Optimization of Friction Behavior Characteristics by Coating with Solid Lubricants
Round 1
Reviewer 1 Report
An interesting work was presented in the paper.
I strongly recommend the author to find a professional editor to read this paper before resubmitting the revision. I only provide some corrections for the first page or two of the paper.
Page 1, Line 17, “on the size of the friction coefficient” shall be “on the friction coefficient”.
Page 1, Line 17, “gray analysis” shall be “grey relational analysis”. In addition, this sentence is suggested to be rewritten as “The grey relational analysis was employed to identify sets of input factors that would lead… “
Page 1, I think “kinetic friction” is more commonly used than “sliding friction” although two terms have the same meaning.
Page 2, Line 46, it shall be “the friction process intensity”.
Page 2, Line 47, it shall be “the bodies’ surfaces found in contact,..”
Page 2, Line 88, “Gray” shall be “grey”
Page 4, Lines 121-134, more references shall be added in this paragraph.
Page 5, after the experimental results were shown in Table 1, some discussions shall be provided in this section.
Page 8, in Table 2, the authors used the grey analysis to rank the experiments. The experiment with the longest lifetime was ranked as #1 for each set of experiments. Why the authors need to use grey relational analysis instead of choosing the lifetime?
11. The authors ranked the experiments based on the testing results. Can the author predict the most “optimal” set of input factors instead of choosing the best experimental setting?
Author Response
The paper authors are grateful to the reviewers for their remarks and took into considerations to improve the paper content.
Reviewer no. 1
1. Page 1, Line 17, “on the size of the friction coefficient” shall be “on the friction coefficient”.
The reviewer is right; the text was changed.
2. Page 1, Line 17, “gray analysis” shall be “grey relational analysis”. In addition, this sentence is suggested to be rewritten as “The grey relational analysis was employed to identify sets of input factors that would lead…
The reviewer’s suggestion was taken into consideration.
3. Page 1, I think “kinetic friction” is more commonly used than “sliding friction” although two terms have the same meaning.
We took into consideration the reviewer’s suggestion.
4. Page 2, Line 46, it shall be “the friction process intensity”.
We took into consideration the reviewer’s suggestion.
5. Page 2, Line 47, it shall be “the bodies’ surfaces found in contact,..”
We took into consideration the reviewer’s suggestion.
6. Page 2, Line 88, “Gray” shall be “grey”
We took into consideration the reviewer’s suggestion.
7. Page 4, Lines 121-134, more references shall be added in this paragraph.
3 references were used and introduced in the list of references.
8. Page 5, after the experimental results were shown in Table 1, some discussions shall be provided in this section.
The following text was introduced:
In the columns nos. 3, 4 and 5, the values of the process input factors were written as fractions, considering the codified values (1 for the minimum value, 2 for the intermediate value and 3 for the maximum value) as numerators and the proper values of the process input factors as a denominators. In the two parts of table 2, the values of the process input factors and of the experimental results were written both for the polyester that includes particles of molybdenum disulfide and for the polyester that contains graphite particles.
The information included in the columns nos. 8, 9, 10 and 12 is the result of a partial processing of the experimental results.
9. Page 8, in Table 2, the authors used the grey analysis to rank the experiments. The experiment with the longest lifetime was ranked as #1 for each set of experiments. Why the authors need to use grey relational analysis instead of choosing the lifetime?
The experiment with the longest lifetime was ranked as #1 for each set of experiments due to the fact that the tests were made using similar enough experimental conditions (process input factors) and the effects of the two solid lubricants have the same action direction.
Such an explanation was introduced in the paper text.
10. The authors ranked the experiments based on the testing results. Can the author predict the most “optimal” set of input factors instead of choosing the best experimental setting?
As it is actually formulated, the grey relational analysis allows only the identification of the most convenient set of the process input factors among many such experimental sets. To refine the results, another sets of experiments could be designed for values of the process input factors found immediately around of the values that correspond to the best results obtained in the first set of experiments; in this way a better prediction of the experimental setting could be made, to obtain a more adequate compromise of the values that correspond to the two output parameters.
This explanation was introduced in the paper text.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article consist the original data about the experimental results and their statistical analysis. The object of studies are well known solid lubricants and anti-friction polyester coatings consisting of fine particles of lubricating pigments, such as MoS2/Ti or graphite. Such coatings and self-lubricating composites are studied in many scientific articles. The authors apply the Grey analysis for optimization of friction behavior characteristics. The application of this methodology is not new and presented in many articles. This is only interesting case of such analysis application for optimization of coating composition and friction characteristics. Authors apply the standard Amsler wearing set for friction testing and electrostatic painting equipment for anti-friction coating deposition. The detail explanation of working principle of such equipment and principal schemes (Fig 1 -3) are not interesting from scientific point of view. These parts of article must be reduced. There is no clear reasoning of application of such wearing testing scheme, because authors noticed that such polyester coating (paints) could be used when friction processes are not very intense. There is no information in the article about effect of such coating application in comparison with coating without solid lubricant or other types of anti-friction coating. Authors must better review the existed scientific sources and more detail explain the properties and advantages of analyzed anti-friction coatings and show the real samples of such polyester coatings application in same conditions, which applied during their experiments. The lifetime of coating according presented results is about 390 min and it is too low for use of this coating in the practice in such conditions. The statement that experiment were achieved on the Amsler type testing machine and results were analyzed using the Grey relational analysis method and Matlab environment can’t be the final conclusions of this research. The article introduction part and conclusions must be improved by adding the information about the studied anti-friction coatings properties in comparison with alternative coatings, effect of their application and friction parameters optimization.
Author Response
The paper authors are grateful to the reviewers for their remarks and took into considerations to improve the paper content.
Reviewer no. 2
1. The article consist the original data about the experimental results and their statistical analysis. The object of studies are well known solid lubricants and anti-friction polyester coatings consisting of fine particles of lubricating pigments, such as MoS2/Ti or graphite. Such coatings and self-lubricating composites are studied in many scientific articles. The authors apply the Grey analysis for optimization of friction behavior characteristics. The application of this methodology is not new and presented in many articles. This is only interesting case of such analysis application for optimization of coating composition and friction characteristics.
2. Authors apply the standard Amsler wearing set for friction testing and electrostatic painting equipment for anti-friction coating deposition. The detail explanation of working principle of such equipment and principal schemes (Fig 1 -3) are not interesting from scientific point of view. These parts of article must be reduced.
The authors took into consideration the recommendations formulated by the reviewer.
3. There is no clear reasoning of application of such wearing testing scheme, because authors noticed that such polyester coating (paints) could be used when friction processes are not very intense.
There are situations when for various reasons, the presence of the oils that include additives on the base of molybdenum disulfide is not admitted; the use of oils with molybdenum disulfide is one of the most known methods of using the molybdenum disulfide to increase the parts lifetimes involved in friction processes. The authors intended to know which could be the results of using molybdenum disulfide particles or graphite particles included in a polyester applied on friction surfaces. Due to the relatively low mechanical strength of the polyester layer, it is difficult to maintain this layer on the surfaces affected by intense friction for a long time. During the experimental tests, one considered as a lifetime the time interval when there is yet a polyester on the surfaces involved in the friction process. One could mention that particles of molybdenum disulfide or graphite could adhere and remain on the part surfaces just after the complete removal of the polyester layer, but this aspect was not considered in the presented research. One mentioned these considerations in the last paragraph from the introduction and in the last part of chapter 5.
4. There is no information in the article about effect of such coating application in comparison with coating without solid lubricant or other types of anti-friction coating.
The following text was introduced in the paper content:
As above-mentioned, conventionally one took into consideration as a lifetime of the polyester layer that includes particles of solid lubricant only the interval of time up to the total removal of the polyester layer from the disks surfaces as these surfaces could be observed by visual examination, but particles of solid lubricant could yet remain on disks surfaces, improving the disks behavior to the friction processes. This aspect could be considered in future research, as comparisons with other types of anti-friction coating will be studied.
5. Authors must better review the existed scientific sources and more detail explain the properties and advantages of analyzed anti-friction coatings and show the real samples of such polyester coatings application in same conditions, which applied during their experiments. We added new references as support for justifying the proposed method of improving the behavior of parts in friction processes.
The following statements were also introduced in the paper text.
An example of the use of layers including solid lubricant particles to improve friction behavior may be gear transmissions that do not work in an oil including solid lubricant particles and when gears can be changed under mild conditions; one considered that in such a case the life of the gears could be higher than the one in which the solid lubricant particles incorporated in a polyester layer are not used. One considered also that the cost of using such a method of coating with a polyester layer including particles of solid lubricants could be lower than that valid in the cases of other coating methods, as the plasma coating, the laser beam coating, the electrochemical deposition etc. are.
6. The lifetime of coating according presented results is about 390 min and it is too low for use of this coating in the practice in such conditions.
We appreciated that an answer to this remark could be that presented in the case of the remark #5.
7. The statement that experiment were achieved on the Amsler type testing machine and results were analyzed using the Grey relational analysis method and Matlab environment can’t be the final conclusions of this research.
The reviewer is right. We changed this conclusion.
The experiments achieved by the disk-on-disk Amsler testing machine and the processing of the experimental results by means of the grey relational analysis and the ratio signal/noise specific to the Taguchi method developed inclusively in the Matlab environment showed that a certain set of the process input factors could ensure convenient values for the considered process output parameters and could highlight the influence exerted by the change of the ratio ξT/ξµ on the size of the grey relational grade γ appreciated as evaluation criterion.
8. The article introduction part and conclusions must be improved by adding the information about the studied anti-friction coatings properties in comparison with alternative coatings, effect of their application and friction parameters optimization.
Additional references were taken into consideration to compare the proposed coating method with other coating methods.
In the chapter of conclusions, the following statement was introduced:
In comparison with other more complex coating methods, one appreciated that the use of polyester layers including particles of solid lubricant could have a lower cost.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
it is fine with me to publish this paper.
Author Response
The authors are grateful to the reviewer, for his comments and suggestions for improving the content of the paper.
Reviewer 2 Report
The authors improve the article responding to big part of reviewers comments. However, some important demerits were not completely removed. Authors add the new citations and information about alternative coatings, but not analyse and compare the properties, advantages and disadvantages of these coatings. Authors only declared, that coatings including molybdenum disulphide - best choice for this case. Authors not clearly explain the reasons of use of Amsler type machine and testing scheme, which consists 2 disks found in contact by their peripheral surfaces. Exist many different methods of measuring friction, the choice should be well argued. There is no information about the coating surface roughness, which first of all influences the friction losses and testing results. There is no analysis of different coatings prices and conclusion about lowest price of analysed coatings is not confirmed and actual in this paper.
Author Response
Authors’ answers to the reviewer’s comments - Stage 2
1. Reviewer’s comment. The authors improve the article responding to big part of reviewers comments. However, some important demerits were not completely removed.
Authors’ answer. The authors are grateful to the reviewer, for his comments and suggestions for improving the content of the paper.
2. Reviewer’s comment. Authors add new citations and information about alternative coatings, but not analyze and compare the properties, advantages and disadvantages of these coatings.
Authors’ answer. The reviewer knows probably that at present there are really many alternative technologies/processes aiming to deposit materials on parts to improve their behavior to wear. There is even an International Society of Coating Science and Technology, there were and there are even conferences that seek to address such a topic (coating technologies/processes). An analysis and a comparison of the properties, advantages and disadvantages of the majority of these coating alternatives could better constitute the objective of a REVIEW PAPER or just of a MONOGRAPH and this was not just the authors’ intention. Moreover, the inclusion of many details requested by the analysis and comparison of properties, advantages and disadvantages of the coating alternatives could increase significantly the length of the introductory chapter of a RESEARCH paper and this fact could not be accepted by the journal editors. However, we took into consideration the reviewer comments and we have introduced some succinct additional information in accordance with the reviewer’s recommendations.
3. Reviewer’s comment. Authors only declared, that coatings including molybdenum disulfide - best choice for this case. Authors not clearly explain the reasons of use of Amsler type machine and testing scheme, which consists 2 disks found in contact by their peripheral surfaces. Exist many different methods of measuring friction, the choice should be well argued.
Authors’ answer. We, as authors, did not declare that the coatings with the molybdenum disulfide is the best choice in this case, but, considering that the question formulated by the reviewer is right, an argumentation was introduced in the paper.
4. Reviewer’s comment. There is no information about the coating surface roughness, which first of all influences the friction losses and testing results.
Authors’ answer. The reviewer is right. Information concerning the value of the surface roughness parameter Ra after applying a grinding (before applying the electrostatic deposition) to the surfaces involved in the research was included in the paper.
5. Reviewer’s comment. There is no analysis of different coatings prices and conclusion about lowest price of analyzed coatings is not confirmed and actual in this paper.
Authors’ answer. A proper and correct analysis of the distinct coatings prices is difficult to be achieved, due to the fact that the prices are characterized by high differences among distinct countries (for example, the prices of the electrostatic deposition made in China could be very low, without the quality of the deposited layers being always low!) and prices are the results of the negotiations between the beneficiary and the manufacturer which operates the electrostatic deposition. On the other hand, a strictly justified analysis of the coatings prices could significantly increase the content of the paper. However, to complete the reviewer’s recommendation, some succinct especially qualitative remarks concerning the prices (operation costs; the prices include yet other components) of applying the electrostatic deposition of the layers that include particles of solid lubricants were introduced in the paper.
Round 3
Reviewer 2 Report
The authors improve the article responding to the all reviewer comments.
