US1864885A - Electric furnace - Google Patents

Description

Jun 28, 1932. A. E. BELLIS ELECTRIC FURNACE -Filed Aug. 27. i930 24 sheets-sheet 1 Lema/e E, @aL/5 Patented June 28, 1932 .PATENT oFFlcs l. BELLIS, OF BRANFOBD, GONNECTIOUT ELECTRIC FURN'ACE Application iled August 27, 1930. Serial No. 478,049.

This invention relates to an improved electric furnace for heat treating metals, and has for its general object and purpose to provide certamimprovements in a furnace of 6 this type as disclosed in m pending application for patent Serial o. 326,002, filed December 14,1928.

Inmy pending a plication there is disclosed a furnace em ying a metal pot or 10 crucible to contain salt materials together with an electrode extending into said -pot and the electrode andthe pot wall bein connected vwith a source of alternating e ectric current whereb the solid salt materials may 15 be fused and the pot wall maintained at a comparatively low temperature. In the u se of such furnace, in order` to initiate melting fth@ ml'i m v.-::: t0 either apply a torch Lame thereto or other- 2 wise initi y heat the material independently of the electrode.

It is the primary present invention to provide means w ereb the heating ofthe salt may z be faci 'tated, and the of using a torch, electrimor other auxiliary heatmeans ob one practical t of the invention, I provide two spaced electrodes adjustj on cru-iand connected with the primary and Nabl mountedtoextmdintothe darywm cib m dmgg rpoctivel of asuitable transformer for alternating'ydlectric current. These are at their m mash thigh i 'm This wire being Mtd i0' l high temperatur, quickly mele a nu in the vicinitythereof,the `ofheatfrom the electrodes throughout the remander of the salt material beingth greatly facilitated,andexpediting fusionofthe salttothedesiredliquidcondion. Alsoby meansofthishighredancewirqdung periodswhenthefurnaceisnotbeingused, 'the current supply may be reduced andthe saltmaterial ataverylow temperature, -fwithasmallv umeofthesaltsurrounding theresistancewimmaintainedinali uid Wconditinn. Thuaitwillheapparent t object and purpose of one simple and practical embodiment of the present invention, and in which similar reference characters designate corresponding parts throughout the several views,-

Figure 1 is a vertical sectional view throught-he furnace, illustrating one practica l embodiment of the present invention.

Fig. 2 is a top plan view thereof. Fig. 3 is a fragmentary vertical sectional Aview showing a slightly modified form of the device; and

f Fig. 4 is a vertical section illustrating another embodiment of the invention.

Referring in detail to the drawings, 5 designites the ppt or cruoible of the furnace, which ma produced from steel, chrome iron, or o er metal alloy, either wrought or cast. Thebath to`be used as a heat transfer medium preferably consists of a number of metallic salt components so selected and mixed as to produce a bath, which when fluid, is of low' viscosity and may be heated to a desirably high temperature without fuming. For the heat treatment of hi h sfpeed tools, this bath should be capab e o attaining a temperature of 2500 without vaporiz'ation. There are well known salt materlals of this character now on the market. However, since v the subject matter of the present application is not concerned with any specific salt bath composition, it will not be herein further referred to 1n detail. W

As shown in-the drawin thev t'is preferably rst encased in the re bric indicated at 6, and thisgre brick setti is inturn enlcaused within a relatively thic` walled insutins however,'that theiform of the bath receiving pot or crucible and the means steel` structure' 7. 7 It will be understood,

direct therefor, as shown in the drawings is purely suggestive and not specifically essential to my present purpose. 4

In conjunction with the metal pot 5, I employ the two spaced electrodes 8, each .of which is vertically adjustable .upon a suitable supporting arm 9 of electrical conduct ing material mounted in an insulatil base 10 which may be suitably fixed upon e lire brick setting 6. These electrodes 8 extend downwardly into the pot .5 in parallel relation to each other and into the salt bath materials which have been placed therein.

Electric current is supplied to the electrodes 8 at proper voltage, the value thereof depending upon the size and type of the pot 5. This necessitates the use of a transformer 11 as a art of the installation, alternating current ing supplied tothe rimary of the transformer as at 12, and in willich a suitable automatic control means may be located.

The transformer to be used in connection with the type is rated at 220 to 11 volts, 20 kva. when using kilowatts. The current in ut at full power is 1820 amperes. The secon ary of the transformer is connected by the conductors 13 and 14 to the supporting arms 9 of the re- P spectivc electrodes` 8.

The lower ends of the s aced electrodes 8 are connected by the hig resistance wire shown at 15, end portions of this wire bein coiled around the respective electrodes an suitably lixc'l thereto.

In thel use of the furnace, the solid salt materials are placed in the pot or crucible in suicient quantity to extend well above the high resistance wire 15. Upon closing the current supplycircuit, the current passes through the spaced electrodes 8 and theresistance wire 15 so that this wire becomes more or less incandescent, and immediately melts the solid salt material surroundin the same to a liquid condition. In view o the Afact that this liquid salt is of very low viscosity, there would be arasid transference of heat so that the remain er of the solid salt will be very quickly fused by the heat radiated from resistance wire.

It will be apparent that the heat eiciency of an electric furnace of the above description will be very hi over of the current ower in ut g develped as heat in ther ath material. y the use of a suita le cover for the pot or crucible and the thick -insulatin walls therefor, the heat losses ma be kept own to a ve low value. In the i ustrated furnace, 10 owatts is suilicient to maintain the tem rature of the bath with a normal amount o removal ofthe pot cover, thus leaving 10 kilowatts avail able to heat the work. By heating the bath material in this manner, the necessity of maintaining the walls of the t or crucible 55 and its external surroundings at a higher of pot 5 shown in the drawings temperature than the bath material is eliminated. In the use of oil or other fuels for generating heat externally applied to the wall of the crucible, the pot wall must necessarily attain a higher temperature than the bath, in order to raise the temperature of the bath to the desired point. Thus, the structure of the got or crucible rapidly deteriorates or is urned out sc that pots must be frequently re- Elaced. In my new furnace, on the other and, the heat is initiallngenerated directly in the bath materials. is a descending temperature adient from the dissolved salt bath materials outwardly through thewalLof the pot. Accordingly, since this pot may be mounted in a heat insulating su port, t e thickne of which need be limi only by the available floor space, great economy in power consumption may be realized with amile external protection to the pot to the oxi izinletfects of the atmosphere. By reason of e relatively low pot temperature for any given bath temperature, the useful life of the pot is prolonged almost indelinitel The heating of the salt bath materials ymeans of an electric furnace of this descri tion, thus achieves ultimate simlicity wit maximum economy both in the mitia installation and in operation and maintenance costs.

By vertically adjusting the electrodes 8 to regulate their depth of penetration into the sa t materials, the heat lnput may be regu lated as required to maintain a desired bath temperature. Notwithstanding lthe factrthat the solid salt material is an insulator, by the provision of the hi h resistancewire 15 connecting the electrodges, the reduction ofthe salt to a liquid condition is quickly accomplished without necessitating the use of other additional heatin mediums, such as a torch, electric arc or t e like. During periods when the furnace is not being used, the electric current sugply may be greatly reduced to hold the hat at a very low temperature, while a small volume of the bath material in the immediate `vicinity of the resistance wire 15 is d therefore, there maintained in a liquid condition. Thus, the

re-fusing of the salt when the furnace is to be again used will be greatly expedited. The current consumption over the period of shutdown of the furnace and the expenses incident thereto will be comparatively trivial.

The electrodes 8 may be of the same material as the wall of the pot or crucible 5, or of any other suitable materials which will not release impurities into the bath solution. 1

The salt bath material is of such composition that it will be neutral to the metal to be treated sothat chemical reactions between the bath material and metal articles at high temperatures which would either carburize or decarburize the metal surfaces will not occur. I am aware of the fact that such salt baths have been commercially used'in thisl art and' tions between the bath material and the refractory material in the t resulting 1n yheavy contamination of the bth and the carburization or itting of the steel-objects .being treated. ince such refractory pots have a very short life, frequent replacements thereof, greatly addin to the operating and maintenance costs o the furnace are required. The use of electrical resistance coils exteriorly ofthe pot are not commercially feasible for the heating of the path to the higher temperatures. In order to maintain the bath temperature, the wall of the potor crucible must'be kept `at an excevelytltxh temperature since the heat is transmi from the coil through the pot wall to the bath materials. The rapid deterioration and breaking down of the. ot or container and contamination of the ath solution would inevitabl result. This fact alone makes the use of suc resistance coils entirely yim ractical without regard to the expense inci ent to the initial installation of such heating equipment and the frequent replacement of the coils owing to the excessively high resistance required.

As .shown in Fig. 3 of the drawings, in lieu of the resistance wire surrounding the lower endv of the electrodes I may provide the resistance 15 in the form of a flat metal strip having its intermediate rtion formed into a p1urality of rectangu arconvolutions 15'A dis osed in the same vertical plane, the upper an lower ends of the strip bemg laterally extended in opposite directions, and suitably connected to t e respective electrodes 8. This form of the resistance strip, insures 'a' high degree of rigidity, even when the strip is heated to incandescence. Usually, however, it is only necessary to heat the resistance to a' glowing red heat in order to fuse the salt materials.

In Fig. 4 of the drawings, I have illustrated another modified form of furnace, in which only a single electrode 8 is used. In this case, the upper end of the metal pot is formed with a flange extension 5 to which the conductor 13 from the transformer is connected. The other conductor 14 is connected to the electrode Isupporting arm 9', said arm belng adJustably mounted in the spaced guides 16, suitably secured to one side` of the rnace casing and insulated therefrom.

The resistance coil 15b is attached to the lower end of the electrode 8 and extends below the same and into a body of lead indiiencc, safety, and ilexibillt mananw-hiena.pumamimboaemofV the furnace pot. Thus, in this case, it will be understood that the circuit is closed through this body of lead, the wall of the pot and its flange 'extension 5 to which conductor 13 is connected. The le electrode 8 in this case may be adjacent to one side of the pot so that ter pot capacity is attainedl for receivingI the metal objects to be tread.

My new-furnace for heating such high tem- Iperature salt baths as herein described, en-

tirely overcomes the serious objections to prior art furnace constructions of the type above referred to, and provides an velectric furnace of very simple construction, which in both its initial installation and maintenance and operatinncosts -will be comparatively inexpensive,w 'le accurately reproducible results in the heat treatment of metal articles of similar form and size and without surface blemish ma be obtained.

From the foregoing description, it will be seen that I have rovided a highly eicient and serviceable' ectric furnace for use in heat treatin metals which in addition to the numerous 'a vantages above referred to. also possess the other collateral merits of the use of electrical heat, viz., compactness, convenetc. I have herein illustrated and descri a practical embodiment of my present improvements which has ven excellent results 1n commercial use. evertheless, it will be understood thatl the essential features of the present disclosure might also be embodied in various other structural forms, and I accordingly reserve` the privilege of resorting to all such legitimate changes in the form, construction and arrangement of the several elements as may be fairly embodied within the spirit and 2. In combination with a furnace crucible adapted to receive metal heat treating salts, electrical means for fus` the salt materials includin spaced electr es, means for vertically a justing said electrodes to position the same with respect to the bottom of the crucible, and a high resistance wire having parts coiled about the lower end of each electrode and bridging thei space therebetween.

3. Inl combination with a furnace crucible of electrically conductive metal, electrical heating means including an electrode extendin vertically into the rcrucible adjacent one si e thereof, a resistance connected to the lower end of the electrode, means for connecting the electll'ode to one side of an electri current au y circuit, means or'connectmg' the wall ofptiie crucibIe to the other side of the supply circuit, and a body of electricall conductive metal in the bottom of the t 'ble at relatively low temperature and mto which the lower end of said resistance extends.y

4. In combination with a furnace crucible adapted to receive salt materials of high melting point, electric means for the salt materials includin a pair of e ectrodes aced apartfor aiistance a reciably less t an the diameter of the cruci e, means su po said spaced electrodes within t e crucib e and at one side of the central region thereof, s rigidly securing said elect es movement with respect to the crucible, and a high resistance conductor of small cross section with respect to the electrodes connected with the latter and sustained in closely juxtaposed relatlon thereto out of contact with the Crucible walls.

In testimony that I claim the foregoing as my invention, I have si ed mxy name hereto.

AR BELLIS.

means for vertically ad'usting andA

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