JP4560826B2 - Stirrer for molten glass - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stirrer for molten glass having a spiral blade.
[0002]
[Prior art]
In the glass manufacturing industry, a stirrer is used in a glass melting furnace for the purpose of homogenizing molten glass in order to obtain glass products free from striae and bubbles, which are inhomogeneous defects generated in molten glass.
[0003]
In particular, plasma display plate glass, liquid crystal plate glass, funnel glass for cathode ray tubes, face glass, glass fibers, glass tubes for lighting, medical glass tubes, glass for optical components, etc., produced industrially for a long period of time Glass products are required to have a high degree of homogeneity. Therefore, a continuous glass melting furnace for producing these glass products requires a stirring device that can stably produce homogeneous molten glass that determines the homogeneity over a long period of time.
[0004]
Conventionally, proposals related to a large number of stirring devices have been made for the purpose of homogenizing molten glass. In order to achieve homogenization of the molten glass, the most important member in the stirring apparatus is a stirrer that is in direct contact with the molten glass. For this reason, the stirrer blade shape of the stirrer is clamped, spiral, propeller, helical ribbon, etc., or a combination of these, and these shapes are significantly deformed and multiple units are attached to the rotating shaft. Have been proposed.
[0005]
[Problems to be solved by the invention]
However, all of the stirrer stirring blades proposed so far have advantages and disadvantages, and it cannot be said that the homogenization of the molten glass has been achieved efficiently. For example, a helical ribbon stirrer 1 as shown in FIG. 5 is known as a relatively effective effect among conventional stirring blades. However, as described in JP-A-11-276872, such a helical ribbon blade 2 has a donut ring-like poorly mixed portion in the molten glass as described in JP-A-11-276872. In order to overcome this and achieve homogenization of the molten glass, it is necessary to devise a method such as combining a plurality of helical ribbon blades as described in Japanese Utility Model Publication 47-3160, and it is difficult to produce and maintain a stirrer. There is.
[0006]
In addition, a stirrer having a spiral blade that is often used in a continuous glass melting furnace is initially made of molten glass by entraining a heterogeneous glass called scum generated on the surface of the molten glass as the glass component evaporates at low speed rotation. Although homogenization can be performed, it is well known that the quality of the homogenization of the molten glass gradually decreases with time during continuous use over a long period of time.
[0007]
Accordingly, in Japanese Patent Laid-Open No. 10-265227, a propeller blade 4 that causes an upward flow along the rotation axis 3a of the stirrer as shown in FIG. A stirrer 3 with a structure attached to the upper part has been devised. However, in the stirrer 3 having the structure of FIG. 6, the propeller 4 attached to the upper part of the rotating shaft 3a and the spiral blade 5 attached to the lower part form a flow in which the upper and lower sides are opposite to each other, which is effective for scum entrainment. However, the upper propeller blade 4 acts so as to inhibit the stirring of the molten glass by the spiral blade 5, and the stirring effect is not improved as compared with the case where the propeller blade 4 is not attached.
[0008]
On the other hand, if the stirrer having only the spiral blade 5 without the propeller blade 4 is rotated at a high speed to increase the stirring effect and homogenize the molten glass dough, the rotating shaft 3a of the stirrer 3 and the surface of the molten glass dough Molten glass wrinkles are generated in contact with the glass, and the wrinkles are drawn into the molten glass along the stirrer while taking in the gas on the surface of the molten glass, which grows into bubbles. As a result, although the molten glass is homogenized, it will be molded with a large number of bubbles entrained in the molten glass, resulting in a defective product that does not satisfy the product standards due to molding defects. There is.
[0009]
The present invention has been made in view of the above-described problems, and even at a relatively low speed rotation without entraining bubbles, it can take in inhomogeneous molten glass and perform efficient stirring, and is industrially continuous for a long time. Various glass products that require a high degree of homogeneity, such as plate glass for plasma display, plate glass for liquid crystal, funnel glass for cathode ray tube, face glass, glass fiber, glass tube for lighting, glass tube for medical use, glass for optical parts It aims at providing the stirrer for molten glass which can implement | achieve supply of the molten glass which has the high homogeneity which determines the quality of this.
[0010]
[Means for Solving the Problems]
The present inventor has studied a detailed shape of a spiral wing having a typical stirrer shape, and has a structure in which another blade is formed in a symmetrical position with respect to the rotation axis within the spiral period of a normal spiral wing. The stirring ability of molten glass is remarkably improved by using two stirring blades having a total of two spiral blades, and the optimum tilt angle range is obtained by variously changing the tilt angle of the spiral blades. That is, it has been found that the molten glass can be more effectively agitated at a low rotational speed that does not entrap bubbles in the molten glass in a twisted shape range corresponding to a lead angle of the spiral blade of 22 ° to 58 °.
[0011]
That is, the molten glass stirrer according to the present invention includes a rotating shaft made of a heat-resistant material and two spiral blades made of a heat-resistant material having an inner end fixed to the outer periphery of the rotating shaft . The locus drawn by the outer peripheral edge of the spiral wing is symmetric with respect to the rotation axis, and the axial length of the two spiral wings is 1.2 times or more the radius of the spiral wing centered on the rotation axis. It is preferable that the spiral blade has a twist shape with a lead angle of 22 ° to 58 °.
[0012]
FIG. 2 is an explanatory view showing the structure of a stirrer having a spiral blade. In the figure, the stirrer 6 has a structure in which an inner peripheral end 8 a of a single spiral blade 8 is fixed to the outer periphery of a rotating shaft 7. According to the terminology used in JISB0101 (1994) that defines the screw, this is a structure having one spiral blade 8 in the spiral period, and can be said to be a single spiral blade stirrer. On the other hand, in the structure of the stirrer 10 for molten glass of the present invention, the spiral blade 12 with respect to the rotating shaft 11 and the other spiral blade 13 within the same spiral period are symmetrically positioned at the inner peripheral ends 12a. , 13a is directly fixed, and it can be said to be a two-row spiral blade stirrer having two spiral blades.
[0013]
FIG. 3 is an explanatory view showing the angle of the spiral shape of the spiral wing. The locus drawn by the outer peripheral edge of the spiral blade of FIG. 3A is schematically shown in the center (B) of the drawing. The twist shape of the spiral wing is β, which is the “lead angle” in the screw term, and L is the “lead” that represents the axial distance when the spiral wing draws a spiral of one rotation along the axis. If the radius centered on the axis is expressed as r, there is a relationship of tan β = L / 2πr. 3B is a locus drawn when the outer peripheral edge of the spiral blade makes one rotation around the rotation axis in the right triangle of FIG. 3C in which the shaded portion of FIG. This is an equation that can be derived from the definition of the oblique angle of a right-angled triangle with the circumference 2πr of the circle formed by projecting on the surface perpendicular to the rotation axis as the base and the lead L as the height.
[0014]
The stirrer 10 having the double spiral blade of the present invention has high stirring efficiency when the lead angle β is 22 ° to 58 °. This is because when the lead angle β is smaller than 22 °, the axial distance between the spiral blade 12 and the spiral blade 13 becomes small, so that the capacity of the molten glass trapped between the spiral blades 12 and 13 becomes too small. Since the amount of molten glass that moves in the vertical direction is reduced by rotating the stirrer 10 once, in order to move the same amount of molten glass in the vertical direction, it is necessary to increase the number of rotations, and the conditions for entraining bubbles Will approach. When the lead angle β is 22 ° or more, the glass can be efficiently stirred with less rotation without entraining bubbles. On the other hand, when the lead angle β is larger than 58 °, the force in the rotational axis direction generated by the rotational movement of the spiral blades 12 and 13 cannot be transmitted well to the molten glass. The slip-through phenomenon occurs. As a result, the molten glass is not efficiently stirred.
[0015]
Furthermore, when the lead angle β of the spiral blades 12 and 13 of the stirrer 10 is in the range of 30 ° or more and 50 ° or less, the force in the rotational axis direction is efficiently transmitted from the spiral blades 12 and 13 to the molten glass. Effective stirring can be performed.
[0016]
In the molten glass stirrer 10 of the present invention, if the lead angle β is in the range of 22 ° to 58 °, the lead angles β of the two spiral blades 12 and 13 are intentionally set to different angles. In addition, the two spiral blades 12 and 13 attached to the outer periphery of the rotary shaft 11 are gradually gradually rotated around the shaft within a lead angle β of 22 ° to 58 °. It is also possible to set a shape that changes the angle, and further change the angle gradually within the range of 22 ° to 58 ° when the lead angle β is gradually changed within the range of 30 ° to 50 °. It is more effective than
[0017]
As the spiral blade used in the stirrer 10 for molten glass of the present invention, the axial length H of the spiral blade of FIG. 1 has a radius r centering on the rotational axis 11 of the spiral blades 12 and 13 centering on the rotational shaft 11. It is important that it is 1.2 times or more. This is necessary in order to effectively move the molten glass taken in by the rotation of the stirrer in the vertical direction, and the axial length H of the spiral blades 12 and 13 is the radius r of the spiral blade about the rotation shaft 11. If it is shorter than 1.2 times, the effect of moving the molten glass is insufficient, so that sufficient stirring cannot be performed, and homogenization cannot be achieved when heterogeneous glass is stirred.
Further, if the axial length H of the spiral blades 12 and 13 is longer than 1.8 times the radius r of the spiral blades 12 and 13 around the rotation axis, the movement of the molten glass becomes more remarkable, which is more desirable. . On the other hand, the longer the axial length H of the spiral blades 12 and 13, the greater the stirring effect, but it is up to about 10 times the radius r centered on the rotating shaft 11, and the long-term structural strength at high temperatures is increased. From the standpoint of maintaining it, it is not desirable to make it larger than 10 times the radius r of the spiral wing centered on the rotating shaft 11. Further, if a structurally safe range is designated, it is more preferable to set it to 7 times or less.
[0018]
The axial length H of the spiral blades 12 and 13 is less than 1.2 times the radius r of the spiral blades 12 and 13 around the rotation axis 11, or the lead angle β is less than 22 ° or exceeds 58 °. In this case, a cylindrical refractory barrier called a guide tube or a tube that squeezes the flow of the molten glass is provided around the spiral blades 12 and 13 in order to overcome a reduction in the stirring effect of moving the molten glass in the vertical direction. There is a case to try to cope with it. However, if such a barrier is installed in the vicinity of the rotating spiral blades 12 and 13, even if it is effective for short-term glass melting, the molten glass surface dough near the barrier becomes difficult to flow if long-term melting occurs. As a result, heterogeneous glass is likely to be generated on the surface, and a large amount of scum that can be homogenized by the stirring ability of the stirrer 10 is generated on the surface of the molten glass. Is not desirable because it is difficult to obtain.
[0019]
Further, in the molten glass stirrer 10 of the present invention, the axial length H of the spiral blades 12 and 13 is set to be different for each of the two spiral blades 12 and 13 in order to improve the stirring effect. Can do. In this case, the axial length H of the spiral blades 12 and 13 is within the range of 1.2 to 10 times the radius r of the spiral blades 12 and 13 around the rotation axis 11 for each of the spiral blades 12 and 13. It is possible to change freely. The range of the axial length H of the spiral blades 12 and 13 is more preferably set within a range from 1.8 times to 7 times.
[0020]
The molten glass stirrer 10 according to the present invention can not only set the radii r around the rotation axis 11 of the two spiral blades 12 and 13 to different sizes, but also the spiral blades 12 and 13. Of the spiral wings 12 and 13 within the range of 1.2 to 10 times, more preferably 1.8 to 7 times the radius r of the spiral wings 12 and 13 centered on the rotating shaft 11. It is also possible to gradually change the size of the radius r of the spiral blades 12 and 13 while the rotors 13 and 13 move around the axis.
[0021]
Further, for each of the two spiral blades 12 and 13, the angle of the lead angle β around the rotation axis, the change in the axial length H of the spiral blades 12 and 13, the spiral blade 12 around the rotation shaft 11, Needless to say, the radius r of 13 can be changed in combination.
[0023]
Moreover, it is important that the stirrer 10 for molten glass of the present invention is the spiral blades 12 and 13 with the inner ends 12 a and 13 a fixed to the outer periphery of the rotating shaft 11. If the inner ends 12 a, 13 a of the spiral blades 12, 13 are not fixed to the outer periphery of the rotating shaft 11, for example, a helical ribbon shape, the force from the blades is not transmitted to the molten glass near the rotating shaft of the stirrer. Effective stirring cannot be performed due to the occurrence of spots.
[0024]
Furthermore, it is important that the stirrer 10 for molten glass of the present invention has two spiral blades 12 and 13. With a stirrer having one spiral blade, the amount of glass that can be captured by one rotation is small, so that the stirring effect is inferior to that of a stirrer having two spiral blades at the same rotational speed. Therefore, if the rotational speed is increased in order to increase the stirring effect, bubbles are entrained in the molten glass, so the rotational speed of the stirrer is limited, and as a result, sufficient mixing cannot be performed.
[0025]
Note that the surfaces of the spiral blades 12 and 13 may be provided with a plurality of irregularities that repeat specific shapes such as dents, grooves or scale-like patterns for smooth flow. It is also possible to make a plurality of holes as long as the flow is not hindered. In particular, it is possible to coat or attach only the tip portions of the spiral blades 12 and 13, which are eroded by molten glass, to the corrosion resistant foreign material. It is also possible to select a plurality of such surface structure changes and simultaneously employ them within a range not impeding the flow of the molten glass.
[0026]
Note that the stirrer 10 of the present invention may be a spiral blade that looks like a spiral as a whole by arranging a plurality of flat plates in a symmetrical manner as a structure of the spiral blades 12 and 13. However, although the strength is structurally high, it is inferior to the curved blade as shown in FIG. 1 in that the flow of the molten glass flows smoothly. A structure can also be adopted.
[0027]
Moreover, the stirrer 10 for molten glass of the present invention is characterized by being used for stirring molten glass after clarification in a glass production process. When the molten glass before clarification is stirred, a large number of fine bubbles of 1 mm or less are generated in the molten glass, so that defoaming from the molten glass becomes difficult after the clarification step, resulting in defects in glass products. It is.
[0028]
In the glass melting furnace, the raw materials prepared are put into the furnace, and bubbles generated from the batch are sufficiently degassed from the molten glass. Specifically, bubbles such as carbon dioxide and oxygen generated by vitrification reaction of the glass raw material by clarification are generated. The molten glass is homogenized by stirring between the time when the molten glass is completely removed and before molding. For this reason, the molten glass stirred by the stirrer 10 is generally at a temperature lower than the temperature in the refining zone for gas defoaming, but is at least a few hundred degrees Celsius higher than the room temperature. Is made of a heat-resistant material that can withstand a high temperature of at least 300 ° C. for a long period of one month or longer. Furthermore, the heat-resistant temperature of this material is preferably as high as possible, but at the same time, it must be sufficient to maintain the corrosion resistance and structural strength of the glass, has low reactivity with the furnace atmosphere, and is economical. In particular, it is necessary that the material has a price suitable for the production of glass products, and more desirably, it has a life of 3 months or more at a high temperature of 500 ° C. or more.
[0029]
Examples of the material used for the stirrer 10 for molten glass of the present invention include platinum group metals such as platinum, platinum-rhodium alloys or alloys thereof, and white metal metals to which strength reinforcing components such as zirconia are added (alumina). Fine ceramics, carbon or carbon fiber, metal-added carbon material, fiber reinforced metal (FRM), fiber reinforced carbon (FRC), functionally gradient material, etc. It is possible to select multiple materials as components, and use different materials at different locations where high temperature and low temperature are required, or where corrosion resistance is required or where high strength is required. It is also possible.
[0030]
Moreover, the molten glass stirrer 10 may have a hollow structure, and a metal material or ceramic material that compensates for high strength or a plurality of them may be selected and filled in the whole, or may be filled locally at a necessary location. Is possible. In particular, a heat-resistant surface coating material can be used for the part of the stirrer 10 for molten glass that requires heat resistance.
[0031]
As a method for manufacturing the stirrer 10 having the two spiral blades 12 and 13 of the present invention, a rod-shaped platinum-based metal material may be used as the rotating shaft, but from an economical viewpoint or a structural strength viewpoint. As seen, one end of a hollow rod made of a platinum-based metal material is sealed, and the blade is directly attached to the rotating shaft by welding the extended platinum-based metal material, and the rotating shaft is filled with a heat-resistant material. It is common to produce by doing.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a stirrer for molten glass having two spiral blades of the present invention. In the stirrer 10 for molten glass, the portions of the spiral blades 12 and 13 are immersed in the molten glass, and are rotated by a power source located at the tip of the rotating shaft 11. The two spiral blades 12 and 13 arranged symmetrically with respect to the rotating shaft 11 have inner peripheral ends 12a and 13a directly attached to the outer periphery of the rotating shaft 11 by welding or brazing. For this reason, it is difficult to generate a dead portion of the flow of the molten glass when rotating along the rotation axis, and a donut ring-shaped heterogeneous portion is not generated unlike the helical ribbon blade, and as a result, the molten glass is homogenized. It can be done quickly.
[0033]
Hereinafter, the stirrer for molten glass of this invention is demonstrated in detail based on an Example and a comparative example.
[0034]
First, as a method evaluation of the stirring effect of the stirrer for molten glass, FIG. 4 shows the flow of the molten glass 14 when the stirrer 10 of the present invention is immersed in the molten glass 14 and rotated. The rotating shaft 11 of the stirrer 10 of the present invention is installed in a direction perpendicular to the flow direction S of the molten glass dough at a position indicated by R in the figure. When the stirrer 10 is rotating so as to generate a downward flow in the molten glass 14, the inhomogeneous molten glass T rotates around the stirrer 10 according to the flow as indicated by the streamline U by the action of the stirrer 10. While being taken into the stirrer 10 and stretched like the streamline V, it is mixed with the other molten glass 14 around the stirrer 10.
[0035]
However, if the force taken by the stirrer 10 is weak, the stirrer 10 passes as it is as indicated by the streamline W and flows to the forming zone, causing non-uniform glass.
[0036]
Therefore, the stirring effect can be measured by directly measuring the force with which the stirrer 10 takes in the dough of the molten glass 14 with a load cell. In this case, as a reference, when the lead angle β of the single spiral blade stirrer is 25 °, the force acting downward on the stirrer is measured by the load cell, and measured by the load cell of the downward force acting on the stirrer of the example and the comparative example. Then, the value obtained by dividing the actual measurement value by the actual measurement value of the single-spindle spiral blade stirrer is defined as the “up and down stirring effect”. The measurement results are shown in Table 1.
[0037]
[Table 1]
[0038]
In No. 1 of the example, when the platinum stirrer 10 of the present invention was measured by stirring the glass dough for the cathode ray tube, the length H in the rotation axis direction of the stirrer 10 was a spiral centered on the rotation axis 11. When the lead angle β is 22 ° with the spiral blades 12 and 13 that are twice the radial length r of the blade, the colored fabric may prevent the flow represented by W in FIG. 4 at a rotational speed of about 25 rpm. It was possible to confirm by using. Further, when the lead cell of the single spiral wing stirrer has a lead angle β of 25 ° and the force acting downward on the stirrer is actually measured by a load cell and the magnitude is 1.0, the stirrer has a No. The actually measured value of the downward force load cell working under the condition of 1 is 1.05, which indicates that the stirring effect of the single spiral blade stirrer is exceeded, so that the stirring can be performed more efficiently than the single spiral blade stirrer.
[0039]
Furthermore, no. 2-No. In No. 6, the other conditions are the same, and when the lead angle β of the spiral blades 12 and 13 is changed from 30 ° to 50 °, the vertical stirring effect is higher than that of the single spiral blade stirrer. No. 7 was 1.37 when the rotation speed of the stirrer was 30 rpm, and it was found that a high stirring effect was obtained in the same manner. No. In No. 8, when the viscosity of the molten glass was changed to 700 dPa · s, the vertical stirring effect was 1.4, and a high stirring effect was recognized. No. No. 9 is a result of investigation on the value obtained by dividing the axial length of the spiral blade by the radial length r of the spiral blade to 1.5. The vertical stirring effect is 1.23, and a sufficiently high stirring effect is obtained. It has been.
[0040]
[Table 2]
[0041]
On the other hand, no. No. 10 has a stirrer double spiral blade lead angle β of 15 °, and when using the same glass and stirring conditions as in the examples, the vertical stirring effect is 0.85, which is 1 or less. It can be seen that sufficient stirring cannot be performed.
No. 11 is a stirrer in which the value obtained by dividing the axial length of the double spiral blade by the radial length of the spiral blade is 0.5, which is a very small stirrer, so a high stirring effect cannot be obtained, and the vertical stirring effect is 0.75. However, good stirring cannot be performed. Furthermore, no. In No. 12, since the lead angle β of the double spiral blade of the stirrer is too large as 65 °, the vertical stirring effect is 0.7 and the stirring effect is low. And No. No. 13 is a single spiral blade stirrer in which the lead angle β of the standard single spiral blade stirrer is 25 °, whereas the lead angle β of the spiral blade is 35 °, but the vertical stirring effect is 0. The stirring effect is insufficient.
[0042]
In addition, although the stirrer for molten glass of the present invention was invented for stirring after clarification of continuously produced molten glass, it can be used for mixing before clarification of molten glass as necessary. Needless to say, it can also be used in batch production using platinum pots or the like other than continuous production.
[0043]
【The invention's effect】
According to the molten glass stirrer of the present invention having the above-described structure, the molten glass stirrer causes a large stirring action in the vertical direction in the molten glass. It is possible to stir, and in particular, it has a practically excellent effect that can make a glass product produced industrially continuously for a long period of time into a homogeneous state.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing the structure of a stirrer according to the present invention, wherein (B) is a plan view of (A).
FIGS. 2A and 2B are explanatory views in which the double-spiral blade stirrer structure of the present invention is compared with the single-spiral blade stirrer, in which FIG. ), (C) is a front view of a single spiral wing stirrer, and (D) is a plan view of (C).
FIGS. 3A and 3B are explanatory views of the lead angle of the spiral blade, wherein FIG. 3A is a perspective view of a single spiral blade stirrer, FIG. 3B is a schematic diagram of FIG. 3A, and FIG. 3C is a hatched portion of FIG. Development view.
FIG. 4 is an explanatory diagram showing the flow of glass and stirring with a stirrer of the present invention in a glass melting tank.
FIG. 5 is an explanatory diagram of a conventional helical ribbon stirrer.
FIG. 6 is an explanatory view of a molten glass stirrer in which a conventional propeller-type stirrer and a spiral stirrer are combined.
[Explanation of symbols]
5, 12, 13 Spiral wing 10 Two-row spiral wing stirrer 11 Rotating shaft 12a, 13a Inner peripheral end 14 of spiral wing Molten glass r Radius H centered on the rotational axis of the spiral wing Length L in the rotational axis direction of the spiral wing Lead β Lead angle R Position of the stirrer for molten glass of the present invention S Flow direction of glass dough T Inhomogeneous molten glass U Flow of molten glass taken around the rotation axis by the spiral blade V Melt stretched by the spiral blade Glass W Flow of molten glass passing through the vicinity of the spiral wing

Claims (4)

A rotating shaft made of a heat-resistant material, and two spiral blades made of a heat-resistant material having an inner end fixed to the outer periphery of the rotating shaft,
The trajectory drawn by the outer peripheral edges of the two spiral wings is symmetric with respect to the rotation axis,
A twist shape in which the axial length of the two spiral wings is 1.2 times or more the radius of the spiral wing centered on the rotation axis, and the lead angle of the spiral wing is 22 ° to 58 ° A stirrer for molten glass characterized by having   The spiral blade has a twisted shape in which the length in the direction of the rotation axis is at least 1.8 times the radius of the spiral blade centered on the rotation axis, and the lead angle of the spiral blade is 30 ° to 50 °. The stirrer for molten glass according to claim 1.   The stirrer for molten glass according to claim 1 or 2, which is used for stirring molten glass after clarification in a glass melting facility.   The molten glass stirrer according to any one of claims 1 to 3, wherein the rotation shaft is installed in a direction perpendicular to a flow direction of the molten glass.