6 results
Search Results
Now showing 1 - 6 of 6
- ItemElectrical modelling and scale-up rules for glass melters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Α scale-up rule is developed to estimate the resistance for each circuit of a projected glass melter. Given all the internal sizes and contours including shapes of the electrodes as well as the power and power ratios and the resistivity of the molten glass for the proposed melter, this rule permits calculating the voltage and current for each of its circuits. Single-phase circuit-interactions, distributions of equipotential surfaces and lines of current and some safety considerations are discussed and illustrated for a multiplicity of electrodes and single-phase power supplies by using two-dimensional, isothermal, salt water models of electric melters. Phase relations that occur between currents in non-linear fluid conductors when additional transformers are used as currentbalancing means are also explored. This material is useful for understanding and designing electric melters.
- ItemGob weight fluctuations due to a stirrer and to glass melting firing reversals(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Spremulli, Paul F.It was difficult to adjust gob weights from a stirred, molten glass delivery System. The difficulty decreased when rotation of the gobbing stirrer was stopped. However, this was not a satisfactory Solution as it left objectional striations in the glass items being produced. The weight changes were due to the superposition of several effects, each of which by itself would have been acceptable. Small temperature fluctuations and spontaneous changes in the stirrer's position and stroke were found but they were not the major causes of the weight fluctuations. Cyclic variations in weight with an amplitude of about 1% and a period of about 11 min were due to the stirrer's rotation. It became clear that close but approximate matching of the gobbing and rotational rates was inadequate and that synchronization of these two rates had to be perfect to eliminate this cyclic weight Variation. The inevitable conclusion was that run-out associated with stirring was the cause of this problem. Α second cyclic Variation with a period of 20 min and an amphtude of about 0.4% was associated with tank reversals of the cross-fired melter with its regenerative checkers. This was the first time that weight changes due to tank reversals were noted. Α composite weight Variation curve was synthesized, with one component representing an 11 min cycle and a second component representing a 20 min cycle formed by a ramp with a linear decay Α comparison of the synthesized and actual weight curves revealed many similarities and strengthened the conclusion that most of the actual weight run changes resulted from the stirrer and from tank reversals.
- ItemCyclic gob weight and loading variations from stirred glass delivery systems(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Spremulli, Paul F.With stirred glass delivery Systems cyelic variations in gob weights and gob throws (the angles at which free falling gobs land in the molds) are caused by wobbly stirrers which are displaced (offset) from the delivery system's center line and rotating at speeds differing from the gobbing rate. This loss of Statistical process control disappears if the stirrer's rotational speed is synchronized with the gobbing rate. However, even in a perfect setup, if the stirrer is offset from its central location, a new steady weight and a constant hooking of the gobs away from the center and toward the smaller gap side result. Three equations are derived. One equation predicts the projected horizontal angle for the orientation of a gob as it lands in a mold. Another predicts the number of gobs before equal or almost equal weights repeat. Α third equation relates weight Variation to wobble and to the radial location of the rotating stirrer or needle. This equation shows the symmetry that may be expected in weight Variation curves. It is used to generate a normalized theoretical weight curve by setting the averaged percent differences between the maximum and minimum weights divided by the average weight to 1 %. This curve may also be used to disclose the number of gobs per cycle. Both loading and weight variations resulted when a non-centered, wobbling stirrer was modelled. The correlation between an experimental and a calculated weight Variation curve, due to the stirrer's rotation and normalized to 1%, was excellent. This investigation also showed that modelling could be extended to disclose changes in the weight (flow) of molten glass exiting from an orifice associated with a stirrer's rotation and alignment.
- ItemElectrical characteristics of horizontal glass melting furnaces and delivery Systems(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Leakage currents and their low resistance paths through refractories from the interior of glass melting furnaces to the binding steel are discussed. By defmition, a ground current flows from an electrode, through the intervening glass to ground through grounding conductors. All melters have leakage currents and may have ground currents. Current and voltage characteristics and phasor diagrams have been analyzed for some circuits that can be used in horizontal melters. The furnaces may be heated solely with electricity or in conjuncdon with fossil fuels. Phasor diagrams may be helpful in the design stage of a melter, may be useful for trouble-shoodng and to display electrical distributions for all parts in a precise form. Hence, totally unexpected voltage differences become easily understandable. Phasor diagrams can disclose wiring errors and/or undesirable voltage distributions and may suggest ways to improve electrical characteristics. For symmetrically built and cross-fired furnaces they show side-to-side symmetry and indicate that the central plane of these units can be Virtual or phantom grounds. They may also indicate the conditions minimizing voltage differences between adjacent electrodes. Voltage phasor diagrams are even more useful for longitudinally fired furnaces. For these units they also explain why ground currents occur and how to minimize them. Data from a salt water model with two cross-fired circuits connected to the same phase disclosed linear relations between the electric currents and voltages over a large range. In this ränge each line current was a hnear function of the two line voltages and vice versa and these variables could be treated as scalars. In addition, either line current could be forced to zero by appropriate voltage(s) in the other circuit. Somewhat similar results were obtained when two different phases were used but now neither current could be forced to zero by adjusting the voltage in the other circuit. Again in the linear range each hne current was a linear function of the line voltages and vice versa but the variables now had to be treated as phasors and not as scalar quantities. Salt water modelling with a longitudinally fired melt end yielded representative data showing how the applied voltages may be located on a ground current's voltage phasor in both the capped and uncapped condition.
- ItemPhysical modelling of flow behavior in a stirred glass system(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Spremulli, Paul F.As stirring efficiency made the use of isothermal models plausible, dimensional analysis was used to extend model laws to include stirrers, gobbing cams and to indicate the conditions required to get data representative of actual or proposed units. Based on fullsize modelling, the production department installed stirred glass set-ups and made excellent products. Correlation between modelling and production was excellent and included mechanical variables and temperatures. Furthermore, a new delivery system, including a new gobbing cam designed for a very fluid photosensitive glass, was based on modelling and behaved exactly as predicted. Upsets in the stirred glass, delivery Systems resulted in slow cyclic weight variations of about 1 %. As the weights of the items being made were specified to within ±1.0%, it was clear that control had to be improved. The weight changes were not caused by compositional changes in the glass but to some Instrumentation problems and to some unique, unknown problem(s) associated with stirring. Thus, a better understanding of how temperature and the stirrers controlled flow was needed. Assuming that flow is inversely proportional to viscosity showed that the change in weight should be about 0.9%/°C. This number is about 1 0% too low compared with the empirical value of 1 %/°C quoted by Operators. Next data from a full-size, stirred model were summarized in an equation which relates flow to the viscosity of the fluid and to the rotational speed and vertical position of the stirrer. Partial differentiations and evaluations of this equation at a nominal operating condition showed that the weight should first, vary by 1.02%o/°C, second, decrease by 0.90% per rpm increase and third, increase by 0.80% when the stirrer was raised (0.006") or 1 % when it was at the 5/8" position.
- ItemPhasors for fluid conductors and vertical electric glass melters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Phasors are useful in electrical engineering but they are even more useful when used to display and/or explain phenomena associated with fluid conductors. Phasor diagrams include not only the applied voltages but all the voltages found in the fluid. This has been illustrated by constructing and discussing phasor diagrams for a variety of circuits used in vertical glass melters. It has been shown that these diagrams can disclose wiring errors and/or undesirable voltage distributions. In many cases they can lead to designing improved circuits and/or alternate circuits which may have equivalent voltage distributions. Phasor diagrams have also been used as an aid in designing new circuitry with symmetrical electrical distributions. Simultaneous consideradon of current and voltage phasors yields correct phase angles and equations to calculate power.