Noriaki Masui

Electrification of Polymer Particles by Impact on a Metal Plate

Impact charge and impact area of particles of nylon 66 and PMMA (3.18 mm and 2.19 mm in diameter, respectively) by a single impact on a metal plate (Cr plated brass plate) were measured under various impact speeds v (3.7 m/s ~ 20.3 m/s) and impact angles θ(0^°~80^°). It was found that both the impact charge and the impact area are junctions of the vertical component of the impact speed, vcos θ, while the horizontal component, vsin θ, was found to have no effect on them. The impact area is calculated using the theory of plastic-elastic deformation, and the measured values are found to agree well with the calculations. The impact charge density is constant within the range of the experimental conditions examined and is determined only by the combination of materials colliding with each other.

A method for measuring the charging tendency of powder in pneumatic conveyance through metal pipes

Abstract The charging tendencies of powders of some synthetic high polymers are measured with a newly developed charging apparatus. The sample is continuously transported through a bent metal pipe using an air flow and is electrified by multiple frictions and collisions against the inner wall of the metal pipe. The transport speed V and the solid load d of the sample are changed from 1.4 to 2.8 m/s and 1.9 to 5.2 kg/m3, respectively. The charge build-up of each examined is given by the empirical equation: Q = Qs [1 − k exp (−t/τ)]. The saturation charge Qs and the initial rate of charge accumulation qo [ = (dQ/dt)t=0] are found to depend on the transport speed and the material of the pipe. The initial rate of charge accumulation qo also depends on the solid load and in the case of a spherical PE sample, it can be described by an experimental equation obtained with aluminium pipe: qo = −2.47 V0.4 d−1.07 × 10−6 C/kg s. The saturation charge Qs of each sample used in this measurement at the same transport speed corresponds to the position of each sample in the familiar previously published triboelectric series [1–3].

Mechanisms of Charge Build-up on a Polymer Particle by Repeated Impact

The dependence of the impact charge of a polymer particle on the charge previously deposited on it (pre-charge) was studied at impact speed v=9.04 m/s~20.3 m/sandimpactangle θ=50^°~60°. The impact charge of a particle decreased almost linearly with increase in the pre-charge. Observation of the optical density of the impact area made visible using electrophotographic liquid developer showed that this phenomenon was caused by the decrease in the charge density on the impact area. The electric field due to the pre-charge was thought to restrict the generation of new charge. This inference was confirmed by an experiment using a polyethylene sheet.

Method for measuring the powder charge in the electrostatic powder‐coating process

A simple method for measuring the electrostatic charge of powder particles in a powder cloud sprayed from an electrostatic powder‐coating gun is described. Powder particles accompanied with ions were drawn into an insulator suction pipe and their charge was measured after they passed through the pipe by employing the suction‐type Faraday Cage. Most ions are eliminated by both electrostatic repulsion force against the charged tip of the pipe and charge recombination against the pipe wall. The suction pipe had almost no effect on the measured value for powder charge.

Electrification of Polymer Powders after Passage through Metal Pipes

The electrification of polymer powder transported through straight copper pipe and copper pipes with 45° and 90° elbows (0.02 m in internal diameter) was studied at a particle speed v=7 m/s~30.8 m/s and a solid load ρ=0.002 kg/m3~15 kg/m3. The charge/mass ratio q of the powder passing through an elbow pipe was from 15 to 20 times larger than that in a 1m-long straight pipe. With elbow pipes, it was found that the charge on the powder Q(C) was mostly generated by the first collision with the inner wall of the bend in the pipe. The impact areas S(m2) of the particles in the elbow pipes were calculated at low ρ and high v, and the charge density σ(Q/S C/m2) was found to be constant in spite of the variation in ρ, v and the shape of the pipes.

Measurement of Charging Tendency of Pellets by Impact Charging

The charging tendency of pellets of some synthetic high polymers are measured with a newly developed charging chamber in which the pellets are charged repeatedly by impacts against a metal plate by the use of a compressed air flow. The charge build-up of the pellets follows an almost exponential growth. It is shown that the saturation charge is limited by air breakdown. Furthermore, the time constant of the build-up curve shows how easily the sample acquires the charge. In the case of nearly spherical pellets of polyethylene, 0.16 cm in radius, the saturation charge density is -2.10 x 10-9 C/cm2. This value is 36.3% of the maximum theoretical value. The charging tendencies of nylon-6, polyethylene, and polystyrene shown by both the value of the time constant and the polarity, of the charge, agree with the triboelectric series.

Impact charging of insulators

Abstract Impact charge and area of a Nylon66 particle (3.18 mm in diameter) by a single impact on plastic plates (PTFE and PVC) were measured under various impact speeds νi (3.46–14.6 m/s) and impact angles θ (20°–80°). Before the measurement, the charge on the plastic plates was reduced to about 10%-1% of the charge previously accumulated on the plates by heat treatment in N2 gas. In the case of collision with a PVC plate, the impact charge density σi of the Nylon66 particles was +1.67 × 10−4 C/m2 which was almost constant for the charge in θ and νi. In the case of collision with a PTFE plate, it was changed from +0.35 × 10−4 C/m2 to +1.90 × 10−4 C/m2. It decreased with an increase in the vertical component of the impact speed νi cos θ and increased with an increase in the horizontal component of the impact speed νi sin θ. These results are interpreted in terms of wear of PTFE. The impact charge and the area were almost the same values as those obtained by the impact on the metal plate.

Relation between the Powder Charge and the Shape of the Pipe in Pneumatic Conveyance

The electrification of a polymer powder transported though U-bend pipes was studied at particle speeds of ν=17.6 m/s and 26.4 m/s, and a solid load p=0.017 kg / m3. The charge / mass ratio, q, of powder passing through the U-bend pipes (seven different radii of curvature) depended on the flow pattern of the powder particles after their first collision with the inner wall of the bend of the pipe.

Mechanism of Charge Build-up on Polymer Powders after Passage through Metal Pipes

The electrification of polymer powders transported through numerous charging units (up to 12 units) was studied at a mean particle speed v=7 m/s~26.4 m/s and a load ρ=0.006 kg/m3~2.5 kg/m3. Each charging unit consisted of a combination of a U bend and a straight pipe. The charge/mass ratio of the powder passing through the units grew exponentially and tended to saturate as the number of units increased. The powder particles were found to be electrified mainly in the U-bend pipes. The electric field Es caused by the charged particle cloud has a considerable effect on the saturation tendency of nylon 12 powder, but no effect on that or HDPE powder.

A Hot Cathode Magnetron Gauge using a Divergence-Type Magnetic Field for Electric Field Control

A new sensitive type of magnetron gauge has been developed in order to obtain a linear response of ion current, Ii, to pressure, P, with a high sensitivity over a wide range. The gauge is equipped with two ion collectors. The ratio of the ion currents of the two ion collectors is measured and kept constant by controlling the filament voltage, in order to keep the electric field constant within the anode over a wide range of pressure measurement. When a divergent-magnetic field is applied to this hot-cathode magnetron gauge, the slope of the plot of the filament voltage vs the ratio of the ion current of the two separate two ion collectors is improved from -0.28 to +1.1–+3.9 (V-1). When the diameters of the ion collectors were investigated, it was found that the current ratio η=1 was attained when the outer diameters of the ion collectors were identical, and their inner diameters were 2 and 8 mm respectively. With this configuration, ion current was directly proportional to pressure in the range of 1×10-8–1×10-4 Pa.