JPH048376B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing float glass.

In the process of manufacturing flat glass using the float method, molten glass at a sufficiently high temperature is fed onto a molten metal bath made of tin, floated forward in the form of a ribbon along the surface of the bath, smoothed the surface, and then cooled. After cooling, it is taken out of the bath and sent to a slow cooling kiln. The molten metal bath is contained in an elongated refractory tank, and the headspace of the bath is provided with a non-oxidizing gas, typically a mixture of nitrogen and hydrogen, to prevent oxidation of the metal.

After the glass ribbon is given the desired dimensions on the molten metal bath and smoothed, it is bent upward near the outlet end of the bath and is gradually lifted by a roll, usually called a lift-out roll, installed behind the outlet end. Transported to cold kiln. The glass ribbon must be cool enough to not be damaged by contact with the rolls when it leaves the bath, but must be flexible enough to be bent upwards. Due to both of these requirements, glass ribbons are conventionally discharged from the bath at a temperature of approximately 600-650° C. at the exit end.

However, during lift-out at a temperature of approximately 600°C, the lower surface of the glass ribbon comes into contact with the roll, resulting in a defect called "roller imprint", in which the unevenness of the roll surface is transferred to the glass and the unevenness is carved into the glass ribbon. Decrease flatness. If the temperature of the glass ribbon is lowered during lift-out, the glass ribbon may crack or break during lift-out, resulting in interruption of operations.

The purpose of the present invention is to eliminate the above-mentioned difficulties by making the level of the molten metal bath match the level of the lift-out roll, and by making it possible to carry out the glass ribbon horizontally from the bath without bending it upward. Another object of the present invention is to provide a method for manufacturing float glass in which an upward flow is formed in a bath and dross, which is an oxide of molten metal, is difficult to adhere to a glass ribbon.

That is, the present invention provides a float glass manufacturing method in which a glass ribbon is transported along a horizontal bath surface of molten metal contained in a bathtub, and is continuously carried out from the bathtub through an upper part of the outlet end wall of the bathtub. is made higher than the outlet end wall of the bathtub, and an electromagnetic thrust is applied in the upstream direction to the bath near the outlet end wall to prevent molten metal from flowing out from the outlet end wall and to form an upward flow in the bath near the outlet end wall. This method of manufacturing float glass is characterized by pulling out a glass ribbon almost horizontally from a bathtub.

According to the present invention, the glass ribbon is pulled out from the bathtub almost horizontally, so that it can come into contact with the roll in a sufficiently cooled state. Therefore, there is no risk of surface defects such as low line prints occurring. In addition, since an upward flow from the bottom toward the bath surface is formed in the bath near the outlet end wall, fresh molten metal containing no impurities is always supplied to this bath surface, and There is no risk of impurities such as dross adhering to the glass ribbon.

In the present invention, the molten metal near the end wall of the bathtub outlet rises from the bottom, flows along the side wall, and further flows upstream along the side wall (i.e., in the opposite direction to the direction in which the ribbon moves). . Oxide of the molten metal called dross flows by the metal flow along the side wall, is usually captured by a dross collecting means provided along the way, and becomes clean molten metal and circulates within the tank.

The outflow of molten metal from the outlet end wall of the bathtub, which is installed at a level lower than the bath surface, is caused by the upstream thrust applied to the molten metal by a linear induction motor installed above the bath surface near the exit end wall. It is prevented by twisting. Further, as a method for forming an upward flow in the molten metal near the outlet end wall, a method shown in the embodiment described later is given as a specific example.

The following will explain based on the drawings.

FIG. 1 is a longitudinal sectional view of an apparatus suitable for carrying out the invention, FIG. 2 is a sectional view along line AA of FIG. 1, and FIG. 3 is a different embodiment of the apparatus.

As shown in the figure, the bath surface of a molten metal bath 2 housed in a bathtub 1 is maintained by a linear induction motor provided above the outlet end wall of the bathtub so as to be at a higher level. The glass ribbon 5 formed to a predetermined thickness and width on the bath surface advances in the direction of the arrow along the bath surface, passes through the bathtub above the outlet end wall, and is carried out to rollers 6, 7 in a substantially horizontal state.

The linear induction motor was developed in the 1970s.
As disclosed in No. 31846, it has been conventionally used in float glass manufacturing equipment to apply a thrust to molten metal by induced electromagnetic action to cause it to flow. As shown in the figure, the linear induction motor 4 includes an iron core 8 having many parallel rims, and a coil 9 made of a hollow copper tube wound around the rims.
The entire structure is housed in a refractory. Cooling water is circulated through the coils of hollow tubes. A moving magnetic field is formed by sequentially exciting the plurality of coils. A current is induced in the molten metal bath near the linear induction motor by the moving magnetic field, and a magnetic field is created by this current. A thrust is generated in the molten metal in the moving direction of the moving magnetic field due to the action of the internally generated magnetic field and the moving magnetic field generated by the coil.

A linear induction motor is placed close to the glass ribbon above the glass ribbon near the outlet of the bath, and applies a thrust to the molten metal due to the induced electromagnetic action in the upstream direction of the bath, that is, in the direction opposite to the direction of movement of the glass ribbon. By applying the liquid, a bath surface having an upward slope from the outlet end is formed on the molten metal surface at the outlet.

As shown in Fig. 2, a rectangular parallelepiped-shaped conductor 10, which has higher electrical conductivity than molten metal, is immersed inside the side wall and is immersed in the bath. It is located at the top. If such a conductor is not provided and the side wall is made of an insulating refractory material, the thrust by the linear induction motor will hardly be obtained near the side wall, making it impossible to maintain the bath surface. You can get thrust. Another method for forming an upward flow in the bath at the end wall of the bathtub outlet is to set the width W of the conductor within a certain range. This W is determined by the ratio of the electrical conductivity of the conductor 10 to the molten metal 2 and the pole pitch τ of the linear induction motor. For example, if Mo is selected as the conductor 10, W is preferably in the range of 0.25τ to τ.

Such a conductor may be any material as long as its electrical conductivity at the operating temperature is higher than that of molten metal, but it is practically preferable to use one that has excellent corrosion resistance to molten metal. Such substances include Mo, W, and Ti, but Mo is preferable in terms of processability and easy availability. Although the entire conductor may be made of these materials, a sandwich-shaped conductor is also used in which the outer peripheral surface of a material having poor corrosion resistance and heat resistance against molten metals such as Cu, Al, and Ag is made of a material such as Mo.

Also, as shown in Figure 2, the bath depth in the center
h _e is configured to be deeper than the bath depth h _E near the conductor. This depth relationship, i.e., h _e /h _E , is preferably in the range of 1 to 3. In this range, an upward flow occurs in the bath near the outlet end wall, and this upward flow further causes a flow from the center toward the side wall. Form. h _e /h _E is 1.2 in the above range
A range of ~1.7 is more desirable.

Another mode of forming such an upward flow is as shown in Fig. 3, in which the gap g _C between the lower surface of the core of the linear induction motor and the bath surface in the central part is larger than the gap g _E near the side wall. That's true. Regarding this gap relationship, g _C −g _E is preferably in the range of 0 to 50 mm, and preferably in the range of 3 to 20 mm.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an example of an apparatus for carrying out the present invention. FIG. 2 is a sectional view along line AA in FIG. 1. FIG. 3 is a cross-sectional view of another device. 1... Bathtub, 2... Molten metal bath, 3... Outlet end wall, 4... Linear induction motor, 5...
...Glass ribbon, 8...Iron core.

Claims (1)

[Scope of Claims] 1. A process for manufacturing float glass in which a glass ribbon is transferred along a horizontal bath surface of molten metal contained in a bathtub and continuously carried out from the bathtub through an upper part of the outlet end wall of the bathtub. The surface is made higher than the outlet end wall of the bathtub, and a thrust due to electromagnetic action directed upstream is applied to the bath near the outlet end wall, thereby preventing molten metal from flowing out from the outlet end wall and rising into the bath near the outlet end wall. A method for manufacturing float glass, which is characterized by forming a flow and pulling out a glass ribbon almost horizontally from a bathtub. 2. The thrust is applied by a linear induction motor provided above the bath surface near the outlet end wall, and the upward flow is formed by a metal member immersed in the side of the bath of the linear induction motor. A manufacturing method according to claim 1. 3. The manufacturing method according to claim 2, wherein the upward flow is formed by making the gap between the linear induction motor and the bottom of the bathtub larger in the center than in the vicinity of the side wall.