Copper Base Gears

Copper Base Gears

Alloys of copper are in wide use for power transmission gearing. Most of these are used in worm gearing where the reduced coefficient of friction between dissimilar materials and increased malleability are desired.

Gear Bronzes.
A family of four bronzes accounts for most of the nonferrous gear materials, mainly because of their “wear resistance” characteristics for withstanding a high sliding velocity with a steel worm gear.
- Phosphor or Tin Bronzes.
  These bronzes are tough and have good corrosion resistance. They possess excellent rubbing characteristics and wear resistance which permits use in gears and worm wheels for severe wear applications. This alloy is the basic gear alloy and is commonly designated as SAE C90700 (obsolete SAE 65) and is referred to as tin bronze.
- Manganese Bronzes.
  This is the name given to a family of high strength yellow brasses. They are characterized by high strength and hardness and are the toughest materials in the bronze family. They achieve mechanical properties through alloying without heat treatment. These bronzes have the same strength and ductility as annealed cast steel. They have good wear resistance but do not possess the same degree of corrosion resistance, wear ability or bearing quality as phosphor and aluminum
  bronzes.
- Aluminum Bronze.
  Aluminum bronze materials are similar to the manganese bronzes in toughness, but are lighter in weight and attain higher mechanical properties through heat treatment. As the strength of aluminum bronze is increased, ductility is reduced. This bronze has good wear resistance and has low coefficient of friction against steel. Bearing characteristics are better than for manganese bronze but are inferior to the phosphor bronzes.
- Silicon Bronzes.
  Silicon bronzes are commonly used in lightly loaded gearing for electrical applications because of their low cost and nonmagnetic properties.
Gear Brasses
Gear brasses are selected for their corrosion resistant properties. The most common gear brass is yellow brass, used because of its good machinability. Other brass materials are used because of their higher strength, but they are more difficult to machine. Wear resistance of these brasses is somewhat lower than for the higher strength manganese bronzes.
Wrought Copper Base.
Wrought copper base materials is a general term used to describe a group of mechanically shaped gear materials in
which copper is the major chemical component. This group of gear materials includes bronzes, brasses, and other copper alloys.
Cast Copper Base.
Copper base castings are specified by melting method, heat treatment, analysis or type, hardness and tensile properties.
- Cast Worm Bronzes.
  Specifications describe type of bronzes according to chemical analysis.
  Refer to the chemical analyses of common cast copper bronze alloys, including phosphor or tin bronze, leaded tin bronze (improved machinability) and higher strength manganese bronze and aluminum bronze.
- General Information for Copper Castings.
  Additional information regarding manufacturing, chemical analysis, heat treating, tensile properties, hardness and hardness control, cast structure and supplementary data for cast copper alloys is as follows:
  1. Casting Manufacture.
    Cast copper base gear materials may be melted by any commercially recognized melting method for the composition involved. Castings should be free of shrink, porosity, gas holes and entrapped sand in the tooth portion. Castings should also be furnished free of sand and extraneous appendages.
    Repair welding in other than the tooth portion may be performed by the casting supplier. Repair welds in the tooth area should be performed only with the approval of the gear manufacturer.
  2. Casting Heat Treating.
    Copper Base castings are heat treated as required to obtain the specified mechanical properties.
  3. Casting Chemical Analysis.
    Chemical analysis shall be in conformance with the type specified or as agreed to by the gear manufacturer and casting producer.
    The chemical analysis shall be determined from a sample obtained during pouring of the heat.
    The gear manufacturer may perform a product analysis for chemistry. In the event of disagreement in chemical analysis, ASTM Designation E54, Standard Methods of Chemical Analysis of Special Brasses and Bronzes, may be used as the referee method.
  4. Casting Hardness.
    Hardness tests are normally made in accordance with ASTM E10, Method of Test for Brinell Hardness of Metallic Materials.
    Hardness tests are to be made on the tooth portion of the part after final heat treatment, if required. The number of hardness tests made should be specified by the gear manufacturer.
  5. Casting Tensile Properties.
    Tensile tests are only required when specified. Tensile tests when specified are made in accordance with ASTM E8, Tension
    Testing of Metallic Materials. Tensile test bars for sand castings may be attached to casting or cast separately.
    Tensile test bars for static chill castings may be cast separately with a chill in the bottom of the test bar mold. Tensile test bars for centrifugal castings may be cast in a separate centrifugal mold for test bars or cast in a chill test bar mold.
    NOTE: An integral or separately cast test bar does not necessarily represent the properties obtained in the casting. The properties in the casting are dependent upon the size and design of the casting and foundry practice.
    Three test coupons shall be poured from each melt of metal or per 1000 lbs (454 kg) of melt except where the individual casting weighs more than 1000lbs (454 kg).
    Heat treated castings should have the test coupons heat treated in the same furnace loads as the casting they represent.
    One test specimen should be tested from each group of three test coupons cast. If this bar meets the tensile requirements, the lot should be accepted. If the first bar fails to meet the specified requirements, the two remaining specimens shall be tested. The average properties of these two bars must meet specified requirements for acceptance of the lot.
  6. Casting Hardness Control.
    The gear manufacturer can select at random any number of castings from a given lot to determine the hardness at
    or within 1 inch (25mm) of the cast OD or as indicated on gear manufacturer’s drawing. The lot should consist of all gears produced from one melt of metal. Determination of hardness at or near the root diameter is optional and should be agreed upon by the purchaser and gear manufacturer.
    The minimum hardness, using a 500 kg load, shall be 80 HB for static chill and centrifugal chill castings, and 70 HB for sand castings. The minimum hardness at or near the root diameter shall be agreed upon by the purchaser and the casting producer. Failure of any gear to meet hardness requirements specified is subject to rejection.
  7. Cast Structure.
    When required, the producer should furnish specified microspecimens or photomicrographs for each melt with the certificate of hardness, chemistry, and mechanical properties.
  8. Supplemental Data.
    The following supplementary requirement should apply only when specified by contractual agreement. Details of this supplementary requirement should be agreed upon by the casting producer and gear manufacturer.
    - With proper foundry technique, the properties of static chilled and centrifugal cast separate test bars should be the same.
    - An integral or a separate test bar simply signifies the melt quality poured into the mold to make the casting. It does not express the specific properties and characteristics of the casting which are greatly dependent on design, size, and foundry technique.
    - The grain size of cast copper base alloys varies as a function of cooling rate and section thickness.
      Recommended maximum grain size for centrifugal castings is 0.035 mm in the rim, 0.070 mm in the web and 0.120 mm in the hub. The grain size for copper base alloys is determined per ASTME 112 at 75X magnification.
    - The grain size of static cast copper base alloys should be mutually agreed upon by the consumer and producer with reference to the various sections of the castings and, in particular, the tooth section. It may be advisable to specify by use of photo micrographic standards both acceptable and non-acceptable phase distributions in the gear rim section.