Evaluation of flow properties of toner powder using conical rotor

In order to accurately evaluate the dynamic flow properties of toner powder, a new rotary shearing tester with a conical rotor was developed. This instrument was equipped with an automatic pressing system to compress toner powder. The tester could simultaneously measure torque and compression load during the intrusion and rotation of the conical rotor into the same packed toner powder. The optimum rotational speed and intrusion rate of the conical rotor for the characterization of the flow properties of toner powder were discussed based on test results; their values were calculated as 0.017 s^− 1 and 0.083 mm/s, respectively. The torque of toner powder changed in proportion to the cube of the depth of intrusion in the toner powder bed. The surfaces of toner powder samples prepared from polymer resin and carbon pigment particles were coated with fine particles (SiO₂, TiO₂) under a different condition. The flow characteristics of toner powder with a different particle surface were evaluated based on the relationship between the shearing torque and the void fraction of packed toner. In the present case, the Rumpf model was applied to estimate the shearing force H at the contact point between two particles of toner powder. The value of H for toner powder with a rough particle surface, which was covered with fine particles (SiO₂, TiO₂), was 41 nN, while that for toner powder with a smooth particle surface, which was not covered with fine particles, was 357 nN. Further the effects of the particle shape of the toner on the torque of toner powder after compression under the same conditions were investigated. The torque of toner powder decreased with an increase in circularity.     

Experimental analysis of dynamic properties in wet sheared granular matter

We performed experiments to measure the dynamic properties of wet granular matter in a shear cell device. The purpose was to quantify the effect of the liquid bridge force on granular systems. The motions of the granular materials were recorded by a high-speed camera. Image processing technology and particle tracking method were employed to measure the velocities, fluctuation velocities and granular temperatures in the streamwise and the transverse directions. The results show that adding small amounts of liquid with different viscosities, and changing the wall velocity, both have significant influences on the dynamic properties of wet granular matter due to the formation and rupturing of liquid bridges. The energy dissipation due to the formation and rupturing of the liquid bridges increases with the increase of wall velocity and the increase of liquid viscosity. The effect of the liquid bridge force on the dynamic properties is not only dependent on the liquid viscosity but also on the kinetic energy of the granular system.     

Evaluation of the particle-particle interactions in a toner by colloid probe AFM

In order to evaluate the particle-particle interactions in a toner particle with a high accuracy, the changes in the adhesion force between a toner particle glued to an AFM cantilever tip and a particle in a compressed layer of toner powder was measured by colloid probe atomic force microscopy. Toner particle layers compressed by a pressure of 54.9 MPa were used as the substrate in this study. The effects of the scan rate, particle diameter, humidity, and surface coating of silica nanoparticles on the adhesion force were discussed on the base of measurement results. The adhesion force between the toner surfaces decreased with an increase in the AFM scan rate; it then reduced to a constant value at 1.95 Hz. The adhesion force between the toner particles increased proportionally with approximately the second power law of the particle diameter; it exhibited a change that differs from the force characteristic that was directly proportional to the first power law of the particle diameter, as given in van der Waals expression. Next, the additives that consisted of SiO₂ were glued on to the surface of the toner particle, and the influence of the surface coverage of SiO₂ on the particle-particle interactions was examined. The particle-particle interactions consequently decreased in inverse proportion with a surface coverage of SiO₂ 26% or less. Moreover, when the SiO₂ surface coverage was 26%, almost no changes were observed in the particle-particle interactions at 80% R.H. It was confirmed that the influence of humidity reduced by coating the toner particle with SiO₂. The relationships between the particle-particle interactions and the flow properties were examined by using a rotary shear tester with a conical rotor. When the mean particle diameters were identical, a first strong positive correlation between the particle-particle interaction and the shearing torque that crossed the zero point was observed. When the shearing force H was calculated from the torque of the conical rotor method by using Rumpf's equation, a first strong positive correlation between the particle-particle interaction Fa and the shearing force H that crossed the zero point was observed.     

An experimental study on the effect of liquid content and viscosity on particle segregation in a rotating drum

The segregation phenomenon of wet granular materials was experimentally studied in a quasi-2D rotating drum. The mono-disperse systems and binary-mixture systems (with 4 mm and 2 mm glass beads and 40% filled volume fraction) were used. All the experiments were controlled so the Froude number of the rolling regime was 2.79 × 10^− 4. The effects of the volume and the viscosity of the liquid added to the granular system on the segregation index and angle of repose in the rotating drum were investigated and are discussed in this paper.The experimental results indicate that the volume and viscosity of the added liquid have significant effects on the wet granular flow. The results demonstrate that the segregation index decreases with an increase of the repose angle of the wet granular materials, regardless of the volume or viscosity of the added liquid.     

Predicting discharge dynamics of wet cohesive particles from a rectangular hopper using the discrete element method (DEM)

Accurate prediction of the discharge rate from hoppers is important in many industrial processes involving the handling of granular materials. The present work investigates the parameters affecting the discharge rate of a wet cohesive system from a quasi-3-D, rectangular hopper using the discrete element method (DEM). The cohesion between the particles is described by a pendular liquid bridge force model and the strength of the cohesive bond is characterized by a Bond number. The Beverloo correlation is applied to cohesive systems by modifying the Beverloo constant as a function of Bond number. The predictions obtained from this modified correlation fit the simulation data reasonably well. In addition, the effect of hopper angle in cohesive systems is shown to follow a trend similar to cohesionless systems, where the discharge rate is insensitive to changes in hopper angle except below a critical angle (with respect to the vertical) where the discharge rate increases rapidly. This critical angle of flow decreases with increasing cohesion.     

Simulation of adhesive joints using the superimposed finite element method and a cohesive zone model

Adhesive joints have been widely used in various fields because they are lighter than mechanical joints and show a more uniform stress distribution if compared with traditional joining techniques. Also they are appropriate to be used with composite materials. Therefore, several studies were performed for the simulation of the bonded joints mechanical behavior. In general for adhesive joints, there is a scale difference between the adhesive and the substrate in geometry. Thus, mesh generation for an analysis is difficult and a manual mesh technique is needed. This task is not efficient and sometimes some errors can be introduced. Also, element quality gets worse.In this paper, the superimposed finite element method is introduced to overcome this problem. The superimposed finite element method is one of the local mesh refinement methods. In this method, a fine mesh is generated by overlaying the patch of the local mesh on the existing mesh called the global mesh. Thus, re-meshing is not required.Elements in the substrate are generated. Then, the local refinement using the superimposed finite element method is performed near the interface between the substrate and the adhesive layer considering the shape of the element, the element size of the adhesive layer and the quality of the generated elements. After performing the local refinement, cohesive elements are generated automatically using the interface nodes. Consequently, a manual meshing process is not required and a fine mesh is generated in the adhesive layer without the need for any re-meshing process. Thus, the total mesh generation time is reduced and the element quality is improved. The proposed method is applied to several examples.