It belongs to materials with high electrical resistance and at the same time to thermo electrode copper-nickel alloys. It is used as heaters for electric furnaces, thermocouple electrodes, and extension leads. The physical properties, application area, grades and product types are presented on this page.
Basic information
Constantan - is a thermally stable electrical copper-nickel alloy consisting of the following elements: nickel (Ni), manganese (Mn), and copper (Cu). It is easily processed. It is used for production of thermocouples, rheostats and electric heating elements with an operating temperature of up to 400-500 °C, and measuring devices of low accuracy class.
History
The material was first obtained by the American inventor Edward Weston in 1888. He used this alloy as a material for coils of electrical measuring devices because its resistance does not depend on temperature. The inventor called it "Alloy №2", but the German manufacturers, from whom he placed an order for the production of wire from a new material, renamed it to "Constantan" and now it is known by this name.
Constantan properties
The material has a high resistivity, which is 0.45-0.52 mkΩ·m, and a low temperature coefficient of electrical resistance - from -0,02·10-3 до +0,06·10-3 °С-1 (according to GOST 5307-77). Due to such small values of this coefficient, it practically does not change its resistance with temperature changes.
Another important characteristic is thermoelectromotive force. Constantan is paired with chromel, as well as with copper and iron, develops a fairly high thermoelectromotive force.
Constantan is easily machined, which indicates its high processability.
Property
Value
Density, g/cm3
8,8-8,9
Melting point, °С
1260
Electrical resistivity, mkΩ·m
0,45-0,52
Magnetic field
Nonmagnetic
Hardness, HB
75-90 (after annealing) 155
Temperature coefficient of linear expansion, °С-1 in the range 20-100 °С
14,4·10-6
Temperature coefficient of electrical resistance, °C-1
from -0,02·10-3 to +0,06·10-3
Constantan grades
The material is produced under the grade CuNiMn 40-1.5. The most weighty component in its composition is copper (Cu) ~59%, followed by Nickel (Ni) 39-41% and manganese (Mn) 1-2%.
Advantages / disadvantages
Advantages:
it has a high electrical resistance;
it has a small temperature coefficient value of electrical resistance;
it has a high thermoelectromotive force when paired with some materials;
it has good technological properties.
Disadvantages:
it has a relatively low melting temperature.
Constantan application area
The application area of this copper-nickel alloy is determined by its characteristics. The first practically useful property is high electrical resistance. It allows to use the described material for the production of electric furnace heaters. Since the melting temperature is relatively small, the maximum operating temperature of the heaters is 500 °C. This property also allows to product of rheostats (resistive elements) from constantan.
The second important practical property is the low dependence of electrical resistance on temperature. This feature allows to use the alloy in cases when it is important to ensure the stability of the electrical resistance.
Paired with copper, chromel alloy and iron, the material develops a sufficiently high thermoelectromotive force that can be counted by the measuring device. This feature allows to use constantan for the production of thermocouples chromel-constantan, copper-constantan, iron-constantan. In addition extension leads are produced from constantan.
Constantan products
The main types of products that the industry produces are wire, filament (small diameter wire) and flat bar. Constantan wire, filament, as well as constantan strip или flat bar are used for the production of wire and strip heaters of electric furnaces, resistive elements. Filament and wire are also used in electrical engineering in temperature measurement devices.