Influence factors and Control Technology of Burning loss in the whole process of melting and casting [SMM Aluminum Summit]

SMM5 March 14: at the "2021 (16th) China International Aluminum processing Summit" jointly held by Shanghai Futures Exchange and SMM, Tang Xinwen, director of the melting and casting plant of Hunan Zhongchuang Hollow New Materials Co., Ltd., introduced the influencing factors and control technology of burning loss in the whole melting and casting process, and specifically explained the influence of material, process, equipment and aluminum ash treatment.

I. concept and algorithm

During the melting process, the burning loss of the alloy is caused by the irrecoverable metal loss caused by oxidation, volatilization and the interaction of furnace wall and refining agent. The metal in burning loss and residue is collectively referred to as melting loss (more in line with factory cost accounting).

The metal oxidation produced in the process of producing, removing, transferring, storing and remelting aluminum slag caused by aluminum slag is composed of the metal contained in the waste slag. Such wear and tear is more likely to be ignored. It is also difficult to manage and control.

Calculation formula

Burning loss = (metal feed-metal output) / metal feed * 100%

Metal output: refers to the metal part that can be returned to the furnace.

II. Material influence

Metal material

Layered, including air layer, coating, etc., poor thermal conductivity, burning loss, even more than 10%. The method of treatment, cutting, repackaging, laying the bottom and loading the furnace.

Double zero foil, clump, poor thermal conductivity, great burning loss, even more than 10%. Treatment method, broken + Whirlpool well added.

Flux

Ordinary refining agent: KCl+NaCl+Na3AlF6 is actually replaced by heating agent, which leads to the widespread existence of cinder.

Granular refining agent: KCl+MgCl2 (+ BCl2) melting, crushing, expensive, loss of about 0.2%.

Third, the influence of process.

Charging furnace

1, leave space for the burner flame properly; 2, pack loose scraps; 3, load leftovers into the bottom of the furnace; 4, immersion feeding.

Stir

1. After the collapse, the forklift is flattened. When some of the peaks or protrusions are melted, the surface gradually melts, falls off and flows (wrapped with oxides), forming a new surface and then being melted.

2. Stir the forklift after leveling. If not stirring, melting usually, the temperature difference of each part of the charge is 70 ℃ 100 ℃, the surface is all melted, but there is still a hard lump or sticky shape at the bottom (electromagnetic stirring is very difficult to have an effect at this time), mechanical stirring with the help of forklift rake can promote melting and reduce surface overheating.

Refining

1. Suitable refining equipment

Quantitative transport of refining agent, argon, chlorine, carbon tetrachloride and other media; there is no refining agent residue in the refining equipment (serious moisture absorption, affecting the effect); furnace side degassing, or mobile refining vehicle (argon uniform injection of flux)

2. Suitable refining medium

Ar+Cl2 > N2+Cl2 (corrosive) > Ar+CCl4 > Ar > N2; granular refining agent is better than powder refining agent.

3. Optimized refining method

The rising height of liquid aluminum is 15cm25cm; the arrangement of breathable bricks; three-phase combined refining of gas, liquid and powder; fine addition of CCl4 (quota permit).

Fourth, the influence of equipment and aluminum ash treatment

Melting furnace combustion system

The flame has good rigidity and high local temperature, which leads to aluminum oxidation and burning loss. Aluminum oxide heat (7230kCal/kg): 4Al+3O2=2Al2O3. Some energy-saving transformations take advantage of this feature to reduce consumption and increase loss. The dispersion combustion system is adopted to reduce the melting local temperature, reduce the oxygen content in the furnace, reduce the burning loss by about 0.2%, and reduce the emission concentration of NO compounds. In addition, the influence of related equipment also includes double-chamber furnace, whirlpool well and so on.

Crucible type

Advantages: low investment, small batch processing, flexibility, strong adaptability.

Paddle pot type

The cost of the equipment is not high, and the effect of hot ash is OK, but it requires a high temperature, otherwise it will solidify. Can deal with cold ash, are the addition of heating agent, the use of aluminum combustion reaction for heating, large loss.

Rotary furnace

Can deal with cold ash (normal temperature ash), large batch (2-15t), high aluminum production rate (50x 60%), a number of enterprises in Henan import, the formation of large-scale treatment, salt slag environmental recovery cycle.

V. Summary

1. Test and evaluate accurately, analyze and improve the whole process.

2. Equipment matching and material matching: equipment and material matching, but there are many materials in the implementation process. Sorting + paint removal (incineration) + preheating + automatic feeding + electromagnetic pump + whirlpool well

3. High threshold for advanced equipment input: pre-paint treatment equipment, two-chamber furnace, three-chamber furnace, electromagnetic pump + whirlpool well.

4. Choose appropriate aluminum ash equipment.