EoW September 2010

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EuroWire – September 2010 70
technical article
Ralf Hojda, Dr Michael Köhler
Sundwiger Messingwerk GmbH
& Co KG – Germany
Website:
James Schraml
The Miller Company – USA
Website:
The difference in electrical conductivity
between BB95 and an 8% tin bronze is
approximately 1% IACS (International
Annealed Copper Standard), ie the tin
has a negligible conductivity-reducing
influence when present in the alloy at
this level.
At SH (spring hard) temper, BB95 exhibits
the same softening properties as an
8% phosphor bronze; a significant reduc-
tion in hardness is first observed at
about 280 °C.
In addition, the relaxation of the new
material (<20% at a temperature of
100°C for a test duration of 10,000h)
is comparable to that of the above
mentioned reference alloy (provided the
stress level is identical).
Given the above mentioned contact force,
these results suggest that it should be
possible to achieve a reduction in the
thickness of the material, and therefore a
reduction of about 20% in the amount of
material needed, by using BB95.
3 Summary
Steep increases in the prices of raw
materials, and especially in the price of
copper, have drastically changed the
relationship between the value added
and the metal value in the manufacture of
semi-finished copper-alloy products.
Savings in recycling and in the materials
used have a greater impact, looked at
in the round, than the total finishing
expenditure. Using low-alloy copper
materials as an example, the influence
of a well-planned choice of alloys and
composites is described. The combination
of a newly developed, low-alloy phosphor
bronze with a tin coating is a worth-
while alternative to tin-coated copper-
iron alloys, also from an ecological and
economic point of view, and yields a
similar properties profile.
An approach to generating added value
for customers by reducing the amount of
material used is made feasible by the new
development of a 10% phosphor bronze.
This has a similar properties profile to
an 8% copper-tin alloy but has superior
bendability.
Moreover, the new alloy facilitates
resource-saving design, as it can withstand
higher levels of stress. Material savings of
20% appear to be realisable. n
This paper was first presented at the
58th International Wire & Cable and
Connectivity Symposium held in Charlotte,
NC 8th–11th November 2009, and is
reproduced with the generous permission of
the organisers.
Figure 5 ▲ ▲ : Bendability of various phosphor bronzes as a function of strength
Tin content in %
r/s BadWay