Experimental Investigation into the Friction Coefficient of Ball-on-Disc in Dry Sliding Contact Considering the Effects of Surface Roughness, Low Rotation Speed, and Light Normal Load
Round 1
Reviewer 1 Report
In my opinion authors should clarify/correct the following issues:
#1) Authors analyze the influence of diverse parameters considering just three cases (see for instance fig. 3 (surface roughness), fig. 5 (normal load) and fig. 7 (rotation speed). As a matter of fact, 3 cases are not enough for analyzing the influence of a variable and consequently, in my opinion I consider that authors should include more cases of study including intermediate values of surface roughness for fig. 3, normal loads for fig. 5 and rotation speeds for fig. 7.
#2) In addition, authors include the analysis of the average values of the friction coefficient in Fig. 4, 6 and 8. For the sake of clarity, authors should include the number of measurements used for obtaining such average values and the standard deviation.
#3) In the paper it is not included any image of the contact surface after testing. Images of the global surface and detail views of the contact zone at diverse positions obtained by SEM seems to be interesting in the analysis for each condition and, in my opinion, they should be included in the paper.
#4) Line 113. Please use “much lower” instead of “much less”
#5) Line 116. Please use “analyze” instead of “analysis”
#6) Line 118. Please for the sake of clarity, please use italics for variables in the main text such as d.
#7) Line 122. Please include units for dimensions of Fig. 1a at less in the figure caption.
#8) Line 144. Please use “load and rotation speed” instead of ”load, rotation speed”.
#9) Line 146. Please do not use “*” in equations for scalar product, please use a blank space instead
#10) Line 163. Please use “that is” instead of “that´s”. Do the same in Line 245.
#11) Lines 163-165. Please provide evidences for this sentence
#12) Line 189. Please use “contact point” instead of “point contact”
#13) Lines 197-199. Please include evidences for this sentence.
#14) Line 206. Please use “more slowly” instead of “most slowly”
#15) please use “faster than the other cases” instead of “fastest”
#16) Line 283. For the sake of clarity, please revise this sentence “… get more…”
#17) Line 290. Something seems to be missed in the sentence “appears earlier than….”
#18) Line 292. This sentence is confusing “contact more frequently buy less fully”. Please be more precise and clear.
#19) Line 302. This sentence is confusing “becomes more serious”. Please be more precise and clear.
#20) Line 340. Reference #3, please delete the “*” in the initial name of author. In addition, please do not use “et al” in reference section, please include the names of all the authors of the paper.
Author Response
Thank you very much for your comments on the manuscript submitted. We have revised the manuscript accordingly, and the detailed corrections we have made are attached below.
(the corrections made are highlighted in blue in the revised manuscript)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
My comments to the manuscript titled Experimental investigation into the friction coefficient of ball-on-disc in dry sliding contact considering the effects of surface roughness, low rotation speed and light normal load are bellow.
1. Section Introduction, last paragraph. Please indicate what is new in the manuscript in the literature review.
2. Section Experimental Materials and Set Up should be rename to the Experimental Materials and Methods.
3. In the description of the tribological tests, please provide the friction details - distance or time.
How many tests have been done for each type of studied material? How many repetitions were there?
4. The Authors write about the surface roughness and then provide the profile parameter Ra. Moreover, they provide a single measurement and not the value resulting from the profile measurement carried out several times (at least 3 times) - no mean value and standard deviation in Table 1.
5. Please provide the justification for choosing the profile parameter Ra instead of the surface parameter Sa or preferably Sq, Sku, Ssk...
6. Please provide details of the NanoFocus device and measurement parameters.
7. Figures 3, 5 and 7. Figures are illegible.
8. Section Conclusion should be completed after the manuscript has been corrected.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Review of the manuscript "Experimental investigation into the friction coefficient of ball-on-disc in dry sliding contact considering the effects of surface roughness, low rotation speed and light normal load". In my opinion minor revision is required. My remarks are as follows:
1. What is the main novelty of this work? I appreciate the thoroughness of the research and the description of the results, but a number of works provide similar conclusions as in the article.
2. What was the roughness of the balls used in tribological tests?
3. How many repetitons of tests with the same entry parameters were performed?
4. What was the wear of balls in tribological tests? You mentioned that it was small, but did it not significantly affect the total wear of the system?
5. Did you measure the temperature during tribological tests? It can be important especially in dry sliding conditions. Were temperature changes correlated with any tribological parameters?
6. Page 5, line 160 „As shown in Figure 3, in the initial time, the friction force rises rapidly to near 0.2”. Something is wrong with this sentense. According to the Figure 3 starting (initial) value of friction coefficient was different for each treatment (0.2 milling, 0.3 turning and so on) and increased rapidly to near 0.9.
7. Subsection 3.1. „Effects of Surface Roughness on Friction Coefficient”. There are no references at least to a few publications where similar conclusions were obtained. For example: Liang G. et al. „An investigation of the influence of initial roughness on the friction and wear behavior of ground surfaces” – https://0-doi-org.brum.beds.ac.uk/10.3390/ma11020237; Dzierwa A. „Influence of surface preparation on surface topography and tribological behaviours” – https://0-doi-org.brum.beds.ac.uk/10.1016/j.acme.2016.12.004; Sedlacek M. et al. „Influence of surface preparation on roughness parameters, friction and wear” – https://0-doi-org.brum.beds.ac.uk/10.1016/j.wear.2008.04.017 and others.
8. It would be also worth clarifying where the results could be applied. Do the results have only cognitive or also more applicable character?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
This paper is correctly written that fits within the scope of the Journal. The originality of paper is reflected in the performed experiment. The presentation of the results is solid, and adequate figures contribute to the clearness of the results.
Terminology is generally acceptable, but minor language, both in the selection of words and proper grammar, as well as some technical improvements should be done according to the following suggestions:
- Line 146 – for each value v, d and n add proper unit, because value v is given by expression v= (pd*n)/60.
- Lines 168 – 173 - Complete sentence must be changed in order to be quite clear. Try to divide it in two shorter sentences to describe everything…
- Line 192 – Delete “Note that…”; simply start this sentence with “During the running-in…”
- Line 217 – Sentence in this line is not complete. An adequate comment on the behavior of “friction coefficient” is missed.
- Line 222 – Change the position of the words in this sentence as following “…ascends by 1.52 % from 0.920 to 0.934 and then descends by 1.82 % to 0.917.”
- Line 228 – Change “we measure the friction coefficients …” into ”..the friction coefficients were measured ..”
- Line 277 – Complete sentence in this line was repeated, see lines 270-273. Simply delete sentence in the line 277.
- Line 295 – Sentence in this line is not complete. An adequate comment on the behavior of “friction coefficient” is missed. Similar lack of description like line 217.
Provided the above listed improvements are implemented, the paper can be recommended for publication.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Reviewer 2 Report
I do not have more comments. Thank you.
