JP7369092B2 - Superheated steam equipment - Google Patents

Description

The present disclosure relates to a superheated steam apparatus.

BACKGROUND ART Conventionally, techniques for performing heat treatment using superheated steam have been known. Patent Document 1 discloses that heat treatment using superheated steam at 600° C. to 1000° C. is performed in a degreasing step in the production of ceramics. Patent Document 2 discloses a configuration in which a superheated steam furnace into which superheated steam is introduced is made of austenitic stainless steel in order to suppress corrosion caused by superheated steam.

Japanese Patent Application Publication No. 2016-166123 JP2019-116986A

The inventor of this application discovered that the dense structure of the passive film of chromium oxide formed on the surface of stainless steel breaks down in a water vapor atmosphere of 400°C or higher, and the chromium contained in stainless steel easily evaporates. I discovered that. Additionally, the vaporized chromium may contain toxic hexavalent chromium. For this reason, for example, if a ceramic precursor (a molded body containing an organic binder) is degreased at a temperature of 400° C. or higher using a superheated steam apparatus, there is a risk that the ceramic precursor will be contaminated by evaporated chromium. Further, for example, in a superheated steam oven for cooking food, if the temperature exceeds 400° C., there is a risk that hexavalent chromium may adhere to the food, and there is a concern that safety may be reduced. Therefore, in a superheated steam apparatus, there is a need for a technology that can suppress chromium contamination on objects to be heat treated.

The present disclosure can be realized as the following forms.
According to one form of the present invention, a superheated steam apparatus is provided. This superheated steam device is a superheated steam device that heats an object with superheated steam, and the portion heated to 400° C. or higher is made of a ferrite metal material on which an alumina coating is formed, and the thickness of the alumina coating is is 100 nm or more and 3 μm or less.
In addition, the present disclosure can also be realized as the following forms.

According to one form of the present disclosure, a superheated steam device is provided. This superheated steam device is a superheated steam device that heats an object with superheated steam, and is characterized in that a portion heated to 400° C. or higher is made of a metal material on which an alumina coating is formed. According to this type of superheated steam apparatus, the part heated to 400°C or higher is made of a metal material on which an alumina coating is formed, so even if the metal material contains chromium, Evaporation of chromium can be suppressed when heated to 400° C. or higher by water vapor. Therefore, it is possible to prevent the heat treatment object from being contaminated by evaporated chromium.

Note that the present disclosure can be realized in various forms, for example, in the form of a method of manufacturing a superheated steam apparatus.

It is a schematic diagram showing a schematic structure of a superheated steam apparatus.

A. Embodiment:
FIG. 1 is a schematic diagram showing a schematic configuration of a superheated steam apparatus 10 as an embodiment of the present disclosure. The superheated steam apparatus 10 of this embodiment is an apparatus for heat-treating an object using superheated steam. In this embodiment, "superheated steam" means steam heated to a boiling point or higher.

The superheated steam device 10 includes a main body 20, a superheated steam generator 30, and an internal heater 40.

The main body portion 20 has a substantially box-like external shape, and has a furnace chamber 22 formed therein. The furnace chamber 22 accommodates the object to be heat treated, and superheated steam is introduced into the furnace chamber 22 . The main body part 20 is formed with an opening/closing part (not shown) configured to be openable and closable. This opening/closing section is closed when the heat treatment target is heated, and opened when the heat treatment target is put into the furnace chamber 22 and when the heat treatment target is taken out from the furnace chamber 22. An introduction path 24 for introducing superheated steam from a superheated steam generator 30 (described later) to the furnace chamber 22 is formed in the main body portion 20 . The introduction path 24 is configured as a flow path that allows the superheated steam generator 30 and the furnace chamber 22 to communicate with each other. The detailed configuration of the main body section 20 will be described later.

The superheated steam generator 30 is a device for generating superheated steam. The superheated steam generator 30 has a heating chamber provided with a heater (not shown), and generates steam at 100° C. or higher by heating water such as city water supplied to the heating chamber with the heater. In FIG. 1, the flow of water or steam is shown by arrows.

The internal heater 40 is provided in the furnace chamber 22 and heats the furnace chamber 22. A power supply device (not shown) is connected to the internal heater 40, and generates heat when energized. In this embodiment, the internal heater 40 has a spirally wound shape, but may have any shape such as a plate shape instead of a spiral shape.

The superheated steam introduced into the furnace chamber 22 via the introduction path 24 is further heated by the internal heater 40 and its temperature increases. The temperature of the furnace chamber 22 is detected by a temperature detector (not shown) provided in the furnace chamber 22, and is controlled by, for example, feedback control using the detected temperature and a set temperature.

In the superheated steam apparatus 10 of this embodiment, the portion heated to 400° C. or higher is made of a metal material on which an alumina film is formed. The reason for this will be explained below.

In conventional superheated steam devices, the portion where superheated steam is introduced is often made of stainless steel in order to suppress corrosion caused by high-temperature steam. In particular, SUS304, SUS316, SUS310S, etc., which are classified as austenitic stainless steels, are easy to weld and are therefore often used for the inner walls of superheated steam devices.

Generally, a passive film of chromium oxide is formed on the surface of stainless steel containing chromium. However, the inventor of this application discovered that the dense structure of the passive film of chromium oxide formed on the surface of stainless steel breaks down in a water vapor atmosphere of 400°C or higher, and the chromium contained in stainless steel evaporates. I found that it was easier. Additionally, the vaporized chromium may contain toxic hexavalent chromium. For this reason, the inventor of the present invention has discovered that when heat treatment is performed at 400° C. or higher using a conventional superheated steam apparatus, there is a risk that the heat-treated object may be contaminated by the vaporized chromium.

Furthermore, the inventors of the present invention have discovered that in stainless steel on which a passive film of alumina is formed, the evaporation of chromium contained in the stainless steel is suppressed by the alumina film. For this reason, the inventor of the present invention has discovered that chromium contamination of the heat-treated object can be suppressed by configuring the portion of the superheated steam device 10 that is heated to 400° C. or higher using a metal material on which an alumina coating is formed. .

As a method for forming an alumina film on the surface of a metal material, for example, a metal material containing 1.5% by mass or more and 10% by mass or less of aluminum is heated in advance at a temperature of 800°C or more and 1200°C or less in an oxygen atmosphere or an air atmosphere. One example is a method of heat treatment under certain conditions. When the temperature of such heat treatment is, for example, 600° C. or more and 700° C. or less, a chromium passive film may be formed instead of an alumina passive film. Therefore, by performing the heat treatment at 800° C. or higher, it is possible to suppress the formation of a chromium passive film. In addition, by performing heat treatment at a temperature of 1200°C or less, the thickness of the alumina film formed can be prevented from becoming too thick, so cracking of the alumina film due to thermal stress can be suppressed, and as a result, , it is possible to suppress a decrease in the durability of the metal material. Note that if the metal material contains less than 1.5% by mass of aluminum, it is undesirable because there is a risk that alumina passive film and chromium passive film may be formed together.

The metal material containing 1.5% by mass or more and 10% by mass or less of aluminum is not particularly limited, but examples include materials equivalent to SUH21 of the JIS standard (18Cr-3Al) and Kanthal (registered trademark, 23Cr-6Al). ), YUS205-M1 (manufactured by Nippon Steel Stainless Steel Co., Ltd., 20Cr-5Al), and the like. SUH21 is a type of ferritic heat-resistant steel, and examples thereof include NCA-1 (manufactured by Nisshin Steel Corporation) and NSSC 21M (manufactured by Nippon Steel Stainless Steel Corporation).

The thickness of the alumina film formed on the surface of the metal material is not particularly limited, but is preferably, for example, 100 nm or more and 3 μm or less. When the thickness is 100 nm or more, chromium evaporation can be effectively suppressed. Furthermore, by setting the thickness to 3 μm or less, it is possible to suppress the occurrence of cracks in the alumina coating caused by thermal stress, and therefore it is possible to suppress a decrease in the durability of the metal material.

In the superheated steam apparatus 10 of this embodiment, an inner wall 26 constituting the furnace chamber 22 of the main body 20 and an introduction path 24 are formed of a metal material on which an alumina coating is formed. In this embodiment, the inner wall 26 means all the inner surfaces of the main body part 20 including the opening/closing part. The outer side of the inner wall 26 of the main body portion 20 may be configured to include a heat insulating material, an arbitrary metal material, or the like. Furthermore, in the superheated steam apparatus 10 of the present embodiment, the internal heater 40 provided in the furnace chamber 22 is also made of a metal material on which an alumina coating is formed. These locations can be heated to 400°C or higher. For example, when the object to be heat treated is a ceramic precursor and heat treatment is performed using superheated steam in the degreasing process of the ceramic precursor, the above-mentioned portions are heated to 600°C to 1000°C. Note that the temperature inside the heating chamber of the superheated steam generator 30 increases due to heating by the heater of the superheated steam generator 30, but the temperature is assumed to be 400° C. or lower. Note that the inner wall 26, the introduction path 24, and the internal heater 40 may be made of the same metal material as long as an alumina coating is formed on the surface, or they may be made of different metal materials. It's okay.

According to the superheated steam apparatus 10 of the present embodiment described above, the portion heated to 400° C. or higher is made of a metal material on which an alumina coating is formed. By the presence of the alumina coating on the surface of the metal material, even if the metal material contains chromium, it is possible to suppress evaporation of chromium when heated to 400° C. or higher by superheated steam. Therefore, it is possible to prevent the heat treatment object from being contaminated by evaporated chromium.

Generally, vaporized chromium may contain hexavalent chromium, which is toxic. However, according to the superheated steam apparatus 10 of the present embodiment, it is possible to suppress evaporation of chromium, and therefore it is possible to suppress adhesion of hexavalent chromium to the object to be heat treated. Therefore, it is possible to suppress a decrease in safety of the heat-treated object.

In addition, in the superheated steam apparatus 10 of the present embodiment, the inner wall 26 constituting the furnace chamber 22 in the main body 20, the introduction path 24, and the internal heater 40 provided in the furnace chamber 22 are equivalent to SUH21 of the JIS standard. It is made of a metal material on which an alumina coating is formed, such as Kanthal (registered trademark, 23Cr-6Al), YUS205-M1 (manufactured by Nippon Steel Stainless Steel Co., Ltd., 20Cr-5Al). For this reason, corrosion due to superheated steam can be suppressed, so that deterioration in the durability of the main body portion 20 and the internal heater 40 can be suppressed.

In addition, since the parts that are heated to 400°C or higher are made of metal material with an alumina coating, damage caused by sudden thermal shock can be suppressed compared to the case where such parts are made of ceramics. As a result, scattering of ceramics into the furnace chamber 22 can be suppressed. In addition, since the parts that are heated to 400°C or higher are made of metal materials coated with alumina, such parts are made of heat-resistant and oxidation-resistant metals that do not contain chromium, such as platinum, gold, silver, and nickel. Compared to the configuration, the material cost of the superheated steam device 10 can be suppressed from increasing.

B. Other embodiments:
The configuration of the superheated steam apparatus 10 in each of the above embodiments is merely an example, and can be modified in various ways. For example, the external shape of the main body portion 20 is not limited to a substantially box shape, but may be any shape such as a cylindrical shape. Further, the superheated steam apparatus 10 may be used, for example, as a superheated steam oven for cooking food. When used for food preparation, it is possible to suppress the adhesion of hexavalent chromium to the food, thereby suppressing a decrease in the safety of the food.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the spirit thereof. For example, the technical features in each embodiment that correspond to the technical features in each form described in the column of the summary of the invention may be used to solve some or all of the above-mentioned problems, or to achieve the above-mentioned effects. In order to achieve some or all of the above, it is possible to replace or combine them as appropriate. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10... Superheated steam apparatus, 20... Main body part, 22... Furnace chamber, 24... Inlet path, 26... Inner wall, 30... Superheated steam generator, 40... Internal heater

Claims (1)

A superheated steam device that heats an object with superheated steam,
The part heated to 400°C or more is made of a ferrite metal material with an alumina coating formed thereon,
The thickness of the alumina coating is 100 nm or more and 3 μm or less,
Superheated steam equipment.

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