Kasuga Denki Inc.

Kawasaki, Japan

Kasuga Denki Inc.

Kawasaki, Japan
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Choi K.S.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Kim S.C.,Chungbuk National University | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2013

As a method to prevent or mitigate electrostatic charge and/or discharges, we have developed a novel AC electrostatic ionizer. In this study, we evaluated experimentally the practical version of the novel AC electrostatic ionizer with a modeling test system and a pneumatic powder transport facility. In addition, electrostatic discharges generated inside a silo while loading polypropylene (PP, 3 mm) granules were observed visually with/without the novel AC ionizer. The specific charge was clearly decreased with the novel AC electrostatic ionizer. The specific charge obtained with the four arranged AC electrostatic ionizers used was approximately one eighth of that without the AC ionizer. The incendiary bulk surface discharges completely died out inside the silo by using the four arranged ionizers. © 2012 Elsevier Ltd.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc.
Review of Scientific Instruments | Year: 2014

To detect electrostatic discharges generated by polymer granules within a metal silo, we developed a novel and simple electrostatic discharge detector that utilizes a photosensor. The novel detector consists of a photosensor module in a metal cylinder, an optical band-pass filter, a quartz glass, a power supply, an amplifier for the photosensor module, and a digital oscilloscope. In this study, we conducted experiments at a real pneumatic powder transport facility that includes a metal silo to evaluate the novel detector using polypropylene granules. To determine the performance of the novel detector, we observed the electrostatic discharge within the metal silo using a conventional image intensifier system. The results obtained from the experiments show that the novel detector worked well in this study. The signals obtained with the novel detector were identical to the electrostatic discharges obtained with the conventional image intensifier system. The greatest advantage of this novel detector is that it is effective even when placed under external lights. In addition, the influence of various optical band-pass filters on the performance of the novel detector was discussed. Our study confirmed that an optical band-pass filter with a center wavelength of λ 330 nm (λ 1/2: 315-345 nm) was the best performer among the optical band-pass filters used in this study. © 2014 AIP Publishing LLC.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Global Congress on Process Safety 2014 - Topical Conference at the 2014 AIChE Spring Meeting and 10th Global Congress on Process Safety | Year: 2014

This paper is a report on the relationship between the charge amount (charge to mass ratio) of polypropylene (PP) granules and the electrostatic discharges that occur while loading a metal silo. The feedback control system was used in order to control the charge to mass ratio of PP granules. The electrostatic discharges inside the silo were also observed using a conventional image-intensifier system. The results obtained from the experiments show that (1) two kinds of electrostatic discharges were clearly observed inside a metal silo while loading PP granules, i.e., brush discharges and incendiary bulk surface discharges; (2) the number of brush discharges and incendiary bulk surface discharges increased with the increase in the charge to mass ratio of PP granules, almost reaching saturation; and (3) brush discharges and incendiary bulk surface discharges began to occur at the -1.16 μC/kg and -2.33 μC/kg points in the charge to mass ratio, respectively, in this study.


Mogami T.,Ibaraki University | Suzuki T.,Kasuga Denki Inc. | Choi K.S.,National Institute of Occupation Safety and Health | Ikehata T.,Ibaraki University
Journal of Loss Prevention in the Process Industries | Year: 2010

As a method to prevent or mitigate cone discharges in a specific section such as a large silo, we have developed a new feedback control-type ionizer system. The feedback control-type system is composed mainly of an ionizer, an electrostatic field strength meter, and computer control equipment. In this study, we evaluated experimentally the practical version of the feedback control-type ionizer system through several tests in a pneumatic powder transport facility. The specific charges of the falling pellets in the silo were also measured for 10 s using a Faraday cage. Polypropylene (PP) pellets with a mean particle size of 3 mm were used in this experiment. The results of the experiment revealed that the feedback control-type ionizer system had the following characteristics: (1) it is possible to control the performance of the ionizer with a supply current; (2) the electrostatic field strength in the loading pipe from the charged powder is reduced and maintained at near zero by using the feedback control-type system; and (3) the performance of the feedback control-type system is superior to that of others, such as the conventional AC- or DC-type ionizers. © 2009 Elsevier Ltd. All rights reserved.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2016

As a method of preventing or mitigating explosion due to electrostatic discharges during the loading of polymer granules in a metal silo, we have developed a novel bipolar electrostatic ionizer. In this study, we investigated experimentally a practical version of the bipolar electrostatic ionizer with a modeling test device to measure the charge-neutralizing current, and a full-sized pneumatic powder transport facility. The electrostatic discharges generated inside a silo while loading polypropylene (PP) granules were also observed visually with/without the novel bipolar electrostatic ionizer. As a sample, 300 kg of polypropylene granules 2-3 mm in size was used in this study. The specific charge of the polypropylene granules was clearly decreased by approximately 85 percent with the novel bipolar electrostatic ionizer. The brush discharges, as well as the incendiary bulk surface discharges, completely died out inside the silo when the novel bipolar electrostatic ionizer used. © 2016 Elsevier Ltd.


Choi K.,National Institute of Occupation Safety and Health | Mogami T.,Kasuga Denki Inc. | Suzuki T.,Kasuga Denki Inc. | Yamaguma M.,National Institute of Occupation Safety and Health
Journal of Loss Prevention in the Process Industries | Year: 2014

This paper is a report on the relationship between the charge amount (charge to mass ratio, q/. m) of polypropylene (PP, 2-3mm) granules and the frequency of electrostatic discharges that occur while loading a metal silo. The feedback control system was used in order to control the q/. m of PP granules. The electrostatic discharges inside the silo were also observed using a conventional image-intensifier system. The charging control range for PP granules was from 0 to-12μC/kg in the q/. m. The results obtained from the experiments show that (1) two kinds of electrostatic discharges were clearly observed inside a metal silo while loading PP granules, i.e., brush discharges and incendiary bulk surface discharges; (2) the number of brush discharges and incendiary bulk surface discharges increased with the increase in the q/. m of PP granules, almost reaching saturation; and (3) brush discharges and incendiary bulk surface discharges began to occur at the-1.16μC/kg and-2.33μC/kg points in the q/. m, respectively, in this study. © 2014 Elsevier Ltd.


Sugimoto T.,Yamagata University | Yamaguchi K.,Yamagata University | Yamaguchi K.,Showa Denko K.K. | Higashiyama Y.,Yamagata University | Nomura N.,Kasuga Denki Inc.
IEEE Transactions on Industry Applications | Year: 2014

Real-time monitoring of the cure state of sprayed paint is important for industrial painting processes to determine appropriate leveling and drying times. Paints contain pigment, resin, solvent, and other additives. The solvent is generally conductive and is finally evaporated during the paint-curing process, which results in a change in the electrical properties of the painted layer, from conductive to insulative. Therefore, we propose a technique to measure the cure state of a painted layer from the change in its surface resistance. The measurement apparatus includes a corona charger and surface potential probes. The surface resistance can be estimated from the increase in potential during corona charging. The degree of cure Dc is determined as a function of the surface potential. Pencil hardness, which is a general measure of the degree of cure, was also measured for comparison. A linear relationship between Dc and the pencil hardness was determined for various paints, which suggests that the degree of cure can be monitored according to Dc estimated from surface potential measurements. © 1972-2012 IEEE.


Yamaguma M.,Japanese National Institute for Occupational Safety and Health | Choi K.S.,Japanese National Institute for Occupational Safety and Health | Mogami T.,Kasuga Denki Inc.
Journal of Loss Prevention in the Process Industries | Year: 2010

While filling a large silo with coarse nonconductive powders, strong electrostatic sparks known as a cone discharge, which can become sufficiently energized to ignite a flammable dust cloud, often occur on the surface of a powder heap. In an attempt to mitigate or eliminate a cone discharge, a long metal rod with a pointed tip or a flat tip was vertically installed in the center of an experimental silo (1.5 m in diameter, 2 m in effective height) with the objective that the static charge might be released by the corona discharges or the surface potential of the powder heap reduced by the electric field reducing effect. The experimental results are summarized as follows:. (1) No cone discharges were observed while the silo was being filled with polypropylene pellets when either a pointed tip or a flat-tip rod was installed so that its lower end was located 10 cm above or 30 cm below the heap surface level. A corona discharge that occurred on the pointed tip was shown to be effective to some extent in reducing the charge of the powder heap.(2) Brush discharges were observed near the metal rod and its support. However, we assume that the maximum energy was not high enough to ignite a dust cloud with minimum ignition energy greater than 3 mJ. © 2010 Elsevier Ltd.


Ohsawa A.,Japanese National Institute for Occupational Safety and Health | Nomura N.,Kasuga Denki Inc.
Journal of Electrostatics | Year: 2013

We present an experimental demonstration of a prospective idea obtained from 2-D electrohydrodynamic simulations in which continuously emitting balanced positive and negative ions from corona ionisers can yield zero offset voltage. © 2013 Elsevier B.V.


Ohsawa A.,Japanese National Institute for Occupational Safety and Health | Nomura N.,Kasuga Denki Inc.
Journal of Electrostatics | Year: 2016

In our previous work, the AC type of ionisers was employed to demonstrate a prospective theory obtained by numerical simulations in which continuously emitting quasi-neutralised positive and negative ions from corona ionisers can transport ions effectively to a charged object and yield zero offset voltage. In this paper, we show that this can also be applied to pulse-DC ionisers, resulting in significant improvements in the offset voltage as well as charge-decay times. In addition, we present an implementation method with an electronic circuit design to create such an ion emission from a pulse-DC ioniser. © 2015 Elsevier B.V.

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