Theoretical Film Thickness Research Articles

An improved method for film thickness measurement of cylindrical roller bearings based on a straight-beam probe

PurposeConsidering the industrial site environment and installation requirements, the straight-beam ultrasound probe with easy installation and good coupling agent adaptability is adopted to replace the traditional water immersion focusing probe for film thickness measurement in cylindrical roller bearings. The straight-beam probe has a large echo receiving range, which will result in measurement regions overlapping and bring about large measurement errors. In this paper, an improved measurement method for film thickness of cylindrical roller bearing with the straight-beam probe is developed.Design/methodology/approachAn improved method is proposed to enhance the spatial resolution of the straight-beam probe. By introducing a correction coefficient based on the percentage of the effective measurement area, the method improves the measuring accuracy successfully.FindingsThe experimental results demonstrate that the lubricant-film thickness can be measured to reasonable accuracy by this method and have a better agreement with the theoretical film thickness solutions.Originality/valueThis paper used analytical method and model that is helpful for the improvement of the spatial resolution, which has great influence on the measuring accuracy, is mainly determined by the echo reflection area size of the ultrasound transducer.

Effect of yerba mate (Ilex paraguariensis St. Hil.) extract on the drying behavior of cassava starch films enriched with rebaudioside A

AbstractIn this study, the drying behavior of cassava starch‐based edible films was investigated. Formulations were elaborated with rebaudioside A, glycerol, and low concentrations (0.5, 2, and 4%, w/w) of yerba mate (Ilex paraguariensis St. Hil.) extract (YM%). Physicochemical properties (pH, apparent viscosity, and density) and film‐forming capacity (dip‐coating method) were evaluated at 25°C. Films were casted by drying and mathematically described using the Henderson and Pabis thin‐layer model. Effective moisture diffusion coefficients (Deff) were determined using theoretical film thicknesses evaluated at the critical moisture content. The Deff dependency on temperature and YM% was analyzed using an Arrhenius‐type model. Based on the results, as YM% increased, values of pH, and apparent viscosity decreased. Low YM% increased the drying rates and the values of Deff of cassava starch‐based edible films elaborated with rebaudioside A as a sweetener and bioactive compound, obtaining the highest values at 4% (w/w) and 70°C.Novelty impact statementThe optimization and control of the drying process are important to produce coated foods with high‐quality and nutritional value in the industry. Yerba mate extract powder added to cassava starch‐based formulations at low concentrations (<5%, w/w) is suitable for obtaining edible films and coatings with higher drying rates and effective moisture diffusion coefficients that control film casting due to the better hydrophobicity and plasticizing effect. This information could be useful to manufacture new film‐forming fluids with bioactive compounds (e.g., rebaudioside A), such as alternative bio‐packages that allow to replace the disposable composite synthetic plastic containers, and products for people with special diet requirements due to its low or sugar‐free nature.

(Invited) Electrodeposition of Si in CsF–CsCl Eutectic Melt

1.Introduction In recent years, the demand for solar cells as a clean energy source has been increasing. Among the various types of solar cells, crystalline Si solar cells dominate the solar cell market due to their high efficiency, excellent stability, and abundant natural resources. However, the major disadvantages of the conventional Si substrate manufacturing method are the low productivity of the Siemens process and the considerable kerf loss in the Si slicing process. As the demand for crystalline Si solar cells continues to grow, there is a strong need to develop alternative manufacturing methods for Si substrates. As a promising method, the direct formation of Si films on inexpensive substrates has been investigated [1]. We have proposed the electrodeposition of Si films from molten KF–KCl which has relatively high fluoride-ion concentration at eutectic composition (KF:KCl = 45:55 mol%, m.p.: 878 K) and high solubility in water [2]. We have already studied the optimum conditions for obtaining adherent, compact, and smooth Si films in molten KF–KCl–K2SiF6 at 923 K [3]. Furthermore, good Si films was obtained from KF–KCl after bubbling SiCl4 as a Si-ion source [4]. In this study, we focused on CsF–CsCl eutectic melt (CsF:CsCl = 50:50 mol%, m.p.: 713 K [5]) as a new electrolyte for Si electrodeposition. Molten CsF–CsCl has lower operable temperature and higher fluoride-ion concentration than molten KF–KCl at the eutectic composition. Moreover, CsF and CsCl have extremely high solubility in water (CsF; 573, CsCl; 191 g per 100 g H2O at 293 K [6]), indicating that the solidified salts can be easily removed. In this study, Si was electrodeposited on Ag plate substrates at 923 K at various Si-ion concentrations and cathodic current densities. The obtained Si films were analyzed by XRD and SEM/EDX to determine the optimum electrodeposition conditions.2. Experimental The experiments were conducted in CsF–CsCl eutectic melt in an Ar glovebox. The experimental temperature was 923 K and Cs2SiF6was used as the Si ions source. Ag plate and Ag flag electrodes were used as the working electrodes. The counter and reference electrodes were Si rods. The potential of the reference electrode was calibrated by Cl2/Cl− potential measured at a glass-like carbon electrode. Samples prepared by galvanostatic electrolysis of Ag plates substrates were analyzed by SEM/EDX after washing with distilled water to remove adhered salts.3. Results and Discussion The electrodeposition was carried out by changing the added amounts of Cs2SiF6 from 0.50 to 3.5 mol%. The cathodic current density was also varied in the range of 25–800 mA cm−2. As typical deposits, Fig. 1 shows SEM images of Si prepared at (a) 600, (b) 100, and (c) 50 mA cm−2 in CsF–CsCl–Cs2SiF6 (2.0 mol%). At a higher current density, Si was nodule-shaped because the concentration gradient of Si(IV) ions increased near the electrode, and Si deposition proceeded preferentially on the convex part close to the bulk molten salt. At medium current densities (e.g., 100 mA cm−2), the electrodeposited Si was film-like and the surface was smooth. Fig. 2 shows a cross-sectional SEM image of the film, indicating the smooth and compact deposit. The thickness is about 20 μm (the theoretical film thickness: 25 μm), indicating a relatively high current efficiency. Furthermore, it was found that the upper current limit to obtain Si with smooth surface is higher at the higher Cs2SiF6 concentration; Si films with smooth surface were obtained even at 600 mA cm−2 in CsF–CsCl–Cs2SiF6 (3.5 mol%). At low current density, Si was film-like, but many humps were observed due to insufficient overvoltage and difficulty in nucleation.AcknowledgementThe present address of Kouji Yasuda is Graduate School of Engineering, Kyoto Univ.

On surface area coverage by an electrostatic rotating bell atomizer

An electrostatic rotating bell atomizer was used to produce a spray of a 20 wt% aqueous glycerol solution. Droplet size distributions were measured by photographing droplets in-flight and using image analysis software to measure their diameters. Increasing the rotational speed of the bell-cup resulted in a decrease in the average droplet diameter. The fraction of area covered by spray droplets was measured for various bell-cup speeds using a high-speed camera positioned behind a vertical glass substrate on which the liquid was sprayed. An analytical model, based on probability theory, was used to predict the fraction of surface covered solely using the droplet flux and the droplet size. Results from the model were compared to experimentally measured fractions of surface coverage and showed good agreement. The minimum theoretical film thickness assuming full coverage was derived from the probabilistic model. When the minimum theoretical film thickness was divided by the droplet diameter, it was found to be only dependent on the spread factor. Experiments to measure the fraction of area covered were also conducted using an automotive paint. Increasing the paint flow rate increased the fraction of area covered. Increasing rotational speed reduced splat size but had little effect on coverage. Increasing shaping air 1 flow rate reduced splat size and increased surface coverage significantly. Application of an electrostatic potential increased splat diameter but enhanced surface coverage only slightly.

Cu/Diamond Interfacial Adhesion Improved By Using Amino Group Modified Diamonds to Electroplating of Cu/Diamond Composite

Introduction Heat spreaders are used to ensure operation of electronic devices, such as smart phones, pads, LED and screen displays, by dissipating heat generated form integrated circuits. The ideal material working as heat spreaders should have high thermal conductivity. Cu and Cu alloys have been used as heat spreader materials from this point of view, but their heat dissipation performances are approaching their upper limit. Therefore, a heat dissipation material exhibiting even higher thermal conductivity is required for future electronics. Meanwhile, carbon materials are expected as next-generation heat spreader materials due to their extremely high thermal conductivities. Our group has previously reported on electroplating of Cu/carbon composites. In this study, we focused on electroplating of Cu/diamond composites because diamond is an interesting filler material that do not require orientation control due to its isotropic thermal conductivity.Typically, it has been suggested that the major issue for Cu/diamond composites is the adhesion at Cu/diamond interface because Cu and diamonds show low affinity. Surface modification with a silane coupling agent has been reported to be effective for improving the affinity of the interface, leading to improvement in thermal conductivity by reducing the thermal barrier at the interface [1]. Amino groups (-NH2) are expected to be attracted to the cathode side along with Cu2+ because it is positively charged in acidic solutions and to improve the Cu/diamond interface by forming complex with Cu. In addition, it has been reported that the -NH2 modification of BN improves the thermal conductivity of BN/epoxy resin composites [2]. In this study, we performed electroplating of Cu/diamond composites using -NH2 modified microdiamonds and investigated its effect on adhesion at Cu/diamond interface.ExperimentalThe -NH2 modified diamonds were prepared beforehand by the following procedure. As a pretreatment, the microdiamonds (MDs: average diameter of 180 μm) were heated at 1350 ℃ for 2 hours in a vacuum (5 Pa or less), and subsequently heated at 425 ℃ in air. The pretreated MDs were added to 50 cm³ of toluene solution containing 5 wt% of 3-aminopropyltrimethoxysilane (APTMS) and stirred for 6 h at 65 ℃ for silanization. Then, 30 ml of methanol was added to prevent further reaction of unreacted APTMS molecules. -NH2 modified MDs were collected by filtration, sequentially washed with methanol, water and acetone and dried at 80 °C in a vacuum oven over night. Existence of -NH2 on diamond surface was confirmed by using ninhydrin reaction.Electroplating was performed at room temperature. The bath composition was 1.0 mol/dm3 CuSO4.5H2O aqueous solution adjusted to pH 2.0 using H2SO4. The -NH2 modified MDs were added to the bath. The cathode used was Cu and the anode used was Pt coil, the reference electrode was Ag/AgCl. Galvanostat was used to apply a constant current of 10 mA/cm2. The quantity of electricity was 250 C (theoretical film thickness of 92 μm). The adhesion at the Cu/diamond interface in the composite plating was evaluated by observing the surface and cross section using a scanning electron microscope (SEM).Results and DiscussionProtrusions were formed on the surface of microdiamond after silanization. Silane oligomer aggregates formed by the self-condensation reaction of APTMS may have bonded to the diamond surface as reported elsewhere [3]. The ninhydrin solution turned from colorless to purple by ninhydrin reaction, implying the presence of -NH2 on modified MDs. From observation of Cu/diamond interface in the composite plating, well adhesion was obtained when using -NH2 modified MDs while an obvious void was observed when using pristine MDs. The result indicated that modification of diamond surface by -NH2 was effective to improve the adhesion at Cu/diamond interface.ConclusionsMD surface was modified by -NH2 groups through silanization. Surface and cross-sectional observation of Cu/diamond composite platings using -NH2 modified MDs showed well adhesion at Cu/diamond interface. It was found that -NH2 modification of diamond surface was effective to improve the adhesion between Cu and diamond.AcknowledgementThis work was partially supported by the JST-OPERA Program, Japan [grant number JPMJOP1843] and “Knowledge Hub Aichi”, Priority Research Project and Aichi Prefecture Research, Development Subsidy from Aichi Prefectural Government. Reference Y. Yamada, M. Miki, NIPPON GOMU KYOUKAISHI, 2013,86,5,133-139K. C. Yung, H. Liem, J. Appl. Polym. Sci.,2007,106,3587-3591Y. Nakamura, N. Karyu, M. Noda, S. Fujii, Journal of the Adhesion Society of Japan, 2016,52,1,9-15

(Invited) Electroplating of Bright Aluminum on the ABS Resin Substrate Covered with Cu Film in EmImCl-AlCl3 Ionic Liquid

Al is widely used in daily necessities, automobiles, building materials and plating materials. In addition, since Al formed into a mirror surface has a reflectance of more than 90% in the visible light region, it has been used as a reflection plate of an optical device such as a microscope and an LED light in the optical field. Our group aims to deposit bright aluminum electroplating on a resin that is even lighter than aluminum. This technology can contribute to further weight reduction of mobile devices. However, there is a few reports of formation of bright aluminum electroplating film with a thickness of several 10 μm. Therefore, research was conducted focusing on the bright condition of aluminum electroplating and the uniformity of the thicker plating film. In this study, 1-ethyl-3-methylimidazolium chloride (EmImCl) and AlCl3 a mixture ionic liquid and 1,10-Phenanthroline were selected as the electrolyte for Al plating and additive, respectively.EmImCl-AlCl3 ionic liquid (molar ratio of 1 : 2) with 20 mM 1,10-Phenanthroline was prepared in the glove box with Ar atmosphere. A Cu plate or a Cu-plated ABS resin was used for the working electrode and an Al plate or Al mesh was used for the counter electrode. Electrodeposition experiments were carried out by current pulse electrolysis with 20 mA cm-2 and duty ratio of 0.83 (ton = 1.0 s, toff = 0.2 s). Charge density was 59.7 Ccm-2 (Theoretical film thickness of 20μm). For the electroplated surface, surface observation and cross-sectional observation were carried out by SEM. The surface roughness and reflectance were measured by AFM and optical reflection probe(reference: Al mirror of 90% reflectance)In the experiment using Cu plate working and Al plate counter, bright Al formed at only edge of the Cu plate with non-stirring condition of electrolyte. When the stirring rate of the electrolyte was increased, the area of the bright part increased, and the stirring rate of 400 rpm was appropriate rate for formation of bright surface. This may because the additive reaches the whole surface of the Cu surface by stirring. The roughness and the reflectance of the Al electroplated surface formed under the condition of the 400 rpm was 2-3 nm from the AFM measurement and 75%(for the reflectance of the Al mirror) from the optical reflection measurement. However, since the flow of the electrolyte for the Cu substrate was not uniform, bright part was not also uniform, then electroplating in a non-stirring condition was investigated. As a result, it was found that the same effect as stirring of the electrolyte was obtained by using an Al mesh as the counter electrode.When the cross section of the electroplated specimen was observed by SEM, thickness was thick at the edges and thin at the center of the specimen. Next, in order to reduce a current concentration for the edge part of Cu substrate, support electrodes were placed around the Cu substrate. It was found that the thickness of Al electroplating was almost uniform for the substrate by the supporting electrode. Even if the underlayer was replaced with a Cu-plated ABS resin from the Cu plate, a bright Al-plated film was formed with a uniform thickness. Since the heat resistant temperature of ABS resin is about 100 oC, Al electroplating on ABS resin cannot be achieved in molten salt electrolysis (150 oC). These results were achieved by using an EmImCl-AlCl3 ionic liquid.

Electrodeposition of Al-W Alloys in AlCl3-NaCl-KCl Molten Salt Containing WCl4

Introduction Aluminum and aluminum alloys are widely used in a variety of industrial products like cars and electric appliances due to the lightweight and excellent electrical and thermal conductivity. Furthermore, aluminum oxide which is very thin and chemically stable forms on the surface. The oxide film contributes the corrosion resistant property of the surface. However, in the presence of halogen ions (ex. Cl-, F-, I- and Br- ions), corrosion takes place for the oxide surface. Al‐transition metal alloys have better corrosion resistance for chloride solution. Al-W alloys especially show the good corrosion resistance for pitting corrosion of the surface. Al-W alloys are also expected the increase of the hardness compared with pure Al. One of the available method to obtain Al alloys is an electrodeposition. Tsuda et al. previously reported the electrodeposition of Al-W alloy in the Lewis acidic AlCl3-[EtMeIm]Cl room temperature ionic liquid1). When higher temperature molten salts are used for electrodeposition of Al-W alloys, rapid electrodeposition may be achieved. AlCl3-NaCl-KCl molten salt is useful melt because the eutectic point of this system is 366 K at the composition of AlCl3 : NaCl : KCl = 61 : 26 : 13 (molar ratio). In this study, we report the mechanism of electrodeposition of Al-W alloys in the AlCl3-NaCl-KCl melt and discuss the relationship between the composition of the electrodeposit and the electrolysis potential. Experimental Electrodeposition of Al-W alloys was carried out in AlCl3-NaCl-KCl melt containing 10 mM WCl4 at 423 K. The electrochemical cell was used three-electrode system. A glassy carbon plate or a pure copper plate was used as working electrode at the voltammogram measurements or constant current electrolysis, respectively. An aluminum plate or a tungsten plate was used as counter electrode. Pure aluminum wire placed in a Pyrex glass tube filled with the AlCl3-NaCl-KCl melt was used as a reference electrode. All electrochemical measurements were performed under air atmosphere. The composition, surface morphology and identification of the electrodeposits were used X-ray fluorescence spectrometer (XRF), scanning electron microscope (SEM) and X-ray diffraction (XRD) instrument. Results and discussion A voltammogram was measured between 1.5 V and -0.2 V vs. Al/Al (III) at a sweep rate of 0.01 Vs-1 on a glassy carbon electrode in the AlCl3-NaCl-KCl melt with or without WCl4. In the melt without WCl4, the voltammogram showed a cathodic current at lower than -0.03 V with steep increase. An anodic current was observed from -0.02 V in the reverse scan. The cathodic and anodic currents correspond to the Al deposition and dissolution reactions, respectively. In the melt containing WCl4, two small cathodic currents were observed from 1.05 V and 0.45 V in the cathodic scan. The two cathodic currents correspond to a reduction of tungsten ions. When the potential is reversed at -0.2 V, an anodic current appeared from 0 V. The anodic current corresponds to dissolution of Al and Al-W alloy formed by the previous cathodic scan. In the results, the reduction steps of W ions lower than 1.05 V may occur from W (IV) to W (III), and from W (III) to W (0) below 0.45 V. To examine the relation between the electrolysis potential and the composition of the electrodeposits, constant potential electrolysis of Al-W alloys was carried out on Cu substrate at the potential range from -0.05 V to 0.4 V with electric charge of -30 Ccm-2(theoretical film thickness, 10 μm). The results suggested that when the electrolysis potential becomes higher, the W content in the electrodeposits increases. SEM images of the Al-W alloy prepared at -0.05 V and -0.025 V showed size of particle of about 5 μm, and cover the entire surface uniformly. On the other hand, it was found that a relatively small electrodeposit was formed on the substrate at higher than 0 V. The results of XRD showed the peaks corresponding to Al when the W content is less than 1 at%. When the W content is higher than 19 at%, Al peaks disappeared. However, broad peak showing the presence of an amorphous phase of W was observed at 0.4 V. Reference 1) Tetsuya Tsuda et al, J. Electrochem.Soc. 161, D405 (2014). Acknowledgment This paper is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Improved of effective wetting area and film thickness on a concentric helical bank of a generator for an absorption heat transformer

This work was performed in the generator of an absorption heat transformer (AHT) applied for water purification, which has two concentric helical coils. The AHT used LiBr-H2O to 55%wt for the heat transfer through a heat exchange by falling film. The objective of this study was to define the operating condition of the generator. Different falling film regimes were analyzed: drop mode, liquid column, and jet mode. The effective area of heat transfer of the two helical coils, wetting efficiency, and experimental film thickness were determined for the four operating flows (0.003, 0.008, 0.014, 0.019kg/s) through digital image processing. The theoretical film thickness was measured and compared with the one calculated by the Nusselt equation. The flow of 0.008kg/s maintained a drop mode distribution favoring a homogeneous fall along the helical test bank. A wetting efficiency of 99.52% was obtained, so it is proposed as operating flow in the generator. The theoretical film thickness for this flow was 0.289cm and the one obtained experimentally through digital image processing was 0.293cm. It was concluded that the distribution in the drop mode was more favorable for a better efficiency in the values of the falling film exchangers.

Electrodepotision of Metallic Silicon in P13TFSI Ionic Liquids Containing SiCl4

Introduction Silicon (Si) is used at various places in our life including a solar cell and an integrated circuit. The demand for Si increases year by year. The raw materials in the Si production are silica which exists in the earth crust, and Clarke number of Si is the second major after oxygen. However, production volume of Si is not much more than iron or aluminum. Generally, the metallic Si is produced by carbothermal reduction of silica, the purity of the Si is about 97 ~ 99 %, and the produced Si is used as alloying element. High purity Si is used for the photovoltaic and semiconductor industry. The production process of the high purity Si is chemical vapor deposition, but the production cost is relatively high. In this study, we propose the electrochemical process using ionic liquids for Si production, because electrolysis process can be achieved lower cost production. The electrodeposition of Si in TMHATFSI ionic liquids was reported by Nishimura et al.1) In the ionic liquids, 1-methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide（P13TFSI）has high conductivity in TFSI ionic liquids. In this paper, we investigated the electrochemical behavior of Si ions and electrodeposition of Si by constant potential electrolysis in P13TFSI ionic liquids. Experimental The electrolyte for Si electrodeposition was P13TFSI ionic liquid containing 0.9 M SiCl4. The electrochemical cell was used three-electrode type cell as shown in Fig. 1. For cyclic voltammetry (CV), a glassy carbon plate (G.C.) was used as working and counter electrode, Pt rod (2 mm in diameter) was used as a quasi reference electrode(Q.R.E.). For constant potential electrolysis, a Cu plate was used as a working electrode. All electrochemical measurement was performed in the glove box filled with Ar at 323 K. The composition analysis, observation of surface morphology and identification for the electrodeposits formed by constant potential electrolysis were carried out by X-ray fluorescence spectrometer (XRF), scanning electron microscope (SEM), and X-ray diffraction (XRD) instrument, respectively. Result and discussion The voltammogram on G.C. electrode in P13TFSI ionic liquid containing SiCl4 is shown in Fig. 2. In the cathodic scan from 0.2 to -0.4 V vs. Q.R.E., cathodic current started from -2.7 V and peak current was seen at -3.4 V. Then, cathodic current increased linearly in lower than -3.5 V. In the anodic scan from -4.0 to 0 V, it was observed that cathodic current flowed during the anodic scan and peak current was seen at around -2.5 V. In addition, anodic current was not observed during cathodic and anodic scan. From the result, it was found that the reduction reaction of the Si ions started from -2.7 V to -3.5 V, decomposition reaction of electrolyte can be occured below -3.5 V. The constant potential electrolysis was carried out at potential of -3.4 V with electric charge of -3.2 Ccm-2 (theoretical film thickness: 1 μm). The purity of Si in electrodeposits were 90~97 at% by XRF analysis. In the SEM observation, a lot of cracks were found in most observed part. The XRD pattern of electrodeposit was shown in Fig. 3. From the figure, it was seen that the diffraction pattern of the electrodeposit corresponds with that of metallic Si of good crystalline. Figure 1

Rheological Properties of a Commercial Food Glaze Material and Their Effect on the Film Thickness Obtained by Dip Coating

AbstractGlazing refers to the application of a coating material onto the surface of foods to enhance their shine and appearance. The objectives of this work were to analyze the rheological properties of a commercial food glaze material and to study their effect on the film thickness obtained by dip coating. Glazing suspension (83.33% total solids content) was obtained using a commercial powder product. Apparent viscosity was determined (shear rate 0.6–50/s) and yield stress was estimated with a creep test (0.5–10 Pa for 5 s). Experimental data were analyzed by applying the generalized Herschel–Bulkley model. A comparison between average thickness values obtained by dip coating and using a phenomenological mathematical model was carried out. All determinations were carried out at 20, 30, 40 and 50C. Rheological parameters were obtained with satisfactory root mean square errors. Good agreement between experimental and theoretical film thickness as affected by temperature was obtained.Practical ApplicationsGlazing refers to the application of a coating glaze material onto the surface of foods to enhance their shine and appearance, contributing to extend the shelf life of foods (like in bakery and confectionery products). In the present paper, the rheological properties of a commercial food glaze material were analyzed and their effect on the film thickness obtained by dip coating was evaluated. This study provides new experimental data to validate the mathematical modeling of the dip‐coating process developed in our research group. The general approach proposed to face the food glazing process will be of great significance for industry mainly to improve the control of film thickness of glazes.

Lubrication Regimes in High-Performance Polymer Spur Gears

Little has been published on the behaviour of polymer gears operating under lubricated conditions. An experimental and analytical programme was undertaken to classify the regimes of EHL under which polymer spur gears operate. In doing so theoretical film thicknesses were calculated and then used to classify the regime according to Johnson's Map. The effects of lubrication on the operating efficiencies of high-performance polymer gears were interpreted and from these results coefficients of friction were derived. In addition to this the effect of tooth geometry was investigated and the beneficial influence of high-pressure angle tooth geometry is demonstrated. At loads typically associated with polymer gears the operating regime is shown to be mixed film lubrication. When high-pressure angle gears were tested at high loads the operating regime became full film lubrication and relatively little tooth flank damage occurred.

The Influence of Longitudinal Roughness in Thin-Film, Mixed Elastohydrodynamic Lubrication

The spacer layer imaging method (SLIM) has been used to investigate the influence of longitudinal asperities, with their major axis along the direction of lubricant entrainment, on the thickness and shape of thin, elastohydrodynamic (EHD) films. The effects of entrainment speed and rolling-sliding conditions on film thickness are shown for two different asperity heights. The morphology of the films formed and their thicknesses are used to discuss the influence of longitudinal roughness on film-forming capability and pressure perturbation within EHD contacts. Direct comparisons between the measurements and predictions of a theoretical model reveal the combined effects of longitudinal roughness and extremely low lambda ratios on surface compliance and, thus, EHL film formation. It is shown that the micro-EHL film thickness can be calculated by applying theoretical film thickness regression equations for smooth EHD contacts to the elongated, elliptical contacts formed by longitudinal ridges in thin-film conditions. Presented at the STLE Annual Meeting, in Las Vegas, Nevada, May 15-19, 2005 Review led by Liming Chang

ポリビニルホルマールの摩耗特性(第2報)(S04-4 医療とバイオエンジニアリング,工学技術の医療応用(4),S04 医療とバイオエンジニアリング,工学技術の医療応用)

Wear characteristics have been investigated in polyvinyl formal (PVF) as an artificial articular cartilage for joint prostheses. This bearing of the joint has been designed and constructed to produce larger initial contact areas and thicker theoretical film thickness than the conventional UHMWPE bearing. The main advantage of using the bearing may be associated with micro-elastohydrodynamic lubrication, and the low elastic modulus layer may also produce local deformations, which enhance squeeze film action. Wear tests were performed with a knee joint simulator. The PVF was adopted as the articular cartilage for the flat tibial component. The compliant bearing had a spherical surface that was made of stainless steel. The results showed that no detectable wear debris was generated in the simulation tests conducted over 1.0 million cycles. Although there still remain some problems to solve, the PVF seems to be a very interesting and promising material, which meets the requirements of artificial articular cartilage.

Comparison between Theoretical Calculations and Oil Film Thickness Measurements Using the Total Capacitance Method for Crankshaft Bearings in a Firing Engine

Comparisons were made between theoretical calculations and experimental measurements for minimum bearing oil film thickness (MBOFT) in main and connecting rod bearings of a typical automotive V6 engine running at 1500 rpm under three load conditions (64, 128, and 192 Nm.). Data for five oils (SAE grades 5W–20, 20W–20, 5W–30, 10W–30, and 20W–50) were obtained for the main bearing and for two oils (SAE 5W–30 and 10W–30) for the connecting-rod bearing. The theoretical calculations were done using the FLARE computer code while the measurements were made using the total capacitance method (TCM). Considering the complexities involved in a firing engine, overall, reasonably good agreement between theory and experiment was observed, especially for the absolute minimum of the MBOFT (MBOFTmin). The experimental data showed higher dependence on the Sommerfeld number than that of the theoretical calculations for the main bearing. The shapes of the MBOFT vs. crank angle curves were also similar between theoretical predictions and experimental measurements, although there were differences as well. Several causes of discrepancy affecting both the calculations and the measurements were investigated. Bearing non-circularity, cavitation, and crankshaft flexibility and dynamics were identified to be the main causes of the discrepancy. A novel approach based on analysis was developed for estimating the error in the based on analysis was developed for estimating the error in the oil film thickness measurements using TCM due to cavitation and bearing non-circularity, including the presence of holes and grooves. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Hydrodynamic lubrication of the ironing process

AbstractA theoretical model is presented to calculate the lubricant film thickness in an unsteady hydrodynamic lubrication of cup‐shaped products to be formed by the ironing process. The model covers the development of hydrodynamic lubrication in various phases of the ironing process. The model provides equations for estimating the lubricant film thickness for each phase.Experiments were conducted to study the effect of lubricant viscosity on die expansion and punch force in making cup‐shaped products by the ironing process. It was found that the die expansion varied between unlubricated and lubricated cups and depended on the lubricant viscosity. The film thickness was estimated from the difference between the increased die/punch clearance, which was calculated from the expansion, and the lubricated cup wall thickness. The theoretical film thickness was compared with the estimated film thickness based on the die expansion measurement.

Debris and Roughness in Machine Element Contacts: Some Current and Future Engineering Implications

The influence of surface roughness and third-body particulates on tribological contacts will be reviewed in general, but in particular their influence on rolling contacts and contacts where rolling and sliding occur simultaneously will be considered in some detail. Such non-conforming contacts are often referred to as Hertzian, and when lubricated are often considered to be protected by an elastohydrodynamic (EHD) lubricant film. Transferring these concepts to the loaded interfaces of real engineering components such as gears, rolling bearings, constant-velocity joints and cams, etc., can have serious shortcomings and lead engineers to many misconceptions. Roughness often appears to dominate over the theoretical size of lubricant films and can create a contact geometry and local stress distribution far removed from the smooth surface case. Even in ball-bearings where surfaces are some of the smoothest of all mass-produced engineering components, lubricant-borne debris particles are usually many times the theoretical film thickness and the damage they can cause can quickly destroy the production engineer's good work in creating smoothness, as well as having a significant influence on component performance. The paper reviews such aspects in terms of recent research and explains some of the many practical implications of roughness and debris that are faced at present, and also speculates on the implications for the future, when roughness geometry and surface properties might be engineered to suit a particular lubricant and its potential contaminant population.

Cushion form bearings for total knee joint replacement. Part 2: Wear and durability.

Cushion knee prostheses have been designed and constructed to produce larger initial contact areas and thicker theoretical film thicknesses than a conventional UHMWPE (ultra-high molecular weight polyethylene) joint. The compliant bearing had a flat tibial component which imposed fewer biomechanical constraints and allowed greater range of movement. Wear tests were performed in a knee joint simulator and creep tests were carried out in a servo-hydraulic apparatus. Various failure modes of cushion joints that require further study were identified. However, the results showed that adequate durability was achieved from a 20 MPa polyurethane material in joint simulating tests carried out over 0.5, 1.0 and 5.0 million cycles. Most importantly, during these tests, no detectable wear debris was generated. It is believed that this is the first time that the full potential of cushion bearings has been demonstrated in a joint simulator over periods corresponding to about five years of service in vivo.

Application of a two-dimensional model of continuous sliding friction to stick-slip

The authors have previously developed two-dimensional dynamic friction models for boundary and mixed lubricated line contacts, operating, under continuous sliding conditions. The performance of one of these friction models under intermittent sliding, involving stick-slip and slip-stick transitions is examined in this paper. The friction model includes the sliding velocity, the instantaneous separation of the sliding bodies, normal to the sliding direction, the normal load and fluid properties. The normal motions at the sliding contact were detected indirectly by contact resistance measurements which were, in turn related to the theoretical film thickness. It is known that at or near rest, a tangential contact stiffness and partial slip are observed, making it difficult to unambiguously identify a particular point at which slipping or sticking actually begins. Nevertheless, we investigate the applicability of a continuous sliding friction model to such situations. It becomes clear that normal motions play a critical role in determining the interaction between friction and vibration and that friction fluctuations into the sticking range can be described by the model as long as the duration of stick is not long.

Two-Dimensional Models of Boundary and Mixed Friction at a Line Contact

Two-dimensional dynamic friction models at a lubricated line contact, operating in boundary and mixed lubrication regimes, are developed. The friction coefficient is shown to be a function of the sliding velocity and the instantaneous separation of the sliding bodies, normal to the sliding direction. The models are based on unsteady friction experiments carried out under constant normal loads and under time-varying sliding velocities. The normal motions at the sliding contact were detected indirectly by contact resistance measurements. The contact resistance is related to the theoretical central film thickness for smooth surfaces. An advanced system identification technique (Minimum Model Error) is implemented to identify the most important terms in a number of nonlinear friction models. Two friction models are then nondimensionalized and parameterized. The validity and range of application of the models are then tested, by comparing them with experiments and with selected models proposed by other researchers.

Investigation of the Failure of Heavily Loaded Journal Bearings

This paper gives details of a combined theoretical and experimental investigation of a plain journal bearing under heavily loaded conditions together with a metrological study of the bearing geometry. It was found that under high loading conditions a simplified analytical expression relating the Sommerfeld number to the non-dimensional minimum film thickness, using a hydrodynamic solution of the isoviscous form of the Reynolds equation, could be developed. An alternative theoretical solution based on elastohydrodynamic lubrication was also considered. In addition, experimental work determined a variety of operating conditions that produced metal-to-metal contact. These operating conditions were then compared with the theoretical minimum film thickness calculations and bearing manufacturing data. This process was used to determine combined failure criteria based on operating conditions and machining capability.