The aluminum electrolytic industry is a very large energy-consuming industry and one of the largest consuming materials. The category of materials consumed in the technology of obtaining aluminum by electrolysis includes carbon anodes [1
]. Aluminum electrolysis is a complex, nonlinear, and multivariate industrial control process. As a result, the problem of its optimization continues to arise [2
In order to ensure the sustainable development of the aluminum industry, new strategies are needed to modernize existing production facilities, namely the use of new technological equipment capable of meeting existing standards in terms of environment, industrial safety, and efficiency. Thus, it is necessary to identify technical solutions for the conservation of materials and energy, and it is important to carry out studies aimed at identifying technological possibilities to reduce the consumption of materials and energy in the aluminum industry [3
A particular problem concerns the durability of consumable carbon anodes. In this sense, one solution is the use of inert anodes in the Hall–Héroult electrolysis process, but this is still a goal that has only been partially achieved in the primary aluminum industry. The creation of a non-carbon anode has become increasingly important with increasing pressure on the aluminum industry to reduce greenhouse gas emissions [5
Due to the difficulties of introducing new types of anodes in practice, carbon anodes are currently used in primary aluminum production. These types of anodes have rather low durability and must be changed at short intervals. A particular problem that arises when changing carbon anodes refers to the technological process of cleaning the support on which they are disposed by the materials that were used to fix them on the support. In this sense, in most cases, the fixing of the anodes on the support is performed by means of cast irons. Thus, the replacement of a carbon anode involves the removal of the cast iron layer to clean the anode support in order to mount a new anode.
In order to increase the productivity of the process of cleaning the anode supports, in practice, a series of tools have been designed to allow the removal of the cast iron layer. This process is quite complex, and, to increase productivity, a number of trimming dies have been created, which generally have low durability. Under these conditions, the question arises of identifying possibilities to increase the durability of these trimming dies. Given the above, the process of cleaning the anodes is similar to the process of cutting cast iron.
During the use of anodes, due to the heat released, the cast iron that fixes the carbon anode on the support undergoes a series of changes in properties. Thus, cast iron can change its hardness in the sense of increasing it, but also the metallographic structure, and all this negatively influences the process of crushing it. In addition, the thermal effect can cause the accumulation of residual stresses in cast iron that can generate certain cracks that can compromise the structure of the components and can lead to economic losses [7
In the operations of grinding the castings, it was found that there is a big difference in the life of the tools used, depending on their structure, finding major differences between conditions for crushing compacted graphite (CGI) iron and spheroidal graphite iron (SGI) [9
]. Thus, depending on the structure, the cast irons can be crushed with the help of tools with a certain geometry made of different materials [12
Some studies recommend using polycrystalline cubic boron nitride (pcBN) for high-speed processing of cast iron [13
], but this cannot be applied in the case of the trimming dies used to clean anode supports. In addition, in addition to the possibility of conducting experimental research on cast iron cutting processes, cutting simulation methods can be applied, such as the finite element method (FEM), which allows us to obtain information on the process of splinter formation, distribution voltages, temperature distribution [16
Given the above, the main objective of the research was to identify the technological possibilities of making trimming die-type tools that are used to clean the support of carbon dioxide in the primary industry of aluminum in order to increase their durability. Thus, the research focused mainly on choosing an optimal material from which these tools can be made but also on identifying the possibilities of plating by welding the active parts of the trimming dies and establishing an optimal geometry for them. Under these conditions, the material usually used to make matrix was replaced with five other materials, and plating by welding was performed using two technologies: hot and cold, respectively. In addition, to optimize the geometry of the active part of the trimming dies, FEM was used, and thus, it was possible to make a trimming dies from a new material with an optimal geometry that allowed a substantial increase in its durability.
Conceptualization, D.G., C.B., G.G. and D.D.; methodology, validation, C.M., M.D. and L.C.D.; formal analysis, S.-G.R., L.C.D., G.G. and D.G.; investigation, D.G., C.B. and G.G.; resources, D.G., C.B., G.G. and D.D.; data processing, D.G., C.B., G.G., C.M. and S.-G.R.; writing—original draft preparation, D.D. All authors have read and agreed to the published version of the manuscript.
This research received no external funding.
Conflicts of Interest
The authors declare no conflict of interest.
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Rod assembly—tetrapod: 1—aluminum bar; 2—bimetal plate; 3—rondon.
Presentation of the trimming dies used in the cleaning operation: (a)—cleaning trimming die—3D representation; (b)—image of the real trimming die used for cleaning.
Wear of the active parts of the half-trimming dies: (a)—accentuated wear, disposed approximately symmetrical on the entire length of the active part; (b)—accentuated asymmetrical wear.
The shape of the cracks that appear in the active area of the trimming dies made of the steel K360.
The shape of the material flows that appear in the active area of the trimming dies made of steel K105.
Distribution of temperatures when heating the trimming die. (a)—side view of the temperature distribution in the material in the active area of the trimming die, (b)—front view of the temperature distribution in the material from the active area of the trimming die, (c)—side view of the temperature distribution of the base material of the trimming die, (d)—front view of the temperatures distribution of the basic material of the trimming die.
The metallographic structure of the transition area between the metal deposited by welding and the base material: (a)—the metallographic structure in case of cold plating welding of the trimming die; (b)—metallographic structure in case of hot plating welding of the trimming die.
The loads and restrictions imposed on the trimming die for FEM modeling: (a)—undeformed trimming die; (b)—deformed trimming die.
Deformation values (a) and of the equivalent stresses (b).
Trimming die with the active part geometry modified: (a)—3D representation; (b)—the image of the real trimming die.
The deformation values (a) and equivalent stresses (b) for the trimming die with the modified active part geometry.
The chemical composition of the steel used to make the trimming dies X210Cr12, %wt [20
The physical properties of the steel used to make the trimming dies X210Cr12 [20
|Physical Properties||20 °C||200 °C||400 °C|
|Coefficient for thermal expansion (per °C from 0 °C)||-||11.0 × 10−6||10.8 × 10−6|
|Thermal conductivity (cal/cm·s °C)||49 × 10−3||51.3 × 10−3||54.9 × 10−3|
|Modulus of elasticity, MPa||194,000||189,000||173,000|
The chemical composition of the steels used to make the trimming dies, %wt [20
Mechanical properties of steels used in the execution of trimming dies [20
|Material||Yeld, Rp0,2, MPa||Impact, KV/Ku J||Elongation, A, %||Brinell Hardness, HBW||Modulus of Elasticity, GPa|
|K105||≥497||≥151||12||123||894 (463 °C)|
|K107||≥347||≥223||34||242||474 (571 °C)|
|K110||≥212||≥32||13||433||967 (448 °C)|
|K360||≥595||≥13||32||213||763 (423 °C)|
|K460||≥731||≥22||41||413||755 (736 °C)|
Durability of trimming dies made of different materials.
|Material||Number of Stress Cycles, N, Up to Which Maximum Allowable Wear Has Been Reached|
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