Evaluation of Tribological and Mechanical Properties of Carbon Steel with Fluoroligomeric Film at Piezoelectric Actuator Contact

Round 1

Reviewer 1 Report

Review Comments:

The paper performs analysis on the evaluation of tribological and mechanical properties of Carbon steel with Fluoroligomeric film at piezoelectric actuator contact. The present researches are very interesting. It is well-organized and well-written. It can meet the requirements of the journal and can be accepted for publication after careful revision.

1. The abstract should be revised. The significances in engineering field should be highlighted.
2. The authors are suggested to explain the novelty of the paper.
3. In Section 2, the authors are suggested to add a diagram or picture of the flow chart of the procedure.
4. Model verification should be added before the discussion to ensure the validation of the simulations. Add it please.
5. For the simulation results for start-up conditions in Section 3.2, further step analysis should be added, especially the lubrication regime and mechanism of the lubrication. The authors are suggested to add comments as well as the references below. They are closely related with the present research.

[1] Theoretical and experimental exploration into the fluid structure coupling dynamic behaviors towards water-lubricated bearing with axial asymmetric grooves[J]. Mechanical Systems and Signal Processing, 2022, 168: 108624.

[2] Analysis on the Lubrication Performances of Journal Bearing System Using Computational Fluid Dynamics and Fluid–Structure Interaction Considering Thermal Influence and Cavitation[J]. Tribology International, 2013, 64: 8-15.

6. For the conclusions, it is a little long. Several brief points of conclusions are enough. The authors are suggested to rewrite the conclusions.
7. The English should be improved considerately.

Author Response

Yes, the abstract was formulated not correctly, we revised the abstract including the explanation of the novelty of the paper. The paper presents before not performed investigation on the influence of fluoroligomer coating on the performance of a piezoelectric actuator with respect to the actuator load. It is important that for PEA with a fluoroligomeric coating under short-term overloads, the drive speed recovers easily, i.e. when the braking load is released, it starts rotate again. The results of wear value of PEA frictional element are very important explaining the higher longevity of PEA with FOM processed roller and is also novelty of this study.

Flow chart of the procedure is included (fig. 2b). We added additional comments on test procedure and test cycles scheme.

The research was based on testing the friction pair of piezoelectric actuator with our test rig and presentation of test results. We not performed any modelling or simulation of the measured data. That was not objective in our research.

The suggested references for the analysis of lubrication regime and mechanism are really valuable and interesting. However it not pass the dry friction mechanism at the piezoelectric actuators and can not used under this particular friction pair analysis.

We revised the conclusions making them shorter.

English language was improved.

Reviewer 2 Report

Well written paper and may prove interesting to the readers. But there are few comments to improve the paper that should be addressed:

Abstract:

1. Clarify the % concentration of the film? Was it varied from 0.5 to 10% as mentioned in the abstract? Results did not show any variation in the concentrations.

Introduction: 

Please include a review of other types of films used for the same purpose in comparison to the FOM suggested in this paper. 

Methods: 

1. Description on the composition of the film should be included in the paper and authors should attempt to correlate the results to the composition of the film.
2. What is the process of depositing the film? Only mentioned immersion and drying. For the particular film used in this paper, there should be mentioned the standard technique of depositing the layer to the substrate. 
3. Please include a cross-sectional view of the sample which will be helpful to describe the various layers which are the carbon steel, epoxy and film and their thicknesses. 

Results: 

1. Fig 3 and Fig4 should be combined and for each loading parameter, the performance without and with film should be side by side, easier to compare. eg. 3a and 4a side by side and so on. Revise the discussion as well to accomodate the corrections suggested. 
2. In fig 6 and 7, please label the defects and observations accordingly. 
3. Line 206, rotor is wrongly spelled as roto. 

References: 

Out of 16, 9 references are from the current authors. I suggest to include a wider scope of papers from other papers as well such as on the research of other types of polymeric films. 

Author Response

The abstract and conclusions were formulated not correctly, we revised it.

We know (that is mentioned in introduction) that carbide, ceramic and silver coatings were used for improvement of piezoelectric actuators’ performance. However we not found in the literature the information about possible use of other than FOM polymeric applications for piezoelectric actuators.

Composition of the film includes complex polymeric compound of fluorine with carbon, oxygen and hydrogen. The used fluoroligomer Foleox is trademark F5, structural formula R_f-CONHR₂. Exact structure of this fluoroligomer is not open access and can not be unclosed. We made some clarification regarding treatment procedure, and it seems to be comprehensive.

We agree that cross-sectional view of the sample can help describing the layers and its thickness, but we not performed it because main aim of the study was to investigate the influence of FOM coating on efficiency of piezoelectric actuators’ performance.

We agree on remark to re-group of pictures 3 and 4. In revised paper version the pictures and discussion are changed accordingly.

The defects and observations in figures 6 and 7 are marked accordingly in revised version.

Correction in line 206 is made.

Reviewer 3 Report

In this paper we investigated the tribological (mechanical properties, microhardness, etc.) properties of pure carbon steel and modified with fluoroeligomer materials. The paper is of scientific interest and may be published in the journal Coatings after minor corrections.

1. Figures

- I suggest that the graphs in Figures 3 and 4 are not below each other, but next to each other (make two columns instead of one).

- In Figures 6 and 7, not all of the photos show the scale. Please indicate the scale on each photo.

2. References

- a lot of links where the authors are referring to their own work. This is not entirely correct. The topic is interesting, most likely that there are many researchers working in this direction, in this regard, it is necessary to add more sources of literature and refer to the works of other scientists.

Questions for authors:

1. Why did you modify the epoxy with only 30% silicon oxide. Why this concentration was chosen? If you used a similar concentration of this additive in previous works, I suggest you give a reference.

2. Why was mild steel chosen as a substrate? Is it possible to do a similar modification on non-ferrous metals?

Author Response

We agree on remark to re-group of pictures 3 and 4. In revised paper version the pictures and discussion are changed accordingly.

The scales (and additionally - defects marks) in figures 6 and 7 are provided in revised version.

We reduced the own publications in the list of references and added additional reference sources together with the amendment of comments in discussion.

Formation of frictional element material from epoxy with 30% silicon oxide is based on our investigations and evaluation hat lower content of silicon oxide will not guarantee the hardness and wear resistance of element and increasing the silicon oxide content to higher than 30% makes the frictional element brittle and reduces it longevity.

Our practice show that harder than chosen steel C45 can cause additional slip possibility of piezoelectric actuator contact. Similar modification with fluoroligomeric compounds could be used also for surface of different metals. However the authors of this Foleox compound formulated it adjusting to most efficient interaction with steel surfaces.

Round 2

Reviewer 1 Report

The authors have revised the paper point by point. Accept