.

NOTE: There is a compound which will ensure that the bearing will not be heated at more than 120°C (cutting oil). The bearing can also be heated by electric flux density. To determine the temperature, one can either use special chalks that melt at given temperatures, or read a thermocouple mounted on the device. Once the bearing has been heated, a number of precautions need to be taken, namely: use of clean safety gloves or rags to keep the bearing clean; removal of oil that could remain in the inner ring or wiping of the bore; quick positioning of the bearing; firm hold on the bearing against the shoulder until it has sufficiently cooled.

Tight adjustment into the housing If the bearing needs to be held tightly inside the housing, it is preferable to apply a thin coat of oil on the bearing's surface. An installation bushing or a clean tube must be used (placed against the outer ring). NOTE: Make sure that the bearing is not positioned obliquely (cocked) in the housing. One can also use a mechanical or a hydraulic press. Sometimes, it is necessary to heat the housing to be able to position it. One can use an electric light bulb or hot oil.

Bearings on a sleeve The inner ring of conical bore bearings is always tight fitted, usually on an adapter sleeve or a withdrawal sleeve. Place the adapter sleeve on the shaft at the position noted before removal.

Before positioning the bearing, the radial play must be determined with the blade of a thickness gauge. Just before installation, remove the rust proofing compound from the bearing. Put the bearing and the locknut on the shaft, then tighten the locknut, using the appropriate wrench, so as to affix the bearing around the shaft. The lock washer must be installed only once the proper tightness has been reached.

After this, regularly check the decrease in play during the positioning. The measurement must be made in that segment of the bearing which is not carrying the load. The mechanic will have to follow the recommendations given on the following charts to ensure maximum performance.

Bore diameter Radial play d C2 Normal C3 C4 over up to min. max. mm 30 40 50 65 0.025 0.030 0.040 0.035 0.045 0.055 0.050 0.060 0.075 0.065 0.080 0.095 0.085 0.100 0.120 80 100 120 0.070 0.110 0.135 0.140 0.170 0.150 0.180 0.220 140 160 180 0.090 0.130 0.160 0.200 0.230 0.260 0.300 0.340 200 225 250 0.250 0.270 0.290 0.320 0.350 0.370 0.410 0.450 280 315 355 0.190 0.240 0.330 0.360 0.390 0.430 0.460 0.470 0.490 0.540 0.590 400 450 500 0.210 0.400 0.440 0.520 0.570 0.630 0.650 0.720 0.790 560 630 710 0.510 0.600 0.670 0.680 0.760 0.850 0.870 0.980 1.090 800 900 1 000 0.640 0.710 0.750 0.840 0.930 0.960 1.070 1.190 1.220 1.370 1.520 1 120 1 250 0.530 0.770 0.830 1.030 1.120 1.300 1.420 1.670 1.830

For bearing sizes 04 to 96, the diameter on the smaller side of the bore, in millimeters, corresponds to five times the size number. For bearing sizes 500 and above, the size number corresponds to the bore diameter on the smaller side of the tapered bore Example: Bearing 22244CCK/C3W33 (bore diameter of 220 mm) to be installed on conical shaft. Measure the initial play using calibrated blades. The above chart shows that the initial play will be between and mm. Using a locknut (or other equivalent means), push the bearing on its conical shaft until the play is brought down to the value shown in the following chart

* Valid only with solid steel shafts.
Bore diameter d Reduction of radial play Axial * positioning Conicity 1:12 Acceptable residual play after assembly with initial play over up to min. max. Normal C3 C4 mm 30 40 50 65 0.020 0.025 0.030 0.040 0.35 0.4 0.45 0.6 0.015 0.035 0.050 0.055 80 100 120 0.045 0.060 0.070 0.7 0.75 0.9 1.1 0.065 0.080 0.100 140 160 180 0.075 0.090 0.110 1.2 1.3 1.4 1.6 1.7 0.130 0.150 200 225 250 0.140 2.0 2.2 2.4 0.120 0.160 0.180 0.200 280 315 355 0.170 0.190 0.210 1.9 2.7 3.0 3.3 0.220 0.240 0.260 400 450 500 0.230 0.280 2.6 3.1 3.6 4.0 4.4 0.290 0.310 0.350 560 630 710 0.300 0.320 0.400 3.7 4.6 5.0 5.4 6.2 0.250 0.360 0.410 0.450 800 900 1 000 0.340 0.370 0.500 0.550 5.3 5.7 6.3 7.0 7.8 8.5 0.270 0.390 0.430 0.510 0.570 0.640 1 120 1 250 0.490 0.600 0.650 6.8 7.4 9.0 9.8 0.480 0.540 0.700 0.770 * Valid only with solid steel shafts.

Bearing Failures

Main Causes Of Bearing Failure And Stoppages Causes Premature failure is generally caused by one or more of the following: contamination misalignment incorrect lubrication flow of an electric current through the bearing Distortion incorrect adjustment vibration when the bearing is not in motion poor maintenance practices.

Contamination Contamination is defined as any foreign substance causing damage to the bearing. Humidity or an abrasive, such as sand or dust, will cause premature failure. The figure to the right shows scratches caused by grains of sand (a) and rust caused by humidity (b).This kind of failure can be avoided by using the appropriate lubricant, by keeping the bearing clean during handling and by using seals that are clean and free of damage.

Distortion When the shaft or the housing has been distorted, the bearing can wear out faster. If the shaft or the housing is no longer round, the rolling parts of the bearing will be subjected to extra pressure where the shaft or the housing is too large. This will cause cavities on the running surface. This problem can be solved by correcting the shaft or the housing. If neither can be repaired, the defective parts will have to be replaced.

Misalignment Misalignment can be caused by a shaft that has been twisted, by shoulders that are not square, by a housing that is not parallel or by foreign objects caught between the bearing and its support. The figure to the right shows the classic consequence of misalignment: notice the path that the balls follow. The cause of such misalignment must be determined and corrected, otherwise the same problem will appear with the new bearing.

Incorrect adjustment The figure to the left shows a failure caused by an incorrect alignment. The example shows that the inner ring is broken; this is the result of forcing a bearing onto a shaft that is too large.

Incorrect lubrication Figure (a) shows an example of smeared metal. This happens when the rolling components slide instead of roll, which stems from over or under lubrication Figure (b) shows a rusted bearing, which happens when humidity enters the lubricant and causes the bearing to rust. Then the rust is mixed with the lubricant, which creates an abrasive compound. It is imperative to use the proper lubricant and to apply the appropriate amount.

Vibration in the absence of motion This figure shows a bearing damaged by vibrations while it was not in motion. This is referred to as False Brinelling. This kind of stress will quickly break a bearing. Flow of an electric current through a bearing When an electric current flows through a bearing in motion, it causes electric arcs. These, in turn, melt the metal, which leads to failure. Such electric currents are usually produced by electric arc welding where the ground goes through the bearing.

Poor maintenance practices If improper practices are adopted when installing or removing a bearing, failures may occur.

Consequences of too small or too worn a shaft It is imperative that a bearing be installed on the appropriate shaft and housing. Shafts that are too small or housings that are too large accelerate the failure of bearings. When the shaft is too small, the inner ring turns freely; when the housing is too large, the outer ring is not adjusted enough. In both cases, there is heating, scoring of the components subjected to rubbing and finally cracks, all of which accelerate the failure. Too small a shaft

Causes of incorrect installation Misalignment will impart abnormal tension of the housing. Indeed, this condition, as well as incorrect lubrication, are the two major causes of problems. This leads to a rolling groove which is not parallel to the edge of the groove. When the rolling groove caused by misalignment is carved on the outer ring (the case there the inner ring turns), this means that the housing bore is not parallel to the shaft. If the rolling groove is carved on the inner ring, this means that the ring is caught against the shaft, or that the shaft shoulder is not perpendicular to the support surface, or that the shaft is curved. Causes of incorrect tolerance The space between the shoulders must be figured out in function of the exact distance between the bearing shoulders on the shaft; otherwise, there will be an excessive axial thrust on the bearing, which will lead to premature wear.

Bearing Identification

Bearings Categories Most bearings can be classified under one of three groups. Radial bearings Axial bearings (Thrust bearings) Dual-purpose bearings

Bearing Identification

Radial bearings have either balls or rollers and are designed to withstand forces that are perpendicular to the axis of the shaft. Axial bearings, also known as thrust bearings, can have either balls or rollers and are designed to withstand forces that push or pull in-line with the axis of the shaft. Dual-purpose bearings can have either balls or rollers and are designed to withstand a combination of radial, axial, and angular forces. The following are some common bearings used in industry and their functions.

Radial bearings and their functions Ball bearings Name Function Single Row Ball Bearing Designed mainly to support high speed and radial loads, but can also take a bit of axial load. Name Function Single Row Ball Bearing with filling notch. (Maxiball) Designed to take a higher radial load than a standard Single Row Ball Bearing. However, the filling notch prevents the support of axial loads.

Name Function Double Row Ball Bearing These bearings have the same feature as the single‑row bearings, but can take heavier radial loads. Roller and Needle Bearings Name Function Cylindrical Roller Bearing These bearings can withstand high radial loads and function at high speeds.

Name Function Needle Bearing To take moderate radial loads and use less radial space Note: As a general rule, a “Needle Bearing” is defined as having the length of its rollers at least 3 times as long as their diameter. Needle Bearings can come with a removable inner race, a removable outer race, or with an outer race only. In the case of an outer race only, the shaft on which the bearing rides, must have a hardened bearing journal diameter.

Double Row Self-aligning Ball Bearing Name Function Double row Self‑aligning Ball Bearing Particularly suited to compensate for installation defects or shaft bending Spherical Roller Bearing Name Function Spherical Roller Bearing Designed to support heavy loads. Cope with alignment defect or shaft bending

Axial bearings and their functions (Also called Thrust Bearings) Thrust ball bearings Name Function Single row thrust Ball bearing Designed to support axial loads in one direction. Does not support radial loads. Name Function Double row thrust Ball bearing Designed to support axial loads in both directions. Does not support radial loads.

Thrust cylindrical roller bearings Name Function Roller Thrust Bearing Designed to support very high axial loads. Little sensitivity to shocks and space saving. Dual-Purpose Bearings and their functions Dual-Purpose Bearings are designed to support a combination of radial, axial, and angular loads.

Single-row Angular contact ball bearing Name Function Single row angular contact ball bearing. Support radial loads and axial loads in one direction only. Double-row Angular contact ball bearing Name Function Double row angular contact ball bearing. Support radial loads and axial loads in both directions.

Tapered Roller Bearing Name Function Tapered Roller Bearing Support radial loads and axial loads in one direction only. Typically used in pairs. Strongest bearing for combined loads. Bearing Symbols The following is a list of Bearing symbols typically found on Assembly drawings.

Fill these out using Handbook pages 39 to 44
Designed to support high speed and radial load, but can also take a bit of axial load Single Row Ball Bearing 1 Good 1 ±15’ Fair Excellent 0.88 Fair 1.08 ±3’ Excellent Fair 0.75 1.47 0º 0.94 Fair Fair 0.9 ±4º

Good in one direction 1 Good 1.19 0º Good in both directions 0.75 Excellent 1.42 0º Excellent in one direction 0.32 1.82 0º Excellent in both directions 0.30 2.17 0º

Excellent 0.94 1.94 ±5’ 0.94 Excellent 1.94 ±5’ 0.94 Excellent 1.94
1.94 ±5’ 0.94 Excellent 1.94 ±5’ Poor in one direction 0.94 Excellent 1.94 ±5’ 0.63 Excellent Fair 1.92 ±1º

0.88 Good 0.94 ±2’ 0.88 Good 0.94 ±2’ Good in one direction 0.63 Good 2.77 ±5’

Bearing Theory

Bearing Theory for Ball Bearings Lock the two outer races both radially and axially. Lock one inner race axially to locate the assembly. The second inner race remains free to float for thermal expansion and contraction. Round dot = axial lock - ex. shoulders, lock-nuts, circlips, end caps, spacers Heavy line = radial lock, interference fit

Lock the two outer races both radially and axially. Lock one inner race axially to locate the assembly. The second inner race remains free to float for thermal expansion and contraction.

To summarize Rotating Shaft Ball Bearing Theory: Interference fit on both inner races (Shaft toleranced at k6) Clearance fit on both outer races (housing toleranced at H7) Lock both inner races axially (KM nuts, circlips, etc.) Lock one outer race axially (End cap, circlip, etc.) Leave one outer race free to float for thermal expansion.

To summarize Rotating Housing Ball Bearing Theory Interference fit on both outer races (Housing toleranced at N7) Clearance fit on both inner races (shaft toleranced at g6) Lock both outer races axially (circlips, end caps, etc.) Lock one inner race axially (KM nut, circlip, etc.) Leave one inner race free to float for thermal expansion.

Bearing Theory (For Tapered Roller Bearings) Rotating Shaft: (“X” Mounting Configuration) Lock the two inner races (cones) both radially and axially. Position one outer race (cup) axially, and adjust the end-play with the other outer race, 0.07 to 0.12 mm - cold. (0.003” to 0.005”) The normal configuration for a rotating shaft assembly with tapered roller bearings is “X”.

Rotating Housing: (“O” mounting configuration) Lock the two outer races (cups) both radially and axially. Position one inner race (cone) axially, and adjust the end-play with the other inner race, 0.07 to 0.12 mm - cold. (0.003” to 0.005”) The normal configuration for a rotating housing assembly with tapered roller bearings is “O”.

Rotating Shaft Assembly - “X” Configuration

Rotating Housing Assembly - “O” Configuration

Rotating Shaft Assembly - “O” Configuration
Lock both outer races radially and axially. Position one inner race to locate the assembly. The second inner race is used to adjust end play to 0.0 mm (cold).

End of Chapter Seven Exit

07 – Bearings and Bushings

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