JPH04208397A - Heat exchanger and manufacture thereof - Google Patents

Abstract

PURPOSE:To form the surface layer of an aluminum sheet with a hard nitriding layer and make compact the whole size by holding the surface layer of an aluminum sheet for heat exchange to be installed in a fluid passage of a heat exchanger under a heating condition in a fluorine gas environment, then generating a fluoride film on the surface, holding the heating condition in a nitriding environment and forming a hard nitriding layer. CONSTITUTION:A heat exchange aluminum sheet to be installed in a fluid passage of a heat exchanger is degrease-cleaned, for example and then inserted into a heat treatment furnace 1 where a fluorine gas is introduced into this furnace and heated up to specified reaction temperature. This removes the contamination on the surface of a flat bar 22 and corrugated fins 23. The fluorine reacts with the oxide on the surface of the flat bar 22 and the corrugated fins 23 where a very thin fluoride film AlF3 on the surface of the flat bar 22 and the corrugated fins 23. They are continuously heated up to a nitriding temperature and then a mixed gas with a gas having NH3 or NH3 and a carbon source is added thereto, which forms a more active metal basis. At the same time, active N atoms enter the metal layer where they are dispersed in the layer, thereby forming a nitriding layer which contains AlN on the surface of the metal basis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat exchanger in which the surface layer of an aluminum plate provided in a fluid passage is formed of a hard nitride layer, and a method for manufacturing the same.

[Prior Art] In general, members constituting the high-temperature fluid passage and the low-temperature fluid passage of a heat exchanger, for example, the flat plate 22 and corrugated fins 23 of the plate-fin type heat exchanger 21 shown in FIG.
Aluminum alloy is used. 24 is a horizontal frame. Heat exchangers using such aluminum alloy corrugated fins are widely used due to their good performance.

[Problems to be Solved by the Invention] However, if the thermal conductivity of the aluminum alloy corrugated fin itself can be improved and the strength can be increased at the same time, the entire heat exchanger can be made smaller.

The present invention was made in view of the above circumstances, and an object thereof is to downsize a heat exchanger.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heat exchanger in which the surface layer of an aluminum plate for heat exchange provided in a fluid passage of a heat exchanger is formed of a hard nitrided layer. With the vessel as the first gist,
An aluminum plate for heat exchange provided in a fluid passage of a heat exchanger is held in a heated state in a fluorine-based gas atmosphere to generate a fluoride film on its surface, and then held in a heated state in a nitriding atmosphere to heat the aluminum plate. The second gist is a method for manufacturing a heat exchanger that forms a hard nitrided layer on the surface layer of a plate.

[Effect]

That is, in the heat exchanger of the present invention, the surface layer of the aluminum plate for heat exchange provided in the fluid passage is formed of a hard nitride layer, so that the strength of the plate body is improved and at the same time the thermal conductivity is also improved. As a result, miniaturization can be realized.

Furthermore, in the method of the present invention, an aluminum plate for heat exchange provided in a fluid passage of a heat exchanger is held in a heated state in a fluorine-based gas atmosphere to form a fluoride film on its surface, and then a fluoride film is formed on the surface of the aluminum plate, which is then heated in a nitriding atmosphere. While the fluoride film is removed by keeping it in a heated state, a trace of the removal (on the surface of the aluminum plate) is formed in a hard nitride layer. This method is
By performing the fluoridation treatment prior to the nitriding treatment, the surface of the aluminum plate is cleaned and activated at the same time, so that the nitrided layer can be formed uniformly and considerably deep.

Next, the present invention will be explained in detail.

The fluorine gas used in the fluorination treatment of the present invention is NF
,,BF,,CF,,HF,SF,,F.

It refers to a product in which at least one fluorine source component selected from the following is contained in an inert gas such as N2. Among these fluorine source components, NF,
is the best and most practical.

As mentioned above, in the nitriding method of the present invention, the aluminum plate provided in the fluid passage of the heat exchanger is heated at 250 to 400° in the fluorine-based gas atmosphere.
After treating the surface of the aluminum plate by heating and maintaining the aluminum plate at a temperature of C, nitriding treatment (or carbonitriding treatment) is performed using a known nitriding gas such as ammonia. The concentration of the fluorine source component such as NF3 in such a fluorine-based gas is, for example, 1,000 to 1,100,000 ppm, preferably 20,000 to 70,000 ppm, and more preferably 30,000 to 50,000 ppm. The holding time in such a fluorine-based gas atmosphere can be selected appropriately depending on the type of aluminum alloy, the shape and dimensions of the aluminum plate, the heating temperature, etc., and is usually several minutes to several tens of minutes. .

The method of the present invention will be described in more detail.
2 and the corrugated fins 23), for example, are degreased and cleaned, and placed in the heat treatment furnace 1 shown in FIG. This furnace 1 is a pit furnace in which an inner container 4 is placed inside a heater 3 provided in an outer shell 2.
A gas introduction pipe 5 and an exhaust pipe 6 are inserted. The gas introduction pipe 5 has a flowmeter 17. from the cylinder 15.16. Gas is supplied via the pulp 18 and the like. The atmosphere inside is motor 7.
The mixture is stirred by a fan 8 that rotates at . The flat plate 22
The corrugated fins 23 are placed in a metal container 11 and loaded into a furnace. In the figure, 13 is a vacuum pump, 14 is an abatement device, and 27 is a pedestal. In this furnace, fluorine gas,
For example, a mixed gas of NF and N2 is introduced and heated to a predetermined reaction temperature. NF3 generates active group fluorine at a temperature of 250 to 400°C, thereby removing organic and inorganic contamination from the surfaces of the flat plate 22 and the corrugated fins 23, and at the same time, this fluorine 23 reacts with oxides such as A2□O1゜Al(OH)3 as shown in the following formula, and the flat plate 22 and the corrugated fins 2
A very thin fluoride film AlF is formed on the surface of 3.

Aj2□O, +5F→2AI! , F, +3/202Ai
(OH) 3+3F-+ANF, +3/2H! By this reaction, the oxide film on the surface of the flat plate 22 and the corrugated fin 23 is converted into a fluoride film, and the 0□ adsorbed on the surface is also removed. And, such a fluoride film is
0□, Hz, 600°C in the absence of Hz O
It is stable at the following temperatures and prevents the formation of an oxide film on the metal substrate and the adsorption of 02 until the subsequent nitriding treatment. In addition, in such fluoridation treatment, a fluoride film is formed on the surface of the furnace material in the first step, so this film prevents damage caused by fluorine gas to the surface of the furnace material thereafter. will be prevented.

The flat plate 22 and the corrugated fins 23 treated with the fluorine-based gas in this manner are subsequently heated to a nitriding temperature of 450 to 550°C, and in that state, NH is applied.

, or NH, and a gas containing a carbon source (for example, RX gas). As a result, the fluoride film is reduced or destroyed by N2 or a small amount of moisture, for example, as shown in the following equation, thereby exposing and forming an active metal matrix.

AlF3 +3/2H2→A1+3HF In this way, an active metal base is formed, and at the same time active N atoms penetrate and diffuse into the metal, resulting in a compound layer containing AIN on the surface of the metal base. (nitride layer) is formed.

This kind of nitrided layer is formed in the same way in the conventional nitriding method, or in the conventional method, an oxide film is formed during the rise from room temperature to the nitriding temperature, and O adsorbed at this time.
Since the activity of the surface is reduced by the number x, the degree of adsorption of N atoms on the surface is low and non-uniform. Furthermore, such non-uniformity is amplified by the fact that it is practically difficult to maintain a uniform degree of decomposition of NH within the furnace. In the method of the present invention, the N atoms are adsorbed uniformly or quickly on the surfaces of the flat plate 22 and the corrugated fins 23, so that the above-mentioned problem does not occur.

The flat plate 22 and corrugated fins 23 thus obtained
As shown in FIG. 2, since its surface layer is formed of a hard nitride layer A, its strength and heat conduction are significantly improved.

The corrugated fins 23 of the plate-fin type heat exchanger shown in FIG. Opening 2 on the side by cutting and raising
6 is on the downstream side. The other parts are substantially the same as FIG. 4. In this case, the fluid flowing along the corrugated fins 23 collides with the projections 25 and becomes turbulent.
Further, a part of the fluid that has become turbulent after this collision flows into the back side from the opening 26 at the rear of the projection, making the fluid on the back side also turbulent. By making the fluid turbulent in this way, the effect of further improving thermal conductivity can be obtained.

〔Effect of the invention〕

As described above, the heat exchanger of the present invention uses an aluminum plate whose surface layer is formed of a hard nitride layer and which has excellent strength and thermal conductivity as the aluminum plate for heat exchange provided in the fluid passage. This makes it possible to downsize the entire device. Further, in the method of the present invention, fluoridation treatment is performed prior to nitridation treatment. As a result, a passive film such as an oxide film on the surface of the aluminum plate is changed into a fluoride film, and the surface of the aluminum plate is protected. Therefore, even if there is a lapse of time between the formation of the fluoride film and the nitriding process, the fluoride film formed on the surface of the aluminum plate protects the surface of the aluminum plate in good condition. This prevents the formation of an oxide film on the surface of the aluminum plate again. This fluoride film is decomposed and removed during the subsequent nitriding process, thereby exposing the surface of the aluminum plate. Since this exposed metal surface is in an active state, the N atoms in the nitriding process easily diffuse into the surface of the aluminum plate, and the N atoms diffuse deeply and uniformly. As a result, the surface layer of the aluminum plate is formed into a thick (and uniform) hard nitride layer.

Example C] Aluminum alloy flat plate (150 x 25 cm) and corrugated fin (130 x 25 cm) of plate fin type heat exchanger
) was washed with trichloroethane, placed in a heat treatment furnace as shown in Figure 1, and subjected to NF.

300°C in a N2 gas atmosphere containing 5000 ppm of
It was held for 15 minutes. Then heat to 530°C and
A mixed gas of %NH and +50%N2 was introduced into the furnace to carry out nitriding treatment for 3 hours, and then it was air cooled and taken out.

The thickness of the nitrided layer of the obtained flat plate and corrugated fin is 5 to 1
0μm, and its surface hardness is 1900~2100Hv
Met. This surface hardness is much higher than that of a material nitrided by a conventionally known method.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a heat treatment furnace used in an embodiment of the present invention;
Fig. 2 is a cross-sectional view showing the state of the nitrided layer of the corrugated fin of the plate-fin type heat exchanger, Fig. 3 is a partial perspective view of the corrugated fin of another embodiment, and Fig. 4 is the plate-fin type heat exchanger. FIG. 1... Heat treatment furnace 21... Plate fin type heat exchanger 22... Flat plate 23... Corrugated fin patent applicant Daido Oxygen Co., Ltd. Representative Patent attorney Yukihiko Nishifuji Figure 3 Figure 4

Claims (4)

[Claims] (1) A heat exchanger characterized in that the surface layer of an aluminum plate for heat exchange provided in a fluid passage of the heat exchanger is formed as a hard nitrided layer. (2) Claim (1) wherein the aluminum plate is at least one of a flat plate and a corrugated fin of a plate-fin type heat exchanger.
) listed heat exchanger. (3) After heating an aluminum plate for heat exchange provided in a fluid passage of a heat exchanger in a fluorine-based gas atmosphere to generate a fluoride film on its surface, the aluminum plate is held in a heated state in a nitriding atmosphere. A method for manufacturing a heat exchanger, characterized in that a hard nitrided layer is formed on the surface layer of the aluminum plate. (4) Claim (3) wherein the aluminum plate is at least one of a flat plate and a corrugated fin of a plate-fin type heat exchanger.
) The manufacturing method of the heat exchanger described in ).