DE102019108873A1 - Rotary hearth furnace for the heat treatment of metallic workpieces and the corresponding process for heat treatment - Google Patents

Abstract

Rotary hearth furnace (1) for the heat treatment of metallic workpieces (9), comprising an inner housing (3) rotatable about an axis of rotation (2) for applying furnace gas (16) to heat treatment locations (6), the inner housing (3) being heat treatment locations (16) radially on the outside. 6) for the workpieces (9), which are non-rotatably connected to the inner housing (3) and lie outside the inner housing (3), the inner housing (3) having nozzle devices (10) through which furnace gas (16) from the interior of the inner housing (3) can be guided to the heat treatment stations (6) and each heat treatment station (6) is assigned a nozzle device (10) which is non-rotatably connected to the inner housing (3) Oven gas (16) can be guided past at least one heat source (14) into the interior of the inner housing (3).

Description

The subject matter of the present invention is a rotary hearth furnace for the heat treatment of metallic workpieces, in particular for the annealing of metallic workpieces, and a corresponding method for heat treatment.

For annealing workpieces, for example, from WO 2015/128416 A1 Known ring furnaces in which a static outer housing and a static inner housing are present and a corresponding ring base for receiving the workpieces is formed between the inner housing and the outer housing and which can be rotated relative to the outer housing and the inner housing. Slot nozzles are formed in the outer housing and in the inner housing, through which furnace air can be introduced into the space between the inner housing and the outer housing to heat the workpieces, which can be transported past the slot nozzles by rotating the ring base. A method is known from WO 2006/050209 A2 in which the furnace air is passed over the workpiece without a nozzle.

This procedure has the disadvantage that the workpieces can be heat treated unevenly, as they are moved past the slot nozzles or the oven air is guided over the workpiece without nozzles and consequently the workpieces can be heated inhomogeneously.

Proceeding from this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art and, in particular, of providing a rotary hearth furnace and a method for heat treatment in a rotary hearth furnace in which the workpieces are heated homogeneously in terms of time and location.

This object is achieved with the features of the independent claims. Further advantageous refinements of the invention are specified in the dependent claims. The features listed individually in the dependently formulated claims can be combined with one another in a technologically meaningful manner and can define further embodiments of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred embodiments of the invention being presented.

The rotary hearth furnace according to the invention for the heat treatment of metallic workpieces comprises an inner housing rotatable about an axis of rotation for applying a furnace gas to heat treatment locations, the inner housing having heat treatment locations for the workpieces radially on the outside, which are non-rotatably connected to the inner housing and are located outside the inner housing Inner housing has nozzle devices through which furnace gas can be guided from the interior of the inner housing to the heat treatment places and each heat treatment place is assigned a nozzle device which is non-rotatably connected to the inner housing, with at least one flow machine being formed through which furnace gas passes at least one heat source into the Interior of the inner housing can be guided.

The inner housing is also known as the nozzle plenum. The invention is thus based on a fixed assignment of the nozzle device to the heat treatment station and the non-rotatable connection of the heat treatment station and the nozzle device to the rotatable inner housing. During operation, the workpiece to be processed is placed on a heat treatment station and guided through the rotary hearth furnace by rotating the inner housing. By fixing the nozzle device to the heat treatment station, the nozzle device and the heat treatment station are in a constant relationship. There is no relative movement between the nozzle device and the heat treatment station, so that during the entire journey through the rotary hearth furnace, the workpiece can be constantly exposed to the heat treatment station, so that the heating can be significantly more homogeneous compared to approaches known from the prior art.

The at least one heat source is preferably designed as a gas burner, in particular comprising a radiant tube or a flame guide tube and / or as an electrical heating element. A radiant tube is understood to mean an element in which a gas burner burns in a closed housing and the smoke gases are discharged in such a way that they do not enter the inner housing. A flame guide tube is preferably understood to mean a perforated metal tube in which the combustion exhaust gases of the gas burned in the gas burner are distributed outside the burner in the desired manner.

In particular, the furnace atmosphere can be used as furnace gas, which in particular comprises air and optionally combustion exhaust gas from a gas burner. For this purpose, the atmosphere in the furnace is in particular circulated. The rotary hearth furnace has at least one access opening through which workpieces can be inserted into or removed from the heat treatment stations. In this case, the introduction of the heated furnace gas and thus the heat treatment through the nozzle devices can be continued uninterrupted during the loading and unloading. The turbo machine generates an overpressure in the interior of the inner housing compared to the surroundings of the inner housing, which leads to the furnace gas flowing through the nozzle devices from the inner housing through the nozzle devices to the heat treatment stations.

The metallic workpieces are preferably workpieces made of aluminum, an aluminum-based alloy, a non-ferrous metal and / or a non-ferrous metal-based alloy. The workpieces are preferably rims, engine blocks, chassis parts and the like for motor vehicles.

The rotary hearth furnace preferably has a gas return from the heat treatment stations to the turbomachine. The at least one heat source is preferably arranged in the gas recirculation on the suction side upstream of the turbomachine in order to bring about a uniform temperature control of the furnace gases. The rotary hearth furnace is therefore preferably designed as a convection furnace.

In particular, it is preferred in this context that the at least one heat source is formed in the gas return. This brings about a further equalization of the temperature of the furnace gas before it enters the inner housing through the turbomachine.

According to an advantageous embodiment, a fan is designed as a flow machine.

In particular, a fan, preferably an axial fan, has proven to be particularly advantageous because it is easy to implement and operate. A configuration in which the fan is arranged in such a way that the furnace gas is guided axially into the interior space with respect to the axis of rotation is particularly preferred. The fan is preferably formed on the opposite side of a motor causing the rotation. A semi-axial fan, in which air is sucked in radially and blown out axially into the interior of the inner housing, is particularly preferably used as the fan.

According to an advantageous embodiment, downstream of the turbomachine, a flow equalizer for introducing the furnace gas into the inner housing in a distributed manner is formed. A flow equalizer ensures that the entire interior is exposed to a flow of the furnace gas that is as uniform as possible. A flow equalizer is designed, for example, as a tube into which the furnace gas flow from the fan flows inside and which leaves the tube via holes in the circumference of the tube. The holes can vary in their size and shape, in particular as a function of the distance from the fan. A tapering tube can preferably be used. The holes are preferably designed so that there is a uniform flow out of the pipe over the length of the pipe.

According to an advantageous embodiment, each nozzle device has at least one first partial nozzle device with a first blowing direction and a second partial nozzle device with a second blowing direction, the first blowing direction and second blowing direction enclosing an angle different from zero.

In particular, the first blowing direction and the second blowing direction are opposite to one another. By dividing each nozzle device into at least two nozzle sub-devices, it is possible to act on the workpiece from at least two sides, preferably also from three sides by three nozzle sub-devices. The first partial nozzle device and the second partial nozzle device are preferably opposite one another. Each nozzle sub-device preferably has at least one nozzle which is connected to the interior of the inner housing. If several nozzles are formed per nozzle sub-device, the blowing direction is understood to be the vector sum of the exit directions of the individual nozzles. In particular, the nozzle device comprises at least one nozzle and each nozzle sub-device comprises at least one nozzle. The nozzle device is preferably designed such that it comprises nozzles which can be blown into the workpiece from several sides, in particular from at least two sides. In particular, the nozzle device can be designed so that the workpiece can be blown from above, below and from the side. The number, position and / or type of nozzle, for example with regard to the opening cross-section, the size of the opening and / or the blowing direction of the nozzle, is preferably adapted to the shape, the material and / or the mass of the workpiece.

According to an advantageous embodiment, at least two levels of heat treatment stations are formed which have different positions in the direction of the axis of rotation.

The rotary hearth furnace preferably has a level of heat treatment places which has a specific position in the direction of the axis of rotation. This can be particularly advantageous when comparatively tall workpieces are to be heat-treated. By forming two or more such levels, the number of workpieces to be treated at the same time can be increased and thus the throughput of the rotary hearth furnace can be increased.

Furthermore, a method for heat treatment of a metallic workpiece in a rotary hearth furnace, in particular a rotary hearth furnace according to the invention, is proposed, in which the workpiece is moved in a heat treatment station with at least one nozzle device assigned to the heat treatment station on a circular path through the rotary hearth furnace and through the nozzle device with a furnace gas of a predeterminable Temperature is applied.

According to the invention, the workpiece is transported through the rotary hearth furnace together with the nozzle device assigned to it in the heat treatment station. There is therefore always a defined relationship between the nozzle device and the workpiece, in particular a constant distance and a constant flow profile with which the furnace gas hits the workpiece. In this way, uniform and homogeneous heating of the workpiece can be achieved.

According to an advantageous embodiment, the workpiece is acted upon by the nozzle device with the furnace gas from at least two directions, preferably from two opposite directions. In this way, even asymmetrical workpieces can be efficiently flown with furnace gas and thus temperature controlled.

According to an advantageous embodiment, the furnace gas is fed back.

According to an advantageous embodiment, the furnace gas is guided past at least one heat source for setting the predeterminable temperature downstream of the heat treatment station and upstream of the nozzle device.

The heat source is preferably a gas burner, in particular a radiant tube, and / or an electrical heating source.

The details and advantages disclosed for the rotary hearth furnace can be transferred and applied to the method and vice versa.

As a precaution, it should be noted that the numerals used here (“first”, “second”, ...) primarily (only) serve to distinguish between several similar objects, sizes or processes, so in particular no dependency and / or sequence of these objects, sizes or mandatory processes for each other. Should a dependency and / or sequence be required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described embodiment.

• 1 ein erstes Beispiel eines Drehherdofens im Längsschnitt;
• 2 das erste Beispiel eines Drehherdofens im Querschnitt;
• 3 ein Beispiel für eine Düsenteileinrichtung in perspektivischer Ansicht; und
• 4 ein zweites Beispiel eines Drehherdofens im Längsschnitt.

The invention and the technical environment are explained in more detail below with reference to the figures. It should be pointed out that the invention is not intended to be restricted by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description and / or figures. In particular, it should be pointed out that the figures and in particular the size relationships shown are only schematic. The same reference symbols denote the same objects, so that explanations from other figures can be used in addition, if necessary. Show it:

• 1 a first example of a rotary hearth furnace in longitudinal section;
• 2 the first example of a rotary hearth furnace in cross section;
• 3 an example of a nozzle dividing device in a perspective view; and
• 4th a second example of a rotary hearth furnace in longitudinal section.

Identical elements are provided with identical reference symbols. 1 shows schematically a rotary hearth furnace 1 in longitudinal section. The rotary hearth furnace 1 has one about an axis of rotation 2 rotatable inner housing 3 on, which is in a static outer housing 4th with lockable access openings 5 is trained. The rotary hearth furnace 1 has several heat treatment stations 6th on that in a first level 7th and a second level 8th are arranged. The heat treatment stations 6th are used as supports or supports for workpieces 9 educated. The heat treatment stations 6th are non-rotatably with the inner housing 3 connected. The heat treatment stations 6th are radially outside on the inner housing 3 educated. The heat treatment stations 6th are thus outside the inner housing 3 between inner housing 3 and outer casing 4th . being the inner case 3 Nozzle devices 10 has, by the furnace gas 16 from inside the inner housing 3 to the heat treatment stations 6th is feasible. For the sake of clarity, not all of the reference symbols are used for the nozzle devices 10 executed. Every heat treatment station 6th is a nozzle device 10 is assigned, which rotatably with the inner housing 3 connected is. In this example, each nozzle device 10 each a first nozzle sub-device 11 and a second nozzle dividing device 12 on, which are opposite to each other and thus an impact on the workpiece 9 in the heat treatment station 6th from two directions (above and below in this example).

Furthermore, there is at least one flow machine 13 formed by the furnace gas 16 at at least one heat source 14th passing into the inside of the inner case 3 is feasible. This creates inside 15th of the inner housing 3 an overpressure compared to the area between the inner housing 3 and outer casing 4th . This causes the furnace gas 16 through the first nozzle sub-assemblies 11 and the second nozzle dividing means 12 from the interior 15th of the inner housing 3 towards the heat treatment stations 6th pushed. The heat sources 14th are in this example designed as a gas burner, preferably with a flame guide tube. The rotary hearth furnace 1 is thus directly gas-heated. The turbo machine 13 is designed as a semi-axial fan.

The furnace gas 16 flows from the interior 15th through the nozzle devices 11 or the nozzle sub-devices 11 , 12 in the space between the inner housing 3 and outer casing 4th , the furnace gas 16 thereby the workpieces 9 flows around. From the space between the inner housing 3 and outer casing 4th the furnace gas flows 16 through a gas recirculation 17th , in which the heat source 14th are formed by the furnace gas 16 are flowed around, after which they are from the turbomachine 17th back to the interior 15th of the inner housing 3 be promoted. This causes the furnace gas 16 in the circuit through the rotary hearth furnace 1 guided. The inner case 3 is done by a drive 18th turned.

2 shows the rotary hearth furnace 1 out 1 in cross section. This one shows 8th Work pieces 9 on that with I. to VIII are designated. The rotation of the inner case 3 against the outer casing 4th takes place around the axis of rotation 2 in direction of rotation 19th .

3 Fig. 10 shows an example of a first nozzle dividing device 11 in perspective view. The inner case 3 has a heat treatment station 6th on, the two keepers 20th includes. The workpiece is on top of this 9 (not shown) placed. The nozzle sub-device in this case has four nozzles 21st on that at an angle to the vertical of the inner housing 3 are aligned in this area. Instead of four nozzles 21st per nozzle sub-assembly 11 , 12 can also have a single nozzle 21st be trained. In particular, first nozzle sub-devices 11 with a different number of nozzles 21st be designed as a second nozzle sub-devices 12 . The heat treatment place 6th and the keepers 20th and optionally the nozzle device 10 is preferred to the workpieces to be treated 9 , especially with regard to the shape, the material and / or the mass of the workpiece 9 customized.

4th shows a second example of a rotary hearth furnace 1 . It is based on the description given above 1 and 2 referred, only the differences are to be explained here. In addition to the first example, the rotary hearth furnace 1 here a flow equalizer 22nd for distributing the furnace gas 16 into the interior 15th of the inner housing 3 on. The flow smoother 22nd is as a tapered tube 23 with holes 24 formed through which the flow of furnace gas 16 through the individual nozzle devices 10 with first nozzle dividing device 11 and second nozzle dividing device 12 is equalized. For the sake of clarity, not all are holes 24 provided with reference symbols.

List of reference symbols

1

Rotary hearth furnace

2

Axis of rotation

3

Inner casing

4th

Outer casing

5

Access opening

6th

Heat treatment place

7th

First floor

8th

second level

9

workpiece

10

Nozzle device

11

First nozzle part device

12

Second nozzle part device

13

Turbo machine

14th

Heat source

15th

inner space

16

Furnace gas

17th

Gas recirculation

18th

drive

19th

Direction of rotation

20th

holder

21st

jet

22nd

More uniform flow

23

pipe

24

hole

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2015/128416 A1 [0002]

Claims (12)

Rotary hearth furnace (1) for the heat treatment of metallic workpieces (9), comprising an inner housing (3) rotatable about an axis of rotation (2) for applying a furnace gas (16) to heat treatment locations (6), wherein the inner housing (3) has heat treatment places (6) for the workpieces (9) radially on the outside, which are non-rotatably connected to the inner housing (3) and lie outside the inner housing (3), wherein the inner housing (3) has nozzle devices (10) through which furnace gas (16) can be guided from the interior of the inner housing (3) to the heat treatment places (6) and each heat treatment place (6) is assigned a nozzle device (10) which is non-rotatable is connected to the inner housing (3), wherein at least one turbo machine (13) is formed, through which furnace gas (16) can be guided past at least one heat source (14) into the interior of the inner housing (3). Rotary hearth furnace (1) after Claim 1 , having a gas return (17) from the heat treatment places (6) to the turbo machine (13). Rotary hearth furnace (1) after Claim 2 , in which the at least one heat source (14) is formed in the gas recirculation (17). Rotary hearth furnace (1) according to one of the preceding claims, in which a fan, in particular a semi-axial fan, is designed as the flow machine (13). Rotary hearth furnace (1) according to one of the preceding claims, in which a flow equalizer (22) for distributing the furnace gas (16) into the inner housing (3) is formed downstream of the turbomachine (13). Rotary hearth furnace (1) according to one of the preceding claims, in which each nozzle device (10) has at least one first nozzle component device (11) with a first blowing direction and a second nozzle component device (12) with a second blowing direction, the first blowing direction and the second blowing direction being zero Include different angles with each other. Rotary hearth furnace (1) after Claim 6 , in which each nozzle sub-device (11, 12) has at least one nozzle (21) which is connected to the interior of the inner housing (3). Rotary hearth furnace (1) according to one of the preceding claims, in which at least two levels (7, 8) of heat treatment stations (6) are formed which have different positions in the direction of the axis of rotation (2). Method for heat treatment of a metallic workpiece (9) in a rotary hearth furnace (1), in particular according to one of the preceding claims, in which the workpiece (9) is in a heat treatment station (6) with at least one nozzle device (10) assigned to the heat treatment station (6) is moved in a circular path through the rotary hearth furnace (1) and is acted upon by the nozzle device (10) with a furnace gas (16) of a predetermined temperature. Procedure according to Claim 9 , in which the workpiece (9) is acted upon by the nozzle device (10) with the furnace gas (16) from at least two directions. Method according to one of the Claims 9 to 10 , in which the furnace gas (16) is returned. Procedure according to Claim 11 , in which the furnace gas (16) downstream of the heat treatment station (6) and upstream of the nozzle device (10) is guided past at least one heat source (14) for setting the predeterminable temperature.

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