EP3110981B1 - Method and system for thermally treating elongate, flat metallic material, in particular aluminum rolled ingots, in a ring hearth furnace - Google Patents

Description

The invention relates to a method for the thermal treatment of elongated, flat metallic material, in particular aluminum ingots, in an oven, which is connected to the temperature control and monitoring and furnace control with a higher-level process control system, as a furnace, a ring hearth furnace is used between a heat-insulated outer casing and a heat-insulated inner casing having a sealed against the housing, rotary ring hearth bottom, said closed with a heat-insulated ceiling ring hearth furnace is formed with at least one closable loading and discharge opening and is heated with gas or electric. Furthermore, the invention relates to a system comprising a ring hearth furnace for carrying out the method.

In a ring hearth furnace is a special form of a rotary hearth furnace, both types of furnace in the industry for a long time prior art and in the special form as a ring hearth in the steel industry, there especially in the forging industry for heating forging blocks, but also in the heat treatment , especially for carburizing example of transmission parts, are used. A rotary hearth furnace in ring type for heat treatment of such workpieces is by the DE 8422370.7 U1 known.

Also DE-A 32 31 225 relates to a ring furnace with a single, closable loading and unloading opening and lifting beam as a transport device wherein heating and cooling devices are provided in the furnace housing, which are arranged as tubes for blown air circulation.

Like from the DE 10 2009 053 343 A1 known, heating or homogenization of aluminum ingots until today almost always done in pusher heaters, which are operated with convection heating and in which the material moves through the furnace housing in the process and is heated up to the rolling temperature of 500 - 560 ° C.

The pusher furnace comprises the heat-insulating bricked housing with a seen in the direction of travel of the goods front end wall and a rear end wall, two the two end walls interconnecting longitudinal walls and a transport device for conveying the material to be treated through the oven housing. The transport device is designed such that it receives the elongated, flat Good transversely to the direction of passage. For this purpose, the material to be treated is placed on sliding shoes, which can be moved to arranged in the furnace chamber rails, usually by means of a hydraulic impact device.

The existing for loading and unloading of the goods on the front sides of the furnace doors have an opening cross-section, which must correspond to at least the dimensions of the treated, elongated flat metallic Guts. This indicates for aluminum billets whose length is a multiple of the thickness and which typically have a thickness up to 0.8 m, a width of up to 2.6 m and a length of up to 8.4 m, the loading and unloading or . Loading and unloading openings must release an extremely large passage, even if the aluminum ingots are pushed standing on their narrow, long end face through the oven.

As a result of the strong circulation of the blown air in the furnace, which also takes place immediately in front of the large frontal doors, a part of the blowing air, which is heated up to 650 ° C, is inevitably forced out of the kiln when the doors are open. At the same time, cold outside air flows into the furnace chamber, which then has to be brought to the treatment temperature. In addition, the hot aluminum ingots standing in front of the doors during loading and unloading emit a large amount of heat to the outside, which further worsens the energy balance.

For heating or homogenization of aluminum ingots continue to Tieföfen (see DE 2758292 C ), which are operated by means of convection heating. Such a deep furnace has a limited by insulated outer walls, rectangular furnace chamber which is closed at the top of a abheb- or attachable or horizontally movable stable furnace lid.

The lot sizes, which are equipped with low-temperature ovens, is usually between 30 t and 300 t, wherein the aluminum ingots standing upright on one of their narrow end faces in corresponding receptacles at the bottom of the furnace or flat lying on each other, separated by spacers, in the Tiefofen be charged.

During the convection heating of the deep furnace, the aluminum ingots are blown at high air speed. In the case of the aluminum ingots, which are stationary from the time of loading to the time of removal, uneven heating or partially excessive heating, so-called hot spots, can occur.

The aluminum rolling ingots are loaded and unloaded with the help of a block tongs movable over the deep furnace or a hall crane. If a heated aluminum ingot removed from the deep furnace, which is at least over a partial length and over the entire width of the furnace chamber extending furnace cover lifted or driven up, with a large part of the hot Bleglasungsluft exiting the furnace, which inevitably leads to a reduction of the preset oven temperature leads.

The invention has for its object to provide a method as defined in claim 1, a plant as defined in claim 11, to provide for the thermal treatment of aluminum ingots, with which the advantages of a proven in the steel industry with a simplified structure Ring hearth furnace with the proven in the aluminum industry Combine convection heating to allow significantly reduced energy consumption and variable modes of operation.

This object is achieved with a method according to the invention in that for convection heating introduced into the ring hearth furnace aluminum ingots provided on the ceiling, distributed over the circumference of the ceiling circulation fans from the chambered inside of the outer and inner housing Ringherdinneren upwardly sucked air along along arranged on the ceiling side, projecting into the hearth interior heating means is passed and then flows into itself on the inner walls of the outer and inner housing extending pressure channels from which the aluminum ingots with the during the heating phase increasingly warming air for heating the aluminum ingots via slot dies be blown.

The ceiling side numerous circulating fans and heating means, eg. B. directly heated gas with hot air or gas burners or electrically heated via Elektrostrahlheizrohre, in conjunction with the on the inner walls of the housing from top to bottom extending pressure channels allow in the ring hearth furnace, the heating of aluminum ingots with intensive convection in the closed circuit of the Furnace upwardly sucked and from there after the heating by the heating means along the inner walls down to the bottom with blowing of the aluminum ingots recycled air. The blowing air exits at a rate of about 40 m / s to 60 m / s from the slot nozzles distributed in the pressure channels to below the heating means over the entire height of the furnace interior. Thus, a highly efficient heat transfer with fast heating rate and high throughput can also be achieved for heating or heating of aluminum ingots. The rotation of the ring hearth floor with the aluminum ingots standing thereon ensures a very good temperature uniformity in the annealed material.

According to one proposal of the invention, the aluminum ingots are placed in a vertical position on the ring hearth bottom that their narrow longitudinal sides blown directly with the circulating air and their wide rolling surfaces are flowed around by the air. This results in an all-round flow around the aluminum ingots, which can still be favored by the fact that the aluminum ingots are placed on a resting on the ring hearth bottom, continuous storage rack in honeycomb form of heat-resistant cast steel.

The annular hearth furnace can be operated according to the invention for heating the aluminum ingots to rolling temperature and at the same time elevated temperature also for homogenizing the aluminum ingots, wherein the aluminum ingots cooled superficially after completion of the homogenization by blowing cold air into the ring hearth interior and the End of a certain cooling time by the residual heat of the aluminum ingots are heated again to rolling temperature. To homogenize the aluminum ingots with a residence time in the oven of z. B. 20 to 25 hours required temperature of the aluminum ingots of about 600 to
650 ° C is detected via thermocouples and reference junction directly in the programmable logic controller (PLC), in which also the temperature control takes place. For monitoring and control of the ring hearth furnace is formed with independent control zones and zone-independent control loops. The setpoints and parameters required for an annealing program are loaded from the existing higher-level process control system into the corresponding furnace control.

The ring hearth furnace advantageously allows operation with batchwise or continuous loading. Depending on the oven diameter and thus the dimensions of the usable, heated Ofenraums aluminum ingots with a total weight of for example 430 t, 530 t or 620 t are introduced at maximum load.

According to the invention, it is provided that during the batch operation, the empty ring hearth furnace or its utilization space is completely filled at the beginning of an annealing and completely emptied after reaching the rolling temperature of all aluminum ingots. In optional continuous operation, a heated aluminum ingot is removed and then the ring hearth bottom is further rotated one cycle before a cold aluminum ingot is introduced for reheating. It is thus created an empty space shortly before the removal of the heated to rolling temperature bar and the newly charged, cold ingot to avoid a negative temperature influence. For the same reason, the loading and unloading opening is closed after each removal or loading.

The heating process starts after the glow plug to be used has been called from the PLC. The air temperature is set to an excess temperature (max 650 ° C) and automatically maintained at this excess temperature. During the time in which is operated with excess temperature, the annular hearth bottom is advantageously continuously rotated slowly to avoid overheating on the narrow longitudinal sides of the aluminum ingots and to even out the temperature, which also significantly contributes to the rotation of the ring hearth bottom.

The ring hearth furnace allows for always constant loading and unloading a load with the aluminum ingots from above, z. B. by means of a hall crane, or from the side, z. B. by means of a handling robot.

Regardless of whether it is loaded from above or from the side, different loading strategies can be carried out, namely by circumferentially distributing the aluminum ingots with their wide rolling surfaces spaced one-lane or two-lane with then also spaced apart narrow longitudinal sides, ie on an outer circular path and a concentric inner circular path, can be placed in the hearth interior, the two-lane loading can be done with in-line or offset aluminum ingots. The two-lane loading with offset aluminum ingots and no fixed positions in relation to the ring hearth furnace allows a maximum batch weight, z. B. 620 t, compared to a two-lane loading of series shut down aluminum ingots with a batch weight of about 440 t, assuming the same dimensions and weights of the individual aluminum ingots.

A further measure according to the invention provides that the actual temperature of the aluminum ingots per zone, which is predetermined by each of the ceiling-side circulating fans, is periodically checked, for which purpose the rotational movement of the annular hearth bottom is briefly stopped. The measured values are processed in the PLC or the higher-level process control system and loaded into the furnace control.

In a system for carrying out the method according to the invention, the annular hearth furnace is distributed over the annular surface of the hearth floor flush with its annular surface on the one hand circulating fans and on the other hand both the inner wall of the outer housing and the inner wall of the inner housing associated heating means, wherein the circulation fans and the heating means are passed through the ceiling reaching into the upper annular hearth inside, and formed with slot-nozzle having pressure channels extending below the heating means on the inner walls of the outer and the inner housing. The units required for the convection heating of a ring hearth furnace are thus easily accessible for the maintenance personnel, wherein a simple removal and installation of the circulation fans and the heating means with the help of the hall crane is possible. It is proposed that gas burners are provided for heating the annular hearth furnace formed with exhaust pipes and cooling air supply lines as heating means, which are spaced from one another forming an outer housing burner ring and an inner housing burner ring, wherein their burner tubes adjacent to the inner walls of the outer and the inner housing proceed in the upper ring hearth inside. The aluminum rolling ingots parked in the upright position with their short end faces on the ring hearth bottom are thus blown from their two narrow longitudinal sides with the air which accelerates out of the slot nozzles. The over the circulating fans sucked in from the bottom upwards air is passed after its heating by the two burner rings on the inner walls of the outer and inner housing in the local pressure channels.

An advantageous embodiment of the invention provides that the rotationally driven ring hearth bottom is mounted on fixed rollers and has a toothed ring for driving, with which a pinion acted upon by a frequency-controlled electric motor meshes. It is thus only a working according to the operating principle drive block drive unit needed to ensure the stopping of the rotary motion or the positionally accurate clocking of the driven ring hearth floor. The rollers on which the ring hearth bottom expires offer a long service life due to central lubrication of their rolling bearings.

Another embodiment of the invention provides that in each predetermined by a circulation fan fan zone is provided at least one with its measuring lance through the inner or outer housing in the ring hearth interior immersed Andrück thermocouple. The pressing thermocouples can be actuated electromechanically and serve on the one hand to measure the air temperature and on the other hand to measure the temperature of the aluminum ingots.

According to one embodiment of the invention, the at least one loading and unloading opening of the annular hearth furnace for loading and unloading from above or from the side formed with a horizontally in the ceiling or on the outer circumference of the outer housing laterally movable oven door. Regardless of whether a loading and unloading opening or whether two such openings are present, in which case one opening for loading and the other is used for unloading, a flexible loading is guaranteed at always constant loading and unloading and energy efficient always only one small section of the annular hearth furnace open at the top of the ceiling or on the side of the outer housing.

In this case, it is recommended that in the case of two loading and unloading openings which can be closed by an oven door for thermal separation of the discharge opening for hot aluminum ingots and the loading opening for cold aluminum ingots between the two openings, a separating dam is provided.

Further features and details of the invention will become apparent from the claims and the following description of simplified illustrated in the drawings embodiments of the invention.

Figur 1

in einem Längsschnitt von einer Anlage zur thermischen Behandlung von Aluminium-Walzbarren einen mit Mitteln zur Konvektionserwärmung der Aluminium-Walzbarren ausgebildeten Ringherdofen;

Figur 2

den Ringherdofen der Figur 1 in der Draufsicht;

Figur 3

in der Draufsicht einen Ringherdofen wie zuvor in Figur 1, demgegenüber eine Öffnung zur Beladung und eine davon getrennte Öffnung zur Entladung der Aluminium-Walzbarren aufweisend;

Figur 4

als schematische Draufsicht des deckenseitig eine Be- und Entladungsöffnung aufweisenden Ringherdofens, die einbahnige Beladung des Ringherdes mit den Aluminium-Walzbarren;

Figur 5

eine Draufsicht wie zuvor in Figur 4, demgegenüber mit zweibahniger Beladung von symmetrisch in Reihe abgestellten Aluminium-Walzbarren; und

Figur 6

eine Draufsicht wie zuvor in Figur 5, demgegenüber mit nicht symmetrisch in Reihe, sondern von Bahn zu Bahn versetzt abgestellten Aluminium-Walzbarren.

Show it:

FIG. 1

in a longitudinal section of a plant for the thermal treatment of aluminum ingots a ring hearth furnace formed with means for convection heating of the aluminum ingots;

FIG. 2

the ring hearth furnace the FIG. 1 in the plan view;

FIG. 3

in the plan view of a ring hearth furnace as previously in FIG. 1 in contrast, having an opening for loading and a separate opening for discharging the aluminum ingots;

FIG. 4

as a schematic plan view of the cover side, a loading and unloading opening ring hearth furnace, the one-lane loading of the ring hearth with the aluminum ingots;

FIG. 5

a plan view as previously in FIG. 4 on the other hand, with two-lane loading of symmetrically rowed aluminum ingots; and

FIG. 6

a plan view as previously in FIG. 5 In contrast, with not symmetrically in series, but offset from train to train parked aluminum ingots.

From an industrial plant for the thermal treatment of elongated, flat metallic Good a ring hearth furnace 1 for heating or heating and / or homogenization of aluminum ingots 2 is shown in the drawing figures. The annular hearth furnace 1 consists of an outer housing 3 and an inner housing 4, the inside complete with a heat insulation 3a, 4a, z. As ceramic and mineral mats are provided. The furnace roof 6 closing the furnace chamber or the hearth hearth interior 1a is likewise lined with a heat insulation 6a. The below the space between the outer casing 3 and the inner housing 4 bridging furnace bottom 7, which has a thermal insulation 8, for example, lightweight concrete, has in its use space corresponding central region a rotary-driven ring hearth bottom 7a, here opposite the furnace housing or the furnace bottom 7 at both Pages, ie the separation points, is sealed by a circumferential water cup 9. The rotary-driven ring hearth bottom 7 a is mounted on fixed rollers 10 and is of a frequency-controlled electric motor 11 driven, which meshes via a pinion 12 with a ring gear 13 of the ring hearth bottom 7a. On the outer circumference of the furnace housing lines 14 are provided for the introduction of cooling air and discharge of exhaust gases.

The loading and unloading of the ring hearth furnace 1 is carried out in the embodiments from above by means of the hall crane, to which the loading and unloading opening 15 can be temporarily temporarily opened and closed by a horizontally movable in the ceiling 6 by an electric motor with rack drive oven door 16. The aluminum ingots are made in the FIG. 1 to be taken edgewise position with their narrow end faces on a honeycomb-shaped Ablagerost 17 of the ring hearth bottom 7a parked. As in FIG. 3 shown, two openings 15a, 15b can be provided side by side lying in the furnace roof instead of the one loading and unloading opening 15, which can alternately be closed or opened alternately by a horizontally displaceable oven door 16, wherein the opening 15a of the charge with cold aluminum Roll bar, and the opening 15b is for discharging the warmed up aluminum ingots. A divider 18 provides thermal separation of the "hot" unloading station from the "cold" loading station.

For heating or heating and / or homogenization of the aluminum ingots 2 of the annular hearth furnace 1, which is assigned to control and control a higher-level process control system or a higher-level computer, not shown, formed with means for convection heating. How the Figures 2 and 3 For this, with the exception of the area of the loading and unloading opening 15 and the openings 15a, 15b for loading and removal on the furnace roof 6 in alignment with the rotary-driven ring hearth bottom 7a lying circumferentially distributed numerous circulating fans 19 are arranged, with their Vane wheels 19a in the ring hearth inside 1a ends with some air above the upright set aluminum ingots 2 ends. Still protruding through the furnace roof 6 are numerous an outer burner ring and an inner burner ring arranged heating means 20a, 20b arranged in the form of gas burners with their burner tubes 21 on the one hand close to the outer housing 3 and its heat insulation 3a and close to the inner housing 4 and its heat insulation 4a and in the ring hearth inside 1a approximately in Height of the impellers 19 a of the circulation fans 19 end. At some distance below the burner tubes 21 are distributed to the heat insulation 3a of the outer housing 3 and the heat insulation 4a of the inner housing 4 over the entire circumference of the Ringherdinninneren 1a - except again only the area of the loading and unloading opening 15 and the openings 15a, 15b, what also applies to the heating means - up to the furnace bottom 7 out extending pressure channels 22 formed distributed over the height of numerous slot nozzles 32, the air outlets are aligned with the narrow longitudinal sides 24 of the switched on or off aluminum rolling ingots 2.

For convection heating during heating / heating or homogenization of the aluminum ingots 2 sucked by the circulation fans 19 from bottom to top from the annular hearth inside 1a supported by baffles 25 deflected to the burner tubes 21, further heated and in a closed circuit on the lateral pressure channels 22 returned to the bottom. When passing through the pressure channels 22, the aluminum ingots are blown on both sides of their narrow longitudinal sides 24 and flow around the wide rolling surfaces 26 via the slot nozzles 23. For measuring and monitoring the temperature of the Bleglasungsluft be in the flow and return of Umwälzers permanently installed thermocouples used to measure the temperature of the aluminum ingots 2 are in each of a circulating fan 19 with its effective range predetermined fan zone in the embodiment of FIG. 1 provided externally by the inner housing 4 with its measuring lances 27 in the ring hearth inside 1a immersed, electromechanically operated pressure-thermocouples 28. A heating process can thus be controlled and regulated.

A heating process begins after the glow plug to be used has been called from the PLC. This can be done so that the air temperature is set to an excess temperature (max 650 ° C) and automatically maintained at this excess temperature. During this time, in which is operated at excess temperature, the annular hearth bottom 7a is continuously rotated slowly to avoid overheating on the narrow longitudinal sides 24 of the aluminum ingots 2. The current temperature of the aluminum ingots is periodically checked via the pressing thermocouples 28 per fan zone, for which purpose the rotational movement of the annular hearth bottom 7a is briefly stopped. Shortly before reaching the corresponding material setpoint temperature, the temperature of the recirculation air is automatically reset to the desired rolling-block temperature in order to avoid overheating. After all aluminum ingots are in the tolerance range, the material-dependent holding time starts. The end of the cycle is indicated acoustically or visually, whereupon the rolled aluminum bars 2 brought to a rolling temperature of about 520 ° C. can be removed and rolled individually with the existing hall crane.

The assignment of the ring hearth furnace 1 with aluminum ingots 2, for the different AL alloys come into question, the bars are for example 1350 mm wide, 600 mm thick and 4500 mm long, can be done according to variable strategies. As in FIG. 4 illustrated, the aluminum ingots 2 have been circumferentially distributed on a circular path with their wide rolling surfaces 26 spaced from each other in the hearth interior 1 a turned off. To FIG. 5 are the aluminum ingots 2 - and thus consistent with, inter alia FIG. 1 - Have been placed on two circular paths in the hearth interior 1a, wherein the aluminum ingots 2 of the outer circular path are at a distance in series with the narrow longitudinal sides 24 of the aluminum ingots 2 of the inner circular path. The FIG. 6 shows a two-lane loading, as previously in FIG. 5 , however, not with radially in-line aluminum ingots 2, but the aluminum ingots 2 of the concentric inner Circular path offset from the aluminum ingots 2 of the outer circular path in the ring hearth inside 1a parked.

The thus flexible loading takes place at always constant loading and unloading position, namely predetermined by the in the embodiments with at least one in the oven ceiling 6 horizontally movable oven door 16 formed loading and unloading 15 instead. The two-lane loading enables the highest possible throughput with correspondingly high batch weights. The ring hearth furnace designed for heating and homogenizing aluminum rolling bars with convection heating brings numerous advantages over the impact and deep-furnace furnaces used in industry, as achieved by the small loading and unloading opening, minimized heat losses, high thermal efficiency through combustion air. Preheating, low NO _x levels in the exhaust gas, reduced energy loss due to low O ₂ levels in the exhaust gas and overall lower specific energy consumption.

LIST OF REFERENCE NUMBERS

1

Ring hearth furnace

1a

Ring stove inside

2

Aluminum rolling ingot

3

outer casing

3a

thermal insulation

4

inner housing

4a

thermal insulation

6

Ceiling / oven ceiling

6a

thermal insulation

7

furnace bottom

7a

Rotary ring hearth bottom

8th

thermal insulation

9

water cup

10

Roller / roller

11

frequency-controlled electric motor

12

pinion

13

sprocket

14

Line (supply of cooling air and / or discharge of exhaust gas)

15

Loading and unloading opening

15a

loading opening

15b

removal opening

16

oven door

17

down grid

18

separating military

19

Circulating fan

19a

impeller

20a / b

Heating means (gas burner)

21

burner tubes

22

pressure channel

23

slot

24

narrow longitudinal side

25

baffle

26

wide rolling surface

27

measuring probe

28

Press-on thermocouple

Claims (16)

1. Method for thermal treatment rolled aluminium ingots (2) in a furnace, which for temperature regulation and temperature monitoring as well as furnace control is connected with a superordinate process management system, wherein a ring hearth furnace (1) is used as the furnace and has between a thermally insulated outer housing (3) and a thermally insulated inner housing (4) a rotationally driven ring hearth base (7a) sealed relative to the housings (3, 4) and wherein the ring hearth furnace (1), which is closed by a thermally insulated ceiling (6), is constructed with at least one closable charging and discharging opening (15; 15a; 15b) and is heated by gas or electrically, wherein for convection heating of the rolled aluminium ingots (2) introduced into the ring hearth furnace (1) air is sucked upwardly from the ring hearth interior (1a), which is enclosed by the outer and inner housings (3, 4), by circulating fans (19) provided at the ceiling side and distributed over the circumference of the ceiling (6), characterised in that the inducted air is initially conducted along heating means (20a, 20b; 21), which are arranged at the ceiling side and project into the hearth interior (1a), and thereafter flows into pressure channels (22), which extend, at the inner walls of the outer and inner housings (3, 4), below the heating means (20a, 20b; 21) to the furnace base (7) and from which air increasingly heating during the heating-up phase is blown against the rolled aluminium ingots (2) by way of slot nozzles (23) in order to heat the rolled aluminium ingots (2).
2. Method according to claim 1, characterised in that the rolled aluminium ingots (2) are so deposited in on-end position on the ring hearth base (7a) that the circulated air is directly blown against their narrow longitudinal sides (24) and the air flows around their wide roll surfaces (26).
3. Method according to claim 1 or 2, characterised in that the ring hearth furnace (1) can be operated for heating the rolled aluminium ingots (2) to rolling temperature and, in the case of a temperature elevated relative thereto, equally for homogenising the rolled aluminium ingots (2), wherein the rolled aluminium ingots (2) after the homogenisation time has elapsed are cooled by blowing cold air into the ring hearth interior (1a) and at the end of a defined cooling time are heated back to rolling temperature by the residual heat of the rolled aluminium ingots (2).
4. Method according to any one of claims 1 to 3, characterised in that the ring hearth furnace (1) is operated with batch or continuous charging.
5. Method according to claim 4, characterised in that in the case of batch operation the empty ring hearth furnace (1) is completely filled at the start of annealing and after reaching the rolling temperature of all rolled aluminium ingots (2) is completely emptied.
6. Method according to claim 4, characterised in that in the case of continuous operation a heated-up rolled aluminium ingot (2) is removed and thereafter the ring hearth base (7a) is further rotated through one cycle before a cold, rolled aluminium ingot (2) is introduced for heating.
7. Method according to one or more of claims 1 to 6, characterised in that the rolled aluminium bars (2) can be deposited in the ring hearth interior (1a) in circumferential distribution with the wide roll surfaces (26) thereof at a mutual spacing on a single track or on two tracks, in the latter case additionally with mutually spaced narrow longitudinal sides, wherein the twin-track loading can be carried out with rolled aluminium ingots (2) lying in a row or offset from circular track to circular track.
8. Method according to one or more of claims 1 to 7, characterised in that in the heating-up phase of the ring hearth furnace (1) with set and maintained elevated temperature the ring hearth base (7a) is continuously rotated so as to avoid overheatings at the narrow longitudinal sides (24) of the rolled aluminium ingots (2) and to equalise the temperature.
9. Method according to one or more of claims 1 to 8, characterised in that the actual temperature of the rolled aluminium ingots (2) is periodically checked per zone predetermined by each of the circulating fans (19) at the ceiling side by the effective region thereof, for which purpose the rotational movement of the ring hearth base (7a) is briefly stopped.
10. Method according to one or more of claims 1 to 9, characterised in that the ring hearth furnace (1) is loaded from above or the side with the rolled aluminium ingots (2).
11. Plant for thermal treatment of rolled aluminium ingots (2), comprising a furnace which for temperature regulation and temperature monitoring as well as furnace control is connected with a superordinate process management system, wherein a ring hearth furnace (1), which has between a thermally insulated outer housing (3) and a thermally insulated inner housing (4) a rotationally driven ring hearth base (7a) sealed relative to the housings (3, 4) is used as the furnace and wherein the ring hearth furnace (1), which is closed by a thermally insulated ceiling (6), has at least one closable charging and discharging opening (15; 15a, 15b) and is heated by gas or electrically, wherein for convection heating of the rolled aluminium ingots (2) introduced into the ring hearth furnace (1) air is sucked upwardly from the ring hearth interior (1a), which is enclosed by the outer and inner housings (3, 4), by circulating fans (19) provided at the ceiling side and distributed over the circumference of the ceiling (6), for carrying out the method according to one or more of claims 1 to 10, characterised in that the ring hearth furnace (1) comprises in distribution over the annular surface, which is aligned with the rotationally driven ring hearth base (7), of its ceiling (6) on the one hand circulating fans (19) and on the other hand heating means (20a, 20b; 21) associated with both the inner wall of the outer housing (3) and the inner wall of the inner housing (4), wherein the circulating fans (19) and the heating means (20a, 20b; 21) are led through the ceiling (6) to reach into the upper ring hearth interior (1a), and is constructed with pressure channels (22), which have slot nozzles (23) and which extend, at the inner walls of the outer and inner housings (3, 4), below the heating means (20a, 20b; 21) to the furnace base (7).
12. Plant according to claim 11, characterised in that gas burners arranged at a spacing from one another to form an outer housing burner ring and an inner housing burner ring are provided as heating means (20a, 20b; 21), wherein the burner tubes (21) thereof run adjacent to the inner walls of the outer and inner housings (3, 4) to enter the upper ring hearth interior (1a).
13. Plant according to claim 11 or 12, characterised in that the rotationally driven ring hearth base (7a) is mounted on stationary rollers (10) and has a rim gear (13), with which a pinion (12) acted on by a frequency-regulated electric motor (11) meshes, for the drive.
14. Plant according to one or more of claims 11 to 13, characterised in that at least one press-on thermoelement (28) entering by its measuring lance (27) into the ring hearth interior (1a) through the inner or outer housing (3, 4) is provided in each fan zone predetermined by a circulating fan (19).
15. Plant according to one or more of claims 11 to 14, characterised in that the at least one charging and discharging opening (15; 15a, 15b) of the ring hearth furnace (1) is, for charging and discharging from above or from the side, constructed with a furnace door (16) horizontally movable in the ceiling (6) or a furnace door laterally movable at the circumference of the outer housing (3).
16. Plant according to claim 15, characterised in that in the case of two charging and discharging openings (15a, 15b) each closable by a respective furnace door (16) a separating weir (18) is provided between the two openings (15a, 15b) to thermally separate the discharging opening (15b) for hot, rolled aluminium ingots (2) and the charging opening (15a) for cold, rolled aluminium ingots (2).

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