WO2016111024A1 - Engine valve with ceramic coating layer - Google Patents

Abstract

An engine valve with a ceramic coating layer obtained by forming a ceramic coating layer of a ceramic starting material on the back surface of a valve head, characterized in that: the ceramic coating layer has a thickness of 220-1,000 μm; pores are formed within the ceramic coating layer; the pores have an average pore diameter of 0.5-15 μm; and the ceramic coating layer has a porosity of 10-60%.

Description

Engine valve with ceramic coating layer

The present invention relates to an engine valve with a ceramic coat layer.

In vehicles such as automobiles equipped with an engine, a large amount of heat is generated in the engine part, but the generated heat is easily diffused to the surroundings through the engine member, and the generated heat is not necessarily fully utilized. It is.

Therefore, researches have been actively conducted to effectively use the heat generated in the engine and improve characteristics such as fuel efficiency, and attempts have been made to insulate engine valves in order to reduce heat loss. It has been broken.

Japanese Patent Laid-Open No. 2003-307105

Patent Document 1 discloses a technique for thermal insulation of an engine valve, in which a film is formed by spraying ceramics or an alloy on the umbrella front and back of the valve.

However, the coating formed by thermal spraying has a problem that it is difficult to form pores in the coating and a sufficient heat insulating effect cannot be obtained. When a sufficient heat insulation effect cannot be obtained in the engine valve, the following problem occurs. For example, on the back of the umbrella of the in-valve, heat generated in the engine combustion chamber is conducted to the in-valve, and the temperature of the in-valve rises. When the temperature of the in-valve becomes high, the intake air that is sucked into the cylinder from the intake passage in the intake process is heated by the in-valve, so that the intake efficiency decreases. Also, for example, on the back of the umbrella of the exhaust valve, the heat of the exhaust is dissipated through the exhaust valve, so that when exhaust gas reaches the carrier mounted for exhaust gas purification, sufficient heat cannot be transferred from the exhaust gas to the carrier. There is a problem that the exhaust gas cannot be sufficiently purified because the temperature does not rise.

The present invention has been made in view of the above-described problems. If the back of the engine valve is on the back of the in-valve, the heat of the exhaust is not transmitted to the intake air. It is an object of the present invention to provide an engine valve with a ceramic coat layer that can improve heat insulation performance so as not to be transmitted to an exhaust valve.

In order to achieve the above object, an engine valve with a ceramic coat layer of the present invention is provided.
An engine valve with a ceramic coat layer in which a ceramic coat layer made of a ceramic material is formed on the back of the umbrella,
The ceramic coat layer has a thickness of 220 to 1000 μm,
Pores are formed in the ceramic coat layer, the average pore diameter is 0.5 to 15 μm, and the porosity of the ceramic coat layer is 10 to 60%.

In the engine valve with a ceramic coat layer of the present invention, since the thickness of the ceramic coat layer is 220 to 1000 μm, it is possible to prevent the intake efficiency from being lowered without the heat of the in-valve being transferred to the intake air. Further, since the heat of the exhaust gas is not easily transmitted to the exhaust valve, and the temperature of the exhaust gas is less likely to decrease, the exhaust gas can be purified by sufficiently warming the carrier when the exhaust gas reaches the carrier. If pores are formed so that the thickness of the ceramic coat layer is less than 220 μm, bubbles easily escape from the ceramic coat layer, and as a result, the surface roughness of the ceramic coat layer surface increases. Since the back surface of the umbrella is in contact with the airflow, there is a problem that if the surface roughness increases, heat transfer between the airflow and the ceramic coat layer increases and the heat insulation performance decreases. On the other hand, if the thickness of the ceramic coat layer exceeds 1000 μm, cracks may easily occur when a thermal shock or the like is applied to the ceramic coat layer. There is also a problem that the intake or exhaust path becomes narrow.
Further, the average pore diameter of the pores formed in the ceramic coat layer is controlled so as to be fine pores of 0.5 to 15 μm. When the average pore diameter of the pores is about this level, the pores exist as independent pores in the ceramic coat layer, and effectively function as a structure that enhances heat insulation. Further, since the porosity is 10 to 60%, sufficient heat insulation is maintained.

In the engine valve with a ceramic coat layer of the present invention, carbon particles are present in the ceramic coat layer, and the amount of the carbon particles is 0.005 to 1 weight with respect to 100 parts by weight of the entire ceramic coat layer. Part is desirable.
If carbon particles are present in the ceramic coat layer, crack propagation is hindered by the carbon particles, so that cracks due to thermal shock are less likely to occur in the ceramic coat layer.

In the engine valve with a ceramic coat layer of the present invention, it is desirable that no air hole having a pore diameter exceeding 45 μm exists in the ceramic coat layer.
If there are no air holes, the progress of cracks is likely to be hindered, so that cracks due to thermal shock are less likely to occur in the ceramic coat layer.
Further, since the wall thickness between the pores can be increased as compared with the case where the air holes exist, the strength of the heat insulating film as a whole increases. Moreover, since the pore diameter is small, convective heat transfer in the pores is suppressed, and the heat insulation effect is improved.

In the engine valve with a ceramic coat layer of the present invention, it is desirable that the surface roughness Rz _JIS of the ceramic coat layer is 0.05 to 5 μm.
It is technically difficult to produce a ceramic coat layer having a surface roughness Rz _JIS of less than 0.05 μm. On the other hand, when the surface roughness Rz _JIS of the ceramic coat layer exceeds 5 μm, there is a problem that the heat transfer coefficient between the intake or exhaust and the ceramic coat layer is increased and the heat insulation performance is lowered.

In the engine valve with a ceramic coat layer of the present invention, the ceramic coat layer is preferably made of an amorphous inorganic material and a crystalline inorganic material.
The amorphous inorganic material functions as a glass layer covering the engine valve. Further, the crystalline inorganic material plays a role as a member for improving heat resistance. Further, the presence of the amorphous inorganic material and the crystalline inorganic material in the ceramic coat layer increases the strength of the ceramic coat layer.

In the engine valve with a ceramic coat layer of the present invention, the amorphous inorganic material is preferably a low softening point glass having a softening point of 300 to 1000 ° C.
When the amorphous inorganic material is the low softening point glass, the amorphous inorganic material is softened and melted by heating at a temperature exceeding the softening point, and spreads on the surface of the engine valve to form a ceramic coat layer.

In the engine valve with a ceramic coat layer of the present invention, the crystalline inorganic material is preferably made of at least one selected from the group consisting of alumina, zirconia, yttria, calcia, magnesia, ceria, and hafnia.
The ceramic coat layer containing the crystalline inorganic material having excellent heat resistance performance is improved in heat resistance. Also, the heat insulation performance is improved.

In the engine valve with a ceramic coat layer of the present invention, the crystalline inorganic material is preferably an oxide of at least one metal selected from manganese, iron, cobalt, copper, chromium, and nickel.
By using an oxide made of the above material as the crystalline inorganic material, the adhesion between the ceramic coat layer and the engine valve can be improved.

FIG. 1A is a cross-sectional view schematically showing an example of the structure of an engine combustion chamber in which the engine valve with a ceramic coat layer of the present invention is used, and FIG. 1B is a cross-sectional view of FIG. It is sectional drawing which shows typically the position of the umbrella back surface of an in-valve and the umbrella back surface of an exhaust valve. 2 (a) and 2 (b) are perspective views schematically showing an example of an engine valve with a ceramic coat layer of the present invention. FIG. 3 is a partially cut cross-sectional view of the engine valve shown in FIGS. 2 (a) and 2 (b). FIG. 4 is a schematic cross-sectional view of a sample for coating layer strength measurement. FIG. 5 is an external view of a tensile test by a tensile tester.

(Detailed description of the invention)
The engine valve with a ceramic coat layer and the method for producing the engine valve with a ceramic coat layer of the present invention will be specifically described below. However, the present invention is not limited to the following configurations, and can be applied with appropriate modifications without departing from the scope of the present invention. Note that the present invention also includes a combination of two or more desirable configurations of the present invention described below.

The engine valve with a ceramic coat layer of the present invention,
An engine valve with a ceramic coat layer in which a ceramic coat layer made of a ceramic material is formed on the back of the umbrella,
The ceramic coat layer has a thickness of 220 to 1000 μm,
Pores are formed in the ceramic coat layer, the average pore diameter is 0.5 to 15 μm, and the porosity of the ceramic coat layer is 10 to 60%.

Fig.1 (a) is sectional drawing which shows typically an example of the structure of an engine combustion chamber in which the engine valve with a ceramic coat layer of this invention is used.
In the engine combustion chamber 100, an engine valve 110 including an intake in-valve 110 a and an exhaust exhaust valve 110 b is provided on an upper portion of a cylindrical cylinder 120, and a piston 130 is provided inside the cylinder 120. .
The engine valve with a ceramic coat layer of the present invention is suitable for being provided in such an engine combustion chamber.
FIG.1 (b) is sectional drawing which shows typically the position of the umbrella back surface of an in-valve and the umbrella back surface of an exhaust valve in Fig.1 (a).
The positions of the umbrella back surface of the engine valve are the umbrella back surface 112a of the in-valve 110a and the umbrella back surface 112b of the exhaust valve 110b, which are hatched positions in FIG.

Although the material of an engine valve is not specifically limited, The material conventionally used as a material of each member is applicable.
For example, stainless steel, heat resistant steel, aluminum, aluminum alloy, iron, inconel, hastelloy, invar, and the like can be given. Moreover, various cast products (for example, cast iron, cast steel, carbon steel, etc.) etc. are mentioned.
An example of the material of the engine valve (back surface of the umbrella of the engine valve) is heat resistant steel (SUH). Specifically, martensitic heat resistant steel (SUH3, SUH11, etc.), austenitic heat resistant steel (SUH35, etc.), ferritic heat resistant steel (SUH446, etc.) and the like can be mentioned. Further, Ni-based heat-resistant alloys such as Inconel (NCF751 etc.) are also included.

In order to improve the adhesion between the engine valve and the ceramic coat layer, a sandblasting process or a roughening process using a chemical may be performed on the back surface of the engine valve.

The surface roughness Rz _JIS on the back surface of the umbrella of the engine valve formed by the roughening treatment is preferably 0.3 to 20 μm. The surface roughness Rz _JIS described above is a ten-point average roughness defined by JIS B 0601 (2001).
If the surface roughness Rz _JIS of the engine valve umbrella back surface is less than 0.3 μm, the surface area of the engine valve umbrella back surface becomes small, and sufficient adhesion between the engine valve umbrella back surface and the ceramic coating layer can be obtained. It becomes difficult. On the other hand, when the surface roughness Rz _JIS of the engine valve umbrella back surface exceeds 20 μm, it becomes difficult to form a ceramic coat layer on the engine valve umbrella back surface. This is because if the surface roughness Rz _{JIS of the} back surface of the engine valve umbrella is too large, slurry (composition for forming a ceramic coat layer) does not enter the uneven valley portion formed on the back surface of the engine valve umbrella. This is considered to be because voids are formed in this portion.
The surface roughness Rz _JIS on the back of the umbrella of the engine valve can be measured according to JIS B 0601 (2001) using Handy Surf E-35B manufactured by Tokyo Seimitsu.
The measurement is performed at 25 ° C. and atmospheric pressure.

2 (a) and 2 (b) are perspective views schematically showing an example of an engine valve with a ceramic coat layer of the present invention.
The engine valve 1 with a ceramic coat layer shown in FIG. 2A has a ceramic coat layer 12 formed on an umbrella back surface 112 of the engine valve 110.
In the engine valve 1 with a ceramic coat layer shown in FIG. 2A, the ceramic coat layer 12 is formed on the entire umbrella back surface 112 of the engine valve 110.
Further, in the engine valve with a ceramic coat layer of the present invention, the ceramic coat layer may not be formed on the entire back surface of the umbrella of the engine valve, and the ceramic coat layer may not be formed on a part of the back surface of the umbrella.
For example, as shown in FIG. 2B, the ceramic coat layer 12 does not have to be formed near the bottom of the umbrella back surface 112 (the part where the umbrella spreads).
If the ceramic coat layer is not formed in the vicinity of the bottom of the back of the umbrella, it is preferable because the airtightness of the portion that comes into contact with the cylinder head when the engine valve is closed is maintained.
Further, as shown in FIG. 2B, the ceramic coat layer 12 may be formed on the shaft 113.

FIG. 3 is a partially cut cross-sectional view of the engine valve with a ceramic coat layer shown in FIGS. 2 (a) and 2 (b).
FIG. 3 shows a cross section including a cross section of the ceramic coat layer and a cross section of the back side of the umbrella of the engine valve. Hereinafter, the ceramic coat layer provided in the engine valve with a ceramic coat layer of the present invention will be described with reference to FIG.

The ceramic coat layer 12 is made of a ceramic raw material, and examples of the ceramic raw material include an amorphous inorganic material.
The amorphous inorganic material is preferably made of glass, and more preferably low-softening point glass having a softening point of 300 to 1000 ° C.
Examples of the low softening point glass having a softening point of 300 to 1000 ° C. include SiO ₂ —B ₂ O ₃ —ZnO glass, SiO ₂ —B ₂ O ₃ —Bi ₂ O ₃ glass, and SiO ₂ —PbO glass. SiO ₂ —PbO—B ₂ O ₃ glass, SiO ₂ —B ₂ O ₃ —PbO glass, B ₂ O ₃ —ZnO—PbO glass, B ₂ O ₃ —ZnO—Bi ₂ O ₃ glass, B ₂ O ₃ —Bi ₂ O ₃ glass, B ₂ O ₃ —ZnO glass, BaO—SiO ₂ glass, SiO ₂ —B ₂ O ₃ —RO glass, SiO ₂ —B ₂ O ₃ —R ₂ O-type glass (R is a transition metal) etc. are mentioned.
The softening point should be measured, for example, using a glass automatic softening point / strain point measuring device (SSPM-31) manufactured by Opt Corp., based on the method specified in JIS R 3103-1: 2001. Can do. The measurement is performed at atmospheric pressure.

Furthermore, the ceramic coat layer is preferably a layer made of a crystalline inorganic material in addition to an amorphous inorganic material.
The crystalline inorganic material is preferably made of at least one selected from the group consisting of alumina, zirconia, yttria, calcia, magnesia, ceria, and hafnia.
The crystalline inorganic material is also preferably an oxide of at least one metal selected from manganese, iron, cobalt, copper, chromium, and nickel.
FIG. 3 shows a layer in which the amorphous inorganic material and the crystalline inorganic material contained in the ceramic coat layer 12 are mixed without being distinguished.

The content of the crystalline inorganic material contained in the ceramic coat layer is preferably 1 to 50% by weight and more preferably 10 to 45% by weight with respect to the weight of the ceramic coat layer.

The ceramic coat layer has a thickness of 220 to 1000 μm.
The thickness of the ceramic coat layer can be measured by cutting an engine valve with a ceramic coat layer and observing the cross section using an SEM or the like.
When the thickness of the ceramic coat layer is in the above range, the intake efficiency can be prevented from being lowered without the heat of the in-valve being transmitted to the intake air. Further, since the heat of the exhaust gas is not easily transmitted to the exhaust valve, and the temperature of the exhaust gas is less likely to decrease, the exhaust gas can be purified by sufficiently warming the carrier when the exhaust gas reaches the carrier. If pores are formed so that the thickness of the ceramic coat layer is less than 220 μm, bubbles easily escape from the ceramic coat layer, and as a result, the surface roughness of the ceramic coat layer surface increases. Since the back surface of the umbrella is in contact with the airflow, there is a problem that if the surface roughness increases, heat transfer between the airflow and the ceramic coat layer increases and the heat insulation performance decreases. On the other hand, if the thickness of the ceramic coat layer exceeds 1000 μm, cracks may easily occur in the ceramic coat layer when a thermal shock or the like is applied to the ceramic coat layer. There is also a problem that the intake or exhaust path becomes narrow.

In the ceramic coat layer 12, pores 13 are formed.
The average pore diameter of the pores formed in the ceramic coat layer is 0.5 to 15 μm.
The average pore diameter is preferably 3 to 13 μm, more preferably 5 to 10 μm.
When the average pore diameter of the pores is 0.5 to 15 μm, the pores are present as independent pores in the ceramic coat layer, and function effectively as a structure that enhances heat insulation.

The porosity of the ceramic coat layer is 10 to 60%.
The porosity is preferably 15 to 50%, more preferably 20 to 40%.
When the porosity is 10 to 60%, sufficient heat insulation by the pores is maintained.

The average pore diameter of the pores can be measured by cutting an engine valve with a ceramic coat layer and observing the cross section using an SEM or the like.
Specifically, the SEM image is taken so that the whole area of the ceramic coat layer in the thickness direction is included, the photographed image is divided into nine regions, and the pore diameters of all pores present in each compartment are measured. And an average pore diameter is obtained by calculating | requiring an average value. When the shape of the pores is not substantially spherical, the diameter of the pores is the diameter corresponding to the projected area circle (Haywood diameter).
The porosity of the ceramic coat layer is calculated by calculating the bulk density from the thickness of the ceramic coat layer and the thickness of the ceramic coat layer measured with a film thickness meter (dual scope), and calculating the ratio of the true density calculated by the pycnometer. Then, the value obtained by subtracting the value from 1 can be calculated as the porosity.
The SEM measurement magnification is 500 times when the thickness of the ceramic coat layer is less than 220 to 300 μm, 200 times when the thickness is less than 300 to 500 μm, and 150 times when the thickness is 500 to 1000 μm.

Moreover, it is preferable that no air hole having a pore diameter exceeding 45 μm exists in the ceramic coat layer. The presence or absence of air holes can be determined by measuring the pore diameter of the pores present in the SEM image and confirming that there are no pores exceeding 45 μm.

In the engine valve with a ceramic coat layer of the present invention, carbon particles are preferably present in the ceramic coat layer.
FIG. 3 shows a state in which the carbon particles 14 are present in the ceramic coat layer 12.
The amount of carbon particles is preferably 0.005 to 1 part by weight, more preferably 0.008 to 1 part by weight, based on 100 parts by weight of the entire ceramic coat layer.

The amount of carbon particles is measured by peeling the ceramic coat layer, melting the ceramic raw material constituting the ceramic coat layer, filtering the solution with a filter, and quantifying the remaining carbon particles by the combustion infrared absorption method. be able to.
When the ceramic raw material is glass, it can be melted using hydrochloric acid or hydrofluoric acid.
When the ceramic raw material is melted by the above method and the carbon particles do not remain after the solution is filtered, it is presumed that the carbon particles are not contained in the ceramic coat layer.

The carbon particles are preferably particles that can be vaporized by heat treatment to form pores, and are blended as a material for forming pores in the ceramic coat layer in the process of manufacturing an engine valve with a ceramic coat layer. Material.
A part of the blended carbon particles remains in the ceramic coat layer.
If a part of the carbon particles is left without being vaporized, the progress of cracks is inhibited by the carbon particles, so that the ceramic coat layer is less likely to be cracked by thermal shock.

As specific examples of the carbon particles, graphite particles are preferable, and specifically, ET-10 manufactured by Ibiden Co., Ltd., pitch, coke and the like are preferably used.
The average particle size of the carbon particles is preferably 0.1 to 30 μm.

The thermal conductivity of the ceramic coat layer at room temperature is preferably 0.1 to 1.0 W / m · K.
If the thermal conductivity is less than 0.1 W / m · K, the porosity required to achieve the above thermal conductivity is increased, so that the mechanical strength of the formed ceramic coat layer may be excessively lowered. is there. On the other hand, if the thermal conductivity exceeds 1.0 W / m · K, there is a problem that a sufficient heat insulating effect cannot be obtained. In order to obtain a desired heat insulation effect, it is necessary to increase the thickness of the ceramic coat layer, so that the heat capacity of the ceramic coat layer is increased.
The thermal conductivity is measured based on JIS R 1611 (2010) using a laser flash device (thermal constant measuring device: NETZSCH LFA457 Microflash).
The measurement is performed at 25 ° C. and atmospheric pressure.

The thermal resistance of the ceramic coat layer is preferably 500 to 4000 mm ² · K / W, and more preferably 600 to 3500 mm ² · K / W.
If the thermal resistance is less than 500 mm ² · K / W, the heat insulation is not sufficient, and it is technically difficult to produce a ceramic coat layer having a thermal resistance exceeding 4000 mm ² · K / W.
The thermal resistance of the ceramic coat layer can be calculated by the equation “thermal resistance = thickness of the ceramic coat layer / thermal conductivity of the ceramic coat layer”.

The film strength of the ceramic coat layer is preferably 15 to 50 MPa.
The film strength can be measured by the coating layer strength measurement procedure described in the Examples section.
When carbon particles are present in the ceramic coat layer, the film strength of the ceramic coat layer can be increased. The measurement is performed at 25 ° C. and atmospheric pressure.

The specific heat of the ceramic coat layer is preferably 650 to 900 J / kgK.
Specific heat can be measured by DSC (differential scanning calorimetry).
The heat capacity (heat capacity per unit area) of the ceramic coat layer is preferably 200 to 2500 [J / m ² · K]. The heat capacity of the ceramic coat layer can be calculated by multiplying the specific heat, density and film thickness of the ceramic coat layer.

The surface roughness Rz _JIS of the ceramic coat layer is preferably 0.05 to 5 μm.
It is technically difficult to produce a ceramic coat layer having a surface roughness Rz _JIS of less than 0.05 μm. On the other hand, when the surface roughness Rz _JIS of the ceramic coat layer exceeds 5 μm, there is a problem that the heat transfer coefficient between the intake or exhaust and the ceramic coat layer is increased and the heat insulation performance is lowered.

Next, a method for producing an engine valve with a ceramic coat layer of the present invention will be described.
As a method of manufacturing an engine valve with a ceramic coat layer of the present invention,
A coating layer forming step of forming a coating layer for forming a ceramic coating layer by applying a raw material mixture made of a ceramic raw material and carbon particles for forming a ceramic coating layer on the back surface of the umbrella of the engine valve;
It comprises a heat treatment step in which heat treatment is performed on the engine valve on which the coating layer is formed, and carbon particles are vaporized in the coating layer to form a ceramic coat layer and pores in the ceramic coat layer. The manufacturing method characterized by these.

(A) Preparation of engine valve First, an engine valve is prepared.

Since the shape, material, and the like of the engine valve are the same as those described in the description of the engine valve with a ceramic coat layer of the present invention, description thereof is omitted here.

In preparing the engine valve, it is preferable to perform a cleaning process to remove impurities on the back surface of the umbrella, which is a surface on which the ceramic coat layer is formed.
The cleaning treatment is not particularly limited, and a conventionally known cleaning treatment method can be used. Specifically, for example, a method of performing ultrasonic cleaning in an alcohol solvent can be used.

When it is desired to further improve the adhesion between the back surface of the engine valve umbrella and the ceramic coat layer, the back surface of the umbrella may be roughened. Examples of the roughening treatment include sand blast treatment, etching treatment, and high temperature oxidation treatment. These may be used alone or in combination of two or more. You may perform a washing process after this roughening process.
In addition, it is preferable to perform a roughening process ahead of the coating layer formation process mentioned later.

(B) Coating layer forming step (b-1) Raw material mixture preparation step Subsequently, a raw material mixture for forming a coating layer is prepared.
A raw material mixture is obtained by mixing ceramic raw materials and carbon particles.

Since the ceramic raw material and the carbon particles are the same as those described in the description of the engine valve with a ceramic coat layer of the present invention, the description thereof is omitted here.

The raw material mixture can be obtained, for example, by mixing ceramic raw materials, carbon particles, and water and wet-mixing them with a ball mill or the like. The order and combination of mixing the above three components are not particularly limited. For example, the ceramic raw material and water may be mixed first, and then carbon particles may be added, or water may be added after mixing the ceramic raw material and carbon particles. Alternatively, the ceramic raw material, carbon particles, and water may be mixed at a time.

The carbon particles contained in the raw material mixture burn in the subsequent firing step to generate CO and CO ₂ to form pores. That is, the carbon particles function as a pore forming agent.
Moreover, it is preferable that a part of carbon particle remains in a ceramic coat layer after a baking process.

The mixing ratio of the ceramic raw material and water is not particularly limited, but about 100 parts by weight of water is preferable with respect to 100 parts by weight of the ceramic raw material. This is because when the ceramic raw material and water are mixed in such a weight ratio, the viscosity is likely to be suitable for application to the back of the umbrella of the engine valve. Moreover, you may mix | blend dispersion media, such as an organic solvent, and an organic binder with the said raw material mixture as needed.

As the dispersion medium, for example, water or an organic solvent such as methanol, ethanol, or acetone can be used. The content of the dispersion medium in the raw material mixture is not particularly limited. For example, the dispersion medium is preferably 50 to 150 parts by weight with respect to 100 parts by weight of the ceramic raw material. This is because, by blending the dispersion medium at such a ratio, the viscosity of the raw material mixture becomes a viscosity suitable for application to the umbrella back of the engine valve.
Examples of the organic binder include polyvinyl alcohol, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and the like. These may be used alone or in combination of two or more. Further, a dispersion medium and an organic binder may be used in combination.

The content of carbon particles in the raw material mixture is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the ceramic raw material.
The content of carbon particles is more preferably 0.05 to 8 parts by weight, and further preferably 0.08 to 5 parts by weight.
By setting the content of the carbon particles in such a range, a large number of pores are formed, so that a ceramic coat layer having a desired porosity and a desired heat insulating performance can be formed without growing the pores so much.
Since the pores do not grow so much, every single pore becomes small, and since it is not necessary to take a long heating time for growing the pores, the degree of pore formation is uniform and the ceramic coating has a sharp pore size distribution A layer can be formed.
In addition, when a large amount of carbon particles is blended, carbon particles that have not been gasified tend to remain in the ceramic coat layer.

If necessary, a crystalline inorganic material may be further added to the raw material mixture.
When the crystalline inorganic material is added to the raw material mixture, the timing of adding the crystalline inorganic material is not particularly limited. For example, before mixing the ceramic raw material, the carbon particles, and the water, the ceramic raw material and the crystalline inorganic material are mixed. You may have the process of mixing.
Since the crystalline inorganic material is the same as that described in the description of the engine valve with a ceramic coat layer of the present invention, the description thereof is omitted here.
In addition, when adding a crystalline inorganic material as a raw material mixture, you may have the process of mixing a ceramic raw material and a crystalline inorganic material, before mixing the ceramic raw material mentioned above, carbon particle, and water.

(B-2) Coating step Next, as a coating step, a coating layer for forming a ceramic coating layer is formed by coating a raw material mixture for forming a ceramic coating layer on the back surface of the umbrella.

The thickness of the coating layer is not particularly limited, but is preferably 220 to 1000 μm, and is preferably thick enough to form a ceramic coat layer having a thickness of 220 to 1000 μm.
If pores are formed so that the thickness of the ceramic coat layer is less than 220 μm, bubbles easily escape from the ceramic coat layer, and as a result, the surface roughness of the ceramic coat layer surface increases. Since the back surface of the umbrella is in contact with the airflow, there is a problem that if the surface roughness increases, heat transfer between the airflow and the ceramic coat layer increases and the heat insulation performance decreases. On the other hand, if the thickness of the ceramic coat layer exceeds 1000 μm, cracks may easily occur when a thermal shock or the like is applied to the ceramic coat layer. There is also a problem that the intake or exhaust path becomes narrow.

Examples of the method for forming the coating layer on the back surface of the umbrella include spray coating, electrostatic coating, ink jet, spin coating, transfer using a stamp or roller, and brush coating.

(C) Heat treatment step Next, heat treatment is performed on the engine valve on which the coating layer is formed, and carbon particles are vaporized in the coating layer to form a ceramic coat layer and pores in the ceramic coat layer. A heat treatment process is performed.
In the heat treatment, before the heat treatment at a high temperature, the engine valve on which the coating layer is formed may be dried at about 50 to 150 ° C. as necessary.
The conditions of the heat treatment process can be arbitrarily set in consideration of the material of the engine valve, etc., but when the material of the engine valve is stainless steel, it is 400 to 1100 ° C., and when it is heat resistant steel, it is 400 to 1100. It is preferable to perform the heat treatment at ° C. The heating time is preferably 3 to 120 minutes.
Moreover, it is preferable that heat processing temperature shall be more than the softening point of a ceramic raw material. By setting the heating temperature to a temperature equal to or higher than the softening point of the ceramic raw material, the applied ceramic raw material is softened and melted, and the formed ceramic coat layer and the back surface of the umbrella of the engine valve are firmly adhered.
At this time, the carbon particles contained in the raw material mixture are dispersed in the softened ceramic raw material, and pores are formed by causing thermal decomposition.
Further, when the pores are exposed on the surface of the ceramic coat layer during the heat treatment step, the ceramic raw material forming the ceramic coat layer is softened, so that the portion where the pores are exposed can be closed quickly. Therefore, pores are not exposed on the surface of the fired ceramic coat layer, and a ceramic coat layer with high flatness (low surface roughness) can be obtained.

In addition, the heat treatment process conditions are adjusted based on the blended amount of carbon particles, the target pore diameter, porosity, etc., and heat treatment is performed to such an extent that some of the carbon particles do not vaporize. It is preferable to perform heat treatment to such an extent that it remains in the ceramic coat layer.
By preventing the heat treatment from being performed excessively, it is possible to prevent the generation of atmospheric pores having a pore diameter exceeding 45 μm, and it is possible to form a ceramic coat layer in which the pores are uniformly dispersed.

Below, the effect of the engine valve with a ceramic coat layer of this invention is enumerated.
(1) In the engine valve with a ceramic coat layer of the present invention, since the thickness of the ceramic coat layer is 220 to 1000 μm, it is possible to prevent a decrease in intake efficiency without the heat of the in-valve being transmitted to the intake air. . Further, since the heat of the exhaust gas is not easily transmitted to the exhaust valve, and the temperature of the exhaust gas is less likely to decrease, the exhaust gas can be purified by sufficiently warming the carrier when the exhaust gas reaches the carrier. Further, the average pore diameter of the pores formed in the ceramic coat layer is controlled so as to be fine pores of 0.5 to 15 μm. When the average pore diameter of the pores is about this level, the pores exist as independent pores in the ceramic coat layer, and effectively function as a structure that enhances heat insulation. Further, since the porosity is 10 to 60%, sufficient heat insulation is maintained.

(2) In addition, if carbon particles are present in the ceramic coat layer of the engine valve with a ceramic coat layer of the present invention, the crack development is hindered by the carbon particles. It becomes difficult to occur.

(Example)
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
(Example 1)
(1) Preparation of engine valve An engine valve (in-valve) made of stainless steel (SUS430) was prepared as an engine member, and ultrasonic cleaning was performed in an alcohol solvent. Subsequently, the back of the umbrella was roughened by sandblasting. The sandblast treatment was performed for 10 minutes using # 100 Al ₂ O ₃ abrasive grains.
Using a surface roughness measuring machine (Handy Surf E-35B, manufactured by Tokyo Seimitsu Co., Ltd.), the surface roughness of the rear surface of the umbrella of the engine valve was measured. The surface roughness was Rz _JIS = 5 μm.
The measurement was performed at 25 ° C. and atmospheric pressure.

(2) Coating layer forming step As an amorphous inorganic material powder, 100 parts by weight of barium silicate glass (softening point 770 ° C.) was prepared.
Furthermore, 1 part by weight of methylcellulose (product name: METOLOSE-65SH) manufactured by Shin-Etsu Chemical Co., Ltd. was prepared as an organic binder.
Moreover, 0.23 parts by weight of graphitized carbon particles were prepared.
A raw material mixture was prepared by adding 100 parts by weight of water to 100 parts by weight of the powder of the amorphous inorganic material, 1 part by weight of the organic binder, and 0.23 parts by weight of the carbon particles, and wet mixing with a ball mill.
And it apply | coated to the umbrella back surface of an in-valve by the spray coat method using the prepared raw material mixture.

(3) Heat treatment step Subsequently, the substrate was dried in a dryer at 70 ° C. for 20 minutes.
Furthermore, a 500 μm-thick ceramic coat layer was formed on the back of the in-valve umbrella by heating at 800 ° C. for 90 minutes in a firing furnace in the air, and an engine valve with a ceramic coat layer was manufactured.

(Example 2)
A ceramic coating layer having a thickness of 1000 μm was formed in the same manner as in Example 1 except that the blending amount of the carbon particles was changed to 0.35 parts by weight and the coating amount of the raw material mixture was changed. Manufactured.

(Example 3)
(1) Preparation of engine valve An engine valve (in-valve) made of heat-resistant steel (SUH3) was prepared as an engine member, and ultrasonic cleaning was performed in an alcohol solvent. Subsequently, sandblasting was performed to roughen the back of the umbrella. The sandblast treatment was performed for 10 minutes using # 100 Al ₂ O ₃ abrasive grains.
When the surface roughness of the umbrella surface of the engine valve was measured using a surface roughness measuring machine (Handy Surf E-35B, manufactured by Tokyo Seimitsu Co., Ltd.), the surface roughness was Rz _JIS = 5 μm.
The measurement was performed at 25 ° C. and atmospheric pressure.

(2) Coating layer forming step As an amorphous inorganic material powder, 100 parts by weight of SiO ₂ —B ₂ O ₃ —RO glass (softening point 650 ° C.) was prepared.
Furthermore, 1 part by weight of methylcellulose (product name: METOLOSE-65SH) manufactured by Shin-Etsu Chemical Co., Ltd. was prepared as an organic binder.
Moreover, 0.46 parts by weight of primary-fired carbon particles (carbonaceous) were prepared.
A raw material mixture was prepared by adding 100 parts by weight of water to 100 parts by weight of the amorphous inorganic material powder, 1 part by weight of the organic binder, and 0.46 parts by weight of the carbon particles, followed by wet mixing with a ball mill.
And it apply | coated to the umbrella surface of the in-valve by the spray coat method using the prepared raw material mixture.

(3) Heat treatment step Subsequently, the substrate was dried in a dryer at 70 ° C. for 20 minutes.
Furthermore, a ceramic coating layer having a thickness of 1000 μm was formed on the back surface of the umbrella of the in-valve by heat treatment at 700 ° C. for 90 minutes in a firing furnace in the air, and an engine valve with a ceramic coating layer was manufactured.

Example 4
A ceramic coating layer having a thickness of 220 μm was formed in the same manner as in Example 1 except that the blending amount of the carbon particles was changed to 2.3 parts by weight and the coating amount of the raw material mixture was changed. Manufactured.

(Example 5)
The thickness is 500 μm in the same manner as in Example 1 except that the blending amount of the carbon particles is changed to 1.15 parts by weight, the firing temperature is changed to 780 ° C., the firing time is changed to 50 minutes, and the coating amount of the raw material mixture is changed. An engine valve with a ceramic coat layer was manufactured.

(Example 6)
A ceramic coating layer having a thickness of 220 μm was formed in the same manner as in Example 1 except that the blending amount of the carbon particles was changed to 3.34 parts by weight and the coating amount of the raw material mixture was changed. Manufactured.

(Example 7)
Thickness of 1000 μm in the same manner as in Example 1 except that the amount of carbon particles was changed to 2.3 parts by weight, the firing temperature was changed to 780 ° C., the firing time was changed to 50 minutes, and the coating amount of the raw material mixture was changed. An engine valve with a ceramic coat layer was manufactured.

(Example 8)
A ceramic coat layer having a thickness of 1000 μm was formed in the same manner as in Example 1 except that the blending amount of the carbon particles was changed to 0.017 parts by weight and the coating amount of the raw material mixture was changed. Manufactured.

(Comparative Example 1)
A ceramic coat layer having a thickness of 210 μm is formed in the same manner as in Example 1 except that the blending amount of carbon particles is changed to 4.6 parts by weight, the firing time is changed to 50 minutes, and the coating amount of the raw material mixture is changed. An engine valve with a ceramic coat layer was manufactured.

(Comparative Example 2)
A ceramic coat layer having a thickness of 220 μm was formed in the same manner as in Example 1 except that the blending amount of carbon particles was changed to 1.15 parts by weight, the firing time was changed to 120 minutes, and the coating amount of the raw material mixture was changed. An engine valve with a ceramic coat layer was manufactured.

(Comparative Example 3)
An engine valve with a ceramic coat layer was formed by forming a ceramic coat layer having a thickness of 300 μm in the same manner as in Example 1 except that carbon particles were not blended, the firing time was changed to 50 minutes, and the coating amount of the raw material mixture was changed. Manufactured.

(Comparative Example 4)
A 300 μm thick ceramic coating layer was formed in the same manner as in Example 1 except that the amount of carbon particles was changed to 0.002 parts by weight, the firing time was changed to 30 minutes, and the coating amount of the raw material mixture was changed. An engine valve with a ceramic coat layer was manufactured.

(Evaluation of engine valve with ceramic coating layer)
About the engine valve with a ceramic coat layer manufactured in each Example and each comparative example, the characteristic was evaluated in the following procedures.

(Measurement of ceramic coat layer thickness, porosity, average pore diameter)
For the measurement of the thickness of the ceramic coat layer, a dual scope MP40 manufactured by Fisher Instruments Co., Ltd. was used. After performing film thickness correction using arbitrary 30 points, film thickness measurement was performed on 10 points, and the measured values were averaged. When film thickness measurement is performed on 10 points, it is desirable to take any 10 points so that there is no bias in the measurement region within the measurement region. For example, a method of performing measurement at regular intervals of 1 mm can be mentioned.
Further, the density of the ceramic coat layer was measured with a Pycnometer Pentapyc 5200e manufactured by Cantachrome Instruments Japan.
The bulk density was calculated from the thickness of the ceramic coat layer, the ratio with the true density calculated with a pycnometer was calculated, and the value was subtracted from 1, and the value obtained as a percentage was calculated as the porosity of the ceramic coat layer.
Moreover, the surface of the engine valve with a ceramic coat layer manufactured in each Example and each Comparative Example was cut perpendicularly, and the cross section was randomly selected at five locations and photographed by SEM.
The average pore size was measured by measuring the size (pore size) of all pores having a pore size of 0.1 μm or more and averaging the obtained numerical values. The results are shown in Table 1.

(Measurement of carbon particle amount)
The amount of carbon particles is measured by peeling the ceramic coat layer, melting the ceramic raw material constituting the ceramic coat layer with hydrochloric acid, filtering the solution with a filter, and quantifying the remaining carbon particles by the combustion infrared absorption method Went by.
The measurement by the combustion infrared absorption method was performed by using a carbon sulfur analyzer (CSLS600 manufactured by LECO) as a measuring device.
As a pretreatment (removal of disturbing components), the glass component SiO ₂ constituting the ceramic coat layer was removed by heating in the presence of HF.
At the time of measurement, oxygen gas was allowed to flow and carbon particles were burned in a high-frequency induction heating furnace in the presence of high-purity iron.
The amount of carbon particles is shown as parts by weight with respect to 100 parts by weight of the entire ceramic coat layer.
The results are shown in Table 1.

(Measurement of coat layer strength)
FIG. 4 is a schematic cross-sectional view of a sample for coating layer strength measurement.
The stud pin 50 was attached to the back of the umbrella of the ceramic coat layer 12 of the engine valve 1 with the ceramic coat layer using a clip, and was fixed by heating at 150 ° C. for 1 hour to prepare a measurement sample. As the stud pin 50, P / N901106 (2.7mm epoxy adhesive Al stud pin made by QUAD GROUP) was used.

FIG. 5 is an external view of a tensile test by a tensile tester.
Using the tensile tester 500, the stud pin 50 fixed to the ceramic coat layer 12 was pulled. The coating layer strength was calculated from the maximum value of the force applied until the ceramic coating layer 12 in contact with the stud pin 50 peeled from the engine valve 110 and the cross-sectional area of the stud pin 50. As the tensile tester 500, an autograph AGS50A manufactured by Shimadzu Corporation was used.
The measurement was performed at 25 ° C. and atmospheric pressure.

(Measurement of thermal conductivity)
The raw material mixture prepared in the coating layer forming step in the examples and comparative examples was applied to a SUS plate, and heat-treated under the same conditions as in the examples and comparative examples, thereby producing test pieces for measuring thermal conductivity. .
The thickness of the test piece for measuring thermal conductivity was set to be the same as in each example and comparative example.
About this test piece, it measured based on JISR1611 (2010) using the laser flash apparatus (thermal constant measuring apparatus: NETZSCH LFA457 Microflash), and measured the heat conductivity of the thickness direction of the ceramic coat layer. The results are shown in Table 1.
The measurement was performed at 25 ° C. and atmospheric pressure.

(Measurement of heat capacity)
The specific heat of the ceramic coat layer was measured by a DSC method (differential scanning calorimetry) using a Rigaku high-sensitivity differential scanning calorimeter Thermo plus EVO2.
The density of the ceramic coat layer was measured with a Pycnometer Pentapyc 5200e manufactured by Cantachrome Instruments Japan Co., Ltd., and the film thickness was measured with a dual scope (manufactured by Fisher Instruments Co., Ltd., dual scope MP40).
The heat capacity was calculated by multiplying the specific heat, density, and film thickness.
The heat capacity obtained here is the heat capacity per unit area [J / m ² · K].
Each measurement was performed at 25 ° C. and atmospheric pressure.

(Measurement of coat layer surface roughness)
The surface roughness of the surface of the ceramic coat layer was measured using a surface roughness measuring machine (Handy Surf E-35B manufactured by Tokyo Seimitsu Co., Ltd.).
Each measurement was performed at 25 ° C. and atmospheric pressure.

In the ceramic coat layers of Examples 1 to 8, carbon particles remained, and pores having a small average pore diameter were dispersed. In addition, a ceramic coat layer having high heat resistance, high heat resistance, low heat conductivity, and high heat resistance was formed.
On the other hand, the ceramic coat layer of Comparative Example 1 had a low thermal resistance due to its thin thickness and high thermal conductivity. The ceramic coating layer of Comparative Example 2 had low thermal resistance because no carbon particles were present, the thickness was thin, and the thermal conductivity was high.
Since the ceramic coating layers of Comparative Examples 3 and 4 have a low porosity, the thermal conductivity is high, the thermal resistance is low, and the heat insulating property is insufficient.

1, 2 Engine valve with ceramic coating layer 12 Ceramic coating layer 13 Pore 14 Carbon particles 110 (110a) Engine valve (in-valve)
110 (110b) Engine valve (exhaust valve)
112 (112a) Umbrella back surface 112 (112b) of engine valve (in-valve) Umbrella back surface 113 of engine valve (ex-valve) Shaft

Claims (8)

An engine valve with a ceramic coat layer in which a ceramic coat layer made of a ceramic material is formed on the back of the umbrella,
The ceramic coat layer has a thickness of 220 to 1000 μm;
The ceramic coating layer is characterized in that pores are formed in the ceramic coating layer, the average pore diameter is 0.5 to 15 μm, and the porosity of the ceramic coating layer is 10 to 60%. With engine valve. The ceramic coat according to claim 1, wherein carbon particles are present in the ceramic coat layer, and the amount of the carbon particles is 0.005 to 1 part by weight with respect to 100 parts by weight of the entire ceramic coat layer. Layered engine valve. The engine valve with a ceramic coat layer according to claim 1 or 2, wherein no air hole having a pore diameter exceeding 45 µm is present in the ceramic coat layer. 4. The engine valve with a ceramic coating layer according to claim 1, wherein the ceramic coating layer has a surface roughness Rz _JIS of 0.05 to 5 μm. The engine valve with a ceramic coat layer according to any one of claims 1 to 4, wherein the ceramic coat layer comprises an amorphous inorganic material and a crystalline inorganic material. The engine valve with a ceramic coat layer according to claim 5, wherein the amorphous inorganic material is a low softening point glass having a softening point of 300 to 1000 ° C. The engine valve with a ceramic coat layer according to claim 5 or 6, wherein the crystalline inorganic material is at least one selected from the group consisting of alumina, zirconia, yttria, calcia, magnesia, ceria, and hafnia. The engine valve with a ceramic coat layer according to claim 5 or 6, wherein the crystalline inorganic material is an oxide of at least one metal selected from manganese, iron, cobalt, copper, chromium, and nickel.

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