JP2946975B2 - Ceramic coating with heat insulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic film having heat insulating properties. This coating can be applied to equipment used in a high temperature range, such as an exhaust manifold used in an engine.

[0002]

2. Description of the Related Art As disclosed in JP-A-3-223455, a Ni plating layer is laminated on a metal substrate as a heat-insulating ceramic film used in a high temperature range.
Further, a ceramic sprayed material composed of zirconia and yttria is plasma-sprayed and a sprayed coating is laminated.

[0003]

However, the thermal expansion of the thermal spray coating cannot follow the thermal expansion of the metal substrate, and the thermal spray coating may be peeled off. Therefore, the present inventor has proposed FeO, Fe ₂ O ₃ , which have a thermal expansion coefficient very close to that of a metal,
Iron oxide such as Fe ₃ O ₄ (α = 13 × 10 ^{−6 to} 16 × 10
Focusing on ^-6 ), we developed a technology that employs a coating that is formed by applying a slurry paint, which is a mixture of fine iron oxide-based powder and an inorganic binder such as water glass, to a metal substrate, firing and solidifying it. doing. According to such an iron oxide-based film, it is advantageous to avoid the problem of peeling of the film, as compared with the zirconia (ZrO ₂ ) film and the alumina (Al ₂ O ₃ ) film, and the durability in the thermal cycle is improved. .

Further, as shown in Table 1, the thermal conductivity of iron oxide is 2 W / mK to 3 W regardless of the valence oxide.
/ MK, which is smaller than other ceramic materials.
It has a small thermal conductivity after O ₂ , and is very excellent in heat insulation.

[0005]

[Table 1] By the way, in recent years, in equipment used in a high-temperature region, there is a demand for not only a heat insulating property for a metal base material constituting the equipment, but also an improvement in heat retention of an atmosphere gas flowing in the equipment.

The case of an exhaust manifold, which is a vehicle exhaust system part, will be described below. That is, when starting the engine, it is necessary to raise the temperature of the exhaust gas flowing into the catalyst at an early stage in order to activate the catalyst at an early stage. From this point, in the exhaust manifold, it is preferable that the exhaust gas pass through the exhaust manifold while keeping the temperature of the exhaust gas without transmitting the heat to the exhaust manifold.

In this case, it is preferable that the film laminated on the inner surface of the exhaust manifold has a small thermal conductivity. In addition, it is important how the heat is reflected without absorbing the heat. This is a performance called heat reflectance, and is related to the material of the film and the surface roughness and color tone of the surface of the film. Here, when an iron oxide powder such as FeO, Fe ₂ O ₃ or Fe ₃ O ₄ is used as a coating material, the influence of the reflectance due to the material and surface roughness is the same as that of other ceramic powders. However, there is a problem in color tone.

That is, Table 2 shows the reflectance of a general coating film.

[0009]

[Table 2] As shown in Table 2, it can be seen that the reflectance of white is higher than that of other colors. However, iron oxide is Fe ₂ O ₃
Is red, FeO and Fe ₃ O ₄ are black, and it is considered that the reflectance is lower and the gas heat retention is inferior to white ceramics.

The present invention relates to FeO, Fe ₂ O ₃ , Fe ₃ O ₄
The purpose of the present invention is to improve the problem of the iron oxide-based film whose main component is iron oxide-based ceramics, in which both the heat conductivity and the heat reflectance are small, and thus the heat insulation and the heat retention are more excellent. To provide a film.

[0011]

SUMMARY OF THE INVENTION A ceramic film having heat insulating properties according to the present invention is laminated on a metal base material,
An iron oxide-based film containing at least one of O, Fe ₂ O ₃ and Fe ₃ O ₄ as a main component, and a ceramic surface layer made of a white ceramic laminated on the iron oxide-based film directly or via another layer. It is characterized by comprising.

The white ceramic is zirconia (Zr
O ₂ ), alumina (Al ₂ O ₃ ), magnesia (Mg
O) is suitable, but other materials may be used as long as they are white. The thickness of the ceramic surface layer made of white ceramic can be set to 100 μm or less. FIG. 1 is a schematic diagram.
As can be understood from FIG. 1, the film forming surface 1a of the metal substrate 1
, An iron oxide-based film 2 is laminated, and a ceramic surface layer 3 is further formed thereon.

[0013]

The thermal expansion coefficient of an iron oxide film is close to that of a metal substrate. The ceramic surface layer made of white ceramic has excellent heat reflectivity.

[0014]

【Example】

 (Embodiment 1) This example is directed to a casting system used in an automobile exhaust system.
Exhaust manifold made of iron (material: FCD40)
This is the case when applied to. (1) First, attach the alumina grid to the inner surface of
Shot blasting process using a steel material (about 100 μm)
And the surface of the coating layer is roughened to a surface roughness Rz of 50 μm.
You. (2) Water glass water with a concentration of 30 wt% as an inorganic binder
Solution (Na_TwoO ・ SiO _Two) And Fe_TwoO_ThreePowder (particle size
1-2 μm), and the volume ratio of Fe_TwoO_ThreePowder: water moth
Lath aqueous solution = 20: 80. Further Fe_Two
O_ThreeWhen the powder is 100 wt%, 1 wt% dispersant
And agitate well with a ball mill to form a slurry coating.
Make a charge. Note that Fe_TwoO_ThreePowder particles are used in general paints.
Finer than those used. Dispersant is polycarbon
Commercial product containing acid (San Nopco Co., Ltd. SN Disper
Santo 5040). (3) Slurry-like paint is applied to the exhaust manifold.
Pour inside and apply paint to the inner wall surface. That
After that, it is dried at room temperature and calcined at 500 ° C. for 5 hours.
U. Thereby, an iron oxide-based film is formed. This film thickness is 3
It was set to 00 μm. (4) ZrO_TwoPowder (8 wt% Y_TwoO_ThreeStabilized Z containing
rO_TwoPowder, particle size 1-2 μm), and ZrO
_TwoPowder: water glass aqueous solution = 20:80, ball mill
To produce a slurry-like paint. (5) ZrO_TwoPaint containing powder adheres on iron oxide film
Then, drying and firing (500 ° C. × 5 hours) are performed. to this
More ceramic surface layers are stacked. This film thickness is 30 μm
And

Observation of the film with an electron microscope revealed that the iron oxide film and the particles constituting the ceramic surface layer had a high degree of bonding to each other. (Example 2) In this example, an iron oxide-based film and a ZrO ₂ ceramic surface layer were basically laminated under the same conditions as in Example 1. However, the diameters of the particles constituting the slurry-like paint are different. That is, a fine powder of Fe ₂ O ₃ having a thickness of 1 to ₂ μm,
m ₂ of Fe ₂ O ₃ coarse powder. Then, a fine powder: coarse powder was sufficiently mixed with a V-type mill so that the weight ratio was 30:70, whereby a slurry-like Fe ₂ O ₃ -based paint was formed. A fine powder of ZrO ₂ of 1 to ₂ μm;
４０40 μm ZrO ₂ coarse powder and 30: 7
The powder was mixed at a weight ratio of 0 to prepare a slurry-like ZrO ₂ -based paint.

Also in this example, when the film was observed with an electron microscope, it was found that the iron oxide-based film and the particles constituting the ceramic surface layer had a high degree of bonding to each other. (Embodiment 3) In this embodiment, a coating is formed on a stainless steel exhaust pipe used in an exhaust system by thermal spraying. (1) Used for a stainless steel (SUS430) automobile exhaust pipe (straight pipe with a diameter of 50 mm), and the inner surface of the straight pipe is subjected to a shot blast treatment with an alumina grid material (about 100 μm) to roughen the film laminated surface. The surface is made to have a surface roughness Rz of 70 μ. (2) using the spray coating apparatus, co a thickness of about 500 [mu] m Fe ₂ O ₃ powder (particle size 10～44Myuemu) on the inner surface of the straight tube - and computing, thereby forming iron oxide based film. The spraying conditions were as follows: output 500A, 75V (37.5K
W), the spraying distance is 100 mm, and the gas flow rate is N ₂ : 33 l / min, H ₂ : 9 l / min. (3) Then, Al ₂ O ₃ powder (particle size: 10 to 44 μm)
Is coated on the iron oxide-based film with a thickness of about 50 μm by a similar plasma spraying apparatus, thereby forming a ceramic surface layer. The spraying conditions were as follows: output 500A,
75 V (37.5 KW), spraying distance is 100 mm, gas flow rate is N ₂ : 33 l / min, H ₂ : 9 l / min.

(Test Example) The following tests were conducted to clarify the durability, heat insulation and heat retention of the film. The durability of the coating was tested by thermal cycling. The cooling cycle is
The film was heated with a burner so as to reach 700 ° C., and then a cycle of cooling in water in a normal temperature range was defined as one cycle. By repeating the cycle, it was examined whether cracks or peeling of the film occurred.

Regarding the heat insulating property and the heat retaining property of the film, a film is formed on the inner surface of an automobile exhaust manifold made of cast iron, and this exhaust manifold is 3,000 cc.
30 seconds after the ignition of the engine was started, the temperature of the exhaust gas discharged from the outlet of the exhaust manifold was measured, and the heat insulation and heat insulation of the film were examined based on the temperature of the exhaust gas. . Here, it can be said that as the temperature of the exhaust gas is higher, the heat insulating property and the heat retaining property of the film are better, and the heat of the exhaust gas is not transmitted to the exhaust manifold.

Further, the steady state of the engine (4000 rpm)
In m), it was also examined how much heat was blocked. This was performed by measuring the temperature of the outer wall of an exhaust manifold made of cast iron. It can be said that the lower the temperature of the outer wall, the better the heat insulation of the film. Table 3 shows the specifications of the coatings tested and the test results. In Table 3, No. as a comparative example. 1 is a case where a film is not formed. As shown in Table 3, N
o. In No. 1, the temperature of the exhaust gas is as low as 400 ° C., the outer wall temperature of the exhaust manifold is as high as 700 °, and the heat insulating property and the heat retaining property are inferior. In Table 3, the column of exhaust gas temperature,
In the column of the outer wall temperature of the exhaust manifold (
No.) indicates that no film was formed. The difference (ΔT) from 1 is shown.

[0020]

[Table 3]

No. 2-No. 6 used in Example 1
Using slurry paint, Fe_TwoO _ThreeZ on iron oxide film
rO_TwoThis is the case where ceramic surface layers are laminated, and ZrO_Two
The effect of the thickness of the ceramic surface layer was examined. Zr
O_TwoWhen the thickness of the ceramic surface layer is 20 to 100 μm, 10
No peeling was observed even in the 00 cycle, but ZrO_TwoC
If the thickness of the lamic surface layer exceeds 150 μm,
It can be seen that separation occurred and the durability of the coating deteriorated. This
The reason is that Fe_TwoO_ThreeIron oxide film has a thermal expansion coefficient of metal
Since it is close to the material, thermal stress does not easily occur._TwoCerami
Since the surface layer has a smaller coefficient of thermal expansion than the metal base material,
rO_TwoWhen the thickness of the ceramic surface layer increases, the iron oxide-based layer and Z
rO_TwoThermal stress between the ceramic surface layer increases,
It is presumed that peeling occurs at this portion.

In addition, No. 2-No. 6 is white on the surface
ZrO_TwoBecause the ceramic surface layer is laminated,
The emissivity is high, and therefore, No. 7 (Fe
_TwoO _ThreeOnly an iron oxide-based film of ZrO_TwoCeramic table
Exhaust gas temperature is 460 ° C
Higher, and also outside the exhaust manifold
Wall temperature is low. That is, No. 2-No. 6 is thermal insulation
It can be said that the film is rich in properties and heat retention.

In addition, No. No. 8 shows a case where an Al ₂ O ₃ ceramic surface layer having a thickness of 50 μm is laminated on an Fe ₂ O ₃ iron oxide-based film. No. No. 9 is a case where a 50 μm thick MgO ceramic surface layer is laminated on an Fe ₂ O ₃ iron oxide-based film. No. 10 has a thickness of 50 μm on the iron oxide film of FeO.
This is a case in which m ZrO ₂ surface layers are laminated. No. 11
Is a 50 μm thick ZrO ₂ film formed on an iron oxide film of Fe ₃ O _4.
This is the case where the surface layers are laminated.

No. as a comparative example. 12 is thickness 500
μm ZrO_TwoWhen only ceramic films are laminated
You. No. as a comparative example. 13 is a 500 μm thick A
l_TwoO _ThreeThis is a case where only ceramic films are laminated. here
No. 8 to No. 11 is leather even for 1000 cycles
No film peeling, excellent durability, and exhaust gas
Temperature is as high as 460 ° C and exhaust manifold
The outer wall temperature is low, and the film has excellent heat insulation and heat retention.
It can be said.

On the other hand, no. In No. 12, peeling occurred at 400 cycles, and No. 12 in which no iron oxide-based film was similarly laminated. In No. 13, peeling occurred in 200 cycles, which means that the durability was poor. Note that N
o. 7-No. The conditions of the slurry paint used in Example 13 were basically the same as those used in Example 1.

FIG. 2 shows a part of an exhaust system of a vehicle. As shown in FIG. 2, the exhaust system includes an exhaust manifold 100, a front pipe 102, a pre-muffler 104, a center pipe 106,
It has a muffler 108. The coating according to the present invention may be applied to any part. Furthermore, not limited to this,
It can be applied to equipment used in other kinds of high temperature regions.

[0027]

The heat-insulating film of the present invention has excellent durability, heat retention and heat shielding properties. By the way, generally, FeO, Fe ₂ O ₃ , F
e ₃ O ₄ is inferior in sinterability and tends to be a soft layer, and therefore may be cut off by particles contained in exhaust gas. In this regard, in the present invention, since the ceramic surface layer made of white ceramic is laminated on the iron oxide-based layer, it is advantageous to avoid such a problem of shaving.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a film according to Example 1.

FIG. 2 is a perspective view showing an application example.

[Explanation of symbols]

In the figure, 1 is a metal substrate, 1a is a film forming surface, 2 is an iron oxide-based film, and 3 is a ceramic surface layer.

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the metal substrate is laminated with FeO, Fe ₂ O
_{3. An} iron oxide-based film containing at least one of Fe ₃ O ₄ as a main component, and a ceramic surface layer made of a white ceramic laminated directly or via another layer on the iron oxide-based film. A heat-insulating ceramic film characterized by the following.