Melting copper at home. Safe work with metal at home: melting point of copper and other alloys. The process of smelting copper products in a muffle furnace
Every metal has the ability to melt. They all differ in their own melting point, which depends on various factors. First of all, this indicator is affected by the structure of the metal and the presence of any impurities in it. The melting point of copper is 1080 degrees.
Metal melting process
When metals are heated, their crystal lattice begins to gradually collapse. In the initial stage, as it heats up, the temperature increases. Having reached a certain value, it continues to remain at the same level, despite continued heating. At such a moment the melting process begins. It continues until the metal is completely melted. After this, a further increase in temperature continues. Thus, melting of all metals occurs, without exception.
During cooling, the opposite phenomenon occurs. The temperature begins to decrease until the metal begins to harden. It will remain at the same level until final hardening, and then begin to decrease again. All ongoing processes can be displayed graphically in the form of a phase diagram. It accurately shows the state of a substance when exposed to a certain temperature.
If the molten metal is heated further, then when it reaches a certain limit it will begin to boil. However, unlike a liquid, liquid metal begins to release not gas bubbles, but carbon, which is formed during oxidation processes.
Properties of copper
Man has used copper for his purposes since ancient times. Melting copper at relatively low temperatures made it possible to carry out a variety of operations with this metal. Thus, bronze was obtained, which is an alloy of copper and tin. In terms of its strength, it was significantly superior to pure copper, which made it possible to produce higher-quality weapons and tools.
Currently, copper is also not used in its pure form. Composed of copper, in large quantities There are different components. Their content reaches 1%. The main additives used are nickel, iron, arsenic and antimony. However, despite the additives, copper is technically considered a pure metal with high thermal and electrical conductivity. Therefore, it is an ideal material for cable and wire products.
Alloy of copper with other metals
The relatively low melting point of copper is 1084°C. This makes it possible to obtain metal alloys based on it that have completely different properties.
Among them, brass is well known, which is an alloy of copper and zinc, in a percentage ratio of approximately 1:1. The resulting substance has a lower melting point, ranging from 800 to 950 degrees. The specific value of this indicator depends on the ratio of metals contained in the alloy: with a decrease in the amount of zinc, the melting of brass occurs at a lower temperature. This material is used in foundries, as well as sheet and rolled products. In addition to zinc, other components are added to various brands of brass that affect the melting process.
Another well-known alloy is bronze, which contains copper and tin. In some cases, iron, aluminum or manganese additives may be used instead of tin. The alloy with tin melts in the range from 900 to 950 degrees. For bronze without tin, this figure ranges from 950 to 1080 degrees. This material is used for the production of various rubbing parts, as well as in the manufacture of decorative jewelry.
Due to the fact that the melting point of copper is quite low, this metal was one of the first that ancient people began to use to make various tools, dishes, jewelry and weapons. Copper nuggets or copper ore it could be melted at the stake, which is what our distant ancestors actually did.
Despite its active use by mankind since ancient times, copper is not the most common natural metal. In this respect, it is significantly inferior to the other elements and occupies only 23rd place in their series.
How our ancestors smelted copper
Thanks to the low temperature of 1083 degrees Celsius, our distant ancestors not only successfully extracted from ore pure metal, but also produced various alloys based on it. To obtain such alloys, copper was heated and brought to a liquid molten state. Then tin was simply added to such a melt or its reduction was performed on the surface of molten copper, for which tin-containing ore (cassiterite) was used. Using this technology, bronze was obtained, an alloy with high strength, which was used to make weapons.
What processes occur when copper melts
Typically, the melting temperatures of copper and alloys obtained on its basis are different. At , which has a lower melting point, bronze is obtained with a melting point of 930–1140 degrees Celsius. And an alloy of copper and zinc (brass) melts at 900–10500 Celsius.
In all metals, the same processes occur during the melting process. When a sufficient amount of heat is received during heating, the crystal lattice of the metal begins to collapse. At the moment when it goes into a molten state, its temperature does not increase, although the process of transferring heat to it by heating does not stop. The temperature of the metal begins to rise again only when it has completely turned into a molten state.
When cooling, the opposite process occurs: first the temperature drops sharply, then for some time it stops at a constant level. After all the metal has passed into the solid phase, the temperature begins to decrease again until it cools completely.
Both melting and reverse crystallization of copper are associated with the specific heat parameter. This parameter characterizes the specific amount of heat that is required to convert a metal from a solid to a liquid state. When a metal crystallizes, this parameter characterizes the amount of heat it gives off when cooling.
A phase diagram showing the dependence of the state of the metal on temperature helps to learn more about the melting of copper. Such diagrams, which can be drawn up for any metals, help to study their properties, determine the temperatures at which they radically change their properties and current state.
In addition to the melting point, copper also has a boiling point, at which the molten metal begins to release bubbles filled with gas. In fact, no boiling of copper occurs, it’s just that this process looks very similar to it. It can be brought to this state by heating it to a temperature of 2560 degrees.
As is clear from the above, it is the low melting point of copper that can be called one of the main reasons that today we can use this metal, which has many unique characteristics.
TO category:
Foundry
Melting and casting of copper alloys
Copper alloys, which include tin and tin-free bronze and brass, are smelted mainly in electric arc and induction furnaces and less often in flame furnaces operating on liquid fuel. For small production volumes, crucible furnaces are sometimes used.
Since almost all the elements that make up copper alloys are easily oxidized, the smelting process is carried out in an accelerated manner, while measures are taken to protect the alloys from the surface (with protective or covering fluxes), and individual easily oxidized elements are used in the form of alloys.
1. Charge materials
Charge materials for copper alloys can be fresh (pure) metals, secondary alloys, recycled alloys, as well as various alloys supplied by industry or home-made.
To deoxidize alloys, phosphorous copper is used in the form of tiles weighing about 12 kg in accordance with GOST 4515-78, which are broken into small pieces before use.
Alloys are alloys of two or more elements that are added to the alloys. Their use is due to the fact that individual refractory components of the alloy have a higher melting point than the permissible overheating of the alloy. The melting temperatures of alloys and the metal to which they are attached must be close, and at the same time, the alloys must have a high content of refractory element.
2. Charge calculation
To obtain the alloy, various combinations of charge materials are possible. The charge may consist of fresh metals alone, of fresh metals or secondary alloys with the addition of alloys, of a recycled alloy with the addition of fresh metals and alloys, of one recycled alloy or of secondary alloys alone. Typically, a charge consisting of 50-60% fresh metals, 25-35% recycled alloy and 10-12% purchased scrap is used, or smelting is carried out using secondary alloys.
When calculating the charge, the waste of various alloy elements is taken into account, the value of which depends on the nature of the elements, the purity of the charge and the type of smelting furnace.
Let's consider an example of calculating a charge for smelting bronze grade BrZTs7S5N1.
In the manufacture of alloys for less critical castings, in order to save pure metals, only secondary alloys can be used - passport grade bronzes BrZTs8S4N1.
3. Copper alloy smelting technology
Melting in crucible furnaces. A wide variety of crucible furnaces are used for melting copper alloys. For small melting volumes they provide high quality alloy, since in them there is no direct contact of the alloy with combustion products, and the surface of the metal mirror is very small. Graphite or corundum crucibles are used for melting.
Rice. 1. Electric furnace type DMK: 1 - lining; 2 - steel casing; 3-tooth rims; 4 - hoses for water supply; 5 - graphitized electrodes; 6 - gears; 7 - water-cooled seals; 8 - doors; 9 - drain sock; 10 - electric motor; 11 - drive mechanism.
Melting in electric furnaces. Electric furnaces for melting copper alloys are divided into arc and induction.
Melting in electric arc furnaces. For melting, electric arc furnaces with indirect heating are used, i.e., those in which an electric arc is formed between two horizontal graphite electrodes.
The DMK furnace (Fig. 1) has the form of a drum with a loading knob, holes for electrodes and a chute for draining the alloy.
The furnace casing is lined with silica or fireclay bricks. Toothed rims are mounted on the ends of the casing, coupled with gear wheels, which make it possible to rock the furnace during the melting process, thereby ensuring the production of an alloy that is homogeneous in composition and evenly heated.
Melting begins with preparatory work: thoroughly cleaning the furnace from the remnants of the previous melt, checking the serviceability of the mechanisms and supplying water to the water-cooled seals. After this, the lining is heated to a temperature of 700-800 °C, the electrodes are removed from the furnace and several shovels of dry calcined charcoal are poured onto its bottom, then charge materials preheated to 150-200 °C are loaded: first, fines, sprues, scrap and on top - large pieces. The charge should be located no closer than 50 mm from the electrodes and should not interfere with their free movement along the furnace. After installing the electrodes, close the loading window and excite an electric arc, which is accomplished by bringing the electrodes closer together and quickly removing one of them a short distance using the hand wheel of the mechanism for moving them.
The process of melting the charge is carried out intensively. After 20-30 minutes, turn on the reverse mechanism for rocking the furnace, first by 25-30°, then gradually increase the rocking to 90°, and after melting the entire charge, to 160°. This avoids local overheating of the alloy and promotes better mixing. The alloy is deoxidized, low-melting additives are added, refined, heated to the required temperature and released from the furnace.
Melting in induction furnaces. For melting copper alloys, induction furnaces with and without a steel core are used.
An induction furnace with a steel core, a schematic section of which is shown in Fig. 2, is a transformer, the primary winding of which is a copper coil mounted on a core made of electrical steel plates 0.35-0.5 mm thick. The secondary winding is a ring of Liquid Alloy located in the melting channel. An alternating current of industrial frequency, passing through the primary winding, creates a magnetic flux around it, which closes through the magnetic steel core of the transformer, and induces a current in the alloy located in the ring channels. The alloy filling the channels communicates with the liquid alloy bath and transfers heat to it due to the circulation created by the temperature difference of the alloy along the height of the furnace.
Rice. 2. Diagram of an induction furnace with a steel core: 1 - chamber; 2- lining; 3- thermal insulation; 4 - primary winding; 5 - melting channel; 6 - magnetic core.
The peculiarity of melting in induction furnaces is that the liquid alloy filling the channels must remain in the furnace even after the melt is released to form a closed electrical circuit during subsequent melting. In this regard, the transition to melting a new alloy in induction furnaces is difficult. In this case, it is necessary to drain all the alloy from the channels and make one or two wash melts of the non-critical alloy.
After filling the annular channels and the “swamp” (a layer of liquid alloy 30-50 mm thick, located above the channels) with liquid alloy and heating the furnace, a preheated charge is loaded: first copper, and after it is melted, return and secondary alloys. When the entire charge is melted, deoxidation is carried out, slag is removed from the surface and easily oxidized elements are introduced. When draining the finished alloy, it is necessary to leave it in the channels and above them in a layer of 30-50 mm.
Melting in induction crucible furnaces. IN last years Induction crucible furnaces of the ILT type began to be used for melting copper-based alloys - bronze and brass. Metal waste in these furnaces does not exceed 0.5-1%.
4. Features of melting and casting copper alloys
When melting copper alloys, the charge usually includes red electrolytic copper, which is melted and deoxidized with phosphorous copper before loading the remaining components of the charge into the furnace. Copper smelting should occur very quickly under a layer of well-dried and calcined charcoal. The furnace must be well heated before loading copper. The quality of deoxidation can be checked by a technological test: when bent, a poured and cooled block should not produce cracks at the bend site.
Melting tin bronze.
A portion of the secondary and recycled alloys is loaded into a heated furnace and covered with a layer of dry charcoal, which, after melting the charge, should evenly cover the entire surface of the liquid alloy. As the initial portion of the charge melts, the remainder of the charge, heated to a temperature of 150-200 °C, is introduced into the furnace in parts or in full. Of the fresh metals used for sub-charging, copper and nickel are loaded into the furnace simultaneously with the first portion of the charge, and zinc, lead and tin are introduced directly into the bath towards the end of the smelting to reduce their waste.
After melting the entire charge and reaching the required temperature, the alloy is deoxidized with phosphorous copper in an amount of 0.2% by weight of the charge and coated with a well-dried flux consisting of 60% soda ash, 33% fluorspar and 7% borax. Flux consumption is 2-3% of the charge weight. Then the alloy is heated to a temperature of 1250-1300 °C and kept under flux for 20-30 minutes, stirring it periodically. After this, the resulting slag is cleaned off and the alloy is released into a ladle for pouring into molds.
Melting brass. Let's consider the technology of melting silicon brass grade LKS80-3-3.
When melting a charge of fresh metals, copper is first melted and deoxidized with phosphorous copper, then a copper-silicon master alloy, zinc and lead are introduced.
If the charge contains a recycled alloy of the same grade, then it is loaded together with copper in the case when the mass of fresh metals does not exceed 30-40% of the mass of the entire charge. If there is a large amount of fresh metals, the recycled alloy is loaded after the copper has been melted and the remaining elements have been introduced. Given the tendency of this alloy to absorb gases, melting must be accelerated, maintaining a neutral or slightly oxidized atmosphere in the furnace. Broken glass and borax can be used as flux.
For degassing, the alloy is heated to a temperature of 1150-1160 °C and maintained at this temperature for 10-15 minutes. The zinc vapor released during aging mechanically carries along dissolved gases and removes them from the liquid alloy. To compensate for the increased loss of zinc during aging of the alloy, before pouring it into the furnace, an additional amount of zinc is introduced.
After the end of exposure, the alloy is cooled to a temperature of 1050-1100 ° C and the gas content in it is checked (by taking a sample). When there is an excess amount of gases in the alloy, the sample in the glass “grows”. In this case, the alloy is “frozen” by cooling it to the solidification temperature and then quickly heating it to the casting temperature.
At the end of the melting, a sample is taken for chemical analysis, as well as a technological sample, which makes it possible to determine the quality of the alloy and the content of gases in it by the fracture; the sample is compared with standards.
To obtain high-quality copper alloys, careful monitoring of compliance with the rules for the preparation of source materials and the smelting process is necessary. Particular attention should be paid to controlling the temperature of the liquid alloy both during the melting process itself and when it is released from the furnace and casting.
Typically, immersion thermocouples with protective covers made of heat-resistant steel are used to measure the temperature of the alloy. Thermocouples, in combination with automatic equipment, can independently regulate temperature regime in furnaces or by means of light or sound alarms to attract the attention of a worker to a violation of the temperature regime.
Due to the fact that copper alloys tend to absorb gases and oxidize, when pouring molds, it is necessary to maintain a low jet height, not interrupt it, and prevent splashing of the alloy. Pouring is carried out through the toe of hand and crane ladles, similar to those used for casting cast iron.
Copper conducts electricity well, which allows it to be used in electrical and industrial equipment. It is also very plastic and can be easily processed with grinding and carving equipment. Products made from this metal are widely used not only in production, but also in everyday life. Therefore, many craftsmen are wondering how to melt copper at home and make something useful out of it.
Main characteristics of the metal
This non-ferrous metal occurs in the ground in the form of ore. Its reserves are available in Russia, Kazakhstan, and South America. Due to the oxide film, the metal has a reddish-yellow tint. In addition, the oxide not only gives an interesting color, but also enhances the anti-corrosion qualities of the metal. Without an oxide film, the material is painted in a light yellow tone.
The melting point of pure copper is 1082°C; for alloys this figure ranges from 930–1100°C. This is not too much value and is enough to melt copper at home.
The characteristics of this metal are as follows:
- copper gives off heat well, this figure is 390 J/kg;
- density – 8.93 x 103 kg/m²;
- during the boiling process of the metal at t = 2595°C, carbon is released;
- resistivity at temperatures from 20 to 100°C is 1.78*10 Ohm/m.
The melting point of bronze is lower than that of copper due to the tin present in its composition - 960–1050°C. The alloy of this metal with zinc melts at a temperature of 900°C. This allows it to be melted using simple heating devices.
Melting graph
The metal melting schedule consists of five stages:
- First stage– at t = 20–100°C the material remains solid. The next heating helps remove the oxide film, and the copper changes its color.
- Second stage– at t = 1082°C the metal turns into a liquid state, its color becomes white. During this period, the crystal lattice of the material is destroyed.
- Third stage– at t = 2595°C, the non-ferrous metal begins to boil, releasing carbon.
- Fourth stage– heating stops, the metal cools, and the peak temperature gradually decreases.
- Fifth stage– the material returns to a solid state, and the metal cools completely.
When choosing scrap for recycling, it is necessary to take into account that pure copper is used in electrical devices. Bronze or brass alloys, from which many antiques are made, often contain toxic substances. Therefore, when working with them, precautions should be taken.
Methods Used to Melt Copper at Home
Melting copper at home is possible in several ways. To do this you will need certain tools:
- raw materials;
- heat-resistant crucible;
- fireproof stand;
- wire hook;
- tongs for removing the hot crucible;
- protective equipment: glasses, suit, gloves.
Melting copper at home and in production occurs in the same way. This is achieved by the following methods:
- using a muffle furnace;
- using oxygen flame;
- mountain;
- blowtorch;
- melting in a microwave oven.
Using a muffle furnace
Casting copper using a muffle furnace is a fairly simple and convenient method. Copper raw materials are crushed into pieces so that they melt faster. The finished material is placed in a graphite crucible and placed in a heated oven. The casting mold must have a higher melting point than the non-ferrous metal.
When the raw material becomes liquid, the crucible is removed from the furnace using tongs. Use a hook to remove the oxide film from the metal surface. Then the liquid is poured into a pre-prepared form.
Gas torch or blowtorch
A special oven can be replaced by a gas burner or a blowtorch. It is placed under the bottom of the container with metal and care is taken that the flame covers the bottom completely.
When using this method, the material quickly oxidizes, therefore, to prevent the formation of a thick oxide film, the raw material is sprinkled with charcoal particles on top.
To melt low-melting alloys made of brass or bronze, a gas torch or blowtorch is sufficient.
Horn
You can melt copper using a forge. To do this, a crucible with crushed raw materials is placed on hot charcoal. To speed up the melting, use a home vacuum cleaner turned on in blowing mode. The pipe must have a metal tapered tip, since the plastic will melt under the influence of high temperatures. This method is suitable for those who regularly smelt copper at home.
To increase the temperature, more air must be blown into the forge.
Microwave
A powerful microwave oven will help you melt copper at home. To do this, remove the rotating plate. To preserve the functionality of the internal parts of the equipment, it is necessary to place the crucible in a heat-resistant material, for example, line it with refractory bricks.
The scope of application of copper is very wide. Therefore, many people ask questions: how to properly melt copper and what is its melting point? Copper has a fairly low melting point, as do its alloys, but conditions vary depending on the amount of impurities.
Copper and its uses
According to scientists, the primitive ancestors of modern man found copper nuggets, which were sometimes of enormous size. In Latin it has the name Cuprum. The ancient Greeks mined it in Cyprus - hence the name.
It is worth noting that environmentalists are concerned about the consequences of metal mining. With the open mining method, the quarry turns into a source of toxic substances. The most toxic lake in the world - Berkeley Pit (Montana, USA) - originated from the crater of a copper mine.
Due to the fact that the melting point is quite low (1083 ° C), it was not difficult to melt copper ore or nuggets directly on the fire. This ease of melting made it possible to use this metal everywhere to make household items, tools, weapons, and jewelry.
Tools made from this metal and its alloys do not create sparks. This determines their wide application in those areas where there are increased safety requirements (in flammable and explosive industries).
Since ancient times, people have used copper regularly, the scope of its use was quite extensive, but Cuprum ranks only twenty-third among other chemical components in terms of the amount found underground. Most often it can be found in nature in the form of various compounds, components of sulfide ores. The most popular are copper luster and copper pyrite. There are several methods for extracting pure metal from ore.
How copper was smelted before
We have already written the following information above: Cuprum melts easily, since the melting temperature is low. This fact made it possible to process metal even at the beginning of civilization. It is worth saying: we are indebted to the ancient metallurgists. They found ways to mine and melt both pure metal and alloys.
Melting is the process of changing from a solid to a liquid. This was done by simple heating, which was possible due to the low melting point. Next, tin was added. This is how bronze was obtained. Copper was inferior to bronze in strength, which is why weapons were made from the alloy. 
Copper and its alloys
Copper
The copper used by industry today is not pure Cuprum metal. Composition contains great amount other components: iron, nickel, antimony, arsenic. The quality, and therefore the brand, is determined by the percentage of impurities (their content is up to 1%). This metal is technically pure. Very important qualities this metal - high performance electrical conductivity, thermal conductivity. This determines the low temperature for melting. The melting point of copper is 1084°C.
By itself, it is a fairly flexible ductile metal, so it is very widely used in various technical branches and industries. How to melt copper? The ideal method for melting red copper is with an oxy-acetylene flame, a carbon arc or resistance welding.
Brass
Brass is a mixture of copper and zinc, the percentage ratio can be up to equivalent: 50 to 50.: melts at 800-950 degrees Celsius, the melting point varies depending on the percentage ratio of the two metals. The rule is this: the less zinc, the lower the melting point.
What is the scope of use of this alloy? It is often used as a foundry material, as well as sheet metal.
In addition to zinc, various brands contain aluminum, lead, tin, manganese, and iron. The content of other components will influence the smelting process.
It is good to weld brass with an oxy-acetylene flame. Other types are not so preferable, since zinc will evaporate rapidly.
Bronze
The alloy of Cuprum and Stannum (tin) is called bronze. There are also tin-free ones - they do not contain tin. For example, with a certain percentage of aluminum or iron and manganese.
The scope of application of bronze is not so wide. Most often it is used as a casting material in the production of friction bearings, and sometimes also for the manufacture of jewelry and interior items.
As for smelting, the temperature depends on the presence, quantity and composition of impurities. In general, most often the temperature is as follows: tin-bearing types of bronze - 900-950°, tin-free types with the presence of aluminum and other elements - 950-1080°C. They can be welded with an oxy-acetylene flame, or by electric arc welding.
