GB2047678A - Production of glass articles - Google Patents

Abstract

A process for the production of glass articles comprises melting glass, from which the articles are to be formed, in a continuous tank furnace 1, gradually supplying the melt to a machine 13 for forming glass ball-like elements, transferring the glass elements formed by the said machine to a closed tank furnace 20 wherein the elements are melted, and supplying the melt to moulds 22 for forming the finished articles (e.g. high quality lead crystal). <IMAGE>

Description

SPECIFICATION Process for the production of domestic and ornamental glass articles of high quality, and tank intended for use in the process In the present-day manual and semi-mechanical production of domestic and ornamental glass articles of high quality, especially lead crystal articles, the operator is faced with the difficult problems connected with capital investment, power consumption, work environment, air pollution, wish to work without the need for shifts, maintenance of the desired quality and homogeneousness of the glass, and the possibility of changing the type of glass as soon and as cheaply as possible.

The difficulties connected with the solution of these problems lie to a great extent with the glass-melting methods involved. With small concerns, which do not have a sufficient sales turnover for continuous round-the-clock operation, or with those concerns which are unable to obtain sufficient personnel for continuous round-the-clock operation, it has been necessary to melt glass in pots or in day tanks. Pots consume a high amount of power, pot maintenance is expensive and considerable air pollution is caused. A really perfect glass melt, especially in the case of lead crystal melt, requires covered pots, but even in such a case it is difficult to produce non-slip products, when repeated gathering is required, as it is not possible to an adequate degree to prevent the evaporation of the glass constituents, particularly lead evaporation.Day tanks, in their simplest design, require relatively small investments, but power consumption is high, even if lower than with pots. However, with day tanks, it is difficult to maintain perfect homogeneousness in the glass, particularly freedom from bubbles. There arises considerable air pollution, and it is difficult to prevent the formation of cracks and corrosion in the fire-proof wall material of the day tanks.With the concerns which have an adequate sales turnover and can obtain personnel for shift work, it is possible to use continuous tank furnaces which require to be operated round-the-clockto achieve good glass quality and a low power consumption, which are considerably less demanding in power consumption than pots and day tanks. Acommon drawback with continuous tanks is that it is time and moneyconsuming to change over from one type of glass to another, so that great demands are made on planning of production and adaptability to the market situation is poor.

The present invention has made it possible to reduce considerably the problems defined above.

Thus, the invention has for its object a process which possesses the features described in Claim 1.The invention relates also to a closed tank intended for use in the process which possesses the features described in Claim 2.

Many substantial advantages are achieved through the invention. Thus, a very good homogeneousness is secured in the glass of the finished articles. The first step of the process can operate for lengthy periods on the same type of glass, while in the second step of the process it is very quick and cheap to go over from one type of glass to another, so that production can be easily adapted to the market situation. The total power consumption remains low. The working environ ment remains good, and little air pollution arises.

The great advantage supplied by both the first and the second stages of the process according to the invention is that only a minimum of shift-working personnel is required, who are the very few workers who are required for carrying out the first step of the process, while the second step of.the process can be carried out completely in the daytime. Small con cerns can manage fully working during the day through obtaining glass pellets from a concern which carriesout the first step of the process, and restrict its own activities to performing the second step of the process, whereby, in addition, the ivestment needs of the small concern are relatively small, as a consequence of the concern not needing to invest in a continuous tank furnace.

The invention will be more closely described in the following with reference to the attached drawings.

Figure 2 shows a flow diagram of the process according to the invention. Figures 2 and 3 show schematically in vertical longitudinal section and cross-section respectively a small melting unit which may be used in the second step of the process according to the invention. Figures 4 and 5 show in vertical longitudinal section and cross-section re spectively another type of small melting unit which can be used the second step of the invention.

As will be seen from Figure 1,. the process according to the invention comprises two steps, In the first step,-operating continuously, i.e. round-the clock, a glass batch intended for domestic and ornamental glass articles, particularly lead crystal articles, of high quality, is melted in a continuous tank furnace, preferably an electrically-heated cold-top tank 1, and from the molten batch small glass pellets are made with a diameter of about 15-20 mm. The cold-top tank 1 is of known type and may, for example, be of a type developed by Penelectro Ltd., Great Britain.In the embodiment diagrammatically represented in Figure 1 the completely closed tank has a melting chamber 2, which by means of a channel 3 is in communication with a supply cham ber 4, which through an outflow channel 5 is in communication with a feeding apparatus with cut ting shears 7. Heating in the tank furnace 1 is effected by means of electrodes, in the known manner; these electrodes, which have not been represented, are connected with the molten glass batch in the furnace. The glass batch is dispensed to the melting chamber 2 through a dispenser 8. To avoid the dust problem in the most practicable way possible it is appropriate to supply the glass batch in pelletized form.The glass batch dispensed into the melting chamber 2 forms a layer 9 of unmolten material above the molten glass batch and thereby effectively- prevents the evaporation of the glass constituents, especially lead compounds, so that the composition of the molten glass batch can be precisely controlled and air pollution is avoided. The molten glass batch flows from the melting chamber 2 through the channel 3 to the supply chamber 4 and further to the feeding channel 5 and the feeding apparatus 6. From the outflow of the feeding apparatus 6 the glass batch flows down to a mouthpiece 10 on the solid portion of glass shears 7 and further to any of a plurality of small drop moulds 11 on the movable slide of the glass shears.Each time a drop mould 11 is filled, the slide moves along, so that the contents of the mould becomes separated from the glass batch in the mouthpiece 10 and falls as a small lump of glass into the feeding tube 12 to a glass ball forming machine 13 of known type, while another of the drop moulds 11 fills with glass batch from the mouthpiece 10. The machine 13 fas two rotating rolls 14, 15 with a groove in the shape of a screw thread on the mantle surface, in which the glass lumps supplied are formed into balls, as they roll against the rolls and are carried by the screwthread shaped groove along the longitudinal direction of the rolls to fall, along a groove 16, for example, down into a supply container 17. When the balls leave the rolls 13, 14 they are sufficiently cooled to retain their shape when stored in the supply container 17.It is also possible to form glass balls in moulds, following the technique that is used for the moulding of plastics. To achieve a very high quality of glass balls it may be necessary after moulding to acid-polish the glass bails.

For the operation of the first step carried out on a round-the-clock basis the minimum of shift-working personnel is required.

The second step of the process may be performed entirely during the daytime with the aid of a plurality of small melting units 18, of which three are shown as an example in Figure 1 and which are suitably mounted in an area other than the continuous tank furnace 1 or also in a different place from the latter.

Each unit 18 has a supply container 19 to which the glass balls made in step 1 are transported in any suitable manner from the storage container 17.

Possibly, between the storage container 17 and the supply container 19 of the units 18 there may be an intermediate store for the glass ball, especially if it is desired to work with several types of glass, made at different times in process stage 1. From the supply container 19 of each unit 18 the glass balls are supplied to a small closed tank furnace 20, electrically heated and operating discontinuously, preferably only in the daytime; there, they are melted. The molten glass batch in the tank furnace 20 is supplied along an outflow pipe 21 to gathering moulds 22 in the usual manner to be subsequently processed into finished articles in any usual manner through forming and finishing, as diagrammatically shown at 23 in Figure 1.

A melting unit of a design known in principle usable in process step 2 is shown in Figures 2 and 3.

The actual tank furnace consists here in a closed container 24 of platinum or platinum alloy and is surrounded with heat-insulating material 25. The supply container 19 is connected by means of two supply pipes 26 with the upper part of the container 24forsupplying glass balls into the container, it being possible to regulate the rate of feed by means of a device not represented in aperse known manner. In the end gables of the container 24 electric electrodes 27, 28 are disposed for melting the glass balls to a glass batch in the container. In the bottom of the container 24 there is an outflow pipe 29 of platinum or platinum alloy which leads to the gathering moulds.

Figures 4 and 5 show another construction of a melting unit which can be used in step 2 of the process according to the invention. The actual tank furnace has here the shape of a closed horizontal elongated channel 30 which is limited by walls 31 of fireproof material, e.g. chamotte. Into the channel a plurality of supply pipes open out for the glass balls from the supply container 19. From the bottom of the channel three supply pipes 29 of platinum or platinum alloy run out and lead to the gathering moulds.

On the outside of the walls 31 of the channel 30 electric resistor heating elements 32 are disposed inside an external heat insulation 33 for the indirect heating of the glass balls and of the glass batch formed from these in the channel 30. It is also possible to carry out the heating by means of microwave or high frequency power. Naturally, the number of supply containers 19, supply pipes 26 and outward supply pipes 29 can vary depending upon the desired capacity of the melting unit.

For the two melting units according to Figures 2 and 3 and the melting units according to Figures 4 and 5 it is to be aimed at that the glass batch formed from the glass balls should have good homogeneousness and be free from air bubbles. The composition of the glass remains very constant because of the fact that the escape of glass constituents in gas form from the molten batch in the glass furnace can both be held small by using low temperatures in the furnace, and prevented by the layer of not yet molten glass balls lying over the glass batch together with still cooled glass balls in the supply pipe 26 on which the vapours from the glass batch condense and thereby are subsequently returned to the glass batch. No problems arise with air pollution, and the working environment remains very good both because of the fact that the glass balls used in the second step of the process do not cause a dust problem, and because the operation of the melting units in the second step is practically free from noise. It is also very easy to empty and clean the melting units and to go over to another type of glass.

Claims (11)

1. A process for the production of glass articles, comprising melting glass from which the articles are to be formed, in a continuous tank furnace, gradually supplying the melt to a machineforforming glass ball-like elements, transferring the glass elements formed by the said machine to a closed tank furnace wherein the elements are melted, and supplying the melt to moulds for forming the finished articles.

2. A process according to claim 1 wherein the glass is lead crystal.

3. A process according to claim 1 or claim 2 wherein the glass is supplied to the continuous tank furnace in pelletised form.

4. A process according to any one of claims 1 to 3 wherein the continuous tank furnace is an electrically heated cold top furnace.

5. A process according to any one of claims 1 to 4 wherein the continuous tank furnace is electrically heated.

6. A process according to any one of claims 1 to 5 wherein the closed tank furnace includes a supply container to which the glass elements are transferred, the container being connected to the furnace by tubes through which glass elements are supplied to the furnace.

7. A closed tank furnace for use in the process of claim 1 comprising a heating tank which is connected by at least one feeder tube to one or more supply containers for supplying ball-like glass elements to the tank, the tank including heating elements at the sides thereof and an outlet pipe for molten glass, which outlet pipe is formed from platinum or platinum alloy.

8. A closed tank furnace according to claim 7 wherein the heating tank comprises a channel defined by walls of heat resistant material and enclosed by outer insulating walls, the heating elements being disposed in a space between the outer and the heat-resistant walls.

9. A closed tank furnace according to claim 7 or claim 8 wherein the heating elements are electric resistance or microwave or other high frequency heating elements.

10. A process for the production of glass articles substantially as hereinbefore described.

11. A closed tank furnace for use in carrying out the process of any one of claims 1 to 6 and 10, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.