Bearing Design Guide: Chapter Twelve: Recommended Shafting and Journal Material

           The shaft or journal is the mating part of any bearing application and, therefore, requires ample consideration when mated with one of the many bronze alloys which have varying mechanical properties compatibility and hardnesses.

          The designer must first choose a shaft or journal material that will satisfy the applications requirements of torque, shear stress, fatigue strength, fracture toughness, rigidity, wear resistance, corrosion resistance and have the ability to provide a good surface finish and sufficient hardness.

          Various type of shaft or journal materials such as cast gray iron, modular iron, forged steel, induction hardened steel, case hardened, chrome-plated and polished steels are used.
The cast iron, gray and modular iron shafts offer low cost but since they do not pose all of the desirable shaft properties of steel, they have somewhat limited usage. Further, they require specific grinding and polishing instructions.
    
          The more popular shafting steels are mild SAE 1020 and low-carbon steels of SAE 1040. The highercarbon steels- AISI 1045, 1060,4140,4340, 52100 and M 50 tool steels and stress-proof steels are used after hardening, grinding and polishing finish.

                      The general range of such shafts are classified by hardness as follows:

                                                      Soft 165 BHN to 290 BHN
                                                      Medium 300 BHN to 390 BHN
                                                      Hard 400 BHN to 1000 BHN

          There are commercially available standard shafts which have soft cores but a sub-surface which is case hardened to various depths, chrome-plated and polished.

          Tests have proven that various hard bronze alloys, when mated with a soft shaft, will tend to seize or weld to the shaft at substantially lesser loads than when mated with a hard shaft.

          The harder shaft will permit an appreciably higher unit load to be sustained with a lower wear rateresulting in extending the life of the assembly.

          With the high leaded bronze aUoys, which range in hardness of 50 to 70 BHN, a soft or mild steel, or cold-rolled steel shaft ranging in hardnesses of 165 BHN to 290 BHN are a suitable combination.

          Shafts mated with the high copper-tin alloys which contain little or no lead having a range of hardnesses of 70 BHN to 80 BHN, would be adequately served by the medium shaft hardness range of 300 minimum.

           The aluminum bronze alloys, not heat-treated, with average hardness of 140 BHN to 170 BHN are best combined with the hard shaft category of 400 BHN minimum.

          Heat-treated aluminum bronze alloys, including the manganese bronzes with hardness ranges from 180 BHN to 240 BHN, require the shaft hardness range to be above 500 BHN or recommended to be used with shafts RC60 minimum being preferred.

          In bearing tests conducted by various sources, the results indicated that the harder shafts with the highest polished finishes offer the best combination for improved load carrying ability over the speed ranges tested with the lowest wear rate.
 
          Initially, most bronze alloys will show a high wear rate while "bedding" or "running in" but will level off to a more constant lower value.

          The surfuce finishes of the shaft have a profound effect in any bearing application on the lubricating mode.

          In full hydrodynamic conditions, the bronze bearing alloy should have a RMS finish in the range of 25 to 32 RMS and the shaft or journal held to polished to 6 RMS to 12 RMS.

          In mixed film conditions, the bronze bearing alloy can range between 32 RMS to 43 RMS and the journal polished to 8 RMS to 16 RMS. Since the bearing goes in and out of full hydrodynamic mode, the better the finish the less the initial wear.

          For boundary conditions, where the surface speed is much lower, the relative roughness of the bearing .and journal are not as critical. However, it is best to maintain at least a 43 RMS to 63 RMS finish on the bronze bearing and the journal to 32 maximum.

          A hardened and super finished shaft has the ability to double the load before seizure when compared to a soft shaft finished to 10 RMS under the same conditions. In loads over 3000 PSI, a 10 RMS shaft finish is recommended.

          In the case of sintered powdered metal self-lubricating bearings, a cold-rolled steel or mild steel shaft would be acceptable. However, a hardened carbon steel shaft such as C1137 with chrome-plating will double the PV factor while reducing shaft and bearing wear.

          Whenever a stainless steel shaft must be considered because of corrosion conditions, it is not
recommended that the 303 austenitic stainless series be used in combination with sintered bronze bearings unless it is chrome-plated or the sintered bearing is re-impregnated with a special lubricant containing oxidation and corrosion inhibiting additives.

          If a stainless steel shaft is necessary, it is recommended the 400 SS Series with the 440 C being the preferred shaft since it does not require the special lubes.

           Remember, in all cases, that the harder the shaft, the greater the load-capability and the better the surface finishes, the less the wear rate with longer bearing life. Shaft roundness and shaft size control without nicks, gouges or sharp edges will offer the most satisfactory performance.

 Next Up: Chapter Thirteen: Lubrication & Lubricants

And

Chapter Fourteen: Lubricant Selection

Bearing Design Guide: Chapters Eight through Eleven

Bearing Design Guide: Chapters Eight through Eleven

Since the next four chapters are on the short side and they all relate to Grooves, Grease & Graphite, I have decided to put them all together on this weeks post.  

Bearing Design Guide: Chapter Eight: Grooves for Grease and Graphite Filled Bearings

   

         The groove width (W) for grease lubricated bearings should be increased by 1/32" of that of oil grooves with depth (D) remaining the same or slightly deeper by 1/64".
          The wider grooves permit the shaft a longer contact period with the less mobile grease supply and permit a greater surface coverage of graphite filled grooves.













The suggested groove width (W) and depth (D) as shown below:



          Bearing ID           Groove Width              (W)       Groove Depth            (D)
             0.5                         3/32                     0.094           3/64                    0.046
             1                            5/32                     0.156           5/64                    0.078
             2                            3/16                     0.188           3/32                    0.094
             3                            1/4                       0.25             1/8                      0.125
             4                            9/32                     0.281           9/64                    0.14
             5                            5/16                     0.312           5/32                    0.156
             6                           13/32                    0.406           13/64                  0.205
             7                           15/32                    0.469           15/64                  0.234
             8                           17/32                    0.531           17/64                  0.265
             9                           19/32                    0.593           19/64                  0.296
            10                          21/32                    0.656           21/64                  0.328
            11                          23/32                    0.719           23/64                  0.36
            12-20                     25/32                    0.781           25/64                  0.39
     
         Since these grooves are not as critical as oil grooves, they can be toleranced looser to plus-or-minus 1/64 to plus-or-minus 1/32.

          In grease lubricated bearings where exposed to contaminants such as dirt, ash or other debris, it is advisable to provide an annular or circular groove near the end of the bearing within 1/8" to 1/411 to create a dam effect. Such an effect will act as a reasonable seal, preventing contaminants from entering the bearing surface.

Bearing Design Guide: Chapter Nine: Graphited and Solid Lubricated Bearings

          Solid lubricated bearings such as graphite or molybdenum disulfides are used in severe environmental situations where normal fluid or grease lubricants cannot be used because of abnormal temperatures which would tend to carbonize or freeze the lubricant to brittle solids.
        

         They find usage constantly in chemically-reactive environments, in nuclear radiation and vacuum environments and where normal lubricants cannot be tolerated. They also are used where there is limited access to resupplying the lubricant or where it can be neglected.
        

        These solid lubricants can be used in form of colloidal powders in suspension of a grease carrier or held and bonded by various binders.
        

        Graphite itself, although one of the most popular solid lubricants, requires some absorbable gases, moisture or hydrocarbon vapors to develop low-shear strength.
        

         The gases and water vapor in the normal atmosphere are usually sufficient to ensure an adequate supply of absorbable medium but a brief immersion in a heated oil eliminates chance.
         

          Graphite in excellent through temperatures ranges through 1000 degrees F but are generally not
satisfactory in high altitudes nor in a vacuum conditions since desorption occurs.
 

          Molybdenum disulfide is an excellent solid lubricant below 750 degrees For in a vacuum since it does not require presence of adsorbable vapors. However, above 750 degrees Fin the presence of air or oxygen, it deteriorates and becomes an abrasive. It is also more expensive than graphite so it has limited usage.

          As with graphite, molybdenum disulfide and the other solid lubricants require a binder to make it adhere to the bearing surface. There are various binders available that can be formulated.

         The thermoplastic resins such as cellulesic or acrylic resins are easily sprayed, fast drying, requiring no baking but are limited to 150 degrees F.

         The thermosetting phenolics have a service temperature of 400 degrees F with good adherence.

         The epoxy resins adhere well and are safer than phenolics being stable through 600 degrees F but requiring heat-curing.
 

         Some inorganic binders such as sodium silicate would exceed the 750 degrees F and would be suitable for graphite but limited to a lower temperature for molybdenum disulfide.

         For an economical solid lubricant containing bearings, the standard available sintered powdered metal bearing with 18% porosity offers an excellent surface for retaining graphite or molybdenum disulfide formulation that would require a burnish operation of the lubricant into the surface.

Molybdenum Disulfide-Natural State

Molybdenum Disulfide Powder

Molybdenum Disulfide Grease

Bearing Design Guide: Chapter Ten: Graphited Wall Thickness Calculation

Graphite Plugged Bearing

            Since the solid lubricant must be held in form of grooved configurations, plugs or sticks in a series of drilled holes, they require a substantial depth to be retained properly.

          The minimum wall thickness of groove-filled solid lubricated bearings can follow the width (Y'/) and depth (D) described in Chapter VIII. Plug lubricated bearings with a .5 diameter should be held to 3/16" minimum wall thickness and then increased 1/32" for each nominal half-size above. That is, for a 1" ID bearing, a wall thickness of 7/32" should be considered for plug graphited bearings.

Graphite Plugs

                     A general rule of thumb: wall thickness= .08D + 1/8'' (where Dis the bearing ID.)

          The overall length on solid lubricated sleeve bearings can range in various lengths depending on the load, speed, and type of the application. The normal recommended LID ratio is 1. 5. This is to minimize possible shaft deflection and to offer greater stability and surface area. The maximum LID ratio recommended should rarely exceed a ratio of 3 since misalignment edge-loading and frictional heat can be appreciably increased.

The accepted standard solid lubricant coverage should average 30 to 3 5% of the surface area. However, the calculation of plug size and lubricant coverage is shown below. The plug diameter and drill size should be no larger than the wall thickness but no less than half.

Graphite Sticks

                       CALCULATION OE LUBRICANT COVERAGE AND PLUG SIZE:
                                   Percentage of Graphite or Solid Lube Coverage

Drill Size        10%        15%       20%       25%         30%        35%        40%        45%        50%         3/16              8.95        13.43     17.9        22.38        26.85       31.33       36.81        40.28       44.5  

    1/4                5.03          7.54     10.05      12.57        15.08       17.6         20.11        22.62       25
    5/16              3.22          4.83       6.44        8.05          9.66       11.27       12.88        14.49      16.1

    3/8                2.23          3.35       4.47        5.59          6.7         7.82         8.94          10.06      11.1     

    7/16              1.64          2.46       3.28        4.1            4.92       5.75         6.57          7.39         8.2
    1/2                1.26          1.89       2.51        3.14          3.77       4.4           5.03          5.66         6.28
 

1. Choose the appropriate drill or plug size.
2. Locate the desired solid lubricant coverage
     Use factor number opposite drill or plug size
3. Multiply bushing ID x bushing length.
    Multiply factor number to obtain the number of holes or plugs.
 

Example: 2" ID x 2 112 OD x 2" length
 

1. 1/4 plug diameter
2. 35% coverage from chart 17.6
3. 2 x 2" length x 17.6 = 70 drilled holes or plugs.

 
                 Bearing Design Guide: Chapter Ten: Graphited Wall Thickness Calculation

           The running clearances for solid lubricated bearings must be substantially greater than in oil and grease lubricated bearings because the frictional heat generated is not dissipated.
          

          An allowance of .002 minimum per inch of diameter should be considered. Further, since solid lubricated bearings are not generally machined or bored after assembly 11close in11 of the ID must be allowed for. This allowance must be increased further if the bearing is to be used in abnormal temperature service to allow for expansion or contraction of the shaft.
 

          For more specific clearance allowances, use the attached calculation sheet either for normal temperatures or for abnormal temperature service. (Reference Chapter 6.)
 

Surfaces Finishes: Solid lubricated sleeve bearings do not require the high degree of surface finishes of oil lubricated bearings. The slightly rougher bearing ID finish is desirable to permit the solid lubricant to coat its surface. Therefore, a bearing surface ID finish of 63 RMS to 125 RMS should be satisfactory. The shaft finish, however, should be ground or polished smooth to approximately 32 RMS.

          Upon installation of the solid lubricated bearing, there will be instant wear until the shaft and bearing become coated with the solid lubricant. It would be advisable to submerge the graphited bearing in an oil bath of slightly heated oil to penetrate the plugs or filled graphite grooves to enhance its initial "running in" or "bedding in" to reduce this initial wear to an acceptable minimum.
 

          Note that the drilled and plugged holes do reduce the strength and structure of the bearing while adding to the cost.
    

          Many times it would be more economical to utilize filled groove configurations since they do not weaken the bearing to any noticeable degree.

         Although a solid lubricant can be retained in a serrated ID which can be broached for economy, tests have shown that such a structure weakens the lands in the bearing ID and limits the load and speed capabilities to less than 50 PSI and 30 fms.

General Information: Some commercially available solid lubricants containing compounds of graphite and molybdenum disulphide are sold by Lubriplate and Emhart Companies as Never-Seize and Dri-Slide.

         The coefficient of friction for solid lubricated bearings are appreciably higher than those for oil and grease ranging from .15 to .35 initially then reduced to a lower acceptable level.

Ok...I'm done.  I know that was a lot of information all at once, but I thought they should go together.  I have watched the plugging process a few times here in our warehouse and I gotta say it was pretty cool.  From sticking them in, to watching them get ground down to become one with the bearing or wear plate is a neat thing to watch.

I hope you find this as interesting as I do, that's it for now.  Until next time my metal loving friends...

Next Up: Chapter 12: Recommended Shafting and Journal Material

Bearing Design Guide: Chapter Seven: Oil Holes and Oil Grooves

          Oil?....Like vegetable oil?...olive oil??  Nooooo...don't be silly.  In this chapter we will learn about the different types of holes and grooves used to lubricate a bearing.

         Oil holes and oil grooves are important features of a journal bearing to introduce and distribute the lubricant adequately to the bearing surface as needed.

         Oil holes in the sleeve bearing are the simplest and most effective method in introducing the lubricant into the bearing area but must be located in the unloaded area of the bearing. The oil hole also can be located in the shaft. The oil entering through the shaft will be centrifuged into the sleeve-bearing area in the same amount or more.
         Grooving is rarely necessary in short bearings with an LID ratio of .5 or less unless high-surface speeds require a larger volume of oil to pass through to dissipate the frictional heat generated. In those cases, an annular or circular groove will enhance the results.

         For bearings with an L/D ration of 1 or more, oil grooves may be necessary depending upon the speed, load and type of lubricant viscosity.

         Grooves are generally required for grease lubricated bearings since grease does not have the mobility of oil nor does grease dissipate the frictional heat being generated.

         Oil inlet holes should be at least as wide as the groove it is supplying. Any smaller inlet hole can be blocked with sludge or other debris and result in restricting the lubricant from entering the bearing surface and starve the application which will result in failure.

         The oil inlet holes should be chamfered and have all edges rounded and broken to form unrestricted entrances for the lubricant to enter.
         All grooves should be blended and rounded to reduce the effects of sharp edges that interfere and scrape the lubricant and prevent the formation of an oil film.

          In high-speed bearings or pressure-lubricated bearings, a small "V" or vent groove may be added to remove entrapped air or permit dirt or other wear debris to escape and permit slight oil leakage to reduce frictional heat.

 Types of Grooving

Oil hole: A single oil hole without any grooving is commonly used in short bearings with an L/D ratio of .5 or less. Oil will flow axially unaided to each side of the oil inlet hole by as much as 1/2". The oil hole should be centrally located and in the unloaded area to ensure that oil is distributed equally to both sides.

The bearing with a single oil hole can have approximately three times the load bearing capacity then a bearing with an annular or circumferential groove in the same length bearing.

Straight axial groove: is used when the bearing length exceeds an L/D ratio of 1.5 but stops short of
each end by 1/8" to 1/4". The groove must be located in the unloaded area.

Circular or annular groove: is generally used when lubrication is pressure-fed or direction of load
varies and a low-pressure region cannot be located. This type of groove divides the bearing into two shorter bearings which do not carry the same load as a single bearing. When an annular or circumferential groove is used, it is important that it is placed exactly along the center of the bearing. If the groove is placed off center, then half of the bearing will tend to operate with a greater eccentricity than the other.

This groove can be used in combination with a straight axial groove but the axial groove must be located in the unloaded area.

The oil flow of a bearing with a circular groove is about 2.5 times that of a bearing with an oil hole only.

Oval groove: A single- or double-oval groove connected with an oil entry hole will distribute the
lubricant more positively and more copiously.

Although the groove passes angularly through the loaded area, only a small measure of load pressure will be affected. The oval groove also should run short of each end by 1/8" to 1/4" unless the lubricant is introduced from the bearing end, then that groove side should be open into the reservoir.

Figure-S Groove: is a modification of the double-oval groove and is generally preferred in grease
lubricated applications or to offer a greater exposure of graphite in graphited bearings.

The "V-Shaped" Groove: and radiused, cross-sectioned grooves are best suited for oil lubrication since the groove edges, blended or rounded, promote the formation of the oil film.

The Rectangular, Cross-Sectioned Groove: is better suited for grease and graphite or other solid
lubricants since it offers a larger surface area for the grease or graphite to adhere or offer a larger reservoir of grease.

If two bearings are used in line in an oil- or grease-lubricated mode, a central reservoir should be located between the two bearings by at least twice the wall thickness or more.

Any angular groove should be open only on the reservoir side if the lubricant is not introduced through the bearing length. Again, oil grooves or grease grooves should extend to within 1/8" to 1/4" of each bearing end when using a centrally-located inlet hole.

The groove width and depth will depend on the volume of oil which must pass through the bearing to
maintain the viscosity within the range of operating temperatures.

Precision-Groove Applications: The groove width (W) should be taken as .06 times the bearing bore diameter and the depth (D) to (.5W).

Medium-Groove Applications: The groove width (W) should be taken as .08 times the bearing bore
and depth (D) to (.5W).

Loose-Groove Applications: The groove width (W) can be taken as .10 times the bearing bore and
depth (D) to (.5W).

Although the generally-accepted print tolerances are usually given as plus-or-minus .005 to plus-or-minus .010, the width and depth can be specified in less restricted tolerances.

In general, the suggested widths and depths of oil-lubricated grooves can be taken as follows:

       Bearing ID                 Groove Width                (W)        Groove Depth            (D)
         0.5                                  1/16                      0.062              1/32               0.032
           1                                   1/8                        0.125              1/16               0.062
           2                                   5/32                      0.156              5/64               0.078
           3                                   3/16                      0.188              3/32               0.094
           4                                   1/4                        0.25                1/8                 0.125
           5                                   5/16                      0.312              5/32               0.156
           6                                   3/8                        0.375              3/16               0.188
           7                                   7/16                      0.437              7/32               0.219
           8                                   1/2                        0.5                  1/4                 0.25
           9                                   9/16                      0.562              9/32               0.281
         10                                   5/8                        0.625              5/16               0.312
         11                                   11/16                    0.687              11/32             0.344
         12-20                             3/4                        0.75                3/8                 0.375

Well that was GROOVY...Haha, ya see what I did there?!  Anyway, that's it for now.  Until next time my metal loving friends...

Next Up: Week Seven, Chapter 8:Grooves for Grease and Graphite-Filled Bearings

Bearing Design Guide: Chapter Six: Recommended Assembly and Retention Practices

         There are many methods used to assemble to retain sleeve bearings in an assembly to prevent movement under rotation and load in service. Some of these methods include bolting the bearing with a retainer, a lugged end plate, set screwing, knurled or coarse threading the sleeve OD, key retention or retained by cap screw, press fitting and shrink fitting.

         Although the latter two methods are the most popular and give the most positive, efficient, economical and simplest means with little or no specialized equipment being necessary, each method will be described briefly.




FIGURE 1: BOLTED:                                                              
The sleeve bearing is slip-fitted into the housing
against the shoulder in the housing bore. The
bolted plate is counter bored to permit the
bearing to be in contact with it; the bearing
length tolerance should not be greater than .005"
and ends must be parallel and square.












FIGURE 2:
Bearing pressed or slide fit into housing and
retained by lugged end plate. Slot is milled in
end of bearing to a depth of slightly below
bottom surface of the lug.











FIGURE 3:
Headless setscrew tightened against flat on
bearing. Be careful not to deform bearing. The
flat on the bearing is not necessary but the setscrew
will form a burr on the bearing surface
and make removal difficult. The setscrew may
be locked in by another screw or by locking
compound. Bearing can be press or slip fitted.







FIGURE 4:
Knurled or coarse-threaded outer surface used
where a die casting is to be made around the
bearing. Located one end surface of the bearing
flush with surface of housing.












FIGURE 5:
Bearing dimensioned for key retention. Key seat
depth 112 wall thickness or less on small and
medium bearings. Length is specified same as key
length but milling-cutter overrun is shown. Finish machine
inner surface after key is in place.









FIGURE 6:
Bearing pressed or slide fit into housing. Retained
by cap screw. Hole is drilled through wall of bearing.
End of cap screw is below inner surface of bearing.










Press-fit Method: The receiving hole or bore must be within certain described limits for a given method of installation or assembly.  Maximum surface contact for heat dissipation are of the utmost importance in high-speed applications, therefore a housing bore tolerance of .001" with a finish of approximately 32 RMS is recommended.

A housing bore of. 002 tolerance would generally have a finish of 63 RMS and a . 003 tolerance bore
would indicate a 125 RMS finish. This latter tolerance bore would be suitable for slow or negligible speeds with high loads.

The receiving hole or housing bore should always have an entry chamfer to facilitate bearing alignment and entry without excess shearing. The chamfer should never be greater than 40 degrees.

For press fitting, a shouldered arbor with a piloted shaft should be used with an arbor press to prevent
eschewing or tilting the sleeve bearing at press-fit operation.

Since the sleeve bearing ID will "close in" the bore after press-fit assembly, certain allowances or
adjustments may be required to the sleeve-bearing bore.

If the sleeve-bearing ID is to be used as is, then the ID should be adjusted for the "close in" depending upon the interference fit. (Refer to the calculation sheet attached to this chapter.)

If the bearing is to be used in a high-temperature service, less OD interference fit should be considered since the bronze will expand at a greater rate than the steel or cast iron housing. Further the shaft expansion must be calculated and the final bearing bore size must be adjusted. (Refer to the temperature calculation sheet attached to this chapter.)

If the bearing is to be used without machining, a thin-walled bearing (1/8" wall thickness in a 2" diameter bearing) will"close in" the ID approximately 80% to 100% of the interference fit.

A heavier-walled bearing (1/4" wall thickness in a 2" diameter bearing) will "close in" the ID 60% to 80% of the interference fit. (For full particulars, refer to the calculation sheets at the end of this chapter.)

A press fit should retain a bearing rigidly in a housing within the bronze alloys elastic limit. Excessive interference fit will prevent the intended results by deforming the bearing OD and giving it a permanent set which could result in the bearing working loose in the assembly under load and speed service.

Since bronze alloys have a higher coefficient of linear thermal expansion rate, i.e. leaded bronze (1 0. 8 X 10 -6) than a steel or cast iron housing (6.3 X 10 -6) operation from normal temperatures will require additional adjustment to the ID for these differences in expansion of mating parts. (Refer to the calculation sheet at the end of this chapter.)

In press fitting, a light coating of oil will generally prevent galling or shearing. The pressure in press
fitting must be applied uniformly and in one continuous motion. Do not use any driving means such as a hammer which tends to peen the end of the bearing and distort the ID.

The press-fit stress put on a cast bronze bearing for every .001" of interference fit is approximately
12,500 PSI. Therefore, a .001" minimum press fit allowance should be minimally sufficient for bearings up to 3" OD.

For bearings above 3" OD, use .002 minimum through 6" OD.

Click here to get an idea of how press-fitting works

Shrink fitting: If an arbor press is not available or its capacity is insufficient for the assembling force
necessary, the bronze bearing can be assembled by the shrink-fit method. This method requires chilling reduction of the bronze bearing or by causing a temperature increase of the housing bore by use of an induction heater. However, the plug induction heater may not be practical because of
the housing bulk. In lighter housings, a plug induction heater can be used to an advantage.

The shrink-fit method is used commonly, is economical and simple. It requires the sleeve bearing to be packed in dry ice or chilling it in a commercial deep-freeze, or more desirable, by direct immersion of the bearing in liquid nitrogen. Click here to see a video.

Liquid nitrogen is particularly suitable since it is inert and free of corrosion, fire or toxic hazard.
However, precautions should be taken to avoid contact with an employee's skin and it is advisable to have a ventilated space or area.

The time for chilling by immersion varies between 4 minutes for a 1" diameter bearing to contract for a .001" of interference fit to an hour for a 10" diameter bearing to contract for a .005" interference fit.




                                                   Calculation for Temperature
                                                    Adjustment of Bearing ID

Maximum Operating Temperature = __ (-) 70° F = __ .AT° F

Bushing OD & Housing Bore Expansion:

LB= 10.8 X 10-6 (Leaded Bronze)
AB= 9.0 X 10-6 (Aluminum Bronze)
S= 6.3 X 10 -6 (Stl. Housing & Shaft)

Maximum Bushing OD_____X______AT°F X _______ = _______
                                                                                  B
Minimum Housing Bore ______ X ______ AT° F X_______ = (-)_______
                                                                                         S
Net ID Restriction From Press Fit & Temperature .................. = ________

Shaft Diameter Expansion:

Shaft Diameter ______ X ______ AT° F X ________=________
                                                                            S
Net Total Expansion Adjustments(+) ....................................... __________

Running Clearance Allowance:
* . 0015 per inch of diameter (graphite lube)
* . 0025 per inch of diameter (or other solid lube)
* Allowance based on size and temperature

Shaft diameter at room temperature _____ X _____ = _____

Bushing ID adjustment for "close in" and temperature:

Shaft diameter@ room temperature = ________
Net total expansion adjustment = _________
Running clearance allowance = _________
Net bushing ID adjustment = _________Minimum ___________Maximum


                                    Calculations for determining bearing ID
                                      Before press fit "close in" adjustment
 
Interference fit:
Bushing OD:     ________Maximum ________Minimum
Housing Bore:   ________Minimum ________Maximum
Interference Fit: ________Maximum ________Minimum

"Close in" Calculations:
Thin wall approximately 80 % to 100%
Heavy wall approximately 60% to 80%

Maximum amount of "close in" expected: ______ % X _______ = Int. Fit ______
Mininimum amount of "close in" expected: ______% X _______ = Int. Fit ______

Running Clearance Allowance:
* .001" per inch of diameter (oil)
* .0015" per inch of diameter (grease)
* .0020" per inch of diameter (graphite)

Shaft diameter: _________ X ________ Clearance allowance = _______

Bushing ID Before Press Fit:

Shaft Diameter        ________Maximum ________Minimum
"Close in"                ________Minimum ________Maximum
Running Clearance  ________--------__________--------
Bushing ID              ________Minimum ________Maximum


Who would've thought there were so many different ways to place a bearing into a machine.  We take so many things for granted these days and don't realize the hard work that goes behind it.  It sure opened my eyes and taught me to appreciate things more in all aspects of my life.  

Well, I say goodbye for now.  Until next time my metal loving friends...

Next Up: Week Seven, Chapter 7:Oil Holes and Oil Grooves