4.2 recycled aluminum components and pre-processing of raw materials
4.2.1 recycled aluminum raw material composition
4.2.1.1 aluminum scrap sources
Currently the use of renewable aluminum aluminum scrap mainly from two aspects, one is imported from abroad aluminum scrap, aluminum scrap and second, domestically generated.
1, imports of aluminum scrap
In recent years a large number of domestic and imported aluminum scrap from abroad. On the import of aluminum scrap the ingredient, except for a few outside classification clear majority are mixed. Can generally be divided into the following categories:
① single species scrap
Such scrap parts are generally a certain type of waste, such as a piston internal combustion engine, the vehicle deceleration chassis, car wheels, front and rear safety catch. Aluminum doors and windows. These scrap imports have clear classification when a single species, and are imported in bulk, so is the quality of recycled aluminum materials.
② aluminum scrap slice
Aluminum scrap slice slicing is also known, it is a high-grade aluminum scrap. It is called a slice, because many countries in dealing with scrap cars, scrap equipment and various types of waste household appliances, are whirling mechanical methods to break into the debris, and then mechanized sorting, sub-elected The scrap is scrap slices. The method is also used crushing In addition, some of the scrap recycling sector reprocessing large volumes of parts of its broken into scrap, aluminum scrap such scrap also known as slices. Scrap slice convenient transportation and easy sorting, texture is relatively clean, but also high-quality scrap material. Currently scrap trade again in the international market, the largest share of slices, slice forward standardization of various types of development. On slices of ingredient, it is generally divided into several grades, wherein the mixture of high-grade sections are relatively pure various scrap and alloys, most without any treatment into the furnace to smelt, a small amount compared with the grade Low slices containing different amounts of other impurities, typically containing more than scrap another 80% to 90%, including when impurities are mainly iron and steel waste and scrap copper and other nonferrous metals, also contain small amounts of waste rubber, etc., and then by hand-picked to give pure The scrap material. Smelting scrap slice is relatively easy, convenient into the furnace smelting, easy cleaning, less flux consumption, metal recovery, low energy consumption, low processing costs are also very popular with users, are generally large-scale renewable slice of aluminum The main raw material.
Quality scrap slice expensive than other aluminum, large-scale adaptation of the modern enterprise, and in the international market difficult to obtain, so our wholly-owned or joint ventures in addition to its own imports, general rarely use such renewable aluminum scrap .
③ mixed scrap material
Such aluminum scrap complex composition, physical shapes, in addition to aluminum scrap, but also contain a certain amount of scrap steel, scrap lead, zinc and other metal scrap and waste rubber, waste wood, waste plastics, stones, and sometimes part scrap and scrap iron and steel machinery together, these wastes are complicated, a few large blocks of scrap, clear surface, easy sorting. Such waste material before smelting process must be pre-sorting, ie, artificial pick scrap and other impurities.
④ incinerated crushed aluminum aluminum-containing material
Such low-grade aluminum material is an aluminum-containing waste, mainly a variety of household appliances and other scrap crushed, sorted and then by burning scrap material part of the formation. The purpose is to remove the burning rubber, waste plastics and other combustible materials. Such aluminum-containing scrap aluminum content is generally about 40% to 60%, the rest is mainly rubbish (brick stone), scrap iron and steel, extremely small amounts of copper (copper) and other nonferrous metals. Block of aluminum is generally 10 cm or less, in the incineration process, some aluminum and low melting point materials such as zinc, lead, tin and so melted glass material surface is formed with other materials, visually indistinguishable, unable sorting .
⑤ mixed shredded scrap material
Such waste is the lowest grade of aluminum, its composition is very complex, which contains a variety of scrap in 40% to 50%, the rest is scrap iron and steel, a small amount of lead and copper, a lot of garbage, stones and soil, waste plastics, waste paper, about 25% of the soil, scrap accounted for 10% to 20%, gravel accounted for 3% to 5%.
2, the domestic shredded scrap material recycling
Domestic recycling aluminum scrap most pure, substantially free of impurities (except for man-doping) can basically be divided into three categories, namely waste recycling sector often say cooked aluminum, aluminum waste and scrap raw aluminum alloy, primary aluminum scrap raw cast aluminum scrap and aluminum scrap alloy. Mostly used machine parts (such as scrap auto parts, waste mold, scrap aluminum pots and pans, engine pistons, etc.). Waste cooked aluminum generally refers to an aluminum content of more than 99% of the scrap (such as scrap cable, scrap household utensils, kettle, etc.). Waste aluminum alloy (such as aircraft aluminum scrap, aluminum frames, etc.). On the production sector, life can be divided into aluminum scrap and industrial scrap.
① scrap produced in the areas of life such as waste household utensils, kettle scrap aluminum pots and pans, waste household appliances in the scrap parts, scrap wire, waste packaging materials. Waste electrical and mechanical equipment in the aluminum and its alloys used machine parts (such as waste automotive parts, aircraft aluminum scrap, waste mold, the internal combustion engine piston waste, scrap cables, aluminum tubes.
② manufacturers produce scrap material such scrap is generally referred to new waste, including scrap, aluminum and its alloys from waste materials in the production process of raw aluminum, aluminum produced during processing; machining system scrap produced aluminum and its alloys, aluminum scrap and waste end products; Riser and waste castings of scrap cable and cable plant produced the foundry industry, in addition to the end of the stick with the new waste oil outside of debris, all grades higher scrap material, if waste generation in the enterprise can clearly classify conservation, use a high value.
③ smelting aluminum and aluminum dross generated during the growth of such waste that is often said aluminum gray, where there will be a place where molten aluminum gray aluminum produced, for example, in aluminum production, smelting, processing and scrap regeneration will have a lot of gray aluminum, especially aluminum scrap produced during regeneration smelting aluminum ash is more complex composition of aluminum scrap, the more impurities, the more severe surface contamination, the more aluminum gray. Aluminum gray aluminum content and the choice of cover agent and smelting technology, generally below 10% aluminum content, high up above 20%.
4.2.1.2 composition characteristics of aluminum scrap
The main source of aluminum scrap is industrial waste, recycling of materials, as well as casting pouring run system. Its composition is relatively complex. In most cases, which contain more foreign materials, including various organic substances such as plastics, water, etc., such substances before the melting process if you do not clean up, can cause serious breathing alloy melt in the subsequent solidification blowholes, porosity and other defects in the process. In addition, some non-aluminum metal components mixed in the same cause material failure, deterioration of performance. Various non-metallic mineral non-metallic inclusions caused mixed performance quality of the material will also decrease. Because of such characteristics, pretreatment recycled aluminum production process is an important part of the first aluminum scrap in order to purify the material as much as possible, to reduce the quality of recycled aluminum is not conducive factor to a minimum.
4.2.2 Pretreatment of aluminum scrap
4.2.2.1 domestic aluminum scrap pretreatment basic principles
Since aluminum scrap composition is quite complex, and therefore its capacity as the main raw material for secondary processing alloy material must be necessary pretreatment.
In theory, all impurities are removed should all actual industrial processes taking into account cost factors, can only solve the principal contradiction. The usual principles are:
Of raw material components according to broad categories, the classification is based so close to some grade aluminum components.
Of aluminum scrap has classified the necessary dismantling, removing chunks of non-aluminum metals or organic impurities.
The raw materials necessary for cleaning, including cleaning water or an organic solvent, such as sandblasting.
After the above processing of aluminum scrap can be used as the basic raw material alloy melting of use.
4.2.2.2 Status pretreated aluminum scrap
Aluminum scrap pretreatment One purpose of the removal of other metals and impurities inclusions of aluminum scrap, aluminum scrap the second is to classification according to their composition, so that one of the alloy components get maximum use. Third, the oil surface of aluminum scrap, oxides and coatings disposed of. The end result is pretreated aluminum scrap into the furnace treated to comply with the conditions of the charge, the four aluminum-containing waste material to make aluminum (including alumina) to give the most economical and rational use.
Domestic aluminum scrap pretreatment technology is also very simple and backward, even in a large aluminum plant regeneration, the pretreatment of aluminum scrap is also not the more advanced technology. From the current point of view, mainly the following pretreatment technology.
① single species or substantially free of other impurities of aluminum scrap is generally not as complex pretreatment, only by species and composition of waste classification, individually stacked scrap a single species as long as the testing by using a component, you can know quantities of ingredients, is the quality of recycled aluminum raw material, generally without any pre-treatment to the smelting furnace. When a metal smelting, often choose the appropriate ingredients and a large variety of scrap directly into the smelting furnace reflection, which can easily melt into corresponding grades of aluminum. Some copper, zinc scrap high, but also master alloy used as an adjustment component. In a small reflection furnace or crucible furnace business, they have needed to be broken into large volumes of scrap into the furnace slug line with the specifications.
② for the higher grade scrap sections, the main ingredients are cast aluminum, aluminum alloys, aluminum, etc., many of which the first two grades, grade classification is still difficult to press, in large regeneration aluminum, generally after sieved to remove dirt and other mixed, ie directly into the furnace smelting. Small renewable aluminum, for such scrap will have artificial dividing it into cast aluminum, aluminum and aluminum alloy, and then were used.
③ For the low-end chips and burned broken scrap material (which generally do not have large-scale renewable aluminum) to perform complex sorting, its complex composition, in addition to scrap also contains copper, scrap, scrap lead and other metals, and contains other waste. Sorting of such waste mainly by labor, one screening to screen out dirt and garbage, and then hand selected work points. Mostly manual sorting at station conducted mainly by visual inspection and experience worker selection, the first sub-elected non-metal waste and sorting of scrap metal, which for copper and aluminum scrap exceptionally careful selection, because copper can increase value, aluminum scrap such as scrap wire, are renewable smelting adjust the composition of the finest raw materials. The separation of the scrap is mixed, generally no longer subdivision.
Currently domestic scrap aluminum pretreatment basically no mechanization and automation, mainly by labor, tools using magnets, steel file, with the experience, this sorting method low efficiency, poor quality, high cost, and waste Most non-ferrous metals such as copper, aluminum have been contaminated, manual sorting difficult, has lagged far behind. Urgent need to study advanced scrap pretreatment technology.
4.2.3 advanced aluminum scrap pretreatment technology
Advanced aluminum scrap pretreatment technologies aimed at achieving aluminum scrap sorting mechanization and automation to maximize the removal of metal impurities and nonmetallic impurities, aluminum scrap and effective classification sorting by alloy composition, the best sorting method is based on the main component of the alloy scrap is divided into several categories, such as aluminum alloy, magnesium alloy, aluminum and copper alloys, aluminum and zinc alloy, aluminum-silicon alloy. This can reduce the difficulty of the smelting process and adjust the composition of impurity removal technology, and comprehensive utilization of waste aluminum alloy components, especially zinc, copper, magnesium high scrap, should be stored separately as aluminum smelting intermediate adjustment component alloy materials. Current advanced aluminum scrap pretreatment technologies are:
① winnowing separation of waste paper, waste plastics and dust. Contain more or less of various scrap paper, waste plastic film and dust, the ideal process is winnowing law. Law winnowing process is simple, most of the light can be separated waste efficiently, but with the wind election law needs with better dust collection system to prevent dust pollution of the environment, sub-elected to waste paper, waste plastic film Usually not appropriate to continue sorting, can be used as fuel.
② using magnetic separation equipment magnetic sorted scrap waste. Iron, aluminum and its alloys harmful substances affect the mechanical properties of the aluminum alloy of the largest maximum points should be selected in the miscellaneous aluminum scrap steel in the pretreatment process. Slice and the low level of scrap to scrap material. Sorting of scrap steel is more ideal technique is magnetic separation. This method has been widely adopted in a foreign country, the device is relatively simple magnetic separation, magnetic source from the electromagnet or permanent magnet, process design are varied, to be relatively easy to implement cross belt law. Scrap along the lateral movement of the conveyor belt, when scrap steel is drawn into the magnetic field from the left lateral belt, it was immediately taken with the longitudinal, vertical belt operation after leaving the field, scrap iron and steel lost ground and automatically gravity together . Magnetic separation process is simple, low investment, it is easy to be used. The volume of scrap materials magnetic separation process should not be too large, generally sliced and shredded aluminum scrap are more suitable, large pieces of waste to be broken in order to enter after magnetic separation process.
Magnetic separation of waste iron and steel sub-elected but also further processing, because there are a number of iron and steel scrap non-ferrous metal parts mechanical devices combined with aluminum-based, it is difficult to separate, such as nuts scrap member, wires, bond , plumbing parts, pinions, etc., this sorting section is very necessary because sub-elected can increase the value of non-ferrous metals and improve the quality of scrap iron and steel, but separation more difficult, the general manual dismantling and points election, but inefficient. In order to improve production efficiency, to sort out the combination of aluminum and steel parts difficult dismantling, the most effective approach is a dedicated melting furnace heated to Bachu aluminum melted scrap steel.
③ water as the medium of flotation separation of light impurities in aluminum scrap mixed waste plastics, waste wood, waste rubber and other lightweight materials, you can use water as a medium of flotation. The main device is a spiral propeller, aluminum propeller with the launch, in the process, the process of winnowing the remaining dirt and dust, etc. Most of soluble substances dissolved in water and washed away into the settling tank. After a multi-channel sewage sedimentation clarification, return recycling, sludge regularly cleared. This method can be completely separated light substance specific gravity less than water, it is a simple way.
④ sorting technology heavy non-ferrous metals such as copper from scrap carve. Scrap copper and other heavy non-ferrous metals have largely been contaminated with oil, the employer credits at selected non-ferrous metal, selected from the more difficult to re-carve scrap. Effective method is parabolic beneficiation method. This method uses a variety of volume substantially identical objects when subjected to the same force was thrown placement on different principles. Aluminum scrap can be a variety of different density of ferrous scrap separately. When a straight line with the same force and volume of different density emitted substantially identical objects, various objects along a parabolic direction, landing in different placement. The easiest test can be performed on a horizontal conveyor, when mixed with the waste conveyor belt at high speed when running to the end of aluminum scrap was thrown out along a straight line, due to the different kinds of waste of gravity, respectively, in different point landing, so as to achieve the purpose of sorting. This method enables split evenly aluminum, copper, and other wastes. According to this principle design of equipment has been used in foreign countries, but expensive land prices daunting. China is in the research stage.
⑤ surface coating surface pretreatment scrap many of scrap are coated with paint and other protective layer, in particular aluminum scrap containers so that the maximum number of the cans and other waste containers and toothpaste and the like. In the small smelters, which generally do not make any pre-treatment of waste on direct smelting, patent leather rekindle burned in the smelting process. But such wastes are thin-walled, patent leather will make part of the aluminum oxide in the combustion process, and increase the aluminum impurities and bubbles. More advanced secondary aluminum smelting process in general be pre-treated before the coating is disposed of, the main technologies of dry and wet. Soaking wet scrap is to use a solvent to make the paint or solvent melted off, the disadvantage of this method is that a large amount of waste, hard to deal with. Generally should not be used. Dry namely Fire, kiln firing method generally used.
Major equipment rotary kiln calcination law, its biggest advantage is high thermal efficiency, ease of separation in carbide scrap. Hot and scrap paint baking carbonization process furnace heat source to the heat generated. Production, a rotary kiln at a constant speed of rotation, scrap paint surface at a certain temperature gradually charring, due to the rotation of the rotary kiln so that the collision between materials and vibration, and finally detached from the scrap carbide. Part of the carbide off at one end of the rotary kiln collection, as well as part of the recovery in the dust collector.
Pretreated aluminum scrap is an important part of the scrap recycling process, with regeneration raise the technical level of aluminum pretreatment technology will become increasingly important. Non aluminum scrap and alloy material and completely separated from the high efficiency grade classification according to alloy scrap, aluminum scrap to achieve the most effective utilization, which is the direction of the development of renewable technology in aluminum pretreatment technology research.
