Aluminum Melting Furnace：The key to Recycling Scrap Aluminum

Aluminum is the world's most important nonferrous metal. Due to its characteristics of light weight, corrosion resistance, good electrical conductivity and good heat transfer, aluminum plays an important role in defense, construction, transportation, packaging and other industries and daily life. At the same time, aluminum is recyclable and can be used repeatedly. The recycling process of scrap aluminum is inseparable from an important piece of equipment - the aluminum melting furnace. Today, we will start from the entire process of scrap aluminum recycling and give a comprehensive introduction to aluminum melting furnaces.

The entire process of scrap aluminum recycling includds scrap aluminum pretreating, smelting, refining, alloy blending, ingot casting, and slag treatment. Obviously, the aluminum melting furnace will work in the second step.

Scrap Aluminum Sources

Cast aluminum scrap

Foundry companies will produce a certain amount of scrap aluminum during the production process, which mainly includes:

1. Aluminum alloy scrap castings, pouring risers, remaining aluminum alloy liquid ingots, etc.

2. Waste casting process equipment, such as aluminum alloy patterns, templates, core boxes, sand boxes, sand pressing plates, sand box pallets, casting system molds, core baking plates, etc.

3. Aluminum parts from scrap casting equipment.

Aluminum alloy scrap castings, pouring risers, remaining aluminum alloy liquid ingots, etc., also known as foundry return materials (return materials), are the main sources of scrap aluminum for foundry companies to produce cast aluminum alloy parts.

Industrial Scrap Aluminum

1. Mechanical processing scrap aluminum: scrap aluminum alloy castings and scrap aluminum chips during mechanical processing, as well as aluminum alloy parts when machine products are permanently discarded;

2. Metallurgical scrap aluminum: scrap heads and leftovers of metallurgical aluminum rolling products, scrap heads and leftovers of aluminum forgings, etc.

Domestic Scrap Aluminum

Waste aluminum doors and windows, aluminum-containing scraps and aluminum wires after scrapping automobiles, motorcycles, machinery, electrical appliances, and power lines, aluminum-containing scraps after scrapping aerospace aircraft, and scrap aluminum cans for beverages.

Scrap Aluminum Classification

Aluminum alloy waste can be divided into cast aluminum alloy waste, deformed aluminum alloy waste, aluminum alloy chips, etc.

Cast Aluminum Scrap

Casting aluminum alloy old scrap is divided into two types: gravity casting aluminum alloy old scrap and die-casting aluminum alloy old scrap. The former often contains elements such as Si, Cu, Mg, Zn, Sn, Cr, Mn, Ni, and Be. The latter often contains elements such as Si, Mg, and Cu. The two main types of scrap aluminum are:

1. Aluminum alloy castings whose impurity content should not exceed the standard and be scrapped;

2. Aluminum alloy castings scrapped due to chemical composition;

3. Various aluminum alloy products;

4. Smelting and casting aluminum alloy base material;

5. Aluminum alloy ingots cast from remaining aluminum liquid, etc.

Deformed Scrap Aluminum

Deformed aluminum alloy old waste mainly refers to waste processed by modified aluminum alloy products (thick plates, thin plates, strips, foils, thick-walled tubes, thin-walled tubes, bars, profiles, wires, free forgings, die forgings, etc.) Parts box scraps, scraps, etc.

Aluminum Scrap

Aluminum chips include chips or sawdust when casting aluminum or aluminum alloy parts and deformed aluminum or aluminum alloy profiles are processed into parts.

Scrap Aluminum Smelting

Scrap aluminum smelting is to add old aluminum alloy scrap to the normal furnace charge in a certain proportion, smelt and process it in a resistance furnace, medium frequency aluminum melting furnace, electric melting aluminum furnace, fuel-fired aluminum melting furnace, and reverberatory furnace, and directly cast it to meet the requirements. Aluminum alloy castings or aluminum ingots.

Scrap Aluminum Pretreating

The purpose of pretreatment of scrap aluminum is: first, to remove other metals and impurities contained in scrap aluminum; second, to classify scrap aluminum according to its components so that the alloy components in it can be utilized to the greatest extent; third, to remove scrap aluminum Remove surface oil, oxides and paint. The ultimate purpose of pretreatment is to process aluminum scrap into furnace materials that meet the conditions of human furnaces, so that the aluminum (including alumina) in the aluminum-containing waste can be utilized in the most economical and reasonable manner.

1. Pretreatment of high-quality scrap aluminum: Scrap aluminum of a single variety or basically containing no other impurities generally does not undergo complex pretreatment. It is just classified according to the type and composition of the scrap and stacked separately. When using a single type of scrap aluminum, you only need to randomly check and test one component to know the composition of the batch. High-quality recycled aluminum raw materials generally can be smelted in the furnace without any pretreatment.

2. For higher-grade scrap aluminum slices, the main components include cast aluminum alloy, alloy aluminum, pure aluminum, etc. There are many brands of the first two items, and it is currently difficult to classify them by brand. In large-scale recycled aluminum plants, they generally only go through after screening to remove mixed soil, etc., it can be directly put into the furnace for smelting.

3. For low-grade sliced and incinerated shredded scrap aluminum (the latter is generally not used by large recycled aluminum plants), more complicated sorting is required because its composition is extremely complex. In addition to scrap aluminum, it also contains scrap steel, scrap copper, Scrap lead and other metals also contain other wastes. The sorting of such wastes mainly relies on manual labor. The soil and garbage are first screened out and then sorted manually.

The purpose of scrap aluminum pretreatment technology is to realize the mechanization and automation of scrap aluminum sorting, remove metallic impurities and non-metallic impurities to the greatest extent, and enable effective sorting of scrap aluminum.

Smelting

Reverberatory Furnace Melting

Reverberatory furnaces are mainly used to smelt scrap aluminum at home and abroad. The reverberatory furnace is highly adaptable and can handle aluminum scraps, old aircraft, and massive scrap aluminum with steel components. Industrial reverberatory furnaces include one-chamber furnaces, two-chamber furnaces and three-chamber furnaces. Commonly used single-chamber reverberatory furnaces are mainly horizontal flame reverberatory furnaces, with a rectangular furnace body and a furnace top that is inclined along the direction of the flame. Common single-chamber reverberatory furnaces have a capacity of 4 to 8 tons. The thermal efficiency of the reverberatory furnace is 25%-30%.

Medium Frequency Induction Furnace Melting

Groove type cored induction furnaces and crucible induction furnaces are commonly used in industrial production. Induction furnaces are particularly suitable for melting aluminum chips, which can reduce oxidation losses and increase metal recovery rates.

Groove type cored induction furnaces

The molten trench induction furnace consists of two parts, the vertical furnace body and the detachable induction heating system. The main disadvantage of the molten trench type induction furnace is that aluminum oxide is deposited on the inner surface of the molten trench, which rapidly reduces the molten trench, worsens the circulation of the alloy melt, and changes the electrical characteristics of the furnace, which not only reduces the furnace's production capacity but also Reduce the life of furnace bottom lining. The thermal efficiency of the molten trench induction furnace is 65%~70%, and the unit power consumption of the alloy is about 450kw·h/t alloy. It can process baled scrap aluminum, pelletized scrap aluminum chips, packaging scrap aluminum chips, pipes and other materials with low oxidation rate and no iron components.

crucible-type electric furnace

The crucible-type electric furnace can smelt block aluminum scraps without steel components, dry granular aluminum chips and briquettes, and prepared alloys in the form of raw metal or ingots. During smelting, lump materials are added first, and then small materials and chips are added. . The metal recovery rate of induction crucible for processing scrap aluminum chips is 91% to 92%, and the metal recovery rate for processing scrap aluminum and high-grade aluminum scrap is 97% to 98%.

Rotary Furnace Smelting

The rotary kiln is mostly used to smelt packaged waste cans and slag as well as lower quality scrap. The rotary kiln has a movable fume hood. Due to its good heat transfer and rotatability, the charge is in the melt and the metal loss is small. When conditions are suitable, the aluminum recovery rate can reach 93%~94%.

Shaft Furnace Smelting

This type of furnace has been used both at home and abroad. On the basis of the shaft furnace, an open furnace is added afterwards. The shaft furnace is mainly responsible for preheating and melting the charge, and the melt flows into the open furnace for insulation and refining. This furnace type takes advantage of the advantages of shaft furnaces and open-hearth furnaces, and combines them for the smelting of block and briquette scrap aluminum. The working principle is based on the convective heat transfer of high-speed and high-temperature airflow of 200~300m/s to the aluminum to be melted and the full use of waste heat. The furnace generally consists of a preheating zone, a melting zone and a fore hearth. It has a compact structure, small floor space, can realize mechanized feeding, has fast melting speed, low unit heat consumption, and has outstanding advantages in energy saving and rapid melting. However, there are also disadvantages such as large burning loss of materials, short service life of the refractory materials inside the furnace, and prone to material arching. It is only suitable for smelting a single aluminum alloy or pure aluminum.

Resistance Furnace Melting

A resistance furnace is an industrial furnace that uses electric current to heat the electric heating element or heating medium in the furnace to heat workpieces or materials. It is a heating furnace that uses electric current to pass through resistive materials to generate heat energy.

Resistance furnaces are used in the machinery industry for heating before metal forging, metal heat treatment heating, brazing, powder metallurgy sintering, glass ceramic roasting and annealing, low melting point metal melting, sand molding and drying of paint film layers, etc.

Compared with flame furnaces, resistance furnaces have the advantages of simple structure, uniform furnace temperature, easy control, good heating quality, no smoke, no noise, etc., but the usage fee is higher.

Refining

Refining is an important part of the smelting process. During the smelting process of scrap aluminum, the liquid aluminum inevitably contains impurities such as gases and non-metallic inclusions, which must be removed by refining methods. This includes adding flux to cover the surface of the molten aluminum liquid or alloy liquid to prevent the liquid aluminum from being oxidized by air, and at the same time introducing gas to stir the liquid to promote the separation of inclusions and hydrogen.

Commonly used methods are air blowing and filtration, where the gas is passed through to drive away the hydrogen. Alumina is removed by filtration. Sometimes a combined purification method that combines ventilation and filtration is also used.

The refining temperature is generally 75~100℃ higher than the melting point of aluminum or aluminum alloy, that is, around 750℃. If the temperature is too low, the oxide inclusions will not be easily separated; if the temperature is too high, the amount of hydrogen dissolved in the aluminum alloy and aluminum will increase.

Alloy Blending

Since some alloy components are lost during the smelting process, alloy elements must be added to the liquid aluminum alloy after the refining process to ensure that the smelted aluminum alloy meets product standards. After the aluminum-containing scrap is smelted and refined, its composition is quickly analyzed and adjusted in front of the furnace to produce qualified products.

Ingot Casting

According to the process requirements of aluminum and aluminum alloy products, the aluminum liquid is cast into qualified aluminum ingots after adjusting the temperature. There are two methods of aluminum ingot casting, one is manual ingot casting and the other is continuous ingot casting machine.

Slag Treating

A large amount of slag is bound to be produced during the recycling, smelting and refining process of scrap aluminum. Slag contains aluminum and other useful components, and its composition is very uneven. It contains 10% to 30% of metallic aluminum, 7% to 15% of alumina, 5% to 10% of oxides of iron, silicon, and magnesium, potassium, sodium, Chlorides of calcium, magnesium and other metals 55% to 75%. It can be seen from this that the slag generated in the aluminum recycling process is also a resource and must be recycled.

In order to recover the aluminum and useful components, two processing methods, wet and dry, are generally used. Wet processing of slag allows complete utilization of all components in the slag. The dry treatment of the filter residue is to crush and grind the residue into powder form. After screening, use an exhaust fan to remove the fine particles, and collect the fine waste through a cyclone dust collector. The coarse particles contain 60 %~70% of the alloy aluminum is returned to be smelted into aluminum alloy. The magnetic separation process is used many times in order to separate the metallic iron in the slag. The recovered metallic iron can be used for steel production after drying.

Summarize

The recovery and recycling of aluminum is not only effective, but also can reduce Co and CO2 emissions in the aluminum production process. This is of great significance to the prevention and control of air pollution. Luoyang HTGP is a manufacturer specializing in the production of various aluminum melting furnaces and aluminum ingot automatic casting production lines. Welcome to inquire about aluminum melting furnaces.