Glass melting furnace, and method of operating a furnace

Abstract: A glass melting furnace comprises a base structure (6) defining a melting chamber (8) an intermediate chamber (10), and a working chamber (12), in which chambers heating means are located. An opening (22) is provided into the melting chamber (8), through which batch material may be deposited on the body of molten glass in the melting chamber. Glass flows from the melting chamber (8) through an outlet (26) at a lower part thereof, which opens into the intermediate chamber (10), and flows over a weir (30) from the intermediate chamber (10) into the working chamber. Located in the outer walls of the working chamber are working outlets (34), through which blowing irons or the like tools may be entered, for a manual withdrawal of molten glass from the chamber (12). The rate of production of molten glass by the melting chamber (8) is lower than the rate of utilisation, such that during a working shift the level of glass in the working chamber falls from a maximum level towards a minimum level, and outside the working shift (e.g. overnight) the level in the working chamber increases from the minumum level to a maximum level. Overflow ducts are provided, at locations which define the maximum level of glass in the working chamber i.e. a short distance below the locations of the working outlets (34).

Description: This invention is concerned with improvements relating to the melting of glass, particularly by a method involving the use of a furnace comprising a melting chamber wherein glass is melted, and a working chamber from which molten glass is withdrawn from time to time. The invention is particularly concerned with the melting of glass for use in the production of hand made articles, molten glass being withdrawn from the working chamber as it is required for use by an artisan for the production of an article. The term "glass" is used herein generically, and includes a variety of heat fusable vitreous materials of differing compositions. A convenient form of glass melting furnace comprises a melting chamber containing a body of molten glass, heating means in the chamber to supply heat to the molten glass, and means to deposit solid state batch material generally onto the top of the body of molten glass. The batch material is progressively melted from the lower surfaces of the layer, whilst molten glass flows from an outlet of the furnace chamber, via an intermediate chamber, into a working chamber fresh batch material being supplied to the top of the melting chamber to retain the layer of batch material at a desired depth. Such a furnace is hereinafter referred to as being of the kind specified. Molten glass is withdrawn for use in a production process, (which may be manual or automatic) from the working chamber. Furnaces of the kind specified are well suited to continuous, uniform production, and whilst efforts have been made to enable the output of such furnaces to be varied, it has not proved possible satisfactorily to utilise such furnaces in circumstances where the requirement for glass varies widely, particularly in a way in which the temperature of the furnace is not subjected to potentially damaging fluctuations. This is particularly the case where the heating means comprises electrodes to heat the body of molten glass by the Joule effect. In particular, in the production of hand made articles, it has heretofor been generally necessary, when using a glass melting furnace of the kind specified, to work a full three shift system, which is in many instances unacceptable or unsatisfactory. Suggestions have been made to solve this problem by allowing the level of glass in the melting chamber to fall during a working shift, and to rise during a non-working shift, continued production whilst at maximum level causing glass to be overflowed to solidify, for subsequent reintroduction into the melting chamber of the furnace. The above problem occurring with furnaces of the kind specified is solved in accordance with the present invention by the characterisation that the molten material produced in the melting chamber is flowed over a weir located in the intermediate chamber between the melting chamber and the working chamber whereby the level of molten glass in the melting chamber is maintained at a constant level, whilst the level of glass in the working chamber falls during a working period and rises during a non-working period. By thus enabling glass to be melted in the melting chamber at optimum unchanging conditions, a highly reliable quality of glass may be produced, together with optimum power consumption. Thus when operating on a single shift (8 hour) system, the relationship between V, the volume of the working chamber, P, the daily production rate of glass from the melting chamber and R, the daily rate of utilisation of glass will be approximately as follows: V = 2 3 P+C; and R = 1 3 P + (V-C) the volume of glass in the working chamber being reduced to a minimum volume C at the end of a shift and being increased to a maximum by the commencement of the following shift. For days without working (such as Sundays) drainage outlets may be provided for excess glass to flow from the working chamber when it is full, the glass being allowed to solidify and subsequently being re-introduced into the melting chamber as cullett. Desirably the glass is continuously stirred in the working chamber, conveniently by a stirrer operative adjacent to the surface of the glass in the working chamber. Thus preferably a stirrer is used which follows the level of the glass in the working chamber, to retain a position just below the surface as the glass level in the chamber rises and falls. Desirably the body of the molten glass in the working chamber is heated by heating means operative in conjunction with sensor means. Desirably the heating means comprises electrical heating means, including electrodes in the working chamber, below the minimum level, and desirably also means to direct heat to the surface of the body of molten glass in the working chamber. Preferably molten glass is introduced into the working chamber into a lower region of the working chamber, preferably below the minimum permissible level therein. Desirably the molten glass in the intermediate chamber is heated by heating means operating in conjunction with temperature sensors, and desirably said heating means comprises electrical heating means, including electrodes in the intermediate chamber below the level of glass therein, and desirably also means to direct heat to the surface of the body of molten glass in the intermediate chamber. According to this invention there is also provided a furnace comprising: (1) a melting chamber including (a) means for feeding solid material into said melting chamber, and (b) means for melting the solid material in said melting chamber, (2) an intermediate chamber, and (3) a working chamber for receiving melted material from said melting chamber including: (a) at least one working outlet means for said melted material, and (b) an overflow outlet means in said working chamber at a level below said working outlet; characterised in that in the intermediate chamber between the melting chamber and the working chamber is located a weir means over which melted material flows as it passes from the melting chamber to the working chamber whereby a constant level of material is maintained in the melting chamber whilst the level of material in the working chamber varies. There will now be given a detailed description, to be read with reference to the accompanying drawings, of two glass melting furnaces which have been selected for the purposes of illustrating the invention by way of example. FIGURE 1 is a vertical sectional view of the furnace which is the first embodiment of this invention; FIGURE 2 is a horizontal sectional view of the furnace shown in FIGURE 1; FIGURE 3 is an underneath plan view of the first embodiment; FIGURE 4 is a vertical sectional view of the furnace which is the second embodiment of the invention; and FIGURE 5 is the view corresponding in part to FIGURE 2, and in part to FIGURE 3, of the second embodiment. The furnace which is the first embodiment of this invention comprises a base structure 6 defining a melting chamber 8, an intermediate chamber 10, and a working chamber 12, the base structure comprising an inner layer 14 of an AZS refractory, an outer layer 16 of refractory brick, and an intermediate bedding layer 18, conveniently of a bedding material such as "Ersol" which is a combined insulating-and-bedding cement material produced by the company "SEPR" of Le Pontet, near Avignon, France. Mounted on the base structure is a roof structure 20, effectively enclosing the three furnace chambers. Extending into the melting chamber 8 is an opening 22, through which batch material, optionally comprising cullett, may be deposited generally continuously on the body of molten glass within the melting chamber, conveniently by mechanical means, if desired to cover the body of molten glass to a uniform depth. Located in the walls of the melting chamber are electrodes 24, such as of tin oxide. In use, passage of electrical current between the electrodes 24 heats the body of molten class in the melting chamber 8 by the Joule effect, causing the blanket of batch material on the surface to be progressively melted, and assimilated continuously into the body of molten glass. Extending from the melting chamber 8 at a lower part is an outlet 26, which opens into the intermediate chamber 10. Extending upwardly from the floor of the intermediate chamber 10 is a weir 30, which extends to a level approximating to that of the interface between batch material and molten glass in the melting chamber 8. The weir 30 effectively divides the intermediate chamber 10 into an upstream or riser section 10 a , wherein wall electrodes 28 are located, and a downstream section 10 b , from the base of which an outlet 32 extends into the bottom of the working chamber 12. Radiant heaters 29 extend downwardly into the intermediate chamber 10 from the roof 20. Located in the outer wall of the working chamber are working outlets 34, through which blowing irons or the like may be entered, for a manual withdrawal of molten glass from the chamber 12, conveniently located a short distance above (e.g. 25 mm) the maximum level of glass in the working chamber, as determined by the position of drainage channels 44. Mounted in the roof structure is a stirrer assembly 36, comprising means (not shown) to raise and lower a head 38 of the stirrer assembly. The stirrer assembly also comprises sensing means (not shown) to sense the level of molten glass in the working chamber, and to cause the head 38 to rise and fall with rising and falling movement of the level of molten glass, so as to retain the head 38 somewhat below the level of molten glass. Located in the wall of the working chamber adjacent the bottom thereof are wall electrodes 40, and located in the roof of the furnace above the working chamber are a plurality of radiant heaters 41. As with the intermediate chamber, sensing means is provided continuously to sense the temperature of the body of molten glass in the working chamber, than to control the operation of the electrodes 40 and radiant heaters 41 accordingly. In the use of the furnace which is the first embodiment of this invention, batch material introduced into the melting chamber 8 through the opening 22 is continuously melted, and flows through the outlet 26 in to the riser section 10 a of the intermediate chamber, upwardly and over the weir 30, the glass being further conditioned or refined during this process. Glass will be withdrawn manually through the openings 34 from the body of molten glass in the working chamber, and during the working shift this volume will fall, being withdrawn at a rate which is greater than that of replenishment by freshly melted glass from the intermediate section. As the level falls, the stirrer head 38 is lowered, retaining the glass in good condition. As the shift progresses, the level will fall progressively, until it reaches the minimum level, marginally above the position of electrodes 40. At the end of the shift, the openings 34 will be plugged with stoppers 35, to minimise lost heat, and continually melting glass by the melting chamber will replenish the reduced volume by the commencement of the following shift. Thus, by the use of the invention, glass may be produced in the melting chamber, to flow into the working chamber, on a generally continuous basis, allowing bath for the maintenance of a high quality of production, and for the maintenance of a generally unchanging temperature throughout extended periods of operation of the furnace, minimising any subjection of the furnace, particularly the walls and electrodes thereof, to potentially damaging thermal shock. To cater for the circumstances where the working chamber 38 is filled to a desired level prior to commencement of the following shift (which may be caused by an extensive period between adjacent shifts, such as a weekend or Public Holiday, or by an under utilisation of glass during the previous shift) surplus gloss may flow through the drainage channels 44 to a cooling area, within which the surplus glass solidifies, to be used subsequently as cullet. In addition, a main bottom drain 46 is provided, which will only be utilised when it is required to empty the chamber 12. It has been found, surprisingly, that an adequate relationship between the volume of the melting chamber 8, and the rate at which fresh glass is meted, and the volume of the working chamber 12, and the rate at which glass is utilised, is such that a furnace may be provided in accordance with this invention which adequately copes with a withdrawal of glass over only an 8 hour shift, and the accumulation of glass during a following two shift, 16 hour period within which glass is not removed from the working chamber. In this manner, the benefits of of a furnace of the kind specified may be utilised in glass making areas where previously this was not practical. In addition, it has been found that the specific energy requirements (kilowatt hours per kilo) for the production of glass by the method in accordance with this invention is not significantly higher, and indeed may be less, than the energy requirements of a comparative contemporary method. The capability of almost wholly enclosing the furnace, particularly during periods where glass is not being withdrawn from the working chamber, allow for relatively small heat losses, and the achievement of a more uniform and constant temperature distribution thoroughout the furnace, reducing damage caused to the furnace through the occurrence of thermal shock. The furnace which is the second embodiment is similar to the first embodiment above described, and similar numerals with an apostrophe (') are used to indicate equivalent parts. Primarily the furnace which is the second embodiment differs from the first in geometry, but additionally electrodes 28 a and 28 b are provided in both the riser section 10 a ' and the downstream section 10 b ' of the intermediate chamber 10'. These electrodes, as with the roof electrodes 29', control the temperature of glass as it flows through the intermediate chamber in response to temperature sensing devices. It has however been found that passage of electricity between the electrodes 24 and 28 a through the outlet 26, and between the electrodes 28 b and the electrodes 40' through the outlet 32, provides for the maintenance of a higher quality of glass in the working chamber.

Claims: A method for melting glass in a furnace having a melting chamber (8), an intermediate chamber (10) and a working chamber (12) in which said solid material is fed into said melting chamber (8), to be continuously melted therein, and via said intermediate chamber continuously flowed into said working chamber (12), and melted material being withdrawn from said working chamber (12) during working periods at a rate greater than the rate at which fresh molten glass is produced, characterised in that molten material produced in the melting chamber is flowed over a weir (30) located in said intermediate chamber (10) between the melting chamber (8) and the working chamber (12) whereby the level of molten glass in the melting chamber is maintained at a constant level, whilst the level of glass in the working chamber falls during a working period and rises during a non-working period. A method according to claim 1 including maintaining a predetermined temperature of said melted material in said working chamber (12). A method according to one of claims 1 and 2 including overflowing said melted material from said working chamber (12) to prevent the melted material from rising in said working chamber (12) above a predetermined level. A method according to any one of the preceding claims including stirring said melted material in said working chamber with a stirring means (36, 38). A method according to claim 4 including maintaining the stirring means (36, 38) at a constant depth below the surface of said melted material in said working chamber, regardless of the changes in level caused by difference in flow of said melted material into and out of said working chamber. A furnace comprising: (1) a melting chamber (8) including (a) means (22) for feeding solid material into said melting chamber (8); and (b) means (24) for melting the solid material in said melting chamber, (2) an intermediate chamber (10), and (3) a working chamber (12) for receiving melted material from said melting chamber (8) including: (a) at least one working outlet means (34) for said melted material, and (b) an overflow outlet means (44) in said working chamber at a level below said working outlet; characterised in that in said intermediate chamber (10) between the melting chamber (8) and the working chamber (12) is located weir means (30) over which melted material flows as it passes from the melting chamber to the working chamber whereby a constant level of material is maintained in the melting chamber whilst the level of material in the working chamber varies. A furnace according to claim 6 including means (40, 41) for maintaining a predetermined temperature of said melted material in said working chamber, comprising electric heating means above and below the surface of said melted material. A furnace according to one of claims 6 and 7 including stirring means (36, 38) in said working chamber (12) for stirring said melted material. A furnace according to claim 8 including means for adjusting said stirring means (36, 38) to maintain a predetermined position below the level of said melted material, regardless of the variations in said level. A furnace according to claim 9 wherein said means for adjusting said stirring means includes a sensor for measuring the level of said melted material in said working chamber. A furnace according to any one of Claims 6 to 10 wherein melted material flows from said intermediate chamber (10) into a lower portion of said working chamber (12). A furnace according to any one of the preceding claims wherein said working outlet means (44) in said working chamber includes means for plugging said outlet means. The invention according to any one of the preceding claims wherein the means for melting said solid material in the melting chamber comprises electrodes (24, 28, 40) employing the Joule effect. The invention according to any one of the preceding claims wherein said melting chamber (8) and said working chamber (12) are substantially wholly enclosed with a roof means (20).

Inventors: DULY RAYMOND KENNETH, FLAVELL JAMES ALAN, DULY, RAYMOND KENNETH, FLAVELL, JAMES ALAN
Applicants: TOLEDO ENGINEERING CO INC, TOLEDO ENGINEERING CO. INC.
Application year: 1989
Main classification: C03B5
IPC codes: C03B5, F27B14