Investigation of the Lubricating Conditions in a Reciprocating Sliding Tribotest with Applied Electric Voltage

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work was carried out on a current topic - increasing the performance of electric motors is an urgent task due to their widespread distribution in most aspects of human life.

The authors, using modern equipment and testing techniques, conducted interesting experimental studies and obtained excellent new results. At the same time, the article has some significant shortcomings that can be easily eliminated through more careful preparation of the text and graphic material.

 

1. The first section provides a literature review. In terms of volume and content, the review quite well conveys the current state of research in the field of research into the friction process with electric current flowing in a tribocontact. The purpose of the work is formulated logically.

2. The second section provides a description of the lubricant used, equipment and parameters for conducting tribological studies, as well as equipment for assessing the condition of wear surfaces. The methods and equipment are modern and common in this field of research. The description of materials needs to be corrected.

3. The third section provides a description of the results obtained. Graphic material is sufficient to present the results obtained, but its design requires adjustment.

4. The fourth section provides a brief discussion of the results, which, against the background of a more qualitative description of the results in section 3, is meaningless.

5. The fifth section provides conclusions based on the new results obtained. The conclusions are formulated concisely and logically.

 

Notes:

The main note about this work is that the captions to the graphic material are done carelessly, which makes it very difficult to understand what the authors actually want to show with these drawings.

 

1. The work in Section 2 does not indicate the material of the ball and counterbody (or sample).

2. The work does not provide a rationale for using paraffin as a lubricant.

3. Section 4 provides a short formal discussion of the results. At the same time, the authors do not discuss the occurrence of a cause-and-effect relationship between the observed phenomena. Only a statement of the fact already described in the results is given. It is clear that a change in polarity affects the formation of tribofilms, etc. But there is no significant discussion about the cause of this phenomenon. In fact, when describing the results, the authors provide more detailed discussions of the most interesting phenomena than in this section. As a result, the question arises: is it necessary to leave this section and maybe it is better to simply merge it with the results?

4. It is also worth noting that section 4 provides only 1 reference to a literary source. To discuss the results, it is necessary to conduct a more qualitative analysis of the results and provide a comparison with known literature data.

5. The captions for figures 3, 4, 7, 9, 11, 12 are not done very well. The authors should reconsider the description of polarity, since they do not present it correctly in its current form.

6. Figure 10 From the caption it is not clear where what voltage is. If you follow the caption, is a and c a positive voltage? Or are the authors trying to display polarity with color?

7. Figure 11. Again, incorrect design. A is followed by d, then b, and so on.

8. It’s not clear why there are figures 12 a and 12b? This is essentially one graph continuing another in time. Its design needs to be reconsidered.

9. I would recommend adding current literature to the review or discussion of the results. In its current form, the article contains only 7 references to literary sources published over the past 5 years.

Author Response

Raimondas Kreivaitis, Albinas Andriušis, Jolanta Treinytė, Artūras Kupčinskas, Vytenis Jankauskas

  

Manuscript ID: lubricants-2895098

Title: Investigation of the lubricating conditions in the reciprocating sliding tribo-test with applied electric voltage

 

Author's comments on reviewers' remarks

 

Reviewer #1:

Reviewer's comments

(1) The first section provides a literature review. In terms of volume and content, the review quite well conveys the current state of research in the field of research into the friction process with electric current flowing in a tribocontact. The purpose of the work is formulated logically.

Author's response

The authors are thankful to the reviewer for the positive word.

 

Reviewer's comments

(2) The second section provides a description of the lubricant used, equipment and parameters for conducting tribological studies, as well as equipment for assessing the condition of wear surfaces. The methods and equipment are modern and common in this field of research. The description of materials needs to be corrected.

Author's response

The authors supplemented the methodology according to the reviewer's remarks.

 

Reviewer's comments

(3) The third section provides a description of the results obtained. Graphic material is sufficient to present the results obtained, but its design requires adjustment.

Author's response

The authors improved the figures according to the reviewer's remarks.

 

Reviewer's comments

(4) The fourth section provides a brief discussion of the results, which, against the background of a more qualitative description of the results in section 3, is meaningless.

Author's response

The authors agree that this section could be improved and be more comprehensive. However, we would like to keep it as a separate section because it summarises the main findings, which are too broad to be included in the conclusion. Moreover, we have improved it slightly.

Reviewer's comments

(5) The fifth section provides conclusions based on the new results obtained. The conclusions are formulated concisely and logically.

Author's response

The authors are thankful to the reviewer for the positive word.

 

Reviewer's comments

Notes: The main note about this work is that the captions to the graphic material are done carelessly, which makes it very difficult to understand what the authors actually want to show with these drawings.

Author's response

The authors improved the captions of the figures, making them more descriptive.

 

 

 

Reviewer's comments

(1) The work in Section 2 does not indicate the material of the ball and counterbody (or sample).

Author's response

The authors supplemented the methodology according to the reviewer's remarks.

 

Reviewer's comments

(2) The work does not provide a rationale for using paraffin as a lubricant.

Author's response

Paraffin oil was used as a reference mineral base oil for no particular reason except that it does not contain additives and has a purity certificate. We have supplemented the methodology with a short description.

 

Reviewer's comments

(3) Section 4 provides a short formal discussion of the results. At the same time, the authors do not discuss the occurrence of a cause-and-effect relationship between the observed phenomena. Only a statement of the fact already described in the results is given. It is clear that a change in polarity affects the formation of tribofilms, etc. But there is no significant discussion about the cause of this phenomenon. In fact, when describing the results, the authors provide more detailed discussions of the most interesting phenomena than in this section. As a result, the question arises: is it necessary to leave this section and maybe it is better to simply merge it with the results?

Author's response

In this study, we wanted to emphasize that even a small current can change the tribological response in the friction pair lubricated with low-polarity base oil. Moreover, we showed that the average ECR in reciprocation can be misleading. The use of high-frequency continuous ECR recording can provide more sophisticated information. A more detailed explanation of the mechanism is planned for the next publication, in which we will compare different lubricants. We hope that this comparison will provide more answers. The authors also agree that section 4 could be improved and be more comprehensive. However, we would like to keep it as a separate section because it summarises the main findings, which are too broad to be included in the conclusion. Moreover, we have improved it slightly.

 

Reviewer's comments

(4) It is also worth noting that section 4 provides only 1 reference to a literary source. To discuss the results, it is necessary to conduct a more qualitative analysis of the results and provide a comparison with known literature data.

Author's response

We have added three more literature sources to the discussion.

 

Reviewer's comments

(5) The captions for figures 3, 4, 7, 9, 11, 12 are not done very well. The authors should reconsider the description of polarity, since they do not present it correctly in its current form.

Author's response

The authors improved the captions of the figures, making them more descriptive. We changed the term “polarity” to “positive or negative voltage” to make it more consistent.

 

Reviewer's comments

(6) Figure 10 From the caption it is not clear where what voltage is. If you follow the caption, is a and c a positive voltage? Or are the authors trying to display polarity with color?

Author's response

We improved the caption of Figure 10 and added the marks on the figures. The colours represent the temperatures throughout the manuscript.

 

Reviewer's comments

(7) Figure 11. Again, incorrect design. A is followed by d, then b, and so on.

Author's response

We have changed the arrangement of graphs to make them clearer.

  

Reviewer's comments

(8) It’s not clear why there are figures 12 a and 12b? This is essentially one graph continuing another in time. Its design needs to be reconsidered.

Author's response

We have changed the arrangement of graphs to make them clearer. There was no continuing in the graphs. These are different graphs. As can be seen in Figures 10 c and d, the ECR for positive and negative voltages has different behaviour. The scales of contact resistance in Figure 12 are also different.

 

Reviewer's comments

(9) I would recommend adding current literature to the review or discussion of the results. In its current form, the article contains only 7 references to literary sources published over the past 5 years.

Author's response

We have supplemented the references accordingly.

 

 

• All the changes made are highlighted in the revised manuscript.
• The changes that occurred due to grammar and spelling checks were not highlighted.
• As a result of the revision, ten additional references occurred.
• Considering the reviewers' comments, the supplementary material was added.

  

The authors are very grateful to the editor and reviewers for the opportunity to improve this manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The work still needs to be refined. I suggest a mandatory review of the following points to increase the quality of the paper.

1. Why were the tests carried out at temperatures of 30 and 80 degrees Celsius?

2. Why were these friction wear test parameters chosen?

3. Explain the sentence: "As was expected, lubrication with base oil provides relatively high COF." What do you think is the desired coefficient of friction?

4. Correct the caption in Fig. 4. It probably concerns testing at a temperature of 80oC.

5. The EDS method is not suitable to determine the carbon content. This result is subject to a large error. If it is justified for the purposes of the work, it should be explained in the text of the article why it was decided to show the quantitative result.

6. In addition, the results of SEM observations and EDS maps for tests at 80C should be added for comparison.

7. Authors should take SEM images of wear paths at higher magnification. And interpret these images.

8. There are no comparisons of the results to the work of other authors in the discussion. The work resembles a research report.

 

This manuscript in the presented form is not acceptable for publication in Lubricants. A major revision is necessary.

Author Response

Raimondas Kreivaitis, Albinas Andriušis, Jolanta Treinytė, Artūras Kupčinskas, Vytenis Jankauskas

  

Manuscript ID: lubricants-2895098

Title: Investigation of the lubricating conditions in the reciprocating sliding tribo-test with applied electric voltage

 

Author's comments on reviewers' remarks

 

Reviewer #2:

Reviewer's comments

(1) Why were the tests carried out at temperatures of 30 and 80 degrees Celsius?

Author's response

The temperatures were chosen to represent low and high-temperature conditions similar to the start and working temperature of the mechanisms. Moreover, we wanted to have different viscosities of the same oil.

 

Reviewer's comments

(2) Why were these friction wear test parameters chosen?

Author's response

There was no particular reason behind the choice. We used them because we perform most of the tests at these premises and are familiar with the process and conditions there.

 

Reviewer's comments

(3) Explain the sentence: "As was expected, lubrication with base oil provides relatively high COF." What do you think is the desired coefficient of friction?

Author's response

With this sentence, we wanted to say that the magnitude of the COF did not surprise us. In this study, we did not want to get a particular COF; we wanted to show its changes, which appeared due to applied voltages.

 

Reviewer's comments

(4) Correct the caption in Fig. 4. It probably concerns testing at a temperature of 80oC.

Author's response

We have made the corresponding changes in the manuscript.

 

Reviewer's comments

(5) The EDS method is not suitable to determine the carbon content. This result is subject to a large error. If it is justified for the purposes of the work, it should be explained in the text of the article why it was decided to show the quantitative result.

Author's response

Despite the recognised limitations of the EDS method in accurately quantifying carbon content, we have deliberately chosen to include its quantitative results in our analysis. This decision results from our aim to comprehensively understand the sample's composition. Not considering the detected carbon content carries the risk of distorting the overall concentration of all elements.

 

Reviewer's comments

(6) In addition, the results of SEM observations and EDS maps for tests at 80C should be added for comparison.

Author's response

The EDS results observed at 80 °C showed no consistency, so we did not show them. Moreover, the phenomenon seen at 30 °C was not observed at high temperatures.

 

Reviewer's comments

(7) Authors should take SEM images of wear paths at higher magnification. And interpret these images.

Author's response

We made the SEM images but found no particular features distinguishing between test modes, so they were not included. However, considering the reviewers' comments, we added this information to the supplementary materials.

 

Reviewer's comments

(8) There are no comparisons of the results to the work of other authors in the discussion. The work resembles a research report.

Author's response

The authors agree that this section could be improved and be more comprehensive. However, we would like to keep it as a separate section because it summarises the main findings, which are too broad to be included in the conclusion. Moreover, we have improved it slightly.

 

• All the changes made are highlighted in the revised manuscript.
• The changes that occurred due to grammar and spelling checks were not highlighted.
• As a result of the revision, ten additional references occurred.
• Considering the reviewers' comments, the supplementary material was added.

The authors are very grateful to the editor and reviewers for the opportunity to improve this manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

This research study the effects of applying an electric voltage to friction system. For that task, the authors used a mineral-based paraffin oil, observing interesting results like small currents flowing through the tribocontact could modify the lubricating conditions. Nevertheless, some changes are needed:

-Indicate more information about the reciprocating ball-on-plate tribometer (brand, model, country…)

-Table 1 seems to be very large, probably it is sufficient to put one type of viscosity: dynamic or kinematic.

-Last sentence of section 2.2 should be connected to the last paragraph.

-In lines 179-181, the authors write that the application of electric voltage noticeably affected mean COF only when negative voltage was applied to the ball at 30 °C. Nevertheless, the graphs show that with positive voltage the COF also increases. Please correct this.

-Regarding, the wear volume observed in tribo-tests it is evident that with negative voltage the produced wear is quite higher. How can this fact be explained? Please improve this part.

-In general, it is a very interesting research, out of curiosity, do the authors planning to carry out this type of tests by adding different nanoparticles to the base oil?

Author Response

Raimondas Kreivaitis, Albinas Andriušis, Jolanta Treinytė, Artūras Kupčinskas, Vytenis Jankauskas

  

Manuscript ID: lubricants-2895098

Title: Investigation of the lubricating conditions in the reciprocating sliding tribo-test with applied electric voltage

 

Author's comments on reviewers' remarks

 

Reviewer #3:

Reviewer's comments

Indicate more information about the reciprocating ball-on-plate tribometer (brand, model, country…)

Author's response

We have supplemented the methodology according to the reviewer's remarks.

 

Reviewer's comments

Table 1 seems to be very large, probably it is sufficient to put one type of viscosity: dynamic or kinematic.

Author's response

We provided both viscosities to give more information on the investigated lubricant. Moreover, the density is provided only at one temperature, making it difficult to calculate dynamic viscosity if only kinematic is presented.

 

Reviewer's comments

Last sentence of section 2.2 should be connected to the last paragraph.

Author's response

We have made corresponding changes according to the reviewers’ remarks.

 

Reviewer's comments

In lines 179-181, the authors write that the application of electric voltage noticeably affected mean COF only when negative voltage was applied to the ball at 30 °C. Nevertheless, the graphs show that with positive voltage the COF also increases. Please correct this.

Author's response

We did not mention other changes, which can be seen in Figure 2, because they were insignificant. According to the calculated Least Significant Difference (LSD), the only significant difference occurred in the case of negative voltage at 30 deg. C. We have supplemented the manuscript with the explanation.

 

Reviewer's comments

Regarding, the wear volume observed in tribo-tests it is evident that with negative voltage the produced wear is quite higher. How can this fact be explained? Please improve this part.

Author's response

The negatively charged surface tends to oxidise, while positively charged – reduces oxidation. In this case, the positively charged plate surface was vulnerable to wear. However, we do not have a clear explanation for why wear is reduced at 30 deg. C and increased at 80 deg. C. We have supplemented the manuscript with some discussion on that.

 

Reviewer's comments

In general, it is a very interesting research, out of curiosity, do the authors planning to carry out this type of tests by adding different nanoparticles to the base oil?

Author's response

We are planning to continue the research by applying lubricants of different polarities. The results will make a more comprehensive picture and understanding of the lubricant's behaviour.

 

• All the changes made are highlighted in the revised manuscript.
• The changes that occurred due to grammar and spelling checks were not highlighted.
• As a result of the revision, ten additional references occurred.
• Considering the reviewers' comments, the supplementary material was added.

 

The authors are very grateful to the editor and reviewers for the opportunity to improve this manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors took into account the main comments. After making corrections, the text of the publication and the material presented became better.

I believe that in its current form the article can be accepted for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have taken into account the comments of the reviewer and made corrections in this article. They have responded to all the comments from the reviewer.

Recommendation: This manuscript in the presented form is acceptable for publication in Lubricants