Resistive heating can be used to efficiently anneal
copper wire; the heating system employs a controlled electrical short circuit.
It can be advantageous because it does not require a temperature-regulated
furnace like other methods of annealing. Seko Machinery Company's Annealing Equipment is use the
resistive heating.
The process consists of two conductive pulleys (step
pulleys), which the wire passes across after it is drawn. The two pulleys have
an electrical potential across them, which causes the wire to form a short
circuit. The Joule effect causes the temperature of the wire to rise to
approximately 400 °C. This temperature is affected by the rotational speed of
the pulleys, the ambient temperature, and the voltage applied. Where t is the
temperature of the wire, K is a constant, V is the voltage applied, r is the
number of rotations of the pulleys per minute, and ta is the ambient
temperature:
The constant K depends on the diameter of the pulleys and
the resistivity of the copper.
Purely in terms of the temperature of the copper wire, an
increase in the speed of the wire through the pulley system has the same effect
as an increase in resistance. Therefore, the speed of the wire can be varied
quadratically as the voltage is applied.
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