On the Effectiveness of Rotary Degassing of Recycled Al-Si Alloy Melts: The Effect on Melt Quality and Energy Consumption for Melt Preparation

Round 1

Reviewer 1 Report

The author studied the influence of rotary degassing on defect formation and mechanical properties of ENAC 46000 aluminum alloy castings, as well as the impact of rotary degassing on energy consumption of casting furnaces. The author's experimental design seems too simple, and I suggest the author to add more experiments and data analysis.

1. In the abstract, the author needs to emphasize the focus of the study and the main research significance of the article. Some research results can be written in the abstract, but the author needs to highlight the key points.

2. In the introduction, the author should follow the main research of the article to introduce relevant literature. I think the author needs to make substantial improvements to the introduction section. The author's introduction seems to have little relevance to the article, and I suggest a careful revision of the literature in this part.

3. In section 2, the materials and methods, the author needs to explain in detail the materials and equipment used, and label the manufacturers and countries, as well as their detailed compositions.

4. The relevant data on fluidity in section 3.2 is not presented with any related images or tables.

5. In section 3.3 on mechanical properties, the data could be presented in the form of graphs, which would be more convincing.

6. The conclusion section is too simple.

Author Response

The author studied the influence of rotary degassing on defect formation and mechanical properties of ENAC 46000 aluminum alloy castings, as well as the impact of rotary degassing on energy consumption of casting furnaces. The author's experimental design seems too simple, and I suggest the author to add more experiments and data analysis.

Thanks for your comment; the experiment investigated chemical composition, melt quality, fluidity, and mechanical properties in the different process routes. In this field, these methods are the most common and most sufficient tools to provide a good amount of data to validate the quality of the melt. Our investigation validates more steps in the process compared to the traditional analysis of only one step. Adding energy consumption in this process compared with energy consumption provides novel information about the process. Furthermore, the Weibull analysis shows the structural quality of the melt in a novel way. 

In the abstract, the author needs to emphasize the focus of the study and the main research significance of the article. Some research results can be written in the abstract, but the author needs to highlight the key points.

Thanks for your comments; the majority of the abstract (lines 18-24) actually contains the main results of this research, and the last two sentences are the key points in energy consumption.

In the introduction, the author should follow the main research of the article to introduce relevant literature. I think the author needs to make substantial improvements to the introduction section. The author's introduction seems to have little relevance to the article, and I suggest a careful revision of the literature in this part.

Thanks for your comment; unfortunately, it is not possible to understand what the reviewer means by little relevance. We believe the complexity of understanding the melt quality in an aluminum foundry is explained thoroughly in the introduction. Hence, the reader understands the mechanical properties results and hydrogens influence in the RPT test. Furthermore, the understanding of the production flow in an HPDC foundry has been elaborated to show the different process routes. Combining this with energy consumption is a new way to approach this topic, which has been highlighted in the introduction section.

Additional details are updated (page 2, lines 87 to 93)

“Favi et al. [25] performed analytical cost estimation models in the HPDC process, taking cost, process parameters, product features, accessory and set up cost in there analysis. The energy cost was based on thermodynamical formulas depending on furnace and the amount of internal remelting. However, the temperature of the molten metal during transfer was not taken into consideration. Bonollo et al. [26] highlighted the importance of maintaining the temperature at a desired level in the casting furnace to minimize the amount of defects in the final component.”

(page 3, lines 104 to 106).

“Weibull analysis was used with a novel approach to present how the extent of damage evolves in the two process routes.”

In section 2, the materials and methods, the author needs to explain in detail the materials and equipment used, and label the manufacturers and countries, as well as their detailed compositions.

Thanks for your comment, additional details are updated (page 3, lines 132 to 137).

“Then the transport ladle, filled with ~400 kg melt, was transported to where the 800-ton HPDC machine was located, and the melt was poured into the casting furnace for subsequent casting. Specimens were tested in a Zwick/Roell Z100 with a clip-on extensometer to measure the strain. The temperature of the melt in the transport ladle was measured with a Testo 735 logger and a type-N thermocouple.“

The relevant data on fluidity in section 3.2 is not presented with any related images or tables.

Thanks for your comment, the fluidity result is presented in the text in section 3.2:

“The test length in the route with and without degassing is 27.6 ± 0.75 cm and 27.7 ± 0.80 cm, respectively.”

So, as described, the results overlap within the error bars, showing insignificant change. Kindly, we believe this insignificant result is enough to be presented only in the text.

Additional details are updated (page 4, lines 171 to 172)

“The fluidity is reported by Kwon et al.[31] to decrease with more oxide films in the melt as expected in the route of the degassing.”

In section 3.3 on mechanical properties, the data could be presented in the form of graphs, which would be more convincing.

Thanks for your comment; we updated the Table to a graph to be more convincing (Figure 3 was added).

Figure 3. The mechanical properties obtained from the different routes in the study. S_T, σ_Y and e_F are presented with standard deviation.

The conclusion section is too simple.

Thanks for your comment. It is updated as follows.

“The current study of an aluminium EN-AC-46000 alloy with requirements of elongation to failure below 1 % clearly shows that the rotary degassing process is not improving the properties of the material since the molten metal was already damaged from the beginning of the melting process. If the rotary degassing is removed from the process under the circumstances of this study, the following conclusions can be made.

• The mechanical properties of the cast component show a slight trend of improvement rather than reduction.
• The novel way to use Weibull distribution show how the melt quality change in the process. Whereas the degassing route eliminates the Weibull distribution mixture and produces only one distribution. This shows that the rotary degassing under these circumstances damages the melt.
• The melting and casting process had a 75 % reduction of energy consumption in the investigated set-up, saving around 124000 kWh in the yearly production of a 1500 kg casting furnace.
• The removal of the rotary degassing reduces the CO₂ emission by 1500 kg from one casting furnace in Sweden per year, ~ 32000 kg in Europe on average, and ~93000 kg in Poland. Moreover, the settings and parameters in this study are equivalent to 1.7 g CO₂ per kilogram cast AlSi₉Cu₃(Fe) in Sweden.

This result shows that with minor adjustments in the production flow, a significant reduction in CO₂ emissions with no decrease in mechanical properties is achieved.”

Reviewer 2 Report

The ABSTRACT section is well–presented, relevant for this subject in area of metal matrix composites. The aims and objectives of the research are well defined. The paper is structured properly (INTRODUCTION, MATERIAL & METHODS, RESULTS & DISCUSSIONS, CONCLUSIONS, REFERENCES, etc.).

The INTRODUCTION section provide the necessary background information needed to understand the paper.

The METHODOLOGY / MATERIALS & METHODS section is relatively well described and include detailed informations. The mathematical terms in the model and the assumptions are well–presented.

The body of paper describe the important RESULTS of the research, followed by several DISCUSSIONS.

The authors proceed directly to CONCLUSIONS, which succinctly summarize the major points of the paper, derived from the results. 

The CONCLUSION section is quite succinctly presented. Are only technical comments, very briefly presented, without other opinions, conclusions or remarks. I would recommend presenting the novelties of this study, the main characteristics and the major conclusion that individualize this research. Indicate what you have done that is new compared to the already known works.

FIGURES are particularly important because they show the most objective support of the research.

The list of REFERENCES is long and relatively well chosen. The entire bibliography is current and modern works are mainly used. Literature review provides comprehensive information about the current state of research.

Author Response

The ABSTRACT section is well–presented, relevant for this subject in area of metal matrix composites. The aims and objectives of the research are well defined. The paper is structured properly (INTRODUCTION, MATERIAL & METHODS, RESULTS & DISCUSSIONS, CONCLUSIONS, REFERENCES, etc.).

Thanks for your comments and support.

The INTRODUCTION section provide the necessary background information needed to understand the paper.

Thanks for your comments and support.

The METHODOLOGY / MATERIALS & METHODS section is relatively well described and include detailed informations. The mathematical terms in the model and the assumptions are well–presented.

Thanks for your comments and support.

The body of paper describes the research's important RESULTS, followed by several DISCUSSIONS.

Thanks for your comments and support.

The authors proceed directly to CONCLUSIONS, which succinctly summarize the paper’s major points, derived from the results. 

Thanks for your comments and support.

The CONCLUSION section is quite succinctly presented. Are only technical comments, very briefly presented, without other opinions, conclusions or remarks. I would recommend presenting the novelties of this study, the main characteristics and the major conclusion that individualize this research. Indicate what you have done that is new compared to the already known works.

Thanks for your comment, the conclusion section updated.

“The current study of an aluminium EN-AC-46000 alloy with requirements of elongation to failure below 1 % clearly shows that the rotary degassing process is not improving the properties of the material since the molten metal was already damaged from the beginning of the melting process. If the rotary degassing is removed from the process under the circumstances of this study, the following conclusions can be made.

• The mechanical properties of the cast component show a slight trend of improvement rather than reduction.
• The novel way to use Weibull distribution show how the melt quality change in the process. Whereas the degassing route eliminates the Weibull distribution mixture and produces only one distribution. This shows that the rotary degassing under these circumstances damages the melt.
• The melting and casting process had a 75 % reduction of energy consumption in the investigated set-up, saving around 124000 kWh in the yearly production of a 1500 kg casting furnace.
• The removal of the rotary degassing reduces the CO₂ emission by 1500 kg from one casting furnace in Sweden per year, ~ 32000 kg in Europe on average, and ~93000 kg in Poland. Moreover, the settings and parameters in this study are equivalent to 1.7 g CO₂ per kilogram cast AlSi₉Cu₃(Fe) in Sweden.

This result shows that with minor adjustments in the production flow, a significant reduction in CO₂ emissions with no decrease in mechanical properties is achieved. ”

FIGURES are particularly important because they show the most objective support of the research.

Figures number 3 and 4 were updated.

Figure 3. The mechanical properties obtained from the different routes in the study. S_T, σ_Y and e_F are presented with standard deviation.

Figure 4. The Weibull distributions of the structural quality in the two routes of production.

The list of REFERENCES is long and relatively well chosen. The entire bibliography is current and modern works are mainly used. Literature review provides comprehensive information about the current state of research.

Thanks for your comments and support.

Reviewer 3 Report

1. In the section of 3.4 energy consumption, references should be appropriately added, such as the source of some datas, to increase the authenticity and validity of the calculation results.

2. It is suggested to make the chart more standard and beautiful, as shown in Fig. 4.

3. The title of the third part “results” should be revised as “results and discussion”, and more analysis and discussion suggested be added.

4. Please note the correct use of bold and italic letters in formula, such as the formula (4).

Author Response

1. In the section of 3.4 energy consumption, references should be appropriately added, such as the source of some datas, to increase the authenticity and validity of the calculation results.

Thanks for your comments; in this section, the values of temperature and energy consumption have been measured in the production flow. To clarify, the below explanations were added to this section (lines 286-288 and 295-297)

“The 1500 kg casting furnace is used 24 hours per day, and with these energy measurements, a yearly production with the degassing route will use 165000 kWh. However, the route without degassing result in an average yearly reduction of about 124000 kWh.”

And “This reduction of ~124000 kWh in one 1500 kg casting furnace for a year lowered the CO₂ emissions from the foundry located in Sweden with 12 g CO₂ per kWh resulting in a total of 1500 kg CO₂ reduction [27].“

2. It is suggested to make the chart more standard and beautiful, as shown in Fig. 4.

Thanks for your comment; we updated one Figure and added one new Figure instead of a table.

Figure 3. The mechanical properties obtained from the different routes in the study. S_T, σ_Y and e_F are presented with standard deviation.

Figure 4. The Weibull distributions of the structural quality in the two routes of production.

3. The title of the third part “results” should be revised as “results and discussion”, and more analysis and discussion suggested be added.

Thanks for your comment. It was changed according to the reviewer’s suggestion.

4. Please note the correct use of bold and italic letters in formula, such as the formula (4).

Updated according to suggestions

Thanks for your comment. It was changed according to the reviewer’s suggestion.

Reviewer 4 Report

This paper was well written. The topic of this paper is interesting for readers. The experimental data and discussion are complete and reasonable. But it had some typographical errors, e.g. AlSi9Cu3 (should be AlSi₉Cu₃), Conclussions (should be Conclusions), Table 2 (Typeseting error), Table 3 ( Weibull? have ? , or no ?). I reommend this paper can be accepted for publication in Sustainability after minor revision. 

Author Response

This paper was well written. The topic of this paper is interesting for readers. The experimental data and discussion are complete and reasonable. But it had some typographical errors, e.g. AlSi9Cu3 (should be AlSi₉Cu₃), Conclussions (should be Conclusions), Table 2 (Typeseting error), Table 3 ( Weibull? have ? , or no ?). I reommend this paper can be accepted for publication in Sustainability after minor revision. 

Thanks for your comment; we updated the paper according to your feedback.

Round 2

Reviewer 1 Report

Agree to accept.