The Tribological Performance of Frictional Pair of Gas–Liquid Miscible Backflow Pumping Seal in Oil–Air Environment

Round 1

Reviewer 1 Report

Journal: Lubricants (ISSN 2075-4442)

Manuscript ID: lubricants-2362344

 Review Report#

 The authors presented an article on “The tribological performance of frictional pairs of gas-liquid miscible backflow pumping seal”. The subject of the article falls within the scope of the journal "Lubricants". However, the article will be ready for publication after a major revision. Comments are listed below. (The similarity rate is 20%.)

1.      In the last paragraph of the introduction, the difference of this article from previous studies should be clearly stated. The original side of the article should be specified.

2.      The references given in the introduction are insufficient. The introduction should be supported by giving more and up-to-date references.

3.      The MQL system is not mentioned in the introduction.

4.      According to which standards were the wear and friction tests performed?

5.      Results are devoid of discussion. The results of similar studies in the literature should be compared and discussed.

6.      The relationship of surface morphologies obtained before and after the friction test with hardness and wear should be further detailed.

7.      The SEM images given in Figure 8 are not clear.

8.      The article contains numerous typographic and language errors. It should be corrected.

The article should be rearranged by taking into account the journal writing rules and citation rules.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents experimental results of friction and wear behaviour of typical materials used for the rings of spiral groove mechanical face seals (SGMFS) operating with oil-air mixture. The sealing of high-speed bearing chamber is certainly of important relevance.

The operation of the seal was simulated on a classical tribological tester (disc with spiral grooves -on-flat disc configuration), in lubricating conditions at low and medium speed. Six pairs of materials have been tested The results are summarized in terms of friction coefficient (COF) and surface micro-morphology.

The experiments are well done, the procedure of the  experiments and the results are clearly presented (except some details listed below). I found a few errors of grammar but they do not affect the readability of the text.

However, in this form, the paper has no relevance for the SGMFS.

The testing conditions do not correspond to the operating conditions of SGMFS. You can find below my arguments.

·        the low speed operation is valid just for a very short period of time

·        in these experiments the two rings are loaded with a constant force- this comes in contrast with real SGMFS were there is a back spring which control the normal load.

·        wear was not assessed (too short experiments) but only evaluated through 3D image analysis.

How was the support of the applied normal load: elastic or rigid ? Normally the friction regime is boundary and hydrodynamic effects are not sensible with a rigid support.

What about planarity and parallelism of the two rings ? It is great importance for such tests.

In tribological tests temperature plays an important role; however, there is no data regarding the temperature (despite the presence of a thermocouple). The temperature affects also the viscosity of the mixture. This is a subject which must be addressed.

If friction in air-oil lubrication conditions is the objective of the experiments details about the mixture and its properties. Surely the air-oil percentages could be varied to find its importance. One cannot find any detail about this aspect. Contrarily, useless information like lubricant rate of flow is provided.

The results are not relevant as long as only a single series of test has been done for each pair of materials. Reproducibility of the results is an important issue in such experiments.

There is also a repeated error in the manuscript: page 7 row 214- "the COF of Al2O3 coating..." and similar expressions (page 2 row 78 and in several parts of chapter 3) are unacceptable comments. Friction is a property of a PAIR of materials.

Some other comments:

Introduction covers subjects which are not directly connected the reported work:

page 2 row 76 (dry friction or some special lubricant conditions...) - what is "special lubricant conditions"?

page 2 row 80 - why is relevant the friction in seawater ?

In view of these the title does not describe correctly the content of the paper: it is not a seal tested and the presence of the air-gas lubricant is not addressed at all.

This can be seen also if we read the list of references: there is none dealing with SGMFS, despite a large amount of work dedicated during last 60 years.

Good.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Journal: Lubricants (ISSN 2075-4442)

Manuscript ID: lubricants-2362344

Review Report 2#

The authors made the desired corrections. But they forgot to add Figure 8. In my opinion this article is acceptable for publication in the "Lubricant" journal.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The conclusions must be more elaborated.

Reared attentively the text.

Example:

ceramic materials are often used as surface coatings for ductile materials - sentence repeated twice at line 55 and 67 (page 2)

Author Response

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Author Response File: Author Response.docx