Bushes & Bushings

Copper Alloy Suitability

Copper alloys and bronzes in particular are generally superior to other bushing/sleeve materials, and can be selected to meet particular ambient operating conditions. Different alloy compositions are used to optimize the material properties for specific applications, such as high load-bearing capacity or resistance to corrosion. They 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.

Copper alloys also allow for easy and economical manufacture, and bespoke applications to be made in uniue configurations are simple and relatively inexpensive.

The attributes of a decent bearing material are:

• High compressive strength,
• High fatigue resistance,
• Corrosion resistance,
• Low shear strength (at the bearing-to shaft interface) for self lubricating properties,
• A low coefficient of friction at the working surface interfacing with hard shaft materials,
• Good wear resistance behaviour in frictional interfaces (scoring resistance),
• The ability to absorb and discard small contaminant particles (embeddibility),
• The ability to adapt and adjust to play and misalignment (conformability),
• Structural uniformity with fine grain structures, and no casting defects,
• Reasonably priced and
• Readily available.

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Design Considerations

It is not at all unusual to come across a bronze sleeve bearing that has been performing satisfactorily for decades, even under harsh operating conditions. A properly designed and maintained bronze bearing can easily outlast the application it serves. Such longevity and reliability requires sound and appropriate design, the correct choice of alloy, quality manufacture and, as with any mechanical equipment, diligent maintenance.

Good design involves three fundamental elements:

1. understanding or accurately predicting the service conditions and operating environment,
2. designing for realistic lubrication and maintenance in the context of its use,
3. selecting the most appropriate bearing alloy to meet the unique combination of tribological demands.

Accurately assessing expected service conditions cannot be overemphasized; it is the basis for all subsequent decisions. Creating or at least identifying the lubrication mode in which the bearing will operate is equally important.

Available Alloys

The copper alloys we cast for machining bushings, bushes and sleeves are cast using either Continuous or Centrifugal methods. There are many copper alloys that are used, depending on various factors.

Please note, we use UNS, European Std and old British Standard designatons below.

Tin Bronze

UNS-> C90200 to C91700 - These alloys have high hardness, and so require reliable lubrication, good alignment, and a minimum shaft hardness of 40 Rockwell-C. They are used in high-load, low-speed applications such as trunnion bearings, gear bushings for off-road vehicles, rolling-mill bearings, and in internal combustion engines for connecting-rod bearings, valve guides, and starters.

Tin bronze bearings offer good compatibility, easy machining characteristics, and high load capacity. They do not require a separate overlay or any steel backing. The Tin's principal function as an alloy in these bronzes is to strengthen. 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.

1. CC483k - CuSn12 -
2. CC481k - CuSn11P - PB1
3. C90300
4. C90500
5. C90700
6. C91600
7. C91700

Leaded Tin Bronzes

UNS-> C92000 to C92900 – The tin content of 4 to 10% in leaded bronze increases strength, maximum load capacity, fatigue resistance, and hardness above that which is available with other simpler copper leads. Zinc which strengthens the alloy is sometimes used as a replacement for tin (which is expensive), and nickel is often added to improve corrosion resistance and toughness.

Since lead is practically insoluble in copper, a cast copper-lead microstructure consists of lead pockets in a copper matrix. These pockets of lead serve as reservoirs for maintaining a continuous lead film on the bearing surface. A higher lead content promotes compatibility with soft alloy shafts and reduces friction in poor-lubrication scenarios (start-up, for example) while slightly sacrificing wear resistance. Thus, copper lead and leaded bronzes are often used where compatibility outweighs the downside of lower mechanical properties.

Leaded bronzes have better compatibility than tin bronze because the spheroids of lead smear over the bearing surface under conditions of inadequate lubrication. These alloys are generally a first choice for intermediate loads and speeds. They are used in machine tools, home appliances, farm machinery, and pumps. 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. The leaded bronzes in this family otherwise have similar properties and application as the tin bronzes.

1. C92200
2. C92300
3. C92700

As per ASTM B427-21 Standard Specification for Gear Bronze Alloy Subject to tensile strength, yield strength, elongation, and hardness tests.

>High Leaded Tin Bronze

UNS-> C93000 to C94500 - These have a wider range of applicability, and more often specified/applied/used than any other bearing material. As with other bearing bronze families the differences among individual alloys are minor. 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. Because of their comparatively lower strength and somewhat reduced ductility Alloys C93800 and C94300 should not be specified for use under high loads or in applications where impacts can be anticipated. They operate best at moderate loads and high speeds, especially where lubrication may be unreliable. They conform well and are very tolerant of dirty operating conditions.

1. C93200
2. C93400
3. C93500
4. C93700
5. C93800
6. C94300

Aluminium Bronzes

UNS-> C95000 to C95999 – The 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 and thus used at loads 50% greater than for leaded tin bronze Alloy C93200. 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. Careful 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.

1. C95200
2. C95220
3. C95300
4. C95400 - HT
5. C95410
6. C95500 - HT

Manganese Bronzes

UNS-> UNS-> C86100 to C86800 - 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.

1. C86300
2. C86400
3. C86500
4. C86700

ASTM B271 Centrifugal Csting Specificaion, ASTM B505 / B505M Continuous Casting

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