JP2012176891A - Float forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a float forming method for forming glass having a high forming temperature without shortening life of a strap for power feeding to a heater.SOLUTION: A float bath 10 comprises a bottom 12 filled with molten tin 11 and a roof 14 covering the bottom 12, wherein a space in the roof 14 is divided into an upper space 20 and a lower space 21 by a roof brick layer 16 and a heater 18 is disposed while penetrating a through-hole 17 formed in the roof brick layer 16. When the surface area and emissivity of a feeding part 18A of the heater 18 located in the upper space 20 are expressed by S'and ε, respectively, and the surface area and emissivity of a non-feeding part 18B are expressed by S'and ε, respectively, the following relationships: S'×ε+S'×ε≥3,630 mmand S'≥1,089 mmare satisfied.

Description

The present invention relates to a float bath for producing a glass plate suitable for float forming a glass having a viscosity of 10 ⁴ poise (hereinafter referred to as a molding temperature) higher than that of soda lime silica glass. The present invention relates to a simple float forming method.

  Conventionally, glass plates produced by float forming soda lime silica glass in a molten state have been widely used for windows for buildings and automobiles, glass substrates for STN liquid crystal displays, etc. This is the main method for producing soda lime silica glass plates (see Non-Patent Document 1).

  The float bath is a huge molten tin bath, and the upper space (the space covered with the roof) of the molten tin is divided into an upper space and a lower space by the roof brick layer, and a large number of roof brick layers are provided. A large number of heaters (usually SiC heaters) are installed in the holes. These heaters are connected to, for example, a bus bar disposed in the upper space of the roof brick layer by an electric wire via an aluminum strap, and the heat of the heating portion of each heater protruding into the lower space of the roof brick layer is caused by the heat generated in the upper part of the molten tin. The atmosphere is heated.

  By the way, in recent years, alkali-free glass whose molding temperature is higher by 100 ° C. or more than soda lime silica glass is used for a glass substrate of a TFT liquid crystal display (TFT-LCD). When this glass substrate is manufactured by the float process, the temperature of the molten tin bath must be higher, and therefore the temperature of the upper space in the bath must be maintained higher.

Edited by Masayuki Yamane et al., “Glass Engineering Handbook”, first edition, Asakura Shoten Co., Ltd., July 5, 1999, p. 358-362

  However, when an alkali-free glass having a molding temperature of 100 ° C. or higher compared to soda lime silica glass is formed into a glass plate using a float bath or float method established for soda lime silica glass, various problems occur. . One such problem is an increase in the atmospheric temperature of the upper space (hereinafter sometimes simply referred to as the upper space) as described below.

  In the upper space, as described above, for example, an electric wiring member such as a bus bar, an electric wire, etc., a heater end (a portion other than the heater power supply unit and the heater power supply unit to which a strap for supplying power to the heater is attached), Etc. exist. Of these, the highest temperature is the flat mesh wire strap made of aluminum that is directly attached to the heater power supply part whose temperature is high due to heat conduction from the heater heat generating part in the lower space.

  If this strap is damaged due to its high temperature and power cannot be supplied to the heater to which the strap is attached, sufficient heating cannot be performed. If such damage occurs, control of the set temperature of the float bath upper space is impaired, which causes inconvenience in manufacturing a high-quality glass plate, and if this strap is damaged in large numbers, it may become a serious problem in manufacturing. There is.

The upper space atmosphere temperature _Tr is normally controlled so as not to exceed 300 ° C. in order to prevent troubles due to such strap damage. The control upper limit temperature of 300 ° C for the upper space ambient temperature T _r guarantees that strap damage will not occur for a long period of time, for example 10 years, based on the experience and experience obtained by applying the float method to soda lime silica glass for many years. Established as temperature.

By the way, when trying to mold glass with a higher molding temperature than soda lime silica glass (hereinafter sometimes referred to as high viscosity glass) by the float method, it floats more than when trying to mold soda lime silica glass by the float method. The molten tin temperature of the bath must be kept higher and the upper space ambient temperature T becomes higher. When the upper space atmospheric temperature _Tr is likely to exceed 300 ° C., the volume flow rate V _g of the atmospheric gas (typically, a mixed gas of nitrogen and hydrogen) is increased. That is, the temperature of the strap is lowered by forcibly convection of the atmospheric gas and removing heat from the surface of the heater end by the atmospheric gas flowing in the vicinity of the strap. The atmospheric gas is introduced into the upper space through a hole provided on the upper surface of the roof casing and the like, and after cooling the electric wiring member or the like, it flows into the lower space through the hole in the roof brick layer to prevent oxidation of molten tin.

However, such an increase in the volume flow V _g is a vicious cycle of increased, again rise → volume flow V _g of the heater output, up → upper space atmospheric temperature T _r to compensate the attenuation → the offset of heater Not only is there a possibility of bringing about this, but it also increases the possibility of generating or increasing tin defects (top spec) on the glass ribbon. In recent years, glass substrates for TFT-LCDs have been increased in size and the demand for higher quality has been increasing. However, the increase in top specs as described above increases the production efficiency, especially the manufacture of large glass substrates. Reduce efficiency.

In addition, the requirements for the characteristics of the glass used for the substrate have become more sophisticated, and glasses that can cope with it have been developed. However, the molding temperature of such glass is generally higher. That is, the upper space ambient temperature _Tr becomes higher. Therefore, when float-forming the glass for TFT-LCD substrate, without increasing the volume flow rate V _g as the upper space atmosphere temperature T increases (in other words, without generating or increasing the top spec), It has become necessary to suppress the temperature rise of the strap.

  An object of the present invention is to provide a float bath and a float forming method capable of solving such problems.

The present invention has a bottom on which molten tin is given and a roof that covers the bottom, and a space in the roof is divided into an upper space and a lower space by a roof brick layer, and is provided in the roof brick layer. The heater end is located in the upper space, and has a power supply portion to which a strap for supplying power to the heater is attached. Where S ′ _k and emissivity are ε _k, and S ′ _n and emissivity are ε _n and the surface area of the heater end other than the power feeding portion is S ′ _n and emissivity are S ′ _k · ε _k + S ′ _n Provided is a float bath characterized in that the heater end is configured to satisfy ε _n ≧ 3630 mm ² .

Further, there is provided a float bath characterized in that a radiation rate ε _{k of the} power feeding unit is 0.7 or more and a radiation rate ε _n of a portion other than the power feeding unit at the heater end is 1.0. .

  The heater is made of silicon carbide (SiC), the power feeding portion has a surface metallized with aluminum, and the strap is made of aluminum.

  Further, the float bath is characterized in that the heater is formed in a cylindrical shape and has an outer diameter of 23 to 50 mm.

  Further, the molten glass is continuously poured onto the molten tin from one end of the float bath, the glass is formed into a glass ribbon on the molten tin, and the glass ribbon is continuously formed from one end of the float bath. A float forming method is provided.

The inventor has reached the present invention through the following process. Alkali-free glass AN635 (trade name of Asahi Glass Co., Ltd., molding temperature: 1210 ° C) has been used for a long time as a glass for TFT-LCDs, but it is alkali-free to meet the higher requirements for glass properties as described above. AN100 (Asahi Glass Co., Ltd. trade name, molding temperature: 1268 ° C.) was developed as a glass. However, when trying to float-form AN100 using a float bath that had been float-formed AN635, the load per unit area of the heater became too large, and it proved difficult for long-term stable production. did. Further, in order to reduce the same load of the heater, the upper space atmospheric temperature T _r be increased volume flow V _g to the extent that risk of increasing top speck does not significantly increase does not decrease only to 320 ° C., the float bath It has been found that it is not preferable to use and produce AN100 for a long time.

On the other hand, the present inventors paid attention to the heat dissipation performance of the heater, and prevented the strap from being overheated even when the upper space ambient temperature _Tr increased by efficiently radiating heat from the surface of the heater end. In other words, by improving the surface area of the heater end and the emissivity of the surface of the heater end, the heater end in a state where the upper space atmosphere temperature _Tr has increased by 20 ° C. (for example, from 300 ° C. to 320 ° C.). the temperature T _s, were examined condition that allows to reduce to the heater end temperature T _s in the previous state (e.g., 300 ° C.) to the upper space atmospheric temperature T _r is increased.

  First, in the conventional float bath, the heater is formed of silicon carbide (SiC) in a substantially cylindrical shape, and the length of the heater end located in the upper space is 46 mm. The power supply portion is provided with a surface of 40 mm from the protruding end of the heater by metalizing the surface with aluminum by impregnating SiC with aluminum, and the power supply portion has a flat mesh wire made of aluminum. Further, a portion other than the power feeding portion (hereinafter referred to as a non-power feeding portion) at the heater end is provided with a length of 6 mm so that SiC is exposed.

  In addition, regarding the radiation rate of the surface of the heater in the power feeding portion (with the strap attached; the same applies hereinafter in the calculation) and the non-power feeding portion, the radiation rate of the carbon paste showing characteristics very close to a black body is 1.0. In this case, the feeding portion is 0.7, and the non-feeding portion where SiC is exposed is 1.0. Here, the emissivity of the surface in the power feeding part and the non-power feeding part of the heater was calculated as follows.

First, in a substantially cylindrical member made of SiC, a test piece a having a carbon paste (Nisshinbo Co., Ltd. carbon adhesive ST-201) applied on the surface, a test piece b having a metallized surface, Prepare a test piece c with metallization and a strap attached, and a test piece d with SiC exposed, and store each test piece in an electric heating furnace maintained at an ambient temperature of 300 ° C. And it heats for a predetermined time (5 hours or more) until the temperature of each test piece will be 300 degreeC.
Next, each test piece heated to 300 ° C. was taken out of the electric heating furnace, and immediately after (within 30 seconds) the surface temperature of each test piece using an infrared thermal imager (thermotracer TH3104MR manufactured by NEC Sanei Co., Ltd.). Measure.
Assuming that the emissivity of the test piece a to which the carbon paste is applied is 1.0, the test piece b subjected to metallization, the test piece c to which the strap is attached, and the test piece d to which SiC is exposed. Is calculated by the following equation (A).
1.0 × (T _c +273) ⁴ = 1 / ε × (T + 273) ⁴ (A)
Here, T _c is the surface temperature (° C.) of the test piece coated with the carbon paste, T is the test piece b subjected to the metallization treatment, the test piece c attached with the strap, or the test in which SiC is exposed. The surface temperature of the piece d, ε is the emissivity of the test piece b subjected to the metallization treatment, the test piece c attached with the strap, or the test piece d where SiC is exposed, and the test piece from the formula (A) The emissivities ε of b, c, and d were 0.7, 0.7, and 1.0, respectively.

  The inventor then performed various measurements and calculations on the float bath, and based on the results, constructed the following calculation model. FIG. 1 is an explanatory diagram of this calculation model.

This calculation model is a heat balance model of the upper space 20. It is considered that the heat input Q _in to the upper space 20 is all due to radiant heat from the heater end, and the heat input Q _ink from the power feeding portion of the heater is expressed by Equation (1).
_{Q ink = ε k h · S} k · N (T s -T r) ··· (1)
Further, the heat input Q _inn from the non-power-feeding portion of the heater is expressed by Equation (2).
Q _inn = ε _n h · S _n · N (T _s −T _r ) (2)
Here, S _k is the surface area of the power feeding portion of the heater, S _n is the surface area of the non-power feeding portion of the heater, ε _k is the emissivity of the power feeding portion of the heater, and ε _n is the emissivity of the non-power feeding portion of the heater. , N is the number of heaters per unit area on the horizontal plane of the roof brick layer 16, h is the heat transfer coefficient due to radiation, T _s is the temperature of the heater end.
Accordingly, the heat input Q _in to the upper space 20 is expressed by the equation (3).
Q _in = Q _ink + Q _inn (3)

Meanwhile, the heat output _{Q out} from the upper space 20, a portion in contact with the upper space 20 of the roof casing 19 atmosphere gas supplied (hereinafter, referred to as the wall portion.) Heat dissipation _{Q outa} to the outside world, and the upper space 20 a quantity of heat _{Q OUTG} spent temperature _{rise, Q outa} is ambient temperature _{T a,} the area _{a w} of the wall portion, represented by the formula (4) using the overall heat transfer coefficient _{h c.}
Q _outa = h _c A _w (T _r −T _a ) (4)
Moreover, Q _outg is represented by Formula (5) using T _r , T _a , volume flow rate V _{g of} ambient gas, density ρ _g , and specific heat C _g .
Q _outg = V _g ρ _g C _g (T _r −T _a ) (5)
Therefore, the heat output Q _out from the upper space 20 is expressed by Expression (6).
Q _out = Q _outa + Q _outg (6)

Equation (7) is established from Q _in = Q _{out in the} thermal equilibrium state.
_{Q ink + Q inn = Q outa} + Q outg ··· (7)
When the upper space ambient temperature T _r = 320 ° C. is suffix 1 and when the upper space atmosphere temperature T _r = 300 ° C. is suffix 2, Equation (7) is rewritten as Equation (8) and Equation (9), respectively. It is done.
ε _kh · S _k · N (T _s1 −T _r1 ) + ε _n h · S _n · N (T _s1 −T _r1 )
_{= H c A w (T r1} -T a) + V g ρ g C g (T r1 -T a) ··· (8)
ε _kh · S _k · N (T _s2 −T _r2 ) + ε _n h · S _n · N (T _s2 −T _r2 )
_{= H c A w (T r2} -T a) + V g ρ g C g (T r2 -T a) ··· (9)
The equations (8) and (9) are rearranged to obtain the equation (10).
(T _s1 −T _r1 ) / (T _s2 −T _r2 ) = (T _r1 −T _a ) / (T _r2 −T _a ) (10)

Here, when the ambient temperature T _a = 40 ° C., the heater end temperature T _s at the location where the upper space atmosphere temperature T _r = 200 ° C. was measured, and Ts = 400 ° C. Since the heater end temperature T _s1 at the location of the upper space ambient temperature T _r1 (= 320 ° C.) is substantially difficult to measure due to the structure and operation of the roof of the float bath, it is temporarily 520 ° C. (400+ (320−200 )). In equation (10), when T _s1 = 520 ° C., T _r1 = 320 ° C., and T _a = 40 ° C. are substituted, the heater end temperature T _s2 at the upper space ambient temperature T _r2 (= 300 ° C.) is T _s2 = 486 ° C is expected. Note that the heater end has an outer diameter L ₃ = 25 mm (in the calculation, the thickness of the strap is assumed to be 0), and the feeding portion is exposed to SiC by L ₁ = 40 mm from the protruding end of the heater end. The non-feeding portion is L ₂ = 6 mm, ie, the feeding portion of the heater has a surface area S _k = 3632 mm ² and an emissivity ε _k = 0.7, and the non-feeding portion of the heater has a surface area S _n = 471 mm ² and The emissivity ε _n = 1.0. The surface areas S _k and S _n of the power supply unit and the non-power supply unit of the heater refer to the surface area of the outer surface (outer peripheral surface and protruding end surface) of the heater.

Next, by appropriately setting the surface area of the power feeding portion of the heater and the surface area of the non-power feeding portion of the heater (respectively S ′ _k and S ′ _n ), the upper space atmosphere temperature T _r1 (= 320 ° C.) Consider that the heater end temperature T _s is lowered from T _s1 to T _s2 .

In Equation (9), T _r2 is replaced with T _r1 to obtain Equation (11).
_{ε k h · S'k · N} (T s2 -T r1) + ε n h · S'n · N (T s2 -T r1)
_{= H c A w (T r1} -T a) + V g ρ g C g (T r1 -T a) ··· (11)
Expression (12) is obtained from Expression (8) and Expression (11).
_{{(Ε k S k + ε} n S n) (T s1 -T r1)} / {(ε k S'k + ε n S'n) (T s2 -T r1)} = 1 ··· (12)

In Expression (12), T _r1 = 320 ° C., T _s1 = 520 ° C., and T _s2 = 486 ° C. are substituted to obtain Expression (13).
_{ε k S'k + ε n S'} n = 1.2048 (ε k S k + ε n S n) ··· (13)

In equation (13), S _k = 3632 mm ² , ε _k = 0.7, S _n = 471 mm ² , and ε _n = 1.0 are substituted to obtain the following equation.
ε _k S ′ _k + ε _n S ′ _n = 3630 mm ²
That is,
ε _k S ′ _k + ε _n S ′ _n ≧ 3630 mm ² (14)
Thus, the heater end temperature T _s1 at the upper space atmosphere temperature T _r1 = 320 ° C. can be made equal to or lower than the heater end temperature T _s2 at the upper space atmosphere temperature T _r2 = 300 ° C.

  According to the present invention, a high-viscosity glass in which the equipment life is remarkably shortened or the top spec is likely to be generated or increased when trying to float form using a conventional float bath, It becomes possible to float so as not to cause an increase.

It is a calculation model which shows the heat balance of upper space. It is sectional drawing which shows notionally the float bath which is one Embodiment which concerns on this invention. FIG. 3 is an enlarged cross-sectional view of a main part of the float bath in FIG. 2.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 2 is a diagram conceptually showing a cross section (part) of a float bath according to an embodiment of the present invention. The float bath 10 includes a bottom 12 on which molten tin 11 is given and a roof 14 that covers the bottom 12. The maximum value of the width of the molten tin 11 is typically 1 to 10 m.

  The roof 14 includes a steel roof casing 19 that is suspended from an upper structure (not shown) such as a beam of a building in which the float bath 10 is installed, and a heat insulating brick that is a lining of a lower portion of the roof casing 19. And a steel box-shaped side seal 13 mounted on the edge of the bottom 12. The space in the roof 14 is divided into an upper space 20 and a lower space 21 by the roof brick layer 16.

  The roof brick layer 16 is composed of a large number of silimanite support tiles (not shown) and a grid-like framework in which rail tiles (not shown) are orthogonally crossed on the support tiles (not shown). A block is placed. The support tile is suspended from a ceiling portion of the roof casing 19 by a member called a hanger (not shown). That is, the roof brick layer 16 is horizontally held at a desired height above the molten tin 11 by the hanger. Note that the side surface of the roof brick layer 16 is in contact with the upper portion of the side surface of the sidewall 15, and the upper surface of the roof brick layer 16 is set to be substantially the same height as the upper surface of the sidewall 15. The roof brick layer 16 is formed with a hole 17 for allowing the heater 18 to pass therethrough. The thickness of the roof brick layer 16 is conventionally about 292 mm.

  In the upper space 20, three bus bars 22 are arranged in parallel, and are connected to the heater 18 through electric wires 23 and flat mesh-like straps 24 made of aluminum. The heater 18 is usually made of SiC, and the lower end thereof is connected as a unit by a connecting member 25 as a unit.

As shown in FIG. 3, the end portions of these heaters 18 are located below the power supply portion 18A, and a power supply portion 18A in which the surface is metallized by impregnating aluminum and the strap 24 is attached by caulking 41. A non-feeding part 18B whose surface is not metallized and SiC is exposed, and the feeding part 18A and the non-feeding part 18B protrude above the roof brick layer 16 (that is, in the upper space 20). The Further, the heater 18 has 18C below 18B and positioned in the hole 17 (18A, 18B, and 18C are non-heat generating portions), and a heat generating portion 18D that protrudes into the lower space 21 below 18C. A through hole is formed in the heater 18 in the vicinity of the boundary between 18B and 18C, and the heater 18 is suspended from the roof brick layer 16 by a mounting pin 51 inserted into the through hole. The outer diameter L ₃ of the heater 18 is preferably 23 mm to 50 mm, more preferably 23 mm to 30 mm, and particularly preferably about 25 mm. In this embodiment, the heater 18 is formed in a substantially cylindrical shape with an outer diameter L ₃ = 25 mm. Yes.

In the heater 18 having an outer diameter L ₃ (25 mm in the present embodiment), the surface area of the power feeding portion 18A is S ′ _{k and the} emissivity is ε _k, and the surface area of the non-power feeding portion 18B is S ′ _{n and the} emissivity. in case of the epsilon _n, so as to satisfy the _{S'k · ε k + S'n} · ε n ≧ 3630mm 2 from equation (14), the feeding portion 18A and the non-feeding part 18B, respectively, of _{L 1} and _{L 2} It is formed with a length.

In the present embodiment, the power supply portion 18A of the heater 18 is preferably metallized by impregnating aluminum or the like in consideration of reduction in contact resistance with the strap attached to the power supply portion. It is preferably made of aluminum and is preferably a flat mesh wire. However, it is not limited to the flat net line. Therefore, the emissivity ε _k of the power feeding unit 18A to which the strap is attached is 0.7 as described above. However, when the surface of the heater power feeding unit and the strap are other metal, the emissivity ε _k of the power feeding unit 18A is Let it be the emissivity of other metals.

In the present embodiment, SiC is exposed in the non-feeding portion 18B of the heater 18, and thus the emissivity ε _n of the non-feeding portion 18B is 1.0 as described above. Even when the heater 18 is made of SiC, when the manufacturing method is less than 1.0, or when the heater 18 is made of a material other than SiC, a carbon paste is applied to the surface of the non-power-feeding portion 18B. It is preferable that the emissivity ε _n is equivalent to 1.0. Further, it is possible to apply carbon paste to the power feeding portion 18A and the strap within a range that does not hinder the power feeding structure, and to set the radiation rate of the power feeding portion to which the strap is attached to 0.7 or more.

As described above, the heater 18 has an outer diameter L ₃ = 25 mm (assuming that the strap thickness is 0), the emissivity ε _k = 0.7 of the power feeding unit 18A and the strap 24, and the non-power feeding unit 18B. When the emissivity ε _n = 1.0, for example, when the length L ₁ = 40 mm of the power supply unit 18A and the surface area S ′ _k = 3632 mm ² ((25/2) 2 × π + 25π × 40), In order to cope with the problem by increasing the surface area S ′ _n of the non-feeding portion 18B, S ′ _n ≧ 1089 mm ² may be satisfied from the equation (14). In this case, the non-feeding portion may be 18B length L ₂ ≧ 13.9 mm (1089 / 25π).

  The circumferential average distance of the gap between the inner surface of the hole 17 of the roof brick layer 16 and 18C located in the hole 17 is generally 20 mm or less, more preferably 10 mm or less, and the circumferential average distance is 20 mm or less. It is preferable that a certain part is 80% or more of the depth of the hole 17, and it is more preferable that it is 100%.

Returning again to FIG. 2, atmospheric gas (mixed gas of N ₂ and H ₂ ) is supplied to the upper space 20 from the supply port 26 of the roof casing 19 as shown by the arrow, and passes through the gap between the holes 17 and 18C. Then, it flows into the lower space 21 and suppresses oxidation of the molten tin 11. Thereby, the rise in the atmospheric temperature _Tr of the upper space 20 is also suppressed. The flow rate of the atmospheric gas used in this case can be set so as not to cause an increase in top spec.

In the float forming method of the present invention, glass having a forming temperature (temperature at which the viscosity becomes 10 ⁴ poise) of 1100 ° C. or higher can be float formed using such a float bath 10. That is, the glass melted in a glass melting kiln or the like is melted from the known tin spout (not shown in FIG. 2, for example, on the back side) located at one end (upstream end) of the float bath 10. Pour continuously on top. The molten glass continuously poured onto the molten tin 11 is formed into a glass ribbon 27 having a desired shape by a known method. The glass ribbon 27 is continuously drawn out from the float bath 10 by a lift-out roller (take-up roller) located adjacent to the other end (downstream end) of the float bath 10. The glass ribbon 27 is typically drawn continuously at a rate of 1 to 200 tons / day.

The glass ribbon drawn out by the lift-out roller is gradually cooled in a layer (slow cooling kiln), and then cut into a desired size to obtain a glass plate. By using the float bath 10 described above, the high-viscosity glass can be produced without particularly increasing the number of top specs and without increasing the possibility that production will be forced to stop even in a short period of time. Float molding is possible.
It should be noted that a conventional heater can be used at a location where the upper space does not exceed 300 ° C. (for example, the float bath layer side).

  The present invention is not limited to the above-described embodiment, and appropriate modifications, improvements, and the like are possible. The bottom, roof, roof brick layer, upper space, lower space, heater, exemplified in the above-described embodiment, The atmosphere gas, temperature, draw-out amount, float bath member material, shape, dimensions, form, number, arrangement location, thickness, etc. are arbitrary as long as the object of the present invention is not impaired.

  Further, the high-viscosity glass is not limited to glass for TFT-LCD substrates, and may be glass for plasma display panel substrates, for example. The float bath of the present invention may be used not only for high-viscosity glass but also for float molding of soda lime glass, for example.

DESCRIPTION OF SYMBOLS 10 Float bath 11 Molten tin 12 Bottom 14 Roof 16 Roof brick layer 17 Hole 18 Heater 18A Power supply part 18B Non-power supply part 20 Upper space 21 Lower space 24 Strap

Claims (7)

It has a bottom covered with molten tin and a roof covering the bottom, and the space in the roof is divided into an upper space and a lower space by a roof brick layer and penetrates a hole provided in the roof brick layer Then, using a float bath in which a heater is installed, a float forming method for forming a glass having a viscosity of 1100 ° C. or higher at a viscosity of 10 ⁴ poise,
The heater is formed of silicon carbide (SiC);
The heater end located in the upper space includes a power supply unit to which a strap for supplying power to the heater is attached, and a non-power supply unit that is a part other than the power supply unit,
When the surface area of the power feeding part is S ′ _k and the emissivity is ε _k , the surface area of the non-power feeding part is S ′ _n and the emissivity is ε _n ,
Configure the heater end so that S ′ _k · ε _k + S ′ _n · ε _n ≧ 3630 mm ² and S ′ _n ≧ 1089 mm ² ,
Heating with the heater while supplying atmospheric gas, continuously pouring the molten glass onto the molten tin from one end of the float bath, forming the glass into a glass ribbon on the molten tin, the glass A float forming method, wherein the ribbon is continuously pulled out from one end of the float bath. 2. The float forming method according to claim 1, wherein an emissivity ε _{k of the} power feeding unit is 0.7 or more and an emissivity ε _n of the non-feeding unit is 1.0.   3. The float forming method according to claim 1, wherein a surface of the power feeding portion is metallized with aluminum, and the strap is made of aluminum.   The float forming method according to any one of claims 1 to 3, wherein the heater is formed in a cylindrical shape and has an outer diameter of 23 to 50 mm.   The float forming method according to any one of claims 1 to 4, wherein the non-feeding portion is formed by exposing silicon carbide (SiC).   The float forming method according to claim 1, wherein the strap has a flat mesh shape.   The float forming method according to any one of claims 1 to 6, wherein an average distance in a circumferential direction of a gap between a heater penetrating the hole and an inner surface of the hole is 20 mm or less.

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