Akihiro Yabuki

Contact forces and mechanisms in a vibratory finisher

The normal and tangential contact forces in a vibratory finishing machine were measured using a newly developed force sensor. A video system was used to record the motion of the finishing media as it collided with the test surface. Media contact occurred in three different modes. The ratio of the normal and tangential forces was compared with the measured friction coefficient under dry and water-wet conditions. This confirmed that media sliding occurred under water-wet conditions.

Tribological behavior of aluminum alloys in a vibratory finishing process

Abstract The contact forces and tribological behavior of aluminum alloys (AA6061-T6 and AA1100-O) in a vibratory finishing process have been investigated. A new surface force sensor was used to measure simultaneously the normal and tangential forces produced by the ceramic media in a tub vibratory finishing machine. These forces were then correlated with the resulting changes in surface roughness, hardness and wear rate of aluminum disks attached to a cylindrical carrier, as well as with the residual curvature of the finished metal sheets. The principal variables were the degree of lubrication, finishing duration, and aluminum alloy. Further observations of media motion obtained using a miniature video camera and SEM micrographs of impact craters helped determine the contact mechanics of the finishing media and the wear mechanisms of AA1100-O and AA6061-T6 alloys. Comparisons are made throughout with similar data obtained previously with a smaller, less energetic bowl finisher. Experimental results revealed that, in the dry finishing condition, media contact tends to the normal direction, with increased media sliding occurring in the water-sprayed condition. Hardness and roughness changes of the workpiece were strongly dependant on the lubrication condition. Furthermore, in the dry condition, mass gain was observed as media debris became embedded in the workpiece surface, while in the water-sprayed condition this effect was prevented by the washing action of the water. The residual curvature of the disks increased with finishing duration until it reached a steady value. Residual curvature was also measured on Almen strips fastened to the ends of a second carrier, and differences between wet and dry finishing are discussed.

Critical impact velocity in the solid particles impact erosion of metallic materials

Abstract Solid particles impact erosion of metallic materials proceeds through two kinds of damage processes. One is the removal of material due to repeated plastic deformation, and the other is cutting. These processes occur simultaneously and the ratio of each contribution to the total damage depends not only on the impact angle (the predominant parameter) but also on the impact velocity. As the impact velocity goes down, a solid particle tends not to skid on the target material surface, and hence the cutting damage is reduced. At a certain lower velocity, the particle does not skid at all, resulting in no cutting damage but plastic deformation damage only. This velocity was defined as the “critical impact velocity”. In this study, the methodology to determine the critical velocity through a measurement of the coefficient of friction was established, that is, the dynamic friction coefficient during skidding and the static friction coefficient during rolling without skidding. In order to measure the coefficient of friction at the moment of particle impact, a rotating target apparatus was developed. The critical impact velocity thus determined depended on the hardness of both material and particle, as well as on the shape and size of the solid particles.

Theoretical equation of the critical impact velocity in solid particles impact erosion

In the previous paper (Yabuki and Matsumura, this issue), the critical impact velocity in the erosion of metallic materials by solid particles impact was experimentally determined. In this paper, the critical impact velocity was theoretically derived through analyzing the behavior of the material surface obliquely impacted by a spherical solid particle, where the material is strained tangentially to the surface in the direction of particle movement. As the extent of strain goes over the elastic limit, the impacted solid particle does skid over the surface, which brings about wear (to the surface) by cutting. The threshold strain was theoretically derived as a function of the impact velocity and the rotating velocities as well as the duration of particle surface contact. Those parameters which characterized the impact behavior were derived from the coefficient of friction and the rebounding coefficient, all of which were obtained from the mechanical properties of the target material and particle, and other factors concerning the particle. Consequently, the theoretical value of the critical impact velocity was given solely as a function of the mechanical properties of the target and the particle. The calculated critical impact velocity attained the lowest value at a low impact angle, and a good correlation was found between the critical velocity determined by experiment and that predicted by the theoretical equation.

Slurry erosion properties of ceramic coatings

Abstract The effectiveness of ceramic coatings on pump impellers used in the acidic gypsum-fly ash slurry environments in desulphurisers was assessed by using two kinds of slurry erosion tester. The experimental results from the two testers did not always coincide, although in general they did. The possible reasons and the implications of this distinction between the two testers were discussed, and the following conclusions were reached: (1) Generally, although ceramic coatings, in particular Cr 2 O 3 and Al 2 O 3 , have much improved slurry erosion resistance, the resistance of ceramic coatings to slurry-erosion is closely related to the techniques of plasma spraying. At optimum manufacturing conditions, ceramic coatings are about two times as resistant as the base metal (SUS329J1); (2) Vickers hardness ( H v ) is an effective parameter for the assessment of slurry erosion properties of ceramic coatings, as well as bulk ceramics; (3) The most deleterious environment for slurry pumps used in desulphurisers is pure fly ash, therefore, fly ash should be removed as much as possible before desulphurising in thermal power plants.

The anti-slurry erosion properties of polyethylene for sewerage pipe use

Abstract Sewerage systems are more common in Japan. The pipes and fittings in the systems are exposed not only to a corrosive environment, but also to the impact by solid particles contained in mud drains, resulting in an erosive wear on the surface. A strategy for coping with these problems involves replacing the more traditionally used iron and steel pipes with polymeric materials, which have excellent anti-corrosion properties. In this study, a slurry erosion test were carried out using a jet-in-slit apparatus on seven types of polyethylenes, three other types of polymers, and two types of iron and steels, thoroughly taking into account the fact that erosion damage is highly dependent on the impact angle of the particles. As a result, all the polyethylenes proved to have excellent anti-erosion properties, compared with the other materials over the entire range of particle impact angle. Further, a model was proposed to account the impact angle dependency of the erosion damage. The model aided in clarifying the reasons why the erosion rate of the polyethylenes is satisfactorily correlated with a complex parameter in which the fracture energy and the elastic modulus are combined.

Heating Profile Effect on Morphology, Crystallinity, and Photoluminescent Properties of Y2O3:Eu3+ Phosphor Nanofibers Prepared Using an Electrospinning Method

Europium-doped yttrium oxide (Y2O3:Eu3+) nanofibers were successfully prepared via an electrospinning method followed by annealing at temperatures up to 1200 °C. Mixed solutions of yttrium nitrate, europium nitrate and poly(vinyl pyrrolidone) (PVP) were used as precursors. Poly(vinyl pyrrolidone) polymer was used as a template for obtaining fiber morphology and was then removed during the annealing process to yield Y2O3:Eu3+ fibers. The fibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR), and photoluminescence (PL) spectrometry. The effect of the heating profile on the morphology, crystallinity, and photoluminescent properties of the nanofibers was systematically investigated. The diameter of the prepared fibers decreased with increasing temperature and a high heating rate caused the polymer to melt quickly and cross-links to form between the fibers. In addition, crystallite size and photoluminescent intensity of Y2O3:Eu3+ phosphor fibers increased with increasing temperature.

Critical Ion Concentration for Pitting and General Corrosion of Copper

Abstract Corrosion tests for copper were carried out in solutions containing various concentrations of chloride or sulfate ions under both static and flowing conditions. Pitting corrosion occurred at lower ion concentrations and was then transformed to general corrosion with increasing ion concentration. The critical ion concentration was determined by observing the surface of the specimen after the test, the average corrosion rate, and the number of pits that occurred on the copper surface. The value was found to be approximately 2,000 ppm of sodium chloride (NaCl) under static conditions. The effect of flow, dissolved oxygen, and the type of ion on the critical ion concentration was also investigated. The value under flowing conditions using a jet-in-slit testing apparatus was lower, 500 ppm. However, the values for a solution saturated with nitrogen and a solution containing sulfate ions were only slightly different. The critical ion concentration was related to ions adsorbed to the surface of the copp...

One-Step Fabrication of Short Nanofibers by Electrospinning: Effect of Needle Size on Nanofiber Length

The effect of needle size on the fiber length was studied and investigated. A polymer solution of cellulose acetate (CA) and organic solvent was ejected from various sizes of needle gauge then the electrospun polymer fibers were adhered on a collector plate. The diameter of fibers was ranging from 80 to 570 nm and the length could be controlled from 10 to 240 µm by increasing the needle size. The breakaway to shortened nanofibers occurred due to the imbalance of force from the surface tension of the polymer solution and the longitudinal force of the applied voltage.

Mapping the influence of electrospinning parameters on the morphology transition of short and continuous nanofibers

A theoretical model for the morphology transition of short and continuous nanofibers by electrospinning has been proposed. The influences of polymer concentration, applied voltage, and flow rate on the fabrication of short and continuous nanofibers were mapped for use as a reference in the design and construction of the theoretical model. The morphology transition of short and continuous nanofibers occurred mainly due to changes in the flow rate and voltage. According to the concentration of the polymer in the solution, the map of the short nanofiber region was narrowed as the polymer concentration increased. The theoretical model derived from the conservation of kinetic energy and potential energy experienced by the polymer solution resulted in an equation that could be used to calculate the voltage and flow rates under certain boundary conditions when cutting nanofibers. The boundary conditions for voltage were 4.7-4.9 kV, and the boundary conditions for flow rate were 0.1-1.1 µl/min.