CopperEasy to work, ductile and malleableExcellent resistance to corrosionGood machinability

Non magneticGood electrical and thermal conductivity

Can be soldered, brazed and welded.

Ease of forming alloys with other elements like Zn, Sn, Al, Pb, Si, Ni etc.

Brass- Cu-ZnBronze- Cu-Sn

Copper alloysIn general,

Copper plus zinc is Brass.

Any other alloy of copper other than brasses is termed as bronze (previously only copper -tin alloy was called as brass)

Copper alloys - bronzesTin bronze 2-4% Zn,8-10% Sn remaining copper

Pressure castings, bushings and bearings

Leaded tin bronze4%Zn, 6-8.5% Sn, o.5-1.5% Pb , remaining copper.

Can be used upto 550 deg F Pressure castings,bushings, electrical castings, gears , pumps etc

High leaded tin bronze:1-3%Zn, 5-10%Sn, 7-15%Pb

Bearings operating at high speeds and high pressure and for corrosion resistant pumps.

Copper alloys - bronzes

Gun metal:

5-10% Sn, 2-5% Zn, remainder copper.Good tensile strength and resistance to corrosion.

Used for bearings, steam pipe fittings, marine castings, hydraulic valves and gears.

Simpler way to compile2 to 58 to 10Use lead as differentiator

Copper alloys - bronzesAluminium bronze 1-4% Fe, 9-11% Al , remaining copper

For heavy duty parts, marine equipments, gears, bearings, bushings, valve seats, guide stems, acid resisting pumps, parts resisting corrosion and oxidation,

Components requiring strength at elevated temperatures.

Copper alloys -brassesAlloys of copper and zinc

Addition of zinc improves ductility and strength

Good corrosion resistance and good working properties.

1.Alpha brasses-upto 36% zinc

20-36 % -yellow5-20%-red

2.Alpha plus beta brasses 54 to 62 % copper

Copper alloys -brassesYellow alpha brasses are subjected to a pitting corrosion called dezincification.

This happens when brass is in contact with sea water or with fresh waters that have a high content of oxygen and carbon dioxide.

Dezincification involves dissolution of the alloy and a subsequent deposition of non adherent copper.

This will lead to leakage through the porous layer of copper.

Small amounts of tin or antimony reduce dezincification in yellow brasses.

Copper alloys -brassesStress relief anneal is done to avoid season cracking.

Season cracking or stress corrosion cracking is due to high residual stress left in the brass after cold working.

These stresses make the brass more susceptible to intergranular corrosion.

Intergranular corrosion: corrosion happening preferentially at grain boundaries.

Copper alloys -brassesAddition of 0.3 -0.5% lead improves machinability so that leaded brass is used for

screw machine parts,

engraving plates,

keys,

lock parts,

tumblers,

gears and

watch parts.

Parts that need to be machined to minute details

Copper alloys -brassesAdmiralty metal 71Cu-28zn-1Sn

Improved strength and corrosion resistance.Used for condenser and heat exchanger tubes in steam power plant equipment

Aluminium brass 76Cu-22zn-2Al

Forms a tenacious self healing film which protects the tube against high cooling water velocities in marine and land power stations.

Copper alloys -brassesCartridge brass Cu70, Zn30. and yellow brass Cu65, Zn 35

Automotive radiator cores,headlight reflectors,

Electrical-lamp fixtures, socket shells

Hardware-fasteners, screws, rivets, springs

Ammunition components

Copper alloys -brassesRed brasses5-20% zinc

Better corrosion resistance than yellow brasses and are not susceptible to stress corrosion cracking

Gliding metal 95Cu-5Zn coins, medals, tokens,emblems, plaques, base for items to be gold plated.

Commercial brass 90Cu-10Zn excellent cold working- so used in costume jewelry,marine hardware, forgings, rivets and screws.

Silicon brass: 80Cu-14Zn-4Si-0.5PbFor die cast parts and small gears

Copper alloys -brasses

Red brass 85Cu-15Zn electrical conduit, condenser and heat exchanger tubes, plumbing pipes, nameplates etc

Low brass 80Cu-20Zn

ornamental metal work, thermostat bellows, musical instruments, flexible hose, other deep drawn articles.

Alpha plus beta brassesThese contain 54 -62 % copper

These contain two phases alpha and beta.

The beta phase is harder and more brittle at room temperature and so difficult to cold work.

At elevated temperatures, the beta phase becomes very plastic and so these alloys have excellent hot working properties (when heated to the single phase beta region).

Alpha plus beta brassesMuntz metal 60Cu-40Zn

Rapid cooling will suppress the precipitation of alpha phase.

This can be subsequently precipitated by suitable heat treatments.

Hence this alloy is Hardenable.

Used for

Ship sheathing, condenser heads,perforated metal and architectural work.Also for valve stem and condenser tubes

0.4 to 0.8 Pb improves machinability (leaded muntz)

Alpha plus beta brassesFree cutting brass 61.5Cu-35.5Zn 3Pb has the best machinability plus good mechanical and corrosion resistance properties.Used for automatic high speed screw machine parts

Naval brass:60Cu39.25Zn, 0.75Sn

Also known as TOBIN bronze has increased resistance to salt water corrosion. Used for condenser plates, welding rods, propeller shafts, piston rods and valve stems.

Manganese bronze:58.5Cu-39Zn, 1.4Fe, 1Sn and 0.1MnHigh zinc brass with high strength and wear resistance.Used for clutch discs, shafts, valve stems, welding rods.

CupronickelsCopper nickel alloys that contain upto 30%Nickel

Copper nickel phase diagram is of solid solution type.

At all compositions, the cupronickel alloys are single phase in nature.

Not susceptible to heat treatment and their properties can be altered only by cold working.

Have high resistance to corrosion fatigue.High resistance to corrosive and erosive action of rapidly moving sea water.

Used for Condenser, distiller, evaporator and heat exchanger tubes. (where evaporation of salts are expected)

Cupronickels-Nickel silverAlloys of copper, nickel and zinc

Copper 50-70Nickel 5-30Zinc 5-40

Addition of nickel to Cu-Zn givesa pleasing silver -blue-white colour and good corrosion resistance to food chemicals, water and atmosphere.

Used for rivets, screws, tableware,radio dials, costume jewelry.

Cupronickels-Nickel silverMore than 60 Cu -single phase

Between 50-60 Cu, two phase.

Hence hot workable and have high modulus of elasticity.

Used for springs and contacts in telephone equipment,

resistance wire,

surgical and dental equipment.

AluminiumLight weight (density about one third of steel)

Good malleability, formability and corrosion resistance.

High strength to weight ratio than steels.

High electrical and thermal conductivity

Non magnetic,- can be used for electrical shielding purposes like enclosure for electrical equipment.

Strength is 13,000 psi. can be improved to 100,000 psi by cold working.

Extensively used cooking utensils, food and beverage cans and welded assemblies.

Aluminium and copperMax solubility o copper in aluminium is 5.65% at 1018 deg FIt decreases to 0.45% at 572 deg F

So, alloys containing 2.5 to 5 % copper will respond to heat treatment by age hardening.

Solution treatment is carried out by heating the alloy to the singel phase region, followed by rapid cooling.

An intermediate alloy phase( - theta) is formed. This is similar in composition to CuAl2.

Subsequent aging, precipitates the theta phase , thus increasing the strength of the alloy.

Bearing alloysA bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement.

Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

A bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.Outer surfaceInner surfaceball

Good bearing needs....The general attributes of a good bearing material are: A low coefficient of friction versus hard shaft materials,

The ability to absorb and discard small contaminant particles (embedibility),

High compressive strength,

High fatigue strength,

Corrosion resistance,

Reasonable cost and ready availability.

Bearing alloysLead base alloys known as BabbitsUsed for bearings

SAE13 Pb85, Sb10, Sn5SAE14Pb75, Sb15, Sn10SAE13 Pb83, Sb15, Sn1 Arsenic 1

The microstructure consists of

cubes of antimony -tin compound

in a binary eutectic mixture of

lead and tin solid solutions.

Bearing alloysUsed for automotive connecting rods, camshaft bearings, diesel engine bearings, car and rail bearings, electrical motor bearings.

Lead is heavy, soft and malleable.

Antimony raises the recrystallisation temperature andimproves strength and hardness.

Tin improves hardness and strength and also decreases the eutectic temperature.

Babbit metalBabbitt metal, also called white metal, is an alloy used to provide the bearing surface in a plain bearing. Babbitt metal is characterized by its resistance to galling.

Common compositions for Babbitt alloys:90% tin 10% copper 89% tin 7% antimony 4% copper 80% lead 15% antimony 5% tin

Originally used as a cast in place bulk bearing material, it is now more commonly used as a thin surface layer in a complex, multi metal structure.

Babbit metalBabbitt metal is soft and easily damaged, and seems at first sight an unlikely candidate for abearing surface, but this appearance is deceptive.

The structure of the alloy is made up of small hard crystals dispersed in a matrix of softer alloy.

As the bearing wears, the harder crystal is exposed, with the matrix eroding somewhat to provide a path for the lubricant between the high spots that provide the actual bearing surface.

The BasicsBearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly.

The concept behind a bearing is very simple:

Things roll better than they slide. That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.

The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be a lot more difficult to push down the road.

Tin Bronzes

Tin's principal function in these bronzes is to strengthen the alloys.

Zinc also adds strength, but more than about 4% zinc reduces the antifrictional properties of the bearings alloy.

The tin bronzes are strong and hard and have very high ductility.

This combination of properties gives them a high load-carrying capacity, good wear resistance and the ability to withstand pounding.

The alloys are noted for their corrosion resistance in seawater and brines. Effect of tin and zinc

Tin BronzesThe tin bronzes' hardness inhibits them from conforming easily to rough or misaligned shafts.

Similarly, they do not embed dirt particles well and therefore must be used with clean, reliable lubrication systems.

They require a shaft hardness between 300-400 BHN.

Tin bronzes operate better with grease lubrication than other bronzes; they are also well suited to boundary-film operation because of their ability to form polar compounds with small traces of lubricant.

Differences in mechanical properties among the tin bronzes are not great. Some contain zinc as a strengthener in partial replacement for more-expensive tin. Tin Bronzes

Leaded Tin Bronzes

Some tin bronzes contain small amounts of lead.

In this group of alloys, lead's main function is to improve machinability.

It is not present in sufficient concentration to change the alloys' bearing properties appreciably .

A few of the leaded bronzes also contain zinc, which strengthens the alloys at a lower cost than tin.

The leaded bronzes in this family otherwise have similar properties and application as the tin bronzes. Leaded Tin Bronze

High-Leaded Tin Bronzes

The family of high-leaded tin bronzes include the workhorses of the bearing bronze alloys. Alloy C93200 has a wider range of applicability, and is more often specified, than all other bearing materials. It, and the other high-leaded tin bronzes are used for general utility applications under medium loads and speeds, i.e., those conditions which constitute the bulk of bearing uses.

Strengths and hardnesses are somewhat lower than those of the tin bronzes but this group of leaded alloys excel in their antifriction and machining properties.

High strength is sacrificed for superior lubricity in the bronzes containing 15 and 25 percent lead, Alloys C93800 and C94300.

These high-leaded tin bronzes embed dirt particles very well and conform easily to irregularities in shaft surfaces and permit use with unhardened shafts. As in all leaded bronzes the lead is present as discrete microscopic particlesHigh Leaded Tin Bronze

Aluminum BronzesThe aluminum bronzes are the strongest and most complex of the copper-based bearing alloys.

Their aluminum content provides most of their high strength and makes them the only bearing bronzes capable of being heat treated.

Their high strength, up to 68,000 psi yield and 120,000 tensile, permits them to be used at unit loads up to 50 percent higher than those for leaded tin bronze. Because of their high strength, however, they have fairly low ductility and do not conform or embed well.

They consequently require shafts hardened to 550-600 BHN.

Surfaces must also be extremely smooth, with both shaft and bearing finished to 1520 in RMS. Aluminium Bronze

Aluminum BronzesCareful attention should be given to lubricant cleanliness and reliability, the latter because these alloys do not have the anti-seizing properties typical of the leaded and tin bearing bronzes.

On the other hand, the aluminum bronzes have excellent corrosion resistance and are ideally suited for such applications as marine propellers and pump impellers.

The aluminum bronzes also have superior elevated temperature strength. They are the only bronzes - and the only conventional bearing material able to operate at temperatures exceeding 50OF. Aluminium Bronze

Manganese Bronzes: Alloy Nos. C86300, C86400

Manganese bronzes are modifications of the Muntz metal-type alloys (60% copper 40% zinc brasses) containing small additions of manganese, iron and aluminum, plus lead for lubricity, anti-seizing and embeddibility.

Like the aluminum bronzes, they combine very high strength with excellent corrosion resistance.

Manganese bronze bearings can operate at high speeds under heavy loads, but require high shaft hardnesses and nonabrasive operating conditions. Manganese Bronze

Summary

Bearing bronzes offer

broad ranges of strength, ductility, hardness, wear resistance, anti-seizing properties, low friction and the ability to conform to irregularities, tolerate dirty operating environments and contaminated lubricants.

The corrosion resistance of bearing bronzes is generally superior to other bearing materials, and can be selected to meet particular ambient conditions.

Summary

Summary

Bronzes permit easy and economical manufacture, allowing bearings to be made in special and one-of-a-kind configurations simply and at low cost.

No bearing metals have better machinability than the leaded and high-leaded bearing bronzes.

Almost without exception, a bearing bronze can be selected to satisfy any bearing application that exists.

More info from :Copper Development Association Inc copper.orgSummary