Composition

The name of the Constantan received from the Latin. — constans is «constant», «constant», because its electric resistance is virtually not dependent on temperature. It is an alloy of silver-yellow color, containing 58−60% copper, 32−40% Nickel, 1−2% manganese. The melting point of the alloy составляет1260°C, Tcrit is equal to 14 • 10−6 1/°C and a density of 8.9 g/cm3.

Dignity

Heat resistance, plasticity, stability of electrical properties. At 20 °C electrical resistivity equal to 0.48, Mhmm²/m. After special treatment (stabilizing annealing) temperature coefficient of electrical resistance reaches 2x10−6 1/K, annealed (soft) Constantan -EP = 40 — 50%, SP = 400 — 500 MPa and r = 0,45 — 0,48, Mhmm²/m; and the solid-EP = 2…5%, SP = 650 — 720 MPa and r = 0.46 — 0.52 Omhm²/m.

Disadvantages

The main disadvantage of the alloy is significant thermoelectric power (40−50 µv/°C) in a pair with copper, thus limiting its use in precision instrumentation and stable resistors because the heating of the terminals of the contacts leads to the appearance of currents that distort the evidence. In this regard, if necessary, to achieve high accuracy used manganin.

Constantan is quite expensive because of the deficit of Nickel, included in its composition. The main disadvantage of this alloy is the susceptibility with increasing temperature the destructive effects of sulfur, leading to embrittlement and corrosion.

Use

Constantan has found wide application in the manufacture of rheostats, compensating wires, heating devices. Of this alloy to produce the wire dia. Of 0.03−5 mm and the tape thickness is more than 0.1 mm. High thermoelectric power of Constantan in a pair of copper provided it is used in thermocouples for measurements at small working temperatures (up to 500 °C). For these purposes, generally used in thermocouple with positive thermoelectrode — copper, iron and chromel, negative — Constantan, Copel and alumel.

Constantan is widely used in pyrometry is often in the form of wire, at least — tape and circle for the production of thermocouples (wire diameter of 0.2 — 3.2 mm), thermostats and compensation wires. A thermocouple consists of coaxial conductors placed in the environment to measure the temperature (so-called «hot contact») and free the two ends immersed in a thermostat (so-called «cold contact»). Alloying allows to withstand high temperature up to 1300 °C when operating in a hostile environment.

Alloy put in the following form:

Circle (diam.12 — 100 mm);

Tape (thick.0.1−5.0 mm wide.3−600mm);

Wire (dia.Of 0.1 — 12 mm).

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