Influence of external vibration and frictional surface roughness on friction-reduction performance of granular flow lubrication

Gravity-driven powder flow and the influence of external vibration on flow characteristics

PurposeThe purpose of this study is to reveal the friction reduction performance and mechanism of granular flow lubrication during the milling of difficult-to-machining materials and provide a high-performance lubrication method for the precision cutting of nickel-based alloys.Design/methodology/approachThe milling tests for Inconel 718 superalloy under dry cutting, flood lubrication and granular flow lubrication were carried out, and the milling force and machined surface quality were used to evaluate their friction reduction effect. Furthermore, based on the energy dispersive spectrometer (EDS) spectrums and the topographical features of machined surface, the lubrication mechanism of different granular mediums was explored during granular flow lubrication.FindingsCompared with flood lubrication, the granular flow lubrication had a significant force reduction effect, and the maximum milling force was reduced by about 30%. At the same time, the granular flow lubrication was more conducive to reducing the tool trace size, repressing surface damage and thus achieving better surface quality. The soft particles had better friction reduction performance than the hard particles with the same particle size, and the friction reduction performance of nanoscale hard particles was superior to that of microscale hard particles. The friction reduction mechanism of MoS2 and WS2 soft particles is the mending effect and adsorption film effect, whereas that of SiO2 and Al2O3 hard particles is mainly manifested as the rolling and polishing effect.Originality/valueGranular flow lubrication was applied in the precision milling of Inconel 718 superalloy, and a comparative study was conducted on the friction reduction performance of soft particles (MoS2, WS2) and hard particles (SiO2, Al2O3). Based on the EDS spectrums and topographical features of machined surface, the friction reduction mechanism of soft and hard particles was explored.

The demand for highly controllable droplet generation methods is very urgent in the medical, materials, and food industries. The droplet generation in a flow-focusing microfluidic device with external mechanical vibration, as a controllable droplet generation method, is experimentally studied. The effects of vibration frequency and acceleration amplitude on the droplet generation are characterized. The linear correlation between the droplet generation frequency and the external vibration frequency and the critical vibration amplitude corresponding to the imposing vibration frequency are observed. The droplet generation frequency with external mechanical vibration is affected by the natural generation frequency, vibration frequency, and vibration amplitude. The droplet generation frequency in a certain microfluidic device with external vibration is able to vary from the natural generation frequency to the imposed vibration frequency at different vibration conditions. The evolution of dispersed phase thread with vibration is remarkably different with the process without vibration. Distinct stages of expansion, shrinkage, and collapse are observed in the droplet formation with vibration, and the occurrence number of expansion–shrinkage process is relevant with the linear correlation coefficient.

It is important to examine the contact mechanism between metal surfaces for the accuracy improvement of guideway motion and for the pre-estimates of contact rigidity and damping capacity of mechanical systems. In the present study, the contact between a hard steel sphere and soft aluminium or duralumin surfaces are treated, and the effects of lubrication or the interference effect of soft metal deformation between protuberances are discussed. The effect of lubrication is significant in the mean contact pressure variation by the reduction of friction. The deformation by one sphere indenter is confirmed to be ruled by Meyer's law. When the soft metal is pressed by two sphere indenters, the deformation is similar to that of one indenter for a small press load. However, the load becomes sufficiently large, interference is initiated and the size of the indentation becomes small. The influence of this interference can be estimated by a simple equation of indenter size and material properties.

A numerical and experimental study on the interface friction of ball-on-disc test under high temperature

Effect of magnetic field on the tribological behaviors of Fe3O4@MoS2 as polyalphaolefin additive in the steel/steel friction interface

The requirement for intervention operations in extended-reach wells continues to grow. It is estimated that globally around 30-40% of the end sections of the extended-reach wells are inaccessible by the current coiled tubing (CT) friction reduction technologies, such as lubricants, vibratory tools, and tractors. Although many of the extended-reach wells are open-hole, there is a lack of understanding in the industry regarding the predictable and consistent friction reduction performance at downhole conditions of the existing CT technologies in those open-hole wells. Conventional friction reduction techniques for CT operations have been focused around mechanical or chemical methods for cased wells. For instance, following an extensive laboratory testing research program, a lubricant was recently developed that lowers the CT coefficient of friction between 40 and 60% in new, clean wells (Livescu et al. 2014; Livescu and Craig 2015; Livescu and Craig 2018). Friction reduction of this magnitude roughly translates in doubling the CT lateral reach. However, the friction reduction performance of lubricants is diminished in wells filled with sand of proppant. In addition, very limited studies are available for open-hole wells. To reach the remaining 30-40% un-reachable length of open-hole wells and cased-wells with sand or proppant, lubricants are required to work in conjunction with other technologies such as vibratory tools and tractors. The instrument previously used for metal-on-metal friction reduction research was modified to mimic the downhole conditions of CT sliding movement in open-hole wells and cased-hole wells with sand or proppant. That is, the coefficients of friction between the CT metal surface and the non-metal surface of a rock and sand or proppant layer can be measured. This instrument was designed for researching the effects of temperature, pressure, CT sliding speed, surface roughness, and fluid composition on the coefficient of friction. For clean cased-hole wells, the effects of pressure and sliding speed were weak in the laboratory tests, while the effects of temperature, surface roughness, and fluid type and composition were strong. For the friction reduction in open-hole wells, several rock samples taken from formations and reservoirs with different properties, such as porosity, permeability, pore size, etc., were used. The tests were performed with several CT coupons of different grades and both proprietary and third-party lubricants, to better understand the factors affecting the lubricity in open-hole wells. It was found that, at downhole conditions, the friction performance of the lubricant previously developed decreases from 40-60% for cased wells to 30-40% for open-hole wells. This is the first study available in literature consisting of laboratory friction tests performed with lubricants to mimic the CT operations in open-hole wells and sand/proppant-filled cased-hole wells. Detailing the testing procedures and results are of significant help to the industry for understanding the downhole factors affecting the CT friction in extended-reach open-hole wells and for obtaining predictable and consistent friction reduction results for CT operations in those wells.

Recently, the engineering structural ceramics as friction and wear components in manufacturing technology and devices have attracted much attention due to their high strength and corrosion resistance. In this study, the tribological properties of Si3N4/Si3N4 sliding pairs were investigated by adding few-layer graphene to base lubricating oil on the lubrication and cooling under different experimental conditions. Test results showed that lubrication and cooling performance was obviously improved with the addition of graphene at high rotational speeds and low loads. For oil containing 0.1 wt% graphene at a rotational speed of 3000 r·min−1 and 40 N loads, the average friction coefficient was reduced by 76.33%. The cooling effect on Si3N4/Si3N4 sliding pairs, however, was optimal at low rotational speeds and high loads. For oil containing 0.05 wt% graphene at a lower rotational speed of 500 r·min−1 and a higher load of 140 N, the temperature rise was reduced by 19.76%. In addition, the wear mark depth would decrease when adding appropriate graphene. The mechanism behind the reduction in friction and anti-wear properties was related to the formation of a lubricating protective film.

Reduction of the interfacial friction for the contact of a silicon oxide surface with sodium borosilicate in aqueous solutions has been accomplished through the adsorption of poly(L-lysine)-graft-poly(ethylene glycol) on one or both surfaces. Spontaneous polymer adsorption has been achieved via the electrostatic attraction of the cationic polylysine polymer backbone and a net negative surface charge, present for a specific range of solution pH values. Interfacial friction has been measured in aqueous solution, in the absence of wear, and on a microscopic scale with atomic force microscopy. The successful investigation of the polymer-coated interfaces has been aided by the use of sodium borosilicate microspheres (5.1 microm diameter) as the contacting probe tip. Measurements of interfacial friction as a function of applied load reveal a significant reduction in friction upon the adsorption of the polymer, as well as sensitivity to the coated nature of the interface (single-sided versus two-sided) and the composition of the adsorbed polymer. These measurements demonstrate the fundamental opportunity for lubrication in aqueous environments through the selective adsorption of polymer coatings.

A novel eco-friendly water lubricant based on in situ synthesized water-soluble graphitic carbon nitride

A new class of more effective lubricants could lead to huge energy savings. Limited recent literature has suggested potential for using room-temperature ionic liquids as lubricants, however, only a few out of millions (or more) of species possible have been evaluated. In this study, a series of new protic alkylammonium ionic liquids were synthesized by neutralization and metathesis reactions, and have demonstrated promising lubricating properties as neat lubricants or lubricant additives, particularly for use with difficult-to-lubricate metals like aluminum. More than a 30% friction reduction was observed with ammonium-based ionic liquids compared to conventional hydrocarbon oils in reciprocating sliding tests of 52100 bearing steel on aluminum alloy 6061-T6511. The inherent polarity of ionic liquids is believed to provide strong adsorption to contact surfaces and can form a boundary lubricating film leading to friction and wear reductions. Other advantages of ionic liquids include (1) negligible volatility, (2) high thermal stability, (3) non-flammability, and (4) better intrinsic properties that may eliminate the need for more complex and expensive additive packages. With very flexible molecular structures, this new class of lubricants, particularly ammonium-based ionic liquids, can be tailored to fit a variety of applications.

Dependence of high temperature tribological performance of MoS2-based composites on type of oxides

Effect of external vibrations on Electro-Mechanical impedance signatures in damage detection

Static friction processes under dynamic loads and vibration

In this paper, a vibration isolated design of a Coriolis mass-flow meter (CMFM) is proposed by introducing a compliant connection between the casing and the tube displacement sensors, with the objective to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of external vibrations. The transfer from external vibrations to the relative displacement measurement is analyzed and the design is optimized to minimize this transfer. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimized. The optimal tuning of the parameters is done actively by acceleration feedback. Based on simulation results, a prototype is built and validated. The validated design shows more than 24 dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.