Constantan CuNi44 Sheet and Strip

Technical characteristics

Constantan alloy consists of cuprum (60%), nickel (40%), manganese additions (2%). By virtue of copper presence, alloy gains a yellow colour. Alloy is used in a pyrometry, where a wire has the greatest application. Strip and rod are less used.

Main characteristics:

1. A permanent real resistance in a wide temperature range;

2. Melting point is 1260 °C;

3. A density is 8,9 g/cm³;

4. A coefficient of a thermal expansion is 14•10^-6 °C-1.

Constantan is utilized for a manufacture of thermocouples, rheostats, electrical heaters at a not very high temperature (500°C). This alloy is a workable, deformable, ductile material which is easy to weld. It is used for producing thermocouples and other details with a working temperature up to 500 °C. It has got its name from Latin — constants — which means «unchanged», «permanent» because its real resistance virtually does not depend on temperature.

Percentage composition

Advantages

A heat resistance, a plasticity, a constancy of electrical properties. At a t° of 20 °C a specific electric resistance equals to 0,48 Ohm-mm²/m. After a special process (stabilizing annealing), a coefficient of thermal real resistance rises to 2x10^-6 1/К, in an annealed (soft) constantan eр = 40 — 50%, sр = 400 — 500 MPa and r = 0,45 — 0,48 Ohm-mm²/m; in hard constantan -eр = 2…5%, sр = 650 — 720 MPa and r = 0,46 — 0,52 Ohm-mm²/m.

Demerits

Constantan wire is quite expensive because of nickel presence in its composition. Besides, nickel is prone to damage of a sulfur effect when raising a temperature. The main demerit of alloy is a huge thermoelectromotive force (40−50 mkV/°С) in a combination with cuprum. Thereby, it limits its usage in precise instruments and stable resistors because clue heating of contact elements leads to an appearance of current intensity that impair indicated values. In this regard, there can be used manganin if it is necessary to achieve a high accuracy.

Application

Constantan wire is commonly used in a manufacture of rheostats, compensating lead wires and heating units. The most popular wire is Ø 0,03−5 mm, a strip of no more than 0,1 mm. A thermocouple made of constantan wire with cuprum differs with significant thermoelectromotive force and is used at a not very high working temperature (up to 500°С). In such thermocouples, cuprum, chromel or ferrum are positive electrodes; negative are copel and alumel (except of constantan). Thermocouple consists of electric conductor fumes, that are soldered in one end and placed into environment oriented for thermometry («hot junction»). Then, the exposed ends are going to be placed into a thermostatic regulator (so-called cold junction). An alloying allows withstanding a short-range effect of a high temperature up to 1300 °C while working in aggressive environment. Constantan wire, less often a strip or a rod are utilized for manufacturing the heating controllers and compensating lead wires.

Alloy is delivered in the following way:

Rod (Ø 12,0 — 100,0 mm);

Strip (0,1−5,0 mm of thickness; 3−600 mm of wideness).

Wire (Ø 0,10 — 12 mm);

Physical characteristics at a temperature 20°C