EP0151700B1 - Industrial furnace, especially a multiple chamber vacuum furnace, for heat treating batches of metal workpieces - Google Patents

Abstract

An industrial furnace for heat-treating metallic workpieces has separate heating and cooling chambers. The latter uses a circulating cooling gas, the flow of which against or past the workpieces produces cooling or gas-quenching. The furnace may have another chamber for oil-quenching lying below the gas-cooling chamber. In order to enable the gas cooling to operate quickly and efficiently, a cooling box fed with air by ventilator fans is provided in the shape of a tunnel, with internal surfaces above and at both sides of the effective cooling space constituted by interchangeable nozzle plates (or blank plates if no nozzle openings are desired at the top or at the sides). The workpieces to be cooled rest on a platform which may be raised or lowered to adjust the distance from the top nozzle plate or lowered into an oil bath. The nozzle plates provide a choice of nozzle patterns for different articles or groups of articles to be cooled after heat treatment. The nozzle plates may have setbacks or protrusions in order to vary the spacing of the nozzle openings from the median plane of the cooling tunnel.

Description

The invention relates to an industrial furnace, in particular a multi-chamber vacuum furnace for the heat treatment of batches of metallic workpieces, with a heating chamber and a cooling chamber containing a cooling device acted upon with cooling gas, in which a heat-treated batch is flowed with cooling gas which is circulated via a heat exchanger, and optionally with a Oil bath.

Industrial furnaces of this type are used to a large extent for hardening steel parts, in particular all types of parts made of tool steels, as well as for various cooling processes and other heat treatments of metal parts. An example of such an industrial furnace is described in DE-A-1 933 593.

This vacuum oven has a heating compartment and an adjoining cooling compartment. The cooling compartment contains a cooling chamber housing which is open at the bottom and in which there is a bell-shaped partition. At the upper tapered opening there is a fan through which the cooling gas is to be circulated in the cooling chamber. Between the cooling chamber housing and the intermediate wall, a heat exchanger surrounding the intermediate wall is arranged over its entire longitudinal extent.

If the pallet with the workpieces is introduced from below through the opening into the interior of the cooling chamber housing, the interior of the cooling chamber housing to the cooling compartment is thereby closed off by the lifting device for the pallet. However, an annular gap remains between the pallet and the lower edge of the partition. The fan of the cooling chamber sucks the cooling gas up through the annular gap past the hot charge, from where it passes down again to the annular gap via the water-cooled heat exchanger. Since the opening for the fan has a smaller cross-section than the base area of the space surrounded by the intermediate wall, there is essentially a flow along a cone shell through the charge.

From DE-C-863 070 it is known to guide a double-walled cylindrical tube, the inner tube of which has holes, into a single-chamber furnace via the batch, which remains in the furnace for heating and cooling at the same place. From above, the air is blown into the annular channel between the inner and outer tubes via an annular air supply and then flows through the holes towards the batch. In addition to the fact that the furnace has to be opened to insert the cylinder - this leads to an uncontrolled cooling of the batch - the complete pipe must also be exchanged for another batch with holes adapted to the batch in the case of different batches.

The object of the invention is therefore to provide an industrial furnace, in particular a multi-chamber vacuum furnace with a cooling chamber containing a gas cooling device, in which an optimal adaptation of the flow conditions of the respective batch to be cooled to the conditions of this batch is possible with simple means, without the need for expensive , expensive or difficult to use facilities would be required.

To achieve the object, the industrial furnace mentioned at the outset has a nozzle box which is arranged in the cooling chamber and is supplied with cooling gas and in which at least one nozzle plate arranged opposite the batch is interchangeably used to change the blowing conditions of the batch.

In a preferred embodiment, the exchangeable nozzle plates differ by nozzles with different nozzle arrangements and / or with different nozzle diameters and / or with different distances from the batch.

The new industrial furnace only allows high cooling gas speeds to be generated in the cooling chamber by means of a corresponding nozzle plate arrangement and thus a corresponding selection of the nozzle arrangement, nozzle distribution and other nozzle characteristics at or within the batch to be cooled, where maximum cooling effect is required. The design effort for the simple nozzle box with the interchangeable nozzle plates is low.

It is advantageous if at least some nozzles of at least one nozzle plate are arranged in an orientation resulting in a baffle flow and / or a parallel flow of the cooling gas on the charge. For a given cooling gas circulation capacity, the maximum cooling speed of the batch depends on the heat transfer values achieved. It is known that the gas inflow of the charge has a decisive influence on the degree of heat transfer from the cooling gas / charge, with higher heat transfer values being achieved in the case of an impact flow than in the case of parallel flow, in which the cooling gas flows parallel to the workpiece surface. Other parameters for heat transfer include Nozzle outlet speed, nozzle diameter, nozzle distance from the batch, distance between the nozzles, average cooling gas temperatures and average batch temperatures.

The nozzles are advantageously arranged surrounding the batch on several sides in the cooling chamber, which results in particularly simple structural conditions if the nozzle box has guide devices into which the respective nozzle plate can be inserted.

By simply replacing the nozzle plates, the above-described adaptation of the cooling device to the parameters mentioned for the heat transfer can be achieved in a very simple manner. The individual, interchangeable nozzle plates can not only have different nozzle arrangements (nozzle images) and nozzle diameters, etc., but it can also have, for example, a nozzle plate projecting into or out of the interior of the cooling chamber, in order to reduce the distance between the nozzles and the Change batch according to the respective circumstances.

As a rule, the heat-treated batch will be surrounded by nozzles on several sides, for which purpose the nozzle box is expediently tunnel-shaped and is delimited on its inner wall by at least one nozzle plate. In addition to the nozzle plate, at least one gas-impermeable blind plate can be detachably used. In this way, an effective impingement flow can be achieved with plate-shaped workpieces by inserting lateral nozzle plates and a blind plate above the charge, so that the stationary workpiece can be optimally cooled from all sides. With a batch of cylindrical stationary tools, only parallel flow can be used as through-flow cooling, because cooling by means of impingement flow is not possible due to the shape of the workpiece and the large number of workpieces. For this through-flow cooling, a nozzle plate is inserted above and dummy plates on both sides of the batch. The nozzle distance from the batch can then be optimized on each side by means of the nozzle plates already mentioned, with an area projecting into or out of the interior of the cooling chamber. In order to be able to carry out the aforementioned arrangement of the nozzle plates in a simple manner, it is advantageous if the nozzle box is delimited on at least three inner sides by nozzle plates, two of which are arranged opposite one another and the third nozzle plate is arranged between the other two nozzle plates.

In addition, a lifting and lowering device receiving the batch can be arranged in the cooling chamber, by means of which the batch can be brought into a predetermined distance from at least part of the nozzle orifices of at least one nozzle plate.

Characterized in that in the nozzle box, the nozzle plates are evenly charged with cooling gas, an equal exit speed is guaranteed at all nozzles of the respective nozzle plate, and thus a uniform cooling effect on the entire loaded batch area. Such a uniform cooling effect is important to achieve a desired structural state in the batch to be cooled.

In the new industrial furnace, the cooling device is not located in the heating chamber, but in its own cooling chamber. The cold batch environment in the cooling chamber not only exploits the convective heat transfer from the batch to the cooling gas, but also the heat dissipation by radiation, which helps in the upper temperature range in particular to increase the cooling effect. Compared to single-chamber vacuum ovens, there is the advantage that the heating chamber, the heating elements and the batch hearth do not have to be cooled together with the batch after the heat treatment in the critical cooling range, so that the cooling capacity achieved on the batch is not reduced by the heat dissipation of the heating chamber device . The cooling chamber separate from the heating chamber enables the described adaptability of the nozzle cooling device to the conditions of the respective batch, while on the other hand the heating chamber can be designed for optimum heating conditions regardless of the cooling of the batch required after the heat treatment.

• Fig. 1 einen Doppelkammer-Vakuumofen gemäß der Erfindung, im axialen Schnitt, in einer Seitenansicht,
• Fig. 2 den Doppelkammer-Vakuumofen nach Fig. 1, geschnitten längs der Linie 11-11 der Fig. 1, in einer Seitenansicht,
• Fig. 3 den Dpppelkammer-Vakuumofen nach Fig. 1, geschnitten längs der Linie 111-111 der Fig. 1, in einer Seitenansicht,
• Fig. 4 den Doppelkammer-Vakuumofen nach Fig. 1, geschnitten längs der Linie IV-IV der Fig. 1, in einer Seitenansicht,
• Fig. 5 den Düsenkasten des Doppelkammer-Vakuumofens nach Fig. 3, in einer schematischen Seitenansicht, im Querschnitt, in einem anderen Maßstab, unter Veranschaulichung einer bestimmten Charge und einer bestimmten Düsenanordnung,
• Fig. 6 das an der oberhalb der Charge angeordnete Düsenblech der Anordnung nach Fig. 5, in einer Draufsicht,
• Fig. 7 den Düsenkasten nach Fig. 5, mit einer anderen Anordnung der Düsenbleche, in einer entsprechenden Darstellung,
• Fig. 8 ein oberhalb der Charge angeordnetes Düsenblech der Anordnung nach Fig. 7, in einer Draufsicht,
• Fig. 9 den Düsenkasten nach Fig. 7, in einer entsprechenden Darstellung,
• Fig. 10 ein seitlich der Charge angeordnetes Düsenblech der Anordnung nach Fig. 9, in einer Draufsicht,
• Fig. 11 den Düsenkasten nach Fig. 5, mit einer anderen Anordnung der Düsenbleche, in einer entsprechenden Darstellung,
• Fig. 12 ein oberhalb der Charge angeordnetes Düsenblech der Anordnung nach Fig. 11, in einer Draufsicht,
• Fig. 13 den Düsenkasten nach Fig. 5, beschickt mit einer anderen Charge, in einer entsprechenden Darstellung,
• Fig. 14 ein seitlich der Charge angeordnetes Düsenblech der Anordnung nach Fig. 13, in einer Draufsicht,
• Fig. 15 den Düsenkasten nach Fig. 5, beschickt mit einer anderen Charge, in einer entsprechenden Darstellung,
• Fig. 16 ein seitlich der Charge angeordnetes Düsenblech der Anordnung nach Fig. 15, in einer Draufsicht,
• Fig. 17 den Düsenkasten nach Fig. 5, mit einer anderen Anordnung der Düsenbleche, in einer entsprechenden Darstellung, und
• Fig. 18 das oberhalb der Charge angeordnete Düsenblech der Anordnung nach Fig. 17 in einer Draufsicht.

In the drawing, an embodiment of the object of the invention is shown. Show it:

• 1 is a double-chamber vacuum furnace according to the invention, in axial section, in a side view,
• 2 shows the double-chamber vacuum oven according to FIG. 1, cut along the line 11-11 of FIG. 1, in a side view,
• 3 shows the double chamber vacuum furnace according to FIG. 1, cut along the line 111-111 of FIG. 1, in a side view,
• 4 shows the double-chamber vacuum furnace according to FIG. 1, cut along the line IV-IV of FIG. 1, in a side view,
• 5 shows the nozzle box of the double-chamber vacuum furnace according to FIG. 3, in a schematic side view, in cross section, on a different scale, illustrating a specific batch and a specific nozzle arrangement,
• 6 is a top view of the nozzle plate of the arrangement according to FIG. 5 arranged above the batch,
• 7, the nozzle box according to FIG. 5, with a different arrangement of the nozzle plates, in a corresponding representation,
• 8 is a top view of a nozzle plate of the arrangement according to FIG. 7 arranged above the batch,
• 9, the nozzle box according to FIG. 7, in a corresponding representation,
• 10 is a top view of a nozzle plate of the arrangement according to FIG. 9 arranged on the side of the charge,
• 11 shows the nozzle box according to FIG. 5, with a different arrangement of the nozzle plates, in a corresponding representation,
• FIG. 12 shows a nozzle plate of the arrangement according to FIG. 11 arranged above the batch, in a Top view,
• 13 shows the nozzle box according to FIG. 5, loaded with another batch, in a corresponding representation,
• 14 is a top view of a nozzle plate of the arrangement according to FIG. 13 arranged to the side of the batch,
• 15 shows the nozzle box according to FIG. 5, loaded with another batch, in a corresponding representation,
• 16 is a top view of a nozzle plate of the arrangement according to FIG. 15 arranged on the side of the charge,
• FIG. 17 shows the nozzle box according to FIG. 5, with a different arrangement of the nozzle plates, in a corresponding representation, and
• 18 shows a top view of the nozzle plate of the arrangement according to FIG. 17 arranged above the batch.

The double-chamber vacuum furnace shown in FIGS. 1 to 4 has a double-walled, water-cooled housing 1, in the rear part of which a heating chamber 2 and in the front part of which a cooling chamber 3 are accommodated. The essentially cylindrical housing 1 is closed on the front side by a water-cooled double-jacket door 4 which serves for loading and unloading the furnace and can be pivoted or pushed. On the rear side in the area behind the heating chamber 2, a double-walled swing door 5 is provided, which closes a housing opening available for assembly purposes. A double-walled, water-cooled container 6 adjoins the housing 1 below the cooling chamber 3, which is flanged to the housing 1 and in which there is an oil bath, the level of which is indicated at 7.

In the front part of the cooling chamber 3, the housing 1 carries three radially projecting flanges 8 distributed around its circumference in the manner shown in FIG. 2, onto which double-walled, water-cooled hoods 9 are placed, each of which covers a fan drive unit 10 .

The heating chamber 2, which is essentially rectangular in cross section, is constructed in a lightweight steel construction and is lined with a multi-layer insulation made of high-quality ceramic fiber material and the purest graphite felt. Large-area graphite heating elements 12 are arranged on both sides and above the batch indicated at 11. This all-round arrangement of the graphite heating elements 12 ensures rapid and uniform heating of the batch 11. The current supply of the graphite heating elements 11 takes place via heating element connecting bolts 13 and one heating element connecting flange 14 in each case.

The batch 11 is located in the heating chamber 2 on a stove 15, which can be raised and lowered for transport purposes. The end wall of the heating chamber 2 adjoining the cooling chamber 3 is closed by a horizontally movable heating chamber door 16.

Otherwise, the heating chamber 2 is optimally designed for the lowest possible storage heat and for heat treatment according to a preselected temperature program. Compared to single-chamber furnaces, neither the cooling gas flow and cooling gas speed nor other parameters for heat dissipation from the batch need to be taken into account.

The cooling chamber 3, which is arranged approximately coaxially to the heating chamber 2, contains a cooling device 17 which has a nozzle box 18 which is tunnel-shaped with an essentially U-shaped cross section and a heat-treated batch 11a to be cooled in the manner shown in FIG. 3 above and covering on both sides. The nozzle box 18 carries on the open inner sides pointing towards the batch 11a in pairs mutually associated side guide grooves 19 into which the nozzle plates 20, 20a or blind plates 21 are optionally inserted interchangeably, as will be explained with reference to FIGS. 5 to 18.

At its front end, the nozzle box 18 is directly connected to three fan housings 22, each of which contains a high-performance fan wheel 23, which sits directly on the shaft end of the associated drive motor 10, the vacuum-tight current feedthroughs of which are indicated at 24. The suction opening of each fan housing 22 is preceded laterally by two heat exchangers 25, which are supplied with cooling water via vacuum-tight feed and discharge ducts and to which gas guide plates 26 are assigned.

In the embodiment shown, three fan housings 22 and three associated fan units 10, 23 are provided. Embodiments are also conceivable in which only two fan housings 22 or also a single fan housing 22 are or are present.

The oil bath contained in the container 6 can be circulated evenly and vigorously by a hydraulic oil circulator 27, the speed of rotation of the oil circulator 27 being adjustable as required. An oil bath heater 28 allows the vacuum quenching oil to be brought to the desired temperature and to be kept at this temperature.

In the container 6, a lifting and lowering platform 29 is arranged, which makes it possible to bring a heat-treated batch 11 a coming from the heating chamber 2 in the cooling chamber 3 to a certain height with respect to the nozzle box 18 - as will be explained in more detail below - Or immerse the batch 11 a in the quenching oil contained in the container 6.

If the double chamber vacuum furnace is designed without oil bath quenching, the container 6 with the oil bath contained therein is dispensed with.

When the door 4 is open, the double-chamber vacuum oven can be charged manually or automatically, the batch 11 being automatically moved into the open heating chamber 2. The heating chamber door 16 and the door 4 closing the loading opening are then closed, whereupon the vacuum furnace is evacuated. The batch 11 is then heat-treated in the heating chamber 2 according to a preselected temperature program. At the end of the heating cycle, the vacuum furnace is filled with inert gas under a maximum pressure of 6 bar abs. fumigated again. The fan drive motors 10 are switched on. The heating elements 12 are switched off and the batch 11 is moved into the cooling chamber 3, where it takes the place of the batch 11a and is quenched with cooling gas.

By appropriate actuation of the lifting and lowering platform 29, the charge in the cooling chamber 3 can be moved up to the nozzle plate 20 of the nozzle box 18 located above as required.

If the batch 11 is to be quenched in oil after the heat treatment in the heating chamber 2, it is lowered into the oil bath after it has been moved out of the heating chamber 2 by means of the lifting and lowering platform 29. If necessary, you can pre-cool briefly with inert gas before quenching the oil. The double chamber vacuum furnace is controlled automatically; the complete heat treatment cycle can be selected.

The nozzle box 18 is designed so that only low gas speeds occur in it, which on the one hand cause only small flow losses and on the other hand create the same pressure conditions at the nozzles of the nozzle plates 20, 20a, which lead to the same nozzle outlet speeds, which are the prerequisite for uniform cooling of the batch 11 are.

Since the nozzle plates 20, 20a are arranged interchangeably in the nozzle box 18 and, if appropriate, can be replaced by blind plates 21, the quenching conditions in the cooling chamber 3 can be optimally adapted to the shape and composition of each batch 1a. This is illustrated by way of example in FIGS. 5 to 18:

In the arrangement according to FIG. 5, the batch 11 a to be quenched consists of a number of slim, cylindrical tools, for example twist drills or milling cutters, with a diameter of 45 mm × 300 mm. In order to keep the distortion during heat treatment and quenching to a minimum, the cylindrical workpieces designated with 30 are charged standing, whereby they are evenly distributed on the base of the batch. The base area of the batch corresponds to the rectangular outline area of the nozzle plate 20 shown in FIG. 6.

Through-flow cooling with parallel flow is required for uniform and intensive gas quenching. For this purpose, a horizontal nozzle plate 20 is inserted into the nozzle box 18 above the charge 11a, while blind plates 21 are attached to the side of the charge 11a. The nozzle plate 20 carries nozzle openings 35 (FIG. 6) which are uniformly distributed over its entire surface and which ensure uniform and simultaneous cooling of all workpieces 30.

The distance between the nozzle openings 35 and the batch 11a has been optimized by lifting by means of the lifting and lowering platform 29. The overstroke is indicated at 32 in FIG. 5.

Workpieces that occupy the entire available batch length must be loaded horizontally. This is illustrated in FIGS. 7, 8:

In order to be able to fully utilize the heat transfer by radiation to the round cold cooling chamber walls, the batch 11 a consists only of a workpiece 33 in the form of a cylindrical mandrel. Since this mandrel has a relatively small inflow area in comparison to the batch base area given by the rectangular outline of the nozzle plate 20a of FIG. 8, a cooling gas flow concentration in the region of the workpiece 33 to be cooled is necessary in order to achieve maximum cooling speeds. This requirement can be achieved either by reducing the number of nozzle openings 35 while simultaneously increasing the nozzle outlet speed, or with a constant number of nozzles by reducing the nozzle spacing 36 (FIG. 8).

For the above considerations, a nozzle plate 20a is inserted in the nozzle box 18 above the charge 11, which has a region 40 projecting into the interior of the cooling chamber 3, in which the nozzle openings 35 are arranged. The nozzle plate 20a thereby has a channel-like or box-like shape; the area containing the nozzle openings 35 is delimited on both sides by an unperforated area 41.

In addition, the workpiece 33 has been brought up to the nozzle openings 35 through the lifting and lowering platform 29, as is indicated at 32 in FIG. 7.

In this case, the nozzle pattern is determined in the manner shown in FIG. 18 by nozzle bores 35 of the same diameter arranged in a rectangular pattern with the same height and lateral spacings.

To the side of the workpiece 21, dummy plates 21 are inserted in the nozzle box 18 in order to prevent opposing cooling gas flows colliding against one another in the vicinity of the workpiece because this would substantially reduce the cooling gas velocity directly on the workpiece 33.

In the arrangement according to FIGS. 9, 10 there is the batch 11 from a heavy, compact tool, for example a cylindrical die, which in comparison to the batch base area given by the rectangular outline shape of the nozzle plate 20 (FIG. 10) has a small projecting inflow area. The most effective cooling results from a combination of impingement cooling of the upper flat surface on the one hand and a parallel flow on the cylindrical lateral surface or the bores of the workpiece 33 on the other hand, while two blind plates 21 are inserted in the nozzle box 18 on the side of the workpiece 33.

As can be seen in FIG. 9, the nozzle pattern of the upper nozzle plate 20 is approximately diamond-shaped, again all the nozzle openings 35 having the same height and side distances 36.

To optimize the cooling effect, the workpiece 33 is moved to the upper nozzle plate 20 by means of the lifting and lowering platform 29 in the cooling chamber 3, as is indicated at 32.

11, 12 a batch 11 a is illustrated, which consists of several cylindrical stamps 33. In this case, two blind plates 21 are inserted in the nozzle box 18 to the side of the charge 11, while a nozzle plate 20 is provided above the charge 11, the nozzle image of which can be seen in FIG. 12:

The nozzle openings 35 are each arranged in rectangular groups corresponding to the stamps 33, which are separated from one another by gas-impermeable intermediate spaces 34. The side and height spacing 36 of adjacent nozzle openings 35 is the same again.

The batch 11a can be brought to the nozzle plate 20 through the lifting and lowering platform 29, as is indicated at 32 in FIG. 11; however, it is also conceivable to quench the charge 11a at a greater distance from the upper nozzle plate 20, which is illustrated in broken lines.

A typical example of a batch 11 quenched by intensive impingement cooling is illustrated in FIGS. 13, 14. Above the batch 11 consisting of two plate-shaped workpieces 33, for example in the form of a die-casting mold, a blind plate 21 is arranged in the nozzle box 18, while two nozzle plates 20a are provided to the side of the upright standing plate-shaped workpieces 33, which are shown in FIG. 13 Have a region 40 projecting into the cooling chamber 3, in which the nozzle openings 35 are arranged.

The plate-shaped workpieces 33 are vertical to avoid distortion in the upper temperature range during the dwell time in the heating chamber 2 in the vacuum oven. The nozzle openings 35 of the box-like nozzle plates 20a are brought close to the batch side surface, the nozzle openings 35 being arranged, according to the nozzle image shown in FIG. 14, uniformly distributed over the entire batch side surface with equal height and side spacings 36, in order thereby to ensure uniform and simultaneous cooling of the Ensure workpieces 33.

15, 16, a single plate-shaped workpiece 33, for example in the form of a compression mold, is quenched in the cooling chamber 3, which - similar to FIG. 13 - with an overhead blind plate 21 and two lateral box or trough-like nozzle plates 20a is equipped.

In order to achieve extreme optimization of the cooling conditions, the nozzle plates 20a are designed in the manner shown in FIG. 16 with a nozzle pattern which is matched to the side face of the batch:

The nozzle openings 35, which have the same height and side spacing 36, are concentrated on a rectangular region approximately corresponding to the batch side surface, which is surrounded by gas-impermeable regions 41. The resulting reduction in the number of nozzle openings 35 results in an increase in the nozzle outlet speed. In addition, the distance of the nozzle openings 35 from the workpiece or batch side surface is optimized in the described manner by using the nozzle plates 20a. The impingement flow applied to the workpiece on both sides guarantees a distortion-free and intensive cooling of the batch 11a.

17, 18 is finally the quenching of a batch 11 a, which consists of workpieces for which not too high critical cooling speeds are required and which can be cooled with parallel flow in consideration of their small wall thickness. For this purpose, a nozzle plate 20 is arranged in the nozzle box 18 above the batch 11 consisting of three workpieces 33, while dummy plates 21 are inserted on the side of the batch 11a.

The nozzle openings 35 - as can be seen from FIG. 17 - are again combined according to the three workpieces 33 into three adjacent, rectangularly delimited groups, between which gas-impermeable areas 41 are arranged.

The charge 11 a is brought up to the upper nozzle plate 20 by the lifting and lowering platform 29, as indicated at 32.

In the exemplary embodiments described above, nozzle openings 35 of the same diameter are provided in the nozzle plates 20, 20a in different nozzle patterns. In principle, it is of course also conceivable to vary the diameter of the nozzle openings 35 according to the respective requirements and also to use differently designed nozzle openings, for example in the form of slots, instead of cylindrical nozzle openings 35. It is also possible that the nozzle plates 20a instead of one in the cooling chamber 3 inwardly projecting part 40 have an outwardly projecting area, while for special cases the arrangement can also be such that a nozzle plate is present in the area of the batch base in order to allow the flow of the batch 11 from below.

The drive motors 10 of the fans can be designed to be controllable in order to be able to select the cooling gas speed in the cooling chamber 3 in accordance with the requirements. The maximum cooling gas pressure is usually 2 bar abs. If necessary, it can also be higher.

With the new industrial furnace, 3 cooling intensities are achieved in the cooling chamber, which correspond to those of conventional and commercially available vacuum furnaces with high-pressure gas quenching. Conventional vacuum furnaces (predominantly single-chamber furnaces) must, for example, with 5 bar abs. Cooling gas pressure work in order to achieve a cooling effect comparable to that of the new industrial furnace in the cooling chamber 3 even at a cooling gas pressure of 2 bar abs. is obtained. The decisive advantage of the low cooling gas pressures that can thus be achieved is a substantial saving of cooling gas (in particular nitrogen) during a heat treatment cycle, which means a correspondingly high cost saving. In addition, low cooling gas pressures allow the production of cost-effective system housings that are not subject to official approval.

Claims (10)

1. An industrial furnace (1), more particularly a multichamber furnace for the thermal treatment of charges (11, 11a) of metallic workpieces, having: a heating chamber (2); a cooling chamber (3) which contains a cooling device (17) supplied with cooling gas and in which a cooling gas circulated over a heat exchanger (25) flows against a thermally treated charge (11,11 a); and if necessary an oil bath (6), characterized in that the cooling device (17) has a nozzle box (18) which is disposed in the cooling chamber (3) and supplied with cooling gas and in which at least one nozzle plate (20, 20a) disposed opposite the charge (11a) is interchangeably inserted to change the conditions in which the charge (11 a) is blown.

2. An industrial furnace according to claim 1, characterized in that the interchangeable nozzle plates (20, 20a) differ by nozzles with different nozzle arrangement (configuration) and/or with different nozzle diameter and/or with a different distance from the charge.

3. An industrial furnace according to claims 1 or 2, characterized in that at least some nozzles (35) of at least one nozzle plate are disposed in an alignment producing a rebound flow and/or a parallel flow of the cooling gas on the charge (11a).

4. An industrial furnace according to one of the preceding claims, characterized in that the nozzles (35) of the nozzle plates (20, 20a) are disposed enclosing the charge (11a) on a number of sides.

5. An industrial furnace according to one of the preceding claims, characterized in that the nozzle box (18) has guide devices (19) into which the nozzle plate (20, 20a) can be inserted.

6. An industrial furnace according to claim 5, characterized in that the nozzle plate (20a) has a zone (40) projecting inwardly into the cooling chamber (3) or outwardly therefrom.

7. An industrial furnace according to one of the preceding claims, characterized in that the nozzle box (18) is tunnel-shaped in construction and bounded at its inner wall by at least one nozzle plate (20, 20a).

8. An industrial furnace according to one of the preceding claims, characterized in that in addition to the the nozzle plate (20, 20a) at least one gas-impermeable blind plate (21) is releasably inserted in the nozzle box (18).

9. An industrial furnace according to one of the preceding claims, characterized in that the nozzle box (18) is bounded on at least three inner sides by nozzle plates (20, 20a), of which two are disposed opposite one another, the third nozzle plate being disposed between the two other nozzle plates.

10. An industrial furnace according to one of the preceding claims, characterized in that disposed in the cooling chamber (3) is a raising and lowering device (29) which receives the charge (11a) and by means of which the charge can be moved to a predetermined distance from at least some of the nozzle mouths of a nozzle plate (20, 20a).

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