US2681971A - Electric furnace and control therefor - Google Patents

Description

June 22, 1954 H. A. STRICKLAND, JR., ET AL 2,681,971

ELECTRIC FURNACE AND CONTROL THEREFCR 7 Sheets-Sheet l Original Filed Jan. 16, 1948 June 22, 1954 H. A. STRICKLAND, JR., ET AL 2,681,971

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ELECTRIC FURNACE AND CONTROL THEREFOR Original Filed Jan. 16, 1948 7 Sheets-Sheet 4 "mum r l I wcm-wm.

lll/1 INVENTORS HHROLD Q. BY 0%0 W R/DOELL ATTONEY j Ill IIIIIVIIIIAIIIIIIIIIII'II'I'IIIII'III'II' lll June 22, 1954 H. A. sTRlcKLAND, JR., ET AL 2,581,971

ELECTRIC F'URNACE AND CONTROL THEREFOR Original Filed Jan. 16, 1948 7 Sheets-Sheet 5 INVENT HQROLD H. sTR/C/(MA/O, JR.. if BY DOA/BLD IM Q/D DELL June 22, 1954 H. A. STRICKLAND, JR., ET AL 2,681,971

ELECTRIC FURNACE AND CONTROL THEREFOR 7 sheets-'sheet e Original Filed Jan. 16, 1948 June 22, 1954 H. A. s'rRlcKLAND, JR., ET AL 2,681,971

ELECTRIC FURNACE AND CONTROL THEREF' OR Original Filed Jan. 16, 1948 '7 Sheets-Sheei'I 7 COIL N97.

COIL N0. 3

M1/TM ATTORNEY Patented June 22, 1954 ELECTRIC FURNACE AND CONTROL THEREFOR Harold A. Strickland, Jr., and Donald W. Riddell,

Detroit, Mich., assignors, by mesne assignments, to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Original application January 16, 1948, Serial No. 2,615, now Patent No. 2,572,073, dated October 23, 1951. Divided and this application December 14, 1950, Serial No. 202,616

2 Claims. l

This invention relates to heating furnaces, particularly to through feed, or continuous heating furnaces of the high-frequency, induction-heating type disclosed in the patent to Strickland 2,325,638 of August 3, 1943, and has for an object a provision of improvements in this art. This application is a division of our copending application Serial No. 2,615, filed January 16, 1948, now Patent No. 2,572,073, dated October 23, 1951.

One of the particular objects of the invention is to maintain the now of cooling fluid to the heating coils for a predetermined time after the current has been cut off in order to avoid overheating by hot billets which still remain in the furnace.

Herein, there will be described certain stockfeeding details, coil hoods, soaking-chamber hood, heat shields for the coils, certain time-sequence controls of general application, and various other detailswhich form the subject matter of applications of one or the other of the present coinventors; namely, application Serial No. 790,154, filed December 6, 1947, now Patent No. 2,604,577, dated July 22, 1952, on an invention entitled Heating and Work-Handling Apparatus by the present inventors; application Serial No. 2,613, led January 16, 1948, now Patent No. 2,563,883, dated August 19, 1951, on an invention entitled Workpiece Support and Guide for Induction- Heating Furnaces, the inventor there being Harold A. Strickland, Jr., as the sole inventor; and Serial No, 2,614, led January 16, 1948, now Patent No. 2,578,760, dated December 18, 1951, on an invention entitled Electric Furnace and Stock-Feeding Means Therefor, the inventor there being Harold A. Strickland, Jr., as the sole inventor.

The above and other objects and advantages of the invention will be apparent from the following description of an exemplary embodiment of the invention, reference being made to the accompanying drawings thereof, wherein:

Figure 1 is a right-side elevation, with some of the cover panels or doors removed and part of the coil hood cut away, of a three-coil furnace and related feeding apparatus embodying the present invention;

Figure 2 is a left-side elevation of the same apparatus with the doors in place and with the hood in raised position;

Figure 3 is a top plan view with the hoods closed and with the soaking-chamber hood swung out to one side;

Figure 4 is an enlarged partial vertical section of the rear or discharge end ofthe furnacathe section being taken on the line 4--4 of Figure 3 but with the soaking-chamber hood returned to its normal operating position;

Figure 5 is a transverse vertical section and elevation taken on the line I5 5 of Figure 1;

Figure 6 is a partial vertical transverse section taken on the line 6-6 of Figure 2;

Figure 7 is a left-side elevation and section taken on the line 'I--l of Figure 6;

Figure 8 is an inclined longitudinal section and elevation taken about on the line 8 8 of Figure 5;

Figure 9 is a transversev vertical section taken on the line 9-9 of Figure 8;

Figure 10 is a perspective view of the cooled stock guide rails and related parts;

Figure l1 is a schematic view and wiring diagram; and

Figure 12 is a cycle diagram.

The furnace herein shown comprises a supporting frame or multiple-unit cabinet I0 with three units Illa, IIIb and IUC associated with a skeleton framework I I which is welded or riveted up from angle, channel or other standard pieces of metal as needed for the number of heating units to be used. Mounted above and in association respectively with each of the cabinets are a like number of electric induction-heating coils I2, here distinguished as I2a, I2b and I2. From front to rear end, or right to left in Figure 2, these heating coils are also referred to as No. 1, No. 2 and No. 3. Preferably, high-frequency heating current is used for heating.

In the upper part of each cabinet, there are placed a number of capacitors I3 and, in the lower part of each cabinet, there are placed suitable contactors I4. There are two contactors for each coil and one of these is shown in side elevation in Figure 5.

Suitable bus bars and connections, all indicated generally by the numeral I5, are shown for serving the contactors, capacitors and coils. Common cooling fluid conduits I6 are provided for the several coils.

A beam I'I, here of I-section, extends above the entire furnace; that is, above all of the coils in whatever number provided, the beam being supported at its ends by end supports I'8. At each side of the beam I1, there is hinged one or more coil-hood members |9 which may be closed, as shown in Figure 1, or opened, as shown in Figure 2.

Aside from the main frame I I, the bus bars I5, the beam I1 and the hoods I9, the apparatus has no parts which extend between units except connear the melting point to endanger the heating coils. This device is indicated only in the wiring diagram where it is designated as PR.

In the coil hoods I9, there are provided vent openings 89 above the open space between coils to release heat, gases or smoke from the billets resting in the space between coils. It will be noted from Figures 4, 8, 9 and l0, that the guide rails 29 are tubular and are cooled by fluid from disconnectible feed and return lines at one end. The cooling tubes are returned outwardly as at 90 at one end and have an outer run 9| which is located within the confines of the coil-insulating lining 92 to keep it and the heating coil cool. The double-rail construction with interconnecting supports 93 also provides strength for holding the insulation in place. The cooling rails are mounted on the coil-end plates 2| by bolts 94, 95 and adjustable connectors gli. It will be noted that the line-connected ends of the rails are returned through a coil support plate 2l and have their line connections above the outside of the coil and between its supporting plates, Where there will be protection from heat. The inner run of the cooling rail is coated with a wear-resisting liner fused thereon. There are a number of suitable materials, one such being a composition of tungsten l2-17%, chromium, IBO-35%, carbon 2.25-2.75%, cobalt, substantially the balance, this being known commercially as Stellite The outer run 9| is provided with wings Sl' which are fused thereon to hold the heat-insulating lining of the coil.

For such coils or portions of coils as are subject to unusual heat from billets after they have been heated to high temperature, there is provided a special heat-dissipating means; for example, of the type shown in Figures 8, 9 and 10. Here, an extensive area of a highly heat-conductive material, such as copper, is soldered to the outer run 9| of the rails so as to lie outside the heat insulation and inside the coil lining. The fins or plates 98 thus provided are slitted as at 99 to avoid buckling or other objectionable features of continuous sheets for such a use. It is found that if the heat shields are coextensive with the last approximately one iifth of the total heating coil length, they will provide adequate coil protection and prolong coil life to a remarkable degree.

Between the ends of adjacent coils, inclined plates |02 may be provided for directing scale and dirt toward the outside of the cabinet assembly, the plates being supported upon brackets |03 on the coil-end plates 2l.

The operation of the apparatus will be described in connection with the circuit diagram, Figure l1.

Theram Si normally stops in its forward position; that is, toward the rear end of the machine as a whole. It is shown slightly back of forward position to illustrate its switches RS-l and RS-Z in their nonoperated position. In the normal full forward stopped position of the ram, its switch RS-I is closed and its switch RSJz is open. RS-I opens and RS-2 closes as soon as the ram starts to move back.

A ram pause timer TI causes the ram to rest at the front end of its stroke. It is settable for a wide range of time merely by moving a fixed contact hand which is engaged after the predetermined time lapse by a movable hand driven by a synchronous motor. This represents one form of timer which may be used. The endof the preset timer period is registered by closure of its switch Tl-I. Its motor is represented by the reference character TI-M. By providing the pause timer TI, a number of control advantages are obtained, including the ability to adjust for different feed rates for billets of different size, different coils, different heats desired, and matching of delivery periods to suit the needs of the forging machines which use the billets heated by this machine.

The ram cylinder is provided with a. valve RV operated by solenoid S02. The arrangement is such that when the solenoid SO2 is not energized, the ram stays in its forward position and when the solenoid is energized, the ram returns to its rear position.

The ram ocam bar 63, which carries the cam 64 for operating the valves CV and GV for the clamp 5| and gate 53 respectively, is shown also in Figure ll. As the ram approaches the rear end of its travel, the associated valve CV causes the clamp 5I to hold the billet which is in nextto-last position. Later, near the rear end of the ram travel, the associated valve GV causes the gate to be lowered to drop the billet from last position to the V-trough 513. When the ram moves forward again, it first y'replaces the gate in the chute and later releases the clamp to allow the stack of billets in the chute to slide down against the gate.

When the billet in last position drops, it opens switches W-I and W-Z, and when another billet drops to the last position, it closes these switches. If no billet drops down, the machine is stopped after a certain lapse of time. Whenever TRS or TR2 becomes deenergized, the auxiliary switches open immediately.

To prepare for the start of operations, the main line switch S-I of Ll, L2 is closed. For heating, as well as ram operation, a switch'S-L which may be referred to as a safe-run switch, is closed. For operation of the ram only, S-E is left open. lThe cooiing water for the coils is turned on. This closes water shut-olf valve switch VS, pressure switch PS and flow switches FS to the coils (three here). The temperature at the coils is assumed to be not excessive so temperature switches TS are closed. The panels or doors of the cabinet are closed so their safety switches DS are closed. The hoods are closed so hood-safety switches HS are closed. The ram is to be actuated and not held to a rear position so the ram-return switch S-3 is opened.

The clutch coil Tf-C of water shut-olf delay timer T2 is keptenergiaed as long as S-l is kept closed. It holds out the timer clutch but when S-l is opened, the clutch is engaged and after a time-delay period, the timer switch is actuated to actuatersolenoid SOI to shut off water to bypass Hill supplying the heating coils. The synchronous motor for T2 is designated as TLM.

A time-delay relay TRA is energized and after a delay to allow bubbles to be removed from the cooling fluid lines, its switch TRE-I is closed. The circuit involved is: Ll, conductor mi, TRI-C, conductor S65, PS, VS, conductor lidia, to L2,

The time-delay relays are represented by separate coils for instantaneous and delay-switch operation, and the delay switch is represented as carrying hinged vanes which can fold together and move rapidly in a fluid in one direction of movement but which spread and cause slow movement in the other direction. This is merely symbolic. Delay-action timers which are settable for timed periods of any predetermined length Vare available ori-the market.

9.. lamp |13 in parallel), conductor |14, C2 2, C2-I, conductor |15, to LB2.

Closure of TRS-l energizes #3 contactor relay R6 which, through its switches RS-I, RG-E, RS-ll, actuates the #3 contactors and these, when closed, close #t3-contacter interlocks C3| and C3-2. The circuit involved to energize R8 is LBI, conductor |11, RS-C, conductor |18, S-S

. (closed to |18 but shiftable to open), conductor |19 (connected by conductor |89 to |51 of S-E), TRS-l, conductor ISI, |1|, |56, R32, |51, S-Z, |58, to LB2.

Closure of C3| and C3-2 energizes TR which, after a delay period, closes TRS-I. The circuit involved is: LBI, conductor |83, TRB-C (pilot lamp |84 in parallel), conductor |85, C3-2, C3-l, conductor |85, to LB2.

Closure of TRS-I energizes relay R1. The circuit involved is: LBI, conductor |88, R1-C, conductor |89, TRS-l, conductor |98, |1|, |56, R3-2, |51, S-Z, |58, to LB2.

Heat is thus placed successively on all three heating coils.

If the heat goes off and remains off for less vthan a predetermined period and R3-2 is closed, this will find the delay switch TRS-i closed and this will cause R1 to be energized which immediately closes R'l-l, R1-2 to supply current to the #2 and #3 coils. R32 causes current to be supplied to coil #l so all coils will be energized at one time. The circuit involved to supply current to the #2 coil is' as follows: LBI, |55, R-C, |66, S-5, |68, |99, |54, conductor |92, R1|, conductor |93, conductor |94, |1|, |55, R3-2, |51, S-Z, |58, to LB2; and for current to #3 coil is as follows: LBI, |11, RE-C, |18, S45, |19, |88, conductor |95, R1-2, conductor |91, conductor |93, I'H, |56, R3-2, |51, S-2, |58, to LB2.

At the end of the waiting period, the timer Tl energizes ram-pilot relay R2 to cause the ram to return, as before. It also energizes TR3, as before. i f 5 Energization of TR3 closes TRS-3 and leaves TRS-l closed (until later opened) so heat-pilot relay R3 is held in when TR2-l shortly opens. If TR2-l opens first, R3 will be deenergized to open R3| so that the latter closure of 'FR3-3 will be ineffective to keep the heat on. However, operation of PB-Z would restore heat.

Similarly, if TRS-I opens (as it should shortly after the gate closes) before TR2-2 closes when the gate closes, R3 will be deenergized and closure of TR2-2 (TRS still being energized and TRS-2 open) will not energize R3. Again, closure of PB-Z would apply heat.

1:0 on at S-i, overload devices connection therewith.`

A pilot lamp '281 indicates when the switch S-l is closed.

The timing of operations will be clearer from consideration of Figure l2, showing the cycle diagram. The duration vof one complete cycle is represented by the top horizontal line 2H! which extends between the vertical start line 2li and the vertical iinish line 2|2. The second. horizontal line 2li!v represents the ram movements. It starts back at line 2H and completes its backstroke at a vertical line 2|4. It starts again at the vertical line l5 and completes its forward stroke at the vertical line 2|6. The ram waits at the forward end of its stroke, as represented by the distance betweenthe lines 2.!6 and 2|2. The third horizontal line 21 represents the gate operation, which opens approximately at the line 2M to feed down a billet, and closes approxi` mately at the line'2l5.

The horizontal line 2|8 represents the action voftime-delay relay TRS. It is energized at ordinate '2H and deenergized at the line Zi OL being provided in "i but its time-delay switch TRS-I is set for actuation at a point 2|5c which is a short time after the ram is'supposed to start forward.. Hence, if thereisany jam in the ram return or in the billet feed, the heating current will Hence, this allows the operator to put in billets and start the heat again without waiting.

The failure of WI to close again after the last billet is fed down would prevent the ram` from being returned from the outer end of its stroke.

The insertion of billets in the chute closes W-E and. W- and causes the ram to start operating again.

The heat contactor circuits are of known type and it is here only necessary to know that there are two contactors for each coil and that they supply the coils with high-frequency current7 derived from an independent source, by way of conductors 2st, 28| for coil #1, 282, 293 for coil #2, and 284, 285 for coil #3. Suitable control of multi-coil furnaces may be provided by using a transformer for one coil only; for example, coil #l as illustrated.

A solenoid MS05 is provided for starting the hydraulic pump motor when current is turned be shut off. If there is no workpiece or billet in the feed-'down'position to close switches W|, W-2, the ram also will stop when it reaches the front end of its stroke, assuming that the rain did not jam on its backstroke but merely failed to get baci: on. time. Y Y. I

The line 2|'9 represents the action of time-delay relay TR2. It is energized at the ordinate 2|5 where the ramstarts forward and remains energized until the ram returns. Its switch TR2-I, however, istirned for. actuation at the point 2||a which'is slightly after the ram is scheduled to start its return movement. Hence, if there is any jam in the forward movement of the ram or if the proper pause at the front end of the ram stroke has not been observed, the heating current is cut off.

To make the original setting, it is only necessary to place the movable contact element of the relay at a point some distance beyond the point required by the operations to be matched and supervised and then gradually to move the contact back until only a slight margin of safety is left. In this way, the supervisory response may be made as ne or coarse as may be desired.

It is thus seen that the invention provides im proved controls for a work-heating furnace, particularly for an induction-heating furnace. The time-delay elements are in part interposed as delay elements in the action of work-feeding devices and in part are matched with the actions of the feeding devices in a supervisory capacity to provide safety in operation in case the feed devices do not function properly. Also, there are provided means for applying current tc a plurality of coils consecutively at time intervals or applying current to all of the coils simultaneously in case current has not been off long enough to allow workpieces to cool beyond a desired amount. There are also provided .means for selectively cutting any of the coils in or out of action and means for shutting down the furnace in case the emerging workpieces are hotter than desired. Also, means are provided for causing cooling fluid to flow to the coils until they and the load of workpieces have Il cooled'. There are various improvements in details of construction and operation which provide great rapidity and facility inchanging from one type of operation to another.

While one embodiment has been described for purposes of illustration, it is to be understood that there may be various' embodiments within the limits of the prior art and the scope of the subjoined claims.

What is claimed is:

1. In a high-frequency induction-heating furnace oi the type adapted to have a billet disposed therein to be heated to an elevated temperature, said furnace comprising a multiturn helical coil on the interior of which the billet is positioned, said coil being formed oi a hollow tube and having means for owing a cooling medium through the hollow of such coil and away therefrom and for controlling such flow, means for preventing a supply of electrical power to the coilk unless the cooling medium is flowing therethrough, said furnace being of the type subiect to damage Iif a. heated workpiece is left in position without cooling medium flowing through saidcoil, the improvement which comprises timing means associated with a. means for controlling the flow of cooling medium through the coil operative upon the failure of electrical powei to the coil for any reason to insure the now of cooling medium through the coil for a time period sumdent to insure thaty any heated Workpieces in the coil will have cooled below a temperature `imillcient to cause damage to the coil.

2. In a high-frequency induction-heating furnace of the type adapted to have a billet positioned therein and heated to an elevated temperature, said furnace comprising a multiturn helical coil in which `the billets to be heated are positioned, said coil being formed of a hollow tube, means for ilowing a `cooling medium through said coil and away therefrom and controlling such flow, means for continuously feeding new billets to be heated into said coil and ejecting heated billets therefrom, means associated with said feeding means to deenergize said coil in the event of a failure to properly feed and eject billets, said furnace being of a type subject to damage if a heated billet is left in position within the coil without the cooling medium flowing through the coil, the improvement which comprises timing means automatically operable upon the deenergization of said coil for any purpose and after a time period at least suioient for billets to cool to a temperature .below that at which they can cause damage to said coil for insuring that damage to said coil will not occur upon the failure of operation of the furnace for any reason.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,680,407 Brace Aug. 14, 1920 1,878,458 Blanchet Sept. 20, 1932 1,987,458 Adams, Jr. Jan. 8, 1935 2,325,638 Strickland, Jr Aug. 3, 1943 2,348,338 Gillespie May 9, 1944 2,359,658 Sonics Sept. 26, 1944 2,404,987 Rudd. July 30, 1946 2,408,350 Strickland, Jr Sept. 24, 1946 2,541,123 Strickland, Jr Feb. 13, 1951 2,563,883 Strickland, Jr Aug. 14, 1951 2,572,073 Strickland, Jr. et al. 1 Oct. 23., 1951 2,578,760 Strickland, Jr 11111 Dec. 18, 1951 2,504,577 Strickland, Jr. et al. 1 July 22, 1952 FOREIGN PATENTS Number Country Date 523,823 Great Britain July 23, 1940

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