4. Materials Selection Guidelines
4.10 Copper Base Gearing
Al-loys 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.
4.10.1 Gear Bronzes. A family of four bronzes accounts for most of the nonferrous gear materials, mainly because of their “wear resistance” character-istics for withstanding a high sliding velocity with a steel worm gear.
(1) Phosphor or Tin Bronzes. These bronzes are tough and have good corrosion resistance. They pos-sess excellent rubbing characteristics and wear resis-tance 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.
(2) 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, wearability
or bearing quality as phosphor and aluminum bronzes.
(3) Aluminum Bronze. Aluminum bronze mate-rials are similar to the manganese bronzes in tough-ness, but are lighter in weight and attain higher me-chanical 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.
(4) Silicon Bronzes. Silicon bronzes are com-monly used in lightly loaded gearing for electrical ap-plications because of their low cost and nonmagnetic properties.
ROLLED RING FORGING
DIRECTION OF METAL AND
INCLUSION FLOW
TANGENTIAL TRANSVERSE TENSILE
LONGITUDINAL PINION FORGING
DIRECTION OF METAL AND INCLUSION FLOW
TRANSVERSE
TENSILE TEST BAR LONGITUDINAL TENSILE
TEST BAR OR PROPERTIES
TEST BAR
TENSILE TEST BAR
NOTE: ASTM E399 may be used if impact testing is required.
TENSILE TEST BAR
Fig 4---2 Directionality of Forging Properties
4.10.2 Gear Brasses and Other Copper Alloys.
Gear brasses are selected for their corrosion resis-tant properties. The most common gear brass is yel-low brass, used because of its good machinability.
Other brass materials are used because of their
high-er strength, but they are more difficult to machine.
Wear resistance of these brasses is somewhat lower than for the higher strength manganese bronzes.
4.10.3 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. Table 4---10 presents chemi-cal analyses of common wrought bronze alloys, while Table 4---11 presents typical mechanical properties of these wrought bronze alloys in rod and bar form.
4.10.4 Cast Copper Base.Copper base castings are specified by melting method, heat treatment, analysis or type, hardness and tensile properties.
4.10.4.1 Cast Worm Bronzes. Specifications de-scribe type of bronzes according to chemical analysis.
Refer to Table 4---12 for chemical analyses of com-mon cast copper bronze alloys, including phosphor or tin bronze, leaded tin bronze (improved machin-ability) and higher strength manganese bronze and aluminum bronze. Mechanical properties of sepa-rate cast test specimens are shown in Table 4---13.
4.10.4.2 General Information for Copper Cast-ings.Additional information regarding manufactur-ing, chemical analysis, heat treatmanufactur-ing, tensile proper-ties, 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 recog-nized 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 analy-sis 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, Stan-dard Methods of Chemical Analysis of Special Brasses and Bronzes, may be used as the referee method.
(4) Casting Hardness. Hardness tests are nor-mally made in accordance with ASTM E10, Method of Test for Brinell Hardness of Metallic Materials. The load in kilograms force listed in Table 4---13 should be used.
Hardness tests are to be made on the tooth por-tion of the part after final heat treatment, if required.
The number of hardness tests made should be speci-fied by the gear manufacturer.
(5) Casting Tensile Properties. Tensile tests are only required when specified. Tensile tests when spe-cified are made in accordance with ASTM E8, Ten-sion Testing of Metallic Materials. Tensile test bars for sand castings may be attached to casting or cast sepa-rately. 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 de-sign 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 1000 lbs (454 kg).
Heat treated castings should have the test cou-pons heat treated in the same furnace loads as the casting they represent.
Table 4---10
Chemical Analyses of Wrought Bronze Alloys
Bronze Alloy UNS NO.
Former AGMAType
(incl Ag) PbCu Fe Sn Zn Al As Mn Si Ni
(incl Composition, Percent Maximum (unless shown as a range or minimum) 1
Co) C62300 --- --- Rem. --- --- 2.0 0.60 --- --- 8.5 --- --- 0.50 0.25 1.0
to to
4.0 11.0
C62400 --- --- Rem. --- --- 2.0 0.20 --- --- 10.0 --- --- 0.30 0.25
---to to
4.5 11.5
C63000 ALBR 6 Rem. --- --- 2.0 0.20 0.30 9.0 --- --- 1.50 0.25 4.0
to to to
4.0 11.0 5.5
C64200 ALBR 5 Rem. 0.05 0.30 0.20 0.50 6.3 0.15 0.10 1.5 0.25
to to
7.6 2.2
C67300 --- --- 58.0 0.40 0.50 0.30 Rem. 0.25 --- --- 2.0 0.50 0.25
to to to to
63.0 3.0 3.5 1.5
1 Unified Numbering System. For cross reference to SAE, former SAE & ASTM, see SAE Information Report SAE J461. For added copper alloy information, also see SAE J463.
Table 4---11
Typical Mechanical Properties! of Wrought Bronze Alloy Rod and Bar
Bronze Alloy UNS NO.
Former AGMAType
Tensile Strength ksi (MPa)
Yield Strength ksi (MPa)
Elongation in 2 in (50 mm)
percent, min. HB and HRB
2 Hardness
C62300 --- --- 90 (620) 45 (310) 25 180HB (1000kgf)
C62400 --- --- 95 (655) 50 (345) 12 200HB (3000kgf)
C63000 ALBR 6 90 (620) 45 (310) 17 100 HRB
C64200 ALBR 5 93 (640) 60 (415) 26 90 HRB
C67300 --- --- 70 (485) 40 (275) 25 70 HRB
2 Unified Numbering System. For cross reference to SAE, former SAE & ASTM, see SAE Information Report SAE J461. For added wrought copper alloy information, also see SAE J463.
1 Typical mechanical properties vary with form, temper, and section size considerations.
Table 4---12
Chemical Analyses of Cast Bronze Alloys
Bronze
Composition, Percent Maximum (unless shown as a range or minimum)
C86200 MNBR 3 60.0 0.20 0.20 22.0 2.0 --- --- 1.0 --- --- --- --- 3.0 --- --- 2.5
C86500 MNBR 2 55.0 1.0 0.5
to
C92700 MNBR 3 86.0
89.0to 9.0 1.0 0.05
* Unified Numbering System. For cross reference to SAE, former SAE & ASTM, see SAE Information Report SAE J461. For added copper alloy information, also see SAE J462.
{ For continuous castings, phosphorus shall be 1.5 percent maximum.
Table 4---13
Mechanical Properties of Cast Bronze Alloys!
Copper
& Condition Tensile StrengthMinimum
ksi (MPa) Yield StrengthMinimum
ksi (MPa) Elongation
Continuous 110 (760) 60 (415) 12 225
Sand, Centrifugal
C92900 Sand, Continuous 45 (310) 25 (170) 8 90
C95200
C95200 ALBR 1
ALBR 1 Sand, Centrifugal
Continuous 65
C90700 Centrifugal 50 (345) 28 (195) 12 100
1 For rating of worm gears in accordance with AGMA 6034---A87, the Materials Factor, ks, will depend upon the particular casting method employed.
2 Unified Numbering System. For cross reference to SAE, former SAE & ASTM, see SAE Information Report SAE J461. For added copper alloy information, also see SAE J462.
3 Refer to ASTM B427 for sand and centrifugal cast C90700 alloy and sand cast C92900.
4 Minimum tensile strength and yield strength shall be reduced 10% for continuous cast bars having a cross section of 4 inch (102 mm) or more (see ASTM B505, Table 3 footnote).
5 BHN at other load levels (1000 kgf or 1500 kgf) may be used if approved by purchaser.
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 av-erage properties of these two bars must meet speci-fied 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 indi-cated 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. Fail-ure of any gear to meet hardness requirements speci-fied is subject to rejection.
(7) Cast Structure. When required, the producer should furnish specified microspecimens or photo-micrographs for each melt with the certificate of hardness, chemistry, and mechanical properties.
(8) Supplemental Data. The following supple-mentary requirement should apply only when speci-fied by contractual agreement. Details of this sup-plementary requirement should be agreed upon by the casting producer and gear manufacturer.
(a) With proper foundry technique, the proper-ties of static chilled and centrifugal cast separate test bars should be the same.
(b) An integral or a separate test bar simply sig-nifies the melt quality poured into the mold to make the casting. It does not express the specific proper-ties and characteristics of the casting which are great-ly dependent on design, size, and foundry technique.
(c) The grain size of cast copper base alloys va-ries as a function of cooling rate and section thick-ness. Recommended maximum grain size for centrif-ugal 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 cop-per base alloys is determined cop-per ASTM E112 at 75X magnification.
(d) 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 photomicrographic standards both acceptable and non---acceptable phase distributions in the gear rim section.
4.11 Other Non---Ferrous Materials. In addition to