Wednesday, December 28, 2016

Bearing Design Guide: Chapter Twenty-Three: CBBI Manual Bearing Procedure and Notes

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1. Identify the particular application from Fig. 6 through 10 in the CBBI Manual.

2. Pick up the recommended value for M from the type of machinery application.

3. A= M(squared)W I D(squared)Z N

 W = load in pounds
 D = diameter of shaft or bush ID
 Z = absolute viscosity ( centipoises)
 A = characteristic number

a. Assume an operating temperature

b. Z can be determined for the lube at assumed temperature T(2)

c. A fair approximate of lubricant temperature rise can be made.
Forced feed or pressure lubrication, temperature rise will average between 5 and 10 degrees F, if less oil is supplied bearing will run hotter, thus for other lubricating techniques, such as oil bath, splash feed and ring oiling, lubricant may rise from 1 0 to 1 00 degrees F.

d. After substitution, if "A" falls in the range of .0005 and .50, practical full-film lubrication is possible.

A large value for "N' indicates a heavily-loaded or slow-speed bearing.

Conversely, light loads and high speeds, a very low "A" number will be obtained.

With a light load or no load, eccentricity ratio "e" will be zero and centered.

As the load increases, the journal moves eccentrically.

While eccentricity "e" is increasing, the minimum film thickness (Ho) is decreasing.
Ho = c-e = c (i-e)

If the load becomes great enough, the journal may eventually touch the bearing for this condition:
"e" = c, (Ho) = 0.

Once the bearing characteristic number is determined, a suitable length for the bearing can be determined.


Hydrodynamic Mode:
1. Surface velocity in excess of 25 FPM
2. Coefficient of friction is .001-.005
3. Proper viscosity of lube
4. Proper lube flows
5. Proper design methods

Mixed film/Lubrication Mode:
1. Surface velocity in excess of 10 FPM
2. Coefficient of friction .02-.08
3. Journal BRG goes through all three modes

Boundry Lubrication Mode:
1. Generally slow rotary motion, less than 10 FPM
2. Oscillating motion
3. Coefficient of friction .08-.14
4. Generally grease lubricated

Press Fits or Shrinkage Fits:
1. Generally . 00 1" minimum press fit should be sufficient for ODS up to 3" OD
2. Adjust press fit for bearings through 6" OD to about .002 minimum
3. Following a press fit or shrinkage fit, the bearing ID will close in on the ID by 100% of the press fit allow. Heavier wall bearings will average 60 to 80% close in based on the interference fit allowance.

Bearing Retention Methods:
1. Press fit or shrinkage fit
2. Set screws
3. Woodruff keys
4. Bolted through flange
5. Threaded/screwed bearing

Clearance Allowances:

1. Machined bearings with ground journals for use in steam turbines, generators, etc., usually have a running clearance of. 001 per inch of shaft diameter.
2. Clearances of .0015 through .0035/ inch of diameter are used for grease and solid lube conditions.

Thank you for joining me on this journey.  Although we are done with The Bearing Design Guide, don't be sad.  I have more exciting things coming in the New Year!

That's all for now.  Until 2017 my metal loving friends! 

Mechanical Bronzes (Brass World & Platers Guide, March 1924)
Development in Centrifugal Casting (Metal Industry, Aug. 1939)
Wear and Surface Finish (Gisholt Machine Co. 1947)
Plain Bearing Recommended Practice (AISI April1951)
·Bearing Materials and Properties (Machine Design March 1966)
Cast Bearings (Machine Design March 1966)
The Science ofTribology (CDA London Engineer 1969)
Plain Bearing (Machine Design Jtme 1970)
How to Install Plain Bearings (Power Transmission Nov. 1970)
Plain and Premounted Sleeve Bearings (Machine Design June 197 4)
Copper Alloy Casting Design (CDA United Kingdom)
Boundary Lubricated Sleeve Bearings (Battelle, Columbus, Ohio)
Wear of Cast Bronze Bearings (Incra Aug. 197 6)
Physical Properties of Copper Alloys (Casting Engineering 197 6-77)
Wear Properties of Heavily-loaded Copper-based Bearing Alloys
Power Transmission Design (1994)
When Designing Journal Bearings (Bruce Dunham, Sun Oil Co.)
Bearing Design & Applications (Wilcox, Booser, McGraw-Hill, 1957

Thursday, December 22, 2016

A Christmas Story Moment "Stuck" In History


Stuck? Stuck?! STUCK! STUCK!  Come back! Don't leave me, come back!
           Who doesn't remember the iconic scene from the movie A Christmas Story where Flick, while surrounded by his instigating school pals in the school yard at Warren G. Harding Elementary School, got his tongue stuck to a pole. In my opinion, its one of the best scenes in the movie.

          Apparently I'm not the only one that thinks its a classic. The small town of Hammond, Indiana where the movie was filmed and where the incident took place felt it needed a permanent reminder of the classic.

          In 2013, on the films 30th anniversary a bronze statue was erected capturing the moment perfectly.  The statue was brought to its new home in a shipping crate appropriately marked with "Fragile" just like Ralphie's fathers "major award", the famous Leg Lamp. A grand Celebration was had and who better to debut the statue was none other than A Christmas Story's own Flick, also know as actor Scott Schwartz.

Scott Schwartz having fun with the statue
          The statue sits in front of the Welcome Center in Hammond, Indiana just off Interstate 80-94.  Travelers are encouraged to visit, but might not want to try and re-enact the famous scene because this flag pole is made of metal and you could very well get your tongue stuck if you try.

          So...take a night this holiday season and watch A Christmas Story, or if you're feeling adventurous, take a trip to visit the now famous landmark.

         I triple dog dare you...


Monday, December 19, 2016

Bearing Design Guide: Chapter Twenty-Two: Soldering, Brazing and Welding of Bronze Alloys

          Copper-based alloys, like other metals, occasionally require joining by soldering, brazing and welding. The following is intended to assist in those procedures.
          In soft soldering, the low melting solders of tin and lead, in varying proportions, are used to join bronzes at relatively low temperatures well below the melting point of the bronze alloy or its lead content (if the lead content is 3% or less). The solders most generally used are the 60 tin and 40 lead solder which melts at 374 degrees F and the 50 tin and 50 lead solder which melts at 477 degrees F.  You can see a great detailed example of this here.

          Soldering is used to provide a convenient joint that does not require any great mechanical strength. It is used in combination with mechanical staking, crimping or folding and used to seal against leakage or to assure electrical contact.

          Fluxes for soldering: Soldering requires the metals being joined to be clean and fluxes clean the surface by removing the oxide coating present, keep the area clean by preventing formation of oxide films and lower the surface tension of the solder by increasing its wetting properties.

          Rosin, tallow and stearic acid are mild fluxes but are not too effective in removing oxides present. Zinc chloride and ammonium chloride used separately or in combination will remove oxide films readily, however, this flux residue must be removed or neutralized to prevent their corrosive effects. Washing with water or with commercial water soluble detergents will neutralize any further corrosive effects.

          Methods of application: Soldering can be done with a soldering iron, a torch, electric induction or resistance heating. There are no special techniques used to solder except the usual precautions of cleanliness and fit of mating surfaces. The advantage of soldering is a low-temperature process, good manual application, no fusion of parent metals, and, therefore, no warpage. It is applicable to most copper-based alloys (with less than 3% lead) with minimum finishing requirements being necessary.

          Brazing is a method of joining two metals through the use of heat and a filler metal below the melting point of the metals being joined. Brazing creates a metallurgical bond between the filler metal and the surfaces of the two metals being joined.

          Again, here in order to obtain a sound joint, the surfaces in the join and around it must be free from oil, dirt and oxides. Cleaning can be achieved by chemical means such as using trisodium phosphate, carbon tetrachloride and trichlorethlene for chemical method and the use of filing, grinding, machining or sand-blasting for mechanical means of cleaning.

          Fluxes are used mainly to prevent formation of oxides and to remove oxides from the base and filter metals and to promote free flow of the filler metal.

          We're in the home stretch.  Only ONE more chapter to go!  Be sure to check out the Blog on Thursday the 22nd for a special Christmas edition of Metalchic.

That is all for today...Until next time, my metal loving friends!

Next Up: Chapter 23: CBBI Manual Bearing Procedure and Notes

Monday, December 12, 2016

Bearing Design Guide: Chapter Twenty-One: Corrosion Resistance Of Some Bronzes

We are going to continue with our chapter, but first a little announcement...

And now onto...Bearing Design Guide: Chapter Twenty-One: Corrosion Resistance Of Some Bronzes

          Corrosion is defined as the eroding of a metal as a result of a reaction with its environment, or exposure to various liquids or gases.

          Some metals and alloys are naturally resistant to certain corrosive environments. The product of a corrosive film which forms when metals are subjected to corrosive attack protects them from speedy damage by virtue of this protective oxide film.

          Corrosion can occur in bronzes as a result of slow dissolution of copper and copper alloys either because no protective film is formed or because as fast as a film is formed, it enters into solution in the corroding medium.

          Outdoors, copper and copper alloys develop a relatively protective skin of sulfides, oxides or soot. The sulfides form as a result of a reaction with sulfuric acid in the atmosphere and oxides as a result of a reaction with oxygen in the air. These reactions speed up in humid and rainy climates. They would cease entirely in the absence of water.

          Galvanic corrosion is caused by compounds which are electrical conductors when in solution in water and are known as electrolytes. The ions in these electrolytes are ever ready to conduct electricity if an anode (the positive ion) and cathode (the negative ion) of any type are present.

           Solutions of carbon dioxide, sulfur dioxide, oxygen, chlorides and fluorides are condensed or precipitated from the atmosphere. When a metal is to be used where there is an electrolytes as in sea water, the coupling of metals must be close together in the EMF series; to reduce the tendency to corrode the least nobler (cathodic) material.

          Galvanic corrosion often can be prevented by separating the less noble material by insulating it with rubber or synthetic resins.

           Although aluminum alone as a base material possesses good corrosion resistance to dry atmospheres, it actually corrodes very rapidly until a surface film forms. The surface film arrests further action to sea water, many fresh waters, chemicals and foods.

          This oxide film is extremely thin and, when damaged or scratched, corrosion will reform another thin film. Aluminum, therefore, depends on the resistance of the formed oxide film to attack rather than to the base metal.

          If aluminum is coupled with a copper-based alloy as bronze in a wet atmosphere, such as in marine environments, corrosion of the aluminum will continue unabated and would be an unfavorable galvanic couple. However, in a dry atmosphere, there is no precipitable galvanic action encountered.

          The high-leaded tin bronzes, leaded tin bronzes and tin bronzes have poor resistance to most acids but good resistance to sea water, fresh water, gasolines, fuel oils, alcohols, Freons and many other mediums. But it is recommended that the copper alloys be tin-coated or plated.

          For the most corrosive resistant alloys, the aluminum bronze alloys offer the greatest protection. The aluminum bronze alloys are used for their strength primarily and extensively used in general outdoors, marine service and exposure to many acids.

Galvanic Corrosion On Propeller

          A brief list follows showing the acceptable and non-acceptable exposure to various corrosive medium by aluminum bronzes.

          In the case of manganese bronzes, which contain less than 80% copper, zinc is selectively removed from the alloy by most acids when diluted in water. Manganese bronzes can be used for marine applications, water pump rotors and in sea water.

That's it for today.  Until next time my metal loving friends...

Next Up: Chapter 22: Soldering, Brazing and Welding Of Bronze Alloys

Wednesday, December 7, 2016

Bearing Design Guide: Chapter Twenty: Thrust Bearings or Washers

We are going to continue with our chapter, but first a little announcement...

And now onto...Bearing Design Guide: Chapter Twenty: Thrust Bearings or Washers


          There are three basic types of thrust washers which are defined by their mode of operation. Thrust bearings designed correctly to operate under either one of the following modes have theoretical justification for their load capacities.

          1. Flat boundary lubricated 100 PSI.
          2. Flat thermal wedge, hydrodynamically lubricated 1200 PSI.
          3. Contoured wedge, hydrodynamically lubricated 5000 PSI.

          However, in actual practice, these values are not achieved other than in theoretical design. In practice, the load capacity of each reduce to about 60% of theoretical values of 60 PSI, 700 PSI and 3000 PSI.

         For the greater majority of flat thrust washers, it is impossible to prevent some degree of hydrodynamic lubrication so that even in the worst design, the allowable loading will be greater than 60 PSI.

         In conditions of a sparse oil supply mated with steel, the high leaded tin bronze alloys (20% or greater lead content) are much more capable of satisfactory service providing their is no large amount of dirt or debris.

         If there is a fair amount of dirt present which is fairly coarse in particle size and movement or motion is infrequent or slow, the lower content leaded tin bronze alloys (20% or less) are preferred.

          For un-lubricated applications against steel, the preferred thrust washer materials are the sintered powdered bronze oil impregnated or Teflon-coated and plastic materials.

         For applications in which the non-lubricating film such as water or silicone fluids are present, the preference should be for Teflon-coated or impregnated bronzes or plastics.

         Oil Distribution Grooves: These are grooves that separate each sector of the thrust washers. The grooves must not go completely across the thrust face of the washer unless the thrust washer is completely immersed in the lubricant.

          If the lubricant is supplied at the ID of the washer, then the grooves should extend from the ID going outward covering about 80% of the distance to the outer edge.

         If the direction of rotation can be in either direction, the grooves should be radial; but if the direction of the rotation is fixed, the grooves should be slanted so that the viscous drag of the rotation will pull the lubricant into the groove in the direction of movement. The slanted angle should be between 10 to 40 degrees to the diameter.

          If the lubricant is supplied from the outer circumference (which is an undesirable condition) then the grooves must be slanted 20 to 60 degrees; but if the grooves are in the stationery member, they should be pointed in the direction of the rotation; if the grooves are on the moving member, they should be pointed against the direction of the rotation.

          Oil Collection Grooves: These grooves, like spreading grooves, should only go part way across the surface from 50 to 80% of the distance is suitable. They also should be slanted in the same direction as the oil-spreading grooves. These grooves are positioned just before the oil distribution grooves if the washer is supplied with oil from the ID.

          Oil Groove Dimension: The length of the groove is controlled by the degree of slant and should go about 80 to 90 % of the way across the annular surface.

          The groove cross-section should be in the form of a wide "V" to promote the formation of an oil film or a tear-drop design which blends into the surface.

          The thrust washer with grooves such as through grooves, tear-drop (or stopped oft) and tapered land grooves are superior to a plain washer. By adding four through grooves to the plain washer, the oil flow increases across the thrust surface and the load-carrying capacity increases by 30%.

          While restricting total oil flow through the washer with tear-drop grooves, an 85% increase can be obtained.

          With the tapered land groove which promotes an oil wedge, the increase in load-carrying capacity increases to 3 00% of a plain washer.

          According to theory, if the plain washer is perfectly flat, it would have no load capacity so surface waviness is not undesirable if it is fitted into a rigid aligned housing.

          The speed of operation of a thrust washer is not generally a problem if the surface speed is at least 25 fpm. At very high speeds - above 2000 to 4000 fpm - it may become a problem to supply ample lubricant although there is a compensating advantage of realizing a higher unit load. There also is the possibility of the oil carbonizing at this high speed, depending upon the load.

          Lubricant is important since the higher viscosity lubes such as SAE 50 offer greater chances that hydrodynamic film formation will be realized.

         The normal hydrocarbon oil lubricants are suitable for washers but the non-polymer modified oils are preferred for their higher viscosity.

          We are coming down to the home stretch, only three more chapters to go.  I know its a lot of information and a lot to take in, but if I have helped one person with this, I will be happy.  

That's it for today.  Until next time my metal loving friends...

Next Up: Chapter 21: Corrosion Resistance of Some Bronzes