Copper-nickel alloy: properties, GOST. Manufacture of copper-nickel alloys. Cleaning coins from copper-nickel alloy

Copper belongs to the group of non-ferrous metals. In its pure form it has a high thermal and electrical conductivity, which is why it is used mainly in electrical engineering. Copper is a very ductile material that can be easily processed by pressure in the cold and hot state.

To enhance the mechanical, design and performance properties of copper, its compounds with other metals are used. As a result of the fusion process, the structure of the crystal lattices changes, additional bonds arise between the ions and atoms. This is what increases the strength of the alloy compared to pure metal.

Why copper is fused with nickel

At fusion, nickel acts as the main alloying element. It has corrosion resistance, therefore, it is mainly used for hardening. When alloying it with copper, continuous solid solutions are formed. Copper-nickel alloy acquires a number of new properties:

• Increases the heat resistance of the material;
• The temperature coefficient of electrical resistivity is significantly reduced;
• There is a high resistance to corrosion, especially in seawater.

Classification

The properties of a copper-nickel alloy depend on the percentage of nickel and other substances in it. At present, many new special materials with unique characteristics have been created. Depending on the field of application, they are divided into structural and electrotechnical.

• Structural - have high anti-corrosion and strength characteristics. Products from them are resistant to aggressive environments. This is nickel silver, nickel silver and kunial. A separate place in this list is Monel, whose composition and proportion of the elements are somewhat different.
• Electrotechnical - are characterized by increased electrical resistance and thermoelectric properties, they are used in power engineering and electrical engineering. This is constantan, manganin and copules.

Knowledge of the chemical composition and physical characteristics makes it possible to determine the copper-nickel alloy in one of the groups.

Melchior

Contains about 80% of copper, about 20% nickel, and also a little manganese and iron. Such an alloy was known to people back in the III century BC. E. Under the name "white copper" thanks to a light silvery color, reminiscent of silver. It has high anticorrosion properties, as well as a large margin of strength and wear resistance, a copper-nickel alloy. The melting point is about 1170 ° C. Good plasticity allows you to handle products from it with pressure. Used in the manufacture of capacitors, it produces medical instruments, inexpensive jewelry, cutlery, coins.

Nickel silver

This copper-nickel alloy with the addition of zinc, which has a silvery, greenish-tinged color. Depending on the brand, it can contain up to 35% nickel and up to 45% zinc, the rest - copper. Such a solid content of zinc significantly reduces the cost of its production. Neusilber has about the same mechanical properties as the nickel silver. It is corrosion resistant, durable, sufficiently plastic for hot and cold treatment by pressure.

Sometimes it is additionally doped with lead for better machining. Most of it is made of parts of instruments, watches, medical instruments. It is interesting that thanks to the cheapness now it is from him that more often than jewelry made from silver, they produce jewelry, medals and medals. Neusilber is also used in the manufacture of enamel.

Cunial

It consists of a copper base, nickel - up to 20%, small additives of aluminum. Fused at a temperature of 1183 ° C followed by quenching and aging, which achieves very high strength and low temperature resistance. It is subdivided into brands A (MNA13-3) and B (MNA 6-1,5).
Mark A has two important characteristics - high strength and unique resistance to corrosion in corrosive environments. For example, in seawater, it can be used for decades. Therefore, the alloy is used for the manufacture of special-purpose parts (propellers).

Mark B possesses springing properties, therefore it is widely used for manufacturing of elastic elements of responsible purpose. Also, it is very resistant to kinks in the frost. It produces structural parts that operate under conditions of low temperatures.

Monel

It contains about two thirds of nickel and one third of copper. The melting point is 1350 ° C. The main property of this copper-nickel alloy is its resistance to corrosion. It has high mechanical properties - strength and plastic deformation. Monel brand НМЖМц contains approximately 28% of copper, 3% of iron, about 3% of magnesium, a small amount of cobalt and nickel.

Monel-400 has the same characteristics. It is a brand of Special Metals Corporation and was patented in 1906. Therefore, other manufacturing companies can not use this name. So there was another alloy - Nicorros. However, these materials are identical in all chemical and technical characteristics. Since the alloy contains more than half of nickel in a percentage, its cost is quite high. However, there is a technology for producing a copper-nickel alloy using raw materials from natural sulphide ores with the content of both elements, without prior separation into separate components. This makes it possible to significantly reduce the cost of the final product.

Monel is used for the production of products used in corrosive environments, conditions of increased mechanical stress. This shipbuilding, chemical and oil industry, the manufacture of medical instruments, responsible parts of machines and devices.

Constantan

Has a white color with a characteristic yellowish flow. The structure includes: copper -59%; Nickel - 39-41%; Manganese - 1-2%. Melting point 1260 ° C. This copper-nickel alloy got its name due to the main property - thermal stability. It has very good electrical resistance values with a low value of the thermal expansion coefficient. The alloy goes for the manufacture of wire for thermocouples, in the production of measuring instruments, as well as for electric heating elements operating at temperatures up to 400-500 degrees.

A wire made of constantan is subjected to special heat treatment, as a result of which the metal on the surface forms a thin oxide film. Thanks to this, the product does not need additional varnishing or protective coating. Constantan is very plastic. This property makes it possible to use it when welding copper-nickel alloys.

The disadvantage of the constantan is its sufficiently high EMF - about 43 μV. This excludes the use of wire and tape from it in high-precision measuring devices.

Manganin

Contains approximately 5% nickel, 12% manganese and a copper base. The melting point is 960 ° C. Interestingly, manganin was invented by the American Edward Venston in about 1888 on the basis of the invented constantan as a special material for the windings of electrical measuring instruments. It really has a high electrical resistivity, as well as an extremely low EMF coupled with copper (not more than 1 μV), which distinguishes it from the constantan.

In order to reduce the temperature coefficient of resistance, the manganese wire is annealed at temperatures of about 600 degrees under vacuum conditions, then slowly cooled. This technology allows you to increase the temperature at which the material retains its electrical properties, up to 200 ° C. The wire already wound up in the coil is additionally heated repeatedly to 150 ° C. This achieves the effect of artificial aging, after which changes in the crystal structure of the metal are minimized.

The main area of application of manganin as a material with stable electrical resistivity indices is the production of a variety of high precision instruments for measuring electrical current (current, voltage, power).

Kopel

Another special alloy. Contains copper, 43% nickel, some iron and manganese. Melting point 1290 ° C. Due to the optimal ratio of stably low resistivity and high TEMP, paired with various metals, the alloy is used for making wires for thermocouples and electrodes. The index of the material's thermal conductivity increases in proportion to the operating temperature:

• At 100 degrees Celsius - 6.95V;
• At 600 to 49V.

Copels are very heat-resistant - without breaking the basic properties it can withstand heating up to 600 degrees and is resistant to corrosion.
Kopel is used in thermocouples of sensor devices for non-contact temperature measurement. They use thermocouples with a maximum TEPS - with chromium, copper or iron. These elements are positive electrodes, and kopel-negative. The thermocouple kopel-chromel is used mainly in pyrometry for constant monitoring of the temperature regime in the range from 200 to 600 degrees in industrial and laboratory installations.

The melting process

In the production of copper-nickel alloys, there are relatively similar technologies. Melchior, neisilber, kunial, constantan, manganin are first melted in induction furnaces under a layer of calcined charcoal. The addition to the charge of waste is allowed up to 80%.

The melting process starts with copper and nickel. As they melt, waste is added in large pieces, then small. The last place is loaded with zinc. After the final melting of the charge, manganese and silicon (nickel silver) are deoxidized, or silicon and manganese (constantan and cupronickel). After that, all the slag is removed from the surface of the melt and more charcoal is added. Heat the incandescent mass to about 1300 ° C, add manganese chloride for refining, if necessary.

The technology of cooking kunialy differs slightly, since they contain aluminum. Before the introduction of aluminum, 0.1% of manganese for deoxidation is necessarily added to the melt. And after dissolving aluminum, the surface of the melt is sprinkled with flux. If this is not done, films are formed from which the melt becomes unfit for pouring.

Chemical, physical and structural properties determine the range of application of various copper-nickel alloys. GOST 492-73, GOST 5063-73, GOST 5187-70, GOST 5220-78, GOST 17217-79, GOST 10155-75 are the main standards for their production.

Coinage

Approximately from the end of the century before last, coins of copper-nickel alloy were minted everywhere. Its composition was very different in different mints. But basically it contained up to 30% nickel, a minor iron impurity and copper as a base. Since the metal for ordinary coins should primarily be ductile, malleable, wear-resistant and inexpensive, the composition of the coin alloy was determined in a practical way. Subsequently, the most popular for the manufacture of coins was used cupronickel.

Modern Russian coins are made of various alloys. In particular, coins, issued before 2009, are entirely made of nickel silver. Steel coins with a face value of one and five cents and copper five-ruble coins are covered with a thin layer of nickel silver. Such a material was called "bimetal". So the cost of manufacturing of metal money decreases more and more.

Alloys of copper and nickel are slightly susceptible to oxidation in air. Therefore, its signs can be found only on old coins, or those that have long been in an aggressive environment. Experts-treasure hunters and numismatists use various means for cleaning valuable copies of coins - from folk recipes to advanced technologies.
Cleaning with a soap solution removes only greenish copper oxides. Olive oil, acetic acid, Goya paste are also used. It should be borne in mind that these funds can not only take off the plaque, but also react with the alloy itself, harming the coin. The most effective, gentle and fast is the cleaning of coins from copper-nickel alloy by electrolysis.