WO1985000801A1

WO1985000801A1 - Manufacture of glass articles

Info

Publication number: WO1985000801A1
Application number: PCT/GB1984/000278
Authority: WO
Inventors: John Henry Craigie
Original assignee: Rockware Group Plc
Priority date: 1983-08-10
Filing date: 1984-08-10
Publication date: 1985-02-28
Also published as: IT8448709A1; ZA846163B; IT1178401B; GB8321525D0; IT8448709A0; EP0152444A1

Abstract

Glass articles are made by remelting and conditioning particulate glass. The glass may be in the form of cullet, optionally crushed and graded, and is fed into a heating vessel (4) and a conditioning vessel (7), from which molten glass is withdrawn to form the desired articles. The heating vessel (4) preferably incorporate a plasma heating device (6) to provide rapid and effective heating of the glass particles to form a glass melt.

Description

MANUFACTURE OF GLASS ARTICLES

This invention relates to the manufacture of glass articles, particularly the manufacture of glass containers, though it is applicable to the manufacture of other articles, for example glass bricks or fibreglass.

Very substantial quantities of glass are used for the manufacture of glass containers, principally bottles and jars. Such manufacture is conventionally carried on in manufacturing plants of very substantial size in which glass is manufactured from its basic ingredients. Usually so-called batch is formed by mixing sand, limestone, soda ash and optionally other ingredients and this batch is then fed in to one end of a large furnace. The furnace is usually a gas or oil fired type, or an electric furnace with gas or oil firing to start it up, and the batch ingredients are heated at the inlet end of the furnace to a temperature at which they fuse to form a glass. Submerged electrodes may be used to provide heating or further heating. This glass then moves slowly down the length of the furnace to one or more sections of the furnace from which molten glass may be extracted. These are generally called forehearths and each will consist of a refractory lined basin having set in its floor one or more apertures through which molten glass may feed. Below those apertures, appropriate feed mechanisms to

OMP control the flow may be located, those mechanisms conventionally producing so-called gobs of molten glass which are fed automatically into container manufacturing machines which are located adjacent each forehearth.

Manufacture is always substantially large scale and continuous, furnaces operating not uncommonly for several years from firing to closedown.

Despite the economies of scale thereby achieved, the manufacture of glass containers in this fashion is highly energy consumptive and requires very substantial capital investment with long pay back terms.

Some economies in operation are conventionally achieved by using, as part of the batch material for making the glass, broken glass, so-called cullet. The presence of cullet in the batch assists in the melting and formation of glass from its ingredients and effectively recycles already formed glass, so reducing the overall energy costs. The supply of cullet over recent years has substantially increased as a result of bottle recycling schemes designed to reduce overall energy consumption in the glass making industry and accordingly to reduce the cost of imported oil, but this has made no major difference to the way in which glass containers are conventionally made.

It is of course possible in theory to manufacture glass articles from glass itself, but hitherto such manufacture has generally been confined to very small scale operations such as the manufacture of small quantities of specialist glasses, and the manufacture of fibre-glass. Thus for example UK Patent Specifications 627863 and 737108 both disclose apparatus for manufacturing glass fibre in which the stock feed material is or can be glass itself rather than batch. However, up till now, attention has not been directed to the use of substantial quantities of cullet as a feedstock. We have now found that it is possible to manufacture glass articles, particularly glass containers, with substantially smaller capital investment than required for a normal glassworks, if adequate quantities of broken glass are available as feedstock and if appropriate apparatus is provided to convert that feedstock into molten glass. The substantial capital investment required in putting up a full size glass making furnace together with its associated mechanical handling and storage plant for the glass making materials can be entirely avoided. In its broadest aspect, the present invention provides a method of making glass articles comprising: a. introducing particulate glass into a molten glass containing vessel and simultaneously heating the particles of glass to melt and fuse them, b. passing molten glass from the vessel to a conditioning chamber having one or more outlets, c. adjusting the temperature of the glass at or near the outlet(s) to a desired temperature, and d. withdrawing molten glass from the one or more outlets of the conditioning chamber and forming glass articles therefrom.

Preferably the particulate glass is heated by means of a plasma heating system. Such a system provides a very efficient way of heating the particulate glass as it is introduced and, if used in the so-called transferred arc mode, it can additionally provide heating to the body of molten glass in the vessel.

OMPI

^ The geometry of the arrangements may vary very widely. For example the initial heating vessel and the conditioning chamber may be combined as a single vessel, e.g. divided into two chambers by a weir under which molten glass passes, or they may be separate with an outlet from an initial heating vessel feeding an inlet to a conditioning vessel.

Conveniently, when separate heating vessel and conditioning chamber are employed, the heating vessel is located above the conditioning chamber and particulate glass is fed into the heating vessel likewise from above. An arrangement of particular and preferred value, however, is to employ a unitary vessel having an upper heating part and a lower conditioning part. In such a case, a number of streams of particulate material may be fed into the top of the upper part where they intersect a plasma. In order to enhance the interaction between the falling streams of particulate material and the plasma, and to even out the temperature in the molten material it is desirable to rotate the plasma, e.g. by sweeping out a cone-shaped area at suitable speed.

In both the heating vessel and in the conditioning chamber, the temperature of the molten glass may be controlled by passing an electric current through it. For this purpose it is convenient to locate, e.g. in the floor or sides of the vessel or chamber, or both, a plurality of electrodes of suitable construction. These may be made e.g. of graphite, molybdenum or other material known for the purpose. The current passed through the glass to maintain it at the desired temperature may be controlled in known fashion and both the heating vessel and the conditioning chamber may be provided with suitable control and monitoring apparatus, for example thermo-couples or pyro etric apparatus to enable control to be exercised adequately. Alternatively, oil or

OMP gas firing may be employed to adjust the temperature.

In addition, suitable level controls may be provided to maintain the desired quantity of glass in the vessel and chamber. This may take the form of a direct level sensor of some appropriate construction or, for example, the amount of molten glass in the ^l vessel or chamber may be monitored by weighing the vessel or chamber and its contents e.g. by mounting it on a plurality of load cells. The invention is illustrated by way of example in the accompanying drawings which show two ways of putting it into practice. In the drawings: Figure 1 is a diagrammatic view of a simplified system including melting and conditioning chambers, and

Figure 2 is a diagrammatic view of an alternative embodiment. Referring to the drawings, Figure 1 shows an arrangement in which cullet is fed from a feed hopper 1 through a suitable feed line or lines 2 to an injection mechanism 3. This projects pieces of cullet onto the surface of a melting zone 4 at one end of a refractory lined or water cooled unit 5. A plasma torch 6 is arranged to create an ultra high temperature region between itself and the melting zone 4 at one end of the unit 5, through which region the pieces of cullet pass. In addition to the heating of the pieces thereby resulting, the melting glass at the end of the unit is fed directly by the current which passes through the plasma and then through the molten glass to be collected via a suitable electrode 14 which is set into the base of the melting zone 4.

Unit 5 consists of a generally elongate enclosure having walls 10, a base 11 and a roof 12. A vertical partition 13 depends substantially vertically from roof 12 but does not reach the base 11. Partition 13 divides unit 5 into melting zone 4 and a refining zone 7.

Molten glass flows during operation from the melting zone 4 into the refining zone 7 below the bottom of wall 13 which constitutes an inverted weir. In this refining zone 7 the temperature of the glass is accurately controlled using sensors of known type (not shown) and burners or coolers (depending upon whether cooling gas is blown through them or whether a combustible and ignited mixture of gas and air is blown through them) 16. If desired, the refining zone 7 can be heated electrically, either by resistance elements or by Joule effect heating.

Near the right hand end of unit 5 as shown in Figure 1 is an aperture 17 in the floor 11 of refining zone 7. Molten glass, now at the appropriate temperature, flows through that aperture to a gob- forming device 18 of known type which forms gobs 19 which are successively fed to a glass container- forming machine of known type. Turning now to Figure 2, this shows in cut-away view a furnace for use in carrying out the present invention. The furnace is generally cylindrical consisting of an outer framework 20 lined with a cylindrical refractory lining 21. The base of the furnace shown is generally conical (though a flat base could be used) and likewise lined with refractory slabs. Set in the middle of the conical base is an orifice block 25 and a suitable orifice closure mechanism 26 of known type is located below block 25.

The top of the furnace is covered by a shrouded lid generally indicated at 30 and consisting of a central ceiling formed of refractory 32 having a central aperture 33 and a plurality of feed apertures 34 in the form of a square array. At the sides of the central section 32, which may be flat as shown or optionally arched or coned, is a depending skirt 35 which fits round the exterior of the main furnace body. Skirt 35 constitutes an annular extraction duct to remo w stε gas?¹? from the furnace chamber via pipes 36 (onl one of which is shown). In order to heat material in the furnace, various heating means are provided. First, a plasma torch 40 is mounted in a mechanism 42 which can be controlled to move the plasma torch so that the plasma issuing from its base, indicated at lines 44, may be directed i.e. the direction of the emitted plasma from the torch may be caused to sweep in a generally conical shape around the interior of the furnace. For clarity of illustration, the torch is shown raised from the lid 32, though in use it is located with its lower end below the ceiling 32. Cooperating with the plasma torch are molybdenum electrodes 46 set into the base of the furnace and connected by means of high current leads 47 so that they may be used in conjunction with the plasma torch to heat molten glass in the furnace by Joule effect heating. A plurality of gas burners (not shown) may be installed in the furnace to assist in starting it up.

In addition, the nozzle block 25 may have an integral electrical heater in it enabling fine control of the temperature of molten glass as it leaves the furnace.

The furnace is supported by a plurality of spaced pillars 50, of which two are visible, each pillar resting on a load cell 51 in turn supported on a metal framework 52.

Not shown in the drawing but associated with the furnace is appropriate electrical control gear both for operating the plasma torch and molybdenum electrodes and for monitoring the weight of the whole unit by detecting signals from load cells 51 and carrying out appropriate calculations. In addition, appropriate electrical control gear is provided to enable the plasma torch to be rotated by mechanism 42 at a suitable rate, and to enable operation of the outlet gate mechanism 26. In the use of the furnace of Figure 2, streams of particulate material are fed using appropriate handling equipment through orifices 34 to intersect the rotating beam from plasma torch 40. The particles are heated very substantially as they pass through the plasma and come to rest on a bath of molten glass which accumulates at the bottom of the furnace and which is kept molten by the passage of electrical current through the mass of molten glass, which current is led away via electrodes 46. The electrical control means may ensure that the ease with which current is fed through electrodes 46 may depend on the momentary position of the plasma torch. The level of molten glass in the furnace may be kept constant by appropriate controls, e.g. by ensuring that the feed of cullet is dependent on suitably processed signals received from the load cells.

Molten glass fed through the orifice block 25 may be led e.g. to a refining chamber or vessel, hence molten glass may be formed into gobs for feeding to an independent section container-forming machine.

Claims

1. A method of making glass articles comprising: a introducing particulate glass into a molten glass containing vessel and simultaneously heating the particles of glass to melt and fuse them, b passing molten glass from the vessel to a conditioning chamber having one or more outlets, c adjusting the temperature of the glass at or near the outlet(s) to a desired temperature, and d withdrawing molten glass from the one or more outlets of the vessel and forming glass articles therefrom.

2. A method according to claim 1 wherein the molten glass containing vessel and the conditioning chamber are laterally separated one from another via a downwardly depending weir under which molten glass passes from one to the other.

3. A method according to claim 1 wherein the vessel and conditioning chamber are integrated into a vertical furnace structure, the vessel comprising an upper portion thereof and the conditioning chamber being constituted by a lower portion of the furnace.

4. A method according to any one of claims 1 to 3 wherein the heating of the particles is effected by a plasma heating system.

5. A method according to claim 4 wherein the plasma heating is effected by means of a plasma torch which is moved to sweep out a heating area into which particulate glass is introduced.

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