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The
U.S. Navy is using nickel aluminum bronze material for propellers for
ice-breaking service, and after a full season of operation excellent results
were noted. Propeller
efficiency. Less
obvious perhaps than the data presented in Table 1, but more important from
a service standpoint, is propeller efficiency. The design engineers are most impressed by the ability of nickel aluminum
bronze to retain its original smooth machined surface over a long period of
time, thereby retaining its high efficiency factor. Numerically the
improvement in efficiency would lie in the order of 1.5-3.0 per cent, with
resultant fuel savings. The exact efficiency increase would depend upon the
propeller size, design factors and length of service. Design
Benefit. As
nickel aluminum bronze is in itself approximately 10 per cent lighter in
weight than manganese bronze, and can be designed to thinner sections
because of its higher
strength, other advantages become apparent. For example, loading
stresses on the tailshaft and bearings are reduce, thus permitting smaller
shafts. Resistance
to Notch Sensitivity.
The ability of nickel
aluminum bronze to resist failure under impact when notched, contributes
greatly to its value as a propeller material. Maintenance.
Maintenance of nickel aluminum bronze propellers is greatly reduced compared
to that of manganese bze it has superior resistance to bending, breaking and
wearing, including cavitation are directly associated with the material properties. Reparability.
Nickel aluminum bronze is readily reparable with the inert gas process,
or by direct electric rod welding. Little or no pre-heat is required, and
unlike to copper-zinc brasses, it is not subject to stress corrosion cracking
and therefore does not necessarily require a stress relief treatment. Propeller
cost.
Reduced weight of nickel aluminum bronze in conjunction with increased strength
of the material allows designing the propeller approximately 15 % less in
weight than a comparable manganese bze propeller. Although the former is
more costly by the price per pound, the long term cost reduction is
appreciable. |
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TABLE 1 - TEST RESULTS OF NICKEL ALUMINUM AND MANGANESE BRONZE
Chemical composition %
Mechanical Properties (Normal Range)
Spin
Test
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