GB2097780A

GB2097780A - Equipment and method for manufacturing thin glass foils

Info

Publication number: GB2097780A
Application number: GB8132159A
Authority: GB
Original assignee: BOJOPLAST GRADJEVINARSTVO
Current assignee: BOJOPLAST GRADJEVINARSTVO
Priority date: 1981-03-06
Filing date: 1981-10-26
Publication date: 1982-11-10
Also published as: GB2097780B; BE895303A; FR2501185A1; DE3141969A1

Abstract

A blow-pipe 1 with an upper end 2 shaped to retain a working amount of molten glass is vertically movable from beneath the surface of molten glass 9 in a furnace to an upper position within orifice, of cover plate 10a and just below a cylindrical guide tube 11. Upward movement brings the blow-pipe generally into a hotter environment, expands the internal air and thus provides an initial bubble at the blow-pipe end. This is progressively expanded into the guide tube, preferably by two-stage air supply at different pressures, to produce a constrained glass bubble, of a few microns thickness. <IMAGE>

Description

SPECIFICATION Equipment and method for manufacturing thin glass foils This invention relates to equipment for manufacturing thin glass foils and to a method of manufacturing such foils using the equipment.

The foils so manufactured are typically of a few microns thickness, and useful in the electrical and allied industries.

In one aspect the invention provides equipment for manufacturing thin glass foils, comprising a furnace for holding a body of molten glass; an orificed cover plate; a vertical cylindrical guide tube, above the orifice, open at its lower end; and a vertical blowpipe slidable in the base of the furnace, coaxialiy with the guide tube between a lower portion where its upper end is below the level of molten glass and an upper position where its upper end is located generally within the cover plate orifice, the blow-pipe upper end being adapted to hold a working amount of molten glass during its upward movement: whereby when the blow-pipe is moved upwards, thermal expansion of the air within the blow-pipe takes place to produce an initial bubble of glass at the blow-pipe upper end for subsequent expansion into the guide tube by air supply to the blow pipe.

Preferably the blow-pipe slides in a thermally insulated base construction of the furnace. This may be achieved by providing a furnace in which a thermally insulated base construction comprises a thermally insulating layer between a furnace base plate and an outermost plate, and the blow-pipe slides within a metal sealing sleeve in the base plate and a suitable orifice in the outermost plate.

In such a case the blow-pipe may be spaced from the thermally insulating layer. It is helpful moreover if the internal space of the blowpipe is of greater diameter than the nozzle outlet. All of these features assist in providing a useful temperature differential on a suitable body of enclosed air within the blowpipe, so that initial bubble formation is readily achieved.

The blow-pipe itself constitutes another aspect of the invention. Many different configurations of blow-pipe end portions are possible.

For example, the blow-pipe may have an upper end face including a glass-retaining groove around the blow-pipe outlet. Alternatively, or additionally it may have a divergent outlet to assist in initial glass-retention.

A method of manufacturing glass foils, using such equipment typically comprises a number of steps, such as: (i) positioning the blow-pipe at a lower position completely beneath the level of molten glass, (ii) sliding the blow-pipe vetrtically upwards to an upper position at which its upper end lies generally within the cover plate orifice, and the blow-pipe body lies generally within the molten glass whereby thermal expansion of air within the blow-pipe causes formation of an initial bubble within the retained molten glass at the blow-pipe upper end, (iii) applying air to the blow-pipe whereby the initial bubble is increased in size and enters the guide tube to form a constrained part cylindrical bubble, (iv) further applying air to the biow-pipe whereby the constrained part cylindrical bubble is increased in size until all of the retained molten glass at the blow-pipe upper end is used up, and (v) discontinuing the supply of air, withdrawing the blow-pipe beneath the surface of the molten glass in the furnace, and removing the expanded part cylindrical bubble from the guide tube.

It is much preferred to operate by procedures in which stage (iii) is continued until the length of the constrained cylindrical portion of the bubble is from 1.0 to 1.5 times its diameter, and in which stage (iv) is carried out at a higher applied air pressure than stage (iii).

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows the major components of the equipment in the configuration adopted in four consecutive operating steps designated as I, II, Ill and IV, Figure 2 is an enlarged vertical cross-section to show detailed features of the equipment of Fig. 1.

A blow-pipe 1 possesses an upper end portion 2 adapted to retain a working amount of molten glass. In the example given, the end portion 2 comprises a deep groove 2a in the blow-pipe end wall and an inwardly tapered recess 2b so that the end of the blowpipe outlet is divergent. Other configurations are possibly provided with some form of temporary reservoir is achieved. Within the end portion 2 of blow-pipe 1 is central duct 2c communicating with larger diameter central duct 1 a of the blow-pipe 1.

This duct 1 a communicates with inlet 3 for primary air and inlet 4 for secondary air.

The blow-pipe is vertically movable and slides in platinum sleeve 5 and plate 6. Between sleeve 5 and plate 6 and surrounding but spaced from blow-pipe 1 are insulating layer 7 and furnace bottom plate 8.

The furnace comprises a layer of molten glass 9 and a top cover plate 10 having an orifice 1 Oa through which, at the top of its vertical movement, the blow-pipe 1 can protrude at a suitable clearance with plate 1 0.

Vertically above oriface 1 Oa is a cylindrical guide tube 11 open at its lower end.

The first stage in the use of such equipment is shown at Fig. 1 stage I. The blow-pipe end 2 lies beneath the top level of molten glass 9.

In stage II the blow-pipe slides vertically upwards, carrying with it a supply of molten glass at the end portion 2, held in and around groove 2a and recess 2b, until it protrudes through orifice 1 Oa. At this stage the blowpipe stem has moved from its spaced relationship with thermally insulating layer 7 to direct contact with molten glass layer 9. This causes expansion of air within duct 1 a and accordingly an initial bubble formation at end portion 2.

In stage Ill primary air is applied to the blow-pipe, increasing the size of this initial bubble until it enters the vertical tube 11, and is constrained to expand as a confined glass cylinder 1 2. This is continued until the cylindrical bubble contact length is from one to one and a half times the cylinder diameter.

Then, at stage IV, secondary air is applied at higher pressure until all of the temporary reservoir of glass at the shaped end 2 is drawn into the expanding bubble. At this point air supply is discontinued, the blow-pipe 1 withdrawn into the molten glass, and the cylindrical glass bubble, of very low wall thickness (of the order of a few microns) is vacuum-withdrawn from cylinder 11. A new cycle is then initiated.

Thin glass foils produced in this way can be used in electrical and like industry.

Claims

1. Equipment for manufacturing thin glass foils, comprising a furnace for holding a body of molten glass; an orificed cover plate; a vertical cylindrical guide tube, above the orifice, open at its lower end; and a vertical blow-pipe slidable in the base of the furnace, coaxially with the guide tube, between a lower position where its upper end is below the level of molten glass and an upper position where its upper end is located generally within the cover plate orifice, the blow-pipe upper end being adapted to hold a working amount of molten glass during its upward movement: whereby when the blow-pipe is moved upwards, thermal expansion of the air within the blow-pipe takes place to produce an initial bubble of glass at the blow-pipe upper end for subsequent expansion into the guide tube by air supply to the blow-pipe.

2. Equipment as claimed in claim 1 in which the blow-pipe slides in a thermally insulated base construction of the furnace.

3. Equipment as claimed in claim 2, in which the thermally insulated base construction comprises a thermally insulating layer between a furnace base plate and an outermost plate, and the blow-pipe slides within a metal sealing sleeve in the base plate and a suitable orifice in the outermost plate.

4. Equipment as claimed in claim 3 in which the blow-pipe is spaced from the thermally insulating layer.

5. Equipment as claimed in claim 2, 3 or 4, in which the internal space of the blowpipe is of greater diameter than the nozzle outlet.

6. Equipment as claimed in any one preceding claim in which the blow-pipe has an upper end face including a glass-retaining groove around the blow-pipe outlet.

7. Equipment as claimed in any one preceding claim in which the blow-pipe has a divergent outlet to assist in initial glass-retention.

8. Equipment as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

9. A method of manufacturing thin glass foils, using the equipment as claimed in any one preceding claim, comprising the steps of: (i) positioning the blow-pipe at a lower position completely beneath the level of molten glass (ii) sliding the blow-pipe vertically upwards to an upper position at which its upper end lies generally within the cover plate orifice, and the blow-pipe body lies generally within the molten glass whereby thermal expansion of air within the blow-pipe causes formation of an initial bubble within the retained molten glass at the blow-pipe upper end, (iii) applying air to the blow-pipe whereby the initial bubble is increased in size and enters the guide tube to form a constrained part-cylindrical bubble, (iv) further applying air to the blow-pipe whereby the constrained part-cylindrical bubble is increased in size until all of the retained molten glass at the blow-pipe upper end is used up, and discontinuing the supply of air, withdrawing the blow-pipe beneath the surface of the motlen glass in the furnace, and removing the expanded part-cylindrical bubble from the guide tube.

10. A method as claimed in claim 9, in which stage (iii) is continued until the length of the constrained cylindrical portion of the bubble is from 1.0 to 1.5 times its diameter, and in which stage (iv) is carried out at a higher applied air pressure than stage (iii).

11. A method as claimed in claim 9, substantially as herein described with reference to the accompanying drawings.