US1979108A - Furnace - Google Patents

Description

C. L. IPSEN Oct. 30, 1934.

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FURNACE Filed lay 28. 1932 6 Sheets-Sheet 4 Piglo.

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Oct. 30, 1934.

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FURNACE Filed May 28, 1932 6 Sheets-Sheet 6 TROLLEY CARRIAGE HEATING RESISTANCE Inventor: Carl L. \psen,

ma K His Attorneg.

Patented Oct. 30, 1934 UNITED STATES PATENT OFFICE FURNACE York Application May 28, 1932, Serial No. 614,173

20 Claims.

Heating apparatus My invention relates to furnaces suitable for the treatment of materials at high temperatures, more particularly to furnaces for heating high carbon or alloy steel bars and the like, and has for an object the provision of a furnace which is arranged to be operated continuously in a manner to insure a uniform product. It is well understood by those skilled in the art that steel bars of high carbon content must be gradually brought up to the desired temperature before quenching in order to prevent undue stresses within the steel bars. Furthermore, where a charge consisting of a, plurality of steel bars is to be raised to a relatively high predetermined temperature, it will be seen that special provision must be made for the support of the bars during heating. When steel bars are heated to a temperature of 1500 to 1600 degrees Fahrenheit, more or less, the metal tends to become plastic and if the bars are supported on a plurality of spaced supports the bars will sag between them. Furthermore, the supports themselves will be deformed due to the high temperature and heavy load imposed upon them by the charge of bars. This load is of considerable magnitude inasmuch as it is contemplated by the present invention to provide an apparatus which will handle a plurality of steel bars of considerable length and diameter; for example, steel bars long and 8" in diameter. Furthermore, while the bars are at standstill on the supports, cold spots exist between the bars and the supports. Due to these cold spots and the consequent unequal heating of the bars and the supports there results unequal expansions of both the work and the supports which expansions cause further deformation of the bars and supports.

For the continuous operation of the furnace, it is important that provision be made to insure that successive charges are each brought to the same temperature just preceding quenching. Otherwise, the properties of the several loads will vary and there will not be a uniformity of product. In the quenching of long steel bars it is necessary to provide some means of insuring a uniform quenching throughout the length of the bars. If this is not done portions of each bar of metal may be harder and more brittle than other portions and as a result under the stress of load there may be a failure of the bars due entirely to the uneven tempering.

In carrying out my invention in one form thereof I provide a furnace particularly suitable for automatic operation so that successive charges of work may be uniformly heated to a predetermined temperature and quenched so as to be uniform in character and properties. More specifically, I provide a charge-supporting roll table which extends throughout the length of a plurality of heating chambers and is arranged to form a run-out table at one end of the furnace. The rollers of the roll table are-operated in synchronism with each other so that the charges may be oscillated during the heating operation. The rollers, therefore, form the supporting means for the charge during heating and by oscillating the rollers the deformation of the charge and the rollers due to the sagging of the metal and to the unequal expansion of the metal, is substantially, if not entirely, eliminated. By rotating the rollers in a single direction the charges are caused to progress through the furnace. A charging mechanism is arranged at one side of the first heating chamber, known as the preheat chamber, and has for its function the introduction of charges of work into the preheat chamber. After a charge arrives on the run-out table located at one end of the furnace, a crane is arranged to transport the charge to a quenching g0 bath. The crane is constructed so that the bars are supported in a horizontal plane. During the quenching operation the crane automatically raises and lowers the charge beneath the level of the quenching liquid, to cause the liquid to wash over the bars first in one direction and then in the other thereby insuring a uniform cooling of each bar throughout its length as well as the uniform cooling of the several bars. The movement of the carriers of the crane and of the charge also introduces a stirring action which is helpful in maintaining the quenching liquid at a more uniform temperature.

For a more complete understanding of my invention, reference should now be had to the drawings in which Fig. 1 schematically illustrat-es a furnace embodying my invention; Fig.

2 shows a complete layout chart of the several units of a furnace embodying my invention in an improved form; Fig. 3 shows a plan view of the 10 charging mechanism, the preheat chamber and a fraction of the high-heat chamber of Fig. 2; Fig. 4 is a sectional elevation taken along the lines 4-4 of Fig. 3; Fig. 5 shows a plan view of a fraction of the high-heat chamber, the runout table, and a fraction of the quench tank; Fig. 6 shows an elevation of Fig. 5 taken on the line 6-6; Fig. 7 is an enlarged sectional elevation taken on line 7-7 of Fig. 3 showing the details of the charging mechanism in relation to the preheat chamber; Fig. 8 shows the charging mechanism in a position for inserting a charge of material in the preheat chamber; Fig. 9 shows an enlarged sectional elevation taken on the lines 9-9 of Fig. 3; Fig. 10 shows a sectional elevation taken on the lines 1010 of Fig. 5; Figs. 11 and 12 diagrammatically illustrate an improved form of an electrical control system applied to my invention; Fig. 13 illustrates the relation of Figs. 11 and 12 to each other, while Fig. 14 shows schematically the operation of a typical limit switch.

Referring now to Fig. 1, I have shown my invention in one form as applied to a preheat chamber 10 and a high-heat chamber 11. Each heating chamber is provided with a plurality of rollers 12 arranged to form a roll table or roller hearth. In addition to the rollers provided in the heating chamber, a plurality of rollers are arranged at one end of the high-heat chamber 11 to form a run-out table 13. A crane 14 has a plurality of charge supporting carriers 15 adapted for movement between the rollers of the run-out table so that the crane may be operated to transport a charge of work from the run-out table to a quenching bath 16. From the quenching bath the crane 14 is arranged to place a charge of work on the discharge rack 18. A charging mechanism 20 is arranged to place charges of work within the preheat chamber 10.

Inasmuch as my invention is particularly suitable for automatic operation, I have indicated at 22 the automatic controller which coordinates the operation of the several units of the furnace in a manner to insure continuous operation of the furnace. It will be understood, of course, that any suitable control system may be employed by those skilled in the art.

In explaining the operation of my invention with reference to Fig. 1, it will be assumed that the line switch 23 has been closed and that a charge 24 has been placed in the preheat chamber 10 and a charge 25 has been placed in the high-heat chamber 11. It will also be assumed that the charges 63 and 62 have been lowered on the charging mechanism 20. The controller 22 in conjunction with a limit switch LSK geared to the roll table will, therefore, cause the roller motor 30 to rotate first in one direction and then in the other direction through predetermined limits. Preferably the roller motor 30 rotates the rollers 12 through an angle greater than 180, for example 190, or through 360 first in one direction and then in the other during the heating operation. Consequently, the charges 24 and 25 located respectively in the preheat chamber 10 and the high-heat chamber 11 are thereby reciprocated. The supporting area of each roller is constantly changed, by reason of the oscillation of the rollers, as well as the area of each bar of metal which is in contact with a roller. Consequently it will be seen that there are no unsupported lengths of metal during the heating operation. The limits of rotation of the rollers with reference to their diameter and their spacing are selected so that the rollers are moved into supporting engagement with substantially the entire lengths of the bars. The sagging of the bars of metal between adjacent rollers is thereby eliminated. Furthermore, the cold spots between each roller and each bar of metal are eliminated because the oscillation of the rollers results in the uniform heating of both the rollers and the bars. With reference to the rollers, the requirement that the rollers shall be oscillated through more than 180 is for the purpose of reversing the bending stresses applied to the rollers so that permanent deflection of the rollers is prevented.

The controller 22 after a predetermined time interval deenergizes the motor 30 and energizes the end door motor 32 in a direction to raise the end doors 33 and 34 of the high-heat chamber 11 and the end door 35 of the preheat chamber 10. As soon as the end doors are raised, a limit switch LSD in conjunction with the controller 22 deenergizes the motor 32 and energizes the roller motor 30 in a direction to rotate the rollers in a counter-clockwise direction to cause the charges 24 and 25 to progress through the furnace. As the charge 25 leaves the high-heat chamber 11 a bumper switch B2 is operated and serves to prevent the lowering of the end doors or the movement of the crane 14 until the charge 25 has been completely transferred from the highheat chamber to the run-out table. As soon as the charge 25 arrives on the run-out table 13 a bumper switch B3 is operated to deenergize the roller motor 30. The charge 25 will then be in position on the run-out table to be transferred to the quenching bath 16, while the charge 24 will have been transferred from the preheat chamber 10 to the high-heat chamber 11. The bumper switch B3 in conjunction with the automatic controller 22 serves three functions viz., the end door motor 32 is energized in a direction to lower the end doors, the hoisting motor 37 is energized in a direction to hoist the carriers 15 and the charge of work from the run-out table 13, and the motor 38 operating the side door 39 of the preheat chamber 10 is energized in a direction to raise the side door. As soon as the side door is raised the limit switch LSBl stops the motor and in conjunction with the controller 22 energizes the motor 81 of the charging mechanism 20 in a direction to raise the charging fork 43 so that the charges 62 and 63 are raised above the stationary rack 60.

As soon as the end doors are lowered the limit switch LSD deenergizes the end door motor 32.

As soon as the hoisting motor 37 raises the carriers 15 a predetermined distance, this motor is deenergized by suitable limit switch mechanism in the controller 22 and the trolley motor 48 is thereupon energized in a direction to drive the crane 14 towards the quenching bath 16. As the crane reaches the desired position over the quenching bath 16 the trolley motor 48 is deenergized and the hoisting motor 37 is energized in a direction to lower the carriers 15 and the charge of work into the quenching bath. The hoisting motor 37 is deenergized as the carriers reach a position corresponding to the broken line 49. Thereafter the hoisting motor 37 is energized first in one direction and then in the other direction, thereby causing the carriers to move the charge up and down between the positions indicated by the broken lines 49 and 50. The movement of the bars and carriers causes a flow of liquid over each length of the material besides creating a stirring action in the quenching liquid itself so that there is a uniform quenching of the material. After a predetermined time interval the hoisting motor 37 is energized in a direction to hoist the charge in the quenching bath and the trolley motor 48 is energized until it reaches the position over the discharge rack 18 whereupon the hoisting motor 37 operates to lower the carriers 15, leaving the charge supported on the dis charge rack 18. The discharge rack is designed with respect to the rim-out table 13 so that the hoisting motor 37 is deenergized to bring the carriers 15 to a standstill in the same horizontal plane they occupy at the run-out table. Therefore, it is only necessary to energize the trolley motor 48, after a charge has been placed on the discharge rack 18, to drive the carriers 15 directly to the run-out table in readiness for the next charge of work from the high-heat chamber. The motors 37 and 48 are controlled by suitable limit switch and timing mechanism which may be incorporated in the automatic controller 22.

Referring again to the charging mechanism, as soon as the motor 81 has operated the levers 71 and 74 to raise the charging fork 43, the limit switch LSA, operated by the motor 81, in conjunction with the controller 22 energizes the carriage motor 97 in a direction to move the charging fork towards the preheat chamber 10. The charging fork is brought to a standstill within the preheat chamber by means of a limit switch LSC driven by the motor 97. This limit switch also serves to energize the motor 81 in a direction to lower the charge of work between the rollers 12. The charge 63 will then be supported by the rollers within the preheat chamber. The motor 97 will then be energized by the limit switch LSA in a direction to drive the fork 43 from the preheat chamber whereupon it is stopped in the position shown by the limit switch LSC. It will also be observed that the charge 62, after the completion of the charging operation, has been transferred to the position on the stationary rack formely occupied by the charge 63. Additional charges can be placed upon the stationary frame 60 by the shop crane or by any other suitable means.

A complete cycle of operations has now been described and it will, of course, be understood that the furnace may be operated continuously.

It will now be assumed that the furnace is empty and that the first charge of work is to be introduced into the preheat chamber. The charging mechanism functions to place a charge in the preheat chamber. After the first charge has been oscillated for the predetermined length of time the end doors raise and the charge is transferred to the high-heat chamber 11. The roller motor 30 is deenergized by means of a bumper switch Bl operated by the arrival of the charge within the high-heat chamber. This bumper switch B1 is only operated by the first charge of work which enters the high-heat chamber. Thereafter the bumper switch B3 at the end of the run-out table 13 controls the operation of the roller motor 30 in a manner which has already been described.

In the improved form of my invention embodied in Figs. 2 to 14, inclusive, the construction of the apparatus will first be described while the operation of the furnace will be described in detail in connection with the wiring diagram shown in Figs. 11 and 12.

charging mechanism Though any suitable charging mechanism may be employed I prefer to utilize the mechanism described and broadly claimed in the copending application Serial No. 600,906, flled March 24, 1932-Smith and Deery-and assigned to the same assignee as the present invention. This charging mechanism is simple in construction and particularly lends itself to the handling of heavy charges of bars. In the present application the charging mechanism will be described by saying that it consists of a stationary rack 60, Figs. 7 and 8, the upper rails 61 of which are arranged to support the charges of steel bars 62 and 63. These bars are held in position by means of the upwardly extending lugs 64. The charging fork 43 is supported by an elevating and transporting mechanism 66. As in the case of Fig. l, the charging fork consists of a plurality of supports 67 supported in cantilever fashion by means of a plurality of downwardly directed extensions. Two of these extensions 68 and 69 are shown in Figs. 7 and 8. The extension 68 is pivotally connected at 70 to one end of a lever 71. On the other end of this lever there are provided a plurality of gear teeth 72 arranged to mesh with a driving gear 73. Similarly, a lever 74 has gear teeth 75 meshing with the gear 73 and is pivotally connected to the downward extension 69 at 76. When the gear 73 is rotated in a counter-clockwise direction the lever 71 rotating about its pivot point 77 exerts an upward thrust on the extension 68. Similarly, the lever 74 rotating about its pivot point 76 exerts an upward thrust on the extension 69. The result is a vertical raising of the charging fork 43. There are provided six sets of similar elevating mechanism each being located beneath one of the supports or forks 67.

Referring to Figs. 3 and 7, it will be observed that one of the driving gears 73 is secured to a shaft 80 which extends the full width of the fork 43. The shaft is driven by a motor 81 which drives the gear 82 secured to the shaft 80 through a suitable speed reducer 83. As the fork is moved from the position shown in Fig. 7 to the position shown in Fig. 8, it will be seen that the steel bars 62 and 63 are transferred from the rails 61 to the fork 43. The lugs 85 provided on the charging fork maintain the bars in grouped relation so that they cannot shift from the position shown. The limit switch LSA geared at 86 to the shaft 80 serves, as a part of its function, to deenergize the motor 81 as the fork is raised to its upper or charging position. The translational movement of the fork is made possible by a transporting carriage 90. The fork 43 and levers 71 and 74 and the motor 81 are supported on the carriage 90. The carriage wheels, which are shown, ride upon a track 93. Supported from the carriage frame is a rack gear 94 arranged to mesh with a driving gear 95. The latter gear is driven by a motor 97 which is mechanically connected through a suitable speed reducer 98 to the shaft 99 to which the gear is secured. A limit switch LSC geared to the shaft 99 serves as a part of its function to control the energization of the carriage motor 97.

The preheat chamber It will be observed that the preheat chamber 10, Figs. 3 and 4, is provided with a plurality of rollers 12 forming a roller hearth within the preheat chamber. This roller hearth serves as a support for the charges of work as well as for the transfer of the work through the furnace. Within the preheat chamber there are provided the heating resistors 100 and 101, Fig. 7.

As shown, the side door 39 can be raised and lowered by the motor 38 geared to the hoisting drums 103 upon which the door cables 104 are wound. The counterweights 105 are secured at one end oi the respective door cables. The moby means of a super-structure 106 formed of steel beainsorthelike. Apair oftracktypelimit switches 1331 and 15132 (see Fig. 4) serve as a part of their function to deenergize the side door motor 38 as the door is driven to one or the other of its positions. The rollers of the roll table are arranged to be driven by the motor 30 which, as will be observed (Fig. 3), isgeared toa shaft 108 which serves to drive each roller of the roll table through suitable connecting gearing.

The end door motor 32 is molmted upon a superstructure 109 and serves to raise and to lower the end door 35 on-the preheat chamber and the end doors 33 and 34 on the high-heat chamber. A limit switch ISD, shown in Fig. 9, serves as a part of its function to deenergize the end door motor 32 as the doors reach one or the other of their limits.

The high-heat chamber The high-heat chamber 11, Figs. 4, 5 and 9, is similar in construction to the preheat chamber but additional heating resistors are provided inasmuch as the temperature of this unit of the furnace is to be considerably higher than the temperature of the preheat chamber. The materials for the construction of the furnace and of the roller hearth will of course be selected with reference to the high temperature at which this unit of the furnace is to operate.

The run-out table The run-out table 13, Figs. 5, 6 and 10, consists of an extension of the roll table. However, the rollers are spaced sufllciently apart to permit the carriers 15 provided on the crane 14 to travel between them. The bumper switches B1, B2 and B3 perform the same functions as described in connection with Fig. 1.

The crane The carriers 15 are supported from one end 112 by the steel supports 113 and 114. These supports are secured to a framework 116 which has mounted upon it a plurality of pulleys, two of which 117 and 118 are shown in Fig. 10. About these pulleys are threaded the supporting cables 119 and 120 which are wound upon the hoisting drum 121. A truck 122 mounted on a track 123 supports the hoisting drum 121 as well as the hoisting motor 3'1 and the trolley motor 48. The track 123 extends over the quenching tank 16 and the discharge rack. A pair of geared limit switches LSH and [ST are respectively provided for controlling the energization of the hoisting motor 3! and the trolley motor 48. There is also provided a track-type limit switch LSH2 operated by the crane to deenergize the hoisting motor 3'7 whenever the carriers 15 are hoisted to a podtion a predetermined distance above the run-out .table.

The automatic control system It is believed that a clear understanding of the arrangement and operation of the various parts of a suitable electrical system will be best understood from a complete description of the operation of the system as a whole, and therefore the construction and arrangement of certain typical devices only will be first described in detail.

The limit switches ISA. 18K. 15D, 15C, 1ST and LSH are constructed as shown in Fig. 14. Each pair of contacts 110 are arranged to be bridged by a conducting member 111, pivotally tor 38 and the hoisting drum 103 are supported mounted at 112 on a support 113. A spring 114 normally biases the conducting member 111 away from the contacts 110. A lug or cam 115 is secured to a disk 116 mounted on a shaft 117, and serves to cooperate with a roller 118 carried by the contact arm 119 so as to operate the conducting segment 111 to close the contacts 110. As the contact arm 119 is rotated about its pivot 112, its lower end 120 is engaged by a latching member 121 holding it in its closed position. The latching member 121 is biased against the lower end 120 of the switch member 119 by a spring 122. A second lug or cam 123 is arranged to engage a roller 124 so that the latching member 121 may be rotated about its pivot point releasing the switch member 119 so that the spring 114 may operate the switch member to open the contacts 110. It will therefore be observed that the limit switch contacts require positive operations for both the opening and the closing of the contacts.

A plurality of sequence relays L1, L2, L3, L4, L5, L6 and L'Iare arranged so that when an energizing circuit is completed for one of the sequence relays, it will be operated and latched into pofition. In other words, it will require a second circuit to be completed to unlatch the sequence relay so that it may be operated into its unlatched position. By means of this type of relay the sequence of operations of the cycle will not be disturbed even though there is a power failure. This will be seen by observing that the relays and contactors normally held closed by reason of energizating circuits completed thru the contacts of the sequence relays, upon power failure will be operated to their open positions. As soon as there is a resumption of power, however, the relays and contactors will be closed, inasmuch as the sequence relays maintain the energizing circuits.

The timing relays TF, TR, 226, 227, 228, 229 and TR2 are similarly constructed. For example, timing relay TF (Fig. 11) is provided with a short circuited winding 230. After the operating coil of the relay TF has been energized to cause its contacts to be opened and thereafter its energizing circuit is broken, it will be understood that the short circuited coil 230 serves to decrease the rate of decay of the magnetic flux thereby maintaining the contacts of the time relay open for a predetermined time interval. A timing relay 'I'Rl is provided with a suitable device 231 arranged to delay the closing of the contacts of this relay.

A master timer 232 is arranged to control the length of time a charge shall remain in one of the heating chambers. This timer has a pair of contacts 233 which are normally open. when the timer is in operation alternating current is applied to its motor 234 and to the operating coil 235. The armature 236 of this motor is thereby rotated and by reason of the magnetic attraction of the coil 235 exerted on a magnetic member 237, the worm gear 238 is rotated into engagement with the gear 239. Just enough movement is permitted by a stop member 240 so that the worm gear 238 may be moved about the pivot 241 into meshing engagement with the gear 239. However, the stop member 240 does not permit the closing of the contacts 233. As soon, however, as the outwardly extending projection or tripping member 242 carried by the gear 239 strikes the latching member 243, the coil 235 closes the contacts 233. By varying the position of the tripping member 242 with respect to the latching member 243, it will be observed that the time required for the closing of the contacts 233 may be varied. A similar timer 738 is arranged to control the time required for the quenching operations.

It is now believed that a comprehensive understanding of the system, including the construction and arrangement of various devices, will be facilitated by a description of the operation of the system as a whole. While any suitable system may be used I have shown the system described and claimed in a copending application of A. F. Betke, Serial No. 614,234, flled May 28, 1932, and assigned to the same assignee as this invention.

Referring to Figs. 11, 12 and 13, a pair of line switches 250 and 251 are shown closed, so that the supply lines 252 and 253 are connected to a suitable source of direct current supply (not shown). The supply line 252 is connected to the source of supply by means of an undervoltage relay 254 which is energized through a circuit which may be traced through the line switch 250, push button stations 255 and 256, conductor 257, operating coil of the relay 254, and by conductors 258 and 259 to the other supply line 253. It will be observed that the supply line 252 serves as the origin of all of the control circuits and therefore if there should be a voltage failure of the supply source, all of the control circuits will be deenergized by reason of the opening of the relay 254. The stop push buttons 255 and 256 may be multiplied indefinitely, that is to say, fifteen or twenty of these push buttons may be distributed at various points about the furnace so that in case of the occurrence of an abnormal condition, the operator may deenergize all of the control circuits by simply pressing a stop push button, which it will be observed, interrupts the circuit to the relay 254.

It will be observed that the supply line 253 is connected to the source of supply by a normally closed switch 253a. While only one of these switches is shown in Fig. 11 of the drawings it is to be understood that each door may be provided with a similar switch. Should the work come into engagement with an end door thereby causing the end door to be swung outwardly from its supporting cables, all of the control circuits will be deenergized by the opening of the switch 253a.

To clarify the description, the line switches 250 and 251 are shown closed. Consequently a number of contactors and relays are shown in their energized positions before the start push button 261 has been depressed to initiate the automatic operation of the furnace. For example, an energizing circuit for the timing relay TR may be traced from the supply line 252, by conductor 262', operating coil of the timing relay TR, contacts 263 of the limit switch LSK, and by conductors 264, 265 and 259 to the other supply line 253. An energizing circuit for the first accelerating relay 226 of the roll motor 30 may be traced from supply line 252, by conductor 266, normally closed contacts 267 of the sequence relay L3, conductor 266a, contact 268 of the forward direction switch 269 provided for the roll motor 30, conductor 270, operating coil of the relay 226, and by conductors 271, 265 and 259 to the other supply line 253. A similar accelerating relay 227 provided for the carriage motor 97 is energized through a circuit which may be traced from the supply line 252 by conductors 274, 276, 277, contacts 279 provided on the direction switch 280 for the out-motion of the carriage motor 97, interlock contacts 281 provided on the direction switch 282 for the in-motion of the carriage, operating coil of relay 227, and by conductors 283 and 285 to the other supply line 253. A field accelerating contactor 287 of the hoist motor is closed by reason of an energizing circuit which may be traced from supply line 252, by conductors 274, 276. 288, contacts 289 of hoisting relay 290, conductor 291, contacts 292 of the lowering relay 293, conductor 294, operating coil 295 of the contactor 287 and by conductor 296 to the other supply line 253. An accelerating contactor 298 provided for the crane hoisting motor 37 is energized by reason of a circuit which may be traced from the supply line 252, by conductor 299, contacts 300 provided on the relay 301, conductor 302, interlock contacts 303 provided on the hoisting relay 290, interlock contacts 304 provided on a lowering direction switch 305, conductor 306, operating coil 307 of the contactor 298, and by conductors 308 and 259 to the other supply line 253. An energizing circuit for the accelerating contactor 309 is derived by means of a conductor 310 from the energizing circuit for the contactor 298 and is completed through the contacts 311 operated with the contactor 298, operating coil of contactor 309 and by conductor 259 to the other supply line 253. The completion of the energizing circuit of the field accelerating contactor 312 of the hoist motor depends on the contacts 313 operated with the contactor 309. This circuit may be traced from supply line 252 by conductors 274, 276, 314, 315, contacts 313 of the contactor 309, contacts of the relay 229, operating coil 316 of the contactor 312 and by conductor 317 to the other supply line 253.

An undervoltage relay 321 is provided to protect the furnace and the work from overheating in case of power failure of the direct current source of supply. Its energizing circuit may be traced from the supply line 252 by conductor 322, operating coil of the relay 321, and by conductors 323 and 285 to the other supply line 253. An energizing circuit for a contactor 327, arranged to connect the heating resistors designated at 328 and located in the preheat and the high-heat chambers to a suitable three phase source of supply as is indicated by the supply lines 329, 330 and 331, may be traced from the supply line 329, contacts 332 of the undervoltage relay 321, conductor 333, operating coil of the contactor 327, and by conductor 334 to the other supply line 330. A control panel 335 is provided with a number of control switches (not shown) which serve to complete the power circuits from the three phase source of supply to the various heating resistors employed for the heating of the furnace.

The contacts 337 provided on the undervoltage relay 321 serve to complete an energizing circuit for the master timer 232.

The circuit for the timer motor 234 may be traced from the alternating current supply line 329, contacts 340 of the timer, conductor 341, motor winding of the timer, conductor 343, contacts 344 of the end door limit switch LSD, conductor 345, contacts 337 of the undervoltage relay 321, and by conductor 346 to the other supply line 330. The circuit to the operating coil 235 of the timer may be traced from the supply line 329 by conductor 347, coil 235, conductors 348 and 343, contacts 344 of the end door limit switch LSD, conductor 345, contacts 337 of undervoltage relay 321 and by conductor 346 to the other supply line 330. It will therefore be observed that as soon as voltage is applied to the supply lines 252 and 253 and to the alternating current supply lines 329, 330 and 331, the master timer 232 begins timing in the manner that has already been explained.

For the sake of clarity of description it will be assumed that the initial heating of the furnace has been completed and that the preheat chamber 10 and the high heat chamber 11 have been brought up to their normal operating temperatures.

To initiate the automatic operation of the furname under the conditions assumed and with the various parts in the positions shown in Figs. 11 and 12, a normally open start button 261 is momentarily depressed to establish an energizing circuit for a normally open relay 351. This circuit may be traced from supply line 252, by conductor 352, push button 261, operating coil of the relay 351, and by conductors 353 and 259 to the other supply line 253. The relay 351 is thereupon closed to complete energizing circuits through its contacts 355, 356 and 357.

The bumper switch B1, which it will be remembered is located in the high heat chamber 11, is rendered effective by reason of the completion of its energizing circuit by the contacts 35'! of the relay 351. This circuit may be traced from the supply line 252 by conductor 359, contacts 357 of the relay 351, conductor 360, operating coil 361 of the bumper switch B1, and by conductor 285 to the other supply line 253. The contacts of the bumper switch B1 are thereupon opened and the pivoted member 88 (see Fig. 5) is moved into the path of the work. This bumper switch serves to deenergize the roll table motor 30 as the first charge of work arrives in the high heat chamber from the preheat chamber. Thereafter this bumper switch is not effective, inasmuch as the roll motor for subsequent operation is deenergized by the opening of the contacts 362 of the relay 301, which relay is operated due to the closing of the contacts of the bumper switch B3 located on the outer end of the run-out table 13 (see Fig. 5).

Incident to the closing of the contacts 356 of the relay 351 the sequence relay L5 is operated to its latched-in position by reason of an energizing circuit which may be traced from the supply line 252 by conductor 364, contacts 356 of the relay 351, conductor 365, operating coil 366 of the uence relay L5, and by conductors 367 and 259 to the other supply line 253. The opening of the contacts 3'10 of this relay removes a shunt circuit around the contacts 3'11 of the relay 3'12, and inasmuch as this relay operates to open its contacts 3'11 following the operation of the bumper switch B1, it will be seen that the energizing circuit for the forward direction switch 269 of the roll motor 30 may thereby be interrupted. The closing of the contacts 3'13 of the sequence relay L5 causes the closing of the relay 3'14 by reason of the completion of its energizing circuit. This circuit may be traced from the supply line 252 by conductor 3'15, contacts 3'13 of the sequence relay L5, conductor 3'16, operating coil of the relay 3'14, and by conductors 3'17 and 285 to the other supply line 253. The contacts 3'18 of the relay 3'14 serve partially to complete an energizing circuit for the direction switch 385 of the cams, while the relay contacts 380 serve partially to complete an energizing circuit for the lower direction switch 381 of the end door motor 32.

The closing of the contacts 355 of the relay 351 completes an energizing circuit for the sequence relay L1, which circuit may be traced from supply line 252, by conductor 364. contacts 355, 0p-

crating coil of the sequence relay L1, and by conductors 383 and 259 to the other supply line 253. The sequence relay L1 is thereupon operated to its latched-in position with its contacts 384 closed. The closing of these contacts completes an energizing circuit for the up-direction switch 385 of the lever motor 81. This circuit may be traced from the supply line 252, by contacts 386 of the bumper switch B2, contacts 387 of the side door limit switch LSB2, contacts 388 of the lever limit switch LSA, contacts 384 of the relay L1. operating coil 389 of the direction switch 385, interlock contacts 391 of the lower direction switch 382 of the lever motor, and by conductors 393 and 259 to the other supply line 253.

The closing of the up-direction switch 385 serves to connect the armature of the motor 81 by conductors 395 and 396 to a suitable source of direct current supply as is designated by the positive and negative symbols. A separately excited fleld winding 397 for this motor is similarly energized as indicated from a suitable source of direct current supply. The lever motor 81 is thereupon caused to rotate in a direction to raise the charging fork 43 as previously described. It will be understood that accelerating contactors may be employed to accelerate the motor 81 though these have been omitted for the purpose of simplifying the drawings.

When the up direction switch 385 closed, the contacts 399 operated with this switch were closed to establish an energizing circuit for the operating coil 400 of the sequence relay L6. This circuit may be traced from the supply line 252 by conductor 401, contacts 399 of the direction switch 385, conductor 403, operating coil 400 of the sequence relay L6, and by conductors 404 and 259 to the other supply line 253. The sequence relay L6 is thereupon operated and latched into position with its contacts 405 closed complete in part and energizing circuit for the in-direction switch 282 of the carriage motor 9'1. At the same time the contacts 406 of the relay L6 are opened to prevent the completion of an energizing circuit for the out-direction switch 280. The interlocking of circuits in this manner maintains the carriage within the furnace until the load transferring operations have been completed.

As soon as the lever motor 81 has raised the charging fork 43 to its upper position, the limit switch LSA is operated to open its contacts 388,

407 and 408, while its contacts 409 and 410 are closed. The opening of its contacts 388 deenergizes the up-direction switch 385, which switch is operated to deenergize the motor 81.

The closing of the contacts 409 of the limit switch LSA serves to complete an energizing circuit for the raise direction switch 412 of the side door motor 38. This circuit may be traced from the supply line 252 by conductor 413, contacts 414 provided on the side door limit switch LSBl, contacts 409 of limit switch LSA, conductor 415, operating coil 416 of direction switch 412, interlock contacts 41'! of the lowering direction switch 3'19 and by conductors 418, 265 and 259 to the other supply line 253. The direction switch 412 thereupon closes to connect the armature of the motor 38 by conductors 419 and 420 to a suitable source oi direct current supply designated by the positive and negative symbols. The motor 38 is provided with a separately excited field winding 421 which is energized from a suitable source of direct current supply as indicated. The motor 38 is therefore caused to rotate in a direction to raise the side door.

As soon as the side door reaches its upper position the track type limit switch LSBl is operated to open its contacts 414 and to close its contacts 422. The opening of the former contacts deenergizes the direction switch 412 which in turn deenergizes the motor 38. The contacts 422 of the limit switch LSBI serve to complete the energizing circuit for the in-direction switch 282 of the carriage motor 97. This circuit may be traced from the supply line 252, by conductor 423, contacts 422 of LSBl, conductor 424, contacts 405 of the sequence relay L6, conductor 425, contacts 426 of the carriage limit switch LSC, conductor 427, operating coil of the direction switch 282, interlock contacts 428 of the out-direction switch 280, and by conductor 285 to the other supply line 253. The direction switch 282 is thereupon closed to energize the carriage motor 97 to cause it to be rotated in a direction to move the carriage and the charging fork 43 towards the preheat chamber 10. A separately excited field winding 430 is provided on the carriage motor 97 to provide excitation therefor.

It will be remembered that the energizing circuit for the accelerating relay 227 of the carriage motor was traced through the contacts 281 on the in-direction switch 282. Therefore, as soon as the direction switch was operated this circuit was broken by the opening of the contacts 281. After a predetermined time interval introduced by reason of the short circuited coil 227a its contacts are closed to establish an energizing circuit for the accelerating contactor 431. This circuit may be traced from the supply line 252 by conductors 274, 276, 277, contacts of the accelerating relay 227, operating coil of the accelerating contactor 431 and by conductors 433 and 285 to the other supply line 253. The accelerating contactor 431 is therefore operated to its closed position to short circuit the resistance 434 connected in series with the armature of the motor 97.

While I have only shown a single accelerating contactor for the carriage motor 97, it will be understood that several accelerating contactors may be used to provide smooth acceleration of the carriage motor. However, as I have indicated in connection with the lever motor 81, the accelerating contactors have been omitted for the purpose of simplifying the drawings wherever the function of these contactors are well known and well understood by those skilled in the art.

As the carriage nears its limit of movement with the charging fork 43 and the load 63 within the preheat chamber, the limit switch LSC is operated to open its contacts 426 and 436 and to close its contacts 437 and 438. It will be observed that the operating coil of the direction switch 282 is deenergized due to the opening of the contacts 426 of the limit switch LSC. As this direction switch is operated to its open position its contacts 439 are closed to establish a dynamic braking circuit for the carriage motor 97 through a resistance 440. This circuit may be traced from one side of armature of the carriage motor 97 by contacts 439 operated with the direction switch 282 dynamic braking resistance 440, contacts 441 operated with the direction switch 280, and by conductor 442 to the other side of the armature of the motor 97.

The positions of the carriage 90 and the charging fork 43 as they come to a standstill are shown in Fig. 8.

The closing of the contacts 437 of the limit switch LSC serves to establish an energizing circuit for the down-direction switch 382 of the lever motor 81. This circuit may be traced from the supply line 252, by conductor 446, contacts 410 of the limit switch LSA (which contacts it will be remembered were closed when the charging fork 43 was raised by the lever motor 81) interlock contacts 448 of the direction switch 385, operating coil of the lower-direction switch 382, conductor 450, contacts 437 of the limit switch LSC, and by conductors 451 and 259 to the other supply line 253. The motor 81 is thereupon caused to be rotated in a direction to lower the charging fork 43 thereby depositing the load 63 on the roll table and the load 62 on the stationary rack 60.

Incident to the closing of the lower direction energizing circuit for the trip coil 452 of the sequence relay L1 is completed by the closing of the contacts 453 operated by the downdirection switch 382. This circuit may be traced from supply line 252 by conductor 454, trip coil 452 of the sequence relay L1, contacts 453 of the down-direction switch 382, and by conductors 455 and 259 to the other supply line 253. Similarly, the contacts 456 operated with this direction switch were closed to complete an energizing circuit for the trip coil 457 of the sequence relay L6. This circuit may be traced from the supply line 252, conductor 458, contacts 456 of direction switch 382, conductor 459, trip coil 457 and by conductors 404 and 259 to the other supply line 253. It will be remembered that the sequence relay L6 was operated to its latched-in position so that the in-direction switch 282 of the carriage motor could be energized, and so that the energizing circuit of the out-direction switch 280 could not be completed. Therefore, it will be seen that as soon as the trip coil 457 releases the sequence relay L6 this relay is operated to its unlatched position to close its contacts 406, thereby partially completing an energizing circuit for the out-direction switch 280 of the carriage motor 97.

As the charging fork 43 is lowered, the contacts 409 and 410 of the lever limit switch LSA are operated to their open positions, while the contacts 388, 407 and 408 of the lever limit switch LSA are operated to their closed positions. The opening of the contacts 410 serves to deenergize the down-direction switch 382, which switch is operated to its open position to deenergize the lever motor 81. At the same time the contacts 408 of the limit switch LSA complete the energizing circuit for the out-direction switch 280 of the carriage motor 97. This circuit may be traced from the supply line 252 by conductor 461, contacts 408 of the limit switch LSA, conductor 462, contacts 406 of the sequence relay L6, conductor 464, contacts 438 of the limit switch LSC, conductor 466, operating coil of the out-direction switch 280, interlock contacts 468 of the in-direction switch 282, and by conductor 285 to the other supply line 253. The outdirection switch 280 is thereupon closed to energize the motor 97 in a direction to drive the carriage 90 and the charging fork 43 from the preheat chamber. As before, the accelerating relay 227 closes after a predetermined interval of time to energize the accelerating contactor 431. In this case the circuit to the accelerating relay 227 is broken by reason of the opening of the contacts 279, operated with the out-direction switch 280.

As the carriage is driven to its outer position as shown in Fig. 7, the contacts 437 and 438 of the carriage limit switch LSC are operated to their open positions while the contacts 426 and 436 of this switch are operated to their closed positions. The out-direction switch 280 is deenergized and operated to its open position as a result of the opening of the contacts 438 of the limit switch LSC. As this switch is operated to its open position the contacts 441 operated with it are closed to establish a dynamic braking circuit for the carriage motor 9'7 so that the motor is quickly braked to a standstill with the carriage and the charging fork in their original positions.

Incident to the closing of the contacts 436 of the carriage limit switch LSC the lower direction switch 3'79 of the side door motor 38 is closed by reason of an energizing circuit which may be traced from the supply line 252 by conductor 4'72, contacts 473 of the limit switch LSB2, contacts 407 of the limit switch LSA, conductor 4'75, interlock contacts 4'76 of the direction switch 412, operating coil of the direction switch 3'79, conductor 477, contacts 436 of the limit switch LSC, and by conductors 478, 451 and 259 to the other supply line 253. As a result of the closing of the direction switch 3'79, the motor 38 is energized in a direction to lower the side door 39.

Inasmuch as the carriage and the charging fork 43 have been driven from the preheat chamber and the door is being lowered, the roll motor may now be energized in a manner to cause the oscillation of the charge in the preheat chamber 10. The sequence relay L3 controlling the energization of the roll motor 30 is therefore closed as soon as the side door motor direction switch 3'79 is operated to its closed position by reason of an energizing circuit completed by the closing of the contacts 480 operated with this direction switch. This circuit may be traced from the supply line 252 by conductors 481, operating coil 482 of the sequence relay L3, conductor 484, contacts 480 of the direction switch 379 and by conductors 485, 265 and 259 to the other supply line 253. The sequence relay L3 is thereupon operated to its latched-in position with its contacts 487 closed and its contacts 267 open.

As soon as the side door 39 reaches its lower limit, the contacts 4'73 of the side door limit switch LSB2 are operated to their open position to deenergize the direction switch 3'79. At the same time the contacts 387 of this limit switch are closed.

As soon as the sequence relay L3 is latched into position the armature of the roll motor 30 is shunted by a resistance 490 while the energizing circuit to the accelerating contactors 495 and 496 are interrupted so that the series resistances 497, 498 and 500 remain effective. Consequently, the motor 30 may only rotate at a very low speed to change progressively the load supporting area of each roller. The opening of the contacts 267 of the sequence relay L3 accomplishes the interruption of the energizing circuits to the accelerating contaetors. The shunt connection of the armature of motor 30 with the resistance 490 is accomplished by reason of the completion of an energizing circuit for the contactor 501. This circuit may be traced from the supply line 252 by conductor 502, contacts 487 of the sequence relay L3, conductor 503, operating coil of the contactor 501 and by conductors 504. 265 and 259 to the other supply line 253. As soon as the contactor 501 is closed, an energizing circuit is completed for the clutch operating coil 515 due to the closing of the contacts 514 operated with the contactor 501. This circuit may be traced from the supply line 252 by conductor 516, clutch operating coil 515, conductor 517, contacts 514 of the contactor 501, and by conductors 518, 265 and 259 to the other supply line 253. The solenoid 515 thereupon operates the clutch member 519 into engagement with a cooperating clutch member 520 thereby establishing a mechanical connection between the driving motor 30 and the limit switch LSK. The forward direction switch 269 of the roll motor 30 is operated to its closed position as a result of the closing of the contacts 487 of the sequence relay L3. This energizing circuit may be traced from the supply line 252 by conductor 502, contacts 487 of the sequence relay L3, conductor 522, contacts of the time closing relay TF, conductor 524, contacts 525 of the push button station 526, conductor 527, contacts 528 of the limit switch LSK, contacts 362 of the relay 301, contacts 3'71 of the relay 3'72, operating coil 530 of the forward direction switch 269, interlock contacts 531 of the reverse direction switch 532 of the roll motor 30, and by conductors 533, 265 and 259 to the other supply line 253. The direction switch 269 thereupon closes to energize the motor 30 so that it drives the rollers in a forward direction. A separately excited field winding 534 provides excitation for this motor. It will be observed that this field winding 534 is connected in series with a resistance 535. A relay 536 has its operating coil connected across the series resistances 497, 498, and 500. As soon as current flows to the armature of the motor 30 the resulting potential difierence existing across the series resistances 497, 498 and 500 is suflicient to cause the operating coil of the relay 536 to dose its contacts, thereby short circuiting the field resistance 535. The result is an increase in field current and a consequent reduction in the speed of rotation of the motor 30.

As soon as the motor 30 has driven the rollers through approximately 190 degrees, the contacts 528 of the limit switch LSK are operated to their open position, thereby deenergizing the direction switch 269. At the same time, the contacts 263 of the limit switch 18K are operated to their open position, while the contacts 538 and 539 are operated to their closed positions.

The closing of the contacts 539 of the limit switch LSK serves partially to complete an energizing circuit for the reverse direction switch 532 of the roll motor 30.

It will be remembered that the energizing circuit for the timing relay TR was traced through the contacts 263 of the limit switch LSK. Therefore, as soon as these contacts were operated to their open position, they served to interrupt this 1.2.30 energizing circuit. After a predetermined interval of time the contacts of the time closing relay TR. are closed to complete the energizing circuit for the reverse direction switch 532 of the roll motor. This circuit may be traced from the su ply line 252 by conductor 502, contacts 487 of the sequence relay L3, conductor 522, contacts of the timing relay TR, contacts 539 of the limit switch LSK, conductor 540, interlock contacts 542 of the direction switch 269, operating coil 543 of the direction switch 532, and by conductors 544,

265 and 259 to the other supply line 253.

The direction switch 532 is thereby closed to energize the roll motor 30 for reverse direction of rotation. The field relay 536 again closes to short circuit the field resistance 535 so that the speed of the motor is very low.

The closing of the contacts 538 of the limit switch LSK serves to complete an energizing circuit for the time closing relay TF. This circuit 1,979,108 supply line 252 by con-- predetermined time interval,

The direction switch 269 is thereby energized by means of the circuit traced above and the motor 30 again rotates in the forward direction at very low speed. The closing of the contacts 263 of the limit switch LSK serves to again complete the energizing circuit for the timing relay TR, which is immediately operated to open its contacts so that it is in readiness for the next operation of the roll motor.

The described cycle of operations serves constantly to shift the work back and forth in the preheat chamber. The result is the uniform heating of the material as well as the prevention of the deformation of the rollers or the work due to uneven heating. It is to be understood that the rollers may be rotated through 180 or more. If the rollers were rotated through 360 first in one direction and then in the other direction, it would not be necessary to introduce the time interval between reversals; that is to say for a 360 cycle the load supported by the rollers is equally distributed over the entire surface of the rollers. I have found, however, that by rotating the rollers through more than 180 but less than 360 and by introducing a time interval between reversals roller bending and/or deformation may be substantially if not entirely eliminated. An economy in furnace size is also attained by decreasing the roller travel to less than 360. i

The contacts 550 and 551 of the limit switch LSK are arranged to be operated to their closed positions as soon as roll motor 30 has rotated through a given angle in a forward direction. Thereafter they are immediately operated to their open positions so that the contacts 550 and 551 remain closed only for a short interval of time as the motor 30 is rotated in a forward direction. These limit switch contacts have for their function the partial completion of energizing circuits for producing at the proper time the high speed operation of the motor 30. In other words the transfer of work from one heating chamber to another may only be initiated with the rollers occupying a predetermined position.

After the load 63 of steel bars has been oscillated in the preheat chamber for a period of t me as determined by the setting of the master timer 232, the master timer times out thereby closing its contacts 233. It will be assumed that these contacts are closed just as the roller position determining contacts 550 and 551 of the limit switch LSK are closed. The raise-direction 'switch 552 of the end doors is immediately closed B by reason of the completion of an energizing circuit which may be traced from the supply line 252, by conductor 554, contacts 551 of the limit switch LSK, conductor 555, contacts 233 of the master timer 232, conductors 556 and 837, contacts 557 of the end door limit switch LSD, conductor 558, operating coil 559 of the raise direction switch 552, interlock contacts 560 of the lower direction switch 381, and by conductors 323 and 285 to the other supply line 253. The motor 32 is immediately energized in a direction to raise The closing of the contacts 562 operated with the direction switch 552 serves to complete an energizing circuit for the trip coil 565 of the sequence relay L3. This circuit may be traced from the supply line 252 by conductor 566, contacts 550 of the limit switch LSK, trip coil 565 of the sequence relay L3, conductors 567 and 568, contacts 562 of direction switch 552 and by conductors 569, 264, 265 and 259 to the other supply line 253. The sequence relay L3 is thereupon operated to its unlatched position with its contacts 267 closed and its contacts 487 open. The opening of the contacts 487 interrupts the energizing circuit of the contactor 501 which is immediately operated to its open position. The opening of the contacts 514 operated with the contactor 501 serves to deenergize the clutch operating coil 515 of the limit switch LSK so that the clutch member 519 immediately disengages itself from the clutch member 520. The opening of the contacts 487 of the sequence relay L3 it will be remembered also serves to deenergize the forward direction switch 269 of the roll motor which switch immediately operates to its open position. As the direction switch 269 opens, the contacts 268 operated with this switch are closed to complete an energizing circuit for the accelermaybe traced from the supply line 252 by conductor 266, contacts 267 of the sequence relay L3, contacts 268 of the direction switch 269, conductor 270, operating coil of the accelerating relay 226, and by conductors 271, 265 and 259 to the other supply line 253. The accelerating relay is thereupon operated to open its contacts so as to be in readiness for the high speed operation of the motor.

As soon as the end doors have been raised to their upper positions, the end door limit switch LSD operates to close its contacts 571, 573, 574 and to open its contacts 557, 575 and 344. The contacts 577 and 578 of this limit switch 'are arranged to be closed only as the end doors are being lowered. The opening of the contacts 557 interrupts the energizing circuit to the direction switch 552 which is immediately operated to its open position to deenergize the end door motor 32.

The closing of the contacts 573 of the end door limit switch LSD serves to complete an energizing circuit for the forward direction switch 269 of the roll motor 30. This circuit may be traced from the supply line 252 by conductor 554, contacts 551 of the limit switch LSK, contacts 573 of the limit switch LSD, conductor 580, contacts 362 of the relay 301, contacts 371 of the relay 372, conductor 582, operating coil 530 of the direction switch 269, interlock contacts 531 of the reverse direction switch 532, and by conductors 533, 265 and 259 observed that the roll for rotation in the forward direction. The accelerating relays 581 and 585 are operated to their open positions by reason of the IR drop across the resistance 497. The opening of the contacts 268 operated with the direction switch 269 interrupted the energizing circuit traced above for the accelerating relay 226. This relay therefore time closes to complete an energizing circuit for the first accelerating contactor 495. This circuit may be traced from the supply line 252 by conductor 266, contacts 267 of the sequence relay L3, conductor 266a, and 582, contacts of the accelerating relay 226, conductor 584, operating coil of the contactor 495, and by conductors 271, 265 and 259 to the other supply line 253. The closing of the contactor 495, it will be observed, short circuits the series resistance 497, and also short circuits the operating coil of the second accelerating relay 581, which coil, it will be observed, is connected directly across the resistance 497. The result is that the motor 30 is accelerated a predetermined amount; after a. predetermined interval of time, the relay 581 time closes to energize the second accelerating contactor 496. This circuit may be traced from the supply line 252 by conductor 266, contacts 267 of the sequence relay L3, conductor 266a and 582, contacts of the accelerating relay 226, conductor 584, contacts of the accelerating relay 581, operating coil of the accelerating contactor 496, and by conductors 265 and 259 to the other supply line 253. This contactor thereupon closes to short circuit the second accelerating resistance 498 from the armature circuit of the motor'30. Inasmuch as the accelerating relay 585 has its operating coil connected across the resistances 497 and 498,'the closing of the second accelerating contactor short circuits the operating coil of the accelerating relay 585. After a predetermined interval of time this relay operates to close its contacts thereby completing an energizing circuit for the third accelerating contactor 588. This circuit may be traced from the supply line 252 by conductor 266, contacts 267 of the sequence relay L3, conductor 266a and 582, contacts of the accelerating relay 226, conductor 584, contacts of the accelerating relay 585, operating coil of the contactor 588, and

- by conductors 265 and 259 to the other supply line 253. The closing of the contactor 588 serves to short circuit the resistances 497, 498 and 500 so that the motor 30 is accelerated to substantially full speed. It will be remembered that the field accelerating relay 536 is connected across the series resistances 497, 498 and 500, so that as soon as the contactor 588 removes these resistances from the armature circuit of the motor 30, the operating coil of the field relay 536 is short circuited. The field relay thereupon opens its contacts to reinsert the resistances 535 in the circuit of the field winding of the motor 30, causing the acceleration of the motor to its full speed.

By thus providing for the rapid acceleration of the motor 30, the load 63 of steel bars is rapidly transferred from the preheat chamber 10 to the highheat chamber 11 so that the work is transferred from one chamber to the other chamber with a minimum loss of heat in the work itself. Furthermore, by interlocking the circuits as described, it will be observed that the end doors are open for a minimum length of time so that the inrush of cold air into the preheat and highheat chambers is minimized.

Inasmuch as the master timer 232 will be set for different periods of time corresponding to the size of the work and nature of the heat treatment, it will be apparent that the master timer will time out and that the contacts 233 will close under some conditions of operation when the roll motor 30 is oscillating the rolls in the reverse direction. Should the contacts 233 of the timer 232 close when the motor 30 is rotating in the reverse direction, it will be seen that the contacts 551 of the limit switch LSK will be in their open position, so that an energizing circuit may not be completed for the raise direction switch 552 of the end doors. The motor 30 will continue to operate the rolls for the reverse direction of rotation until the limit switch LSK is operated to reverse the direction of rotation. As soon as the roll motor 30 is operated through the predetermined angle in the forward direction, the contacts 550 and 551 of the limit switch LSK will be operated to their closed positions as before. The energizing circuit for the raise direction switch 552 of the end doors is thereby completed so that the end door motor 32 immediately operates to raise the end doors. The sequence relay L3 is immediately operated to its unlatched position by reason of the completion of the energizing circuit for its trip coil 565. The roll motor 30 is thereby deenergized; the contactor 501 is operated to its open position, while the accelerating relay 226 is energized preparatory for the speed operation of the roll motor. The high speed operation of the motor 30 is accomplished by the completion of the circuits described above. It will be remembered that the high speed operation is initiated by the closing of the end door limit switch contacts 573, which contacts complete an energizing circuit for the forward direction switch 269. It should again be observed that by interlocking the circuits as described, the end doors are not raised until the rollers and consequently the load of material, occupy a desired position in readiness for the high speed transfer of the work from the preheat chamber to the highheat chamber. Furthermore, this interlocking insures that the charges of work in each heating chamber will occupy the same relative positions with respect to their end doors for each successive change introduced into the preheat chamber.

Continuing with the operation, as the charge of work 63 approaches its final position in the highheat chamber, it will be remembered that the bumper switch B1 located at the end of the highheat chamber is in readiness for operation by the charge of work 63. As soon as the leading ends of the work 63 strike the operating lever 88 of this bumper switch, the switch is operated to close its contacts. An energizing circuit for the operating coil of the relay 372 is thereby completed. This circuit may be traced from the supply line 252, by conductor 590, contacts of the bumper switch Bl, conductor 591, operating coil of the relay 372 and by conductor 285 to the other supply line 253. The relay 372 is operated to open its contacts 371 and to close its contacts 593 and 594. It will be observed that the opening of the contacts 371 immediately deenergizes the forward direction switch 269, which switch is operated to its open position. Inasmuch as the contacts 268 operated with t e direction switch 269 are closed, as this switch opens, to energize the accelerating relay 226, it will be observed that the accelerating contactors 495, 496 and 588 are deenergized. The result is that the series resistances 497, 498 and 500 are connected in series with the armature circuit of the motor 30. Coincident with the closing of the contacts 268, the contacts 595 operated with the direction switch 269 are closed to connect the operating coil 596 of the contactor 597 directly across the armature of the motor 30 and the series resistances 497, 498 and 500. It will be remembered that the motor field winding 534 is separately excited so that as soon as the direction switch operates to deenergize the armature of the motor 30, the motor begins to act as a generator and the resulting electromotive force applied to the operating coil 596 of the contactor 597 causes this contactor to be operated to its closed position. A dynamic braking circuit is thereby established through the resistance ation as determined by the dynamic braking is further increased by reason of the closing of the field relay 536, which it will be observed will have voltage applied to it due to the potential difference existing across the series resistances 497, 498 and 500. The motor 30 is thereby quickly brought to a standstill with the load 63 of steel bars at rest within the highheat chamber 11.

The next step in the sequence of operation is to close the end doors. This is accomplished by the closing of the contacts 593 of the relay 372 which serves to complete the energizing circuit for the lowering direction switch 381 of the end door motor 32. This circuit may be traced from the supply line 252 by conductor 601 and 602, contacts 593 of the relay 372, contacts 380 of the relay 374, conductor 603, contacts 574 of the limit switch LSD, conductor 605, contacts 606 of the bumper switch B2, conductor 607, interlock contacts 608 of the direction switch 552, operating coil 609 of the lowering direction switch 381 and by conductors 323 and 285 to the other supply line 253. The direction switch 381 is thereupon closed to energize the motor 32 in a direction to lower the end doors.

To insure the continuance of the desired cycle of operations should there be a power failure at this point in the operation of the furnace, the sequence relay L4 is operated and latched into position due to the closing of the contacts 617 operated with the direction switch 381. The energizing circuit thereby completed may be traced from the supply line 252 by conductor 615, operating coil of the sequence relay L4, conductor 616, contacts 617 operated with the direction switch 381, and by conductors 323 and 285 to the other supply line 253. With the sequence relay L4 in its latched-in position, it will be seen that its contacts 614 are closed to establish a shunt connection around the contacts 593 of the relay 372 and the contacts 380 of the relay 374.

As soon as the end doors are lowered the end door limit switch LSD operates to open its contacts 571, 573 and 574, while its contacts 344, 557 and 575 are closed. The closing of the contacts 575 energizes the trip coil 620 of the sequence relay L4 through a circuit which may be traced from the supply line 252 by conductor 615, trip coil 620, contacts 575 of the limit switch LSD, and by conductors 621, 323 and 285 to the other supply line 253. The opening of the contacts 574 of the limit switch LSD interrupts the energizing circuit to the lowering direction switch 381 which immediately operates to its open position thereby deenergizing the end-door motor 32. The closing of the contacts 344 of LSD completes the energizing circuit for the master timer 232 which timer begins a new timing operation.

The contacts 577 and 578 of the end door limit switch LSD are so arranged that both of these contacts are closed only as the end doors are lowered to their lower limit. The function of the contacts 577 and 578 is, therefore, to give an indication that the end doors have been hoisted 598. The rate of decelerto their upper positions and are on their way down to their lower limit position. At this point in the cycle with both contacts closed, an energizing circuit for the trip coil 627 of the sequence relay L5 may be traced from the supply line 252 by conductor 628, contacts 577 of the limit switch LSD, contacts 578 of the limit switch LSD, trip coil 627, and by conductors 629, 265 and 259 to the other supply line 253. The sequence relay L5 is thereupon operated to open its contacts 373 and to close its contacts 370. The opening of the former contact serves to deenergize the relay 374 which is thereupon operated to open its contacts 378 and 380. The closing of the contacts 370 serves partially to complete an energizing circuit for the forward direction switch 269. It will be observed that the contacts 370 are connected so as to by-pass the contacts 371 of the relay 372, which relay will remain energized by reason of the energizing circuit completed for its operating coil by the bumper switch B1.

It will be remembered that this bumper switch was operated by the arrival of the charge 63 of steel bars within the high heat chamber and the closing of its contacts causes the energization of the relay 372. When this relay was operated an indication was obtained that the charge of work had been entirely transferred from the preheat chamber 10 to the highheat chamber 11. A circuit was thereby established for the up-direction switch 385 of the lever motor 81 by the closing of the contacts 594 of the relay 372, so that the sequence described above for placing a charge of work in the preheat chamber is again initiated. The energizing circuit for the up-direction switch 385 may be traced from the supply line 252, by contacts 388 of the bumper switch B2, contacts 387 of the side door limit switch LSB2, contacts 388 of the cam limit switch LSA, conductors 630 and 631, contacts 378 of the relay 374, contacts 594 of the relay 372, conductors 632 and 633, operating coil 389 of the direction switch 385, interlock contacts 391 of the direction switch 382, and by conductors 393 and 259 to the other supply line 253. The direction switch 385 is thereupon operated to its closed position to energize the lever motor 81 in a direction to raise the charging fork 43. The closing of the contacts 634 operated with the direction switch 385 serves to complete an energizing circuit for the sequence relay L1, which circuit may be traced from the supply line 252 by conductor 454, contacts 634, conductor 635, operating coil of the sequence relay L1 and by conductors 383 and 259 to the other supply line 253. The

sequence relay L1 is thereupon latched into position with its contacts 384 closed to complete a holding circuit for the up-direction switch 385. This circuit may be traced from the supply line 252, by contacts 386 of the bumper switch B2, contacts 387 of the side door limit switch LSB2, contacts 388 of the limit switch LSA, contacts 384 of the sequence relay L1, operating coil 389 of the direction switch 385, interlock contacts 391, and by conductors 393 and 259 to the other supply line 253. It will therefore be observed that the function of the sequence relay L1 for this part of the sequence of operation is to prevent interruption of the energizing circuit for the direction switch 385 in case of power failure, and also to insure that the lever motor 81 is energized a suflicient length of time to raise the charging fork 43. This provision is necessary, inasmuch as it will be remembered that as soon as the sequence relay L5 is operated to its unlatched position with its contacts 373 open the relay 374 is deenergized. The contacts 3'78 of the relay 374, it will be remembered, form a part of the energizing circuit which initiated the operation of the up-direction switch 385.

The closing of the contacts 399 operated with the up-direction switch 385 serves to complete an energizing circuit for the sequence relay L6 in the same manner as described in the initial operation of the up-direction switch. The sequence relay L6 is thereupon operated to its latched-in position, partially completing by means of the contacts 405 the energizing circuit for the in-direction switch 282 of the carriage motor. As soon as the motor 81 has raised the levers to their upper position in readiness for the placing of the charge 62 of steel bars into the preheat chamber 10, the contacts 388 of the limit switch LSA are operated to their open position to deenergize the direction switch 385 which in turn deenergizes the motor 81. At the same time the contacts 409 and 410 of the limit switch LSA are operated to their closed positions, while the contacts 407 and 408 are operated to their open positions. The function of the limit switch contacts 409 isthe same as described above and serves to complete the energizing circuit for the direction switch 412 of the side door motor. This direction switch, thereupon closes to energize the motor 38 in a direction to raise the side door. As soon asthe side door is hoisted to its upper position the contracts 4l4 of the track limit switch LSBI are operated to their open position to deenergize the direction switch 412 which in turn deenergizes the side motor 38. At the same time the contacts 422 of the limit switch LSBl are operated to their closed position to complete an energizing circuit for the direction switch 282 for the carriage motor 97. The carriage motor 9'7 is thereby energized in a direction to move the charging fork 43 and the carriage towards the preheat chamber. The accelerating relay 227 again functions to energize the accelerating contactor 431 so that the motor is accelerated as described above. As the charging fork and carriage approach the limit of their travel the carriage limit switch LSC operates to close its contacts 43'! and 438 while its contacts 426 and 436 are operated to their open positions. The opening of the contacts 426, it will be observed, deenergizes the direction switch 282. The closing of the contacts 437 of the limit switch LSC completes the energizing circuit for the down-direction switch 382 of the lever motor 81. As before, when this direction switch is closed. the contacts 456 operated with it are closed to complete an energizing circuit for the trip coil 457 of the sequence relay L6, which relay is thereupon operated to its unlatched position, with its contacts 406 closed, partially to complete an energizing circuit for the out-direction switch 280 of the carriage motor 9'7.

It will be observed that the contacts 453 operated with the lever motor direction switch 382 are closed to complete an energizing circuit for the trip coil 452 of the sequence relay L1. This circuit may be traced from the supply line 252 by conductor 454, trip coil 452. contacts 453 of the direction switch 382, and by conductors 455 and 259 to the other supply line 253. The sequence relay L1 is thereupon operated to its unlatched position.

As the lever motor 81 lowers the charging fork 43 it will be observed that the charge 62 of steel bars is placed upon the roll table within the preheat chamber, while the third charge of steel bars which has been placed on the charging fork is transferred to the forward position which was formerly occupied by the charge 62. As the charging fork reaches its lower position the cam limit switch LSA again functions to close its contacts 388, 407 and 408, while its contacts 409, 410 are opened. The opening of the contacts 410 of the limit switch LSA serves to deenergize the down direction switch 382 of the lever motor. The closing of the contacts 408 of the limit switch LSA completes an energizing circuit for the outdirection switch 280 of the carriage motor 9'7, as has been described above. The motor 9'7 thereupon functions to drive the carriage and the charging fork from the preheat chamber. As the carriage approaches its outer limit of travel, the carriage limit switch LSC operates to open its contacts 437 and 438, and to close its contacts 426 and 436. The opening of the contacts 438 interrupts the energizing circuit to the direction switch 280 which is thereupon operated to its open position to deenergize the carriage motor 97 and to establish a dynamic braking circuit through the braking resistor 440 so that the carriage is quickly brought to a standstill.

The closing of the contacts 436 of the limit switch LSC completes an energizing circuit for the lowering direction switch 3'79 of the side door motor 38. This motor is thereupon energized in a direction to lower the side door. The contacts 480 operated with this switch are closed to complete an energizing circuit for the sequence relay L3. This sequence relay is thereupon operated and latched into its closed position with its contacts 487 closed and its contacts 267 open. As soon as the side door 39 reaches its lower position the track limit switch LSB2 operates to close its contacts 387 and to open its contacts 4'73, the latter of which serves to deenergize the lower-direction switch 3'79.

Inasmuch as the oscillation of the rollers is next in order it will be seen that the closing of the contacts 487 of the sequence relay L3 serves to complete an energizing circuit for the contactor 501 which contactor is thereby operated to its closed position to establish the shunt connection through the resistance 490 for the armature of the motor 30. The contacts 514 operated with the contactor 501 are closed to complete the energizing circuit for the clutch operating coil 515. The clutch is thereupon operated to connect the limit switch LSK with the roll motor 30. A circuit is also completed by reason of the closing of the contact 487 of the sequence relay L3 for the forward direction switch 269 of the roll motor. This circuit may be traced from the supply line 252 by conductor 502, contacts 487 of the sequence relay L3, conductor 522, contacts of the timing relay TF, conductor 524, contacts 525 of the pushbutton station 526, conductor 527, contacts 528 of the limit switch LSK, contacts 362 of the relay 301, contacts 3'70 of the sequence relay L5, conductor 582, operating coil 530 of the direction switch 269, interlocking contacts 531 of the direction switch 532, and by conductors 533, 265 and 259 to the other supply line 253.

As described above, the opening of the contacts 267 of the sequence relay L3 serves to de energize the accelerating contactors 495, 496 and 588, so that when the direction switch 269 is closed to energize the roll motor 30, the motor functions to drive the rolls at very low speed. As before, the field accelerating relay 536 operates to short circuit the field resistance 535 to further insure low speed operation of the roll motor 30.

The limit switch LSK thereafter functions to I of the roll motor.

control the energization of the roll motor 30 in conjunction with the timing relays TF and TR so that the charge 62 in the high heat chamber and charge 63 now in the preheat chamber are reciprocated to and fro for the reasons and purposes that I have already explained.

It will be remembered that as soon as the contacts 344 of the end door limit switch LSD were closed, the master timer 232 was again set into operation. As soon as the expiration of the time interval, however, the master timer 232 again times out to close its contacts 233. The roller motor 30, however, continues the reciprocation of the work in the heating chamber until the predetermined point in the forward direction of rotation is reached at which point the contacts 550 and 551 of the limit switch LSK are operated to their closed positions. When this occurs, it will be observed that the contacts 551 serve to complete an energizing circuit for the raise direction switch 552 of the end doors, this circuit being traced as before from the supply line 252 by conductor 554, contacts 551 of the limit switch LSK, conductor 555, contacts 233 of the master timer, conductors 556 and 837, contacts 557 of the end door limit switch LSD, conductor 558, operating coil 559 of the raise direction switch 552, interlock contacts 560 of the lower direction switch 381 and by conductors 323 and 285 to the other supply line 253. Consequent to the closing of the raise direction switch 552, the end door motor 32 is energized in a direction to raise the end doors.

The closing of the contacts 562 operated with the direction switch 552 again serves to complete an energizing circuit for the trip coil 565 of the sequence relay L3, this circuit as before being dependent upon the closing of the contacts 550 of the limit switch LSK and the closing of the contacts 562 of the direction switch 552. The sequence relay L3 is thereupon operated to its unlatched position with its contacts 487 open and its contacts 267 closed. The former contacts as before, serve to deenergize the contactor 501 which is operated to its open position, while the contacts 514 operated with this contactor are open to deenergize the clutch operating coil 515. The opening of these contacts, it will be remembered, also serves to deenergize the direction switch 269 which immediately operates to its open position thereby closing its contacts 268 operated with this switch to complete the circuit partially completed by the contacts 267 of the sequence relay L3 for the accelerating relay 226, which relay is operated to open its contacts.

Consequent to the arrival of the end doors in their upper positions, the end door limit switch LSD operates to close its contacts 571, 573 and 574, while its contacts 344, 557 and 575 are operated to their open positions. The opening of the contacts 557 deenergizes the raise direction switch 552 of the end door motor 32, while the closing of the contacts 573 serves to complete an energizing circuit for the forward switch 269 This circuit may be traced from the supply line 252, by conductor 554, contacts 551 of the limit switch LSK, contacts 573 of the end door limit switch LSD, conductor 580, contacts 362 of the relay 363, contacts 370 of the sequence relay L5, conductor 582, operating coil 530 of the direction 269, interlock contacts 531 of the direction switch 532, and by conductors 533, 265 and 259 to the other supply line 253. Following the closing of the direction switch 269 the roll motor 30 is accelerated to its full speed in the manner described above when the charge 63 was transferred from the preheat chamber to the high heat chamber. The rotation of the motor 30 in the forward direction now serves to transport the charge 63 of steel bars to the runout table, while the charge 62 is transferred to the high heat chamber.

As the leading end of the steel bars 63 passes through the end door 33 of the high heat chamber, the bumper switch B2 will be operated to open its contacts 386 and 606. The opening of the contacts 386, it will be observed, interrupts the supply circuit to the crane hoisting motor 37, normally traced by the conductor 640 in order that the crane may not be operated while the work is on its way from the high heat chamber to the runout table. The opening of these contacts also interrupts the energizing circuit for the up direction switch 385 of the lever motor so that the levers may not be operated while the charge of steel bars in the preheat chamber is being transported to the high heat chamber. The opening of the contacts 606 of the bumper switch B2 serves to interrupt the lowering circuit of the direction switch 381 of the end doors so that the end doors may not be lowered until the work has been entirely transported from its former position to its new position, that is to say, until the charge 63 has been transferred to the run-out table while the charge 62 has been transferred to the high heat chamber. As soon as the trailing ends of the steel bars 63 leave the operating lever of the bumper switch B2, this limit switch is again operated to close its contacts 386 and 606.

It will be remembered that the bumper switch B3 located at the end of the run-out table is arranged to be operated by the leading ends of the work as it arrives in position on the runout table. As soon as the leading ends of the work arrive in position the contacts of the bumper switch B3 are thereby closed to complete an energizing circuit for the operating coil of the relay 361. This circuit may be traced from the supply line 252 by conductor 641, contacts 01' the bumper switch B3, conductor 642, operating coil of the relay 301, and by conductors 643 and 285 to the other supply line 253. The relay 301 thereupon operates to open its contacts 300 and 362 and to close its contacts 644, 646 and 647, the opening of the contacts 362 serving to interrupt the energizing circuit to the direction switch 269. As explained above, the opening of the direction switch 269 serves to complete an energizing circuit by means of its contacts 268 for the accelerating relay 226, which relay operates to open its contacts so that the accelerating contactors 495, 496 and 588 are deenergized and operated to their open position to re-insert the series resistances 497, 498 and 500 in the armature circuit of the motor 30. The contactor 597 is operated to its closed position by reason of the potential difference existing across the armature and the series resistances 497, 498 and 500 of the motor 30. A dynamic braking circuit through the resistor 598 is thereby established and the motor 30 will be braked to a standstill. The field relay 536 again functions to increase the excitation produced by the field winding 534 on the motor 30 thereby increasing the dvnamic braking effort of the motor 30.

The closing of the contacts 646 of the relay 301 serves to complete an energizing circuit for the up-direction switch 385 of the lever motor. This circuit may be traced from the supply line 252 by contacts 386 of the bumper switch B2, contacts 387 of the side door track limit switch LSH2, contacts 388 of the limit switch LSA conductor 630, contacts 646 of the relay 301, conductor 633, operating coil 389 of the up-direction switch 385, interlock contacts 391 of the direction switch 382, and by conductors 393 and 259 to the other supply line 253. The up-direction switch 385 is thereby closed to energize the motor 81 in a direction to raise the charging fork 43. The closing of the contacts 634 operated with the direction switch 385 again serves to complete an energizing circuit for the sequence relay L1. This relay is operated to its latched in position with its contacts 384 closed to maintain the energizing circuit for the up-direction switch 385 until this direction switch is deenergized by the opening of the contacts 388 of the lever limit switch LSA. The closing of the contacts 399 operated with the direction switch 385 again serves to complete an energizing circuit for the sequence relay L6 which is operated to its latched in position partially to complete an energizing circuit for the in-direction switch 282 of the carriage motor 97. The contacts 409 of the lever limit switch LSA are again closed as soon as the charging fork 43 has been raised to its upper position to complete an energizing circuit for the raise-direction switch 412 of the side door motor 38. The energizing circuits described and traced above are again completed so that the side door is raised to its upper position, the carriage is moved towards the preheat chamber until the charging fork 43 is in a position to deposit the next load within the preheat chamber. The levers are operated to lower the charging fork, the sequence relays L1 and L6 are tripped and operated to their unlatched positions. The carriage motor 97 is energized to drive the carriage to the preheat chamber, while the side door motor 38 is again energized to lower the side door.

consequent to the closing of the relay 301 an energizing circuit was completed through its contacts 647 for the lowering direction switch 381 of the end door motor 32. This circuit may be traced from the supply line 252 by conductor 601, contacts 647 of the relay 301, contacts 574 of the end door limit switch LSD, conductor 605, contacts 606 of the bumper switch B2, conductor 60'7, interlock contacts 608 of the raise direction switch 552, operating coil 609 of the lower direction switch 381, and by conductors 323 and 285 to the other supply line 253.

It will therefore be observed that the end doors are lowered just as soon as the steel bars have arrived in position on the run-out table. In each case provision is made so that the end doors are lowered at the same time that the side door is being raised. This interlocking of the circuit serves to minimize the loss of heat due to the hoisting of the side door and of the end doors. For example if both the side door 39 and the end door 35 of the preheat chamber were in their full open positions at the same time, it will be seen that a substantial loss of heat might take place due to a draft which might result through the preheat chamber 10.

The opening of the contacts 300 and the closing of the contacts 644 of the relay 301 initiate the operation of the hoisting motor 37 so that the load 63 which has arrived on the run-out table is immediately transported to the quenching tank. It will be remembered that the energizing circuit for the accelerating contactors 298 and 309 of the hoisting motor 37 were traced through the contacts 300 of the relay 301. Therefore, as soon as the relay 301 operates to open its contacts 300 the contactors 298 and 309 were operated to their open positions, due to the interruption of their energizing circuits.

The closing of the contacts 644 of the relay 301 serves to complete an energizing circuit for the sequence relay L7. This circuit may be traced from the supply line 252 by conductor 299, contacts 644 of the relay 301, conductor 645, operating coil 648 of the sequence relay L7, and by conductors 404 and 259 to the other supply line 253. The sequence relay L7 is thereupon operated to its latched-in position with its contacts 655 closed to complete an energizing circuit for the hoisting relay 290. This circuit may be traced from the supply line 252 by contacts 386 of the bumper switch B2, conductor 640, contacts 655 of the sequence relay L7, contacts of the track type limit switch LSH2, conductor 658, contacts 659 of the limit switch LST operated by the trolley motor 48, conductor 660, interlock contacts 662 of the lowering relay 293, operating coil 663 of the hoisting relay 290, and by conductor 665 to the other supply line 253. The hoisting relay 290 is thereupon operated to open its contacts 303 and 289 while it closes its contacts 666, 667, 668 and 670. The opening of the contacts 303 serves to prevent the subsequent energization of the accelerating contactors 298 and 309 through the circuit completed by the contacts 644 of the relay 301. The opening of the contacts 289 of the hoisting relay serves to deenergize the field accelerating contactor 287, which contactor is thereby operated to its open position. The closing of the contacts 667 of the hoisting relay 290 serves to complete an energizing circuit for the field accelerating contactor 312 which circuit may be traced from the supply line 252 by conductors 274, 276 and 314, contacts 667 of the hoisting relay 290, conductor 672, operating coil 316 of the contactor 312, and by conductor 317 to the other supply line 253. The closing of the contacts 666 of the hoisting relay 290 completes the energizing circuit of the time closing relay TR2. This circuit may be traced from the supply line 252, by conductors 274, 276, 798, contacts 666 of the hoisting relay, operating coil of the relay TR2 and by conductor 665 to the other supply line 253.

The closing of the contacts 670 of the hoisting relay serves to complete an energizing circuit for the hoisting direction switch 676. This circuit may be traced from the supply line 252 by contacts 386 of the bumper switch B2, conductor 640, contacts 655 of the sequence relay L7, contacts of the track type limit switch LSH2, conductor 658, contacts 659 of the trolley limit switch LST, conductor 660, interlock contacts 662 of the lowering relay 293, contacts 670 of the hoisting relay 290, conductor 677, operating coil 678 of the hoisting direction switch 676, and by conductor 665 to the other supply line 253. The hoisting direction switch 676 is thereby closed to energize the hoisting motor 37 through a circuit which may be traced from thepositive source of supply, hoisting direction switch 676, series resistances 680 and 681, the armature of the hoisting motor 37, series field winding 682, series brake coil 683, contacts of the field accelerating contactor 312, (which contacts by-pass the resistances 684 and 686) and by resistance 687 to the negative source of supply.

When the hoisting direction switch 676 closed, the contacts 688 operated with this switch were closed to complete an energizing circuit for the

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