Method and apparatus for delivering a glass stream for forming charges of glass

Abstract: A method and apparatus for delivering a glass stream comprising a first inner layer and a second outer layer, comprising a generally vertical orifice (20), and delivering glass from a second source (24) such that the glass from said second source provides an outer layer about the glass from the first source (22) as it flows through said orifice (20). A resistance heated tube assembly (30) is made of platinum or material having similar resistance heating properties and extends from a glass source to an orifice through which the glass flows from a glass source for the inner layer. The tube assembly (30) includes a tube portion (34) having an inlet end that communicates with the source for the outer layer and an outlet end that communicates with the source. The tube portion (34) has an axis positioned at any angle ranging between the horizontal and vertical but preferably has an axis which is more vertical than horizontal. Flanges (36, 38) are secured to the ends of said tube portion (34), and the flanges are connected to an electric power supply. The cross sectional thickness of said flanges (36, 38) is preferably greater than the thickness of the tube portion (34). Each flange includes an annular groove (42) adjacent its respective end of the tube portion into which the end of said tube portion extends. The flanges (36, 38) are welded to the tube portion (34). Flange heater modules (60, 70) surround each end of the tube portion (34).

Description: This invention relates to an apparatus for forming a glass stream of a first inner layer and a second outer layer, to a resistance heated tube assembly and to a method for forming the glass stream. The purpose of this invention is to deliver a stream of molten glass, at maintained temperature, to a remote location and particularly to combine two streams of molten glass in a location of limited size and accessibility. Background of the invention Existing glass coating techniques involve the introduction of multiple glass streams in the forehearth or furnace section of the glass forming operation. This requires new equipment to be installed for the handling of main glass stream as well as the coating glasses. Typical patents showing such construction, for example, are USs-A-1,828,217, 3,291,584, 3,554,726, 3,960,530, 4,023,953, 4,217,123, 4,299,609, 4,381,932 and 5,204,120. An apparatus of the kind referred to in the preamble of claim 1 is known from US-A-4740 401. The feeder tube for the glass of the second outer layer is surrounded by electrical resistance heating elements, but does not form part of an electrical resistance heating element and does not have flanges at the opposed ends for attachment to a source of electrical power. A resistance heated tube assembly for delivering molten glass from a source to a nozzle feeder with the features of the preamble of claim 9 is known from US-A-3,589,879. Electrical power is supplied to current lead members and bushing members to tubes made of a platinum-rhodium alloy. The tubes do not have flanges. The nozzle feeder does not belong to apparatus for delivering encased glass streams having an inner layer and an outer layer. Conventional forehearths for glass delivery are constructed of refractory brick. The glass is contained in a horizontal bath. Heat is maintained by radiant heating from combustion burners above the bath. Bath depth is limited to about 25.4 cm (10") due to the practical limitations of infrared heat penetration. Alternately, electric current may be passed through the molten glass to maintain temperatures. In either case, the glass is contained within the refractory ceramic brick. In a typical forehearth, the inner-most refractories are very dense to resist glass attack. The outer layers are progressively less dense for their insulation properties. The overall wall thickness is typically from 25.4 to 45.7 cm (10 to 18 inches). The overall width of the forehearth is several feet, therefore the placement of two forehearths in order to combine two glass streams is not possible. Summary of the invention The present invention provides for conveying glass from a remote location without the need for heavy refractories and radiant heating and in close proximity (10.2 to 30.5 cm, 4 to 12") to another glass stream. The method and apparatus of the present invention is directed to delivering a glass stream of a first inner layer and a second outer layer, comprising delivering molten glass from a first source through a generally vertical orifice, and delivering glass from a second source such that the glass from said second source provides an outer layer about the glass from the first source as it flows through said orifice. An objective of the present invention is to improve the method and apparatus for conveying the glass from the second source to provide the outer layer. The invention is defined in claims 1, 9 and 14. The apparatus and method of invention provide the following advantages: The glass is conveyed while efficiently maintaining uniformity of temperature of the glass. The apparatus is similar in function and smaller in design than a conventional foreheath. Changes in existing glass delivery equipment for the primary glass stream can be minimized. Complete glass containment is possible. Desired hydrostatic head pressure of the secondary glass stream can be provided. In accordance with the invention, a resistance heated tube assembly is made of platinum or material having similar resistance heating properties and extends from a glass source for the outer layer to the orifice through which the glass flows from a glass source for the inner layer. The tube assembly includes a tube having an inlet end that communicates with the source for the outer layer and an outlet end that communicates with the orifice The tube has an axis positioned at any angle ranging between the horizontal and vertical but preferably has an axis which is more vertical than horizontal. Flanges are secured to the ends of said tube and the flanges are connected to an electrical power supply. The cross sectional thickness of said flanges is preferably greater than the thickness of the tube Each flange includes an annular groove adjacent to an opening enclosing the respective end of said tube. The portions of reduced thickness of the flanges, formed by said annular grooves, are welded to the tube. Flange heater modules may surround each end of the tube. Description of the Drawings FIG. 1 is a fragmentary part sectional diagrammatic elevational view of a glass delivery system embodying the invention. FIG. 2 is a part sectional elevational view of a resistance heated tube assembly embodying the invention. FIG. 3 is a sectional view of the tube assembly taken along the line 3-3 in FIG. 2. FIG. 4 is a part sectional view taken along the line 4-4 in FIG. 2. FIG. 5 is a fragmentary elevational view taken along the line 5-5 in FIG. 1. FIG. 6 is a fragmentary sectional view of the upper flange of the delivery tube taken along the line 6-6 in FIG. 7. FIG. 6A is a fragmentary sectional view of a portion of the delivery tube shown in FIG. 6. FIG. 7 is a top plan view of the upper flange of the delivery tube. FIG. 8 is a part sectional side elevational view of the upper flange. FIG. 9 is a bottom plan view of the lower flange of the delivery tube. FIG. 10 is a part sectional side elevational view of a lower portion of the delivery tube taken along the lines 10-10 in FIG. 9. FIG. 11 is a schematic of the electrical heating system of the delivery tube. Description of the Preferred Embodiments Referring to FIG. 1, the invention relates to a method and apparatus for delivering a glass stream comprising a first inner layer and a second outer layer, comprising a generally vertical orifice 20, delivering molten glass from a first source 22 through said orifice 20, and delivering glass from a second source 24 such that the glass from said second source 24 provides an outer layer about the glass from the first source 22 as it flows through said orifice 20. Glass sources 22, 24 comprise conventional forehearths. In accordance with the invention, an electrical resistance heated delivery tube assembly 30 is provided for delivery of glass from the second source 24 through a refractory orifice ring assembly 32 which contains glass from the source 22 and the source 24 to provide a molten glass with a core of glass from source 22 and an outer layer from source 24. As shown in FIG. 2, the tube assembly 30 includes a tube 34 through which the glass flows from a glass source for the inner layer. The tube 34 has an inlet end that communicates with the source for the outer layer and an outlet end that communicates with the source. The tube 34 has an axis positioned at any angle ranging between the horizontal and vertical but preferably has an axis which is more vertical than horizontal. Flanges 36, 38 are secured to the ends of said tube 34. The tube 34 and flanges 36, 38 are made of a material that is corrosion resistant and can be electrically resistance heated. Platinum and its alloys are the preferred material. Other materials can be used such as Inconel or molybdenum, but these lack glass corrosion and air oxidation resistance offered by platinum at temperatures normally encountered with molten glass applications. Flanges 36, 38 are welded to tube 34 such that the weld is uniform and electrically continuous around the joint, FIG. 6A. Thin spots cause localized over-heating while thick spots cause localized under-heating. The cross sectional thickness of said flanges is preferably greater than the thickness of the tube 34 and the thickness of the flanges 36, 38 and tube 34 are preferably uniformly thick. Referring to FIGS. 6-10 each flange 36, 38 includes an annular groove 42 adjacent its respective end of the tube 34 into which the end of said tube 34 extends and is welded. An electrical power supply 50 is connected across the flanges 36, 38 by electrical supply bars 52, 54 and connectors 56, 58 (FIG. 1). Refractory blocks 60, 62, 64, 66, 68, 69 and 70 are placed about the tube 34 to provide mechanical support because the tube easily deforms at operating temperatures. Insulation 72 is placed around the blocks 60-70 to limit the loss of heat. Referring to FIG. 11, in a typical example, a stepdown transformer (primary side) supplies (secondary side) power to the tube 30. The tube power supplies just enough heat to overcome normal heat loss when glass is flowing through the tube and additional heat to moderate glass flow during starting. Additionally, flange heater blocks 60 and 70 provide auxiliary heat to the flanged ends of the tube 34. Power for the flange heaters is supplied by an ordinary silicon controlled recitifier (SCR) durable power controller. Temperature control is by means of a thermocouple-PID controller. The flange heaters are turned on only during start-up and shut-down. The amperage necessary for each heater is different because they are different sizes. Typically, they used only 5-25 Amps at 50-150 volts. As shown in FIG. 5, there is a variable gap between refractory blocks 68 and 69 to allow for longitudinally thermal expansion differences between the refractory blocks 60-70 and the tube 34 while at operating temperatures. As shown in FIG. 5, the two sets of arrows on the wedge shaped blocks indicate the position of steel support brackets. These brackets support the entire weight of the refractory blocks. Since, the upper flange 36 rests on the upper flange block 60, the brackets must also support the weight of the tube 34 as well. The two arrows at the lower portion of the tube assembly indicate another set of steel support brackets. These brackets support only the pair of lower flange heater block 70 and refractory block 69. The lower bracket is movable along the axis of the tube. When the tube is hot, it expands downward, for example, nearly 12.7 mm (1/2") which means the end of the tube extends 12.7 mm (1/2") past the lower flange heater. Platinum is very soft, at operating temperatures that can reach 1260°C (2300°F). The exposed tube end and flange are subject to bending if not supported. By adjusting the lower bracket downward, the lower flange heater block can be brought into supportive contact with the flange 38. In operation, it is desired that the tube be heated evenly, but not the flanges. This means that the flanges must be a better conductor than the tube. One way to achieve this is to make the overall cross-sectional thickness of the flanges much greater than the tube. Another way is to make flanges from a material with a much higher conductivity than the tube. Since the tube must carry a high current at high temperatures and provide corrosion resistance to molten glass, it will be difficult to fabricate a tube/flange structure using dissimilar metals. In practice, any type of glass can be used which in its molten state does not exceed the temperature limit of the alloy of tube 34. Heating The delivery tube assembly 30 conveys molten glass from source 24 to orifice 20. To be effective, the tube assembly 30 must supply heat to the glass to make up for natural conduction losses, but it also must maintain a uniform temperature over its length to prevent thermal gradients in the glass. The delivery tube assembly has two types of heating: (1) Direct resistance heat from power being applied to each end, with the tube acting as the resistor; (2) External auxiliary heat applied to each end. Tube Flanges Wide flanges 36, 38 terminate each end of the tube 34. They allow sealing of the tube 34 to adjacent equipment, which in the example shown, is the underside of the spout feeding glass from the source 24 above, and the upper side of the orifice ring assembly 32 into which glass 15 delivered. The flanges 36, 38 also serve as electrical connection points. Flange Design The end flanges 36, 38 are designed to distribute electrical power (for resistance heating) into the tube portion 34. This design allows electrical power to flow evenly around the periphery of the flange thereby heating the circumference. The cross-sectional thickness of the flanges 36, 38 preferably is much greater than the tube 34, such that most of the resistance heating occurs in the tube 34 rather than the flanges 36, 38. Due to the nature of thermal conduction, heat loss will be greater at the ends of the tube 34, so some degree of heating is needed in the flanges 36, 38. Referring to FIG. 6 to make up for thermal losses, the inner area of the flanges 36, 38 where they join the tube 34, have a reduced cross-section 42, causing some resistance heating to occur in the flanges 36, 38. Flange Sealing For a good operation, the flanges 36, 38 must be hot in the inner edge, to minimize thermal disturbance to the glass flowing inside, and cooler on the outer edge to form a seal. The shape of the flanges 36, 38 and the variations in cross-sectional thickness 42 are designed to meet these conditions. When molten glass flows through the tube 34, it flows into the hot flange sealing area and may even leak. However, by design, the outer edge of the sealing surface is at temperature below the devitrification point of glass, typically about 970°C (1800°F). In this cooler area, the flow slows and stops as devitrification crystals form. Flange Heating For electrical resistance heating, power is applied to the flanges by large, water cooled copper clamps. The clamp area must be kept cool (under 94°C (200°F)) so electrical current transfer is maximized and copper oxidation is minimized. Since cooling will draw heat from the flanges 36, 38 (over and above natural conduction losses), and, therefore the ends of the delivery tube, temperatures will be lower than along the length of the tube 34. The reduced cross section 42 in the flange causes an increase in resistance heating, thereby reducing this temperature loss. Flange Seal Separation Since the flanges 36, 38 are designed,to form a seal with molten glass, they do not allow for easy separation. For this purpose, auxiliary flange heating blocks 60, 70 serve to provide extra heat to remelt the sealed ends (from devitrified glass) so the tube can be separated from mating surfaces. Satisfactory results have been obtained utilizing the apparatus shown and described where the tube assembly has its axis at an angle of about 20' to the vertical and has a diameter of about 76 mm. It can thus be seen that there has been provided a method and apparatus for conveying the glass from the second source to provide the outer layer; wherein the glass is conveyed while efficiently maintaining uniformity of temperature of the glass; wherein a tube is heated by resistance heating; wherein the tube is constructed and arranged for efficient and uniform temperature distribution along the length of the tube; which is similar in function and smaller in design than a conventional forehearth; which minimizes changes in existing glass delivery equipment for the primary glass stream; which allows complete glass containment; and which provides for desired hydrostatic head pressure of the secondary glass stream.

Claims: An apparatus for forming a glass stream of a first inner layer and a second outer layer, said apparatus comprising a first source (22) of molten glass, a second source (24) of molten glass, a generally vertical orifice (20), means for delivering molten glass from said first glass source (22) through said orifice (20) for the inner layer and means for delivering glass from said second glass source (24) through said orifice (20)for said outer layer and including a heated tube (34) having an inlet end and an outlet end through which the glass flows from said second glass source for the outer layer, characterized in that said heated tube (34) is of corrosion-resistant electrically conductive material, and flanges (36, 38) are secured to opposed ends of said tube (34) for connection to an electrical power source (50), said flanges (36, 38) each having a flat portion with an opening enclosing a respective end of said tube (34), and an annular groove (42) in said flat portion surrounding said opening, said grooves (42) in said flanges (36, 38) being opposed to each other and forming portions of said flanges of reduced thickness which are directly secured to said tube ends. The apparatus set forth in claim 1 wherein the cross sectional thickness of each said flange (36, 38) is greater than the thickness of the corrosion resistant, electrically conductive tube (34). The apparatus set forth in claim 2 wherein inner ends of said flanges (36, 38) are welded to said corrosion resistant, electrically conductive tube (34). The apparatus of any of claims 1 to 3 wherein said electrical power source (50) is connected across said flanges (36, 38) by electrical supply bars (52, 54) and connectors (56, 58). The apparatus set fort in any one of claims 1 to 4 including auxiliary heating modules (60,70) surrounding portions of said corrosion resistant, electrically conductive tube (34). The apparatus set forth in claim 5 wherein said heating modules (60,70) are adjacent the ends of said corrosion resistant, electrically conductive tube (34). The apparatus set forth in any of claims 1 to 6 wherein sad corrosion resistant, electrically conductive tube (34) has an axis that is more vertical than horizontal. The apparatus set forth in any of claims 1 to 7 wherein said corrosion resistant, electrically conductive material is platinum. A resistance heated tube assembly (30) for delivering molten glass from a source to an orifice, comprising a tube (34) made of platinum or the like corrosion resistant, electrically conductive material and means for supplying electrical power to said tube (34), characterized in that said tube (34) is provided with flanges (36, 38) which are secured to opposed ends of said tube (34) for connection to said means for supplying electrical power, said flanges (36, 38) each having a flat portion with an opening enclosing a respective end of said tube (34), and an annular groove (42) in said flat portion surrounding said opening, said grooves (42) in said flanges (36, 38) being opposed to each other and forming portions of said flanges of reduced thickness which are directly secured to said tube ends. The resistance heated tube assembly set forth in claim 9 wherein the cross sectional thickness of said flanges (36, 38) is greater than the thickness of the tube (34). The resistance heated tube assembly set forth in claim 10 wherein said flanges (36, 38) are welded to said tube (34). The resistance heated tube assembly set forth in any of claims 9 to 11 including auxiliary heaters (60, 70) surrounding portions of said tube (34). The resistance heated tube assembly set forth in claim 12 wherein said heaters (60, 70) are adjacent the upper and lower ends of said tube (34). A method of forming a glass stream of a first inner layer and a second outer layer, comprising the steps of delivering molten glass from a first glass source (22) through an orifice (209, and delivering glass from a second glass source (24) through said orifice (20) such that the glass from said second glass source provides said second outer layer about said first inner layer, said glass from said second source (24) being delivered through a heated tube (34), characterized in that either the apparatus of any of claims 1 to 8 is used for forming said glass stream of a first inner layer and a second outer layer or the assembly of any of claims 9 to 13 is used in delivering glass from said second glass source through said orifice.

Inventors: DEMBICKI MICHAEL T, SCOTT GARRETT L, DEMBICKI, MICHAEL T., SCOTT, GARRETT L.
Applicants: OWENS BROCKWAY GLASS CONTAINER, OWENS-BROCKWAY GLASS CONTAINER INC.
Application year: 1996
Main classification: C03B7
IPC codes: C03B17, C03B7, C03B5