Tuesday, October 18, 2016

Bearing Design Guide: Chapter Fifteen: Comparative Casting Methods

      When I first starting working here and learning the industry, whenever I would think about molds and castings I would automatically picture Play-Doh in my head.  I mean its a little messy, but seriously, who doesn't like playing with it?  I'm a grown woman and still can't keep my hands off it when my kids have it out.  You can basically manipulate that stuff into whatever shape or form you want and how cool is that?!   Here at Atlas, it just puts that end result on a bigger scale and there are so many more methods of casting your material to get to the desired finished product.

         I love learning about new things and teaching others too whenever I can.  About four years ago I had the opportunity to go to a local elementary school and help the 2nd grade class learn about mass, matter, solids and liquids and just how material can go from solids, to liquids, and right back to solids again.  So instead of Play-Doh...I had a better idea.

          When I was explaining to them that a customer can come to us and ask us to make something for them in the exact shape and size that they want, I decided to show them what I meant.  In order to give the kids a visualization, I decided to bring in some candy melts and candy molds.  As the candy melted in the pot the kids were amazed just how quickly the candy melted.  Once it was ready I showed them the candy mold and started to fill them with the melted chocolate just as if we were pouring molten metal into a mold.  And, just like that with in seconds it began to harden and take a solid form again in the exact shape of the candy mold.

          Needless to say they were pretty amazed and of course a little more excited about the candy treat they were about to have.

          There are various casting methods available for casting ferrous and non-ferrous metals. A brief
description of each follows with a listing of advantages and disadvantages as well as other pertinent data.

Sand Casting: Moist bonded sand or resin coated sand is packed around a wood or metal pattern of the item or items to be cast. The pattern is removed and the cavity or cavities are filled with the molten bronze.

          Following the air cooling of the mold, the casting or castings are removed to be cut or sheared off from the gate and runner as individual castings. Watch the video below.


          Advantages: Any metal can be cast -ferrous or non-ferrous- without limitations to size, weight or shape. It is one of the most versatile and low-cost methods available including tooling costs. This method is economical and suitable for low to unlimited quantities.

          Disadvantages: Close tolerances are difficult to achieve and some machining may always be necessary. Interconnected porosity is generally inherent to this process and a fairly rough surface finish averaging 1000 RMS is obtained. The typical tolerances range from plus-or-minus 1/32 to as much as plus-or-minus .090 and greater across parting lines.

     Permanent Mold Casting: The mold cavities are machined out of a nickel steel or cast-iron die blocks since they are designed for repetitive use. Generally, steel cores are used although sand cores of intricate design can be used. Because of the casting heat, the sand cores are expended while the steel cores can be expected to give reasonable life before they are replaced. The mold halves are clamped together and the molten bronze poured into the cavity by gravity without turbulence or under a low-vacuum pressure.

          The mold is opened within a few seconds following approximately a 50-degree drop from casting, temperature with aluminum bronze or manganese bronze alloys. The casting with gate and riser is ejected immediately.

          Advantages: Good dimensional accuracy is obtained, good grain size and structure results from the rapid chill. Casting tolerances possible range from plus-or-minus .010 to plus-or-minus .015 per side or surface and parting lines can beheld to about plus-or-minus .030.

Casting variations from casting are rarely existent except after tooling begins to show signs of wear.

          Disadvantages: This method is normally limited to non-ferrous alloys. Size, shape and intricacies also are somewhat limited, although many sections can be cast thinner than sand castings. To justify this method, a moderate volume of 1,000 through 50,000 pieces yearly would be necessary to offset expensive tooling costs. Each individual casting must have a gate and riser which reduces the effectiveness of the yield.

          Centrifugal Casting: In this process of casting, steel or cast-iron dies are used and the molten metal is poured into the rotating or spinning die. After pouring, a water spray is directed onto the rotating die, cooling it more rapidly.


           Advantages: Since the molten metal is forced by centrifugal action of the rotating die, the metal thus centrifuged is free of porosity, more dense with a structure designed to carry heavy loads with impacts. The alloy cast in this method can withstand substantial hydraulic pressures without leaking. This method is suitable for ferrous and non-ferrous alloys.

          Disadvantages: Although a controlled stock allowance is set by the die, a machining operation is generally required to remove the rough surface finish and excess stock.

         Continuous Cast Method: In this process, the die is made out of carbon graphite which is surrounded by a cooling jacket through which water flows to chill and solidify the cast tube, bar or shape. As it exits from the furnace proper by gravity, the casting solidifies. It is pulled out slowly by pull rolls or pinch rolls. This rapid cooling reduces the grain size and as the casting exits from the lower section of the holding furnace, a homogeneous micro-structure is obtained.

           Advantages: A minimum of stock allowance can be controlled to plus-or-minus . 015 reducing the amount of machining necessary as in other methods. Various shapes are cast reasonably to size without need for precision machining. The resulting structure is generally suitable for acceptance by radiographic tests and will withstand a substantial hydraulic pressure without leaking.

           Disadvantages: Initial high unit cost investment and space; graphite dies must be replaced after each run and each size requires a cooling jacket.

Die Casting: Molten metal is forced into closed steel dies at high velocities by application of pressure.


          Advantages: Excellent dimensional accuracy is obtained across parting lines plus-or-minus .005 and plus-or-minus .001 to plus-or-minus .003 across extremities and surface finishes 100 RMS or less.

          Disadvantages: This process requires high volumes of20,000 to a million pieces or more since the relative die cast is extensively high. It also is limited to non-ferrous metals and porosity may be encountered as a result of entrapped air in the die. Size is limited to 3 feet square and under 15.0 pounds.

           Investment Casting: Various ferrous and non-ferrous materials are used to make a wax or thermoplastic pattern which is expendable in the process. Hot wax or plastic is injected to make a pattern under pressure into the die and multiple patterns are mounted on a common sprull made of the same material. The assembly, called a tree, is dipped into a liquid surry followed by several immersions in dry fluidized bed of fine sand. Each dipping operation requires drying time. As many as five to eight clippings are required to build a shell around the tree. For wax removal, the tree is placed into a steam autoclave. Before pouring, the molds are kiln-dried and tongued from the furnace to the pouring box and poured while cherry red.

          Advantages: There is no parting line and no draft. The surface finishes are less than 125 RMS and shapes are cast which couldn't be produced by other methods. This process becomes most economical when two or three machining operations can be eliminated. The typical tolerances are usually plus-or-minus .005 and high volume is not a criterion. Tooling is less costly than pressure-die casting.

          Disadvantages: Although this method has the fewest design limitations of shapes, size or design, pound for pound the cost of this process is comparatively high.

          There are several other methods of casting which include shell molding as a modified sand casting which offers closer tolerances as plus-or-minus .007 to .015. The surface finish is much better than sand casting and there is better definition of details such as lettering, etc. The cost of pattern equipment is higher than for sand casting and the process necessitates higher quantities.

  Plaster molding and ceramic mold casting are similar to investment casting. But the molding material is more expensive and the processes have never been suitably automated to reduce the labor intensity of making the molds. The casting tolerances are reasonably close to investment casting.

          I have to tell you this was the best post I have done so far!  Watching all the videos was so much fun.  I hope you enjoyed learning about the different options of casting and watching how all of the processes are done.

Well...that's it for today.  I say goodbye for now.  Until next time my metal loving friends...

Next Up: Chapter 16:Effect of the Casting Method on Bronze Alloys

Monday, October 3, 2016

Bearing Design Guide: Chapters Thirteen and Fourteen

Bearing Design Guide: Chapters Thirteen and Fourteen

The next two chapters focus on lubrication and lubricants so I have paired them up for this weeks post.

Bearing Design Guide: Chapter Thirteen: Lubrication & Lubricants

          The importance of an oil depends mainly on its film forming ability which depends further on its viscosity.

         An oil of lowest viscosity is generally more suitable for an application since a higher viscosity oil will waste power to overcome the internal friction of the oil itself

          There are many ways to supply a lubricant to a bearing.  We will explore the different options below.


      Pressure lubrication is probably the most positive and efficient means to provide lubricant to a bearing.
In addition to offering a more copious supply of oil lubricant, up to an average pressure of 50 PSI, it coats the bearing, maintaining a more stable viscosity range and it assists in flushing out dirt and wear debris from the bearing surface.


  Oil bath lubrication is where the bearing is submerged in oil which makes it the next reliable method to the pressure-fed oil. The shaft speed should not be so great as to cause excessive churning of the oil.

          Splash-fed lubrication involves the oil being splattered onto the bearing surface by movement of other adjacent parts. The housing should be reasonably oil-tight to prevent excessive loss and leakage of the lubricant.



Oil ring lubrication involves a revolving or processing ring on a shaft in contact with the oil sump. When the shaft is at low speed, sufficient oil may not be brought to the bearing surface or if the shaft speed is too great, the oil will be centrifuged beyond where it is needed. It also may not keep pace with the oil required.

          For best results, it has been proposed that the peripheral speed should be in the range of 200 to 2000 feet per minute. The safe load based on full hydrodynamic lubrication mode should be reduced by one half of pressure lubricated bearings.

          Wick or waste-pack lubrication delivers oil to a bearing surface by capillary action of a wick or waste-pack as done in many old railroad axles using bobbitted bronze backed partial sleeve bearings.


          The safe load when compared with pressure-fed full hydrodynamic load should be reduced to 1/4 of the load.

         Grease-packed bearings: Grease is generally packed to surround the bearing and although is substantially less effective than oil, it is much more permanent but the bearing will generally operate in boundary conditions.

Bearing Design Guide: Chapter Fourteen: Lubricant Selection

           The selection of a lubricant is based on various factors such as the type of operation, whether full hydrodynamic, mixed film or boundary film conditions in addition to the surface speed and bearing load involved.
          Various lubricant articles suggest some recommended viscosities for specific services.
          As a rule of thumb, the following suggested viscosities should be considered on the basis of surface speed with a qualified load.

                                Speed(fpm)                 Viscosity(sus)                   SAE Oil
                                 30 or less                       1200-1800                           80
                                 70                                    800-1200                           70
                                 150                                  500-800                             60
                                 300                                  300-500                             50
                                 600                                  150-300                             40
                                 1200                                120-150                             30
                                 2400                                  90-120                             20
                                 5000                                  40-90                               10
                                 over 5000                            5-40                                 5

          As a general rule of thumb, heavier oils are recommended for high loads and lighter oils for high speeds.
          In order to obtain a quick conversion of viscosity (sus) to centistokes (cSt), multiply the (cSt) value by 5. The multiple will be the approximate (sus) value.

         To obtain the (cSt) value, divide the (sus) value by 5.

         These results are reported to be accurate within 7% in the range of75 to 7000 (sus) and 15 to 1500 (cSt).

          But also be cautioned that this assumption should not be used below 75 (sus) or 15 (cSt).

          For more explicit lubrication data, we suggest you refer to the CBBI manual or to the Machine Design article of March 10, 1966.

I hope this weeks post wasn't too DRY for you and this helped you learn about lubricating methods with ease.  Anyway, that's it for now.  Until next time my metal loving friends...

Next Up: Chapter 15: Comparative Casting Methods

Tuesday, September 27, 2016

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
Chapter Fourteen: Lubricant Selection

Monday, September 19, 2016

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

                                   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

Monday, September 12, 2016

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

Tuesday, September 6, 2016

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.

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.

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.

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.

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.