CA1080773A - Resistant heating of ceramic refractory channels - Google Patents
Resistant heating of ceramic refractory channelsInfo
- Publication number
- CA1080773A CA1080773A CA242,567A CA242567A CA1080773A CA 1080773 A CA1080773 A CA 1080773A CA 242567 A CA242567 A CA 242567A CA 1080773 A CA1080773 A CA 1080773A
- Authority
- CA
- Canada
- Prior art keywords
- refractory material
- glass
- feeder
- electrodes
- heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
- C03B5/02—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture in electric furnaces, e.g. by dielectric heating
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Glass Melting And Manufacturing (AREA)
- Furnace Details (AREA)
- Resistance Heating (AREA)
- Control Of Resistance Heating (AREA)
Abstract
INVENTOR
HELMUT PIEPER
TITLE
RESISTANT HEATING OF CERAMIC
REFRACTORY CHANNELS
ABSTRACT OF THE DISCLOSURE
In order to maintain glass in its molten state as it passes, during a process, from one region to another as through channels, passages, feeders and feeder heads, heat must be advantageously supplied to the molten glass to maintain its liquid state. If the glass carrying channels, passages, feeders, and feeder heads themselves are designed to carry electric currents and thus are imparted with sufficient heat to insure that the molten glass does not lose its molten state. Thus, in order to effect uniform heating a plurality of heating currents may be conducted through a plurality of electric circuits within the refractory material of the glass carrying channels, passages, feeder or feeder heads.
HELMUT PIEPER
TITLE
RESISTANT HEATING OF CERAMIC
REFRACTORY CHANNELS
ABSTRACT OF THE DISCLOSURE
In order to maintain glass in its molten state as it passes, during a process, from one region to another as through channels, passages, feeders and feeder heads, heat must be advantageously supplied to the molten glass to maintain its liquid state. If the glass carrying channels, passages, feeders, and feeder heads themselves are designed to carry electric currents and thus are imparted with sufficient heat to insure that the molten glass does not lose its molten state. Thus, in order to effect uniform heating a plurality of heating currents may be conducted through a plurality of electric circuits within the refractory material of the glass carrying channels, passages, feeder or feeder heads.
Description
The present invention relates to a method for indirectly heating glass-carrying channels or passages, feeders and feeder heads, and to an apparatus for carrying out such method.
It is already known and commonly practiced to heat the feeders, glass channels or passages and feeder heads either by means of electrodes which are immersed into the molten glass mass, or by means of an indirect resistance heating assembly which is mounted to the -outer side of the refractory material and which is exteriorly surrounded by an insulation.
However, the direct heating by means of electrodes immersed into the molten glass mass suffers from the disadvantage that the generated energy concentrates at the tips of the electrodes such that the glass is heated to a greater degree at these points and thermal inhomogenities are apt to occur at these places. BesidesO the electrodes are either of a redwcing nature (molybdenum) or of an oxidizing nature (tin oxide) whereby undesired contamination may result~ Further, in the case of excessive heating by individual electrodes bubble forrnation may occur in the area of contact between the glass and the electrode.
The indirect heating by means of resistance wires disposed exteriorly of the gutter or ]cennel of refractory material (Zacr`has not proved to be advantageous either, because the cross-sectional areas of these resistance wires must be relatively small in order to receive a sufficient amount of energy, while, , , ~
, on the other hand, the operational life of the wires is too short at the required constant temperatures of about 1300C, partly due to their small cross--sectional areas.
The heating by means of radiators has been found to be not satisfactory either, because in such case a grea~ part of the energy is reflected from the surface and, further, the surface is heated to the highest degree, which likewise may result in tempera-ture inhomogeneity.
Accordingly, it is the object of the present invention to provide a method and an apparatus for the heating of glass flowing within passages, feeders and feeder headsr which makes it possible to obtain a high temperature homogeneity of the flowing glass and which neither show the low heating efficieny and the susceptibility to trouble of the resistance heating assembly, nor produce contamination and gas generation within the glass while preventing consumption of ~0 electrodes.
Furthermore, the recognized and above--discussed disadvantages of the feeder heating means can be avoided and, by following an entirely novel technical way, a feeder heating means insusceptible to trouble can be devised which provides a heretofore not attained degree of temperature homogeneity and which may be utilized economically, which heating means further permits its adaptation to the most varied types -of glass and which readily allows the temperature to be adapted to the most varied processing conditions.
: ' . ~ : : : ' .
, , . , .:: : ' ' According to the present invention, this object is solved in that the heating current flows directly through the refractory material (Zac) of the glass passage, of the feeder or of the feeder head.
Advantageously, in order to render the heating effect uniform and to avoid trouble, the heating current may be conducted in a plurality of circuits each of which is adapted to be switched off when consuming a higher than a predetermined power.
Preferably, the apparatus for carrying out the method of the present invention is characterized by a plurality of flat electrodes which are pressed against the refractory material subjected to high temperatures, and which are supplied with electrical energy via independent circuits.
In order to facilitate control of the separate circuits, the secondary side of an isolating or variable transformer for feeding the respective independent circuits may be divided into a plurality of galvanically isolated coils or windings. Each of the heating current circuits may include an overload relay or a fuse or circuit breaker which serves to turn off the circuit when a given power input is exceeded.
With the feeder heating arrangement according to the invention it is possible to construct the feeder as a glass-carrying passage of tubular configuration which is filled with liquid glass up to its top and wherein the electrodes are strips surrounding the tube material, whereby the current flows from one strip to the next one in succession.
In the regions of gaps ormed, the strips are preferably divided or split, and they do not contact .
.
' ~ ' : . ' ' ' the refractory material in order to prevent the current from flowing through the glass present in the gaps.
The electrodes E~ se may be in the form of strips of tapes, whereby a portion or an end of the strip is bent at an angle and passed to the exterior through the insulation covering of the refractory material such that these lead out as relatively cold ends which may readily be connected to electrical conductors for connection to the transformers.
Furthermore, advantageously the electrodes may be :installed with greatest concentration and supply a maximum amount of energy at those points where the temperature of the flowing glass is lowest.
Thus, according to the present invention, in a manner being surprising to the expert, it is possible to effect an improved heating of the feeder by a technically novel method, namely by utilizing the refractory material as a resistance heating conductor.
The invention therefore conte~lplates a method for indirectly heating molten glass-carrying passages, feeders and feeder heads made of a structural refractory material having a resistivity greater than the resistivity of molten lime-sodium glass which comprisea exteriorly contacting said refractory material forminy said passages, feeders and feeder heads with a plurality of electrodes and passiny heating current directly through said refractory materi~l via said electrodes whereby said refractory material acts as a resistance heating conductor without direct contact between the molten glass and said electrodes.
The invention further contemplates an apparatus for indirectly heating glass-carrying passages, feeders and feeder heads constructed from a conduc~ive refractory material having a resistivity greater than that of lime-sodium glass at high temperatures, the passages thereof formed as a tube which are filled with liquid glass up the level of its top and wherein electrodes substantially surround the refractory material and comprise strips, and means for causing current to flow from one of said strips to the next successive one.
In the following, exemplary embodiments of the invention are described in greater detail by referring to the enclosed drawings, wherein:
Figure 1 shows a schematical cross-section view of a feeder according to the present invention;
Figure ~ shows a schematical cross--sectional view similar to Figure 1, but including 3 electrodes;
Figure 3 shows a similar cross-sectional view as Figures 1 and 2, but including four-electrodes and a transformer having a pair of secondary windings;
Figure 4a shows a schematical plan view and Figure 4b a vertical ~ectional view of a feeder passage having a feeder head, to which the method according to the present invention is applied;
Figure 5a shows a schematical horizontal sectional view and Figure 5b a vertical sectional view of a feeder passage having a tubular configuration ~,, :
and Figure 6 the specific resistance of typical refractory materials for being utilized by the invention.
The method according to the invention is based upon the fact that refractory material having a small glass phase, particularly if material cast in molten or liquid form are involved, is conductive at high temperatures. Material like this is customarily termed ~ac~, Jargal~ or the like in Europe. The structure of Jargal~ e.g. consists of very small ~-alumina(corundum) and ~-aluminia (IIA12O3, Na20) crystals which are strongly inserted into one another. The interspaces between the individual crystals are filled in with glass phase. However, the portion of glass phase is very small. Clearly, the method is useful for such glass carrying passages, feeders and feeder heads in which the necessary high temperatures are present.
Thus the resistivity of the refractory material being of interest at the temperatures involved within a glass-carrying passage i5 about five times as high as the resistivity of a normal lime-sodium glass.
Thus, in the case of the normal wall thicknesses in -such feeder passages tabout 15 centimeters) it is possible to pass a current through the refractory material thereby to heat this material. To this end, there are used voltages of b~tween 200 and 300 volts which necessitate an electrical insulation of the voltage-carrying portions for personnel protection.
The applicable temperature for the refractory ;~' ' ~ '.
material is at least as high as 900 C; i.e. the glass receiving gutter or kennel must be insulated in order to provide such a differential temperature between outer and inner walls, which is as small as possible, and which, as well causes the-exterior ternperature to rise above 900 C.
Electrodes 2 are applied to the outer wall of the refractory material 1 of a correspondingly formed feeder gutter or kennel of a corresponding passage or feeder head, between the insulation 14 and the refractory material 1. These electrodes 2 consist of a hiyhly heat resistant material, e.g. of the well-known hot conductor material "Aluchrome~", or of other highly alloyed refractory steels, e.g. of highly alloyed nickel, chromium or molybdenum steels. Expediently, the insulation of well-known materials is movable in the region of the electrodes 2, and it may be urged against the electrodes 2 by springs 4 such that the electrodes 2, in turn, are pressed against the refractory material and such that a good electrical contact, between the electrodes 2 and the re~ractory material 1 is always ~nsured.
If the electrodes 2 are attached below the refrac~ory material 1, the contact pressure exérted by the weight of the refractory material or of the glass-carrying passage is sufficient to provide an adequate contact.
Expediently, the electrodes 2 are formed in -the shape of an elongate strip, whereby one end 3 thereof is passed through the insulation to serve as a contact lug to which a conductor 5 for supplying ~.
~'. ~il : ' ' ' :
electrical energy may be connected.
For the uniform heating of a feeder, it is required that the electrodes 2, depending on the configuration of the feeder, be arranged such as to provide or the optimum uniform heating of those places where the temperature of the gutter or kennel is normally at its lowest value. Thus, preferably a particularly great number of electrodes 2 will be provided in these regions; the electrodes 2 will be placed such that the corresponding desired current paths are formed. Thus, it has to be taken into consideration that the current will take the path of lowest resistance and, accordingly it will flow across the particularly well heated areas or across the shortest paths, in accordance with well-known laws of physics. It has to be noted that the resistance decreases with increasing temperature in the case of materials as presently employed.
As shown in Figures 1 to 3, a feedex passage being open at its upper side has inserted near the bottom of the passage, electrodes 2 with their ends 3 bent at an angle. The electrodes are pressed against the bottom by springs 4, with the insulation 14 serving to prevent heat losses and to secure the adjustment of the temperature of the refractory material 1 to the proper level.
The approximate principal current path is indicated by lines 15, and as the resistance of the glass, as mentioned, is substantially lower than that of the refractory material, a certain portion of the current will thus flow through the molten glass mass g .
.
proper.
The electrodes 2 are arranged primarily in the lower region of the gutter or kennel in order to heat this lower portion, because an equalization of the temperature is readily e~fected from below to above, but not ~rom above to below.
A substantial advantage of the heating system according to the invention resides in the fact that the plates may be intentionally placed in such a way that every part of the gutter or kennel can be heated, as is clearly evident from the drawings. Hereby, the energy density or the flow of energy within the refractory material may be kept very low in relation to the volume unit, as the surface areas covered by the electrodes 2 may be chosen as large as désired. With an adequate insulation, the temperature of the gutter or kennel may be adjusted to any value as desired, or any desired equalization of temperature may be provided, such that optimum unifoxmity of the temperature within the feeder or feeder head or within another glass-carrying passage can positively be obtained.
As shown in Figure 4, a great number of electrodes 2 may be arranged in side-by-side relation across the entire length of the feeder passage, whereby the current flows transversely through the feeder passage at each electrode location. The feeder head se has a circular electrode 11 positioned underneath the discharge 10 which electrode is coupled to the electrodes 2 arranged around the feeder head.
In this manner, it is easily possible to correspondingly heat the otherwise coldest part of the ,~.4, .~, . .......................................................... ~
7'~l feeder; namely, the bottom of the feeder head, and to avoid temperature inhomogeneities of the discharged glass due to cooling of the glass at the discharge.
According to the invention, it is expedient to divide the heating arrangement of the feeder or of the feeder head into a plurality of separate zones which are independently supplied with electrical energy by galvanically separated (isolated~ secondary windings in separate circuits. Thus, it is further expedient to keep the resistance of a pair of parallel circuits appxoximately equal, or to match to each other the resistancy of corresponding heating circuits arranged in parallel with each other. To this end, the secondary sid~ of an isolating or variable transEormer may comprise a plurality of secondary windings 6 which are excited by a common primary winding 8, whereby - as indicated by arrow 7 - an individual control of the various secondary circuits is possible.
The construction of isolating or varia~le transformers of this type is known to one skilled in the art and, thus, need not be described in any greater detail.
Each of the heating circuits includes a fuse or a corresponding overload relay, indicated at 9, which turns off the respective heating circuit when fed with a higher than a predetermined heating power. In this manner, it is avoided that individual heating circuits are overloaded so as to produce excessive temperatures.
~owever, the sectioning of the heating arrangement into a plurality of independent heating circuit and ~he use of the fuses 9 are also necessary to provide for the situation in which due to crack formation of the refractory material which cannot be avoided at all, the separate curxent paths is affected by the entering of glass into the crack.
If molten glass entered such a crack, the resistance would be substantially reduced at this place by the glass penetrating the crack. This would result in a concentration of energy within the crack and, thus, in further cavitation and in an increase of the size of the crack. Accordingly, each individual heating circuit must be safely protected agai.nst occurence of trouble of this kind. Such positive protection is provided by the above-described division into a plurality of separate (secondary winding) heating circuits which are separately protected by fuses 9.
Figures 1 to 3 illustrate the circuit arrangement of the individual heating circuits whereby, as shown in Figure 1, a secondary winding supplies a pair of oppositely disposed electrodes 2 via conductors 5 and a fuse 9, while according to Figure 2 a center electrode 2' is supplied by the secondary winding via conductors 5 and a fuse, which center electrode is coupled to a pair of likewise oppositely arranged and interconnected electrodes 2; on the other hand, according to Figure 3 a transformer having two secondary windings feeds a total of five electrodes through the abovementioned wires and fuses. In the latter case, the center electrode is also connected in opposition to the two outermost el~ctrodes, and the two ~J~1 7~
electrodes positioned at th~ right and at the left of the center electrode are fed by the second secondary winding.
As shown in Figure 4, a plurality of circuits may be arranged on a feeder in tandem in the direction of flow of the discharging glass, whereby the current at every location flows transversely through the refractory material and, further, through the molten glass mass, and whereby four secondary windings 6 are each energized by a primary winding 8 in a controllable manner. Of course, each circuit includes the customary protective elements on fuse ~, even if not particularly shown.
me first heating area Zl heated at four locations, is followed by a corresponding second heating area 22, and the heating arrangement of the feeder head is then connected *o the abovementioned circular electrode llo In this case, the circuit arrangement is designed such that the current may flow e,g. from electrode 2a to electrode 2b, from which the current is adapted to flow not only to electrode 2a, but also to the adjacent electrode ~c at the opposite ide and to the circular electrode 11. -The electrode 2c, in turn, may have a current connection to the center electrode 2d. Further details are evident to one skilled in the art from Figure 4.
In a modified ernbodiment of the invention according to Figures 5a and 5b, the feeder passage may be of tubular configuration, whereby the level of the glass extends up to the level of the top of the tube -such that formation of a gas cushion is prevented.
.,~.~;. - .
. - 'i . .
- - . .
-Here, ~he electrodes 12 are formed as strips, and the current flows from interior electrode, i.e. 12', 12, to the pair of adjacently disposed electrodes thereof, electrodes 12" each, unless the strip electrode 12 is positioned at the end of the heating area such that the current can 10w in one direction only, as shown in Figure 5a.
In this embodiment, too, each heating circuit i5 separately protected by fuses 9 or the like in order to avoid disadvantageous local overheating. The electrode strips 12 consist of the same highly heat resistant material as described above, and these electrode strips are preferably also split at the locations where a gap 13 exists in the refractory material. The split portion is bridged by a conductive connection; however, it is hereby prevented that any glass present within the gap produces a disadvantageous separate current path which would result in the disadvantages as described above in connection with the crack formation.
Apparently, the solution according to the present invention offers a novel and advantageous means for the heating of all kinds of glass-carrying passages, tubes or pipes and the like.
It is already known and commonly practiced to heat the feeders, glass channels or passages and feeder heads either by means of electrodes which are immersed into the molten glass mass, or by means of an indirect resistance heating assembly which is mounted to the -outer side of the refractory material and which is exteriorly surrounded by an insulation.
However, the direct heating by means of electrodes immersed into the molten glass mass suffers from the disadvantage that the generated energy concentrates at the tips of the electrodes such that the glass is heated to a greater degree at these points and thermal inhomogenities are apt to occur at these places. BesidesO the electrodes are either of a redwcing nature (molybdenum) or of an oxidizing nature (tin oxide) whereby undesired contamination may result~ Further, in the case of excessive heating by individual electrodes bubble forrnation may occur in the area of contact between the glass and the electrode.
The indirect heating by means of resistance wires disposed exteriorly of the gutter or ]cennel of refractory material (Zacr`has not proved to be advantageous either, because the cross-sectional areas of these resistance wires must be relatively small in order to receive a sufficient amount of energy, while, , , ~
, on the other hand, the operational life of the wires is too short at the required constant temperatures of about 1300C, partly due to their small cross--sectional areas.
The heating by means of radiators has been found to be not satisfactory either, because in such case a grea~ part of the energy is reflected from the surface and, further, the surface is heated to the highest degree, which likewise may result in tempera-ture inhomogeneity.
Accordingly, it is the object of the present invention to provide a method and an apparatus for the heating of glass flowing within passages, feeders and feeder headsr which makes it possible to obtain a high temperature homogeneity of the flowing glass and which neither show the low heating efficieny and the susceptibility to trouble of the resistance heating assembly, nor produce contamination and gas generation within the glass while preventing consumption of ~0 electrodes.
Furthermore, the recognized and above--discussed disadvantages of the feeder heating means can be avoided and, by following an entirely novel technical way, a feeder heating means insusceptible to trouble can be devised which provides a heretofore not attained degree of temperature homogeneity and which may be utilized economically, which heating means further permits its adaptation to the most varied types -of glass and which readily allows the temperature to be adapted to the most varied processing conditions.
: ' . ~ : : : ' .
, , . , .:: : ' ' According to the present invention, this object is solved in that the heating current flows directly through the refractory material (Zac) of the glass passage, of the feeder or of the feeder head.
Advantageously, in order to render the heating effect uniform and to avoid trouble, the heating current may be conducted in a plurality of circuits each of which is adapted to be switched off when consuming a higher than a predetermined power.
Preferably, the apparatus for carrying out the method of the present invention is characterized by a plurality of flat electrodes which are pressed against the refractory material subjected to high temperatures, and which are supplied with electrical energy via independent circuits.
In order to facilitate control of the separate circuits, the secondary side of an isolating or variable transformer for feeding the respective independent circuits may be divided into a plurality of galvanically isolated coils or windings. Each of the heating current circuits may include an overload relay or a fuse or circuit breaker which serves to turn off the circuit when a given power input is exceeded.
With the feeder heating arrangement according to the invention it is possible to construct the feeder as a glass-carrying passage of tubular configuration which is filled with liquid glass up to its top and wherein the electrodes are strips surrounding the tube material, whereby the current flows from one strip to the next one in succession.
In the regions of gaps ormed, the strips are preferably divided or split, and they do not contact .
.
' ~ ' : . ' ' ' the refractory material in order to prevent the current from flowing through the glass present in the gaps.
The electrodes E~ se may be in the form of strips of tapes, whereby a portion or an end of the strip is bent at an angle and passed to the exterior through the insulation covering of the refractory material such that these lead out as relatively cold ends which may readily be connected to electrical conductors for connection to the transformers.
Furthermore, advantageously the electrodes may be :installed with greatest concentration and supply a maximum amount of energy at those points where the temperature of the flowing glass is lowest.
Thus, according to the present invention, in a manner being surprising to the expert, it is possible to effect an improved heating of the feeder by a technically novel method, namely by utilizing the refractory material as a resistance heating conductor.
The invention therefore conte~lplates a method for indirectly heating molten glass-carrying passages, feeders and feeder heads made of a structural refractory material having a resistivity greater than the resistivity of molten lime-sodium glass which comprisea exteriorly contacting said refractory material forminy said passages, feeders and feeder heads with a plurality of electrodes and passiny heating current directly through said refractory materi~l via said electrodes whereby said refractory material acts as a resistance heating conductor without direct contact between the molten glass and said electrodes.
The invention further contemplates an apparatus for indirectly heating glass-carrying passages, feeders and feeder heads constructed from a conduc~ive refractory material having a resistivity greater than that of lime-sodium glass at high temperatures, the passages thereof formed as a tube which are filled with liquid glass up the level of its top and wherein electrodes substantially surround the refractory material and comprise strips, and means for causing current to flow from one of said strips to the next successive one.
In the following, exemplary embodiments of the invention are described in greater detail by referring to the enclosed drawings, wherein:
Figure 1 shows a schematical cross-section view of a feeder according to the present invention;
Figure ~ shows a schematical cross--sectional view similar to Figure 1, but including 3 electrodes;
Figure 3 shows a similar cross-sectional view as Figures 1 and 2, but including four-electrodes and a transformer having a pair of secondary windings;
Figure 4a shows a schematical plan view and Figure 4b a vertical ~ectional view of a feeder passage having a feeder head, to which the method according to the present invention is applied;
Figure 5a shows a schematical horizontal sectional view and Figure 5b a vertical sectional view of a feeder passage having a tubular configuration ~,, :
and Figure 6 the specific resistance of typical refractory materials for being utilized by the invention.
The method according to the invention is based upon the fact that refractory material having a small glass phase, particularly if material cast in molten or liquid form are involved, is conductive at high temperatures. Material like this is customarily termed ~ac~, Jargal~ or the like in Europe. The structure of Jargal~ e.g. consists of very small ~-alumina(corundum) and ~-aluminia (IIA12O3, Na20) crystals which are strongly inserted into one another. The interspaces between the individual crystals are filled in with glass phase. However, the portion of glass phase is very small. Clearly, the method is useful for such glass carrying passages, feeders and feeder heads in which the necessary high temperatures are present.
Thus the resistivity of the refractory material being of interest at the temperatures involved within a glass-carrying passage i5 about five times as high as the resistivity of a normal lime-sodium glass.
Thus, in the case of the normal wall thicknesses in -such feeder passages tabout 15 centimeters) it is possible to pass a current through the refractory material thereby to heat this material. To this end, there are used voltages of b~tween 200 and 300 volts which necessitate an electrical insulation of the voltage-carrying portions for personnel protection.
The applicable temperature for the refractory ;~' ' ~ '.
material is at least as high as 900 C; i.e. the glass receiving gutter or kennel must be insulated in order to provide such a differential temperature between outer and inner walls, which is as small as possible, and which, as well causes the-exterior ternperature to rise above 900 C.
Electrodes 2 are applied to the outer wall of the refractory material 1 of a correspondingly formed feeder gutter or kennel of a corresponding passage or feeder head, between the insulation 14 and the refractory material 1. These electrodes 2 consist of a hiyhly heat resistant material, e.g. of the well-known hot conductor material "Aluchrome~", or of other highly alloyed refractory steels, e.g. of highly alloyed nickel, chromium or molybdenum steels. Expediently, the insulation of well-known materials is movable in the region of the electrodes 2, and it may be urged against the electrodes 2 by springs 4 such that the electrodes 2, in turn, are pressed against the refractory material and such that a good electrical contact, between the electrodes 2 and the re~ractory material 1 is always ~nsured.
If the electrodes 2 are attached below the refrac~ory material 1, the contact pressure exérted by the weight of the refractory material or of the glass-carrying passage is sufficient to provide an adequate contact.
Expediently, the electrodes 2 are formed in -the shape of an elongate strip, whereby one end 3 thereof is passed through the insulation to serve as a contact lug to which a conductor 5 for supplying ~.
~'. ~il : ' ' ' :
electrical energy may be connected.
For the uniform heating of a feeder, it is required that the electrodes 2, depending on the configuration of the feeder, be arranged such as to provide or the optimum uniform heating of those places where the temperature of the gutter or kennel is normally at its lowest value. Thus, preferably a particularly great number of electrodes 2 will be provided in these regions; the electrodes 2 will be placed such that the corresponding desired current paths are formed. Thus, it has to be taken into consideration that the current will take the path of lowest resistance and, accordingly it will flow across the particularly well heated areas or across the shortest paths, in accordance with well-known laws of physics. It has to be noted that the resistance decreases with increasing temperature in the case of materials as presently employed.
As shown in Figures 1 to 3, a feedex passage being open at its upper side has inserted near the bottom of the passage, electrodes 2 with their ends 3 bent at an angle. The electrodes are pressed against the bottom by springs 4, with the insulation 14 serving to prevent heat losses and to secure the adjustment of the temperature of the refractory material 1 to the proper level.
The approximate principal current path is indicated by lines 15, and as the resistance of the glass, as mentioned, is substantially lower than that of the refractory material, a certain portion of the current will thus flow through the molten glass mass g .
.
proper.
The electrodes 2 are arranged primarily in the lower region of the gutter or kennel in order to heat this lower portion, because an equalization of the temperature is readily e~fected from below to above, but not ~rom above to below.
A substantial advantage of the heating system according to the invention resides in the fact that the plates may be intentionally placed in such a way that every part of the gutter or kennel can be heated, as is clearly evident from the drawings. Hereby, the energy density or the flow of energy within the refractory material may be kept very low in relation to the volume unit, as the surface areas covered by the electrodes 2 may be chosen as large as désired. With an adequate insulation, the temperature of the gutter or kennel may be adjusted to any value as desired, or any desired equalization of temperature may be provided, such that optimum unifoxmity of the temperature within the feeder or feeder head or within another glass-carrying passage can positively be obtained.
As shown in Figure 4, a great number of electrodes 2 may be arranged in side-by-side relation across the entire length of the feeder passage, whereby the current flows transversely through the feeder passage at each electrode location. The feeder head se has a circular electrode 11 positioned underneath the discharge 10 which electrode is coupled to the electrodes 2 arranged around the feeder head.
In this manner, it is easily possible to correspondingly heat the otherwise coldest part of the ,~.4, .~, . .......................................................... ~
7'~l feeder; namely, the bottom of the feeder head, and to avoid temperature inhomogeneities of the discharged glass due to cooling of the glass at the discharge.
According to the invention, it is expedient to divide the heating arrangement of the feeder or of the feeder head into a plurality of separate zones which are independently supplied with electrical energy by galvanically separated (isolated~ secondary windings in separate circuits. Thus, it is further expedient to keep the resistance of a pair of parallel circuits appxoximately equal, or to match to each other the resistancy of corresponding heating circuits arranged in parallel with each other. To this end, the secondary sid~ of an isolating or variable transEormer may comprise a plurality of secondary windings 6 which are excited by a common primary winding 8, whereby - as indicated by arrow 7 - an individual control of the various secondary circuits is possible.
The construction of isolating or varia~le transformers of this type is known to one skilled in the art and, thus, need not be described in any greater detail.
Each of the heating circuits includes a fuse or a corresponding overload relay, indicated at 9, which turns off the respective heating circuit when fed with a higher than a predetermined heating power. In this manner, it is avoided that individual heating circuits are overloaded so as to produce excessive temperatures.
~owever, the sectioning of the heating arrangement into a plurality of independent heating circuit and ~he use of the fuses 9 are also necessary to provide for the situation in which due to crack formation of the refractory material which cannot be avoided at all, the separate curxent paths is affected by the entering of glass into the crack.
If molten glass entered such a crack, the resistance would be substantially reduced at this place by the glass penetrating the crack. This would result in a concentration of energy within the crack and, thus, in further cavitation and in an increase of the size of the crack. Accordingly, each individual heating circuit must be safely protected agai.nst occurence of trouble of this kind. Such positive protection is provided by the above-described division into a plurality of separate (secondary winding) heating circuits which are separately protected by fuses 9.
Figures 1 to 3 illustrate the circuit arrangement of the individual heating circuits whereby, as shown in Figure 1, a secondary winding supplies a pair of oppositely disposed electrodes 2 via conductors 5 and a fuse 9, while according to Figure 2 a center electrode 2' is supplied by the secondary winding via conductors 5 and a fuse, which center electrode is coupled to a pair of likewise oppositely arranged and interconnected electrodes 2; on the other hand, according to Figure 3 a transformer having two secondary windings feeds a total of five electrodes through the abovementioned wires and fuses. In the latter case, the center electrode is also connected in opposition to the two outermost el~ctrodes, and the two ~J~1 7~
electrodes positioned at th~ right and at the left of the center electrode are fed by the second secondary winding.
As shown in Figure 4, a plurality of circuits may be arranged on a feeder in tandem in the direction of flow of the discharging glass, whereby the current at every location flows transversely through the refractory material and, further, through the molten glass mass, and whereby four secondary windings 6 are each energized by a primary winding 8 in a controllable manner. Of course, each circuit includes the customary protective elements on fuse ~, even if not particularly shown.
me first heating area Zl heated at four locations, is followed by a corresponding second heating area 22, and the heating arrangement of the feeder head is then connected *o the abovementioned circular electrode llo In this case, the circuit arrangement is designed such that the current may flow e,g. from electrode 2a to electrode 2b, from which the current is adapted to flow not only to electrode 2a, but also to the adjacent electrode ~c at the opposite ide and to the circular electrode 11. -The electrode 2c, in turn, may have a current connection to the center electrode 2d. Further details are evident to one skilled in the art from Figure 4.
In a modified ernbodiment of the invention according to Figures 5a and 5b, the feeder passage may be of tubular configuration, whereby the level of the glass extends up to the level of the top of the tube -such that formation of a gas cushion is prevented.
.,~.~;. - .
. - 'i . .
- - . .
-Here, ~he electrodes 12 are formed as strips, and the current flows from interior electrode, i.e. 12', 12, to the pair of adjacently disposed electrodes thereof, electrodes 12" each, unless the strip electrode 12 is positioned at the end of the heating area such that the current can 10w in one direction only, as shown in Figure 5a.
In this embodiment, too, each heating circuit i5 separately protected by fuses 9 or the like in order to avoid disadvantageous local overheating. The electrode strips 12 consist of the same highly heat resistant material as described above, and these electrode strips are preferably also split at the locations where a gap 13 exists in the refractory material. The split portion is bridged by a conductive connection; however, it is hereby prevented that any glass present within the gap produces a disadvantageous separate current path which would result in the disadvantages as described above in connection with the crack formation.
Apparently, the solution according to the present invention offers a novel and advantageous means for the heating of all kinds of glass-carrying passages, tubes or pipes and the like.
Claims (13)
1. An apparatus for indirectly heating glass-carrying passages, feeders and feeder heads constructed from a conductive refractory material having a resistivity greater than that of lime-sodium glass at high temperatures, the passages thereof formed as a tube which are filled with liquid glass up the level of its top and wherein electrodes substantially surround the refractory material and comprise strips, and means for causing current to flow from one of said strips to the next successive one.
2. The apparatus as claimed in claim 1 wherein said electrodes are of strip-like configuration and are not in contact with the refractory material in the regions of gaps between tube portions.
3. The apparatus as claimed in claim 1 or 2 characterized in that the said electrodes are disposed most closely to each other in the location where the feeder or passage has the lowest temperature.
4. Apparatus for indirectly heating molten glass-carrying passages, feeders and feeder heads comprising a structural refractory material having a resistivity greater than the resistivity of molten lime-sodium glass, said refractory material forming said passages, feeders and feeder heads, and a plurality of electrode means in contact with and mounted exteriorly of said refractory material forming said passages, feeders and feeder heads and means to supply said electrode means with electrical energy via independent heating circuit means.
5. Apparatus of claim 4 wherein the secondary side of an isolating and/or variable transformer for feeding the respective, independent circuit means is divided into a plurality of galvanically isolated coils or windings.
6. Apparatus of claim 4 wherein each heating circuit means includes an overload relay or a fuse which turns said circuit off when a given power consumption is exceeded.
7. Apparatus of claim 4 wherein said glass-carrying passage feeder or feeder head is formed as a tube which is filled with molten glass up to the level of its top wherein said electrode means comprise strips substantially surrounding the material of said tube, whereby current flows from one of said strips to the next successive one.
8. Apparatus of claim 7 wherein said electrode strips do not contact the refractory material in the region of the gaps between tube segments.
9. Apparatus of claim 4 wherein said electrode means are strip-like in configuration having at least one end thereof bent at an angle with a current conductor connected thereto.
10. Apparatus of claim 4 wherein said electrode means are disposed more close to each other in areas where the feeder or passage has the lowest temperature.
11. Apparatus of claim 4 wherein resilient means are provided for pressing said electrode means against the refractory material.
12. Method for indirectly heating molten glass-carrying passages, feeders and feeder heads made of a structural refractory material having a resistivity greater than the resistivity of molten lime-sodium glass which comprises exteriorly contacting said refractory material forming said passages, feeders and feeder heads with a plurality of electrodes and passing heating current directly through said refractory material via said electrodes whereby said refractory material acts as a resistance heating conductor without direct contact between the molten glass and said electrodes.
13. Method of claim 12 wherein said electrodes are fed with heating current via a plurality of circuits, each circuit being adapated to be turned off when a higher power than a predetermined power is applied thereto.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2461700A DE2461700C3 (en) | 1974-12-27 | 1974-12-27 | Method and device for heating glass-guiding channels, feeders and feeder heads |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1080773A true CA1080773A (en) | 1980-07-01 |
Family
ID=5934685
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,567A Expired CA1080773A (en) | 1974-12-27 | 1975-12-24 | Resistant heating of ceramic refractory channels |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5514061B2 (en) |
| BR (1) | BR7508651A (en) |
| CA (1) | CA1080773A (en) |
| CS (1) | CS196203B2 (en) |
| DD (1) | DD122369A5 (en) |
| IT (1) | IT1054706B (en) |
| PL (1) | PL104258B1 (en) |
| SE (1) | SE413888B (en) |
| ZA (1) | ZA757969B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62188903A (en) * | 1986-02-14 | 1987-08-18 | Toyota Motor Corp | Measurement of dimension using image processing |
-
1975
- 1975-12-19 DD DD190366A patent/DD122369A5/xx unknown
- 1975-12-23 ZA ZA00757969A patent/ZA757969B/en unknown
- 1975-12-23 SE SE7514603A patent/SE413888B/en not_active IP Right Cessation
- 1975-12-24 PL PL1975186048A patent/PL104258B1/en unknown
- 1975-12-24 IT IT30753/75A patent/IT1054706B/en active
- 1975-12-24 CA CA242,567A patent/CA1080773A/en not_active Expired
- 1975-12-26 BR BR7508651*A patent/BR7508651A/en unknown
- 1975-12-27 JP JP15974975A patent/JPS5514061B2/ja not_active Expired
- 1975-12-27 CS CS758890A patent/CS196203B2/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| CS196203B2 (en) | 1980-03-31 |
| SE7514603L (en) | 1976-06-28 |
| SE413888B (en) | 1980-06-30 |
| JPS5192806A (en) | 1976-08-14 |
| JPS5514061B2 (en) | 1980-04-14 |
| PL104258B1 (en) | 1979-08-31 |
| ZA757969B (en) | 1976-12-29 |
| BR7508651A (en) | 1976-09-08 |
| DD122369A5 (en) | 1976-10-05 |
| IT1054706B (en) | 1981-11-30 |
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