Continuous furnace and method for heat-treating workpieces

Abstract

A continuous furnace for heat-treating workpieces (12) comprises a tunnel housing (16) in which a treatment tunnel (36) is formed in which the workpieces (12) undergo their heat treatment, wherein the workpieces (12) can be conveyed in a transport direction (30) through the treatment tunnel (38) by means of a conveying system (34). There is a heating section (44) having a plurality of heating zones (46) in which the treatment tunnel (36) defines a heating tunnel (52), and a heating system (50) by means of which the heating tunnel (52) can be heated in the heating zones (46), wherein in a heating zone (46) the heating tunnel (52) is separated by a heating wall (53) from a heating space (54) having a heating device (48). There is also a cooling section (64), which is directly adjacent to the heating section (44) in the transport direction (30) and comprises a plurality of cooling zones (66) in which the treatment tunnel (36) defines a cooling tunnel (68). The temperature of the workpieces (12) can be reduced in the cooling tunnel (68) by means of a counter-flow cooling system (78) which is configured such that a cooling gas (84) can flow through the cooling tunnel (68) in a counter-flow direction (6) in relation to the transport direction (30). At the transition (88) from the heating section (44) to the cooling section (64), the treatment tunnel (36) is designed such that at least one bypass portion (84a) of the cooling gas (84) flowing in the counter-flow direction (86) flows into the heating space (54) of the last heating zone (46a). Such a continuous furnace (10) is used in a method for heat-treating workpieces (12). (Figure 1)20

Description

[0001] Continuous furnace and process for heat treatment of workpieces

[0002] BACKGROUND OF THE INVENTION

[0003] 1. Field of the invention

[0004] The invention relates to a continuous furnace for the heat treatment of workpieces, comprising a) a tunnel housing in which a treatment tunnel is formed in which the workpieces receive their heat treatment; b) a conveyor system by means of which the workpieces can be conveyed through the treatment tunnel in a transport direction; c) a heating section with a plurality of heating zones in which the treatment tunnel defines a heating tunnel; d) a heating system by means of which the heating tunnel can be heated in the heating zones, wherein the heating tunnel is separated in each heating zone by a heating wall from a heating chamber with a heating device; e) a cooling section which is directly adjacent to the heating section in the transport direction and comprises a plurality of cooling zones in which the treatment tunnel defines a cooling tunnel;f) a countercurrent cooling system by means of which the temperature of the workpieces in the cooling tunnel can be reduced and which is designed in such a way that a cooling gas can flow through the cooling tunnel in a countercurrent direction with respect to the transport direction;

[0005] The invention also relates to a method for heat treating workpieces. 2. Description of the Prior Art

[0006] In such continuous furnaces, for example, ceramic workpieces are fired; however, the invention generally relates to the heat treatment of other workpieces in such continuous furnaces.

[0007] The heating wall can be a side wall or the heating tunnel ceiling in relation to the heating tunnel; this will be explained again below.

[0008] After the heating section, which usually comprises a heating area in which the workpieces are heated to a target temperature and a holding area in which this target temperature is still maintained, the workpieces are flowed with a cooling gas in the cooling section according to the countercurrent principle, ie in the direction opposite to the transport direction.

[0009] If necessary, the holding area can also include a transfer area with one or more transfer zones in the transport direction, followed by the cooling section. In such a transfer area, neither cooling nor heating is generally used, resulting in a moderate temperature drop in the treatment tunnel in the transport direction.

[0010] If too much cooling gas from the cooling tunnel enters the heating tunnel, this leads to an inhomogeneous temperature distribution in the heating tunnel at the transition to the cooling tunnel, which in turn can reduce the quality of the workpieces after their heat treatment.

[0011] In known continuous furnaces of the type mentioned above, the heating section and the cooling section are fluidically separated, and the cooling gas is extracted from the cooling tunnel at different points and discharged as exhaust air. The energy balance of the continuous furnace therefore always includes the resulting exhaust air loss. However, even in this case, it may not be possible to completely prevent cooling gas from the cooling tunnel from entering the heating tunnel and causing temperature inhomogeneities there. The object of the invention is therefore to provide a continuous furnace and a method of the type mentioned above that enable the most homogeneous temperature distribution possible in the heating tunnel at the transition to the cooling tunnel and lead to a good energy balance.

[0012] SUMMARY OF THE INVENTION

[0013] This object is achieved in that g) the treatment tunnel at the transition from the heating section to the cooling section is designed such that at least a bypass portion of the cooling gas flowing in the countercurrent direction flows into the heating chamber of the last heating zone.

[0014] On the one hand, this measure opens up the possibility of using the bypass portion of the cooling gas as a heating resource, thereby improving the energy balance of the continuous furnace. On the other hand, this can be supported by structural measures that counteract the temperature inhomogeneities described above.

[0015] For this purpose, it is advantageous if the cooling tunnel defines a cooling tunnel wall, in particular a cooling tunnel ceiling, which has a contour at the transition and is designed such that the cooling tunnel partially overlaps the heating chamber of the last heating zone in cross-section, so that the cooling tunnel is in flow communication with this heating chamber. Thus, no separate lines are required to conduct the bypass portion of the cooling gas into the heating chamber of the last heating zone.

[0016] It is structurally advantageous if the cooling tunnel comprises a first cooling tunnel section in the counterflow direction, which directly transitions into a second cooling tunnel section, which in turn directly borders the transition to the last heating zone of the heating section, with the cross-section of the cooling tunnel increasing in the counterflow direction from the first cooling tunnel section to the second cooling tunnel section. Such an increase in cross-section creates a suction effect out of the cooling tunnel due to the flow, effectively causing subsequent cooling gas to flow in, which can then be directed further in a targeted manner. It is particularly structurally simple if the cross-sections of the first cooling tunnel section and the second cooling tunnel section are both constant.

[0017] A favorable upward suction effect is achieved if the cross section of the second cooling tunnel section increases in the upward direction and in particular the second cooling tunnel section is at least partially higher by a factor of 1.1 to 1.5, in particular by a factor of 1.2 to 1.3, than the first cooling tunnel section.

[0018] For this purpose, the cooling tunnel ceiling advantageously has a step offset upwards at the transition from the first cooling tunnel section to the second cooling tunnel section, whereby the cooling tunnel in the second cooling tunnel section comprises an upper flow space.

[0019] It was also recognized that the outflow of the heated cooling air to the heating chamber of the last heating zone and thus the homogenization of the temperature is further supported if the cross section of the second cooling tunnel section increases in the direction of the side and in particular the second cooling tunnel section is at least partially wider by a factor of 1.1 to 1.5, in particular by a factor of 1.1 to 1.3, than the first cooling tunnel section.

[0020] This can be implemented structurally in a simple manner by having one or both cooling tunnel walls at the transition from the first cooling tunnel section to the second cooling tunnel section each have a step offset to the left or right.

[0021] These measures are particularly effective when the heating chamber of the last heating zone is partially or entirely located above its heating wall. In this case, the cooling tunnel wall mentioned above is therefore the cooling tunnel ceiling.

[0022] For the return of the heated cooling gas, it is advantageous if one or more heating chambers define a bypass flow channel which is designed in such a way that the bypass portion of the cooling gas flows back into the heating tunnel as hot gas.

[0023] It is particularly advantageous if the bypass flow channel extends into a holding area of ​​the heating section, in which a target temperature is to be maintained constant, and is configured such that the hot gas flows from the bypass flow channel in the first heating zone of the holding area back into the heating tunnel. This also includes an inflow point of the hot gas at the transition between the heating zone and the first heating zone of the holding area. Since the hot gas heats up to the temperature in the heating tunnel of the holding area on its way through the bypass flow channel, convective heating of the workpieces is promoted after the hot gas flows in.

[0024] For this purpose, the heating devices in the heating chambers are preferably arranged in the bypass flow channel in such a way that, on the one hand, the heating wall there and, on the other hand, the bypass portion of the cooling gas can be heated.

[0025] It is particularly preferred that the heating power in the inlet area of ​​the bypass flow channel be greater than in the other heating chambers, in particular by the heating devices in the bypass flow channel comprising heating units, and by one or more heating chambers associated with the inlet area of ​​the bypass flow channel each containing more heating units than in the heating chambers of the other heating zones of the bypass flow channel. For example, the heating power in the heating chamber(s) in the inlet area can be 1.5 times greater than in the other heating chambers; in fact, such a resulting factor depends on the other design and dimensions of the continuous furnace.

[0026] Preferably, the last heating zone and the preceding heating zone of the heating section define the inlet area of ​​the bypass flow channel.

[0027] The flow of the bypass portion of the cooling gas can be effectively supported by an injector system, which injects an auxiliary flow of auxiliary gas into the cooling tunnel with a directional component toward the heating chamber of the last heating zone. In favorable cases, this auxiliary flow can also increase the bypass portion of the cooling gas, i.e., the portion of the cooling gas flowing into the heating chamber of the last heating zone.

[0028] If the above-mentioned flow chamber is formed, the injector system is preferably configured such that the auxiliary flow can be injected into the flow chamber. It is advantageous if the injector system provides one or more discharge openings for the auxiliary flow gas, wherein, in variant A, one or more discharge openings are arranged on an end wall of the flow chamber opposite the heating chamber of the last heating zone, and / or, in variant B, one or more discharge openings are arranged at a distance from this end wall of the flow chamber opposite the heating chamber of the last heating zone. This will be explained again in the description.

[0029] Advantageously, one or more injector nozzles are provided, in particular one or more injector nozzles which, in variant A, are provided in the end wall and / or, in variant B, are designed as nozzle lances, the free end of which provides the discharge opening and which protrude from the end wall into the flow space.

[0030] It is particularly advantageous if the bypass portion of the cooling gas can be adjusted. For this purpose, the injector system includes a control device by means of which the volume flow of the auxiliary flow can be adjusted.

[0031] In the method, the above-mentioned object is achieved by using a continuous furnace with some or all of the features explained above.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawings. In these drawings:

[0034] Figure 1 shows a longitudinal section of a continuous furnace for the thermal treatment of workpieces, showing partial sections of the continuous furnace;

[0035] Figure 2 shows a section of the continuous furnace in a last heating zone of a heating section in the transport direction along the section line ll-ll in Figure 1;

[0036] Figure 3A shows a section of the continuous furnace in an entry zone of a cooling section along section line IIIA-IIIA in Figure 1, with a view of a transition from the heating section to the cooling section; Figure 3B shows a section corresponding to Figure 3A of a first modification;

[0037] Figure 3C shows a section of a second modification corresponding to Figures 3A and 3B;

[0038] Figure 4 shows a section of the continuous furnace along the section line IV-IV in Figure 1;

[0039] Figure 5 is a perspective view of a part of the continuous furnace with the entry zone into the cooling section, looking at the section along the section line VV in Figure 1;

[0040] Figure 6 shows a longitudinal section of the inlet zone into the cooling section in an embodiment without an injector system;

[0041] Figure 7 shows schematically a cooling air flow pattern in the embodiment without an injector system;

[0042] Figure 8 shows a longitudinal section of the entry zone into the cooling section in an embodiment with an injector system;

[0043] Figure 9 shows schematically a cooling air flow pattern in the embodiment with injector system;

[0044] Figure 10 shows a longitudinal section of the entry zone into the cooling section in an embodiment with a modified injector system.

[0045] DESCRIPTION OF PREFERRED EMBODIMENTS

[0046] 1. Continuous furnace

[0047] In Figure 1, the reference numeral 10 designates a continuous furnace for the heat treatment of workpieces 12, in which a continuous tunnel 14 is arranged within a tunnel housing 16. The workpieces 12 are arranged on support structures 18 in the form of support frames in several support levels, which are conveyed through the continuous tunnel 14. The continuous furnace 10 can be used, for example, for firing ceramic workpieces 12 or the like. The tunnel housing 16 extends between an entrance area 20 and an exit area 22, which are each designed in a manner known per se as an entrance lock 24 and an exit lock 26, so that the workpieces 12 or the support structures 18 loaded therewith can be introduced into the continuous tunnel 14 orcan be removed therefrom again without any exchange of the tunnel atmosphere 28 located in the continuous tunnel 14 with the ambient atmosphere outside the continuous furnace 10. The ambient atmosphere is generally the atmosphere prevailing in the hall in which the continuous furnace 10 is installed. Two arrows illustrate the transport direction 30 of the continuous furnace 10, in which the support structures 18 are conveyed through the continuous tunnel 14 and which simultaneously defines the longitudinal direction in the continuous furnace 10 towards the rear.

[0048] A conveyor floor 32 is arranged in the flow tunnel 14, on which the workpieces 12 are conveyed by means of a conveyor system 34 from the input area 20 through a treatment tunnel 36 to the output area 22. The treatment tunnel 36 is formed in the flow tunnel 14 and there above the conveyor floor 32 and is bounded at the top by a ceiling 38. The workpieces 12 receive their heat treatment in the treatment tunnel 36.

[0049] In the present embodiment, the continuous furnace 10 is designed as a pusher furnace, for which the conveyor system 34 comprises a hydraulic pusher device 40 at the entrance area 20, with the aid of which the support structures 18, which are part of the conveyor system 34, are pushed through the flow tunnel 14 in a manner known per se. The pusher device 40 is only shown in Figure 1 and is only indicated very schematically there. The conveyor floor 32 can, for example, form a pusher track. In this case, the support structures 18 are positioned on so-called pusher plates, which are then pushed along the pusher track. Alternatively, the conveyor floor 32 can also form a roller conveyor, over which so-called base plates are conveyed, which in turn accommodate the support structures 18. The flow tunnel 14 defines a number n of treatment zones 42, i, with i = 1 to n, between the entrance area 20 and the exit area 22.In the present embodiment there are a total of 22 treatment zones 42. i.

[0050] The entrance area 20 of the continuous furnace 10 opens into a heating section 44 of the continuous tunnel 14, wherein each treatment zone 42.i in the heating section 44 defines a heating zone 46.

[0051] In the present embodiment, the heating section 44 comprises the first 14 treatment zones 42.1 to 42.14. Each heating zone 46 is heated by a heating system 48. For this purpose, each heating zone 46 is assigned a heating device 50 of the heating system 48.

[0052] In the heating zones 46 of the heating section 44, the treatment tunnel 36 defines a heating tunnel 52. The heating system 48 heats the heating tunnel 52 with the heating devices 50 separately in each heating zone 46. For this purpose, a heating wall 53 is formed in the heating zones 46, which separates the heating tunnel 52 from a heating chamber 54 in which heating units 56 of the respective heating devices 50 are arranged. The heating units 56 heat the heating wall 53, which introduces heat into the heating tunnel 36 on the opposite side. Not all heating walls 53 and all heating units 56 of the heating zones 46 are provided with reference numerals.

[0053] In the present embodiment, the heating wall 53 is made of silicon carbide (SiC). Furthermore, in the present embodiment, the ceiling 38 of the treatment tunnel 36 is designed as a heating wall 53, and the heating chambers 54 of the heating zones 46 are located above the heating tunnel 52. In modifications not specifically shown, the heating wall 53 can also be, at least partially or entirely, a side wall of the heating tunnel, as already discussed above. In this case, there are one or more heating chambers 54, or at least a section thereof, arranged laterally next to the heating tunnel 52.

[0054] In a modification, the heating system 50 can also operate actively and blow heated hot gas into the heating tunnel 52 with the aid of fans in the heating chambers 54. In this case, the heating wall 53 is provided, for example, with through-openings for the hot gas.

[0055] Furthermore, in the present embodiment, in the heating section 44, each heating zone 46 also includes floor heating chambers 58 below the conveyor floor 32, in which additional heating units 56 of a respective heating device 50 are arranged. These units are not designated by reference numerals for the sake of clarity. These units heat the conveyor floor 32, through which heat is then also introduced into the treatment tunnel 36 from below.

[0056] In a modification not specifically shown, the floor heating rooms 58 and the lower heating units 56 therein can also be dispensed with.

[0057] In the present embodiment, the heating devices 50 of the heating zones 46 are controlled by a furnace control 59 (illustrated only schematically) in a heating area 60 such that the temperature in the heating tunnel 52 gradually increases in the transport direction 30 until an upper target temperature is reached. For ceramic workpieces 12, this target temperature is, for example, 1,200°C.

[0058] In a holding area 62 following in the transport direction 30, the heating device 50 of the heating zones 46 are controlled in such a way that this target temperature is kept largely constant.

[0059] In the present embodiment, the heating area 60 comprises the first 11 treatment zones 42.1 to 42.11, and the holding area 62 comprises the following three treatment zones 42.12, 42.13, and 42.14. As mentioned above, the holding area 62 can also end in a transfer area in the transport direction. Such a transfer area is then also entirely encompassed by the heating section 44 and defined by one or more heating zones 46 of the heating section 44.

[0060] In the longitudinal and transport direction 30, the heating section 44 is followed by a cooling section 64 with cooling zones 66, in which the temperature of the workpieces 12 is successively reduced. In the present embodiment, the cooling section 64 comprises the last eight treatment zones 42.15 to 42.22 and thus eight cooling zones 66. The last cooling zone 66, in the form of treatment zone 42.22, then flows into the exit area 22 and the exit lock 26.

[0061] In the cooling zones 66, the treatment zones 42 i have no radiant ceiling 52 and no heating rooms 54 or floor heating rooms 58 with heating units 56. The treatment tunnel 36 defines a cooling tunnel 68 along the cooling zones 66, which is limited at the bottom by the conveyor floor 32 there, at the top by a cooling tunnel ceiling 70 and at the sides by cooling tunnel walls.

[0062] The continuous furnace 10 comprises an atmosphere system, designated overall by 72, which controls the atmosphere balance of the continuous furnace 10. As an example of the atmosphere balance up to the cooling zones 66 and all the components required for this, Figure 1 shows a supply line 74 with a fan 76 at the inlet area 22 of the continuous furnace. In the present embodiment, ambient air is supplied; however, in modifications, predetermined and conditioned process gases can also be supplied.

[0063] With respect to the cooling zones 66, the atmosphere system 72 comprises a countercurrent cooling system 78, of which a cooling gas supply line 80 with a fan 82 is shown as an example for all required components at the last treatment zone 42.22 and thus the last cooling zone 66 before the exit area 22.

[0064] In the cooling zones 66, the cooling tunnel 68 is supplied with a cooling gas 84 by the countercurrent cooling system 78 based on the countercurrent principle, relative to the transport direction 30 of the workpieces 12 or the support structures 18, which cooling gas is formed in this case by cooling air at room temperature. However, other, differently conditioned cooling gases 84 can also be used here as a modification. The flow of the cooling gas 84 in the countercurrent direction 86 is illustrated by arrows. The countercurrent direction 86 therefore points forward in the continuous furnace 10. A countercurrent supply of cooling gas 84 can alternatively or additionally also occur in other areas of the cooling tunnel 68 in the cooling section 64 of the continuous furnace 10. In technical jargon, the flow of such a cooling gas 84 is referred to as pusher gas.In Figure 1, 88 denotes the transition from the heating section 44 to the cooling section 64; in the present embodiment, the last heating zone 46a of the heating section 44 and the first cooling zone 66a of the cooling section 64 are directly adjacent there in the transport direction 30. At the transition 88, the treatment tunnel 36 is configured such that at least a bypass portion 84a of the cooling gas 84 flowing in the cooling tunnel 68 flows in the counterflow direction 86 from the cooling tunnel 68 into the heating chamber 54 of the last heating zone 46a of the holding area 62. This bypass portion 84a is indicated schematically by an arrow in Figure 1.

[0065] Structurally, a cooling tunnel wall, in the present embodiment this is the cooling tunnel ceiling 70, of the cooling tunnel 68 has a course at the transition 88 and is designed such that the cooling tunnel 68 overlaps in cross section with the heating chamber 54 of the last heating zone 46a in some areas, so that the cooling tunnel 68 is in flow connection with this heating chamber 54.

[0066] If the cooling tunnel wall with this course and this configuration is the cooling tunnel ceiling 70 of the cooling tunnel 68, the heating chamber 54 of the last heating zone 46a is accordingly arranged, at least in part, above the heating tunnel 52. Otherwise, as mentioned above, the heating chamber can also be arranged, at least in part, laterally next to the heating tunnel 52. As already described, the heating chambers 54 of the heating zones 46 are located above the heating tunnel 52 in the present embodiment.

[0067] The cooling tunnel 68 comprises, in the counterflow direction 86, a first cooling tunnel section 90, which directly merges into a second cooling tunnel section 92, which in turn directly adjoins the last heating zone 46a of the heating section 44 at the transition 88. Thus, the second cooling tunnel section 92 defines an inlet zone of the cooling section 64 or the cooling tunnel 68, as viewed in the transport direction 30. In the present embodiment, the first cooling tunnel section 90 leads to the exit area 22, as viewed in the transport direction 30. 2. Cross-sectional enlargement

[0068] In the counterflow direction 86, the cross section of the cooling tunnel 68 increases from the first cooling tunnel section 90 to the second cooling tunnel section 92. In the present exemplary embodiment, the cross sections of the first cooling tunnel section 90 and the second cooling tunnel section 92 are each constant and the cross section of the second cooling tunnel section 92 is larger than the cross section of the first cooling tunnel section 90, which can also be seen from Figures 1 to 5.

[0069] In modifications not specifically shown, the cross section of the second cooling tunnel section 92 can also widen continuously or in stages in the counterflow direction 86 in order to form the flow connection between the heating chamber 54 of the last heating zone 46a and the cooling tunnel 68 at the transition 88.

[0070] In the present exemplary embodiments, the cross section of the first cooling tunnel section 90 along its course corresponds to the cross section of the heating tunnel 52. In modifications not shown, however, the first cooling tunnel section 90 can also have a cross-sectional course that differs from this.

[0071] The cross-section of the second cooling tunnel section 92 widens in the counterflow direction 86 both upwardly and laterally, in the present exemplary embodiment in both directions. In the present exemplary embodiment, the cooling tunnel ceiling 70 has an upward step offset 94 at the transition from the first cooling tunnel section 90 to the second cooling tunnel section 92, whereby the cooling tunnel 68 in the second cooling tunnel section 92 comprises an upper flow space 96 formed above existing support frames 18. In the flow space 96 in the second cooling tunnel section 92, the cooling tunnel ceiling 70 extends on average at a higher level than the cooling tunnel ceiling 70 in the first cooling tunnel section 90. The second cooling tunnel section 92 is higher than the first cooling tunnel section 90 by a factor of 1.1 to 1.5, in particular by a factor of 1.2 to 1.3.

[0072] The cooling tunnel walls designated 98 each have a stepped offset 100 to the left and right at the transition from the first cooling tunnel section 90 to the second cooling tunnel section 92; if necessary, only one stepped offset 100 may be present on the left or right. The second cooling tunnel section 92 is wider than the first cooling tunnel section 90 by a factor of 1.1 to 1.5, in particular by a factor of 1.1 to 1.3.

[0073] As a result, a bypass portion 84a of approximately 30% of the cooling gas 84 flowing into the heating chamber 54 of the last heating zone 46a could be achieved.

[0074] At transition 88, the cooling tunnel walls 98 then merge in the counterflow direction 86 via a respective step offset 102 into the walls of the last heating zone 46a, as can be seen in Figure 3A with a view of transition 88. In contrast, the cooling tunnel ceiling 70 of the second cooling tunnel section 92, which is offset upwards there, merges without any offset into the heating chamber ceiling 104 of the heating chamber 54 of the last heating zone 46a. This configuration is also clearly visible in Figures 4 and 5.

[0075] In a modification not specifically shown, the cooling tunnel ceiling 70 of the second cooling tunnel section 92 can also be located lower, as long as a flow transition from the flow space 96 into the heating space 54 of the last heating zone 46a remains possible.

[0076] In the modification in which the second cooling tunnel section 92 has a cross-section according to Figure 3B along its longitudinal extent, there are no lateral step offsets 100 of the cooling tunnel walls 98.

[0077] These are also missing in the modification in which the second cooling tunnel section 92 has a cross-section according to Figure 3C along its longitudinal extension. Figure 3C illustrates a variant in which the cooling tunnel ceiling 70 has a plurality of upward step offsets 94, such that a plurality of parallel upper flow spaces 96 are formed. In the embodiment illustrated in Figure 3C, these are two flow spaces 96a, 96b, which each border on the left and right of the respective cooling tunnel wall 98. However, lateral step offsets 100 of the cooling tunnel walls 98 can also be present in this variant if necessary.

[0078] The heating chamber 54 of the last heating zone 46a, together with the heating chambers 54 of the counterflow direction 86, i.e. the forwardly following heating zones 46, forms a bypass flow channel 106, which is configured such that the portion 84a of the cooling gas 84 flows back into the heating tunnel 52 as hot gas 108. In the present embodiment, the bypass flow channel 106 extends along the holding area 62. The bypass flow channel 106 is formed by the heating chambers 54 of the holding area 62 of the heating section 44, which is why the hot gas 108 is shown in Figure 1 as an arrow at the treatment zone 42.12. The heating chamber 54 of the first heating zone of the holding section 62, which is additionally designated 46b, is arranged such that the hot gas 108 flows from the bypass flow channel 106 into the heating tunnel 52.

[0079] For this purpose, the heating wall 53 there has a flow outlet 110, which is formed, for example, by through-openings in the heating wall 53. In addition, a flow guide device 112 can be provided, which directs and supports the flow of the hot gas 108. A baffle plate for this purpose can be seen in Figure 1. Alternatively or additionally, the hot gas 108 can also be guided through injector nozzles and thus flow into the heating chamber 52 in a more targeted manner. For example, further alternatively or additionally, the side walls of the heating tunnel 52 can be offset outwards in the inflow area, so that the heating tunnel 52 has a laterally expanded cross-section there, which enables the hot gas 108 to flow into the heating tunnel 52 from the side.

[0080] By means of the heating units 56 of the heating system 50 in the heating chambers 54 of the bypass flow channel 106, the bypass portion 84a of the cooling gas 84 is successively heated to the hot gas 108 on its way to the flow outlet 110.

[0081] Since, precisely in the inlet region of the bypass flow channel 106, the heating units 56 there must heat or heat up both the heating wall 54 and the bypass portion 84a of the cooling gas 84, the heating system 50 is designed such that the heating output in the inlet region is greater than in the other heating chambers 54. In the present exemplary embodiment, this is achieved by having twice as many heating units 56 as in the other heating zones 46 of the bypass flow channel 106, at least in the last heating zone 46a and, in the present exemplary embodiment, also in the preceding heating zone 46. In this case, the last heating zone 46a and the preceding heating zone 46 of the heating section 44 define the inlet region of the bypass flow channel 106.

[0082] Generally speaking, a bypass device 114 is thus formed, by means of which a bypass portion 84a of the cooling gas 84 can be discharged through a bypass flow channel 106 from the cooling tunnel 68 and thereby from the flow space 96 and can be returned as hot gas 108 into the heating tunnel 52 in a heating zone 46b located further forward.

[0083] Such a heating zone 46b located further forward can, for example, also be located in the heating area 60 and may even be the first treatment zone 42.1 of the continuous furnace 10.

[0084] The bypass device 114 can comprise an injector system 116, already shown in Figures 1, 4, and 5, with which an auxiliary flow 118 consisting of an auxiliary flow gas 118a is blown into the cooling tunnel 68, here into the flow chamber 96, or can be designed without such an injector system 116. First, the variant without an injector system 116 will be discussed. Figure 6 again shows a section in the region of the transition 88 of the continuous furnace 10, and Figure 7 illustrates a flow profile 120 of the cooling gas 84 in the region of the flow chamber 98.

[0085] At the step offset 94, a vacuum region 122 forms in the flow space 96, which is why the cooling gas 84 is drawn upward in the counterflow direction 86; this generates the bypass portion 84a, the formation of which is also due to convection effects and the resulting thermal rise of the cooling gas 84, which reaches the second cooling section 92 of the cooling tunnel 68 heated compared to its inlet temperature. The vacuum region 122 is indicated schematically in Figures 6 to 8. However, this does not imply a concrete demarcation; the flow conditions there are constantly changing, not least because the cooling gas 84 flows along and through the moving support frames 18.

[0086] As Figures 6 and 7 illustrate, without any further measures, a moderate upward suction effect on the cooling gas 84 occurs. 3. Injector system

[0087] The suction and thus conduction effect of the cooling gas 84 can be improved by the above-mentioned injector system 116. This increases the bypass portion 84a of the cooling gas 84, which flows into the heating chamber 54 of the last heating zone 46a—and thus into the bypass flow channel 108.

[0088] The injector system 116 is initially generally configured such that the auxiliary flow 118 is blown in with a directional component toward the heating chamber 54 of the last heating zone 46a. For this purpose, the injector system 116 provides one or more discharge openings 124 for an auxiliary flow gas 118a. These are supplied from a source with the auxiliary flow gas 118a for the auxiliary flow 118. In the present exemplary embodiment, the injector system 116 comprises a plurality of injector nozzles 126, each providing a discharge opening 124. In the present exemplary embodiment, in a variant A, the discharge openings 124 are arranged on the end wall 128 of the flow chamber 96 that is opposite the heating chamber 54 of the last heating zone 46a or the bypass flow channel 106. For this purpose, the injector nozzles 126 are provided in the end wall 128.The injector nozzles 126 are arranged there along a horizontal straight line and, specifically in the present embodiment, largely over a width of the flow space 96 which corresponds to the width of the first cooling tunnel section 90.

[0089] The discharge openings 124 are arranged at a distance of approximately 10 cm. The number of injector nozzles 126 or discharge openings 124 for the auxiliary flow gas 118a depends, among other things, on the width of the cooling tunnel 68.

[0090] In a modification not specifically shown, additional injector nozzles 126 may also be present at other positions, for example in the cooling tunnel walls 98 in the direction of the bypass flow channel 106.

[0091] In addition, the auxiliary flow gas 118a can be injected into the cooling tunnel 68 or the flow chamber 96 at one or more different angles. In a modification not specifically shown, the injector nozzles 126 of the injector system 116 can also be designed as slot nozzles with slot-shaped discharge openings 124, which are formed, for example, along the horizontal straight line.

[0092] As Figure 8 schematically illustrates and Figure 9 illustrates with reference to the flow profile 120 therein, the flow auxiliary gas 118 supports the flow of the bypass portion 84a of the cooling gas 84 through the flow chamber 96 into the bypass flow channel 106. This can lead to an acceleration of the flow in the flow chamber 96, which may further reduce the pressure in the negative pressure region 122 and thereby further increase the suction effect.

[0093] In addition, further negative pressure zones 130 can form in the flow space 96 next to the transition 88, so that cooling gas 84 is also drawn upwards there from the underlying area of ​​the second cooling tunnel section 92 of the cooling tunnel 68.

[0094] With the injector system 116, the bypass portion 84a of the cooling gas 84 flowing into the heating chamber 54 of the last heating zone 46a can be increased to up to 70% of the cooling gas 84.

[0095] The embodiment shown in Figure 10 illustrates, as variant B, a further modification of the injector system 116, in which the discharge openings 124 of the injector system 116 are arranged at a distance from the end wall 128 within the flow chamber 96. This is achieved in the present embodiment in that the injector nozzles 126 are designed as nozzle lances 132, the free end of which provides the discharge opening 124 and which protrude from the end wall 128 into the flow chamber 96.

[0096] In a modification, the injector system 116 can also comprise a nozzle bar that projects laterally from the cooling tunnel wall 98 into the flow chamber 96 and has one or more discharge openings 124, which can also be slot-shaped, arranged such that the auxiliary flow gas 118a is discharged as auxiliary flow 118 in the direction of the bypass flow channel 106. The injector system 116 comprises a control device 134, by means of which the volume flow of the auxiliary flow 118 can be adjusted. For this purpose, the control device 134 comprises, for example, a supply fan whose speed can be changed accordingly. Alternatively or additionally, throttle valves or the like can be provided on the injector nozzle(s) 126. Existing injector nozzles 126 or the volume flows of the auxiliary flow gas 118a delivered via them can be controlled individually, in groups or as a whole.

[0097] 4. Homogeneous temperature distribution and energy balance

[0098] Due to the concept described above, the cross-sectional expansion formed in the second cooling tunnel section 92 causes the flow above the support frames 18 with the workpieces 12 to be increased to the bypass portion 84a of the cooling gas flow 84.

[0099] In the cooling tunnel 68, the cooling gas 84 heats up in direct contact with the support frames 18 and the workpieces 12. Due to convection and thermal buoyancy of the cooling air 84, which heats up on its upward path toward the cooling tunnel ceiling 70, temperature differences occur between the cooling air 84 and the workpieces 12.

[0100] In addition, a convective heat transfer between the support frames 18 and workpieces 12 and the cooling gas 84 leads to a significant heating of the cooling gas 84, whereby the temperature of the cooling gas 84 nevertheless remains significantly below the temperature in the holding area 62.

[0101] Because the cooling gas 84 or its bypass portion 84a can flow upwards in the second cooling tunnel section 92, the temperature distribution in the holding area 62 is homogenized. The support frames 18 with the workpieces 12 thus enter a more homogeneously tempered final heating zone 46a with fewer temperature differences on the workpieces 12 than without these measures. Furthermore, the bypass portion 84a of the cooling gas 84 is effectively used as a resource for heating the workpieces 12 in the heating section 44 and, in the present embodiment, in its holding area 62. The cooling gas 84, which has already been passively heated on its way, only needs to be further heated to the temperature required for the heating zones 46 in the holding area 62 with relatively low energy expenditure.

[0102] This can significantly improve the energy balance of the continuous furnace 10.

[0103] Without the injector system 116, up to 30% of the cooling gas 84 can be fed into the bypass flow channel 106 as a bypass portion 84a. When the injector system 116 is present and in operation, up to 70% of the cooling gas 84 can be fed into the bypass flow channel 106 as a bypass portion 84a. By controlling the volume flow of the auxiliary flow 118 through the injector system 116, the bypass portion 84a of the cooling gas 84 can be adjusted, in particular, between 30% and 70%.

Claims

PATENT CLAIMS 1. A continuous furnace for the heat treatment of workpieces (12), comprising a) a tunnel housing (16) in which a treatment tunnel (36) is formed, in which the workpieces (12) receive their heat treatment; b) a conveyor system (34) by means of which the workpieces (12) can be conveyed in a transport direction (30) through the treatment tunnel (38); c) a heating section (44) with a plurality of heating zones (46), in which the treatment tunnel (36) defines a heating tunnel (52); d) a heating system (50) by means of which the heating tunnel (52) can be heated in the heating zones (46), wherein the heating tunnel (52) is separated in each heating zone (46) by a heating wall (53) from a heating chamber (54) with a heating device (48); e) a cooling section (64) which directly adjoins the heating section (44) in the transport direction (30) and comprises a plurality of cooling zones (66) in which the treatment tunnel (36) defines a cooling tunnel (68);f) a countercurrent cooling system (78) by means of which the temperature of the workpieces (12) in the cooling tunnel (68) can be lowered and which is configured such that a cooling gas (84) can flow through the cooling tunnel (68) in a countercurrent direction (86) relative to the transport direction (30); characterized in that g) the treatment tunnel (36) is designed at the transition (88) from the heating section (44) to the cooling section (64) such that at least a bypass portion (84a) of the cooling gas (84) flowing in the countercurrent direction (86) flows into the heating chamber (54) of the last heating zone (46a).

2. Continuous furnace according to claim 1, characterized in that the cooling tunnel (68) defines a cooling tunnel ceiling (70) which has a course at the transition (88) and is designed such that the cooling tunnel (68) overlaps in cross-section with the heating chamber (54) of the last heating zone (46a) in some areas, so that the cooling tunnel (68) is in flow connection with this heating chamber (54).

3. Continuous furnace according to claim 2, characterized in that the cooling tunnel (68) comprises a first cooling tunnel section (90) in the counterflow direction (86), which directly merges into a second cooling tunnel section (92), which in turn directly adjoins the last heating zone (46a) of the heating section (44) at the transition (88), wherein the cross section of the cooling tunnel (68) increases in the counterflow direction (86) from the first cooling tunnel section (90) to the second cooling tunnel section (92).

4. Continuous furnace according to claim 3, characterized in that the cross sections of the first cooling tunnel section (90) and the second cooling tunnel section (92) are each constant.

5. Continuous furnace according to claim 3 or 4, characterized in that the cross section of the second cooling tunnel section (92) increases in the upward direction and in particular the second cooling tunnel section (92) is at least partially higher by a factor of 1.1 to 1.5, in particular by a factor of 1.2 to 1.3, than the first cooling tunnel section (90).

6. Continuous furnace according to claim 5, characterized in that the cooling tunnel ceiling (70) has a step offset (94) upwards at the transition from the first cooling tunnel section (90) to the second cooling tunnel section (92), whereby the cooling tunnel (68) in the second cooling tunnel section (92) comprises an upper flow space (96).

7. Continuous furnace according to claim 5 or 6, characterized in that the cross section of the second cooling tunnel section (92) increases in the direction of the side and in particular the second cooling tunnel section (92) is at least partially wider by a factor of 1.1 to 1.5, in particular by a factor of 1.1 to 1.3, than the first cooling tunnel section (90).

8. Continuous furnace according to claim 7, characterized in that one or both cooling tunnel walls (98) at the transition from the first cooling tunnel section (90) to the second Cooling tunnel section (92) each have a step offset (100) to the left or right.

9. Continuous furnace according to one of claims 1 to 8, characterized in that the heating chamber (54) of the last heating zone (46a) is arranged partially or completely above its heating wall (53).

10. Continuous furnace according to one of claims 1 to 9, characterized in that one or more heating chambers (54) define a bypass flow channel (106) which is arranged such that the bypass portion (84a) of the cooling gas (84) flows back into the heating tunnel (52) as hot gas (108).

11. Continuous furnace according to claim 10, characterized in that the bypass flow channel (106) extends in a holding area (62) of the heating section (44), in which a target temperature is to be kept constant, and is arranged such that the hot gas (108) in the first heating zone (46b) of the holding area (62) flows from the bypass flow channel (106) back into the heating tunnel (52).

12. Continuous furnace according to claim 10 or 11, characterized in that in the bypass flow channel (106) the heating devices (50) in the heating chambers (54) are arranged so that on the one hand the heating wall (53) there and on the other hand the bypass portion (84a) of the cooling gas (84) can be heated.

13. Continuous furnace according to claim 12, characterized in that the heating system (50) is designed such that the heating power is greater in the inlet region of the bypass flow channel (106) than in the other heating chambers (54), in particular in that the heating devices (50) in the bypass flow channel (106) comprise heating units (56) and in one or more heating chambers (54) which are to be assigned to the inlet region of the bypass flow channel (106), more heating units (56) are present than in the other heating zones (46) of the bypass flow channel (106).

14. Continuous furnace according to claim 13, characterized in that the last heating zone (46a) and the preceding heating zone (46) of the heating section (44) define the inlet region of the bypass flow channel (106).

15. Continuous furnace according to one of claims 1 to 14, characterized in that an injector system (116) is provided, by means of which an auxiliary flow (118) of an auxiliary flow gas (118a) with a directional component in the direction of the heating chamber (54) of the last heating zone (46a) can be blown into the cooling tunnel (68).

16. Continuous furnace according to claim 15, characterized in that the flow space (96) is designed according to claim 6 and the injector system (116) is arranged such that the auxiliary flow (116) can be blown into the flow space (96).

17. Continuous furnace according to claim 16, characterized in that the injector system (116) provides one or more discharge openings (124) for the auxiliary flow gas (118a), wherein in a variant A one or more discharge openings (124) are arranged on an end wall (128) of the flow space (96) which is opposite the heating space (54) of the last heating zone (46a), and / or in a variant B one or more discharge openings (124) are arranged at a distance from this end wall (128) of the flow space (96) which is opposite the heating space (54) of the last heating zone (46a).

18. Continuous furnace according to claim 17, characterized in that one or more injector nozzles (126) are provided, in particular one or more injector nozzles (126) which in variant A are provided in the end wall (128) and / or in variant B are designed as nozzle lances (132), the free end of which provides the discharge opening (124) and which protrude from the end wall (128) into the flow space (96).

19. Continuous furnace according to one of claims 15 to 18, characterized in that the injector system (116) comprises a control device (134) by means of which the volume flow of the auxiliary flow (118) can be adjusted.

20. A method for heat treatment of workpieces (12), characterized in that a continuous furnace according to one of claims 1 to 19 is used.

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