Experimental Investigation on Contaminated Friction of Hydraulic Spool Valve
Round 1
Reviewer 1 Report
The topic of the paper fits generally well to the journal (Mechanical Engineering). However the technical and scientific quality of the paper should be improved. There are following general remarks:
- lack of simulation results,
- there are no tests which showing the effect of spool vellocity change on the friction coefficient,
- Did the authors consider the stick-slip phenomenon?
- For proportional valves with proportional solenoids, a dither signal is applied to the spool. Will the authors test the spool behaviour in such conditions?
- figure 6 is unnecessary in my opinion,
- The authors on page 7 indicate the experiment temperature as "room temperature". When the hydraulic valves work in real conditions, this temperature is higher.
Author Response
Response 1: It is a very good advice. This paper focus on measuring the friction force caused by particles, and this paper mainly introduces a kind of measuring test bench which is effective and practical. The problem of friction force caused by particles is complex, in terms of simulation based on the ideal condition, cannot be directly calculated friction force, can only finish the analysis of stagnation mechanism, and the papers researches on the mechanism of stagnation have been published, like Visualization Experiment of Single Particle Motion in Model of Spool Clearance. This paper is a verification of the phenomenon.
Response 2: Thank you for the very good suggestion. At present, what we are doing is analyzing the relationship between stagnation and velocity of spool movement, and we have got some results, but we need further verification. It is believed that we will get detailed conclusions in future.
Response 3: We are grateful for your valuable suggestion. The clearance is much larger than the micron scale, so the stick-slip force are not dominant, we take it as constant value.
Response 4: Thank you for pointing this out. There is no such attempt in this paper, just basic research, but we can try to discover some phenomena and carry out a new research on it.
Response 5:We are benedictory for the good suggestion, figure 6 shows clearly the oil with particulates, but it's very clear in the article, we remove the figure 6
Response 6:Thank you for pointing this out, this paper is basic research to predict trend, we consider the friction force at the same temperature because of same viscosity, so at any temperature, particle hysteresis force by temperature can be ignored. But we'll take temperature as an influence which may be have effect on spool movement to research in the further
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Thank you for the nice work. Following, please find some comments:
- Please rewrite the abstract as it is poor english with too long sentences and nearly no verbs.
- It would be interesting, whether the solutions differ if the velocity would be increased and the dimensions wouldn’t be scaled. A variation of the impact factors and the comparison of the results would be interesting.
- In addition, the use of steel particles would be very interesting for the reader.
- Which effect has a higher pressure or velocity?
- More international references would be adequate for the investigated topic
- The investigated velocity of 3.33 mm/s is very low for such a spool valve. Please show additional investigations with higher velocities as it would be more relevant in hydraulics.
Author Response
Response 1: We sincerely accept your suggestion. The abstract is revised as follows:
Abstract: This paper focuses on the contaminated friction of fit clearance between spool and valve body to explore the influence principles of clamping stagnation phenomenon. From the perspective of surface morphology and particulates size in the clearance, designing and manufacturing the valve body, rough spool, conical spool and standard morphology spool, the test bench was built up and the curves of real-time contaminated friction in the movement of spools were obtained through experiments. The curves show that the contaminated frictions have a feature of pulsation; meanwhile, the stagnation sensitive size of particulates is in the range of 0.7 to 0.9 times that of clearance. Compared to the ideal morphology spool within the range of sensitive size, the contaminated fiction of rough spool is increased, whereas the lower limit of stagnation sensitive size range of particulates on conical spool is decreased. The contaminated friction is gradually increased on cis-conical spool but increased first and then decreased on invert cone spool.
Response 2: It is a very good advice. This paper focus on the sensitive size of particulates which can lead stagnation on spool, so the velocity is a constant. At present, what we are doing is analyzing the relationship between stagnation and velocity of spool movement.
Response 3: We are benedictory for the good suggestion. At this stage, we consider the impact of different metal particles on stagnation of spool, like steel particles, but now we are trouble in injecting into the model because of poor suspension, we will try our best to deal with it in the future.
Response 4: Thank you for the very good suggestion, we will take the influence of pressure and velocity on spool’s stagnation into full consideration in the following research.
Response 5: We are grateful for your valuable suggestion, we also read some articles of researchers on the stagnation of spool, and take them as the reference.
Inoue R. Contaminant Lock in Spool Type Directional Control Valves-Theory and Experimental Verification. BFPR Journal 1980; 13:167-171. Khandaker I, Glavas E and Jones G. A fibre-optic oil condition monitor based on chromatic modulation. Measurement Science and Technology 1993; 4:608. Kwon KO, Kong SH, Han HG, et al. On-line measurement of contaminant level in lubricating oil: US 2000. Edmonds J, Resner MS and Shkarlet K. Detection of precursor wear debris in lubrication systems. 2000 IEEE Aerospace Conference Proceedings (Cat No 00TH8484). IEEE 2000, pp. 73-77. Murali S, Xia X, Jagtiani AV, et al. Capacitive Coulter counting: detection of metal wear particles in lubricant using a microfluidic device. Smart Materials and Structures 2009; 18:037001.Response 6: Thank you for pointing this out, in this paper, we focus on the effect of particle size on the stagnation of spool, because of contingency of stagnation, we take velocity as 3.33 mm/s to research adequately. As for the velocity, we will specialize in it.
Author Response File: Author Response.pdf
