Friday, August 26, 2016

Bearing Design Guide: Chapter Four: LOAD SPEED CATAGORIES AND USAGES-Day 5

Manganese bronzes: Extreme high-loads, low-speed.

Manganese bronzes are actually brasses since they are an alloy of primarily copper and zinc. They are the strongest and one of the more wear-resistant, non-heat-treatable alloys with high tensile strength, high yield strength, hardness and ductility similar to steel.

The manganese bronze alloys require mating with a hardened shaft, good finishes, good lubrication and larger running clearances than the other bronze alloys.

Since they also exhibit a short freezing range in solidification, they are used for permanent molded castings but not to the extent of the aluminum bronzes

The manganese bronzes have a high-compression strength suitable for vibration and heavy rolling contact but with speeds substantially below 250 fpm.

They are corrosion resistant and can be more economical than the heat-treated aluminum bronzes.
The average physical properties are:
Brinell hardness 180 to 225 BHN Coefficient of friction (dry) .25 to .35 Minimum shaft hardness 500 BHN
Maximum operating temperature 400 degrees F


   CDA             Tensile Strength PSI             Yield Strength PSI          Elongation %          BHN
    862                         90000                                    45000                                18                      180
    863                        120000                                   62000                                12                      225

Principal uses: Movable bridge bearings and plates, pump bodies, gears, roller-gate bearings, fixed wheel gates, sheaves hoists, crane wheels and off-road construction equipment and machinery, crushing machinery, and  permanent molded  products  as wear plates, pads, hinges, etc.
            Although CDA 865 Manganese bronze is in this family of brasses, the physical and mechanical properties are somewhat less than the above two, with tensile strength of 65,000 PSI, yield  strength of 45,000 PSI,   elongation of 20%, and a brinell hardness of 100 BHN. It can be used for surface speeds up to 250 fpm, with loads reasonably higher than the leaded bronze  and tin bronze alloys.  Since it has a short-freezing range in solidification in casting, it also can be used for permanent mold castings.

The preceding lists are intended as a working guide to the selection of various bronze alloys to meet certain speed-load categories for the greatest number of desireable properties they offer based on past usage.

Many other factors enter into the final decision and when each factor is refined, they will indicate the most promising alloy to be satisfactory  for that set of conditions.

Well...that's it for the Chapter 4: Load Speed Categories and Usages!  I hope ypu had a fun ride and now feel the need...THE NEED FOR SPEED!  

 Until next time my metal loving friends...

 Next Up: Week Five, Chapter 5:Bearing OD, Wall & Length Calculations

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