JPS642475B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a porous layer with high heat transfer performance on a metal surface.

Methods of forming a high-performance heat transfer surface on a metal surface include roughening the metal surface, creating fins with irregularities formed by machining on the metal surface, or creating a porous layer on the metal surface by sintering. Of these, the last one formed by sintering is superior in terms of heat transfer performance and product adaptability. However, in the case of sintering, there are disadvantages such as performance differing depending on the state of sintering, manufacturing management is complicated, and the strength of the base metal is reduced due to the high heating temperature.

This invention has been made in view of the above circumstances, and is a metal that can obtain a high-performance heat transfer surface, is easy to manage in manufacturing, is low in cost, and has little deterioration in the performance of the base metal. It is an object of the present invention to provide a method for forming a porous layer on a surface.

The first aspect of this invention is to mix a metal powder with a diameter of 20 to 500 μm and a brazing powder with a diameter of 20 to 200 μm with a plastic binder that decomposes and evaporates during brazing, and to moderate the mixture with a solvent. After forming a slurry with a high viscosity, it is applied to a metal surface and heated in a vacuum, non-oxidizing atmosphere or reducing atmosphere to braze and bond the metal powder to the metal surface, and at the same time decomposes the plastic binder. This is a method for forming a porous layer on a metal surface, which is characterized by evaporating and creating a large number of voids in the area where the binder has been applied.

Moreover, the second thing of this invention has a diameter of 20~
A plastic binder that decomposes and evaporates during brazing is mixed with 500 μm metal powder, and the mixture is made into a slurry with a suitable viscosity using a solvent, and then the mixture is made into a slurry that is coated on a metal surface or placed on a metal surface. The metal powder is applied to a sheet of brazing material and heated in a vacuum, non-oxidizing atmosphere or reducing atmosphere to braze and join the metal powder to the metal surface.
This is a method for forming a porous layer on a metal surface, which is characterized by decomposing and evaporating a plastic binder and creating a large number of voids in the areas where the binder is present.

In the first and second inventions, the metal (base metal) on which the porous layer is formed and the metal powder may be metals that can be brazed, and the combination thereof can be selected arbitrarily.

The diameter of the metal powder in the first and second inventions influences the porosity of the porous layer. The porosity varies depending on the purpose of use, but it is more desirable that the diameter of the metal powder is 20 to 200 μm. And if the diameter of metal powder is smaller than 20μm, also 500μm
If it is larger, a high performance heat transfer surface cannot be obtained.

The plastic binder in the first and second inventions is used to form and maintain the metal powder and brazing powder (only in the case of the first invention) as a uniform coating on the metal surface during brazing. It decomposes and evaporates.

In the first and second inventions, metal powder, binder and brazing powder (only in the case of the first invention)
A suitable solvent is added to the mixture to form a homogeneous slurry of appropriate viscosity.

The diameter of the brazing filler metal powder in the first invention is preferably 20 to 100 μm in order to obtain uniform distribution. If the diameter of the brazing filler metal powder is larger than 200 μm, uniform distribution cannot be obtained and good bonding cannot be achieved. Furthermore, it is difficult to industrially obtain brazing filler metal powder with a diameter smaller than 20 μm. The weight ratio of the brazing filler metal powder to the metal powder is preferably about 1:8, but is not limited thereto. 1st
When a brazing filler metal powder is used as in the invention of , the cost is lower than when using a metal coated with a brazing filler metal, and it is more applicable to products.

Methods for coating the metal surface with the brazing material in the second invention include rolling welding, casting, plating, vapor deposition, and the like.

Methods for applying the slurry of the mixture to the metal surface (in the case of the first invention) or the brazing material (in the case of the second invention) include brushing, spraying, and penetration methods.

Brazing in the first and second inventions is performed without using flux. Although it is possible to obtain a porous layer by brazing using flux, it is not preferable because the flux remains even after cleaning after brazing.

The thickness of the porous layer is controlled as follows. That is, in the case of the first invention, it is controlled by the thickness of the coating when the slurry of the mixture is applied. If this coating is to be made thicker, the slurry may be applied several times. In the case of the second invention, it is controlled by the amount of the brazing material coated on the metal surface or the sheet-shaped brazing material placed on the metal surface and the thickness of the coating when the slurry of the mixture is applied. When increasing the thickness of the porous layer, the amount of brazing filler metal supplied is increased and the slurry coating is applied thickly.

According to the first and second aspects of the invention, since the metal powder is bonded to the metal surface using a brazing material, the diameter of the metal powder is maintained at its original value and a porous layer with uniform voids is formed. This results in a high-performance heat transfer surface. Also, if the base metal and metal powder can be brazed,
A porous layer can be easily obtained. Furthermore, since the heating temperature in brazing is lower than that in sintering, the cost is low, the performance of the base metal is less degraded, and manufacturing management is easy. In addition, during brazing, it decomposes into metal powder and brazing powder (in the case of the first invention) or metal powder (in the case of the second invention).
By mixing the plastic binder which evaporates, these powders are formed and maintained as a uniform coating on the metal surface (in the case of the first invention) or on the brazing material on the metal surface (in the case of the second invention). Moreover, this plastic binder is decomposed during brazing.
As the binder is evaporated, many voids are created in the area where the binder was applied, which creates a large number of voids not only between the metal powders but also in the brazing filler metal.As a result, a highly porous layer is formed on the metal surface. Easily formed.

Next, examples of this invention will be shown.

Example 1 Pure aluminum powder (average diameter approximately 50 μm) and brazing filler metal powder (Al-9%Si-1.5% Mg alloy, average diameter approximately 50 μm) were mixed at a weight ratio of 8:1, and these and epoxy resin ( (binder) in a weight ratio of 96:15, and the mixture was diluted with acetone at 40% by weight.
After making a slurry with a viscosity of 1/20°C food cup, it was immediately applied to an aluminum pipe (A3003 alloy, diameter 15.8mm, thickness 1.2mm, length 150mm), left in the air for 10 minutes, and vacuum degree 1 ×
10 ^-4 torr or less (at start), heating temperature 605℃, time 5
Vacuum brazing was carried out under conditions of 30 minutes.

As a result, the thickness is approximately 90 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 50 μm was obtained. Note that the interparticle spacing was measured using a metallurgical microscope.

Example 2 Pure aluminum powder (average diameter approximately 50 μm) and brazing filler metal powder (Al-9%Si-1.5% Mg alloy, average diameter approximately 50 μm) were mixed at a weight ratio of 8:1, and these and epoxy resin ( binder) in a weight ratio of 96:4, and the mixture was diluted with acetone at 40% by weight.
After making a slurry with a viscosity of 1/20°C food cup, it was immediately applied to an aluminum pipe (A3003 alloy, diameter 15.8mm, thickness 1.2mm, length 150mm), left in the air for 10 minutes, and vacuum degree 1 ×
10 ^-4 torr or less (at start), heating temperature 605℃, time 5
Vacuum brazing was carried out under conditions of 30 minutes.

As a result, the thickness is approximately 90 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 50 μm was obtained.

Example 3 Pure copper powder (average diameter approximately 40 μm) and brazing filler metal powder (phosphorous copper solder, Cu-6%P-5%Ag alloy, average diameter approximately 50 μm) were mixed at a weight ratio of 8:1, and these were mixed. The mixture is mixed with acrylic resin (binder) at a weight ratio of 95:4, and the mixture is made into a slurry with a viscosity of 40 seconds/20°C with a commercially available lacquer thinner. Copper, diameter 15.8mm, thickness 1.5mm, length 150
mm) and leave it in the air for 10 minutes, then place it in a nitrogen gas atmosphere at a dew point of -40°C or less and a heating temperature of 780°C.
Brazing was carried out at ℃ for 3 minutes.

As a result, the thickness is approximately 110 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 50 μm was obtained.

Example 4 Stainless steel powder (SUS304, average diameter approx.
50μm) and brazing filler metal powder (AWS standard BNi-1, average diameter approximately 60μm) at a weight ratio of 8:1, and acrylic resin (binder) at a weight ratio of 96:4. The mixture was made into a slurry with the viscosity of a food cup for 40 seconds at 20°C using a commercially available lacquer thinner, and then immediately poured into a stainless steel pipe (SUS304, diameter 15 mm, thickness 1 mm, length
150mm) and left in the air for 10 minutes,
Vacuum degree 1×10 ^-3 torr or less, heating temperature 1150℃, time
Vacuum brazing was performed for 10 minutes.

As a result, the thickness is approximately 100 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 60 μm was obtained.

Example 5 Pure aluminum powder (average diameter approximately 40 μm) and acrylic resin (binder) were mixed at a weight ratio of 96:15, and the mixture was heated for 45 seconds/20°C in a food cup using commercially available lacquer thinner. Immediately after making the slurry into a viscous slurry, a brazing metal-coated aluminum pipe (diameter 15.8 mm, thickness 1.2 mm, length 150 mm, core material A3003 alloy, outer surface clad brazing material)
Coated on Al-9%Si-1.5%Mg alloy, cladding rate 10%) and left in the air for 10 minutes, then vacuum at 1x
10 ^-4 torr or less (at start), heating temperature 605℃, time 5
Vacuum brazing was carried out under conditions of 30 minutes.

As a result, the thickness is approximately 100 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 30 μm was obtained.

Example 6 Pure aluminum powder (average diameter approximately 40 μm) and acrylic resin (binder) were mixed at a weight ratio of 96:4, and the mixture was heated in a food cup at 20°C for 45 seconds using commercially available lacquer thinner. Immediately after making the slurry into a viscous slurry, a brazing metal-coated aluminum pipe (diameter 15.8 mm, thickness 1.2 mm, length 150 mm, core material A3003 alloy, outer surface clad brazing material)
Coated on Al-9%Si-1.5%Mg alloy, cladding rate 10%) and left in the air for 10 minutes, then vacuum at 1x
10 ^-4 torr or less (at start), heating temperature 605℃, time 5
Vacuum brazing was carried out under conditions of 30 minutes.

As a result, the thickness is approximately 100 μm, and the interparticle spacing is 10 ~
A uniform porous layer of 30 μm was obtained.

Example 7 Pure iron powder (average diameter approximately 50 μm) and acrylic resin (binder) were mixed at a weight ratio of 96:5, and the mixture was heated in a food cup at 20°C for 40 seconds using commercially available lacquer thinner. Immediately after making the slurry into a viscous slurry, a steel pipe (STB35, diameter 16 mm, thickness 2 mm,
After being left in the atmosphere for 10 minutes, brazing was performed in a hydrogen gas atmosphere at a dew point of -40°C or less, a heating temperature of 1100°C, and a time of 10 minutes.

As a result, with a thickness of 100 μm, the interparticle spacing is 10 ~
A uniform porous layer of 50 μm was obtained.

Pipe with porous layer prepared as above, aluminum pipe with smooth surface (Comparative Example 1) (A3003 alloy, diameter 15.8 mm, thickness 1.2 mm, length 150 mm), copper pipe (Comparative Example 2) ) (diameter 15.8mm,
1.5 mm thick, 150 mm long), steel pipe (Comparative Example 3)
(STB35, diameter 16mm, thickness 2mm, length 150mm) and stainless steel pipe (Comparative Example 4) (SUS304,
A comparative test was carried out with 15 mm in diameter, 1 mm in thickness, and 150 mm in length, and the relationship between the degree of superheating (wall temperature of the heat transfer surface - temperature of the saturated liquid) and the heat flux on the heat transfer surface was determined. The results are shown in the figure. As is clear from the figure, the heat flux for the same degree of superheating is significantly larger in each example than in each comparative example, and it can be seen that they have high heat transfer performance.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between the degree of superheating and heat flux.

Claims (1)

[Claims] 1. Metal powder with a diameter of 20 to 500 μm and a diameter of 20 to 200 μm
A plastic binder that decomposes and evaporates during brazing is mixed with brazing filler metal powder, and the mixture is made into a slurry with a suitable viscosity using a solvent, and then applied to the metal surface to form a non-oxidizing agent under vacuum. It is characterized by heating in an atmosphere or a reducing atmosphere to braze and join metal powder to a metal surface, and at the same time decomposing and evaporating the plastic binder, creating a large number of voids in the area where the binder was applied. A method of forming a porous layer on a metal surface. 2 Mix metal powder with a diameter of 20 to 500 μm with a plastic binder that decomposes and evaporates during brazing, and use a solvent to make a slurry with an appropriate viscosity. It is applied to a sheet of brazing material placed on a metal surface and heated in a vacuum, non-oxidizing atmosphere, or reducing atmosphere to braze and join the metal powder to the metal surface, and at the same time decomposes the plastic binder. A method for forming a porous layer on a metal surface, which is characterized by evaporating and creating a large number of voids in the area where the binder has been applied.