Tuesday, July 13, 2010

Copper Alloys and How to Check

Copper alloys contain either two or three components with combine with copper as the main substance. The alloying components are zinc, tin, nickel, aluminum and iron. These are classified into forging and casting alloys; the components are specified when designation copper alloys.

Copper-zinc alloy (formerly brass)
These are governed by DIN 17660 norms. Characteristic properties are good castability, workability, corrosion resistance and cold harden ability. The hardness of the alloy increases with rising zinc content.

Copper-nickel-zinc alloy (earlier known as German silver)
These are governed by DIN 17663. the addition of nickel result in a silvery white color. Used in instruments, jewellery, showcases, molding, drawing, instruments.

Copper Tin Alloy (formerly called bronze)
These are governed by DIN 17662. These contain at least 60% copper acid tin as the main alloying additive. Characteristic properties are high strength, corrosion resistance and low coefficient of friction. Copper tin alloys are used in bearing shells, skew gears, tubes membranes, springs, pressure meter.

Copper alloys, DIN 1766 to DIN 17663 , examples

Copper-zinc alloy
Composition in % Of dry weight:
CuZn 39 Pb 2
Cu 58.5 - 59.5
Pb 1.5 – 2.3
Rest Zn
Proposes, use:
Easy to stamp and punch, easy to work. Can be cold reformed slightly by bending and riveting

Copper-tin alloy
Composition in % Of dry weight:
CuSn 6
Sn 5.5 – 7.5
Rest Copper
Proposes, use:
Strips, bearing shells springs

Copper-nickel-zinc alloy
Composition in % Of dry weight::
CuNi 12 Zn 24
Ni 11 – 13
Zn 24 – 26
Rest copper
Proposes, use:
Extrudable, forgeable. Suitable for machine cutting.

Copper Aluminum Alloys
These are governed by DIN 17665 norms. Structural elements continuously exposed to sea water and acid solutions may be made of copper aluminum alloys instead of steel. The alloys contain 70% copper and aluminum as the main alloying component.

Examples:
CuAl 8 Fe – sheets for making chemical apparatuses
CuAl 10 Fe – scale resistant parts such as shafts, screws
CuAl 9 Mn – bearing parts, drive and worm gears.

Working a copper zinc alloy
Strength and hardness increase significantly by cold working while extensibility decreases. The extensibility increases after soft annealing, whereas the strength is reduced.

Check and Expert:
  1. A metal strip has been annealed can be easily bent and retain its form
  2. If the strip is cold forged, it is harder to bend and tends to spring back. Hardness and strength have increased.
  3. If the strip is soft annealed, it becomes soft and flexible once again.

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