JPS6140824A - Forehearth with melt supply channel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a forehearth, and more particularly to a forehearth equipped with electric heating means.

DESCRIPTION OF THE PRIOR ART Forehearths are used, inter alia, in glass manufacturing as heated conduits through which molten fluids, such as glass or metal, exit and are conveyed to forming equipment.

Generally, the forehearth consists of channels that are resistant to molten fluid and equipped with heating means, such as gas burners. The heating means is located above and along the channel to bring the fluid into a molten state and supply it to the forming device at the appropriate temperature.

(Problems with the prior art) In the gas-heated forehearth as described above, it is generally necessary to provide a cooling means by forced air cooling in the supply channel to prevent the molten fluid, such as glass, from overheating or to cool the molten fluid. This is necessary in order to condition the fluid at the desired temperature at its outlet. The cooling means significantly reduces the gas supply to the gas burner without causing significant non-uniformity in the radiant heat of the molten fluid and/or without extinguishing the flame of the gas burner in a manner that poses an explosion hazard. This is necessary because it cannot be done.

The non-uniformity of the radiant heat increases as the gas supply decreases. It also reduces the length of the flame and causes the hottest part of the refractory channel ceiling to move towards the burner, ie along the sides of the channel.

The use of such forehearths is therefore accompanied by the problem of high energy consumption.

Therefore, an object of the present invention is to provide a forehearth that consumes less energy.

(Means and operations for solving the problem) In order to achieve the above object, the present invention uses a heat-resistant insulating material (for example, made of ceramic fiber material) for the ceiling part of the channel, while supplying the front hearth. The use of electrical heating means in the channels reduces the energy consumption of the forehearth by up to about 93%.

That is, the present invention provides a forehearth having a melt supply channel, which includes (a) a channel ceiling member having heat resistance, and (b) an electric heating means for heating the melt moving along the channel. It is characterized by being placed above the body supply channel.

Examples of the supply channel include a molten glass supply channel. Furthermore, ceramic fibers can be used as an insulating member for the channel ceiling.

(Example) Hereinafter, a forehearth according to the present invention will be described with reference to the drawings.

FIG. 5 shows a conventional gas-heated forehearth. In FIG. 5, molten glass 1 moves along channel 2 (towards the front of the paper), which is generally at a temperature in the range of 1050°C to 1300°C. The heat-resistant material of the channel ceiling 3 is heated by a gas burner 8 so as to radiate heat towards the glass. A forced cold air duct 15 and a ventilation hole 5 are provided in the ceiling of the channel to cool the glass.

Next, FIGS. 6A and 6B illustrate the temperature non-uniformity at the outlet of the glass flow channel in the channel of a conventional gas-heated forehearth, near the forming apparatus.

FIG. 1 shows one embodiment of a forehearth according to the invention.

In FIG. 1, an electric heating element 6 is installed in the channel 2 and has a so-called "warm" region 7 in the middle of the so-called "cold" region. (The surface area will be explained later).

The heating element 6 in this embodiment is a silicon carbide tube with a spiral cut 9 cut into its surface to define the "warm" region. The electric current flowing through the electric heating element 6 is supplied via a flexible braided wire IO electrically connected to a portion projecting from the wall of the forehearth.

The channels are suitably formed of Murai (A16 Si20ss), a heat resistant glass contact material commonly used in forehearths and glass furnaces and resistant to glass blows.

The channel ceiling 11 is made of ceramic fiber board. The density of the mounting plate is approximately 0.27 t/c, rtl (this AK vs. mullite z, 5f/crtl).

The ceramic fiber material is preferably made from high purity alumina fibers that are formed with a binder in a vacuum. Further, as the mounting plate, a commercially available 1600 grade plate is particularly preferable.

The channel 2 and the channel ceiling 11 are provided with an insulating back layer 12 in the form of a plate of ceramic fibers or a kerato of ceramic material as described above. The kerato is also of low density and is advantageously made of a mixture of silica and alumina fibers.

In particular, it has a density of 0.096 f /crA and about 1250
Ceratoes having a maximum usable temperature of 0.degree. C. are preferred.

21t:'Cson5 has an insulating layer 18 made of a microcellular silica material obtained under the trade name of CMICORTHERM.

FIG. 2 shows another embodiment of the fore nose according to the present invention.

In FIG. 2, the channel 2 has a conventional fluorocarbon insulator 14 and the channel ceiling 11 has a vent 5.

The channel ceiling is preferably of such thermally insulating quality that the exterior of the ceiling can be touched even when glass with a temperature of, for example, 1250° C. flows along the channel.

(Effects of the present invention) When the ceiling of the supply channel or at least the channel roof portion facing inside the channel is made of the heat-resistant ceramic fiber insulating material, the turbulent air generated from the flame jet can cause the fiber-like insulation to It is not suitable to be used with conventional gas burners as the material will corrode.

On the other hand, if electric heating means are used to heat the molten material, the temperature of the roof and/or the temperature of the molten material is particularly uniform, and even if the thermal output of the heating means increases or decreases, the uniformity can be maintained. It is. Therefore, there is an effect that there is no need to provide forced air cooling ports required in conventional forehearths.

If desired, the heating means according to the invention can provide a ramp that has more or less heating effect to increase the uniformity of the melt temperature in the channel.

Generally, the melt in the forehearth feed channel gets colder toward the channel walls. Therefore, the heating means is designed to exert a greater heating effect on the channel wall side. This is the same as mentioned above.

The electrical heating means of the foreground according to the invention comprises a plurality of heating elements made of tubes or rods of electrically conductive material, such as silicon carbide, as described above.

In order to create a region of high heating effect in such a tube, for example, a longitudinal cut with a spiral cutout as described above is formed on the surface of the tube to interrupt the path of the current flowing along the tube. Reduce the area and increase the electrical resistance and cut the length 90
This increases the heating effect. Therefore, a heating element with "warm" slopes on both sides of a central "cold" region, that is, slopes with a high heating effect, has a high number of helical repeats (i.e., number of cuts per unit length) without a spiral cutting edge. It may take the form of a tubular element with a helical cut in the tube surface on both sides with respect to the central portion of the tube.

If it is not desired to clearly distinguish the above-mentioned "warm" region and "cold" region, it is preferable to gradually increase the number of helical repeats as the region requires a large heating effect. . Alternatively, as described above, in areas where a large heating effect is required, this can be achieved by reducing the cross-sectional area of the silicon carbide tube or rod. In this case as well, the cross-sectional area may be gradually reduced, or a step may be provided to clearly distinguish the "warm" and "cold" regions.

Furthermore, creating "warm" and "cold" regions of the heating element can also be accomplished by varying the electrical resistivity by varying the chemical composition along the heating element.

With the above, an electric heating element with different relative lengths of the "warm" and "cold" regions can be easily achieved and have different heating effects along its length.

Therefore, for example, in a forehearth where the heating state required on the channel or wall side is asymmetric, a heating element having asymmetric regions with different degrees of heating effect can be used.

However, it is particularly preferred that the heating elements used in the forehearth according to the invention have the same overall resistance so that they can be readily replaced by standard heating elements with a uniform heating effect.

As described in the above embodiments, the forehearth according to the present invention comprises a plurality of electric heating elements arranged above at least the main part of the melt supply channel and extending across it. The upper continuous heating element through which the melt passes as it moves along said channel may be an element having a uniform heating effect along its length;
If it is desired to increase the heating effect preferentially on the side of the channel wall, all or some of the elements may be connected to the same or different relative "
It is also possible to have "warm" and "cold" regions depending on the degree of heating effect required.

However, in the case of a heating element of the latter configuration,
The relative size of the central "cold" region increases along the direction of melt flow, providing greater cooling of the channel walls as the melt approaches the forehearth outlet.

The regions that differentiate the heating effect in the forehearth of the present invention do not vary with the current flowing through the heating element. This is in contrast to the conventional 7-oa hearth, whose flame length decreases as the gas supply decreases, and where the most radiant area of the refractory ceiling to the channel moves to either side of the channel.

Another effect of using heating with electric heating elements instead of heating with gas in the forehearth is that the heat-resistant ceiling for the channel can be located at a lower height from the channel, thus reducing the "warm" area of the ceiling. has a more localized heating effect on the melt in the channel.

The ceramic fibers used for the channel ceiling members are lightweight and can withstand temperatures of up to 1800°C, preferably up to 1500°C.

The above ceramic fiber has these temperature values! Ceramic material having properties that can withstand high temperatures, preferably alumina,
Alternatively, fibers made of zirconia or even a mixture with silica are preferred.

In addition, the channel ceiling member is 0.1f/cr/l to 0.5
Density at 1/cdl 1, especially about 0.25f/crt
It preferably consists of alumina fibers having a density of 1 and formed in vacuum together with a binder. Board materials made of such alumina fibers are commercially available as 1600 grade boards. The heat capacity of the channel ceiling made of such lightweight ceramic fiber material is approximately 10% of that of the conventional gas-heated 7-oa hearth, and this reduction in heat capacity allows for faster response speed and temperature control. becomes more precise.

In addition, there is an excellent effect that the temperature of the glass can be more evenly distributed when the glass is supplied to the molding device.

This can be achieved by having a ceiling thickness of at least 7.5 cm. When using such a ceiling member and an electric heating element, the total energy consumption when using the forehearth of the glass according to the invention is as low as that of a corresponding gas-fired forehearth.

3 and 4 each show a separate embodiment with the channel ceiling 11 removed.

The molten glass flows towards the spout 15 located below the electric heating element 6.

In the embodiment of FIG. 3, the central "cold" region of the electric heating element 6 widens continuously towards the spout 15, so that more intense cooling is effected on the channel side.

In the embodiment of FIG. 4, there are heating elements having a "cold" region in the center alternating with heating elements having a uniform heating effect;
In this embodiment, the uniform and non-uniform heating elements can be controlled separately, and by changing the relative power to these two sets of heating elements, the heating effect can be changed by giving priority to the channel side as necessary. be able to.

Although the foregoing description has been made with respect to a forehearth for a melt, the feed channels constructed according to the invention may be used, for example, in the reheating of billets or - in the reheating of formed metal parts. Applicable to processes that require constant heating. Supply channels in such cases are also included within the scope of the present invention.

In addition, since the weight of the glass is closely related to the glass temperature when it is supplied to the molding equipment, better temperature control means better control of the weight of the product. This has the effect of reducing the percentage of failures (improving yield).

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a forehearth having a melt supply channel according to the present invention, and FIG. 2 shows another embodiment of a forehearth having a melt supply channel according to the present invention. 3 is a plan view of another embodiment of a forehearth with a melt supply channel according to the invention with the channel ceiling section removed; FIG. FIG. 5 is a plan view of yet another embodiment of a forehearth having melt supply channels according to the invention in a removed state; FIG. 5 is a cross-sectional view of a conventional gas-heated forehearth; FIGS. FIG. 6B is a schematic cross-sectional view showing the isothermal distribution of molten glass flow in the channels of a conventional forehearth. (Explanation of symbols) 1... Molten glass, 2... Channel, 3... Gas burner, 4... Channel ceiling, 5... Vent hole,
15... Forced cold air duct, 6... Electric heating element,
7... "Warm" region, 8... "Cold" region, 9... Spiral shape 90.10... Braided line, 11... Channel ceiling, 12... Back layer 1, 11 ...Insulating layer, ■4
...Conventional forehearth insulator. l 9 beggar/sushi drinker η'ras

Claims (10)

[Claims] (1) A melt supply channel, a channel ceiling member made of a heat-resistant insulating material disposed above the channel, and heating the melt disposed above the channel and moving along the channel. A forehearth having a melt supply channel consisting of electrical heating means. 2. A forehearth having a melt supply channel according to claim 1, wherein said heat resistant insulating material is a heat resistant ceramic fiber material. (3) A forehearth having a melt supply channel according to claim 1 or 2, wherein the electric heating means comprises a plurality of electric heating elements. (4) The melt supply channel according to claim 3, wherein at least one of the plurality of heating elements has a larger heating effect on the side facing the supply channel than on the central portion thereof. Forehearth with. 5. A forehearth having a melt supply channel as claimed in claim 4, wherein each of said plurality of heating elements has substantially the same total electrical resistance. (6) A forehearth having a melt supply channel according to any one of claims 1 to 5, wherein the electric heating means comprises a plurality of tubular or rod-shaped silicon carbide heating elements. (7) the cross-sectional area of the electrical path in at least one of the plurality of heating elements is reduced on either side of the channel opposite the central portion of the heating element; 6. A forehearth with melt feed channels according to claim 5, wherein the heating effect is increased. (8) The ceramic fiber material has a melt supply channel according to any one of claims 2 to 7, consisting of fibers selected from the group of alumina fibers and zirconia fibers. Vorhaas. (9) The ceramic fiber material has a thickness of 0.1 g/cm^
Forehearth with melt feed channels according to any of claims 2 to 8, having a density of 3 to 0.5 g/cm^3. (10) A forehearth having a melt supply channel according to any one of claims 1 to 9, wherein the channel ceiling member is made of an alumina fiberboard with one or more insulating back layers.