Decrease Of Friction Force Research Articles

MHDエネルギーバイパスを用いたスクラムジェットエンジンの性能

Flow behavior and thrust performance of MHD energy bypass scramjet engine was examined numerically. MHD generator was placed at the isolator to enhance the flow compression. Kinetic energy was converted to electrical energy in the MHD generator. Extracted electrical energy was consumed at the MHD accelerator placed at the downstream of the combustor. When MHD energy bypass system was used, the flow was decelerated and compressed in the MHD generator. Effect of velocity and Mach number on wall friction was analyzed and decrease of friction force was pointed out. Also, high pressure in the combustor resulted in increase of pressure contribution to net thrust. Despite of positive effects, decelerating Lorentz force in the MHD generator was comparably large and no significant difference in net thrust performance is observed.

Surface Friction of Poly(dimethyl Siloxane) Gel and Its Transition Phenomenon

The surface sliding friction of chemically cross-linked poly(dimethyl siloxane) (PDMS) swollen with linear PDMS as an oligomer is investigated. The friction force f increases with the normal pressure P in a power-law relation f∝Pα, where the exponent α changes in a range of 0-1, depending on the degree of polymerization, Npoly, of the linear PDMS oligomer. When Npoly is in a range of 240-320, a dramatic decrease in friction force is observed at a critical normal pressure, Pc, leading to a very low friction coefficient on the order of 10−3 at high-pressure ranges. The Pc increases with decreasing network size Nnetof the gel and also with increasing polymer length related to Npoly. One possible explanation for this transition phenomenon in friction is that linear PDMS molecules are exuded from the gel network beyond a certain pressure and behave as polymer brushes, which are able to reduce the friction.

Development of polymer‐molding‐releasing metal mold surfaces with perfluorinated‐group‐containing polymer plating

AbstractThe polymer‐molding‐releasing properties of metal molds were found to be related to the following factors: (1) interfacial chemical bonding between the surfaces of polymers and metal molds and (2) a friction force or friction coefficient between polar substances and/or low‐molecular‐weight components in the polymers and physical factors on mold surfaces. We theoretically and experimentally confirmed that metal molds with good polymer‐molding‐releasing properties had very small surface free energies. We also proved that the surface free energies in the resulting polymer moldings were lower than before shaping. The molding releasing properties improved with decreasing friction force and friction coefficient between the surface of polymers and metal molds and with decreasing surface free energy. To obtain metal molds with lower surface free energies, we developed a polymer plating method with perfluorinated‐group‐containing triazine dithiol. The Metal mold treated by polymer plating had lower critical surface tension (7.5 mJ/m2) than Teflon (18 mJ/m2), indicating that the surface consisted of CF3− groups. The treated mold showed excellent durability in its releasing properties, which was better than that of the untreated mold. This technique was developed for the production of molds for the Fθ lens and the naturally bright focusing screen. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2549–2556, 2003

A mathematical model for prediction of thickness of mould flux film and friction in continuous casting mould

A mathematical model of mould flux infiltration and heat transfer through the flux film has been developed. The model considers the effect of static pressure of molten steel, temperature dependency of flux viscosity and determination of liquid flux thickness with pressure gradient. Present model gives the results that agree well with actual plant data such as mould flux consumption, mould friction and the heat transfer. The results of the model give remarkable effect of static pressure of molten steel as follows: decrease of the static pressure causes increase of liquid and total flux film thickness, reduction of heat flux and decrease of friction force on solidified shell.

The Effect of Cure Conditions on the Performance of Styrene Butadiene Rubber for Industrial Conveying Applications

AbstractA range of samples were prepared from a commercial styrene butadiene rubber (SBR), over a range of cure temperatures (140d̀C‐170d̀C) and cure times (30–120 min), using a high temperature moulding press held at a constant pressure of 5000 psi. Mechanical analysis of the various samples showed considerable increase in modulus, shore hardness and break strength with progressive increase in cure temperature, especially at lower cure times. Dynamic frictional analysis under different loadings, of the SBR samples with High Molecular Weight Polyethylene (HMWPE) and 90 Shore A Polyurethane (PU), showed a progressive decrease in frictional force with increase in SBR cure temperature and time. Some reversion of the SBR was shown to occur at higher temperatures and longer cure time

In Situ Temperature Measurement During Oxide Chemical Mechanical Planarization

AbstractThis paper presents temperature and friction force data at the pad-slurry-wafer interface during real time CMP polishing with in situ pad conditioning. Experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer down force control. Dual emission laser induced fluorescence (DELIF) techniques are used to optically measure the temperature directly beneath the wafer during polishing using a two camera imaging system. An infrared camera and a thermocouple are alternately used to measure bow wave temperatures. Optically transparent BK-7 glass wafers with either concave (wafer edges sloping toward the pad) or convex (wafer edges sloping away from the pad) curvature were used. When concave wafers are polished, the bow wave temperatures are 3°C to 5°C higher than the corresponding value for convex wafers. Similarly, slurry temperatures under the concave wafers are 5°C to 6°C higher than the value for convex wafers (±0.5°C). The friction force per unit area is typically 2 kPa to 3 kPa higher for concave wafers. Temperatures beneath the wafer are as high as 12°C above the ambient temperature for a concave wafer at a high applied wafer pressure (41.4 kPa) or linear velocity (0.93 m/sec). Bow wave temperatures reach as high as 9°C above ambient at a linear velocity of 0.93 m/sec. The lowest temperatures, within 1°C of ambient at the bow wave and 5°C above ambient under the wafer, were found with convex wafers at low applied wafer pressures (20.7 kPa). Linear velocity has little effect on the slurry temperature while polishing convex wafers. Increasing slurry abrasive concentration causes an increase in temperature, despite a decrease in friction force. A correlation, with an R-squared value greater than 0.96, exists between the bow wave temperature and the temperature beneath the wafer. This correlation holds at constant linear velocities across wafer shapes, applied wafer pressures, and slurry concentrations.

A Mathematical Model for Prediction of Thickness of Mould Flux Film in Continuous Casting Mould.

A mathematical model of mould flux infiltration and heat transfer through the flux film has been developed. The model considers the effect of static pressure of molten steel, temperature dependency of flux viscosity and determination of liquid flux thickness with pressure gradient. Present model gives the results that agree well with actual plant data such as mould flux consumption, mould friction and the heat transfer. The results of the model give remarkable effect of static pressure of molten steel as follows: decrease of the static pressure causes increase of liquid and total flux film thickness, reduction of heat flux and decrease of friction force on solidified shell.

On the Short Journal Bearing Using Power-Law Fluid or Ostwald-deWaele Fluid as Lubricant.

In this work Reynolds' equation is extended to power law fluid or Ostwald-deWaele Fluid used as lubricant for a short journal bearing. The numerical data are obtained for various non-Newtonian fluids such as polymeric liquid comprising colloidal solution or healthy human blood, using the experimental data by G.W.Scott Blair. This thought may be important for fire prevention, simplification of pump system, and decrease of friction force like sigma-phenomenon and wall effect.

Nanotribological behavior of C60 films at an extremely low load

We have studied the nanotribological behavior of C60 films formed on a KCl(001) surface at an extremely low load, using scanning force microscopy (SFM). It has been observed that the SFM tip undergoes molecularly resolved stick–slip motion depending on scanning direction. The frictional force at the relative humidity (RH) of 20% is about a quarter that in dry argon. The decrease in frictional force at 20% RH comes from the lower stiffness of the tip–sample contact, indicating the mobility of C60 molecules, such as rolling and/or translation due to water adsorption.

Non-Newtonian effects of second-order fluids on double-layered porous Rayleigh-step bearings

Theoretical study of double-layered porous Rayleigh-step bearings with second-order fluid as lubricant is presented. An approximate method for the solutions of the governing fluid film equations for a porous region is proposed. The expressions for the pressure distribution, load capacity and frictional coefficient are obtained in compact form. Calculations of the dimensionless load capacity, frictional force and frictional coefficients are presented for specific values of the material parameters. It is found that the double porous layer yields an increase in the load capacity and ensures decrease in frictional force at the porous lining as compared with the conventional porous Rayleigh-step bearings. The maximum dimensionless load-carrying capacity is found to occur at a slightly larger step ratio as compared with the conventional porous Rayleigh-step bearings.

Experimental and Theoretical Analysis of Magnetic Head-Disk Interface Equilibrium in the “Rupture” Regime of the Starved-Liquid Bearing

Previous friction measurements in the magnetic head-disk interface (HDI) indicated some anomalous friction force behavior with low sliding speeds (.25 mm/s to 0.25 m/s) and lubricant film thicknesses in the range of 20–80 nm, showing decreasing friction force with increasing apparent shear rate. The physical explanation for such behavior has not yet been established. Possible explanations for such behavior have included dramatic shear thinning, interfacial slip and partial loss of contact with the lubricant film due to slider tipping. In the present study, we investigate the possibility of slider tipping as an explanation for the decreasing friction force with increasing sliding speed. Measurements with an optical probe indicate that slider tipping does not occur for the conditions tested. Numerical analysis of slider equilibrium also supports this conclusion.

Friction in strongly confined polymer melts: Effect of polymer bridges

We propose a molecular theory of friction in confined polymer melts between atomically smooth surfaces, taking polymer bridges between the surfaces into account. Using the activation friction model, we consider the bridge adsorption-desorption dynamics and calculate the macroscopic friction force (the tangential stress) in the system as a function of the imposed velocity. We show that the bridges result in the regime where the friction force decreases with the increase of the imposed velocity. The friction force passes through maximum and minimum values in the crossover range between linear and nonlinear regimes. We also investigate the stability of sliding in the regime with decreasing friction force.

Effect of salivary viscosity on frictional coefficients of orthodontic archwire/bracket couples

Stimulated whole saliva samples were collected from 30 healthy individuals and analysed with a cone and plate viscometer. On the basis of these dynamic viscosity measurements saliva from patients, who represented the mean value and two standard deviations above and below the mean value, were selected for frictional force testing. Four archwire/bracket couples (SS/SS, SS/PCA, ~-Ti/SS, and I3-Ti/PCA) were each tested in these three salivas as well as in the dry state a total of five times, each at five different normal loads. With two exceptions no significant differences were found between any of the three wet states for any couple studied. When the dry state was compared to any of the wet states, the SS archwire couples showed a singificant increase in frictional forces, while the 13-Ti archwire couples showed a slight decrease in frictional forces, which was not statistically significant.

Study of microstructural transformation of overbased calcium sulphonates during friction

AbstractColloidal dispersions of calcium carbonate stabilised by calcium alkylaryl sulphonates are detergent additives used in lubricant oils, and have particular effects on wear processes. In the present work, such additives were investigated using Small Angle X‐ray Scattering technique (SAXS). Different scattering intensity simulation and curve‐fitting programs were used to determine the size of the overbased calcium sulphonate particles and to characterise the interactions between them. In the additive oil (11 wt% CaCO3), the overbased calcium sulphonates appear as polydispersed micelles having an average calcium carbonate core radius of 2.0 nm. Moreover, an attractive potential between the micelles of less than kT has been observed. In order to investigate the effect of friction constraints on the additive, friction tests were performed on a rotative tribometer. Under specific conditions, there was a decrease in friction force arising from the formation of a viscous deposit. According to the differentanalyses, the viscous deposit contained more polydisperse particles, which did not have the same structure as those contained in the original additive. These particles consisted mainly of calcium carbonate. Some sulphonate chains were expelled from the friction zone. Moreover, the particles contained in the deposit interact with a potential on the order of 10 kT. Wide Angle X‐ray Scattering (WAXS) confirmed the presence of highly crystalline calcite. Moreover, the effects of pressure and the presence of water were studied. The pressure contributes neither to an increase in particle size nor to a crystallisation phenomenon. However, the presence of water in the additive oil alters the interactions between the micelles. The potential observed is 8.2 kT and suggests that the water is a responsible parameter for the agglomeration of micelles consisting of the viscous deposit.

886452 Friction force decrease in drop shaft sinking : Smorodinov, M I; Ostyukov, B S; Arsenev, A A Soil Mech Found EngngV24, N4, July–Aug 1987, P149–153

886452 Friction force decrease in drop shaft sinking : Smorodinov, M I; Ostyukov, B S; Arsenev, A A Soil Mech Found EngngV24, N4, July–Aug 1987, P149–153

Friction force decrease in drop shaft sinking

Friction force decrease in drop shaft sinking

A high-head flat counterbalanced gate

1. In order to increase the capacity of high-head water intakes substantially, it is necessary to develop basically new designs for the gates, providing not only for a decrease in frictional forces in the bearing-guide sections, and, in tum, a reduction in the lifting capacity of the mechanisms, but also a reduction in the loads on the bearing-guide sections. 2. The gate design provides for uniform transfer of the heavy loads received by the gate (of the order of 15,000 tons) onto a large concrete surface. Hydraulic hoists, which have been perfected by industry, are available for maneuvering the gates. 3. Owing to use of a moving structure that operates as a beam on two supports with cantilevers, similar types of gates can be used to close water intakes with even significantly larger cross sections than those designed for the Rogun hydroelectric plant. 4. Model studies of the operation of back-pressure chambers indicated that reliable gate counterbalance is provided for even with complete failure of the chamber seals. 5. As studies indicated, bearing-plate deflectors attached to the basic gate protect the supporting bulkheads under no-head conditions in the outlet section: a flow coursing from beneath the gate has no effect on the lateral surfaces of the bulkheads. 6. The gate is constructed from common grades of steel used at the present time and can be completely fabricated at the plants operated by the Gidromontazh Trust. The gate has no heavy inserted parts fabricated from high-alloy steels. 7. Data from studies conducted on the flat counterbalanced gate and gate chamber indicate that this gate can be applied to deep water intakes at high-head hydrofacilities.