Shigeki Koyanaka

Particle shape of copper milled by swing-hammer-type impact mill

Abstract In order to apply a shape sorting technique to recover the copper component from printed wiring board (PWB) scrap, the particle shape of copper milled by a swing-hammer-type impact mill was experimentally investigated. Copper plate and PWB scraps were used as samples. The effects of mill operating conditions, i.e., hammer circumferential speed (vc) and screen aperture size (diam. ds), on shape and size distribution of milled products were examined. Sphericity and homogeneity in the shape of milled copper particles largely depended on mill operating conditions. In the cases of both copper plate and PWB scrap milling, the most effective operating conditions to obtain spherical copper particles were vc≃50 m s−1 and ds=1 mm, and to obtain homogeneous shaped copper particles vc≃70 m s−1 and ds=1 mm. The most effective operating conditions of the mill to recover the copper component from PWB scrap using an inclined vibrating plate (IVP) were vc≃70 m s−1 and ds=1 mm.

Recovering copper from electric cable wastes using a particle shape separation technique

A particle shape separation technique was used to recover copper from electric cable wastes used in computer devices from the point of view of resource recycling. After the electric cables were crushed by a cutter mill, small pieces of the cables were impact milled for the purpose of liberating the copper wire from the plastic covering. The shape of the copper wires was prepared for separation by shape at the same time. By impact milling, the copper wires were twined and became pill-like particles. However, the shape of the plastic covering was irregular. An inclined conveyor and an inclined vibrating plate were used as the particle shape separator, and the most effective operating conditions for these apparatus were experimentally investigated. As a result, it was possible to separate copper from the plastic covering with high efficiency.

Effect of impact velocity control on selective grinding of waste printed circuit boards

Abstract To develop a low-cost recycling process for printed circuit boards (PCBs) in scrap electronics, a new grinding technique that can enhance the selective grinding effect between ductile and brittle materials was investigated with a personal computer-assisted impact grinding system which can automatically control various operating conditions in real time. The destruction behavior of twokinds of PCBs within the grinding chamber was captured on video with a high-speed camera, and then the effect of real-time control of the impact velocity of the mill on selective grinding between metallic and non-metallic components in the milled product of PCBs was examined. As a result, the destruction process of PCBs was found to be of a totally different form, according to the strength of base materials like paper-mixed phenol resin or glass-reinforced epoxy resin. The variable speed mode, i.e. accelerating the hammer rotation gradually from a very slow speed, was found to be an effectivemethod to enhance the selective grinding because the exfoliation of copper foil was increased, while the size of fragment was relatively large.

Three-dimensional analysis of the movement of various micron-sized particles under laser radiation pressure

The fundamental characteristics of particle movement in a weakly focused laser beam were investigated from the viewpoint of particle separation. A three-dimensional analysis model based on equations of motion was proposed to clarify the characteristics of the long-range transportation of micron-sized particles having various physical properties. The accuracy of the model was confirmed by measuring the actual movement of a glass, nickel, and aluminum oxide particles. For the glass particle, the calculated trajectory was in good agreement with the measured one. For the nickel particle, the calculation gave a qualitatively correct result. From the measured movements of irregular shaped aluminum oxide particles, it was clarified that the shape of the particle affected its transport distance as well as its refractive index. The possibilities of particle separation based on a difference in refractive index and shape were suggested because the transport distance of a particle depended on these factors.

The effect of relative refractive index on monosized particle movement under laser radiation pressure

The purpose of this study is to investigate the fundamental characteristics of particle movement under laser radiation pressure from the viewpoint of particle separation. In this study, the radiation pressure exerted on a spherical particle was calculated by using a simple geometrical optics model and the simulation of particle movement in a laser beam was performed. Further, the movement of particles under the laser radiation pressure was experimentally observed to confirm the accuracy of simulation. As a result, it was possible to simulate particle movement with the two-dimensional equations of motion by considering radiation pressure, viscous drag, gravity, and buoyancy as the forces acting on a particle. The possibility of particle separation according to the refractive index was suggested since the difference in laser radiation pressure was large enough to discriminate the particles.

Numerical simulation of the optical system and medium flow field suitable for particle separation using laser radiation pressure

Abstract From a viewpoint of increasing the throughput of particle separation using laser radiation pressure, the long-range movements of a micron-order particle in a weakly focused Gaussian beam are investigated using a three-dimensional analytical model of the particle movement. The concept of the ‘separation area’ is introduced as an indicator of the throughput. The effects of numerical aperture of the focusing lens, laser power and the medium flow velocity on the throughput are examined through the calculation of the separation area of a soda-lime glass micro-sphere moving in water. Then, the potential applications of this particle separation are discussed on the basis of the difference in the separation area for particles with various refractive indices. Results show that the optimum numerical aperture in a static medium is obtainable in a very narrow region above a critical value. Deterioration of particle throughput due to the flow of a medium is controlled by using a numerical aperture slightly larger than the critical value. A high-power laser is advantageous to increase the particle separation throughput. Furthermore, separation of transparent and non-transparent particles can be readily achieved under optimal conditions of the optical system and a medium flow-field, whereas separation of transparent particles requires a large difference in the refractive index and uniformity in size.

Effect of laser scanning on increase of throughput in particle separation using laser radiation pressure

Abstract The repetitive scanning of a focused laser beam was applied to increase the throughput of particle separation using laser radiation pressure. The relationship between the scanning conditions, specifically laser output power, scanning distance, scanning frequency and the characteristics of particle transportation, was investigated using micron-sized polystyrene latex particles. The improvement of particle throughput by laser scanning was confirmed through a separation experiment using a mixture of micron-sized synthetic diamond and graphite particles. The results showed that the optimized laser beam scan system enables particle separation throughput to be increased by approximately 70% compared to the non-scanning state.