Formation Of Lubricating Layer Research Articles

A novel method for the synthesis of solvent‐free and high‐solid‐content waterborne polyurethanes by introducing a small amount of polyethylene glycol

AbstractIn the study, the synthesis process involved the reaction of dimethylolbutyric acid and polytetramethylene ether glycol 1000 (PTMG1000) with hexamethylene diisocyanate (H12MDI), taking advantage of their mutual dissolution at high temperatures. The chain‐extension reaction with 1,4‐butanediol (BDO) was successfully conducted without the use of organic solvents. The emulsification reaction was carried out using the polyurethane prepolymer at 60% solids content, along with aqueous dispersions of polyethylene glycol (PEG) with varying molecular weights and amounts as interfacially active agents. Fourier transform infrared spectroscopy analysis suggested potential hydrogen bonding interactions between the PEG molecular chain and the polyurethane chain. Rheometer analysis demonstrated a significant reduction in viscosity with the addition of 1–5 wt.% PEG, accompanied by an increase in average particle size. This phenomenon was attributed to the formation of a hydrophilic lubrication layer of PEG around the water‐based polyurethane (WPU) microcells. Among them, WPU films containing 4 wt.% PEG4000 not only exhibited soft properties with a mechanical elongation rate exceeding 2000% but also showed excellent storage stability. The addition of long‐chain PEG facilitated the formation of a lubrication layer between the microcells, contributing to spatial stabilization and reducing particle aggregation at high solids content. It is noteworthy that this solvent‐free process, without any organic solvents, together with the adjusted PEG content, successfully synthesized waterborne polyurethanes with low viscosity and high solids content. This provides a new sustainable and environmentally friendly method for the future production of waterborne polyurethanes.

Four-way CFD-DEM coupling to simulate concrete pipe flow: Mechanism of formation of lubrication layer

This study introduced a four-way CFD-DEM coupling approach to simulate the shear-induced particle migration (SIPM) mechanism leading to formation of the lubrication layer (LL) during concrete pumping. The CFD-DEM simulations considered the coupled effect of concentration (10 %–40 %) and wide size distribution (1–17 mm) of aggregate and rheology of the mortar for forces between the suspending matrix and the particles (and vice versa), as well as force transmission directly between particles (and the pipe wall). The formation of the LL was successfully simulated through a more realistic understanding the SIPM mechanism and rheological evaluation across the pipe with comparable calculation times compared to the one-way coupled DEM approach, especially for high concentrations. The simulated LL thicknesses of 0.8–2.7 mm compared well with experimental values. The flow rate and rheological heterogeneity of pumped concrete, and rheology of the LL, were found mostly controlled by the granular-skeleton characteristics rather than the suspending-matrix rheology.

Tribological behaviour of multi-shape photochemical textured surfaces

The purpose of this paper is to investigate the effect of multi-shape photochemical textured (PCT) steel surfaces on tribological performance. The textured surface with specific arrangement was fabricated by photochemical texturing, a common technique implemented in the microelectronic mechanical systems (MEMS) industry. It involves photolithography and chemical etching processes. The multi-shape studied were circle with line (CL) and circle with wavy (CW). Fabricated samples’ surfaces were characterized by using a 3D optical profiler to check the produced texture’s dimension. The effect of six different etching times on the texture’s dimension was observed. Then, only two sizes of both multi-shape textures were considered for tribological characterization. It was conducted by using ball-on-disk tribo-tester under lubricated conditions. The results obtained are compared with the reference untextured (UT) surface. From the results, it is found that appropriate size and shape of texture could lead to good friction reduction and anti-wear behaviour. The smaller size, size A, of CL multi-shape presented a lower friction coefficient compared to size B. However, different size of CW multi-shape has no effect on the friction behaviour. This is believed due to higher area density of CW compared to CL resulting in detrimental effect on friction for both CW’s size. Additionally, CL(size A) textured surface shows improved tribological behaviour compared to UT surface as lower friction coefficient and better wear resistance is obtained. This is maybe due to effective lubricating layer formation, good debris trapping effect and lower contact stress of the CL(size A) textured surface. These beneficial effects were achieved under lubricating condition through an increase in applied load.

Discrete-element modeling of shear-induced particle migration during concrete pipe flow: Effect of size distribution and concentration of aggregate on formation of lubrication layer

The paper seeks to better understand the particulate mechanics giving rise to the lubrication layer (LL) in flows with wide particle-size distributions (PSD) typical of concrete pumping applications. The study uses a soft-sphere discrete element method (DEM) to simulate the shear-induced particle migration (SIPM) mechanism of formation of the LL. To provide realistic understanding of SIPM and rheological heterogeneity of concrete, three wide PSDs (fine, medium, and coarse) and three different concentrations (10 %–40 %) of five spherical-particle subclasses (1–17 mm diameter) were investigated. The radial evolution of concentration and particle distribution was simulated over time and the LL formation was successfully simulated. The predicted LL thicknesses compared well with experimental values. The coupled effect of PSD, concentration, and mean diameter of particles on wall effect, SIPM, and rheological heterogeneities across the pipe was evaluated. Higher rheological heterogeneity across the pipe was obtained for higher concentration and coarser particle size distributions.

Influence of ground granulated blast furnace slag on the tribological characteristics of automotive brake friction materials

PurposeThe main purpose of this study in the field of automotive brake friction material is to find an effective material to replace the environmentally hazardous copper in the brake pad formulation.Design/methodology/approachCu is used as functional filler in various forms in the friction material formulation. Because of its hazardous impact to the aquatic life, a suitable replacement of Cu is the main focus of this research. Three novel friction composite materials using ground granulated blast furnace slag (GGBFS) as a suitable alternative for Cu were developed by increasing its Wt.% from 5% to 15% in the step of 5%.FindingsThe physical, mechanical and chemical properties of the developed friction composites were tested as per the industrial standards. The tribological properties were analyzed as per SAE J661 standard using the chase test rig. Initial studies revealed that the friction composite having 5% GGBFS exhibited better physical, mechanical and chemical properties with excellent frictional performance having minimal fluctuations even at higher temperatures. Nonetheless, the results showed that the friction composite containing 15 Wt.% GGBFS revealed a better wear resistance property compared with the other two composites due to the tribo lubricating layer formation at the frictional interface. Scanning electron microscope analysis was performed to understand the wear mechanism and tribo layer formations through topography studies.Originality/valueThis paper explains the influence of GGBFS as a replacement of barytes in brake pads formulation to enhance the tribological performance.

Prediction of lubrication layer properties of pumped concrete based on flow induced particle migration

Flow induced particle migration facilitates the formation of lubrication layer, which dominates the pumping performance of concrete. However, the properties of lubrication layer, such as thickness, composition, and rheological properties, are dynamic during the prompting process. In this study, a numerical model is proposed to model the formation of this lubrication layer from a new perspective of particle migration with consideration of wall effects which was often ignored in the past. To predict the properties of lubrication layer, diffusive flux models (DFM) of particle migration in non-Newtonian suspensions are extended to account for the wall effects. The proposed model is validated by ultrasonic velocity profile (UVP) experiments. The results show that, the wall effect induced particle migration makes a major contribution to the formation of lubrication layer, as well as the shear induced particle migration. The lubrication layer is found to be barren of aggregate but enriches in sand. In addition, the material and rheological properties of lubrication layer are inhomogeneous and not necessarily equivalent to that of mortar.

Discrete-Element Modeling of Shear-Induced Particle Migration During Concrete Pipe Flow: Effect of Size Distribution and Concentration of Aggregate on Formation of Lubrication Layer

Discrete-Element Modeling of Shear-Induced Particle Migration During Concrete Pipe Flow: Effect of Size Distribution and Concentration of Aggregate on Formation of Lubrication Layer

A first-order physical model for the prediction of shear-induced particle migration and lubricating layer formation during concrete pumping

For the first time, a first-order physical correlation between pumping parameters (pressure and flow rate), granular skeleton properties (particle diameter and packing properties) and LL properties (thickness and viscosity) is proposed. This correlation is derived from the analysis of the equations driving shear-induced particle migration in dense suspensions. The model predictions in terms of lubricating layer apparent viscosity are compared to experimental measurements in the case of model concretes prepared with glass beads of various diameters, conventional-vibrated concretes and self-compacting concretes. This comparison is carried out for two flow typologies, namely the Sliper, known for its ability to mimic concrete pumping, and a co-axial tribometer. In all cases, the proposed model is shown to be able to capture qualitatively the observed main features and their evolutions despite the absence of any fitting parameters.

Definition of Forming Processes Microparameters for Epitropic Liquid Crystal Boundary Lubrication Layers

The kinetics theory of ordered boundary lubricating layer formation is presented. The theory contains the description of the formation of boundary lubricating layer from liquid lubricating media containing tribo-active adsorbing component. The expressions for specific forming time and thickness of the boundary lubrication layer in the conditions of the considered model are defined. The prospects of the mentioned parameters experimental definition they are marked out. The tribological efficiency parameter of tribological additive is introduced. This parameter can be evaluated in model physicochemical researches or by molecular modelling methods.

Investigating the migration law of aggregates during concrete flowing in pipe

During pumping fresh concrete pipes, aggregate migration is occurred under the action of various forces. In order to study the migration characteristic of aggregates during concrete flowing in pipes, in this paper, we built the test system based on particle tracking technology. Transparent concrete was prepared. The particle capture function of high-speed camera was used to track particle motion. Results showed that the radial displacement of particles depended on the initial location and aggregate size. Small aggregates near pipe wall or center axis had fewer motion. For the particles with larger diameter, the migration direction almost pointed to the axis of pipe. The migration displacement of nature aggregates was smaller than that of ground grinding ball. The migration displacement firstly increased and then decreased with increasing the diameter of particle. Moreover, the effect of particle shape on migration was explored. Finally, the wall effect, gravity induced particle migration and shear induced particle migration were compared based on the phenomenon of flow induced particle migration, results showed that the phenomenon of shear induced particle migration played the main role in the formation of lubrication layer. This study was of great significance to reveal the transport law of dense particle flow in the pipeline.

Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping.

In this paper, the authors have focused on shear-induced particle migration (SIPM), its effect on concrete flow patterns, and lubricating layer formation during pumping. For this purpose, various volume-fractions ϕ of aggregates were selected. The particle migration was analyzed by applying two methods: sampling hardened concrete exposed to pumping and performing X-ray microcomputed tomography (μCT) and image analysis to determine the thickness of the lubricating layer due to SIPM. The results indicate that the first approach is unsuitable due to the nearly equal molecular density of particles and matrix. The second approach indicated that the actual thickness of the lubricating layer depends on the discharge rate as well as on ϕ and viscosity of concrete bulk; hence, it cannot be defined as a constant parameter for all concrete mixtures. Additionally, the concrete pipe-flow pattern, i.e., plug versus shear flow, was captured and studied while considering pumping pressure and discharge rate. It was concluded that particle migration is essential in the cases of both flowable and very flowable concretes with a high volume-fraction of solids. The changes in rheological properties caused by SIPM are severe enough to influence the definition of the flow pattern as plug or shear and the discharge rate of pumped concrete as well.

Coating with boron nitride on SiC fiber using atomic substitution

To increase the mechanical properties of ceramic matrix composite, it is important that formation of lubricant layer for crack deflection between matrix and fiber. Therefore, we fabricated uniform boron nitride (BN) lubricant layer using atomic substitution method. Silicon carbide (SiC) fiber surface was modified with amine groups using (3-amonipropyl)triethoxysilane to coat SiC fiber with BN as a solid lubricant. Then, surface was coated with graphene oxide (GO). Boric acid powder was supplied to the GO-coated fibers and the samples were heat-treated at 1200–1400 ℃ under N2 and NH3 atmospheres. An uniform BN layer could be coated on SiC fiber with 10 nm-1.11 μm. Crystallinity and thickness of BN layer could be controlled by reaction temperature. It was also confirmed that crystalline BN formed under process conditions of higher than 1400 ℃.

Wear Behavior of Spheroidal Graphite Cast Iron in Biodiesel Blends

Biodiesel as an alternative fuel is overcoming to replace petroleum diesel partially. The tribological performance of biodiesel is crucial with respect to application in automobiles. Cast iron is widely used in for manufacturing of many automobile engine parts such as piston, valves, piston rings, etc. This research article evaluates the wear behavior of spheroidal graphite cast iron which is used for the manufacturing of piston rings with respect to different blends of biodiesel. Many experiments were carried out under metal to metal contact and lubricated sliding condition on, pin on disc wear testing machine. This shows the metallographic changes due to wear damage. Previous experimental result shows that friction coefficient and wear loss decreases significantly due to decrease in lubrication percentage of palm biodiesel. The test parameters used under this work were 8 kg, 10 kg, 12 kg, 14 kg and 16 kg loads for 1 h, at speed 300 rpm and at ambient temperature. Wear behavior of spheroidal graphite cast iron is evaluated using five different blends of biodiesel, B0 (100% petroleum diesel), B5 (5% biodiesel), B10 (10% biodiesel), B20 (20% biodiesel), B100 (100% palm biodiesel)).The period for which cast iron can sustain is determined by its wear and abrasion resistance. Due to formation of lubrication layer of ester compounds in palm biodiesel wear resistance of nodular cast iron increases as biodiesel percentage increase in the blend. Therefore, high wear resistance is critical for ensuring a long life of the cast iron in biodiesel environment. The results showed that the B100 has higher coefficient of friction and lowest surface roughness and wear volume loss as compared with petroleum diesel (B0). It also shows that wear and friction decrease as percentage of biodiesel increases. Scanning electron microscopy (SEM) investigations used to analyze the structure and surface morphology. Wear scar diameter (WSD) was investigated using optical microscopy in tested specimen. The wear rate was found to be more in petroleum diesel compared with palm biodiesel than other blends.

Mechanistic Based Cutting Force Model During Ultrasonic Assisted Turning with Self-Lubricating Cutting Inserts

The present research paper presents a mechanistic model for determining the cutting forces during Ultrasonic Assisted Turning (UAT) process using self-lubricating textured cutting inserts. In order to understand the mechanics of the process, forces on chip have been analyzed by using free body diagram. The force and momentum equilibrium on chip have been used to define the governing force equations. The effect of ultrasonic vibrations has been considered by taking the average force of cutting over a complete cycle of vibration. The self-lubricating cutting insert has been modeled to study the effect of intermittent cutting and thin lubricating layer formation at tool-chip interface. The validation of the developed model has been done by performing UAT experiments with self-lubricating textured cutting inserts. It is observed that percentage error of prediction by mechanistic model in determining main and radial components of cutting forces is of the order of 6.73% and 14.67%, respectively with respect to the experimental values.

Formation of lubricating layer and flow type during pumping of cement-based materials

The article at hand builds on previously published work (Secrieru et al., 2017) [1] by providing a detailed discussion on the formation of a lubricating layer (LL) and the flow type during pumping of cement-based materials. It is demonstrated that knowledge of the actual thickness of the lubricating layer (LL), its rheological properties, and the flow type is sufficient to predict the pumping behaviour of fresh material. First, the importance of LL formation is highlighted, and the related, previously published experimental investigation methods are briefly presented. Still further, the flow type of mixtures during pumping is assessed. The cementitious materials under investigation exhibited various principal flow types which are already defined at lower flow rates: Plug flow in the case of a flowable, strain-hardening cement-based composite (SHCC), partial bulk shear in mixtures with round and crushed aggregates, and pronounced bulk shear in the cases of a self-compacting concrete (SCC) and a self-compacting mortar (SCM). To predict concrete pumping behaviour an analytical and experimental methodology based on rheological tools is proposed. This combined methodology quantifies the LL thickness and is compared with simulation results using computational fluid dynamics (CFD). Finally, the prediction of pumping behaviour is verified in small-scale pumping measurements.

Changes in concrete properties during pumping and formation of lubricating material under pressure

This study quantifies the changes in the rheological properties of fresh concrete while focusing on lubricating layer (LL) formation during pumping. Full-scale pumping experiments were carried out on ready-mix concrete accompanied by the state-of-the-art rheological tests. Pumping markedly increased the yield stress. It also led to an increase in the air content, which contributed to a decrease in viscosity of fresh concrete. The dynamic loading from pumping generates a pressure gradient in concrete over the pipe cross-section. The pressure gradient is assumed to facilitate the movement of lubricating material to the concrete-wall interface, completing the formation of LL. This postulate is based on experimental evidence obtained by a portable high-pressure filter press and the extracted filtrate. The amount of filtrate depends on the specific surface of the fines, on concrete bulk viscosity, and on chemical admixtures. Finally, an increase in concrete temperature was observed depending on the concrete's composition and the properties of the LL.

Tribo-mechanical and surface morphological comparison of untextured, mechanical micro-textured (MμT), and coated-MμT cutting tools during machining

In machining process, cutting fluids are used to reduce the tool–chip interface temperature and forces, but it causes various health hazards to machine operators as well as increases the associated costs. To improve machining sustainability, researchers are trying to reduce or eliminate cutting fluid usage during machining by various other techniques (development of better tool material, bio-cutting fluids, use of vegetable oils, near-dry machining, process optimization, surface coatings, etc). In recent years, several researchers applied controlled surface modification (surface texturing/engineering) at the tool–chip interface to improve the tribological properties in the machining performance. In the present study, first mechanical microtextures (MµT) are created on the rake surface, and its structural stability is compared with an untextured/virgin cutting tool. The static structural analyses show a negligible effect of mechanical microtextures on the strength of the cutting tool. Afterwards, MµT cutting tools are coated using molybdenum disulphide (MoS2) solid lubricant (i.e. coated MµT, C-MµT). Subsequently, the machining performance studies of C-MµT were carried out to show its advantages over two other types of cutting tools (UC, MµT). Performance of C-MµT is improved by mechanical microtextures (due to the reduction in the actual contact area between tool–chip interfaces) and proper lubrication of the tool–chip contact area. Thus, due to the reduced contact area and formation of lubricant layer by MoS2 at the tool–chip interface, C-MµT experiences 23.75% lower tool–chip interface temperature, 41.06% reduction in the cutting force, and produces 14.37% less workpiece center line average surface roughness ( Ra) compared to untextured cutting tool. C-MµT experiences 9.55% lower tool–chip interface temperature, 19.02% reduction in the cutting force, and produces 5.34% less workpiece center line average surface roughness compared to the MµT cutting tool. Hence, C-MµT cutting tools are the viable alternative to untextured cutting tools.

Pipe flow of pumping wet shotcrete based on lubrication layer.

Wet shotcrete can reduce dust and improve supporting strength, however, safe and efficient pipage is a key technical part of wet shotcrete process. The paper studied the pipe flow law of wet shotcrete based on lubrication layer by build the experimental pumping circuit of wet shotcrete that can carry out a number of full-scale pumping tests. The experimental results show there was a linear relationship between pressure loss and flow rate. Combined with the Buckingham rheological equation, the computing equations of the yield shear stress and plastic viscosity were deduced through linear regression. A simple analytical method allowing for a rough estimation of the pumping pressure was proposed and used when considering the lubrication layer of wet shotcrete in pipes. In addition, two kinds of particulate distributive models were established along the time axial to analyze the formation of lubrication layer which is related with particles migration. By computational fluid dynamics simulation, the lubrication layer thickness of different mix proportions was estimated. A new method for measuring the thickness of lubrication layer was proposed to verify it by binarization processing. Finally, according to the comparative analysis of experiments, simulation and computed value, it can be seen that the lubrication layer plays a key role in the process of wet shotcrete flow and with the increase of lubrication layer thickness pipe pressure declines gradually.

Friction and wear of solid lubricant films deposited by different types of burnishing

Solid lubricant films based on MoS 2 and WS 2 are widely used for dry air friction and aerospace applications. Different plasma deposition methods are widely used for formation of solid lubricant films on the contact surfaces. One of the simple methods of solid lubricant film deposition is cloth burnishing. The aim of this work is to develop new simple methods for burnishing of steel surfaces providing improved the tribological properties of solid lubricant films. For this cause the solid lubricant particles were burnished by the loading system of balls. MoS 2 as well as some binders were used for formation of lubricant layer. In order to improve the consolidation of particles in the layer, external excitation of loading system has been used. The friction coefficient and the longevity of solid lubricant film were assessed using ball-on-flat and pin-on-disk devices. The effect of burnished films on their tribological properties is discussed.

A Study on the Formation of Lubricant Layer for Magnetic Thin Film Media

A Study on the Formation of Lubricant Layer for Magnetic Thin Film Media