US2802657A - Fast heat and soak furnace for extrusion - Google Patents

Description

5 Sheets-Sheet 1 Aug. 13, 1957 J. D. NESBITT ETAL FAST HEAT AND SOAK FURNACE FUR EXTRUSIOK Filad May 7, 1953 M h, R

Aug. 13, 1957 J, D. NESBITT ETAL FAST HEAT AND SOAK FURNACE FOR EXTRUSION Filed May 7, 19 53 3 Sheets-Sheet 2 5&5 5/2-2 EMPF V FUZAMCE 4 [me/ml: P55

INVENTOR.

United States Patent Office 2,802,657 Patented Aug. 13, 1957 FAST HEAT AND SOAK FURNACE FOR EXTRUSION John D. Nesbitt, Sylvania, and Theodore W. Munford, Toledo, Ohio, assignors to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application May 7, 1953, Serial No. 353,592

16 Claims. (Cl. 263-36) This invention relates to an improved method and apparatus for heating metal billets, and is particularly adapted to the uniform, substantially oxide-free heating of nonferrous billets for extrusion operations.

When billets are heated in high heat head, or high speed, furnaces, some non-uniformity of temperature in the billet is obtained, especially in heating copper base non-ferrous billets whose surface emissivity may vary so very much due to variations in surface finish or reflectivity. Due to the high temperature of the furnace walls, the work must be promptly discharged upon attaining the desired working temperature.

When billets are heated in furnaces whose walls are maintained at the desired final work temperature, such as conventional rotary furnaces, it is necessary to carry a large float" of work in the furnace to maintain a desired rate of delivery of heated work, often as many as or more times as many billets being in such a rotary furnace at any given time as would be in the high speed furnace. When heating relatively large billets of 4 to 10 inches diameter, in non-ferrous extrusion, often the entire run of a given analysis is in the furnace at once, and after that run the furnace must be adjusted to a new temperature and soaked at that temperature before the next heat may be charged into the furnace. With the relatively large mass of furnace refractory and relatively low heat input, a large proportion of furnace time is lost in such rotaries for changing stock Whereas the high speed furnace is easily and quickly adjusted to such a change by rapid change of wall temperature or firing rate, or by merely resetting the time clock for the pusher mechanism.

Some materials require a definite period of time at extrusion temperature before they will extrude properly. For example, some Admiralty brass must be soaked two minutes to avoid crumbling in the die or severe blistering of the extruded shape. The soak time serves to diffuse the dendritic structure out of a cast billet, after which it will extrude properly.

If on the other hand, the billet is exposed to working temperature for too long a time, as when it is by-passed in a rotary furnace and is allowed to remain 90 minutes or so longer in the furnace, the billet may develop large grain structures, low zinc surface, oxidized surface, or other undesirable conditions.

This invention is designed to avoid the shortcomings of the prior art and to provide superior heating of billets in a more flexible, yet economical apparatus.

For a consideration of what we believe to be novel and our invention, attention is directed to the following portion of the specification and the drawings and concluding claims thereof.

In the drawings:

Fig. l is a longitudinal sectional view ratus embodying this invention.

Fig. 2 is a transverse sectional view of the heating furnace shown in Fig. I.

of furnace appa- Fig. 3 is a transverse sectional view of the holding furnace shown in Fig. 1.

Fig. 4 is a horizontal sectional view of the apparatus of Fig. I.

Fig. 5 is a representation of hydraulic control apparatus for the furnace apparatus.

Fig. 6 is a representation of the electrical control circuit for the furnace apparatus.

Fig. 7 is a detail view of a valve and control.

According to this invention a cylindrical heating furnace 11 is maintained at a temperature substantially higher than the final desired work temperature, by tangential, direct firing; work is advanced through the heating furnace on a schedule by automatic conveying means timed to discharge the work at the final desired temperature; the work W is automatically discharged into a holding furnace 12, where it is retained so long as is necessary to equalize its temperature and for such metallurgical reasons as may be extant; and the work is then discharged from the holding furnace for the hot working operation. In the heating furnace a controlled atmosphere which is non-oxidizing for non-ferrous work such as brass prevails by virtue of constant firing of a rich mixture of fuel and air to maintain at least 0.7% CO2 in the furnace. The holding furnace is also a controlled atmosphere furnace by virtue of burners 13, or by admission of steam or specially prepared flue gas or other atmosphere gas through an atmosphere gas inlet 14. Where it is not feasible to maintain rich combustion products from direct fired burners 13, a mufiie or radiant tube furnace may be provided as is well known and is more common in the heating of ferrous Work.

The conveying and control mechanism is designed to normally load work into the heating furnace on a short stroke push by the pusher 15. discharging one billet at a time, or to empty the heating furnace one billet at a time by a successively longer stroke by the pusher, responsive to the operator's selection; and to normally discharge work from the holding furnace by long strokes of its pushers, or to store work in the holding furnace by short pusher strokes, the work from the heating furnace being alternately delivered to the rows of the holding furnace, and the holding furnace pushers l6 and 17 being automatically, alternately actuated. The controls are also designed to provide for independently discharging one of the holding furnace billets responsive to operator selection without disturbing the automatic cycle operation of the heating furnace.

The combination taught herein of a high speed, direct fired heating furnace, a controlled atmosphere holding furnace, and automatic conveying means for moving billets through the heating furnace and into the holding furnace at the desired working temperature has provided industry with a new heating tool which, with a minimum investment in space and equipment, delivers a higher quality product than heretofore obtainable in equipment with the high heating capacity and degree of flexibility hereby provided.

It is well known that excessive scale from long exposure to high temperature oxidizing conditions changes billet dimensions and useful metal volume, and causes severe shortening of die life, or scored tubing, or requires scale removal operations which at best quite unsatisfactory. It is also known that excessive time at working temperatures, varying from 700 F. to 2000 F. for nonferrous work, causes undesirable metallurgical effects such as grain growth or dezincification which are commonly encountered in heating in controlled atmosphere furnaces held at the desired work temperature; and it has been found that due to variations of surface condition of work to be heated, the rate and character of oxide formattion varies from piece to piece and around one piece, so that uniform heating from just a high speed heater is not generally possible due to the resulting variations of surface emissivity of the work.

These inherently poor heating characteristics are all washed out" by the proper combination of a high speed heater and an atmospheric holding furnace. The high speed heating furnace may form a very insignificant amount of scale or oxide unless combustion therein is properly controlled, and heats rapidly with good economy and with few pieces under heat at any time. For example, the heating of an 8 inch diameter Admiralty brass billet to 1485" F. normally requires 90 minutes in a 1485 F. furnace. To deliver one per minute requires a furnace of 90 billets capacity. With a rapid heating furnace wall temperature of about 2600 F., giving a 1115 F. heat head, heating time is reduced to one-tenth, 9 minutes, and a furnace capacity of 9 billets will deliver one billet per minute. Thus a change in billet size or material can be accommodated by a changed push rate or wall temperature in a very few minutes, rather than a matter of hours, due to relatively high heat input rate/ heat storage capacity ratio in the high speed furnace. Once the billet is at temperature, even though scale free, it must be maintained so for a period, hence a small, controlled atmosphere holding furnace is used. It normally holds only one billet per row, so that each billet is held therein two minutes; but when short production delay requires, work is charged into the heating furnace, and the heating furnace is discharged into the holding furnace without delivering billets therefrom. When ready to operate the press again, the stored billets are ready in the holding furnace. If a long delay is encountered, loading is stopped at the heating furnace, and its billets are stored as above. The holding furnace may be cooled below scaling temperatures, and the billets discharged for reheating, when the delay becomes excessively long.

Ordinarily the control mechanism for the valve 40 (shown diagrammatically in Fig. 7) is set to maintain the internal temperature of the heating furnace at the desired high level, the expected heat absorption by billets of predetermined size passing through the heating furnace at a predetermined rate being a factor that is considered in setting the valve control mechanism. If. for hypothetical example. billets of a size such that a row of nine billets will occupy the furnace from inlet end to exit end are to be heated to a temperature of l485 F. and then discharged at the rate of one per minute, the valve control mechanism may be set to maintain the internal wall of the heating furnace at some such temperature as 2600" F.

The controls shown in diagrammatic Fig. 6 are set to actuate the solenoids B1 and B2 shown in diagrammatic Fig. to operate the valve 64 and thus reciprocate the pusher 15 at one minute intervals and to operate the valve 65 and thus swing the rail switch 27 from one side to the other at one minute intervals. Hence, the rail switch delivers a billet alternately to each holding furnace rail every other minute.

In this hypothetical example the controlled atmosphere of the holding furnace is maintained at about 1485 F. After remaining in the holding furnace for two minutes the billets are alternately discharged, being pushed out of the exit end of the holding furnace by the pushers 16 and 17 which are acted upon by liquid admitted to cylinders 62 and 63 by valves 66 and 67 operated by solenoids D and C as indicated in Fig. 5.

Both the heating and the holding furnaces are designed to be self-emptying on an automatic cycle for any size of billet, without requiring the loading of dummy or scrap billets to push out the billets to be worked, and each billet heated including the last one is suitable for normal production use. Other novel and desirable features will be apparent as the apparatus is described.

The heating furnace is preferably of the type disclosed in patent to Bastress et a1. 2,563,908, and comprises a shell 18 lined with refractory 21 and some insulation 22. Work is moved through the furnace on water cooled skid rails 23 by the pusher actuated by a hydraulic pusher cylinder 24 through carriage 9.

The pusher 15 is internally cooled by water supplied thereto by flexibly coupled pipes 19. This pusher is normally operated on a short stroke which scarcely exposes it to the heat of the furnace, so water flow will normally be about five gallons per minute. When the heating furnace is to be emptied, the pusher will be more severly exposed and will require up to 135 gallons per minute of cooling water with the same temperature rise as before. This variation of flow is provided by a bypass solenoid surge valve 20, as will be described in some detail. The skid rails are supported on piers 25. Work in the form of billets W is delivered to the charging platform 26, pushed through the furnace on the skid rails, and delivered therefrom by a rail switch 27 which is actuated by its hydraulic cylinder 61 to deliver the work to alternate left and right hand sides of the holding furnace, as will appear. The heating furnace is supported on framework 30 above base 8 by a plurality of rollers in hinged arms 31 which are adjustable by bolts 32, to allow the furnace to expand from the switch end, or the discharge end of the furnace, where it is fixed to the framework rails 30. Aerated fuel for combustion is delivered from a gas main 39 with a valve 40, through ports 33 by nozzles 34, and is controlled to maintain over 0.7 CO in the furnace, preferably about 1.5%. A temperature reading pyrometer may be used to determine work temperature, but generally speaking the rate of advancing work must be predetermined because such pyrometers are not reliable controls due to surface ternperature variations and surface emissivity variations. Flue gas exhausts from the heating furnace through end tlues 36. A discharge door 37 is desirably adjusted to close down the furnace opening to a minimum while work is advancing to reduce heat loss from the furnace.

The holding furnace may be of any controlled atmos phere type; and for non-ferrous work such as brass, copper and the like, a direct fired furnace heated by rich burners, augmented where necessary with steam or a prer pared atmosphere gas such as flue gas, is preferred.

The holding furnace 12 comprises a shell 38 lined with refractory 41 and insulation 42, and is supported on framework rails 43 by rollers 44 in hinged brackets 45 to expand from the switch end, or charge end, of the furnace, where it is fixed to the rails 43. The height of the furnace is adjusted on the rails by bolts 46, and pin 47 is the pivot for the hinge action. The top half of the furnace chamber is assembled as a separate unit and secured to the bottom half by bolts 48. Thus the furnace is more easily assembled. The rails 51 and 52 are preferably of heat resisting alloy steel suitable for the reducing or non-oxidizing atmosphere maintained in this furnace chamber. The rails 51 and 52 are set on ties 53 which are supported on piers 54 between which the tunnel burners 13 are fired.

The hydraulic circuit is illustrated in some detail in Fig. 5, where a pump 55 is interposed between high and low pressure hydraulic control main pipes 56 and 57. The several hydraulic cylinders 24, 61, 62 and 63 actuate respectively the heating furnace pusher 15, the switch 27, and the left and right hand holding furnace pushers l6 and 17. The hydraulic control valve 64 for the pusher cylinder 24 is a spring centered valve, springs not shown. with solenoid coils B1 and B2 for moving the valve to its forward and reverse pusher positions. The switch cylinder 61 is controlled by valve 65 which is moved into left and left rail positions by solenoid coils A1 and A2. The left holding furnace pusher cylinder 62 is controlled by a spring return valve 66 which is moved to its forward position by solenoid coil D and to its return position, when the coil D is de-energized, by a spring 68 built into the valve. The right holding furnace pusher cylinder 63 is controlled by a spring return valve 67 which is moved to its forward position by a solenoid coil C and to the return position, when the coil C is deenergized, by a spring 69. The motions of the cylinders are integrated by an electrical control system, including limit switches LS3, LS and LS4 contacted by pusher 15, L81 and LS2 contacted by the switch 27, LS9, L810, L811 and L814 contacted by pusher 16 and LS7, LS6, LS8 and L513 contacted by pusher 17, together with photo-electric cells, or photo relays PR1 and PR2 and their corresponding light sources 71 and 72.

The electrical control system, illustrated schematically in Fig. 6, utilizes control relays CR numbered 1 through 7, 9, 1t] and 11, of which CR1, CR2, CR3, CR5 and CR6 have latch and trip coils L and T, the balance of the control relays having single coils and spring trip. The system will include conventional safety devices not shown, and a cycle will ordinarily be initiated by a timer (or a manual push button) of which only the contact T-l is shown. By setting the timer clock to the desired push cycle, such as one minute, the contact T-l will be closed each minute to start the cycle, presuming the hydraulic pump is operative and all other necessary safety conditions are met.

Pushbutton P83 is a selector switch marked Normal- Store. In the Normal" position the holding furnace pushers move forward until reversed when work interrupts the light beam of a photoelectric relay PR2 at the discharge end of the holding furnace. When PB3 is in the Store position, the pushers for the holding furnace are put on short stroke, reversed by L810 or LS6, so they just advance the billet into the furnace.

Pushbutton P84 is a Reset" momentary contact button used to reset a safety circuit. When a billet discharges initially from the heating furnace, it interrupts the light beam of a photoelectric relay PR1 at the discharge of the heating furnace, and starts running of a time clock in CR7. Unless another billet resets the timer by interrupting the beam before the clock times out, it will automatically shut down the heating furnace by closing a fuel valve thereto in the time set, such as six minutes. This is a safety device to prevent overheating an empty furnace.

Pushbutton PBS is a selector switch marked Normal- Empty Furnace. When this is in Normal position and LS3 is depressed by the heating furnace pusher, the holding furnace pushers may be operated momentarily by pushing pushbuttons PB6 and PB7 for the pushers 17 and 16. The last billet cannot be discharged from either row of the holding furnace when PBS is in the Normal position, but it may be discharged by moving PBS to the Empty Furnace position, then pressing PB6 or PB7. Pushbuttons PB6 and P137 are normally to be used to remove stored billets from the holding furnace after a short delay during which the heating furnace was not emptied.

Switch S12 is depressed to empty the heating furnace. Only its three contacts (312-1, S122, and 812-3) are shown.

The various limit switches are depressed as follows. LS3, LS9 and LS7 by the several furnace pushers in a back position; LS1 and LS2 by the switch cylinder, or switch, in the left and right positions thereof; LS5, L810 and LS6 by the respective furnace pushers when a billet pushed thereby is just within the respective furnaces; LS4, LS14 and L513 by the pushers at the extreme ends of their forward strokes; and LSll and LS8 by the holding furnace pushers when they are within one billet length of discharging a billet from the holding furnace. These limit switches may desirably be adjusted for largely varying billet sizes, but generally will remain fixed.

The circuit is designed to provide certain safety features. The holding furnace pushers will not move forrespective I ward unless the heating furnace pusher has finished its forward stroke, nor will the pushbuttons PB6 and PB7 function unless there is also sufficient time for the holding furnace pusher to complete a stroke before start of the next cycle. These switches cannot operate unless both holding furnace pushers are in the back position.

The electrical schematic of Fig. 6 is shown at the start of a cycle with all pushers back and the switch 27 directed to the left hand row. All limit switch contacts are in normal position except for LS3, LS1, LS9 and LS7. Time delay relay CR9 is set for the elapsed time between the end of one cycle and the start of the next cycle, as controlled by the timer which controls contact T-l. Time delay relay CR7 should be set for a time in excess of the normal period between two cycles of the heating furnace, so that a push that does not discharge a billet from the heating furnace will cause the heating furnace to be shut down by closing the valve in Fig. 7.

To initially load the heating furnace, with the holding furnace empty, PB3 and PBS are both placed in their Normal" positions. The timer, or a manual push button, closes the contact T-1 for about 2 seconds, then opens. Coil of CR1 is energized, and CR1 latches, closing contact CR1-1 and opening contacts CR1-2 and CR1-3.

. The closing of CR11 energizes coil A1 and causes the switch to move from the left to the right row of the holding furnace. At the start of the movement LS1 is released, opening LSl-l and LSl-Z and closing LSI3. At the end of the motion LS2 is depressed, closing contacts LS21 and L824! and opening LS2-3.

The solenoid coils A1 and A2 are shown in the third and fourth horizontal leads connected to the vertical line at the right side of Fig. 6 and are shown also at left of center of Fig. 5 for moving the hydraulic control valve 65 for the cylinder 61 which swings the rail switch 27 laterally. It is to be remembered that the lines 56 and 57 of diagrammatic Fig. 5 represent piping and not wiring.

Closing of LS1-3 latches CR3, opening contacts CR3-2, CR3-3 and CR3-4 and closing CR3-l. Closing of LS22 trips CR1, opens CR11 and closes CR12 and CR1-3. Opening of CR11 de-energizes A1; and closing of CR1-3 latches CR2, closing CR2-1 and CR22 and opening CR2-3 and CR2-4, and also latches CR5, which closes CR51 and CRS-Z and opens CR5-3 and CR54. Closing of CR1-3 also energizes B1, causing the heating furnace cylinder to move the pusher 15 into the furnace, pushing the first billet from the loading station 26 into the heating furnace.

The solenoid coils B1 and B2 are shown in the ninth and tenth horizontal leads connected to the vertical line at the right side of Fig. 6 and are shown also at the left side of Fig. 5 for moving the hydraulic control valve 64 for the pusher cylinder 24 which is pictorially shown in Fig. l as operatively connected, through the carriage 9, to the pusher 15.

At the start of the motion LS3 is released, opening its normally open contact LS3-1 and closing its normally closed contacts LS3-2 and LS3-3. When the billet is in the furnace, LS5 is depressed, closing LS5-1. On closing of LS32, CR9 is energized and CR9-1 closes. Closing of LS5-1 trips CR3, opens its contact CR31 and closes CRIS-2, CR3-3 and CR3-4. Opening of CR3-I tie-energizes B1, and closing of CR3-4 energizes B2. The heating furnace pusher starts back, releasing LS5 and opening LSS-l, and when it gets back LS3 is depressed, closing LS3-1 and opening LS3-2 and LS33.

The solenoid coil C is shown in the fifth horizontal lead connected to the vertical line at the right side of Fig. 6 and is shown also at the right side of Fig. 5 for moving the hydraulic valve 67 for the pusher cylinder 63 that acts upon the pusher 17 which causes billets to progress through the holding furnace. The pusher 17 is pictorially shown in Fig. 1.

Similarly the solenoid coil D is shown in the eighth horizontal lead connected to the vertical line at the right side of Fig. 6 and also at right of center of Fig. 5.

Closing of CR3-3 energizes C and as the right hand pusher 17 for the holding furnace starts forward, LS7 is released, opening contacts LS7-1 and LS7-2. When the pusher 17 has advanced to within one billet length of the end of the holding furnace, LS8 is depressed, closing its contact LS81 and opening LS82.

The solenoid coil D is shown in the eighth horizontal lead connected to the vertical line at the right side of Fig. 6 and is shown also at right of center of Fig. 5 for moving the hydraulic valve 66 for the pusher cylinder 62 that acts upon the pusher 16 which causes billets to progress through the holding furnace.

On opening of LS3-3, B2 is de-energized.

On opening of LS3-2, CR9 is tie-energized, and CR9-1 opens after the set time delay.

On closing of LS8-1, CR5 trips, opening CR5-1 and CR52, and closing CR5-3 and CR54.

Closing of CR53 closes circuits to push buttons P136 and PB7 until the circuits are broken when CR91 opens.

Opening of CR5-2 de-energizes C and the right hand pusher solenoid valve is moved by its spring, reversing the motion of the pusher 17. At the start of the reverse motion LS8 is released and at the end of such motion LS7 is again depressed.

The cycle is completed, and the next time the timer closes T1, the left hand holding furnace pusher will be actuated during the cycle, thus pushers 16 and 17 operate on alternate cycles. These alternate cycles will continue until a billet from the heating furnace reaches discharge and as it slides down the rails trips the photo relay PR1, momentarily closing PR11 and FRI-2. Then closing of FRI-1 latches CR6, which energizes CR7,

which starts its safety time.

Closing of PRl-Z trips CR3, which de-energizes B1 and energizes B2, reversing the heating furnace pusher, and the cycle continues as before, the heating furnace pusher now being reversed by discharge of billets through the PR1 light beam. When a billet has been charged into each row of the holding furnace, the next cycle changes by reversing the holding furnace pusher 17 when it pushes a billet past the light beam of the photoelectric relay PR2, closing PR21 and opening PRZ-Z momentarily. Closing of PR21 trips CR5, de-energizing C and reversing the pusher, and on subsequent cycles pushers 16 and 17 will be reversed by tripping photoelectric relay PR2 instead of by depressing limit switch L811 or LS8.

When there is a short delay, and the furnace operator wishes to temporarily store billets in the holding furnace without unloading or interrupting the heating furnace, PBS is placed in the Store position, and then during the next cycles the pushers l6 and 17 for the holding furnace will be reversed by depressing limit switches LSlt) and LS6, respectively, as will be readily apparent from Fig. 6. When the delay is over, PBS is reset to Normal, and billets will again be discharged on cycle. A stored billet may be discharged by depressing push button PB6 or PB7 immediately after each cycle is completed.

To empty the heating furnace, a switch S12 is depressed, opening S12-2 and S12-3. A third contact S12-1 may be used to energize a solenoid E in order to open a bypass valve 20 in a coolant line 19 to the pusher 15 to more effectively internally cool it during this unloading operation. Now the next cycle will advance the pusher 15 until PR] is tripped. This will energize CR7 and trip CR3, opening CR34 which de-energizes B1 and stops the heating furnace pusher from moving, and the balance of the cycle continues as before. On the next cycle, the pusher 15 will advance one billet length more, and it will continue to so advance until the heating furnace 11 has been emptied. On the first cycle after furnace 11 has discharged its last billet, the pusher 15 will advance until limit switch LS4 is depressed. This will close (iii LS4-1, which energizes CR4, which locks in by closing CR4-1, and closes CR42 which energizes B2 and reverses the pusher cylinder for pusher 15.

If only the heating furnace is to be emptied, storing billets in the holding furnace is provided for by placing PB3 in "Store position. The stored billets can then be discharged automatically by returning to a Normal position.

When emptying the heating furnace, with switch S12 depressed. as soon as the pusher 15 releases LS3, solenoid E for valve 20 in the water pipe 19 by-pass line is energized. Flow of water is thus automatically increased for long stroke operation over the flow required for short stroke operation. Since this flow may be increased 27 times from 5 to 135 G. P. M., this provision economizes the use of water for cooling.

We claim:

1. In apparatus for heating copper base alloy billets to a desired billet temperature for hot working, the combination of a heating furnace; a holding furnace; control means for maintaining the heating furnace at a temperature substantially in excess of said desired billet temperature by admitting fuel to be burned in the furnace to maintain a non-scaling atmosphere therein; second control means maintaining the holding furnace at the desired billet temperature means for maintaining a non-scaling atmosphere therein; conveyor means for moving billets into, through and from the heating furnace and into the holding furnace and timing control means for moving said conveyor means on an automatic cycle timed to discharge the billets from the heating furnace at said desired billet temperature.

2. In apparatus according to claim 1, the combination which comprises discharge means for automatically discharging billets from the holding furnace at the rate at which they are delivered thereinto.

3. In apparatus for heating metal billets to a desired billet temperature for hot working, the combination of a heating furnace; a holding furnace; first control means for maintaining the heating furnace at a temperature substantially in excess of the desired billet temperature; second control means for maintaining the holding furnace at the desired billet temperature; means for maintaining in the holding furnace a controlled gaseous atmosphere about the billets therein; conveyor means for moving billets into, through and from the heating furnace and into the holding furnace and timing control means for moving said conveyor means on an automatic cycle timed to discharge the billets from the heating furnace at the desired billet temperature.

4. ln apparatus for healing billets to a desired temperature for hot working, the combination of a heating furnace. a holding furnace; first control means for maintaining the heating furnace at a temperature substantially in excess of the desired billet working temperature; second control means for maintaining the holding furnace substantially at the desired billet working temperature", and means for conveying work into, through and from the heating furnace and into the holding furnace and timing and control means to cause said means for, conveying work to operate on an automatic cycle timed to discharge the billets from the heating furnace at said billet working temperature.

5. ln apparatus for heating metal billets to a desired billet temperature for but working, the combination of a heating furnace; a holding furnace; conveyor means for moving billets into, through and from the heating furnace; a pusher adapted to receive billets from the con veyor means and move them into, through and from the holding furnace; a first control circuit for controlling the length of stroke of the pusher to a short stroke which moves billets just into the holding furnace; a second c0n- 110i circuit cumnrisi means responsive to discharge of a billet frcr-r the h lium; furnace for reversing the pusher stroke after discharge of each billet by the pusher;

and switch means for alternatively connecting said first and second control circuits.

6. In combination, a furnace comprising wall means forming a heating chamber; work support means for supporting work pieces to be heated in the heating chamber; pusher means for pushing work pieces into the furnace; and control means comprising a radiating device and a sensing device arranged to be actuated by a work piece passing therebetween and adapted to reverse said pusher means upon the sensing of a work piece passing between said devices.

7. In combination, a furnace comprising wall means forming a heating chamber; work support means for supporting work pieces to be heated in the chamber; pusher means for pushing work pieces into the furnace; and control means comprising means responsive to discharge of a work piece from the furnace for reversing the pusher whereby to periodically and substantially continuously advance the work pieces through the furnace.

8. In combination, a furnace comprising wall means forming a heating chamber; work support means for supporting work to be heated in the heating chamber; pusher means for pushing work pieces into the furnace; and control means comprising a selector adapted to alternatively control the pusher to 1, repeatedly advance new work into the furnace when the selector is in a first position whereby work is periodically and substantially continuously advanced into, through and from the heating chamber, or 2, repeatedly advance a short distance through the heating chamber when the selector is in a second position whereby work in the furnace is periodically discharged therefrom to empty the furnace chamber.

9. The combination according to claim 8 which comprises means responsive to the discharge of work for interrupting the forward motion of the pusher when the selector is in the second position.

10. The combination according to claim 8 which oomprises means for supplying coolant to the pusher when the selector is in the second position, and for preventing said supply of coolant when the selector is in the first position.

11. In combination, a furnace for heating work pieces comprising support means for supporting a row of work pieces in the furnace, to be heated as they advance therethrough; a pusher for pushing said row at the charge end thereof; means for internally cooling the pusher by flow of coolant thereinto; and control means actuated by movement of the pusher to an advanced position for automatically increasing flow of coolant into the pusher as it progresses into the furnace.

12. The combination according to claim 11, wherein the control means comprises a limit means for maintaining flow of coolant at a reduced rate when the pusher is in a relatively receded position, and for maintaining 10 flow of coolant at an increased rate when the pusher is in a relatively advanced position.

13. In combination, a first furnace; at second furnace; first pusher means for advancing work through and from the first furnace; second pusher means for advancing said work through and from the second furnace; means for supporting a plurality of rows of work in one of said furnaces; and means for alternatively aligning said rows of work with a row of work in the other furnace to form alternative continuous paths of travel for work consecutively through said furnaces.

14. In combination, a direct fired heating furnace; a controlled atmosphere holding furnace; first support means for supporting a row of work in the heating fur nace; second support means for supporting a plurality of rows in the holding furnace; first pusher means for moving work into, through and from the heating furnace; second pusher means for moving work into, through and from the holding furnace; and means for aligning the row in the heating furnace alternatively with rows in the holding furnace to provide alternative paths of travel for work from the heating furnace moving through the holding furnace.

15. In combination, a heating furnace; a holding furnace; first conveyor means for moving work pieces into, through and from the heating furnace, and onto a second conveyor means; second conveyor means for moving work pieces into, through and from the holding furnace; and control means comprising a selector for controlling the second conveyor means to alternatively (l) convey successive work pieces into and through the holding furnace to short of and adjacent the discharge end thereof with corresponding discharge of work pieces therefrom whereby the holding furnace is maintained substantially empty as work progresses therethrough, or (2) convey work pieces into and adjacent the charge end of the holding furnace whereby a plurality of work pieces shall be conveyed into the holding furnace immediately after setting this selection without corresponding discharge of work pieces from the holding furnace.

16. In the combination according to claim 15, second control means for controlling the holding furnace conveyor to advance work in the holding furnace to discharge a work piece therefrom without advancing a corresponding work piece into the holding furnace.

References Cited in the file of this patent UNITED STATES PATENTS 1,697,757 Dahlstrom Jan. 1, 1929 1,742,652 Goodwillie Ian. 7, 1930 1,865,954 Powers July 5, 1932 1,922,888 Engelbertz Aug. 15, 1933 2,604,577 Strickland et a1. July 22, 1952 2,694,246 Hess et al. Nov. 16, 1954

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