The low-temperature ductility of the tungsten wire is the main factor
affecting the winding performance. The main influencing factors are the
purity of raw materials, additives and the surface condition of the
wire.
1 Purity of raw materials
The higher the purity of wire, the more excellent low-temperature
ductility. The low temperature brittleness is mainly caused by harmful
impurity elements. The content of Fe and Ni in the impurity elements is
too high, and the plastic-brittle transition temperature of the W wire
will rise above 700°C, which will result in the failure of processing.
More harmful impurities are mainly reflected in oxygen, nitrogen, and
carbon. The presence of these elements will also increase the
plastic-brittle transition temperature and reduce the winding
performance. These impurity elements can be purified by chemical
methods, such as repeated crystallization of APT, nitric acid treatment,
and ion exchange of sodium tungstate solution. Among them, ammonia
solution purification of tungstic acid to remove impurities is the
lowest cost method.
2 Additives
Doping a proper amount of silicon (SiO2≤0.4%), aluminum (Al2O3≤0.03%),
potassium (K2O≤0.45%) in W wire can improve its high temperature
anti-sag property to a certain extent, but not all for low temperature
ductility benefit. Therefore, it is necessary to add other chemical
elements to reduce the influence of these additives. For example, adding
a small amount of ruthenium or cobalt can improve the winding
performance and elongation.
3 Surface Condition
During processing, tungsten wires are prone to defects, such as tiny
delaminations, cracks, bumps, and surface stains. Among them, if the
surface stain is a tungsten-nickel alloy, the brittleness of the wire
can be increased, and the superposition of these defects is likely to
cause the wire to break during the winding process. Therefore, it is
necessary to continuously use electrolytic cleaning for surface
treatment of semi-finished products in the process of swaging to
increase the surface finish, reduce defects, and improve low-temperature
ductility.
In addition to the above factors,
the low temperature ductility of wire can also be improved by adjusting the
vertical melting system, annealing, improving the mold and graphite emulsion,
etc.
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of tungsten wire, please feel free to contact us:
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