JPH0552485A - Vacuum heating furnace and vacuum heating method - Google Patents

Abstract

PURPOSE:To prevent the generation of preclusion against the increasing of the degree of vacuum due to the evaporation of adhered water by a method wherein the adhesion of water to the internal surface of a furnace shell due to the condensation of water vapor is prevented by keeping the temperature of the furnace shell through a temperature keeping means when the furnace shell is evacuated and a work to be treated is heated. CONSTITUTION:A vacuum device 17 is operated and the inside of a furnace shell 2 is evacuated while a heater 12 is excited and the heating of a work 31 to be treated is started. Heat medium, such as hot-water or the like, is conducted through a water-cooled jacket, for example, as the temperature keeping means for the furnace shell 2, which keeps the furnace shell at a predetermined temperature, whereby the internal surface of the furnace shell is retained at a temperature precluding the condensation of water vapor even when the water vapor, generated from the work 31 to be treated, has arrived at the vicinity of the same. According to this method, water vapor, evaporated from the work 31 in accordance with the heating of the same, is discharged out of the furnace shell 2 through a discharging pipeline 18 without being condensed whereby the water vapor is removed as condensed water by a condenser 19 before arriving at the vacuum device 17. Accordingly, moisture will never arrive at the vacuum device 17 and the deterioration of the vacuum device 11 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum heating furnace and a vacuum heating method, and more particularly to a vacuum heating furnace and a vacuum heating method suitable for heating a processed product whose moisture is evaporated by heating.

[0002]

2. Description of the Related Art When a processed product as described above is heated in a vacuum state, the processed product is placed in a furnace, the inside of the furnace is evacuated, and the processed product is heated. In this case, water is evaporated from the treated product as it is heated. When the steam reaches near the inner surface of the furnace shell, it condenses and water adheres to the inner surface of the furnace shell. This water is evaporated and reduced due to the decompression in the furnace due to the vacuum exhaust and the residual heat accompanying the heating of the processed product.

[0003]

However, in the case of evaporation of the water adhering to the inner surface as described above, the temperature of the water is lowered (freezing in some cases) because the heat is removed along with the evaporation, and the evaporation rate is slow. It takes a long time for everything to evaporate. By the way, while the water content of the treated product evaporates or the water adhering to the inner surface of the furnace shell evaporates as described above, the degree of vacuum in the furnace is regulated by the vapor pressure due to the evaporation, and a good degree of vacuum cannot be obtained. Therefore, if it takes a long time to evaporate the water adhering to the inner surface as described above, even if the water adhering to the inner surface evaporates even if evaporation from the treated product is completed, There is a problem that it is difficult to raise the degree of vacuum to a high degree, and the start of heating of the processed product in a state of a predetermined high degree of vacuum is extremely delayed.

When the processed product is heated in a vacuum state,
If water generated in the process of treating the previous treated product is accumulated in the furnace shell, the vapor pressure due to the evaporation of the water regulates the vacuum degree in the furnace shell, and there is a problem that a good vacuum degree cannot be obtained. It was

The present invention has been made to solve the above-mentioned problems (technical problems) of the prior art, and it is possible to prevent steam from condensing and water adhering to the inner surface of the furnace shell near the inner surface of the furnace shell. Then, the vacuum heating device that can quickly start the heating of the processed product in a predetermined vacuum state, and the water in the furnace shell can be discharged in advance to perform the heating in the state of a good vacuum degree. It is an object of the present invention to provide such a vacuum heating method.

[0006]

In order to achieve the above object, a vacuum heating furnace according to the present invention is installed inside a furnace shell provided with a vacuum device for evacuating the inside. In a vacuum heating furnace provided with heating means for heating the treated product, the inner surface of the furnace shell is set to a temperature at which condensation of vapor generated from the treated product and reaching the vicinity of the inner surface of the furnace shell is prevented. It is provided with a heat retaining means for holding.

The vacuum heating method according to the present invention is a vacuum heating method in which a processed product is placed in a furnace shell provided with a vacuum device, the furnace shell is evacuated, and the processed product is heated.
When the inside of the furnace shell is evacuated, the water accumulated in the furnace shell is discharged to the outside of the furnace shell and the inside of the furnace shell is evacuated.

[0008]

When the processed product is heated by the vacuum heating furnace, the processed product is left in the furnace shell, the inside of the furnace shell is evacuated, and the heating of the processed product is started. When the water vaporizes from the treated product due to heating, the vapor is exhausted to the outside of the furnace shell along with vacuum evacuation. In this case, even if the steam reaches the vicinity of the inner surface of the furnace shell, the inner surface is kept at a temperature that prevents condensation of the steam, so that the steam is condensed and water does not adhere to the inner surface of the furnace shell. Absent. When the evaporation of water from the treated product is completed, the degree of vacuum in the furnace is raised to a predetermined high degree of vacuum, and the treated product is heated in that state.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2, reference numeral 1 denotes a batch type vacuum furnace as an example of the vacuum heating furnace. Reference numeral 2 denotes a furnace shell in the vacuum, which is a cylindrical main body 3, a cooling equipment surrounding wall 3a connected to one end of the main body 3, and a door 4 provided at an entrance on the opposite side.
It consists of and. Each of these is composed of, for example, a water cooling jacket. Reference numeral 5 is a heat insulating wall, and the main body 6 and the main body 6
The door is provided with a door 7 and a door 8 provided on the opposite side to the door 7, and the space inside is a heat treatment chamber. The door 8 is closed when the processed product is heated and opened when cooled. Reference numeral 10 is a mounting table provided in the heat treatment chamber, and the space above the mounting table is a storage space 11 for the processed product. Reference numeral 12 is a heating means arranged around the existing space 11, and an electric heater is used as an example, and is attached to the heat insulating wall. In addition, 13 is a muffle provided as necessary, for example, dewaxing during heat treatment of the processed product, prevention of contamination and damage of furnace shell constituents by harmful gas generated during degassing, or good temperature distribution in the storage space 11. It is for the purpose of conversion. Next, the drainage structure of the furnace shell 2 will be described. Reference numeral 14 denotes a water collecting portion, which is provided at the lowest position in the main body 3 of the furnace shell 2. Reference numeral 15 denotes a drain port provided on the bottom wall of the water collecting section 14, to which a drain valve 16 is attached.

Next, 17 shown in FIG. 2 is a vacuum device for evacuating the inside of the furnace shell 2, and an oil rotary pump or other well-known vacuum pump is used. Reference numeral 18 denotes an exhaust pipe line that connects the inside of the furnace shell 2 and the vacuum device 17, and a condenser 19 (for example, a refrigerator) is provided in the middle thereof. The condenser 19 may be omitted when an oil rotary pump equipped with a hydraulic oil separator is used as the oil rotary pump. Although not shown, the furnace shell 2 is connected to a gas supply means (not shown) for feeding a heat treatment gas (for example, hydrogen or a reactive gas) according to the heat treatment of the processed product.

Next, referring again to FIG. 1, reference numeral 21 denotes a known cooling structure for the processed product, which will be described below. 22 is a cooler, and 23 is a circulation fan, which is driven by a fan motor 24. 25 is a motor cover for holding a vacuum.

Next, processing of a processed product using the above vacuum furnace will be described. The doors 4 and 7 are opened, and the processed product 31 is placed on the mounting table 10. Next, the doors 4 and 7 are closed, the vacuum device 17 is operated to evacuate the furnace shell 2, and the heater 12
It is heated by the energization to, and heating of the processed product 31 is started. Further, as an example of a heat retaining means for keeping the furnace shell 2 at a predetermined temperature, a heat medium such as hot water is flown through a water cooling jacket, and the inner surface of the furnace shell 2 is vaporized in the vicinity thereof (processed product as described below). The vapor generated from 31) is held at a temperature that prevents the vapor from condensing even when it arrives. The temperature is, for example, several tens of degrees although it depends on the vapor pressure.

When heating is started as described above, treated products
When 31 is a material whose water content is evaporated by heating, the water content is evaporated from the treated product 31 as it is heated. The steam is discharged to the outside of the furnace shell 2 through the exhaust pipe line 18 in association with the vacuum exhaust. In this case, even if a part of the steam passes through the heat insulating wall 5 and reaches the vicinity of the furnace shell 2, since the furnace shell 2 is maintained at the temperature as described above, the steam does not condense, It is discharged to the outside of the furnace shell 2 by the vacuum exhaust. The steam discharged to the outside of the furnace shell 2 is condensed by the condenser 19 and removed as water before reaching the vacuum device 17. Therefore, moisture does not reach the vacuum device 17, and the deterioration of the vacuum device 17 is prevented.

When the generation of steam from the processed product 31 is finished, the degree of vacuum in the furnace shell 2 rises to a predetermined high vacuum level, and the processed product 31 is heated in a predetermined state in this state.

When the processed article 31 is heated to a predetermined level as described above, the heater 12 is de-energized, the cooling gas is introduced into the furnace shell 2, and the cooler 22 and the fan 23 are turned on. It is operated in a known manner to cool the processed product 31. When the cooling is completed, the doors 4 and 7 are opened and the processed product 31 that has been processed is taken out.

Next, some examples of the process of evaporating the water from the processed product 31 as described above are as follows. Hydrogen reduction treatment of oxidized alloy steel powder produced by water atomization, reduction treatment of metal whose surface layer is oxidized by reducing gas,
This is, for example, a drying process of water adhering to the powder.

Next, another example of the heat retaining means for the furnace shell 2 will be described. One of them is a method in which a heater is attached to the outside or inside of the furnace shell 2 as a heat-retaining means, so that the inner surface of the furnace shell 2 is kept warm as described above. The other is a method of covering the outside of the furnace shell 2 with a heat insulating material as a heat retaining means when the furnace shell 2 does not have a water cooling structure. Still another is a method in which the heat insulating property of the heat insulating wall 5 is kept small, and the heat emitted from the heater 12 to the outside of the heat insulating wall 5 and reaching the inner surface of the furnace shell 2 is used as a heat insulating means. is there.

Next, as another example of the heat treatment, there is a case where the steam generated from the treated product by heating is condensed near the inner surface of the furnace shell 2 and the treatment is carried out in a state where water is attached to the inner surface of the furnace shell 2. is there. In this case, when the processing of the previous processed product is finished and the processing of the next processed product is to be started, the following may be performed. Since the furnace shell 2 has a cylindrical structure as is clear from FIGS. 1 and 2 and the water collecting portion 14 is provided at the lowest portion thereof, water attached to the inner surface of the furnace shell 2 is naturally collected by gravity. Gathered in part 14. Therefore, when the treatment of the previous treated product is completed, the drain valve 16 is opened and the water is discharged from the drainage port 15 to the outside of the furnace shell 2. After that, the valve 16 is closed, and the charging of the next processed product 31, the vacuum exhaust, and the heating by the heater 12 are started. The water may be discharged after charging the next treated product 31. Further, when a forced discharge means of water, for example, a drain pump is connected to the drain port 15, the water is discharged after starting the vacuum exhaust for the treatment process of the previous treated product or the treatment of the next treated product. Is also good.

Next, FIG. 3 shows a different embodiment of the present invention, showing a continuous vacuum furnace as another example of the vacuum heating furnace. The vacuum furnace 1e includes a front chamber 33, a main processing chamber 34, and a cooling chamber 35. The antechamber 33 has an inlet 36 for receiving a processed product, and a door 37 operated by an opening / closing device 38 is provided therein. The front chamber 33 and the main processing chamber 34 and the main processing chamber 34 and the cooling chamber 35 are partitioned by partition walls 39, respectively. Each partition 39 is provided with an opening for passing a processed product, and each opening is provided with a door 40 operated by an opening / closing device 41. The main processing chamber 34 is provided with the heat retaining means as shown in the previous embodiment and the drainage structure. Separate vacuum devices are connected to the front chamber 33 and the main processing chamber 34, respectively.
The cooling chamber 35 has an outlet 42, which is provided with a door 43 operated by an opening / closing device 44. The cooling chamber 35 is connected to a gas supply means (not shown) for feeding a cooling gas. Reference numeral 45 denotes a transfer means provided through the front chamber 33, the main processing chamber 34, and the cooling chamber 35, which is, for example, a roller.

The vacuum furnace 1e as described above is used, for example, for sintering a powder metal molded product. First, the processed product 31e is in the front chamber 33.
It is placed inside and a well-known pretreatment is performed. Next, the processed product 31e is put into the main processing chamber 34, where the main heat treatment is performed in a vacuum state. In this case, processed product 31e
The vapor generated from this is prevented from condensing as in the previous embodiment. When the prescribed heat treatment is completed in the main processing chamber 34, the processed product 31e
Is placed in a cooling chamber 35, where it is cooled to a normal low temperature and then delivered from outlet 42. In the vacuum furnace 1e, both the front chamber 33 and the cooling chamber 35, or one of them,
Both or either of the heat retaining means as shown in the previous embodiment and the drainage structure may be provided. By doing so,
Even if steam flows from the main processing chamber 34 into those chambers, it is possible to prevent water from adhering to the furnace shells of those chambers and to discharge the water accumulated in each chamber. It should be noted that, in terms of function, parts considered to be the same as or equivalent to those in the previous figure
The same reference numerals as in the previous figure are appended with the letter e, and the duplicate description is omitted.

[0021]

As described above, according to the present invention, when the processed product 31 is heated, it goes without saying that it can be heated under a vacuum condition.

When heating in the vacuum state as described above is started, even if moisture evaporates from the treated product 31 due to heating and the steam reaches the vicinity of the inner surface of the furnace shell 2, the inner surface of the furnace shell 2 still retains the steam. Since the temperature is maintained at a temperature at which the condensation of the above is prevented, the vapor has a feature that it is not condensed and is promptly discharged to the outside of the furnace shell upon evacuation. This means that immediately after the evaporation of water from the treated product 31 is finished, the degree of vacuum in the furnace can be increased toward a predetermined high degree of vacuum by vacuum evacuation. There is an advantage that heating in a predetermined high vacuum state can be started in a short time compared to the one in which the increase of the vacuum degree was regulated by the vapor pressure for a long time until the condensed water was evaporated. ..

Further, according to the method of the present invention, when the heating of the processed product in the vacuum state is started, for example, even if the water generated in the process of the previous processed product is accumulated inside the furnace shell 2, Since the water is discharged and evacuated, the degree of vacuum is not restricted by evaporation of the accumulated water as in the prior art, and the processed product can be heated in a good degree of vacuum. There is.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a vacuum furnace.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a schematic vertical sectional view showing an example of a different vacuum furnace.

[Explanation of symbols]

 2 Furnace shell 12 Heating means 17 Vacuum equipment 31 Processed product

Claims (2)

[Claims] 1. A vacuum heating furnace in which a heating means for heating a processed product existing inside the furnace shell is provided in the furnace shell provided with a vacuum device for evacuating the inside. A vacuum heating furnace provided with a heat retaining means for holding the inner surface of the furnace shell at a temperature that prevents condensation of vapor generated from the treated product and reaching near the inner surface of the furnace shell. 2. A vacuum heating method in which a processed product is placed in a furnace shell provided with a vacuum device, the furnace shell is evacuated, and the processed product is heated, in which the furnace shell is evacuated. Is a vacuum heating method characterized in that the water accumulated in the furnace shell is discharged to the outside of the furnace shell and the furnace shell is evacuated.