US1478375A

US1478375A - Electric furnace

Info

Publication number: US1478375A
Application number: US245485A
Authority: US
Inventors: Morris H Bennett
Original assignee: Scovill Inc
Current assignee: Scovill Inc
Priority date: 1918-07-18
Filing date: 1918-07-18
Publication date: 1923-12-25
Anticipated expiration: 1940-12-25

Description

n U W y C I/L U// .wf w m /1 Ox 7. E A N m om y QW Z B m w. SHQ H my. J M. m .w vw y Nw Dec. 25, 1923.

Patented Dec.,` 25, '1923e UNITED srarss PATENT oFFlcE.

MORRIS H. BENNETT, F WATEBBUEY, CONNECTICUT, ASSIGNOR T0 SCOVILL MANU- vFACJEU'R'ING COMPANY, A. CORPORATICN OF CONNECTICUT.

ELECTRIC FURNACE.

`Application led July 18,

To all wlwm t may concern:

Be it known that I, Mouais H. BnNNm'r, a citizen of the United States, residin at Waterbury, county of New Haven, and tate of Connecticut, have invented certain new and useful improvements in Electric Furnaces, fully described and represented in the following specification and the accompanyin drawings, forming apart of the Same. lus invention relates to improvements in electric furnaces.

In electric furnaces as ordinaril constructed and in which the current 1s conducted directly from electrode to charge, genera-ll speaking, the efficiency of the furnace is etermined by the amount of energy which can be delivered to the charge in a given time.

In furnaces for melting metals havin a 2O high electrical conductivity and low resistance, and particularly such metals as tend to give olf fumes in melting, this limitation is serious because, if it be attempted to force a large quantity of energy into the furnace in a short time, exceive temperatures are produced beneath and immediately aroundv the electrodes, the result of which 1s a tendency to burn the metal, or cause excessive fumes, or both. Further, the high temperatures immediately beneath or around the electrodesy audvilhe heat which is radi- .ated from the electrodes or from the zone between'electrode and charge, raise the temperature in the furnace chamber to such an extent that such fumes as are given oi produce excessive pressures in the furnace chamber, particularly if it vbe of the closed or Bennett type1 Y In such furnaces, furthermore the effec- 4o tivev current heretofore employed has been of low frequency,.that is, approximately between fteen Aand sixty cycles. This 'low frequency current, particularly where the charge is composed of metals havin a high electrical conductivity is, as is wel -known, so distributed through the 'charge that its resulting heating effect in the charge is comparatively low. As has been indicated, any attempt to increase the heating effect by 6o substantially increasing the rate at which energy is introduced into the vfurnace by this effective low frequency current will result: in excessive temperatures in the furnace, which is objectionable, particularly 191s. serial 1ro. 245,485.

Where the metals being melted tend to fume and will result in excessive overheating o the metal immediately around and beneath the electrodes.

It is the object of this invention to employ 1n furnaces such as have been referred to, a current of such characteristics that the heatin effect due to the passage of the current t yrough the charge will be increased.

More specifically considered, it is the object of this invention to employ in furnaces such as have been described an effective heating current of high frequency, the heatlng effect being increased because the resistance of the charge to such current is high. 4

ith these and other objects not specifically referred to in view, the invention consists in the combination with a furnace which employs means for conducting the electric heatlng current directly to the charge in the furnace, of means for supplying thereto an effective current of high frequency.

More specifically, the invention consists in employing in au electric furnace in which the current is conducted from electrode to charge, a low frequency generator, means being employed in connection therewith to increase the effective frequency of current delivered to the charge.

The invention also consists in certain elements and combinations as will be more fully described hereinafter and particularly pointed out.

Figure 1 is a da ammatic view of a furnace and connecte a paratus for car ing the invention into e ect, the furnace being shown in section.

Figure 2 is a horizontal section of the furnace shown in Figure 1.

Figure 3 is a diagrammatic illustration by means of curves, of the results obtained from' the construction shown in F i 1.

'lhc drawing forming a part of tL is specification illustrates diagrammatically a furnace and roper apparatus in connection therewith or carrying the invention into effect. The furnace which has been selected for illustration is a furnace of the closed or Bennett type, illustrated and described in connection with the application of M. H. Bennett, Serial No. 241,914, filed June 17, 1918, in which devices are shown for Bo i prevent the undue production of fumes in trodes. The

controlling the rate et heat delivery as to ing shown as connected on the circuits. De-

lll

vices for properly positioning the electrodes to adjust thev vresistance are shcwn,fthese consisting of drums 8, Worms 9 and worm- Wheels 10. rl`he connections from the worm drums to the electrodes are indicated at l1.

As has been indicated, furnaces which elnbody theinvention will utilize effective currents of high frequency, that,is, very considerably in excess of the low frequency currents ordinarily utilized in electric furnaces in which current is delivered directly from electrode to charge.

As is Well-known, the use of high frequency generators for ordinary conu'nercialv work,

such as furnace Work, presents many diff culties. rlhe expense of installation of such generators is large, and the electrical losses are high, particularly if the current reqires to be transmitted overany considera.

le length of line. Preferably, therefore, in carrying the invention into eiect, the eective high frequency utilized in thefurnace will be obtained by increasing the eftective frequency of current derived from a low frequency generator. ln the commercialv practice of the invention, van edective high frequency of about 1200 cycles has been obtained by increasing the edective requency of current derived from a low frequenc nerator, the generator being de signe to deliver a 'current of about sixty cycles. y The delivery of the edective high frequency current derived from a low frequency generator, When the high frequency is obtained in this manner, may be eciently attained by employing a condenser or condensers. Condensers of various constructions y be employed. A condenser which has been found efficient is of the electrolytic type and consists of a series of closely spaced aluminum plates in an electrolyte consisting of a saturated solution of bicarbonate of soda. rl`hree such condensers are indicated at 12, 13 and 1d, respectively.

e condensers employed for carrying the invention into edect may be variously connec on the circuit. As shown, the

connection is of the if type, one set of thev plates in each cell being connected by a common strap 15 and the other plates in the cells being connected by

Wires

16, 17 and 18 to the circuit wires 7, 6, 5 respectively. lt `will be understood that in the construction shown, these circuits 5, 6, 7 .lead to a suitable low frequency generator of the polyphase uw it necessary a suitable trans- 4 indicated.

Leraars former being interposed in the circuit. As these devices are Well-known, they are not Actual commercial test of the apparatus which .has beendescribed, using a loir, frequency generator delivering a current of about sixty cycles and employing three condensers having a capacity of about 3200 microfarads each, has shown that a much higher tem erature canl be obtained and maintained 1n the metal, and, consequently, better heating, Without undueproduction of fumes, than with the same apparatus withl out the condensers. This, of course, is highlyadvantageous Where metals are being melted, the pouring temperature of which is necessarily considerably above the vaporizing point. The heating effect inthe charge is increased Without increasing the temperature inthe urnaceabove the charge, so that such fumes as are given olf are more readily condensed by the walls of the furnace chamber, the valuable metallic constituents which are carried by fumes being thus returned to the charge.

The results obtained by thus connecting a condenser into the circuit are indicated in Fig. 3; ln thi'sfigure, the upper curve, marked represents the current in the transformer circuit and is a characteristic curve ofthe current obtained from an alternating generator. The lower curve markedy B re resents the current in the condenser c, u c i n l circuit and 1s a characteristic hlgh frequency current curve.

tion of current rB on current A. The irregularities in curve C indicatethe higher frequency obtained rom'this superposition.

The intermediate curve, marked C, represents' the current .in the electric circuit due to the superposif While the invention may begised with furnaces of other types, it is particularly valuable in connection with a furnace ofV the closed or Bennett type referred to.

It will be understood that changes and variations ma be made in the particular construction s own and described. The invention is not, therefore, togbeconlined to frequency, the. resulting current producing y improved heating eects in the furnace due to the resistance of the charge to said current. `v

' 2. The combination with a furnacey for melting metals, said furnace havin electrodes arranged to deliver current, irectly to the charge in the furnace, of a low frequency generatorin circuit with the electrodes, and means ao in circuit with the electrodes for impressingl on the main current a heating current of high frequency, the resulting current being delivered to the charge inthe furnace by the electrodes` and producing improved heating'eifects therein due to the high resistance of the charge to.

said current.

3. The combination with a furnace for melting metals, said furnace having electrodes arranged to deliver current directly to the charge in the furnace, of a low frequency generator in circuit with the electrodes, a condenser also in circuit with the electrodes and operating to impress on the main heating current a heating current of high frequency, the resulting current being for melting metals, of means for delivering current of high frequency', the resulting curi rent producing improved heating effects in -the furnace due to the resistance of the charge to ,said current.

8. The combination With a closed furnace for melting metals, said furnace having electrodes arranged to deliver current directly to the charge in the furnace, of a lowY frequency( generator in circuit with the electrodes, and means also in circuit with the electrodes for impressing on the main current a heating current of high frequency, the resulting current being delivered to the charge in the furnace by the electrodes and producing improved heating effects therein due to the high resistance of the charge to said current.

9. The combination with a closed furnace for melting metals, said furnace having electrodes arranged to deliver current directly to the charge in the furnace, of a low frequency generator in circuit with the electrodes, a condenser also in circuit with the electrodes and operating to impress on the main heating current a heating current of hi h frequency, the resulting current being delivered to the charge in the furnace bythe electrodes and producing improved heating effects therein due to the high resistance of the charge to said current.

In testimony whereof, I have hereunto set my hand.

MORRIS H. BENNETT.