IL47816A - Electrical melting apparatus - Google Patents

Description

Owens-Coming Fi er&Las Corporation The present invention relates to glass furnaces . for use for example in producing continuous glass filaments.

Prior glass furnaces using a heating element employ a sheet^like, usually curved, metal electrical current conducting heater element across a melting chamber. When high amperage electrical "current passes through the sheet-like heating element, ensuing intense heat from the energized element continuously converts input material into a molten mass in the melting chamber. When an arrangement uses the furnace or melter to supply molten material to other apparatus, prior arrangements orient the heater element across the direction of flow of the molten material towards the outlet to the other apparatus. The heating element has perforations- or slots through which molten material travels towards the outlet.

In producing continuous glass filaments, it was found that increased output or "throughput" requires faster molten glass movement through the openings in the sheet-like heating element. As the speed of the molten glass increases, the heating element can not satisfactorily convert batch to molten glass. Accord-ingly, heating capacity became the limiting factor in "throughput" of the .apparatus. The only answer appeared to be larger melting units; however, the expense and difficult operating characteristics of larger melting units based on prior concepts presented . a dismal outlook for effectively increasing "throughput". ..

According to the present invention, there is provided electrical melting apparatus comprising a melting receptacle of high temperature resistant material for holding molten material, the melting receptacle having a bottom opening for discharging the molten material from the melting receptacle, and a plurality of heating elements extending in parallel directions across the interior of the receptacle, each of the heating elements having a depth, from the top to the bottom of the respective heating element, which is greater than the thickness of the heating element, and each of the heating elements comprising two vertically spaced central portions extending longitudinally of the respective heating element, and end portions connecting the ends of the central portions, the end portions connecting the ends of .·' .. the central portions, the end portions each being shorter than the central portions.

When the apparatus is in use, the molten material can readily flow downwardly between the heating elements to the bottom opening of the melting receptacle. If the temperature of the molten material at one of the central portions of one of the heating elements becomes cooler than that at the other central portion of the heating element, the electrical resistance of the cooler central portion becomes less than that of the other central portion, and consequently additional current flows through the cooler central portion to increase the temperature of the latter.

Preferably, the central portions ofeach heating element are straight, cylindrical and mutually parallel.

The invention will be more readily understood from the 1 following description of the embodiments thereof given by way of example with reference to the accompanying drawings, in which: Figure 1 is a front elevation view of apparatus for producing "continuous filament . glass strand -.according to the principles of the invention.

Figure 2 is a side elevation view of the '.apparatus illustrat in "Figure 1. 12855C Figure 3 is a longitudinal sectional view of a melter and feeder arrangement according to the principles of the invention used in the apparatus shown in Figures 1 and 2.

Figure A is a transverse section view taken substantially on the line 4-4 of Figure 3.

Figure 5 is an enlarged side elevation view of one of the heating elements shown in Figures 3 and 4.

Figure 6 is a plan view of the heating element shown in Figure 5.

Figure 7 is an end elevation view of the heating element shown in Figures 5 and 6 taken substantially on the line 7-7 of Figure 5.

Figure 8 is a diagram of an electrical supply arrangement and control circuit for the heating elements.

Figure 9 is another heating element orientation within a ' melting receptacle.

Figure 10 is a side elevation view of another heating element according to the principles of the invention.

Figure 11 is a plan view of the heating element shown in Figure 10.

Figure 12 is a plan view of another heating element according to the principles of the invention.

Figure 13 is a side elevation view of the heating element shown in Figure 12.

DESCRIPTION OF THE PREFERRED EMBODIitEHTS While the invention finds particular use in manufacturing glass filaments, one may use the invention in processing flownble and heat softenable materials generally. The use of glass filament forming apparatus ie an example only to explain the operation of the invention. . 12855C 1 Figures 1 and 2 show apparatus on three levels operating to 2 produce continuous filament glass strand that collects as a wound package. 8 As Illustrated an upper level floor 10 between the upper and intermediate * levels supports a processing assembly 12 that supplies molten glass 8 streams 14 from a feeder or bushing 16. Λ winder 18 on the lower level 6 attenuates the molten glass streams 14 into continuous glass filaments 20. 7 A gathering shoe 22 at the intermediate level combines the advancing 8 continuous glass filaments 20 into a glass strand 24. The winder 18 0 advances the strand 24 downwardly through an opening 26 in the intermediate 10 floor 28 to wind the strand 24 as a package 30 on a suitable collector 11 such as a tubular collector 32 telescoped onto a collet 34. The winder 18 u drives the collet 34 In rotation. A reclprocatable and rotatable strand 18 traversing means 36 reciprocates the advancing strand 24 lengthwise of the M collecting tube 32 to distribute the strand 24 on the strand package 30. 16 At the intermediate level an applicator 40 supported within a 19 housing 42 applies siting liquid or other coating material to the advancing 17 filaments 20. The applicator 40 may be any suitable means known to the art 18 such as an endlaae belt that novae to pass through a sizing liquid or other 10 coating material hald In the housing 42. As the filaments 20 travel across 80 the surface of the moving applicator 40, some of the alsing liquid or al other coating material on the applicator transfers to the filaments. 33 The processing assembly 12 includes a frame 48 supporting a batch 38 feeding section 50, a furnace receptacle or meIter 52 heating batch mineral M material supplied from the feeding suction 50 into molten glass and the 35 feeder or bushing 16 receiving molten glass from the meIter 52. The frame 48 90 includes vertical portions 54 and horleontal bottom portions 56. 27 38 89 12855C In the embodiment illustrated the feeding section 50 includes a batch supply portion 60 and a batch distributing portion 62 that cooperate to continuously provide a layer of batch material in comminuted form over the upper Surface of a body of molten glass lieId in the melter 52. The batch supply portion 60 positions a relatively stationary hopper 64 with a supply of batch mineral material in comminuted form above a supplemental hopper 66 that is part of the batch distributing portion 62. Cross members 68 forming part of the frame 48 hold the relatively stationary hopper 64 above the supplemental hopper 66.

As shown the batch distributing portion 62 both meters and regulates the delivery of batch mineral material into the melter 52 and distributes the batch mineral material over the entire open araa of the open top of the melter 52. Accordingly, apparatus regulates batch material leaving the supplemental hopper 66 and moves the hopper 66 for batch distribution. In the arrangement the supplemental hopper 66 mounts on a shaft 70 held in Journal bearings 72 carried by cross members 74 on the frame 48. An electric motor 76 drives a rotational batch regulating means through a speed reducing mechanism 78 and a drive system. The output shaft 80 of the speed reducing mechanism 78 drives the shaft 70 through a chain 84 connecting a sprocket 82 on the shaft 70 vlth a sprocket 86 on the output shaft 80. The rotational energy of the shaft 70 transfers to the batch regulation means. As the shaft 70 rotates, a sprocket 88 fixed on the shaft 70 drives a sprocket 90 on a shaft 92 through a second chain 94. The shaft 92 is at the outlet region of the supplemental hopper 66 and mounts for rotation in bearings carried by the supplemental hopper 66.

The shaft 92 extends across the outlet of the hopper 66 and has radially extending blades or veins 96. As the electrical motor 76 rotates the shaft 92 through the drive system of chains and sprockets, the veins 96 move to regulate batch material from toe supplemental hopper 66 to the melter 52. 12855C hopper 66 into Che melter 52 by varying Che epeod of rotation of the shaft 92 and consequently the movement of the veins 96 .

The supplemental hopper 66 is swlngable or oscillatable about the axis of the shaft 70 for distributing batch material from thehoppper 66 over the open area of the me ter 32 , such motion providing a substantially uniform layer of batch material on the surface of the body of molten glass in Che meIter 52. The arrangement secures a bracket 102 to one wall of the hopper 66 near Che bottom or outlet region of the hopper 66. A platform 104 on Che upper floor 10 supports an electric motor 106 that drives a speed reducing mechanism 106. The output shaft 110 of the speed reducing mechanism has fixed on it an arm 112 that pivotally connects with a rod or link 114. The other end of he link 114 pivotally connects to the bracket 102. As the electric motor 106 rotates the output shaft 110 of the speed reducing mechanism 108, the arm 112 moves the link 114 Co oscillate Che outlet of the supplemental hopper 66 back and forth across the open entrance to the meIter 52.

Figures 3 and 4 show the construction of the meIter 52 and feeder or bushing 16 arrangement forming part of the processing assembly 12 shown in Figures 1 and 2. The meIter 52 converts batch mineral material to molten glass through heat supplied by spaced apart generally parallel electrical current conducting heating eloments 120 extending across the interior or melting chamber 122 of Che meIter 52. Molten glass in the maIter 52 flows into Che bushing 16 through the melter's outlet or exit passageway 124.

The meIter 52 comprises a refractory cover 128, a liner 130 and a heating arrangement Including the heating elements 120. 12855C The refractory cover 128 ie built of high temperature resistant refractory. The refractory cover 128 includes lengthwise extending portions 134 and transversely extending portions 136. These portions define an entrance region for receiving batch material from the supplemental hopper 66.

The liner 130 conformo to the interior arrangement of the refractory construction of the maIter 52 to define the melting chamber 122. Because the liner 130 must not deteriorate appreciably under high melting temperatures generally present during the operation of the me ter 52, the liner 130 is normally made of platinum or a platinum alloy such as an alloy containing a substantial percentage of rhodium. It is possible to use other high temperature resisting materials for the liner 130.

The liner 130 is not electrically energised; it is separated electrically from electrical circuits and supplies. As more easily seen in Figures 3 and 4 the lower portion of the liner 130 defines the outlet passageway 124 and terminates at its lower portion with flanges 140.

An electrical arrangement supplies low voltage and high amperage electrical energy to the heating elements 120. The electrical arrangement supplying current to the heating elements 120 is electrically separate from the liner 130. Intense heat generated from electrically energising the heating elements 120 melts the batch material into molten glass. 12855C 1 The position of the heating elements 120 is beneath the surface 3 of a body of molten glaee in the melting chamber 122. As shown in Figures 3 * and 4 the heating elements 120 are under the surface of a body of molten * glass 141, the upper surface of the molten glass being covered by a layer 142 6 of unmelted batch mineral material in comminuted form continuously supplied β from the supplemental hopper 66. Both the electrical arrangement supplying 7 current to the heating elements 120 and the heating elements 120 themselves 8 are electrically separate from the liner 130.

* The current conducting heating elements 120 have a width or 10 depth at least as large as their thickness; the depth of the heating elements u 120 is oriented generally normal to the surface of the body of molten glass. 13 In a specific form, which is more plainly seen in Figures 5 through 7, the 13 current conducting heating elements have an appreciable depth compared 14 with their thickness. Αΰ shown the heating elements 120 are made of 10 electrical current conducting tubular material formed into longitudinal 18 units having a somewhat flattened elliptical or race-track shaped central 17 portion 144 and connectors 146 extending from the ends of the central 18 portion 144. The elongated central portion 144 includes two spaced apart 19 parallel straight middle elements 148 and shorter end elements 150 connecting 30 the adjacent ends of the straight element 148. In the form illustrated the 3 end elements 150 are semi-circular. In Figure 5 "w" indicates the width or 33 depth of the heating elements 120; in Figure 6 "t" indicates the thickness 3> of the elements 120. In the specific form shown the thickness of the M heating elements 120 is the diameter of the tubular material comprising the as elements 120. 30 37 38 39 12855C Because of the elongated shape of the central portions 144, electrical current divides as it leavee the connectors 146 to flow into the elongated central portions 144. As shown in Figure 5 the central portions 144 provide two distinct current paths , vis. path I and Path IX.

As with the liner 130, the material tubular units comprising the heating elements 120 is platinum or an alloy of platinum.

The connectors 146 are curved tubular members. A portion 146a extends axial y away from the central portion 144 for a short distance; then the connectors 146 turn with a portion 146b extending obliquely of the element's lengthwise axis before again turning with a portion 146c extending in a direction axially away from the central portion 144.

Moreover, the connectors 146 Include metal strip portions 152 and 154 extending outwardly and generally lengthwise of the portions 146a and 146b. These metal strips provide additional metal for electrical current; the strips assist uniform division of electrical current into the distinct current paths of the elongated central portion 144.

To assist heat distribution that promotes more uniform heat emission throughout the current conducting heating elements 120, heat resistant material In the form of refractory is within the hollow tubular units comprising the current conducting elements 120. In Figure 5 one can see that refractory 156 fills the interior of the connectors 146. Refractory also fills the interior of the curved end elements 150. It has been useful to use an aluminum oxide refractory. A refractory tubing 158 snugly fits against the inner surface of the straight middle elements 148. The tubing 158 strengthens the middle elements 148. An aluminum oxide tubing commercially available from McDanlal Company under the designation "AP-35" gives good results, I A* shown in Figures 3 end 4, the electrical current conducting 3 heating elements 120 extend transversely across the melting chamber 122 in 8 spaced apart adjacent generally parallel relationship. The distance 4 between adjacent elements 120 is normally from 1 to 3 inches, 2 Inches 6 being most common. Moreover, the depth or width "w" of the heating β elements are oriented generally in the direction of low of molten glass 7 moving to the exit passageway or opening 124 to the feeder, 16. In the 8 vertical process shown in Figures 1-4 the heating elements are vertical β and normal to the surface of the body of molten glass 141. 10 Electrical current carrying bus bars support and electrically inter- II connect the current conducting heating elements 120 at their ends. As U shown two sets of bus bars, via. bus bars 160 and 162, each extend lengthwise 13 along the upper surface of the refractory cover 128. Cooling tubes 164 14 extend through each of the upper and heavier bus bars 160 to carry cooling is water that controls the temperature of the bus bars. Each of the bus bars 10 160 and 162 contains generally semi-circular recesses. The recesses in each 17 bar 160 align with the recesses in bar 162 to form gripping regions into 18 which fit the end portions.of the connectors 146. When pressed together 10 such as by bolts 166, the gripping regions of the bus bars rigidly hold the 30 current conducting heating element* 120. 31 An electrical arrangemen supplies electrical current to each set 33 of bus bars 160 and 162 and consequently to the elements 120 from transformers 3 168 and 170 through conductors 172 and 174 respectively. 34 38 8 7 8 > 0 I In operation, electrical current flows from the bus bar 3 arrangement to the central portion 144 of the current conducting heeting 8 elements 120 through the connectors 146. As the current reaches connector * portions 146b and 146a, the current more easily flows through the metal β strips 152 and 154. In a sense, at start-up of the meIter 52 these strips 8 tend to orient the current for substantially uniform current split between 7 the two distinct current paths, I.e. paths X and XX, of the heating 8 elements 120.

» As the supplemental hopper 66 supplies the layer 142 of batch 10 material to the surface of the molten glass 141 in the melting chamber 122, II the energised elements 120 provide intense heat under controlled conditions 3 thet regulate the melter's melting rate with the rate of molten glass is delivery from the feeder 16. Because the heating elements 120 are submerged 1* in the body of molten glass 141, batch normally does not directly engage ift the heating elements 120. Usually the heating elements are from 1-3 inches 1* beneath the surface of the molten glass 141 in the melting chamber 122. 17 If in the melting chamber 122 the temperature of molten glass at 18 the upper leg (Path I) of the heater elements 120 becomes cooler than ie molten glass near the lower leg (Path II), resistance of the metal in the 20 tubular material along path I becomes less than resistance of metal along > Path II. Accordingly additional current flows along path I to increase 33 the temperature of that portion of the heating elements. In similar fashion, 9 if conditions reduce the temperature of the metal in the lower leg (path IX) M of the elements 120, additional current flows along Path II to increase ft temperatures in that leg. Consequently, temperature condition* along the β length and width of the elements 120 effect current flow to somewhat 37 compensate and make more even thermal treatment of molten glass by the heating 38 elements 120. 30 t The refractory within the heating elements 120 promotes more 3 uniform heat emission throughout the heating elements 120. Accordingly > the molten glass recolves a more uniform thermal treatment. The refractory 4 tends to store thermal energy. If for any reason a cool aone develops on β a heating element 120, heat from the refractory flows to that cooler zone β to assist In raising the temperature of the eone to a temperature substantially 7 equal to the surrounding temperature. 8 Figure 8 shows a circuit for controlling electrical energy supplied o to the heating elements 120 from the transformers 168 and 170 and consequently 10 generally controlling the thermal energy emitted by the heating elements 120. u As shown, the secondary 178 of the power transformer 168 and the 13 secondary 180 of the power transformer 170 connect to adjacent ends of the u bus bars at terminals 182 and 184 respectively. Suitable electrical means supplies the primaries 186 and 188 of the power transformers 168 and 170 i 16 respectively with electrical power through leads Lj and Lj. The electrical ie power to the leads and i^, for example, may be 60 cycles alternating current 17 of 440 volts. The secondaries 178 and 180 reduce the voltage from the 18 primaries 186 and 188 to provide around 5 to 6 volts to the bus bars with 1» sufficiently high current flow, for example 5,000 amperes, to heet the 30 elements 120 by conventional resistance heating to the high temperatures 31 needed in the meIter 52 to convert the batch mineral material into molten 33 glass for delivery to the feeder 16. 38 M 38 38 37 38 3» 80 128556 1 Λ control circuit using a silicon control rectifier 190 senses 2 voltage variations caused by resistance changes in the heating elements 120; • cuanges in resistance may occur, for example, upon interruption of normal * glass flow from the feeder 16 occurring as the winder 18 completes a package o 30 and an operator puts a new collector on the collet 34. The sensing β circuit modifies the power supply current to restore e predetermined 7 temperature to the heater strips 120 for better control of molten glass 8 flow through the m Iter 52 to the feeder 16. Because the time-cons ant. 9 characteristlca of the silicon control rectifier 190 are small, any 10 deviation from a preselected flow rata is at a minimum. 11 As shown the control circuit uses a control transformer 192 with 12 its primary 194 connected across the terminals 182 and 184. jlhe transformer 192 is pteferably provides a 4 to 1 reduction in voltage; accordingly, the circuit 14 uses a center tap secondary 196. Diodes 198 rectify the current in the i* secondary 196. A pi filter circuit 200 receives the rectified current. The 19 pi filter circuit 200 comprises a pair of parallel connected condensers 202 17 and 204 having Interposed between them a resistance 206 and an Inductance 208 18 connected in aeries. | 1· The resulting direct output from the pi filter circuit 200 is 30 applied across a voltage divider 210 that gives an exceedingly small output 31 signal, for example an approximately 10 millivolt DC output, to a control 33 unit 212 of conventional construction. The silicon control rectifier 190 33 receives the output of the control unit 212. The silicon control rectifier 190 M holds the time-constant factor of the power circuit below one-quarter cycle. i 25 90 27 28 29 SO 12855C 1 The voltage sensing circuit is a more rapid sensing system a than a thermocouple eye tea. Through the electrical supply and control 8 arrangement shown in Figure 8, the me Iter 52 provides a more stable 4 temperature for melting batch material to molten glass as the winder 18 β attenuates glass fibers from the molten streams supplied at the outlets β of the feeder 16. The result is glass fibers of more uniform dimension 7 throughout package build and between packages produced using the apparatus 8 of the invention. 0 Figure 9 shows another arrangement for the heating elements 120 10 In the as Iter 52. In Figure 9 there are an even number of elements 120 ; 11 the distance "V" between the upper legs (Path I) of the middle two elements 13 120 is approximately twice the distance between the other elements 120. 13 Because the distance between the adjacent elements 120 is normally from 14 1 to 3 inches, the distance "D" is usually from 2 to 6 inches, 4 inches 18 being more common. To give more uniform heat paths for molten glass in the 1β me Iter 52, the arrangement orients most of the elements 120 to slant towards 17 the central region of the melting chamber 122. As shown all the elements 120, 18 except for the outermost or end elements, make an angle Θ with the vertical . 19 While the end elements are vertical, the other elements slant towards the 90 central region of the me Iter 52 with a progressively increasing angle 9 ; 31 normally angle Θ varies from 5 to 25 degrees, angle 0 is largest for the 38 center most heating elements 120. The arrangement shown in Figure 9 orients 31 the lower legs (path XX) at substantially equal distances apart. Μ As the heating element arrangement of Figure 9 operates to convert 35 batch mineral material to molten glass, the molten glass encounters substantially 30 the same thermal treatment as it flows along Its path to the outlet of the 37 melting receptacle. 38 39 80 128S5C I Figures 10 and 11 show another electrical current conducting 8 heating element, I.e. beating element 220, according to the principles * of the invention. The heating element 220 has an elongated generally * rectangular central portion 244 with connectors 246 extending from the β ends of the central portion 244. The central portion 244 includes two 6 spaced apart aide walla 248 and two epaced apart thickness wall portions 250 7 that unite to provide a hollow unit. Refractory 252 fills the interior 8 of the central unit 244. The central portion has a depth or width "w" 0 and a thickness "t". 0 The central portion 244 includes oblique end wall portions 254 II and a middle portion 256 from which extend the connectors 246. 3 The connectors 246 are curved tubular members and have generally is the same configuration as the connectors 146. A portion 246a extends * asially away from the middle end portion 256 of the portion 244 for a short * distance; then the connectors 246 turn with a portion 246b extending obliquely 18 of the element's lengthwise axis before again turning with a portion 246c 17 extending axlally away from the central portion 244. ω As in the case of the heating elements 120, the connectors 246 19 include metal strip portions 258 and 260 running generally lengthwise of 90 the portion 246a and 246b, These metal strips, as in the case of portions 3 152 and 154, provide additional metal that tends to assist uniform division » of electrical current into two generally distinct current paths lengthwise » of the central portion 244.

M As indicated by the dashed lines in Figure 10, the current flow *» from the connectors 246 to the central portion 244 tends to follow two » generally distinct electrical paths, vis. an upper Path X and a lower Path IX. 87 The current conducting heating elements 220 fit across the meIter » 52 like the heating element* 120. » o . ,. 12855C If in · recept&cle, e.g. the melting chamber 122, the temperature of molten glass at the upper ?ath I of tho heater elements 220 becomes cooler! than molten glass near the lower Path II, resistance of the metal in the elements 220 along path I becomes loos than the resistance of the metal along path II. Acco dingly, additional current flows along Path I to Θ increase the temperature of tho upper portion of the heating elements. In similar fashion, if conditions reduce the temperature of the metal in the lower Path II of the elements 120, additional current flows along that path to increase temperatures of the lower portion of the heating elements. 10 Consequently, temperature conditions along the length and width "w" effect 11 current flow to somewhat compensate and make more even thermal treatment U of molten glass treated b the heating elements 220. Thus, the operation 18 of the heating elements 220 is similar to the operation of tha heating elements 120.

Referring to Figures 3 and 4, the feeder or bushing 16, which' is beneath end La registered with the meIter outlet passageway 124, includes 17 a bottom wall 270, side walls 272 and and walls 274. The side and end walls 18 terminate with laterally extending flanges 276. Refractory members 278 10 thermally and electrically insulate the flanges 276 of the feeder 16 from ao the bottom flanges 140 of the liner 130. Moreover, refractory 280 surrounds 31 the exterior of the feeder 16. Frame members 282 support, the high temperature j resistant refractory 230 in a conventional manner.

As in the case of the liner 130 and the current conducting heating elements 120, the walls 272, 274 and 270 are made of platinum or an alloy of platinum.

A group of orlflcod tips or tubular projections 284 extend from the exterior of the bottom wall 270. It is through these tubular projections 284 that molten glass discharges from the feeder 16 in the form of the molten glass streams 14. 1 I' 12855C As more clearly seen in Figures 1-3, the end wells 274 have terminals 286 that receive electrical enorgy from a power transformer 288 through conductors 290. Electrical current supplied to the feeder 16 through the terminals 286 heats the feeder 16 by resistance heating to maintain the molten glass 'in the feeder 16 at desired temperatures and viscosities.

Disposed adjacent to and sos&ewhat below the bottom wall 270 of the feeder 16 la a manifold 292. Extending transversely from the manifold 292 are fins or veins 294 that conduct heat away from the molten glass 10 streams 14 to render the glass of the stroams more viscous for efficient u attenuation of the continuous glass filaments 20. The manifold 292 has 13 an inlet tube 296 and an outlet tube 293 that circulate heat absorbing 18 fluid such as water through the manifold 292. A mounting structure 300 14 secured to a frame member 301 supports the manifold 292.

U As shown In .figures 1 and 2, the processing assembly 12 includes 16 a cover or hood 302 disposed above the batch supply portion 60 and batch 17 distributing portion 62. From the top of the hood 302 extends a stack 18 or pipe 304 preventing the batch distributing portion 62 from contaminating 10 with fine particles of batch the filament forming region at the bottom wall 270. The stack or pipe 304 may connect to a suction blower to initiate forced air circulation around the batch distributing portion 62. 12855C Figures 12 and 13 show yet another embodiment of an electrical current conducting heating element, denoted by the reference numeral 320, according to the principles of the invention. Like the other heating elements, the element 320 has appreciable .depth or width compared with its thickness. And it is made of the same electrical current conducting tubular material as is the element 120; heat resistant material, like the element 120, in the form of refractory (aluminum oxide) is within the tubular material.

The elongated element 320 includes a central portion 324 that I Is formed by two spaced apart parallel elements 326 and 328 and by shorter straight elements 330 connecting the elements 326 and 328 together. ' i Straight connector portions 334 extend from each end of the element 320.

As shown the portions 334 are extensions of the straight element 326.

So, like elements 120, elements 320 each includes; an elongated central portion including two spaced apart parallel straight I cylindrical portions, shorter end portions connecting the straight portions, and connectors extending from each end extending along the longitudinal axle of the element. The connectors (334) are straight.

Elements 320 are connected for melting like the elements 120 as shown in Figures 3 and 4. j ' , .

Claims (17)

WHAT WE CLAIM IS:

1. Electrical melting apparatus comprising a melting receptacle of high temperature resistant material for holding molten material, the melting receptacle having a bottom opening for discharging the molten material from the melting receptacle, and a plurality of heating elements extending in parallel directions across the interior of the receptacle, ' each of the heating elements having a depth, from the top to the bottom of the respective heating element, which is greater than the thickness of the heating element, and each of the heating elements comprising two vertically spaced central portions extending longitudinally .of the respective heating element, and end portions connecting the ends of the central portions, the end portions each being shorter than the central portions.

2. Apparatus as claimed in claim 1, wherein the central portions of each heating element are straight, cylindri-cal and mutually parallel.

3. Apparatus as claimed in claim 1 or 2, wherein the central portions of each element are vertically spaced in a common vertical plane and extend horizontally.

4. Apparatus as claimed in claim 1, 2 or 3, wherein each of the heating elements comprises a hollow outer electrical current conducting portion and heat resistant material within the outer portion.

5. Apparatus as claimed in claim 1, 2, 3 or 4, wherein the heating elements are electrically connected in parallel.

6. Apparatus as claimed in any preceding claim, . wherein the heating elements are electrically separated from the melting receptacle.

7. Apparatus as claimed in any preceding claim, wherein the melting receptacle has walls extending higher than the tops of the heating elements to allow immersion of the heating elements in the molten material in the melting receptacle when the apparatus is in use.

8. Apparatus as claimed in any preceding claim, wherein each heating element includes a connector at each end projecting longitudinally of the heating element from a respective one of the end portions.

9. Apparatus as claimed in claim 8, wherein the ¾ connectors are non-linear.

10. Apparatus as claimed in claim 8 or 9, in which the connectors include metal strips extending outwardly and lengthwise thereof to promote uniform division oif electrical current to the central portions. ,

11. Apparatus as claimed in any preceding claim, wherein means are provided for delivering batch mineral material in comminuted form to the melting receptacle through an opening in the to of the meltin rece tacle.

12. Apparatus as claimed in any preceding claim, provided with a feeder communicating with the melting receptacle through the bottom opening in the melting receptacle for receiving the molten material from the latter, the bottom of the feeder having holes for flow of the molten material through the holes as molten streams.

13. Apparatus as claimed in claim 12, wherein electrical means are provided for heating the feeder.

14. Apparatus as claimed in claim 12 or 13, provided with means for attenuating the molten streams into continuous filaments.

15. Apparatus substantially as hereinbefore described with reference to Figures 1 to 8 of the accompanying drawings. v

16. Apparatus substantially as hereinbefore described with reference to Figures 1 to 8 as modified by Figure 9 of the. accompanying drawings. "k

17. Apparatus substantially as hereinbefore described with reference to Figures 1 to 8 as modified by Figures 10 and 11 of the accompanying drawings.