US3088182A - Furnace - Google Patents

Description

FURNACE 4 Sheets-Sheet 1 Original Filed July 10, 1958 May 7, 1963 M. TAMA Em. 3,088,182

FURNACE Original Filed July 10, 1958 4 Sheets-Sheet 2 INVENTORS MA/o 771/144 W/L BUP JHM/FM4# May 7, 1963 M. TAMA ETAL 3,088,182

FURNACE Original Filed July lO, 1958 4 Sheets- Sheet 3 ,75 /90 74L 73 9/ 72 7a 75 l May 7, 1963 M. TAMA ETAL FURNACE ....Jiiillil i $25!,Si.2215.2215321: En. /l 9.9 f/V i l n.' f 1l QRNRRO Original Filed July l0, 1958 United States Patent O 3,088,182 FURNACE Mario Tama, Morrisville, and Wilbur E. Sllearman,

Yardley, Pa., assignors to Ajax Magnethermic Corporation, Trenton, NJ., a corporation of Ohio Original application July 10, 1958, Ser. No. 747,667, now Patent No. 2,959,757, dated Nov. 8, 1960. Divided and this application June 20, 1960, Ser. No. 37,457 3 Claims. (Cl. 22-79) The present invention relates to furnaces having pouring conduits or spouts for molten metal.

The present application is a division of our copending application Serial No. 747,667, led July 10, 1958, now Patent No. 2,959,757, for Pouring Spout.

A purpose of the invention is to permit extension of the pouring spout well out beyond the furnace so that it can pour directly to the location at which the molten metal or the like is to 'be used.

A further purpose is to reduce the danger of damage to electric heaters by penetration of molten metal around the resistor elements which surround a conduit for molten metal.

A further purpose is to provide a flange which may take the shape of a flare or cone at one or preferably both ends of a refractory heater tube Iand to extend the flange outwardly so as to reduce the possibility that molten metal can reach the resistor of the heater.

A further purpose is to employ a flanged heater tube of silicon-nitride-bonded silicon carbide.

A further purpose is to effectively cool the heater tube .at the end so that :any molten metal penetrating along the end and otherwise likely to pass around the outside of the heater tube will be solidified.

A further purpose is to employ a flange on the heater tube of refractory and to extend it near to the metallic casing in order to effectively cool the refractory in that area and prevent molten metal `from passing around the heater tube.

A further purpose is to secure radially extending metallic terminals in the outside of the heater tube, preferably locking the terminals in -at least some instances intermediate the ends of the heater tube and securing the resistors to the terminals.

A further purpose is to create multiple heating zones of controlled temperatures in a molten metal conduit.

Further purposes appear in the specifi-cation and in the claims.

In the drawings we have chosen to illustrate a few only of the numerous embodiments in which the invention may appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

IFIGURE 1 is a central vertical ydiagrammatic section of an electric induction furnace to which the invention has lbeen applied.

FIGURE 2 is an enlarged side elevation of the pouring spout, parti-ally sectioned away.

FIGURE 3 is a fragmentary section on the line 3-3 of FIGURE 2.

FIGURE 4 is ya fragmentary section on the line 4-4 of FIGURE 2.

FIGURE 5 is a section through the axis of the pouring spout of FIGURE 2.

FIGURE 6 is an 'enlarged fragment of FIGURE 5.

FIGURE 7 is a fragmentary section on the line 7-7 of FIGURE 5.

FIGURE 8 is a top plan view of a modified form of heater tube according to the invention, broken away to show one of the terminal sockets.

FIGURE 9 is a side .elevation of the heater tube of 3,088,182 Patented May 7, 1963 ICC FIGURE 8, broken away to show one of the turn-around pin sockets.

FIGURE 10 is a left end elevation of the heater tube of FIGURES 8 land 9.

FIGURE ll is an enlarged fragmentary axial section of the heater tube of FIGURES 8 to 10.

FIGURE 12 is an axial section of a launder in accordance with the invention.

FIGURE 13 is an enlarged fragmentary axial section of the launder of lFIGURE l2.

lFIGURE 14 is an axial section of a modified form of launder according to the invention.

FIGURE l5 is an enlarged fragmentary axial section of the launder of FIGURE 14.

In the prior art, difficulty has been encountered in producing electrically heated pouring spouts, launders and other -conduits to be used in connection with melting furnaces for metal land the like, due to the tendency of molten metal from the charge to penetrate through or around the heater tube and short circuit the electric resistor elements. This seepage of molten metal has been due to formation of cracks in the inner refractory tube.

In the prior art in many cases the heater support tube, called herein the heater tube, was of metal :and had very little resistance against molten metal attack.

In accordance with the present invention, an improved construction of pouring spout or another conduit for molten metal provided with an electric heater has been produced.

In accordance with the invention, the heater tube is made of refractory, and for best results, silicon carbide bonded with silicon nitride has been employed, which has the following remarkable combination of properties:

(1) The heat conductivity is as high as that of silicon carbide.

(2) T-he refractory i-s very resistant to penetration of molten metals generally and particularly to penetration of .molten aluminum, to which the invention is particularly applicable.

(3) The mechanical strength of the refractory is about three times as high as that of silicon carbide.

(4) It is adequately resistant to variation in temperature, so that spalling and similar difficulties are not likely to occur.

In accordance with the invention, the heater tube at the end nearest the furnace and preferably at both ends is provided with an integral flange which may take the shape of a flare or cone and which extends outwardly preferably to a position near the metallic casing. No heater elements surround this flange, and therefore the outer edge of the flange assumes a temperature well below the melting point of the metal in the conduit. The flange physically acts as a dam or obstruction to prevent molten metal from entering the region of the electric resistor elements, and it also acts as a cooling fin to maintain a temperature low enough so that any molten metal entering this area will solidify. In order to pass around the heater tube, the molten metal would have to ilow out around the flange and then inwardly into contact with the heater elements, and this is very unlikely to occur. At the discharge end the heater tube is desirably carried almost to 4the point at which the molten metal discharges so that there is little danger that molten metal could pass around the heater tube at that end.

The device of the invention desirably incorporates metallic terminals which are mounted in sockets in the heater tube, the feeder terminals in the preferred embodiment being located at the middle of the heater tube so as 4to be well protected from contact with molten metal.

The invention is applicable to any conduit which carries molten metal from one furnace to another, or from a furnace to a casting mechanism or the like. The invention is particularly applicable to pouring spouts which convey molten metal from a melting furnace or otherwise to a die casting machine such as a cold chamber die casting machine.

Considering first the form of FIGURES 1 to 7, we illustrate an electric induction furnace having a furnace chamber 21 and a submerged channel 22. The submerged channel has within it one leg of a core type transformer core 23 which is surrounded with a furnace inductor coil 24.

The furnace chamber has a refractory lining 25 and the submerged channel has a refractory lining 26. Around the refractory lining heat insulation is provided at 27 and the entire furnace is supported by a metallic casing 28. A removable plug 3i) is provided at the bottom of the channel for clean-out purposes.

At the top the furnace chamber is covered by a gas tight refractory cover 31 having a metallic casing 32 and removably secured by fastenings 33. There is also a refractory inlet opening provided at 34 closed by a suitable gas tight cover 35.

At the outlet end, the furnace has a discharge opening 36 through the refractory which connects to the lower and inner end of a pouring spout 37 which discharges to a suitable mechanism, in this case a cold chamber die casting machine 38. Discharge is accomplished by maintaining a positive pressure from a suitable gas such as air, nitrogen, or carbon monoxide introduced through an opening 4i) in measured quantities to control the discharge as known in the art.

The pouring spout 37 has a tubular metallic casing 41 which is secured as by welding to a welded metallic housing 42 which is united as by welding to a spout base plate 43 which is suitably secured to the metallic furnace casing as by bolts passing through openings 44. The mounting plate has a suitable opening through which the refractory extends as later explained.

Within and surrounding the casing 41 of the spout is a heat insulating lining 45 suitably of asbestos within which is placed the refractory heater tube 46 to be described, which has wound thereon metallic resistor elements 47 of any suitable material, such as Nichrome.

Within the heater tube and desirably fitting the inner Wall of the heater tube is placed .the tubular refractory spout lining 48 which has an interior passage 50 connecting to the outlet opening 36 of the furnace and reducing in cross section to an orifice 51, then enlarging at S2 and having a uniform passage 53 extending to the outer end of the spout.

The heater tube in the form of FIGURES l to 7 has a generally right circular cylindrical portion 54 which has suitably placed spiral grooves 55 in the outer circumference for receiving the resistor wire. At the outer end and at the inner end of the cylindrical portion 54, there is a suitably threaded radial socket 56, best seen in FIG- URES 5, 6 and 7, which receive a metallic turn-around pin 58 threaded on the outside and mounted in the socket. The turn-around pin has a groove at 57 in which the resistor Wire is wrapped and supported in the form of a hairpin turn. The turn-around pin is suitably made of Nichrome or the like.

The inner ends of the two coils of resistor elements shown are received on terminals 60' which extend outwardly from radially threaded sockets 61 near the center, best seen in FIGURES 3, 4 and 5. The use of two separate resistor elements enables separate control to the power input of each, thus creating multiple heating zones of controlled temperatures. The terminals at their inner ends are threaded into the sockets and have circular recesses 62 beyond the threaded portions into which the ends of the respective resistors extend, the resistors being united by brazing or Welding as desired.

The terminals 60 have outwardly extending ends 63 beyond the refractory which are engaged by suitable leads 64 connected thereto as by welding. The leads are suitably covered by a terminal box 65.

At the end adjoining the furnace, the heater tube has integral therewith a llange 66 which extends radially outwardly and in this form is conical and progressively reducing in cross section toward the outer end. The flange is surrounded exteriorly by refractory heat insulation 45 and inside the flange and between the flange and the inner tube 48 of the spout at the inner end is placed refractory cement 67.

The flange and the entire heater tube and desirably also the inner refractory lining of the spout are produced from silicon-nitride-bonded silicon carbide in the preferred embodiment.

In operation of the form of FIGURES l to 7 inclusive, let us assume that the inner refractory tube of the spout cracks or breaks, and molten metal penetrates outwardly. It will be impossible for such molten metal to reach the outside of .the heater tube and come in contact with the electric heating elements without passing around one end or the other of the heater tube, unless, of course, the heater tube itself cracks, which is unlikely.

If the molten metal comes to the upper end of the heater tube it will be discharged from the spout. lf the molten metal comes to the lower end of the heater tube, which it is Arnore likely to do under the action of gravity, the molten metal cannot flow around the outside of the heater tube Without flowing outwardly along the flange 66. But since the flange 66 extends well out tow-ard the outside of the spout and extends close to the metallic housing 42 and the metallic casing 41, the molten metal is likely to solidify and cease to flow so that it does not encounter the `outside of the heater tube and does not engage and short circuit the resistors.

In the embodiment shown in FIGURES l to 7, heat is concentrated at the lower end and the upper end of the spout by placing the resistors close together at 68 `and 70 and spacing them more widely in between at 71. The terminals connected to the power leads are remote from the hotter parts of the heater tube.

In FIGURES 8 to l1 we illustrate a modified form of heater tube, suitable for use in a pouring spout as shown in FIGURES 1 to 7. i

In this kcase the heater tube 72, desirably of siliconnitride-bonded silicon carbide, has a cylindrical portion 73 which'is provided with external grooves 74 lto receive an electric resistor and has a flange or flare 75 at the end adjacent the furnace which is conical and progressively'reducing in cross section toward the radial outer end. In this embodiment, one coil is use-d so that a single, continuous length of wire forms the resistor. The ends of the wire are fixed to terminals which are mounted in sockets 77, with intermediate points of the wire being wrapped in grooves of turn-around pins mounted in sockets 76.

In this case radial sockets are provided at the ends at 7,6 having internal threads to receive threaded turnaround pins and `sockets are provided vat the center at 77 which have internal threads to receive terminals which connect to the leads from the power source as previously explained.

In this form also the grooves for the resistors are placed close together at the lower end 78 and the upper end 180 to concentrate the "heat, and are placed more widely apart at 81 at the center.

The forms embodied in FIGURES 12 through 14 are desirably used where the central passage of the launder is well below the surface of the molten metal and completely filled with molten metal under some pressure.

The form of FIGURES 12 and 13 illustrates a launder which is useful in carrying molten metal from one furnace to -another or from one furnace to a casting apparatus.

In this case a refractory lining 82 and metallic casing 83 of the discharging furnace are shown, with a discharge opening 84 through the refractory lining. The launder has a central passage 85 which is formed by a tubular refractory lining 86 desirably of silicon-nitridebonded silicon carbide made in sections which have cooperating groove and recess connections 87 at the ends. The inner refractory tubes 86 are surrounded by heater tubes 88 which have tubular portions in the middle and radial flanges 90 at each end. The heater tubes are desirably made of silicon-nitride-bonded silicon carbide. Electric resistor elements 91 surround the tubular portions of the heater tubes and are wired in any suitable manner, desirably to terminals of the character already described.

The space between the flanges of -adjoining heater tubes is filled with refractory cement at 92 and the space around the tubular portions of the heater tubes is filled with refractory heat insulation such as asbestos 93.

The outside of the heat insulation is surrounded by a metallic casing 94 which is anchored to the casing of the discharging furnace at one end in any suitable way :and at the other end is anchored -to the metallic casing 95 of the receiving furnace which has an yinlet opening 96 and a refractory lining 97.

The heater tubes and the linings of the conduit are desirably made in several sections to eliminate the `danger of damage due to expansion and contraction.

FIGURES 14 and 15 show a modified form of electrically heated launder according to the invention. In this case the construction -is essentially the same as that already shown in FIGURES l2 and 13 except that the flanges 90 o-n the heater tubes are conical, instead of extending directly radially outwardly. Like flanges 90 -they reduce in thickness progressively outwardly. Refractory cement 92 is interposed inside the flanges in this form and refractory or metallic rings 98 are interposed between the end of the fins as a further obstruction to flow of the molten metal outwardly.

In operation of the forms of FIGURES 12 to 15, it will be evident that any molten metal which escapes through the lining of the launder must pass around the flanges to get to the electric heater elements, and in passing around the -anges it is subjected to the cooling effect `of the flanges on the hea-ter tufbes as well :as the mechanical protection which such flanges give. Thus the molten metal will solidify without causing damage.

While the invention will find application in numerous other places, it is believed to be most suitable for use with molten aluminum base alloy, magnesium base alloy, copper base alloy and zinc base alloy.

In view of our invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benets of our invention without copying the structure shown, and we, therefore, claim all such insofar as they fall Within the reasonable spirit and scope of our claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A furnace including a refractory lining for molten metal or the like and a pouring spout attached to the furnace in communication with the interior of the refractory lining, said pouring spout comprising a tubular discharge element, insulating material surrounding said element, a heater tube of silicon-nitride bonded silicon carbide interposed between said tubular discharge element and said insulating material, said heater tube having a cylindrical portion and at the end thereof :adjoining ythe furnace an outwardly extending flange portion, electric heater means surrounding said cylindrical portion of said heater tube, said ange having sufficient length t0 substantially cover that portion of said insulating malterial between sai-d cylindrical portion of Asaid heater .tube and said refractory lining, whereby said flange prevents short-circuiting of said electric heater means by directing molten metal contacting the surface of said flange away from said electric heater means.

2. A furnace having a refractory lining to' receive molten metal or the like, a metallic casing at the outside of the furnace, a pouring spout extending out from the furnace and communicating with the interior of the refractory lining, said pouring spout comprising a casing connected to said furnace casing, a tubular discharge element adapted to convey molten metal from the interior of said refractory lining to the exterior of said pouring spout, a heater tube of silicon-nitride bonded silicon carbide positioned `around sai' tubular discharge element, said heater tube comprising `a cylindrical portion and an outwardly extending flange portion at the end of said heater tube adjoining the furnace, electric heater means surrounding said cylindrical portion of said heater tube, heat insulation means interposed between said pouring spout casing and said heater tube and extending substantially to said refractory lining, said flange having suflicient length to substantially cover that portion of said insulating material between said cylindrical portion of said heater tube and said refractory lining, whereby said flange prevents short-circuiting of said electric heater means by directing molten metal contacting Ithe surface of said flange away from said electric heater means.

3. A furnace for molten metal or 'the like including a refractory lining and a pouring spout -attached to the furnace, said pouring spout comprising a tubular discharge element in communication With the interior of said refractory lining, a heater tube positioned around said discharge element and being provided around a cylindrical portion thereof with electric heating means, said heater tube having a flange portion at the end thereof adjoining the furnace, insulation means positioned around said heater tube and extending closely adjacent to said refractory lining of said furnace, said ilange flaring outwardly of said heater tube towards said furnace and being `disposed between said insulation and the refractory lining of the furnace to form a barrier or shield against the ingress `of molten metal from the furnace whereby to prevent short-circuiting of said electric heater means.

References Cited in the file of this patent UNITED STATES PATENTS 2,674,640 Tama Apr. 6, 1954 2,741,006 Kux Apr. 10, 1956 2,821,378 Tama Jan. 28, 1958

Claims (1)

1. A FURANCE INCLUDING A REFRACTORY LINING FOR MOLTEN METAL OR THE LIKE AND A POURING SPOUT ATTACHED TO THE FURNACE IN COMMUNICATION WITH THE INTERIOR OF THE REFRACTORY LINING, SAID POURING SPOUT COMPRISING A TUBULAR DISCHARGE ELEMENT, INSULATING MATERIAL SURROUNDING SAID ELEMENT, A HEATER TUBE OF SILICON-NITRIDE BONDED SILICON CARBIDE INTERPOSED BETWEEN SAID TUBULAR DISCHARGE ELEMENT AND SAID INSULTING MATERIAL, SAID HEATER TUBE HAVING A CYLINDRICAL PORTION AND AT THE END THEREOF ADJOINING THE FURNACE AN OUTWARDLY EXTENDING FLANGE PORTION ELEDTTRIC HEATER MEANS SURROUNDING SAID CYLINDRICAL PORTION OF SAID HEATER TUBE, SAID FLANGE HAVING SUFFICIENT LENGTH TO SUBSTANTIALLY COVER THAT PORTION OF SAID INSULTING MATERIAL BETWEEN SAID CYLINDRICAL PORTION OF SAID HEATER TUBE AND SAID REFRACTORY LINING, WHEREBY SAID FLANGE PREVENTS SHORT-CIRCUITING OF SAID ELECTRIC HEATER MEANS BY DIRECTING MOLTEN METAL CONTACTING THE SURFACE OF SAID FLANGE AWAY FROM SAID ELECTRIC HEATER MEANS.

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