WO2008110193A1 - Heat treatment furnace with negative pressure compensation - Google Patents

Abstract

The invention relates to a heat treatment furnace for the heat treatment of particularly metal work pieces (2, 20), comprising a furnace chamber (3), which can be closed by means of a furnace door (4) said furnace chamber (3) comprising a heating chamber (5) and a quenching chamber. In order to provide a heat treatment furnace that is improved particularly with regard to the consumption of process gas, the invention proposes that the heating space provided by the heating chamber (7) is connected fluidically to the atmosphere surrounding the heat treatment furnace (1) by means of a gas channel (17) sealable in a gastight manner. The negative pressure in the furnace created after closing the furnace door is compensated for by the automatic intake of outside air.

Description

 WARM TREATMENT OVEN WITH UNDERPRESSURE COMPENSATION

The invention relates to a heat treatment furnace for heat treatment of, in particular, metallic workpieces, with a furnace chamber which can be closed by means of an oven door, the furnace chamber having a heating chamber and a quenching chamber.

Heat treatment furnaces for heat treatment of in particular metallic workpieces in general and heat treatment furnaces with a furnace chamber having a heating chamber and a quenching chamber in particular are well known in the prior art, which is why a separate documentary proof at this point is not required.

Figures 1 to 6 show a generic heat treatment furnace and its operation in the context of a so-called double loading.

The in Figs. 1 to 6 illustrated heat treatment furnace 1 has a furnace housing, which provides a volume space designated in its entirety as a furnace chamber 3. For a workpiece loading or workpiece unloading, the furnace chamber 3 is designed to be open on one end, with the open side preferably being closed in a gas-tight manner by means of an oven door 4.

The furnace chamber 3 has a heating chamber 5 providing a heating chamber 6 and a quenching chamber 8 providing a quenching chamber 7. The heating chamber 5 and the quenching chamber 7 are separated from each other by means of an intermediate door 10. The operation of the in Figs. 1 to 6, the heat treatment furnace 1 is as follows:

A first workpiece 2 to be treated is conveyed by a workpiece holder or dispenser 11 in the direction of the arrow 23 into the quenching chamber 7, where it is taken over by a heat treatment furnace own transport system. Then the oven door 4 is closed. The workpiece 2 is then conveyed by means of the heat treatment furnace own transport system in accordance with the arrow 24 through the "cold chamber", that is, the quenching chamber 7 through into the heating chamber 5. As soon as the workpiece 2 has been brought into the heating chamber 5, the intermediate door 10 between the heating chamber 5 and the quenching chamber 7 is closed and the heating of the workpiece 2 within the heating chamber 5 can begin.

After a successful thermochemical treatment process, such as carburizing, the workpiece 2 is moved out of the heating chamber 5 into the quenching chamber 7 in correspondence of the arrow 25, as shown in FIG.

The quenching chamber 8 provided by the quenching chamber 7 comprises a quenching bath 9 filled with a quenching medium into which the heat-treated workpiece 2 is lowered by means of a lifting and lowering device 12 for deterrence in correspondence with the arrow 26, as shown in FIG.

Even while the previously heat-treated workpiece 2 is in the quenching bath 9, a new workpiece 20 to be treated is conveyed through the quenching chamber 7 into the heating chamber 5 in correspondence with the arrows 27 and 28, which can be seen in FIG.

While the second workpiece 20 in the heating chamber 5 undergoes its thermochemical heat treatment, the first workpiece 2, that is, the previously heat-treated and quenched workpiece 2 is lifted from the quench bath 9 to drain the quenching medium adhering thereto, for example, oil in accordance with the arrow 29, as shown in Fig. 5.

After a predetermined time interval, the finished workpiece 2 is pulled out of the heat treatment furnace 1 in accordance with the arrow 30 and transferred to the outside of the heat treatment furnace 1 formed workpiece receiving or -abgäbe 11, as shown in Fig. 6.

In a fully automatic operation of the in Figs. 1 to 6 illustrated heat treatment furnace 1, a next heat treatment cycle begins with the process step of the previously explained Fig. 2.

The heat treatment furnace 1 according to FIGS. Figures 1 to 6 and its operation are well known in the art.

A problem with the known heat treatment furnaces is that in the course of proper use of an unavoidable vacuum within the furnace chamber, that is, the heating chamber and the quenching chamber forms, which must be compensated. The negative pressure within the furnace chamber arises after closing the furnace door. Namely, as long as the oven door 4 is opened, flammable furnace gases are burned especially for safety reasons by means of a flame veil. The resulting heat leads to an expansion of the furnace interior space. Once the oven door 4 is closed, penetration of oxygen into the oven space is therefore no longer possible, the flame veil goes out due to lack of oxygen supply, resulting in an abrupt stop the heat input with the consequence that the atmosphere located in the furnace chamber contracts, causing a pressure drop within the furnace space generated. The avoidance of such a pressure drop is inherently unavoidable with combustible gases or with external heating.

In a proper use of a known heat treatment furnace this process gas is supplied. To compensate for the negative pressure, that is, the pressure drop after closing the oven door, the amount of process gas to be supplied is to increase. This is considered not least for cost reasons as disadvantageous, because it can lead to a doubling of the amount of supplied process gas during the critical phase to compensate for the thermally induced contraction of the atmosphere located in the furnace chamber.

Although previously known from the prior art heat treatment furnaces have proven in practice in everyday practice, still exists the problem that in the course of a proper use inherent in an unavoidable vacuum within the heat treatment furnace forms, it must be compensated, which is done in known from the prior art heat treatment furnaces by means of the supply of process gas. The gassing costs associated therewith are perceived as disadvantageous, which is why it is the object of the invention to propose a novel heat treatment furnace while avoiding the aforementioned disadvantages.

To solve this problem, the invention proposes a heat treatment furnace for heat treatment of particular metallic workpieces, with a furnace door closable by a furnace chamber, wherein the furnace chamber has a heating chamber and a quenching chamber, characterized in that provided by the heating chamber heating chamber to the heat treatment furnace ambient atmosphere is fluidly connected by means of a gas-tight sealable channel.

The heating chamber of the heat treatment furnace according to the invention is fluidly connected to the atmosphere surrounding the heat treatment furnace. This purpose is served by a gas-tight sealable gas channel, which is provided, for example, by a tube which projects through the heating chamber wall. For a gas-tight closure of this gas channel, a check valve may be provided, which is inserted into the gas channel.

The construction according to the invention is advantageous in that a pressure equalization takes place in the furnace chamber without any additional fumigation by process gas. A pressure compensation can namely take place in that outside air is sucked through the inventively provided gas duct and guided into the furnace chamber, which then leads to a pressure equalization within the furnace chamber. The non-return valve located in the gas channel opens automatically in the event of a pressure drop, just as it automatically closes when the oven overpressures. The construction of the invention thus allows a fully automatic pressure equalization, which is realized in that in the case of a negative pressure, the non-return valve opens and so much ambient atmosphere, that is, air is sucked into the furnace chamber until a pressure equalization has taken place, that is, the pressure within the furnace Ambient pressure corresponds. The provided for the introduction of ambient atmosphere in the furnace chamber gas channel opens according to the invention in the heating chamber, in the space between Heizkammerwandung and muffle. The in the course of a pressure equalization in the furnace chamber incoming air thus passes through the gas channel in the space between the heating chamber wall on the one hand and muffle on the other hand, where a mixing of the externally aspirated air takes place with the furnace atmosphere located in Heizkammerraum.

It was not expected that the "vacuum problem" could be solved by allowing ambient air to flow into the furnace chamber for pressure equalization purposes. The heat treatment of metallic workpieces in the heat treatment furnace takes place under the exclusion of oxygen under a process gas atmosphere. It was therefore not expected that it would be possible without influence on the heat treatment result, oxygen-containing ambient atmosphere, that is, air into the furnace chamber, and even to be able to flow into the heating chamber.

Investigations have shown that the air sucked into the intermediate space between the heating chamber wall on the one hand and the muffle on the other hand from the outside into the heating chamber reacts sufficiently long under the conditions prevailing in the heating chamber with the protective gas in the heating chamber before it flows onto the workpieces located in the heating chamber , Unwanted scaling of the workpiece can therefore be avoided. At an operating temperature of about 750 ⁰ C, no deflagration occur, so that a proper and functional operation of the heat treatment furnace is guaranteed despite suction of ambient air in the heating chamber of the heat treatment furnace.

The gas channel connecting the heating chamber to the atmosphere surrounding the heat treatment furnace in terms of fluidity opens on the heating chamber side in the intermediate space between the heating chamber wall on the one hand and the muffle on the other hand. A direct flow of the workpieces located in the heating chamber by the air sucked from the outside can be avoided in an advantageous manner.

It has also been considered, for the purpose of pressure equalization, not to introduce outside air into the heating chamber but into the quenching chamber. However, an influx of ambient air into the quenching chamber has certain disadvantages, which is why the inventive embodiment is preferred.

Although the heating chamber and the quenching chamber are separated from each other by means of an intermediate door, they are not sealed off from each other gas-tight. This is also the reason why a negative pressure forming in the quenching chamber in the manner described above propagates into the heating chamber at the speed of sound. In this case, the pressure balance between the heating chamber on the one hand and the quenching chamber on the other hand takes place via the common chain case, through which the chains of the transport system for the workpieces are guided. If, for the purpose of pressure equalization between furnace pressure on the one hand and ambient pressure on the other hand ambient air is sucked into the quenching chamber, so the incoming air passes through the chain case from the quenching chamber in the heating chamber. By mixing these air flowing into the heating chamber with usually reducing or neutral inert gas atmosphere, it can lead to a locally oxidizing atmosphere. This manifests itself by unwanted scaling of the workpieces, that is, the charge located in the heating chamber, in particular above the chain outlet openings of the chain case. To avoid these scaling, both the chain case and the quenching chamber can be purged, for example, with nitrogen, but this has a not inconsiderable consumption of nitrogen result.

Unexpectedly, the "vacuum problem" according to the invention is achieved in that ambient air is sucked directly into the heating chamber. As a consequence, neither the supply of process gas nor the supply of nitrogen is required in order to realize a pressure equalization with respect to the ambient pressure. The pressure equalization automatically takes place solely in that ambient air is sucked into the heating chamber, wherein the pressure equalization propagates via the chain case in the quenching chamber, so that the result is the entire furnace chamber is supplied to a pressure equalization with the ambient pressure.

The construction according to the invention allows pressure equalization solely by incoming ambient air, that is without any additional fumigation. Thus, it does not lead to unwanted oxidation, the point of introduction for the ambient air is chosen so that it passes into the space between muffle and brick wall, that is heating chamber wall and thus first with the Inert gas of the heating chamber can react. Subsequent reactions and mixing due to the forced gas flow at this point of introduction, the only locally oxidizing gas in this area in a very short time again reducing character. A scaling to the located within the heating chamber workpieces, that is the batch is so suppressed.

According to a further feature of the invention, the non-return valve integrated in the gas channel in the direction of flow of ambient air into the heat treatment furnace is preceded by a valve, which is preferably a magnetic valve.

The solenoid valve is an additional safety device and is only in an open state when the following three requirements are met. First, there must be workpieces inside the heating chamber. Second, the temperature must be within the heating chamber above about 750 ⁰ C, namely for a predetermined period of time of for example 300 seconds. Third, the oven door must be closed or the closing process of the door must be initiated. If these three requirements are met, the solenoid valve opens, so that the gas channel is virtually "unlocked". Now opens the check valve, so ambient air can flow.

As long as the aforementioned conditions are not met, that is, the solenoid valve is not open, the check valve can not open for lack of pressure on the two sides of the non-return valve. The series connection of the solenoid valve on the one hand and the check valve on the other hand therefore offers particular safety reasons the advantage that the gas duct is "unlocked" by the solenoid valve only if a supply of ambient air in the heating chamber should be basically possible. Whether then actually an influx of ambient air takes place in the heating chamber, results in dependence on the position of the non-return valve, which automatically opens when a negative pressure arises within the furnace chamber. In this case, the check valve remains open only until the negative pressure in the furnace interior balanced and there is ambient pressure.

Due to the check valve upstream solenoid valve is also ensures that even if, for example, when vacuum should prevail within the oven chamber, no ambient air can flow into the oven, for example, if the temperature in the heating chamber is below 750 ⁰ C. This is for safety reasons, therefore advantageous because investigations have shown that it can lead to unwanted deflagration within the heating chamber at temperatures below 750 ⁰ C when this ambient air is supplied. With the solenoid valve so it is ensured that at all ambient air can flow into the heating chamber, if prevail within the heating chamber, the conditions provided for this purpose.

Further features and advantages of the invention will become apparent from the following description with reference to FIGS. Showing:

FIGS. 1 to 6 show schematically a heat treatment furnace according to the prior art,

Figure 7 is a schematic partial view of a heat treatment furnace according to the invention.

Fig. 8 in detail an air supply device according to the invention and

9 is a partial view of a possible embodiment of a

Heat treatment furnace according to the invention.

The Fign. 1 to 6 show a known from the prior art heat treatment furnace 1 and its operation, as already explained in the introduction.

An inventive heat treatment furnace 1 is shown in a schematic partial view in Fig. 7. As can be seen from this illustration, the heat treatment furnace 1 according to the invention is distinguished from the heat treatment furnaces known from the prior art in that the heating chamber 6 provided by the heating chamber 5 is fluidly connected to the atmosphere surrounding the heat treatment furnace 1 by means of a gas-tight sealable gas channel 17 is. In the embodiment according to FIG. 7, the gas channel 17 is provided by a tube 18, which tube 18 into a bore 19 is guided in the heating chamber wall 14. Heating chamber side, the tube 18 opens in the space 15 between the heating chamber 14 on the one hand and muffle 13 on the other.

In the case of a prevailing within the furnace chamber 3 and thus also within the heating chamber 5 and to be compensated vacuum passes in accordance with the arrow 32 ambient air through the tube 18, which is then sucked in accordance with the arrow 33 in the intermediate space 15 between the heating chamber 14 and muffle 13.

The gas channel 17 is formed closed gas-tight. For this purpose, a check valve 21. This opens automatically as soon as there is negative pressure within the furnace chamber 3 compared to the ambient pressure. On the other hand, the check valve 21 closes automatically again when it comes to a pressure equalization, that is, within the oven chamber 3 as desired ambient pressure prevails.

Ambient air should flow into the heating chamber 5 in an advantageous manner only if pre-determinable conditions prevail here. For this reason, the check valve 21 in the inflow direction of the ambient air is a valve, in particular a solenoid valve 22 upstream. This solenoid valve 22 only opens, so only the gas channel 17 is free if prevail in the interior of the heating chamber 5 predeterminable for a permitted air inlet conditions. Otherwise, the solenoid valve 22 is closed, so that an inflow of ambient air into the heating chamber 5 is not possible even if within the heating chamber 5, a negative pressure should prevail in comparison to the ambient pressure.

The prevailing within the heating chamber 5 atmosphere is circulated by means of a rolling device 16, as shown schematically by the arrows 31. In this circulated in the case of operation atmosphere flows from the outside sucked ambient air in accordance with the arrow 33. Before the ambient air flowing in from outside is directed onto the workpiece 2 located within the heating chamber 5, sufficient time passes, so that the ambient air flowing in from outside can react with the protective gas located within the heating chamber 5. By subsequent reactions and mixing due to the forced by the rolling device 16 gas flow at the point of introduction of the air coming from the outside, this has only locally oxidizing acting gas in a short time again reducing character. Unwanted scaling of the workpiece 2 by a direct admission of the same with sucked from the outside ambient air can be effectively prevented.

The total of at least the gas channel 17, the check valve 21 and the solenoid valve 22 having means may be referred to as air supply means. This is shown in detail according to a possible embodiment in Fig. 8.

According to the embodiment of FIG. 8, the air channel 17 is formed by a bore through the heating chamber wall 14. The bore has, for example, a diameter of 45 mm. On the output side, an adapter piece 34 is gas-tightly inserted into the bore forming the gas channel 17. An intermediate tube 35 and a deflecting tube 36 adjoin this on the right side with reference to the plane of the drawing according to FIG. The adapter piece 34 is screwed to the intermediate tube 35, which in turn is in turn bolted to the deflection tube 36.

The air supply device 39 according to FIG. 8 furthermore has a non-return flap 21 and a magnetic valve 22. The function of both the non-return flap 21 and the magnetic valve 22 has been described with reference to FIGS. already described.

The solenoid valve 22 is preceded by a handwheel 38 in Lufteinströmrichtung. By means of this handwheel, the supply of air in the heating chamber 6 provided by the heating chamber 5 can be manually locked or opened.

To actuate the solenoid valve 22 is a drive, for example in the embodiment of a 24 V DC motor.

Preferably, the check valve 21 and the solenoid valve 22 upstream of an air filter 37 in the air inflow direction.

Fig. 9 shows a partial view of the heat treatment furnace 1 according to the invention in a possible embodiment. The heating chamber 5 provided by the heating chamber 6 can be seen in this schematic view. Within the heating chamber 5 there is the workpiece 2 to be heat treated which, according to Art a hood is surrounded by the muffle 13. Above the muffle 13 is the rolling device 16, for example in the form of a fan, which is driven by a motor formed outside of the heat treatment furnace 1.

The heat treatment furnace 1 is equipped according to the invention with an air supply device 39, as shown in detail in Fig. 8.

On the basis of the illustration of FIG. 9, it can easily be seen that outside air can be guided via the gas channel 17 into the interior of the heat treatment furnace 1 by means of the air feed device 39. In this case, the position of the gas channel 17 with respect to the workpieces 2 to be treated is selected such that the heat emerging from the gas channel 17 heat treatment furnace inside air is not directed directly to the workpieces 2. Rather, the air sucked from the outside is guided into the intermediate space 15 between the heating chamber wall 14 and the muffle 13, where mixing with the atmosphere located in the interior of the heat treatment furnace 1 occurs.

The invention further relates to a method for heat treatment of particular metallic workpieces, in which, depending on predeterminable output parameters integrated in an ambient air supply channel check valve is switched so that ambient air can flow into the heat treatment furnace at a self-adjusting in the heat treatment furnace vacuum automatically. This method is used in particular in a heat treatment furnace of the aforementioned type.

The heat treatment furnace has a heating chamber and a quenching chamber in a conventional manner. Via a gas channel, the heating chamber is fluidly connected to the atmosphere surrounding the heat treatment furnace. Within the connecting channel, a check valve on the one hand and a solenoid valve on the other hand are arranged, wherein the solenoid valve is connected upstream in the direction of flow of ambient air into the heat treatment furnace of the check valve.

In terms of the method, it is provided that predefinable operating parameters are monitored within the scope of a heat treatment process. Thus, for example, be monitored as an operating parameter, whether there is a workpiece to be treated within the heating chamber, whether the temperature within the heating chamber for a predeterminable period of, for example, 300 seconds, at least 750 ⁰ C and whether the furnace door is closed or the closing process is initiated. If, for example, the monitoring results in these operating parameters being fulfilled, then the solenoid valve integrated in the gas channel is opened, so that it is fundamentally possible for ambient air to flow into the heating chamber via the gas channel. If a negative pressure within the heat treatment furnace now appears in the further treatment process, then the non-return flap likewise integrated in the gas channel automatically opens or closes until pressure equalization has taken place, that is, ambient pressure prevails within the heat treatment furnace.

LIST OF REFERENCE NUMBERS

1 heat treatment furnace

2 workpiece

3 oven room

4 oven door

5 heating chamber

6 boiler room

7 quenching chamber

8 quenching room

9 quench bath

10 intermediate door

11 workpiece holder or -abgäbe

12 Lifting and lowering device

13 muffles

14 heating chamber wall

15 gap

16 rolling device

17 gas channel

18 pipe

19 hole

20 workpiece

21 check valve

22 solenoid valve

23 - 30 arrow

31- 33 arrow

34 adapter piece

35 intermediate pipe

36 deflecting tube

37 air filters

38 handwheel

39 air supply device

Claims

claims 1. A heat treatment furnace for heat treatment of, in particular, metallic workpieces (2, 20), with a furnace chamber (3) which can be closed by means of an oven door (4), the furnace chamber (3) having a heating chamber (5) and a quenching chamber (7) in that the heating chamber (6) provided by the heating chamber (7) is fluidically connected to the atmosphere surrounding the heat treatment furnace (1) by means of a gas-tight sealable gas channel (17). 2. Heat treatment furnace according to claim 1, characterized in that the gas channel (17) from a heating chamber wall (14) projecting tube (18) is provided. 3. Heat treatment furnace according to claim 1 or 2, characterized in that in the gas channel (17) a check valve (21) is inserted. 4. Heat treatment furnace according to claim 3, characterized in that the non-return valve (21) upstream of a valve in the inflow direction. 5. Heat treatment furnace according to claim 4, characterized in that the valve is a solenoid valve (22). 6. Heat treatment furnace according to one of the preceding claims, characterized in that the gas channel (17) on the heating chamber side in the intermediate space (15) between Heizkammerwand (14) and muffle (13) opens. 7. Heat treatment furnace according to one of the preceding claims 2 to 6, characterized in that the tube (18) has an inner diameter of 1 "to 2", preferably from 1 "to 1, 5".