Browsing by Author "Kawachi, Shinji"

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    Diagnosis and treatment of bubbles in glass production using a numerical Simulator
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Kawachi, Shinji; Iwatsubo, Yoshio
    A methodology to evaluate the bubble removing Performance of a tank furnace was proposed in previous papers. Since the operating data of the furnace being used for actual production can be udlized to examine the effectiveness of the above proposal, this paper deals with the verification issue when this methodology is applied to a real furnace. Additionally, various indirect indices, which have been advocated to evaluate the bubble removing Performance, are compared with the proposed direct Simulation. The results show that the phenomena experienced in the factory can be clearly explained and the direct Simulation has been proved to be very useful to diagnose and to treat bubbles during actual producdon.
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    Evaluation of bubble removing Performance in a TV glass furnace : Part 1. Mathematical formulation
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Kawachi, Shinji; Kawase, Yoshinori
    The bubble evolution and dissolution process in a glass furnace is an extremely complicated physico-chemical phenomenon. Most of the huge number of bubbles, generated in molten glass during the decomposition of the glass batch, are removed during the trajectory from the charging end to the forming section, but some remain in fmal products. On the basis of the two mechanisms, flotation and absorption, in the bubble removing process, a numerical Simulator was developed to evaluate the influence of first, glass and batch composition, including refining agents, second, geometrical tank design and third, furnace operating conditions upon the bubble quality in products. In particular, the Simulator enabled the estimation of the effect of refining gases which are caused by decomposition of the refining agents. Furthermore, an index was devised to synthetically assess the numbers of bubbles in final products. In part 1, the principles of the model which composes the Simulator are described in mathematical formulation. The basic equations with boundary conditions and calculation procedures for thermal flow of molten glass, gas concentration in glass melt and gas evolvement from the refining agents are presented. The calculation strategy of the bubble removing process is also described.
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    Evaluation of bubble removing Performance in a TV glass furnace : Part 2. Verification using real furnace data
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Kawachi, Shinji; Kawase, Yoshinori
    In part 2, a furnace for melting TV panel glass is studied to examine the effectiveness of the Simulator developed by the authors. Because panel glass is used as a part of a cathodic ray tube where the TV image is projected and its defect is easily recognizable, bubble-free glass quality is defmitely required. If the bubble quality becomes worse, a heap of rejected products is piled up, which leads to tremendous economical loss. In order to avoid such trouble designing and operating a TV glass furnace and inspecting glass quality are conducted with great care, and therefore, lots of field data have been accumulated so far. Accordingly, it is meaningful to utilize a TV glass furnace to verify the effectiveness of such simulating technology. The values and phenomena predicted by the Simulator and the data having been observed in real furnaces were found to be in reasonable agreement. Therefore, it may be concluded that the proposed Simulator is useful as a method of scale-up and trouble-shooting for glass furnaces.
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    Evaluation of reaction rate of refining agents
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Kawachi, Shinji; Kato, Mitsuo; Kawase, Yoshinori
    To elucidate the thermal decomposition behavior of antimony oxide which is added to promote (re)fming of bubbles in TV glass, an evolved gas analysis (EGA) was conducted using a newly designed device for detecting the gases from the glass batch at increasing temperatures. Furthermore, a mathematical formulation was made to describe the above behavior. From the results of the EGA measurements, three parameters, which govern the reaction rate constant, viz. reaction order, activation energy and frequency factor, were decided. By coupling this mathematical model and the thermal fluid model of glass melts in tank furnaces, it is possible to simulate the conditions of generating refming oxygen in the furnace.