(57) The invention relates to nonferrous metallurgy, particularly to the methods of processing
of the secondary copper-bearing raw material, for further use of metal in the articles
of electrical engineering purpose. The method includes the preparation of copper melt
at the first stage, copper refining and recovery at the second stage with the carbon-bearing
material and the increase in temperature, formation and pulling of the continuous
cast section, preparation of the produced articles for further transportation and
storage. According to the invention, after melting the copper melt passes into a distribution
chamber through graphite with the density of 1,56-2,2 g/cm
3 in the form of perforated element at the temperature of 1140-1175°C, and the cast
section is subject to rolling by the way of its passing with the linear speed of 1,5-2,5
m/sec through a induction heater providing the high-temperature heating up to 650-800°C
with the subsequent shock cooling of the cast section to 50-55°C. Consequently, the
cast section is subject to double metal structure recrystallization, at the first
stage - at rolling, and at the second stage - at high-speed and high-temperature heating
and shock cooling. For provision of efficiency of oxygen extraction from the copper
melt and provision of the set performance the area of channels of the perforated graphite
element should make 10 - 23 m
2, and the copper melt outflow speed to the distribution chamber through the perforated
graphite element makes 0,1-0,12 m/sec.
The technical result of the invention is the possibility to produce the articles of
electrical engineering purpose from 100% copper alloys with the copper content in
it of at least 98%.
[0001] The invention relates to nonferrous metallurgy, particularly to the secondary copper-bearing
raw material processing methods, for further use of metal in the articles of electrical
engineering purpose.
[0002] The method of processing of the secondary copper-bearing raw material in the form
of copper wires with varnish, polymeric and cotton insulation, including loading of
the initial batch into molten salt, melting in the salt-bath furnace at the temperature
exceeding copper melting point, with the subsequent ingot and semifinished product
pouring, is known. Iron is preliminary removed from the secondary raw material, the
batch is loaded into molten salt of alkaline and alkaline-earth metals and is melted
higher than the copper melting temperature by 10-310°C, then the liquid copper is
recovered, the formed carbon deposit is removed from the salt surface, thereafter
the cycle is repeated, in this case the correlation of volumes of loaded batch and
molten salt is maintained within the limits of (2-3,4):1 (
RU 2181386, cl. C22B7/00, 2002).
[0003] But this method doesn't allow to recover copper of high quality due to the inhomogeneity
of its structure stipulated by the availability of cracks, pores, various inclusions,
as well as by the high content of oxygen not allowing to use copper in the articles
of electric engineering purpose.
[0004] The method of fire refining of copper at processing of the secondary copper-bearing
raw material (
RU 2391420, cl. C22B15/14, C22B9/10, 2010) is known. The method involves the slug feed of batch materials and metal batch.
The temperature of copper melt is maintained at the level of 1220-1240°C. Whereupon
the oxidation refining of the copper melt is conducted by air blasting of the melt
with loading into the bath of flux containing the mixture of aegirine concentrate
and quartz sand into the bath. The flux is loaded portionwise proportionally to its
melting in the bath and to the temperature of slag melting in the furnace 1220-1240°C.
The concentrate includes, in mass %: 82,5 of aegirine - Na, Fe[Si
2O
6]; 6,7 of nepheline - KNa
3 [AlSiO
4]
4; 4,3 of sphene- CaTiSiO
4; 3.1 of apatite - Ca
10 (PO
4)
6; 3,4 of the other substances comprising mainly of the titanomagnetite. Upon the completion
of oxidation refining of the copper melt its air blasting was shut off and the slag
was removed. After slag removal the copper melt was deoxidized according to the familiar
technology with the aid of natural gas.
[0005] But the copper recovered in this way is contaminated by the various impurities and
contains the high quantity of oxygen, its use is not allowed in the articles of electrical
engineering purpose, because the high requirements to availability of impurities are
specified to such articles.
[0006] The method of combined casting and rolling of copper alloys (
RU 2163855, cl. B22D11/12, 2001), including the recovery of melt, its accumulation in mixers, alloying, feeding of
melt by chute to the receiving pit of casting machine, formation of continuous casting
in the rotary-type mold, yield of cast section from the mold, feeding of the case
section to the continuous rolling mill and reeling on of the rods into bulls, is known.
Prior to entry of the melt into the receiving pit of casting machine the oxygen is
removed from the melted copper by the way of formation on the way of the liquid copper
running of the part filled with the ignited pet coke and/or with the graphite pieces.
The melt mirror in the receiving pit of casting machine is covered with the pet coke
and/or the graphite pieces.
[0007] The part on the way of liquid copper running filled with the graphite pieces won't
be able to provide the sufficient contact of copper with graphite along the whole
section, that is why the oxygen content will remain at the sufficiently high level
up to 300 ppm. Such oxygen content doesn't meet the requirements lodged to the oxygen-free
copper, and hence the breakage level is increased at the rolling and drawing of the
cast section, it has an impact on the quality of wire.
[0008] The prototype is the method of horizontal casting of copper including the copper
melting at the temperature of 1084°C by the way of covering of the surface with the
ignited charcoal and carbon oxide atmosphere creation over the melt. At the second
stage the copper refining and recovery at the temperature of 1180-1200°C to the oxygen
content in it of no more than 8 ppm is made. The melt is stabilized by the chemical
composition and temperature with simultaneous removing of the gas products of the
reaction. The casting is made through the graphite mold with the stepwise pulling
of the article. Speed, step and frequency of steps are calculated depending on the
type of the recovered articles. The preparation of the produced articles for further
transportation and storage is made (
RU 2458758, cl. B22D11/04, C22B15/14, 2012).
[0009] But for fulfillment of the familiar method it is necessary to use the high-grade
raw material - the cathode copper of M0, M1 (State standard 859-2001) grades, and
the extraneous impurities uncontaminated by oil and referred to A class,1 group, 1
grade (State standard 1639) are used as copper-mine tailings. It is possible to refer
to the defects the high energy consumption affecting the end cost of the articles,
because the eddy-current furnace, as well as the possible fast breakdown of lining,
and, subsequently, the additional expenses for performance of lining works.
[0010] The task of this invention is the development of the method of combined casting and
rolling of the cast section with the increased physical and technical characteristics
complying with State standard due to the decrease of oxygen in the copper melt to
3-5 ppm.
[0011] The technical result of invention is the possibility of recovery of the articles
of electrical engineering purpose from 100% copper scrap with the content of copper
in them of at least than 98%.
[0012] The task set and, as a consequence, the specified technical result are achieved due
to the fact that the method of combined casting and rolling of copper alloys from
copper scraps includes melt preparation, by the way of copper melting at the first
stage, copper refining and recovery at the second stage with the use of the carbon-bearing
material and temperature increase, formation and pulling of continuous cast section,
preparation of the produced articles for the further transportation and storage. According
to the invention, after melting the copper melt is fed to a distribution chamber through
graphite with the density 1,56-2,2 g/cm
3 in the form of the perforated element at the temperature 1140-1175°C, and the cast
section is rolled by the way of its passing with the linear speed of 1,5 - 2,5 m/sec
through a induction heater providing the high temperature heating to 650-800°C with
the subsequent shock cooling to 50-55°C. So, the cast section is subject to double
metal structure recrystallization, at the first stage - at rolling, and at the second
stage - at high-speed and high-temperature heating and shock cooling.
[0013] For provision of efficiency of oxygen extraction from the copper melt and provision
of the set performance the area of channels of the perforated graphite element should
make 10 - 23 m
2, and the copper melt outflow speed to the distribution chamber through the perforated
graphite element - 0,1-0,12 m/sec.
[0014] Passing of the copper melt to the distribution chamber through the graphite provides
the additional copper recovery to the content in it of the oxygen to 5 ppm and lower.
In this case at the moment of crossflow of the metal from degasification chamber to
the distribution chamber the temperature should be increased to 1140-1175°C, it will
allow to decrease the copper density. If the temperature of melt in the crossflow
area decreases lower than 1140°C, the crystallization of metal can occur in the graphite
channels, as well as the blocking of perforation channels and graphite pores, and
the temperature rise higher than 1175°C is inexpedient, because it results in the
excessive energy consumption. The copper viscosity due to the maintenance of temperature
mode of crossflow is maintained at the level of 7860 kg/m
3, it creates its free egress at the speed of 0,1-0,12 m/sec and conduces the compliance
with the required capacity of the unit. Choice of the graphite with density of 1,56-2,2
g/cm
3 in the form of perforated element encourages the efficient copper deoxidation. In
this case the graphite parameters were chosen experimentally, because at decrease
in its density less than for 1,56 g/cm
3, the deoxidation efficiency decreases and the extraction of oxygen from the melt
decreases due to the decrease in the weight percentage of carbon, and increase in
density for more than 2,2 g/cm
3 increases the graphite value resulting in the increase in the cost of production.
Graphite block perforation channel area is also chosen by practical consideration
and should be within the limits 10-23m
2, because the deoxidation efficiency decreases in case of decrease in the contact
area, and its increase decreases the physical and mathematical characteristics of
the graphite itself and results in the fast deterioration of the graphite perforated
element.
[0015] The cast section pulling is made on the rolling mill with recovery of "rod" which
is subject to combined high-temperature heating and shock cooling. The high-temperature
heating provides the soft condition of the "rod" allowing to expand the range of "rod"
sections from 30 to 100mm
2, in this case the linear speed of rod passing through the induction heater, heating
and cooling temperature were chosen experimentally. The chosen parameters provide
the close-bodied, homogeneous structure of the "rod", increase its physical and mechanical
characteristics required for the articles of electrical engineering purpose.
[0016] The example of fulfillment of the method was conducted at recovery of the rod with
the diameter of 8 mm. The tests were implemented on melting and casting unit "Copper
Up Line ZG" with the capacity of 2t/hour by melt.
[0017] The delivery of batch materials included the fractional loading through the charging
door of the melting bath of furnace with the help of the power-driven loader. The
batch was loaded into the bath in portions by 500 kg - the secondary copper-mine tailings
with copper content of at least 95% - at the switched on burner and natural gas burning
with the excess air coefficient of 1,1. Loading of the subsequent batch portion was
made after melting of the previous portion. The melting temperature was maintained
at the level of 1200 - 1260°C. Due to welding deposition by the melting chamber, the
metal was fed by crossflow into the degassing chamber of the furnace, where it was
adjusted to the predetermined chemical composition and to the oxygen content level
of no more than 100 ppm.
[0018] The further copper deoxidation was made on the way of metal crossflow from the degassing
chamber into the reduction chamber by the way of passing of the melt through the high-carbon
perforated element - graphite. The graphite with density of 1,75g/cm
3 was used in our case. The total contact area with graphite made 20m2, the melt egress
speed at the unit capacity of up to 2t/hour made 0,11m/sec. The melt temperature in
the crossflow area was maintained by the way of induction heating at the level of
1168°C. The oxygen content in melt at the entry to the distribution chamber in those
conditions made 10 ppm. In the distribution chamber the oxygen in melt was additionally
decreased to the level of 5 ppm and lower, after that the melting was fed to the water-cooling
vertical mold for formation of the round cast section with the diameter of 18,5mm.
The rolling into bulls up to 6,0 tons was made after cooling of the cast section.
[0019] Then the cast section was welded for the purpose of provision of process continuity
and directed to the cold pilger mill, where the rod with the diameter 8,0 mm was produced
by the way of unidirectional deformation and the total relative reduction by 81,3%,
i.e. the rolling from the diameter of less than 18,5 mm. Then the rod in the continuous
process was fed to the high-speed heating by the way of its passing with the linear
speed of 2,4 m/sec though the built-in annealing (heating) to the temperature of 800°C
with the subsequent combined shock cooling to the temperature of 54°C
[0020] Accordingly, the rod with the diameter 8 mm from 100% copper scraps was produced.
Due to the development and compliance with the new modes the oxygen-free metal with
the homogeneous finely crystalline structure and with the homogeneous physical and
mechanical characteristics complying with State standard was produced.
Table 1
Nº |
Melt parameters |
Finished rod parameters |
Casting temperature, °C |
Crossflow temperature in the reduction chamber, °C |
Oxygen content in the distribution chamber, ppm |
Rod diameter, Ø MM |
Breaking strength, kg/mm2 |
Breaking strain, % |
1 |
1180±5 |
1140 |
3 |
8 |
22 |
42 |
2 |
1180±5 |
1160 |
4 |
8 |
21,5 |
42 |
3 |
1180±5 |
1175 |
5 |
8 |
21 |
38 |
[0021] The finished rod took
the soft condition, i.e. the strain and the breaking strength complying with State
standard, moreover, the highly efficient gas-shielded unit was used in the applied
method, where the main source of energy was the natural gas (or any liquid fuel),
it essentially decrease the expenses for production of 1 ton of article in comparison
with the prototype.
[0022] At present the method passed the experimental and laboratory tests and its test on
the industrial-scale plant is being prepared.
1. The method of combined casting and rolling of copper alloys from the copper scraps
including the preparation of copper melt at the first stage, copper refining and recovery
at the second stage with the use of carbon-bearing material and the increase in temperature,
formation and pulling of the continuous cast section, preparation of the produced
articles for further transportation and storage, characterized by the fact that after melting the copper melt passes into a distribution chamber through
graphite with the density of 1,56-2,2 g/cm3 in the form of perforated element at the temperature of 1140-1175°C, and the cast
section is subject to rolling by the way of its passing with the linear speed of 1,5-2,5
m/sec through a induction heater providing the high-temperature heating up to 650-800°C
with the subsequent shock cooling of the cast section to 50-55°C.
2. The method according to claim 1, characterized by the fact that the perforated graphite element channel area makes 10-23m2.
3. The method according to claim 1, characterized by the fact that the copper melt egress speed to the distribution chamber through the
perforated graphite element makes 0,1-0,12 m/sec.