Industrial heat treating furnace that uses a protective gas

Abstract

An industrial furnace (1) into which protective gas is admitted for the heat treatment of batches (5) of metal workpieces is described. The heat treating furnace includes an entrance lock (2) which can be sealed with respect to the surrounding environment by means of a first gas-tight closure device (2.2.1). The heat treating furnace also includes a third gas-tight closure device (3.1) disposed between a heat treatment chamber (3) of the furnace and a quenching facility (4) at the exit of the heat treatment chamber. With the foregoing arrangement a pressure of the protective gas admitted into the heat treatment chamber (3) can be maintained during loading and unloading of a batch of metal workpieces (5). The entrance lock may be configured as a dual-chamber vertical arrangement or as a single chamber horizontal arrangement.

Claims

1. An industrial furnace into which a protective gas is admitted for the heat treatment of batches of metal workpieces, comprising: a) a heat treatment chamber that is dimensioned to hold a plurality of batches of metal workpieces, said heat treatment chamber having an entrance end and an exit end; b) an entrance air lock connected to the entrance end of said heat treatment chamber for receiving one of the batches of metal workpieces from outside the industrial furnace, said entrance air lock having a first gas-tight door located for sealing the interior of said entrance air lock from an environment surrounding the industrial furnace, and c) a third gas-tight door disposed at the exit end of said heat treatment chamber, whereby a pressure of the protective gas admitted into the heat treatment chamber can be maintained during loading and unloading of each of the batches of metal workpieces; said industrial furnace further comprising: a gas supply connection disposed in a wall of the heat treatment chamber for admitting the protective gas to said heat treatment chamber and to said entrance air lock; a used-gas conveying line connected to said entrance air lock for conveying used protective gas from said entrance air lock; and a protective gas extraction system connected to said entrance air lock for removing protective gas from the entrance air lock and transferring the protective gas, wherein said protective gas extraction system includes a programmable controller that is programmed with a heat treatment program having a process step of protective gas extraction for the downstream use of the protective gas or for reuse in the industrial furnace itself.

2. The industrial furnace according to claim 1 comprising an exit lock connected to the exit end of said heat treatment chamber in a sealable manner by the third gas-tight door.

3. The industrial furnace according to claim 1 wherein said entrance air lock comprises a vertical arrangement that includes a first lock chamber, a second lock chamber positioned above said first lock chamber, an opening between said first and second lock chambers, and a lift elevator operable for movement between the first and second lock chambers through the opening, said lift elevator comprising a gas-tight closure device for sealing the second lock chamber from the first lock chamber when said lift elevator is in a fully lowered position relative to said second lock chamber and when said lift elevator is in a fully raised position relative to said second lock chamber, the first lock chamber is sealable from the surrounding environment by the first gas-tight door, the second lock chamber is connected to the entrance end of said heat treatment chamber, and the industrial furnace further comprises a gas-permeable door positioned between the second lock chamber and the heat treatment chamber.

4. The industrial furnace according to claim 1 wherein the heat treatment chamber comprises a ring hearth and a single drive mechanism connected to the ring hearth for moving the ring hearth to transport batches of metal workpieces in the heat treatment chamber during a heat treatment cycle.

5. The industrial furnace according to claim 1 wherein said entrance air lock comprises a horizontal arrangement having a single lock chamber, the first gas-tight door is positioned at an entrance side of the lock chamber, and the industrial furnace comprises a second gas-tight door positioned between the lock chamber and said heat treatment chamber.

6. The industrial furnace according to claim 5 wherein the heat treatment chamber comprises a ring hearth and a single drive mechanism connected to the ring hearth for moving the ring hearth to transport the batches of metal workpieces in the heat treatment chamber during a heat treatment cycle.

7. The industrial furnace according to claim 2 wherein said entrance air lock comprises a vertical arrangement that includes a first air lock chamber, a second air lock chamber positioned above said first air lock chamber, an opening between said first and second air lock chambers, and a lift elevator operable for movement between the first and second air lock chambers through the opening, said lift elevator comprising a gas-tight closure device for sealing the second air lock chamber from the first air lock chamber when said lift elevator is in a fully raised position relative to said second lock chamber and when said lift elevator is in a fully lowered position relative to said second lock chamber, the first air lock chamber is sealable from the surrounding environment by the first gas-tight door, the second lock chamber is connected to the entrance end of said heat treating chamber, and the industrial furnace further comprises a gas-permeable door positioned between the second air lock chamber and the heat treatment chamber.

8. The industrial furnace according to claim 2 wherein said entrance air lock comprises a horizontal arrangement having a single lock chamber, the first gas-tight door is positioned at an entrance side of the lock chamber, and the industrial furnace comprises a second gas-tight door positioned between the lock chamber and said heat treatment chamber.

9. The industrial furnace according to claim 7 comprising gas supply connections disposed in a wall of the heat treatment chamber for admitting the protective gas to said exit lock and a second used-gas conveying line connected to said exit lock for conveying used protective gas from said exit lock.

10. The industrial furnace according to claim 9 wherein the protective gas extraction system is connected to said exit lock for removing protective gas from the exit lock and transferring the protective gas for use downstream of the industrial furnace or for reuse in the industrial furnace itself.

11. The industrial furnace according to claim 8 comprising a second protective gas supply line connected to the exit lock and a second used-gas conveying line connected to the exit lock for conveying used protective gas from the exit lock.

12. The industrial furnace according to claim 11 wherein the protective gas extraction system is connected to the exit lock for removing protective gas from the exit lock and transferring the protective gas for use downstream of the industrial furnace or for reuse in the industrial furnace itself.

13. The industrial furnace according to claim 2 comprising a quenching facility connected to said exit lock.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram that shows an arrangement of an industrial furnace according to the present invention with a vertical arrangement of an entrance air lock;

(2) FIG. 2 is a schematic diagram that shows additional details of the entrance air lock used in the industrial furnace according to FIG. 1;

(3) FIG. 3 is a schematic diagram that shows an arrangement of a second embodiment of an industrial furnace according to the present invention;

(4) FIG. 4 is a schematic diagram of an entrance air lock in a horizontal arrangement for the industrial furnace according to FIG. 3;

(5) FIG. 5A is a partial schematic diagram showing details of the vertical arrangement of the entrance lock shown in FIGS. 1 and 2 with a lift elevator in a raised position;

(6) FIG. 5B is a partial schematic diagram showing details of the vertical arrangement of the entrance lock with the lift elevator in a lowered position; and

(7) FIG. 6 is a partial schematic diagram that shows an embodiment of an industrial furnace according to the present invention that has a ring hearth.

DETAILED DESCRIPTION

(8) The invention is directed to resolution of the problem of creating a gas-tight industrial furnace of any type described above into which protective gas is admitted. The industrial furnace according to the present invention includes gas-tight sealable chambers at the entrance to the heat treatment chamber and at the exit from the heat treatment chamber to a quenching facility (such as an oil bath, salt bath or high-pressure gas quenching facility). The arrangement provides a disruption-free, high-quality heat treatment process and enables a heat treatment of batches of metal workpieces that is improved in terms of energy.

(9) An industrial heat treating furnace according to the invention can advantageously be carried out on the basis of the inventive features by means of various plant configurations. Thus, in general, an industrial furnace for the heat treatment of batches of metal workpieces, wherein protective gas being admitted into said industrial furnace includes an entrance lock positioned as shown in FIG. 1. The entrance lock can be sealed with respect to the surroundings by means of a first gas-tight closure device. A third gas-tight closure device is positioned between a heat treatment chamber of the industrial furnace and a subsequent quenching facility. The operation of the industrial heat treating furnace according to this invention allows an applied pressure of the protective gas in the heat treatment chamber to be maintained during the loading and unloading of a batch of metal workpieces that are to be heat treated. As also can be seen in FIG. 1, the quenching facility (4) includes an exit lock (4.1) that is connected to the heat treatment chamber in a sealable manner by the third gas-tight closure device (3.1).

(10) In the case of the vertical arrangement shown in FIG. 2, the entrance lock includes first and second lock chambers positioned one above the other. The first and second lock chambers are separated from one another in a sealable manner by an integrated second gas-tight closure device which can include a lift elevator (2.4) and an associated hoist mechanism (2.4.1) for raising and lowering the lift elevator as shown in FIGS. 5A and 5B. The first lock chamber is sealable with respect to the surrounding environment by the first gas-tight closure device. The second lock chamber is sealable with respect to the heat treatment chamber by a gas-permeable door.

(11) In the case of a horizontal arrangement as shown in FIG. 3 and FIG. 4, the entrance lock has the first gas-tight closure device (2.2.1) and is separated from the heat treatment chamber (3) by the second gas-tight closure device (2.2.2).

(12) Gas supply connections, protective gas supply lines, and used gas conveying lines for safeguarding the loading and unloading of the work-piece batches are preferably provided in the industrial furnace of this invention as shown in FIG. 3.

(13) Furthermore, the entrance lock and the exit lock associated with the quenching facility include a protective gas extraction system that permits downstream use of the protective gas. In addition, the downstream use of the protective gas can be advantageously controlled through the use of a programmable furnace controller with a process step of protective gas extraction integrated into the heat treatment program. The protective gas present and required in the industrial furnace is permanently available in an energy-efficient manner.

(14) Further, in the case of an industrial furnace that includes a ring hearth, only a single drive apparatus 6 for moving the ring hearth is used as shown in FIG. 6.

(15) With this group of features, the invention gives rise to a particular potential for improvement, on the one hand in the quality of the heat treatment on the workpieces and on the other hand in the energy-efficient use of the protective gas.

(16) As a result of the gas-tight separation both of the entrance lock and also of the exit lock and quenching facility from the heat treatment chamber of the furnace, it becomes possible advantageously to carry out both the loading and the unloading of the furnace without reducing the protective gas pressure or the carbon level in the heat treatment chamber. The heat treatment process thus becomes essentially continuous and the requirement of the furnace for fresh gas after the charging is reduced to a considerable extent, since only the locks at the entrance and exit ends of the furnace have to be resupplied with the protective gas after being open to the surrounding atmosphere.

(17) For single- or multi-line arrangements, the furnace arrangement according to the present invention also gives rise to a maximum of efficiency because an optimized heat treatment result can be achieved with a reduced input of protective gas at the same time. The cost for a workpiece to be hardened, for example, can thus be considerably reduced. Pusher-type plants configured according to the present invention thus guarantee an improved, economical production operation.

(18) Moreover, a heat treating furnace equipped according to the invention offers the possibility of reusing protective gas of the high-temperature heat treatment furnace continuously as combustion gas in other parts of the plant or in the furnace itself. This is particularly advantageous in respect of the hitherto common and frequent pressure fluctuations during the loading and unloading associated with interruptions.

(19) Since the loading and unloading of the batches takes place by means of a lock according to the invention, the loading and unloading can, depending on the plant design, take place by means of one and the same lock, or a plurality of locks that are used for this purpose. The exit lock usually represents a part of the quenching facility which forms the unit with the high-temperature heat treatment furnace.

(20) The known ring hearth furnaces are those which, in contrast with the locks configured according to the invention, are connected to one or more annular treatment chambers by internal doors which are not gas-tight. During the batch loading and unloading steps, the aforementioned drawbacks thus arise in the heat treatment process, such as they have already likewise been described for pusher-type furnaces.

(21) The advantages of a heat treating furnace according to the present invention are provided therefore universally, irrespective of whether the furnace is a chamber furnace, a pusher-type furnace, a rotary hearth furnace, or a ring hearth furnace. In the industrial heat treating furnace according to the present invention, an adverse effect of the loading and unloading procedures on the heat treatment process can be avoided by the gas-tight separation of the locks from the heat treatment chamber of the furnace.

(22) In the case of ring hearth furnaces as in the case of the pusher-type furnaces, the invention ensures a continuous use of an energy-saving system, which utilizes the employed protective gas also as a combustion gas for other parts of the plant or for the furnace.

(23) In the case of heat treating plants in which the focus is not on the throughput rate, but primarily on flexibility, use is preferably made of atmosphere chamber furnaces as a high-temperature heat treatment furnace. The atmosphere chamber furnace is characterized by a combination of a heat treatment chamber and a quenching facility. All the steps of the heat treatment, such as for example the heating, the carburizing, the diffusion, and the reduction to the hardening temperature, usually take place sequentially in the heat treatment chamber. The atmosphere chamber furnaces can be distinguished essentially by two types concerning the passage of the batches through the furnace. According to one known type of furnace, the batches are loaded and unloaded by means of the quenching facility of the furnace. According to another type of furnace, the batches are loaded at the heat treatment chamber and unloaded at the quenching facility.

(24) A look at atmosphere chamber furnaces shows that essentially the same heat treatment processes are carried out, as is also the case with pusher-type furnaces, rotary hearth furnaces or ring hearth furnaces. The area of application even goes in part beyond those types of furnaces, because the spectrum can be covered from the individual solution to be loaded manually to the fully automated solution and various plant components can be used in a complete plant. These can then be preheating furnaces, annealing furnaces, washing machines, batch storage units and batch transport systems.

(25) The drawbacks associated with the existing the atmosphere chamber furnaces can be likened to those of the existing pusher-type furnaces, rotary hearth, and ring hearth furnaces, in that the furnace gas pressure and the carbon level collapse during the loading and unloading of the batches and that the furnace temperature cools down a considerable extent because of the large door openings in the furnace chamber.

(26) Here too, the furnace according to the present invention enables loading and unloading through the quenching facility by means of a gas-tight separation between the heat treatment chamber and the quenching facility. By this means and by means of the provision of special gas supply lines and a corresponding furnace controller, the loading and unloading of the batch takes place without an adverse effect on the gas atmosphere in the heat treatment chamber.

(27) The atmosphere chamber furnace with the loading at the heat treatment chamber is further equipped with an upstream loading lock, in a similar manner to that described above in the case of pusher-type furnaces. Here too, the continuous use of the energy-saving system becomes possible, which makes use of the protective gas as combustion gas for other parts of the plant or for the furnace itself.

(28) Embodiments of a heat treating furnace according to the present invention are described using structural examples which can each be implemented optionally in a type of chamber furnace, pusher-type furnace, rotary hearth furnace or ring hearth furnace. FIGS. 1 to 6 show preferred embodiments of an industrial furnace 1 constructed according to the present invention. An entrance lock 2 is provided at an entrance end of a heat treating chamber 3 which can be sealed with respect to the surrounding environment by a first gas-tight closure device 2.2.1. According to FIG. 1 and FIG. 3, a third gas-tight closure device 3.1 disposed between a heat treatment chamber 3 and a following quenching facility 4 which includes an exit lock 4.1 are provided. This arrangement ensures that the pressure of a protective gas (not indicated) admitted into heat treatment chamber 3 can be maintained during loading and unloading of a batch 5.

(29) According to a vertical arrangement of the heat treating furnace of this invention, it can be seen from FIGS. 1, 2, 5a, and 5b that an entrance lock 2 includes a first lock chamber 2.2 and a second lock chamber 2.3, which are positioned one above the other and are separated from one another in a sealable manner by an integrated second gas-tight closure device 2.2.2. The gas-tight closure device is preferably configured with a lift elevator 2.4 for moving a batch 5 of metal workpieces from the first lock chamber 2.2 into the second lock chamber 2.3. First lock chamber 2.2 can be sealed with respect to the surroundings by first gas-tight closure device or door 2.2.1, and second lock chamber 2.3 can be sealed with respect to heat treatment chamber 3 by a gas-permeable sliding door 2.3.1.

(30) According to a horizontal arrangement of the heat treating furnace of this invention, it can be seen from FIG. 3 and FIG. 4 that an entrance lock 2 comprises first gas-tight closure device 2.2.1, such as a door, and is separated in a sealable manner with respect to heat treatment chamber 3 by a second gas-tight closure device 2.2.2.

(31) FIG. 3 shows gas supply connections 2.5, protective gas supply lines 2.6, and used gas conveying lines 2.7, for safeguarding the loading and unloading of the batch 5, by means of which a disruption-free, high-quality heat treatment process is provided and a heat treatment of the batches of metal workpieces that is improved in terms of energy is also provided. The energy efficiency provided by the furnace arrangement according to the present invention is supplemented by the use of a protective gas extraction system 2.8 for a downstream use of the protective gas. The protective gas extraction system 2.8 is connected to entrance lock 2 and to exit lock 4.1 associated with quenching facility 4. A controller is operatively connected to protective gas extraction system 2.8 so that the downstream use of the protective gas can be efficiently controlled in a process step integrated into the heat treatment program.

(32) Irrespective of the type of industrial furnace configuration used, therefore, the required protective gas is available permanently and in an energy-efficient manner.

(33) In an industrial furnace 1 constituted as a ring hearth furnace, only one drive mechanism is needed for moving the ring hearth when transporting a batch 5.

(34) A heat treating furnace plant according to the invention can be produced with conventional technological know-how. A given operator of the furnace plant according to the invention is presented with a greater practical value, which is characterized by a disruption-free, high-quality heat treatment process and a heat treatment of batches of metal workpieces that is improved in terms of energy use.

LIST OF REFERENCE NUMBERS USED IN THE DRAWING

(35) (1) industrial heat treating furnace (2) entrance air lock (2.1) first lock chamber (2.2.1) first gas-tight closure device (2.2.2) second gas-tight closure device (2.3) second lock chamber (2.3.1) gas-permeable door (2.4) lift elevator (2.4.1) lift elevator hoist (2.5) gas supply connection (2.6) protective gas supply line (2.7) used gas conveying line (2.8) protective gas extraction system (3) heat treatment chamber (3.1) third gas-tight closure device (4) quenching facility (4.1) exit lock (5) batch