Patent Description:
During the course of manufacturing glass, a pair of electrodes is often used when manufacturing molten glass in a melting furnace.

Each of the electrodes is mounted "vertically" to penetrate through a bottom portion of the melting furnace from the bottom portion side. Molten glass can be obtained by energizing with an electric current the pair of electrodes in such an arrangement.

<CIT> discloses heaters for melting glass, with heating tubes made of e.g. Inconel <NUM> and cores fitted inside the tubes, the cores being made of a material with a lower electrical resistivity, e.g. nickel.

In a conventional method of melting glass, when directly heating molten glass, the molten glass is Joule-heated by flowing an alternate current between the electrodes inserted into the molten glass. Therefore, through holes for inserting the electrodes are formed at the bottom portion of the melting furnace.

The dimension of the cross-section perpendicular to the extending direction of these through holes is normally selected to be sufficiently greater compared to the dimension of the cross-section perpendicular to the axial direction of the electrodes. This is to prevent breakage of the electrodes or the melting furnace during the course of manufacturing molten glass caused by the electrodes coming into contact with the side walls forming the through holes, due to a difference in magnitude of the thermal expansion between the materials of the melting furnace and the electrodes.

However, due to such dimensioning, while manufacturing molten glass, the molten glass may leak from a "gap" between a side wall and an electrode. In order to avoid such leakage, a cooling member is typically provided around the electrode.

Part of the cooling member is positioned to face the lower surface of the bottom portion of the melting furnace when the electrode is inserted into the melting furnace.

By supplying a refrigerant such as air or water to the cooling member installed in this way, the molten glass that is falling through the gap can be solidified halfway through while manufacturing molten glass. Also, the solidified glass layer can be used as a sealing material to close the gap.

However, such a cooling member is not desirable from the viewpoint of the heating efficiency of glass. In other words, the presence of such a cooling member acts on the molten glass at the bottom of the melting furnace, to move the temperature in a reducing direction. Therefore, the heating efficiency of the glass decreases.

Also, as the electrodes themselves are not the heating elements, in such circumstances, in order to give a desired temperature history to the entirety of the molten glass, an additional facility is required so as to generate convective circulation in the molten glass. For example, it is necessary to make the melting furnace larger, or to install a stirring device. However, such measures lead to the cost increase of the manufacturing facilities.

The present invention was devised in view of such background, and the present invention has an object to provide a heater for melting glass that can significantly increase the heating efficiency of molten glass compared to a conventional heater.

According to the present invention, a heater for melting glass is provided that includes:.

According to the present invention, a heater for melting glass that can significantly increase the heating efficiency of molten glass compared to a conventional method can be provided.

In the following, with reference to the drawings, one embodiment of the present invention will be described.

First, with reference to <FIG>, a conventional method of melting glass and its problems will be described.

<FIG> schematically illustrates a state when a conventional pair of electrodes <NUM> are installed in a melting furnace <NUM> of glass.

As illustrated in <FIG>, the melting furnace <NUM> of glass has a structure capable of containing molten glass MG in a housing space <NUM>. Specifically, the melting furnace <NUM> has a side portion <NUM> and a bottom portion <NUM> surrounded by the side portion <NUM>. The bottom portion <NUM> has an upper surface <NUM> and a lower surface <NUM>. The upper surface <NUM> is a surface of the bottom portion <NUM> in contact with the molten glass MG, and the lower surface <NUM> is a surface of the bottom portion <NUM> opposite to the upper surface <NUM>.

The melting furnace <NUM> has through holes <NUM> that penetrate through the bottom portion <NUM> from the upper surface <NUM> to the lower surface <NUM>.

The electrode <NUM> is formed of a main body <NUM> and a lead member <NUM>. The main body <NUM> is made of, for example, rod-shaped platinum or molybdenum.

The lead member <NUM> is positioned in the vicinity of one end of the main body <NUM>. Also, another end <NUM> of the main body <NUM> (referred to as "tip end") is inserted into the housing space <NUM> via the through hole <NUM> at the bottom portion <NUM> of the melting furnace <NUM>.

Note that normally, the dimension of the cross-section perpendicular to the extending direction of the through hole <NUM> is selected to be sufficiently greater compared to the dimension of the cross-section perpendicular to the axial direction of the main body <NUM> of the electrode <NUM>.

Also, in the example illustrated in <FIG>, only one pair of the electrodes <NUM> is illustrated. However, in practice, more pairs of the electrodes <NUM> are placed in the housing space <NUM> of the melting furnace <NUM>.

As illustrated in <FIG>, normally, the electrode <NUM> is provided with a cooling member <NUM>.

The cooling member <NUM> has a first portion <NUM> and a second portion <NUM>. The first portion <NUM> of the cooling member <NUM> is provided at a position facing the bottom surface <NUM> of the bottom portion <NUM> of the melting furnace <NUM>, when the electrode <NUM> is inserted into the melting furnace <NUM>. Also, the second portion <NUM> of the cooling member <NUM> is provided at a position facing a sidewall <NUM> forming the through hole <NUM> in the bottom portion <NUM> of the melting furnace <NUM>. A refrigerant such as air or water circulates in the cooling member <NUM>.

In such a configuration, the lead member <NUM> of the electrode <NUM> is connected to a power feeding device <NUM> such as an external voltage source. Therefore, an electric current can flow through the molten glass to energize and heat the molten glass between both electrodes <NUM>. As a result, the molten glass can be heated up to a desired temperature. Also, the housing space <NUM> of the melting furnace <NUM> is filled with the molten glass MG, and by flowing an alternate current between the electrodes inserted into the molten glass, the molten glass MG is Joule-heated.

Note that there are "gaps" <NUM> between the through holes <NUM> formed in the bottom portion <NUM> of the melting furnace <NUM> and the electrodes <NUM>. Therefore, the molten glass MG may leak from the gaps <NUM> while heating the molten glass MG.

The cooling member <NUM> is used for managing such leakage. In other words, by supplying a refrigerant to the first portion <NUM> and the second portion <NUM> of the cooling member <NUM>, the molten glass MG moving along the gap <NUM> can be cooled to be solidified halfway through on the sidewall <NUM>. Also, the solidified glass layer can be used as a sealing material of the gap <NUM>.

However, the second portion <NUM> of the cooling member <NUM> is placed at a position relatively close to the upper surface <NUM> of the bottom portion <NUM> of the melting furnace <NUM>, namely, the molten glass MG. Therefore, the second portion <NUM> of the cooling member <NUM> acts on the molten glass MG, to move the temperature in a reducing direction. In particular, on the upper side of the second portion <NUM> of the cooling member <NUM>, it becomes difficult to rapidly increase the temperature of the molten glass MG. As a result, a problem that the heating efficiency of the molten glass is reduced may arise.

Note that the first portion <NUM> of the cooling member <NUM> is installed at a position relatively far from the molten glass MG, and hence, has a smaller effect in lowering the temperature of the molten glass MG than the second portion <NUM>.

In contrast, the one embodiment of the present invention provides a heater that includes:.

In the one embodiment of the present invention, the heater is used for heating molten glass MG instead of the electrodes <NUM>. Also, the heater according to the one embodiment of the present invention has a configuration in which a heating member is housed in a tubular member made of metal.

In such a configuration, heat rays emitted from the heating element can be used for heating the tubular member by radiation, and the heated tubular member can be used for heating the molten glass MG.

Also, the heater according to the one embodiment of the present invention uses a heating member containing carbon (C).

Here, in the case of using metal commonly used in the heating member of a heater (e.g., materials and the like including one or more elements selected from among molybdenum, tungsten, tantalum, niobium, iridium, platinum, and rhodium) as the heating member of the heater according to the one embodiment of the present invention, the heating member may deform by its own weight during use of the heater. This is because the temperature of the molten glass MG often becomes <NUM> or higher, and thereby, the heating member is heated up to <NUM> or higher.

However, the heater according to the one embodiment of the present invention uses a heating member containing carbon (C) that does not appreciably deform even at a high temperature of <NUM> or higher. Therefore, the one embodiment of the present invention can significantly suppress the deformation of the heating member in use.

Further, the heater according to the one embodiment of the present invention has a first heat generating part and a second heat generating part in the heating member.

In this case, the first heat generating part of the heater that is to have a higher temperature can be installed in the housing space of the molten glass MG in the melting furnace <NUM>, and the second heat generating part that does not reach a high temperature as the first heat generating part, can be installed to face the through hole <NUM> (or its sidewall <NUM>) provided in the bottom portion <NUM> of the melting furnace <NUM>.

Note that the boundary between the first heat generating part and the second heat generating part may be somewhat shifted toward the housing space <NUM> side or the through hole <NUM> side on the upper surface <NUM> of the bottom portion <NUM> of the melting furnace <NUM> as long as it does not affect melting of the glass.

In the case where the heater according to the one embodiment of the present invention is positioned in this way with respect to the melting furnace <NUM>, the temperature of the through hole <NUM> (or its sidewall <NUM>) in the bottom portion <NUM> of the melting furnace <NUM> can be kept at a moderate temperature range without rising too high. Therefore, even in the case where the second portion <NUM> of the cooling member <NUM> is not used at all; even if the cooling capability of the second portion <NUM> of the cooling member <NUM> is reduced; or even if the length of the second portion <NUM> of the cooling member <NUM> is shortened and the distance from the housing <NUM> of the melting furnace <NUM> is increased, in the gap <NUM>, the molten glass MG can move along the gap <NUM> for a significant length, to protect the heater surface by being solidified.

As a result, according to the one embodiment of the present invention, a problem that the molten glass MG tends to become colder easily and to become hard to heat over the upper part of the second portion <NUM> of the cooling member <NUM>, can be alleviated. In other words, during the course of manufacturing the molten glass MG, the heating efficiency can be increased significantly.

Also, in the conventional electrodes <NUM>, in the case where the main body <NUM> is formed of molybdenum, a problem of high-temperature oxidation may arise. In other words, if the main body <NUM> is exposed at a portion facing the through hole <NUM>, the main body <NUM> is oxidized by high-temperature air, and the electrode may be degraded.

In contrast, in the one embodiment of the present invention, thanks to the effects described above, the molten glass MG can move along the gap <NUM> to coat the surface of the heater with solidified glass. Therefore, in the one embodiment of the present invention, for the tubular member, materials that are easily oxidized in high-temperature air, like molybdenum, can also be used.

Next, with reference to <FIG>, one example configuration of the heater according to the one embodiment of the present invention will be described.

<FIG> schematically illustrates an example of the structure of the heater according to the one embodiment of the present invention. <FIG> generally illustrates a cross section along the extending axis of the heater according to the one embodiment of the present invention. However, a part corresponding to the heating member <NUM> that will be discussed later is drawn in a form of other than a cross section for the sake of clarity.

As illustrated in <FIG>, the heater <NUM> according to the one embodiment of the present invention (referred to as "the first heater", hereafter) has generally a rod shape extending from a first heater end 102A to a second heater end 102B.

The first heater end 102A is closed by a lid member <NUM>. Also, the second heater end 102B is closed by a closed end of the tubular member <NUM> that will be discussed later. Therefore, inside the first heater <NUM>, an internal space <NUM> that is insulated from the outside is formed.

The internal space <NUM> can be controlled to have a desired atmosphere by a gas supplying means, a gas exhaust means, and/or the like (not illustrated) installed in the first heater <NUM>. In particular, in order to prevent oxidation of various members housed in the internal space <NUM> while using the first heater <NUM>, it is favorable that the internal space <NUM> has an atmosphere of non-oxidizing gas. For example, during the use, the internal space <NUM> may be filled with an inert gas such as argon.

With reference to <FIG> again, the first heater <NUM> includes the heating member <NUM> and the tubular member <NUM>.

The heating member <NUM> is housed in the internal space <NUM>. Meanwhile, the tubular member <NUM> is a member that demarcates the internal space <NUM> of the first heater <NUM> together with the lid member <NUM> described above, and the tubular member <NUM> protects the members housed in the internal space <NUM>. The tubular member <NUM> is closed at one end, and this closed end corresponds to the second heater end 102B in the first heater <NUM>.

The tubular member <NUM> is formed of a metal having heat resistance.

The heating member <NUM> functions as a heating element that generates heat upon being energized. The heating member <NUM> is formed of electrically conducting materials, and contains carbon (C).

The heating member <NUM> includes a first heat generating part <NUM> and a second heat generating part <NUM> that are electrically connected to each other. The first heat generating part <NUM> is arranged at a position closer to the second heater end 102B than is the second heat generating part <NUM>.

Although it may be difficult to see from <FIG>, the first heat generating part <NUM> of the heating member <NUM> is electrically connected to a first lead wire 180A at one end, namely, at the end opposite to another end connected to the second heat generating part. Also, the second heat generating part <NUM> is electrically connected to a second lead wire 180B at its one end, namely, at the end opposite to another end connected to the first heat generating part.

The first lead wire 180A is derived from a first opening 172A provided in the lid member <NUM> to the outside of the internal space <NUM>. Similarly, the second lead wire 180B is derived from a second opening 172B provided in the lid member <NUM> to the outside of the internal space <NUM>. In order to prevent the first lead wire 180A from coming into contact with the lid member <NUM>, a first insulating member 175A is attached to the first opening 172A in the lid member <NUM>. Similarly, in order to prevent the second lead wire 180B from coming into contact with the lid member <NUM>, a second insulating member 175B is attached to the second opening 172B in the lid member <NUM>.

Here, in the first heater <NUM>, in the first heat generating part <NUM>, denoting the unit-length resistance along the extending axis direction of the first heater <NUM> by X (Ω/m), and in the second heat generating part <NUM>, denoting the unit-length resistance along the extending axis direction of the first heater <NUM> by Y (Ω/m), <MAT> is satisfied.

In the following, the unit-length resistances X and Y are simply referred to as the "resistance X" and the "resistance Y", respectively.

Therefore, while using the first heater <NUM>, the first heat generating part <NUM> can reach a higher temperature than the second heat generating part <NUM>.

Note that in the present application, the resistance X of the first heat generating part <NUM> does not need to be constant over the span, and may be increased or decreased within a range of less than ±<NUM>%. The same applies to the resistance Y of the second heat generating part <NUM>.

Also, a portion may be present between the first heat generating part <NUM> and the second heat generating part <NUM> that exhibits a resistance between the two, namely, less than the resistance X and greater than the resistance Y (referred to as "the transition region", hereafter). Such a change in resistance may occur in a form such that the cross-sectional area gradually becomes larger, for example, in the transition region, from a portion contacting the first heat generating part <NUM> to a portion contacting the second heat generating part <NUM>. In such a form, the "boundary" between the first heat generating part <NUM> and the second heat generating part <NUM> is defined as a portion of the transition region that exhibits an intermediate resistance value between X and Y.

Also, the unit-length resistance of the transition region between the first heat generating part <NUM> and the second heat generating part <NUM> may be less than Y. Such a change in resistance may occur, for example, in the case where the first heat generating part <NUM> and the second heat generating part <NUM> that have been manufactured separately are joined via a thick bonding member having high rigidity.

In such a form, the "boundary" between the first heat generating part <NUM> and the second heat generating part <NUM> is defined as an intermediate position in the axial direction of the bonding member.

Here, a calculation method of the resistances X and Y will be described.

The unit-length resistance X of the first heat generating part <NUM> and the unit-length resistance Y of the second heat generating part <NUM> can be determined by software for general-purpose thermal fluid analysis such as STAR-CCM+ (produced by SIEMENS). Taking the unit-length resistance X of the first heat generating part <NUM> as an example, the calculation method will be described in detail.

The unit-length resistance Y of the second heat generating part <NUM> can also be determined in substantially the same way by sectioning a region with one surface crossing the lower end of the heating member <NUM>, and the other surface crossing the boundary between the first heat generating part <NUM> and the second heat generating part <NUM>.

Next, with reference to <FIG>, operations of the first heater <NUM> having such a configuration will be described.

<FIG> schematically illustrates a state when the first heater <NUM> is installed in the melting furnace <NUM> of glass. Note that the configuration of the melting furnace <NUM> has already been described with reference to <FIG> above. Therefore, here, except for matters related to the one embodiment of the present invention, the detailed description of the configuration of the melting furnace <NUM> is omitted.

Note that in the example illustrated in <FIG>, attention should be paid to the first portion <NUM> of the cooling member <NUM> in <FIG> as being attached to the bottom portion <NUM> of the melting furnace <NUM>, not to the first heater <NUM>. Also, in the example illustrated in <FIG>, the second portion <NUM> of the cooling member <NUM> in <FIG> is removed.

As illustrated in <FIG>, when using the first heater <NUM>, at the outset, the first heater <NUM> is installed in the melting furnace <NUM>. The first heater <NUM> is installed "vertically" so that the second heater end 102B side is inserted into the housing space <NUM> via the through hole <NUM> at the bottom portion <NUM> of the melting furnace <NUM>.

Next, raw materials of glass are supplied into the housing space <NUM> of the melting furnace <NUM>.

Thereafter, by using a power feeding device (not illustrated in <FIG>), an electric current is supplied to the first lead wire 180A and the second lead wire 180B of the first heater <NUM>. This makes the heating member <NUM> resistance-heated, and the resulting radiation heats up the tubular member <NUM>. Also, the heat from the tubular member <NUM> heats up the molten glass MG.

Here, the gap <NUM> is present between the through hole <NUM> formed in the bottom portion <NUM> of the melting furnace <NUM> and the first heater <NUM>. Therefore, in a conventional method of melting glass, the cooling member <NUM> has been used to prevent leakage of molten glass MG (see <FIG>).

However, in the case of using the first heater <NUM>, the temperature drop of the molten glass at the bottom portion of the furnaces of due to the conventional cooling member <NUM> can be suppressed.

In the following, this effect will be described.

As described above, in the first heater <NUM>, the heating member <NUM> has the first heat generating part <NUM> and the second heat generating part <NUM> along the extending axis direction of the first heater <NUM>. Also, in the internal space <NUM> of the first heater <NUM>, the first heat generating part <NUM> is installed at a position closer to the second heater end 102B than is the second heat generating part <NUM>.

Therefore, when the first heater <NUM> is arranged in the melting furnace <NUM>, the first heater <NUM> can be arranged, with respect to the melting furnace <NUM>, such that the height position of the first heat generating part <NUM> corresponds to the housing space <NUM> of the melting furnace <NUM>, and the height position of the second heat generating part <NUM> corresponds to the through hole <NUM> of the melting furnace <NUM>. In other words, the first heater <NUM> can be installed, with respect to the melting furnace <NUM>, such that the first heat generating part <NUM> is inside the housing space <NUM>, and the second heat generating part <NUM> faces the through hole <NUM>.

Also, between the first heat generating part <NUM> and the second heat generating part <NUM>, the relationship of Formula (<NUM>) described above is satisfied. Therefore, the first heat generating part <NUM> can provide a greater amount of heat to the tubular member <NUM> than the second heat generating part <NUM>.

Therefore, at a position corresponding to the first heat generating part <NUM>, the tubular member <NUM> can provide a greater amount of thermal energy to the outside, whereas at a position corresponding to the second heat generating part <NUM>, the tubular member <NUM> can suppress the amount of heat provided to the outside. As a result, the temperature of the gap <NUM> can be significantly reduced compared to the temperature of the housing space <NUM>.

Also, in this case, the molten glass MG that moves from the housing space <NUM> through the gap <NUM> is solidified halfway through, and thereby, the gaps <NUM> can be sealed by a glass layer.

In this way, in the case of using the first heater <NUM>, the temperature drop of the molten glass due to the conventional cooling member <NUM> can be suppressed.

Therefore, in the case of using the first heater <NUM>, the heating efficiency when manufacturing molten glass can be increased significantly.

Also, in the case of simply using a heater instead of a conventional electrode, the temperature of the bottom portion <NUM> of the melting furnace <NUM> may become too high, and thereby, erosion of the material of the bottom portion <NUM> may be accelerated. However, in the first heater <NUM>, the temperature of the second heat generating part <NUM> does not become as high as that of the first heat generating part <NUM>. Therefore, in the first heater <NUM>, erosion of the bottom portion <NUM> of the melting furnace <NUM> can be suppressed significantly.

Next, the constituent members included in the heater according to the one embodiment of the present invention will be described in more detail. Note that here, for the sake of clarity, the constituent members will be described taking the first heater <NUM> as an example. Therefore, when referring to each of the members, the reference numeral illustrated in <FIG> will be used.

The external shape of the first heater <NUM> is not limited in particular. The first heater <NUM> may have, for example, a generally cylindrical shape or a generally square column shape. Also, a cross section perpendicular to the extending axis direction of the first heater <NUM> may be generally circular, generally elliptic, generally triangular, generally quadrangular, or may have any other polygonal shape (including a trapezoid).

Note that in the following description, as an example, it is assumed that the first heater <NUM> is generally circular in cross section.

It is favorable that the internal space <NUM> housing the heating member <NUM> has a low oxygen partial pressure while using the first heater <NUM>.

For this reason, the internal space <NUM> may be filled with a non-oxidizing gas such as a reducing gas and/or an inert gas. As the reducing gas, hydrogen may be used, and as the inert gas, one or more elements selected from among argon, helium, neon, krypton, xenon, radon, and nitrogen may be used.

In addition to this or separately from this, the internal space <NUM> may be adjusted to have approximately the atmospheric pressure in the use state of the first heater <NUM>.

In order to implement such an environment, the lid member <NUM> may be provided with one, two, or more ports in communication with the internal space <NUM>. Through these ports, the internal space <NUM> can be filled with gas, and the gas can be exhausted from the internal space <NUM>.

The configuration of the lid member <NUM> is not limited in particular, as long as the environment of the internal space <NUM> can be maintained properly. Therefore, here, the description related to the lid member <NUM> is omitted.

The heating member <NUM> has the first heat generating part <NUM> and the second heat generating part <NUM>. Both the first heat generating part <NUM> and the second heat generating part <NUM> can be formed of materials containing carbon (C).

Materials containing carbon (C) include, for example, graphite, carbon fiber reinforced carbon composite (CC composite), and the like.

Such a carbon material has a feature that deformation does not appreciably occur even at a high temperature of <NUM> or higher. Therefore, by forming the heating member <NUM> with a carbon-containing material, a problem of deformation of the heating member <NUM> due to its own weight while using the first heater <NUM> can be suppressed significantly.

This feature also allows the first heater <NUM> to be used in a "vertical" orientation as illustrated in <FIG>.

Here, the first heat generating part <NUM> and the second heat generating part <NUM> are configured to satisfy Formula (<NUM>) described above.

In other words, in order to satisfy Formula (<NUM>) described above, the second heat generating part <NUM> may have different materials and/or different shapes other than those of the first heat generating part <NUM>.

The shape of the first heat generating part <NUM> is not limited in particular. The first heat generating part <NUM> may have, for example, a circular tube shape having periodic slits as illustrated in <FIG>. Alternatively, the first heat generating part <NUM> may be coil-shaped, rod-shaped (non-hollow), plate-shaped, tubular (hollow), or the like.

<FIG> illustrates an example of a solid figure of the heating member <NUM>.

In <FIG>, the first heat generating part <NUM> has a structure in which a hollow, generally cylindrical electric conductor is provided with multiple slits along the extending axis direction of the first heater <NUM>. The slits are provided alternately from a first direction (e.g., from the upper right side in <FIG>) and a second direction (e.g., from the lower left side in <FIG>) opposite to the first direction.

Similarly, the shape of the second heat generating part <NUM> is not limited in particular. The second heat generating part <NUM> may have, for example, a tubular (hollow) shape as illustrated in <FIG> provided with a small number of slits (two slits in <FIG>) along the extending axis direction of the first heater <NUM>.

Alternatively, the second heat generating part <NUM> may have a coil shape, rod shape (non-hollow), plate shape, or the like. Also, in the case where the first heat generating part <NUM> and the second heat generating part <NUM> have a cylindrical shape with helically periodic slits, the first heat generating part <NUM> and the second heat generating part <NUM> may have slits provided with different periods. Alternatively, in the case where the first heat generating part <NUM> and the second heat generating part <NUM> have a cylindrical shape with multiple slits along the extending axis direction of the first heater <NUM>, as illustrated in <FIG>, the first heat generating part <NUM> and the second heat generating part <NUM> may have slits provided with different periods. Alternatively, the first heat generating part <NUM> and the second heat generating part <NUM> may have different shapes from each other.

Alternatively, both the first heat generating part <NUM> and the second heat generating part <NUM> may be formed to have a coil shape. Between the coil-shaped first heat generating part <NUM> and the coil-shaped second heat generating part <NUM>, the number of turns and/or the thickness of the coil may be varied so as to satisfy Formula (<NUM>) described above.

Meanwhile, as for the material, for example, the first heat generating part <NUM> may be formed of a CC composite having a first carbon content (C1), and the second heat generating part <NUM> may be formed of a CC composite having a second carbon content (C2). By selecting appropriate C1 and C2 and satisfying C1<C2, the first heat generating part <NUM> and the second heat generating part <NUM> that satisfy Formula (<NUM>) described above can be formed.

In addition to this or separately from this, for example, the first heat generating part <NUM> may be formed of a CC composite having a first porosity (P1), and the second heat generating part <NUM> may be formed of a CC composite having a second porosity (P2). By selecting appropriate P1 and P2 and satisfying P1>P2, the first heat generating part <NUM> and the second heat generating part <NUM> that satisfy Formula (<NUM>) described above can be formed.

It would be obvious for one skilled in the art who scrutinizes the description of the present description that there may also be various combinations for the first heat generating part <NUM> and the second heat generating part <NUM>.

In order to compensate for the temperature drop at the bottom portion of the furnace due to the cooling member, as in Formula (<NUM>) described above, the resistance X (Ω/m) in the first heat generating part <NUM> and the resistance Y (Q/m) in the second heat generating part <NUM> satisfy (<NUM>/<NUM>)X < Y. It is favorable that the relationship between the two satisfies (<NUM>/<NUM>)X < Y, and more favorable to satisfy (<NUM>/<NUM>)X < Y.

Meanwhile, the resistance X (Ω/m) and the resistance Y (Q/m) satisfy Y < (<NUM>/<NUM>)X, in order to suppress erosion of the bottom portion of the furnace. It is favorable that the relationship between the two satisfies Y < (<NUM>/<NUM>)X, and more favorable to satisfy Y < (<NUM>/<NUM>)X.

The temperature of the first heat generating part <NUM> while using the first heater <NUM> also varies depending on the type of glass to be melted, for example, within a range of <NUM> to <NUM>. The temperature of the first heat generating part <NUM> may be within a range of <NUM> to <NUM>.

Meanwhile, the temperature of the second heat generating part <NUM> while using the first heater <NUM> is lower than the temperature of the first heat generating part <NUM> by <NUM> or more. The temperature of the second heat generating part <NUM> is favorably lower than the temperature of the first heat generating part <NUM> by <NUM> or more, further favorably by <NUM> or more.

The tubular member <NUM> is formed of a cylindrical metal having its one end sealed, as described above. The tubular member <NUM> may be formed of a material, for example, containing one or more elements selected from among platinum, tungsten, iridium, rhodium, and molybdenum.

Here, some of refractory metals, such as molybdenum and tungsten, are known to have a notably reduced oxidation resistance in a predetermined temperature range. For example, molybdenum in a temperature range around <NUM> or higher, or tungsten in a temperature range around <NUM> or higher has a significantly reduced oxidation resistance. Also, this "dangerous" temperature range corresponds to a temperature range exposed to part of the tubular member of the heater for melting glass that faces the side wall <NUM> of the bottom portion <NUM> of the melting furnace <NUM>.

Therefore, in the case of using metals such as molybdenum and tungsten for the tubular member of the heater for melting glass, at the part facing the sidewall <NUM>, there is a likelihood that air oxidation proceeds accordingly.

However, in the first heater <NUM>, thanks to the effects described above, the gap <NUM> between the side wall <NUM> of the bottom portion <NUM> of the melting furnace <NUM> and the first heater <NUM> are sealed with the molten glass MG and a glass layer formed by the solidified molten glass MG. In other words, the part of the tubular member <NUM> facing the sidewall <NUM> is covered with the glass layer, and is suppressed from contacting with the atmosphere. Also, in the first heater <NUM>, by being heated by the second heat generating part <NUM>, the molten glass MG is prevented from solidifying immediately, enters the depth of the gap <NUM>, and thereby, can seal the tubular member <NUM> by the glass layer down to a location close to the bottom surface <NUM> of the bottom portion <NUM> of the melting furnace <NUM>. Therefore, as illustrated in <FIG>, in the case of providing the second portion <NUM> of the cooling member <NUM> around the tubular member <NUM>, the second portion <NUM> can be provided at a position away from the housing space <NUM>. Accordingly, the oxidation of the tubular member <NUM> can be prevented sufficiently, and the temperature drop of the molten glass MG in the housing space <NUM> can be prevented.

Therefore, in the first heater <NUM>, even if a metal containing molybdenum and tungsten is used as the tubular member <NUM>, the oxidation in the part facing the sidewall <NUM> can be suppressed significantly.

It is favorable that the open end of the tubular member <NUM> has a shape with which flange connection is established with the lid member <NUM>, for example, a shape of a flange portion <NUM> as illustrated in <FIG>. By the flange connection of the flange portion <NUM> and the lid member <NUM>, the internal space <NUM> can be properly closed tightly.

Between the flange portion <NUM> and the lid member <NUM>, an O-ring formed of heat-resistant rubber or a metallic gasket may be installed.

The first lead wire 180A and the second lead wire 180B are formed of a material having electric conductivity.

Here, denoting the unit-length resistance in the first lead wire 180A along the extending axis direction of the first heater <NUM> by Z1 (Ω/m), Z1 is merely less than or equal to <NUM>/<NUM> of the unit-length resistance X of the first heat generating part <NUM>.

Similarly, denoting the unit-length resistance in the second lead wire 180B along the extending axis direction of the first heater <NUM> by Z2 (Ω/m), Z2 is merely less than or equal to <NUM>/<NUM> of the unit-length resistance X of the first heat generating part <NUM>.

Therefore, it is obvious from Formula (<NUM>) described above that the first lead wire 180A and the second lead wire 180B do not correspond to the "second heat generating part <NUM>".

The reachable temperature of the first lead wire 180A and the second lead wire 180B is <NUM> or lower at the highest even while using the first heater <NUM>.

The first insulating member 175A is formed of an insulating material. Also, the first insulating member 175A also needs to have a sealing function of properly sealing a gap between the first opening 172A in the lid member <NUM> and the first lead wire 180A.

Insulating members having such a sealing function are well known to those skilled in the arts.

The same applies to the second insulating member 175B.

Note that the configuration of the first insulating member 175A and the second insulating member 175B illustrated in <FIG> is merely an example. It is obvious to one skilled in the art that the configuration is not limited in particular to the example as long as the first lead wire 180A and the second lead wire 180B can be properly extracted to the outside.

As described above, the configuration of the heater according to the one embodiment of the present invention has been described with reference to the first heater <NUM>.

However, it is obvious to one skilled in the art that the heater according to the one embodiment of the present invention may have other configurations. For example, in the heater according to the one embodiment of the present invention, the heating member is not limited to have two heat generating parts, and may have three or more. Various other changes may also be made.

Claim 1:
A heater for melting glass, comprising:
a heating member (<NUM>) containing carbon (C) configured to emit heat rays upon power feeding; and
a tubular member (<NUM>) made of metal configured to have one end closed, and to house the heating member,
wherein the heating member (<NUM>) includes a first heat generating part (<NUM>) and a second heat generating part (<NUM>) along an extending axis direction of the heater, and the first heat generating part (<NUM>) is arranged at a position closer to the one end of the tubular member (<NUM>) than is the second heat generating part (<NUM>), and
wherein denoting a unit-length resistance of the first heat generating part along the extending axis direction by X (Ω/m), and denoting a unit-length resistance of the second heat generating part by Y (Ω/m), <MAT> is satisfied.