JPS5934658B2 - Molten glass fining method and glass melting tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining molten glass and to an improved apparatus for refining molten glass.

In known methods of producing glass continuously, raw materials are charged to one end of a glass melting tank and form a floating canopy above the existing molten glass bath.

The charge is sufficient to maintain a constant depth of glass in the vessel with the molten glass gradually flowing towards the opposite side of the vessel at the end of the run.

From the end of this tank, the molten glass is sent to the molding process.

The charge envelope is heated into molten glass while passing through a melting zone at one end of the vessel.

This heating is carried out, for example, by burning fuel in a burner installed at a suitable distance from the side wall at a level higher than the surface of the molten glass, or by electric heating.

Molten glass moves from the melting zone to the fining zone.

The upper surface of the molten glass is also heated in this clarification zone.

In the fining zone, gas bubbles remaining in the glass are encouraged to escape or infiltrate from the glass.

The glass moves from the fining zone to the conditioning zone adjacent to the working end of the tank.

In the conditioning zone, the glass is homogenized and subjected to thermal conditions suitable for use in the forming process.

Usually, the working end of the tank and the forming process are connected by a flow path.

In order to prolong the life of the glass melting tank, it is desirable to lower the temperature of the glass in contact with the refractory by a sufficient degree in order to obtain a glass that does not contain bubbles and eroded refractories.

This is achieved in part by creating convection currents in the molten glass within the bath.

This convection is caused by the glass flowing backwards from the low-temperature area to the high-temperature area at the bottom of the tank.

This means that the amount of glass flowing backward in the tank is more than four times the amount of molten glass supplied to the intermediate forming process of the forward flowing molten glass in the upper layer.

In this case, additional heating is required to provide the counter-flowing glass with the temperature required for the forward flow.

It is an object of the present invention to provide an improved method for fining glass in which the ratio of forward to reverse flow in the fining zone is much higher than conventional.

The present invention is a method for refining molten glass in a refining zone in a tank containing the molten glass, in which the molten glass is supported on a heat conductive support material that forms the base of the refining zone, and the upper layer of the molten glass is The molten glass is heated to a temperature sufficient to effect fining, and the molten glass is passed through the support material to minimize undesirable interactions between the support material and the molten glass, which form the base of the fining zone. The depth of the glass layer in the fining zone is such that heat is removed from the lower layer and the upper layer of glass flows forward from the inlet to the outlet of the fining zone while causing a small amount of the lower layer of glass to flow back in the fining zone. Then, fining of the molten glass is carried out, which includes adjusting the length of the fining zone and the temperature difference between the inlet and outlet of the fining zone so that the ratio of reverse flow to forward flow is 1/6 to 1/2. The present invention provides a method.

For typical sheet glass compositions, the temperature of the upper layer of the glass is at least 1,460°C.

By using the present invention, the amount of glass refined per unit area at this temperature is increased by increasing the rate of forward flow through the refining zone.

Furthermore, since the glass leaves the fining zone after spending the necessary time for fining, the small amount of glass that circulates significantly reduces the amount of glass that comes into contact with the refractory in the fining zone, and therefore melts. Improved glass quality.

This means that the area of the fining zone can be reduced, for example by narrowing the width of the known fining zone, or that the output can be increased with a tank of the same size.

It is desirable to prevent the backflowing portion of molten glass from contacting the refractory at the base of the fining zone.

It is therefore preferred that the molten glass is supported by a layer of molten metal at the base of the fining zone.

Preferably, the molten metal is tin, although other metals and alloys including tin alloys can be used.

The ratio of reverse flow to forward flow may vary; the preferred ratio is 1/4.

It is desirable to circulate cooling air below the fining zone to remove heat from the bottom of the fining zone so that the molten metal is maintained at a temperature such that it does not react with the glass.

The present invention still includes at one end of the glass melting tank a melting zone in which the glass-making materials are fed, a conditioning zone in which the desired thermal conditions are provided before the molten glass is removed from the bath, and between the melting zone and the conditioning zone. It has a fining zone, a melting zone and a device that heats the top surface of the glass in the fining zone, a layer of molten tin is provided at the base of the tank where the fining zone supports the molten glass, and a cooling device is installed inside the fining zone. A glass melting tank is provided adjacent to the fining zone and below the base of the tank to remove heat from the bottom of the molten glass.

It is desirable that barriers of refractory material be provided upright from the base at both the inlet and outlet ends of the fining zone to better contain the molten tin within the fining zone.

Advantageously, the cooling device consists of a device for circulating cooling air below the fining zone.

The time required to achieve sufficient fining depends on the temperature at which fining is performed.

Soda lime - at least 1,46 for silica glass
It is desirable to use a fining temperature of 0°C.

For the glass flow leaving the fining zone and entering the conditioning zone, i.e., the charging stream for the conditioning zone, if a fining temperature of 1,460°C or higher is used, contact between the surface of the molten glass and the molten glass and molten metal. It is necessary to maintain a minimum value of the temperature difference with the interface at substantially 200°C.

It is only the charge stream that finally enters the forming process that needs to reach the fining temperature, in this case 1,460°C.

This provides a facility for adjusting the temperature of the molten glass and molten tin contact interface to a temperature that minimizes significant interaction between the glass and tin.

Note that this temperature varies depending on the chemical properties of the glass.

This temperature difference can be reduced to 30KWS by installing a cooling device below the clarification zone.
This is achieved by removing heat at a rate of /2.

The glass flowing back in the fining zone circulates at a relatively higher temperature than originally planned, reducing the amount of reheating that must be imparted to the glass flowing forward again with the forward flow.

The amount of heat required for the fining operation according to the invention is reduced due to the reduced amount of backflowing glass.

Overall thermal efficiency is improved when minimizing the temperature difference between the surface of the molten glass and the support material.

The heat removed from the base of the clearing zone can be recycled.

For example, it can be used in a heat storage chamber or for preheating batch materials to be charged into a tank.

It is preferable that the molten zone in the tank has a deeper structure than the clarified zone to hold the molten glass.

This allows the molten glass to circulate more closely within the melting zone.

Moreover, it is preferable to provide a charging port at the entrance of the melting zone to charge the batch material.

The material is charged in the form of pellets and preheated with hot gas.

The pellets are heated to about 700° C. and fed onto the top of the existing molten glass in a conventional manner.

Preferably, the conditioning zone is shallower than the fining zone so that all of the molten glass flows forward through the conditioning zone.

The present invention can be applied to the case where molten glass is refined in an independent refining device separated from the glass melting tank.

In this case, the molten glass must be fed to the refining device substantially free of stones.

Using a finer separate from the melter means that the supply of molten glass is received from more than one location.

Therefore, operational and life problems occurring in the melting equipment can be prevented from affecting the entire installation.

In conventional glass melting tanks where the melting zone, fining zone and conditioning zone are in contact with each other, a problem in any zone will affect the operation of the entire tank.

One embodiment of the present invention will be described by way of example and with reference to the accompanying drawings.

The accompanying drawing is a longitudinal sectional view of a glass melting tank according to the present invention.

According to this embodiment, the tank 11 has a melting zone 12, a fining zone 13 and a conditioning zone 14.

The melting zone 12 has a charging port 15 on the entry side of the tank.

The conditioning zone 14 is located at the end of the working section of the vessel, from where the conditioned glass is discharged into the channel 9 for being led to the forming process.

The vessel is constructed of refractory material, and the base of the illustrated through-hole vessel is strategically arranged so that the layer of glass in the molten zone is the deepest.

The foundation of the tank is such that an ascending step 16 is provided at the downstream end of the melting zone so that the clarification zone 13 is shallower than the melting zone.

Similarly, the downstream end of the clarification zone has an ascending step 17 so that the adjustment zone 14 becomes shallower than the clarification zone.

The foundation of the fining zone 13 is formed by a highly thermally conductive refractory 18 and supports a bath of molten tin located between the ascending step 17 and a barrier 20 standing upright at the entry side of the fining zone.

The lower part of the base 18 of the clarification zone 13 serves as an air circulation device for circulating cooling air.

It consists of a group of elongated channels 21 between refractory supports 22.

The support 22 stands upright on a refractory foundation 23 at its lower part.

In operation, glass-making raw materials are fed into the charging port 15 in a conventional manner to form a canopy 24 on the surface layer of molten glass.

Heating is provided by gas burners in the melting zone.

The gas burner is positioned above the surface of the molten glass in the melting zone and operates through an opening 26.

Since the glass circulates in the melting tank as shown by the arrows in the figure, there is substantially the same amount of reverse flow as the forward flow.

The molten glass gradually moves along with the tank toward the fining zone 13.

The operating conditions in the clarification zone are arranged such that the forward flow through the clarification zone is substantially greater than the reverse flow, as illustrated by the arrows.

The adjustment zone is made shallow so that all of the molten glass in the adjustment zone 14 moves forward toward the outlet of the tank, so that there is no backflow.

The temperature of the upper layer of glass in the fining zone is about 1,460° C. for sufficient fining.

To prevent interaction between the molten glass and the tin in the fining zone, heat is removed from the bottom of the fining zone in order to reduce the temperature of the glass in contact with the molten tin.

The temperature of the glass in contact with tin is 20° higher than the temperature in the clarification zone 13.
It can be as low as 0°C.

Cooling air circulating through passages 21 below the fining zone removes heat via high heat transfer refractory 18 and molten tin 19.

This removed heat may be recycled by passing the air through a heat storage chamber (not shown).

A unique problem is that the ratio of forward to reverse flow within the fining zone 13 is due to the temperature difference between the glass entering the fining zone at the inlet and the glass exiting the fining zone at the junction with the conditioning zone. , and likewise the depth of the glass layer within the fining zone and the length of the fining zone (which is the distance between the barrier 20 and the climbing step 17).

In this unique example, the temperature difference between the inlet and outlet of the fining zone, the depth of the fining zone, and the length of the fining zone are adjusted such that the ratio of reverse flow to forward flow is 1/6 to 1/2.

This ratio is desired to be 1/4 to maximize thermal efficiency.

The selection of these conditions in the reservoir to obtain this unique backflow depends on the basic design of the reservoir.

Such designs are best determined by building a practical model or by calculating variations in a theoretical computer model for a tank of the planned shape.

In practical work with vessels, the final adjustment to control backflow is made by experimenting with varying temperature differences.

It is undesirable to adjust the depth of the glass layer by changing the depth of the tin in the fining tank.

All other variables are fixed by the tank design.

The depth of the glass layer is usually about 2/3 of 1 meter, and the length of the glass layer is determined by the residence time required for fining each individual glass and the flow rate of the glass throughout the device, as described above. is a function of

All of these factors can be determined by a person skilled in the art on the basis of knowledge of the intended working rate and working conditions of the vessel.

In the above example, molten tin was used at the base of the clarification zone, but
Other molten metals, alloys or other refractory materials may be used provided they prevent excessive interaction with the molten glass at the temperatures of the backflow section of the fining zone.

The invention is not limited to the detailed description of the examples given above.

For example, the fining zone may be a separate fining device.

Although the above example shows one conditioning zone fed with material from the melting zone 12 and the fining zone 13, in some cases two or more conditioning zone channels working in parallel may be provided and these may be combined into one conditioning zone. It may be desirable to receive material from the melt zone or the fining zone.

In order to prevent the free flow of air from one band to the next when three bands of molten glass layer form one body, a barrier of platinum plate is provided between each band in the upper part of the glass. may be desired.

[Brief explanation of the drawing]

The accompanying drawing is a schematic longitudinal cross-sectional view showing one embodiment of a glass melting tank according to the present invention. The numbers in the drawings and their corresponding names are as follows. 9...Flow path, 11...Glass melting tank,
12... Melt zone, 13... Clear zone, 1
4...Adjustment band, 15...Charging port, 16
, 17... Ascending step, 18... Base, 1
9... Molten tin, 20... Barrier, 21.
...Passway, 22...Support, 24...
...Oi, 26...opening.

Claims (1)

[Claims] 1. A method for refining molten glass in a refining zone in a tank containing molten glass, the method comprising supporting the molten glass on a heat conductive support material forming the base of the refining zone. heating the molten glass to a temperature sufficient to effect fining of the upper layer of the molten glass; heating the molten glass to a temperature sufficient to effect fining of the upper layer of the molten glass; To remove heat from the lower layer of molten glass through the material, and to cause the upper layer of glass to flow forward from the inlet to the outlet of the fining zone while causing a small amount of the lower layer of glass to flow backward in the fining zone. , and advance by controlling the depth of the glass layer within the fining zone and the temperature difference of the glass at the entrance and exit of the fining zone, and controlling the length of the fining zone by preventing backflow glass from flowing in from outside the fining zone. A method for clarifying molten glass, characterized in that the ratio of backflow to flow is 1/6 to 1/2. 2. The method according to claim 1, further comprising providing a layer of molten metal at the base of the fining zone so that the backflow portion of the molten glass in the fining zone does not come into contact with the refractory material. How to clear glass. 3. A method for refining molten glass according to claim 2, characterized in that the molten metal further contains tin. 4 Any one of claims 1 to 3
A method for refining molten glass according to item 1, further characterized in that the ratio of convection to forward flow in the refining zone is substantially 1/4. 5 Any one of claims 1 to 4
A method for refining molten glass in the method according to item 1, further comprising removing heat from the bottom of the refining zone by cooling air circulating below the refining zone. 6. A melting zone at one end of the glass melting tank where glass manufacturing materials are fed, a conditioning zone where desired thermal conditions are provided before the molten glass is removed from the bath, and a fining zone between the melting zone and the conditioning zone. and a melting zone and a device for heating the upper surface of the glass in the fining zone: The fining zone 13 is provided with a device for isolating the backflow glass passage in the fining zone from the backflow glass path outside the fining zone, and A layer of molten metal 19 is provided at the base of the vessel supporting the glass, and a cooling device 21 is provided below the base 18 of the vessel adjacent to the fining zone to remove heat from the bottom of the molten glass within the fining zone. A glass melting tank for clarifying molten glass. 7. In the glass melting tank according to claim 6, the isolating device for the backflow glass passage in the fining zone includes barriers 17 made of refractory material provided upright from the base at both ends of the inlet and outlet of the fining zone; 20, a glass melting tank for refining molten glass, characterized in that the molten metal 19 is mostly contained within the refining zone. 8. A glass melting tank for refining glass, characterized in that the molten metal 19 is molten tin in the glass melting tank according to claim 6 or 7. 9 Any one of claims 6 to 8
A glass melting tank for refining molten glass, characterized in that the cooling device further comprises a device 21 for circulating cooling air below the refining zone. 10 Any one of claims 6 to 9
A glass melting tank for refining molten glass, further comprising a melting zone 12 of the tank that holds the molten glass deeper than a fining zone 13.