JPS63295209A - Preparation of ceramic-coated tube-like body - Google Patents

Abstract

PURPOSE:To make it possible to form easily a strong coated layer substantially without air void and release with the inner face of a tube-like body, by filling and sealing small particles whose thermal expansion coefficient is sufficiently larger than that of the tube-like body in the tube-like body when a ceramic-coated layer is calcinated by heating. CONSTITUTION:The inner face of a metal tube-like body having an oxidized film, for example, an exhaust manifold, is coated with an inorganic binder solution such as sodium silicate and so on by means of spraying and so on. A ceramic powder is adhered on the solution layer obtained of a uniform thickness. Then, if necessary, conditioning with humidity is carried out and a ceramic layer is completely immersed and solidified with the inorganic binder solution. It is generally preferable that the ceramic-coated layer is constituted of a fireproof insulating layer and a fireproof layer. Then, small particles such as steel and copper particles are sealed and packed as dense as possible in the tube-like body. Then, baking is carried out at a temp. lower than 780 deg.C where transformation of a casting generally occurs. As the thermal expansion coefficient of the small particles is sufficiently larger than that of the tube-like body, the ceramic layer is strongly pressed on the inner face of the tube-like body. Then, after baking by heating, the tube-like body is cooled in the oven and the small particles are therefrom taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing a ceramic coated tubular body by tightly adhering a ceramic coating layer to the inner surface of a tubular body such as an exhaust manifold made of iron.

[Conventional technique #i] The exhaust system of an internal combustion engine, especially the exhaust manifold, is exposed to high-temperature, high-pressure combustion gas discharged from the engine's cylinders, so it is necessary to have high heat insulation and fire resistance. desired. In particular, in recent years there has been a trend to increase the temperature of engine exhaust gas in order to improve engine efficiency, so it has become important to reduce heat loss in exhaust system equipment such as exhaust manifolds.

JP-A-58-51.214 discloses exhaust gas system equipment for internal combustion engines, such as an exhaust manifold, whose inner surface is coated with a fire-resistant and heat-insulating coating. This exhaust gas system for internal combustion engines has a layer of monolithic refractory made of a mixture of refractory raw material particles and an inorganic binder formed on the inner surface of the metal equipment body that comes into contact with high-temperature exhaust gas. be.

Furthermore, Japanese Patent Application Laid-Open No. 58-99180 discloses a method of applying a fire-resistant and heat-insulating coating to the inner surface of exhaust gas system equipment for an internal combustion engine, such as an exhaust manifold. In this method, a heat-resistant coating layer is formed by attaching a slurry made of a mixture of refractory raw material particles, an inorganic binder, and a frit to the inner surface of a metal device body that is in contact with high-temperature exhaust gas, and then the heat-resistant coating layer is While it is in a wet state, refractory heat insulating material particles are attached to the surface thereof to form a refractory heat insulating layer, the heat resistant coating layer is then solidified, and refractory raw material particles and inorganic bonding are applied to the surface of the refractory heat insulating layer. A heat-resistant coating layer is formed by adhering a slurry made of a mixture of an agent and a frit, and if necessary, a fire-resistant heat-insulating layer of the same thickness as the fire-resistant heat-insulating layer and a heat-resistant heat-resistant heat-resistant layer are applied to the surface of the outer heat-resistant coating layer. The heat-resistant coating layer made of the same material as the coating layer is sequentially repeated to form the required layers. By this method, a coating in which the three layers of the heat-resistant coating layer, the fire-resistant heat insulating layer, and the heat-resistant coating layer are integrated into a GT layer is formed.

Furthermore, JP-A No. 61-163282 discloses that an inorganic binder solution is applied to the inner surface of exhaust system equipment through which high-temperature exhaust gas passes, and a fireproof insulation material powder is immediately applied to the layer of the free binder solution, followed by heat treatment. A fireproof heat insulating layer is formed by carrying out the first step including a step of drying and solidifying at least once, and then a mineral-free binder solution is applied to the surface of the fireproof heat insulating layer, and immediately the inorganic binder solution is applied. Discloses a method for manufacturing exhaust system equipment, characterized in that a refractory layer is formed by performing at least one second step including a step of attaching refractory material powder to the layer and drying and solidifying it by heat treatment. . This method does not use refractory insulation powder or a slurry of refractory material powder and inorganic binder solution, but rather adheres these powders to the coated layer of inorganic binder solution, so it is more effective than the former two methods. Heat treatment produces a fire-resistant and heat-insulating coating that is resistant to cracking and peeling.

[Problems to be solved by the invention] However, even with the method of JP-A-61-163282, if the temperature is rapidly raised in the firing process, only the surface of the coating layer dries and solidifies quickly, and there is still moisture inside. It was found that due to the residual amount, the coating layer may bulge and peeling may occur at the interface with the pipe material. In order to solve these problems, attempts have been made to slow down the hot water speed or use humidified drying, but the firing process takes a long time, resulting in undesirable results such as an increase in firing time and a rise in manufacturing costs. It will lead to it.

Therefore, an object of the present invention is to provide a method for manufacturing a ceramic coated tubular body that can shorten the firing time and prevent blistering and peeling of the coating layer.

[Means for Solving the Problems] As a result of intensive research in view of the above objectives, the present inventors have found that after attaching ceramic powder made of a heat insulating material or a refractory material to a coating layer of an inorganic binder solution, It was discovered that by filling small particles with a larger coefficient of thermal expansion than the body and heating and firing them, it was possible to make the ceramic coating layer denser and to achieve strong adhesion through a chemical reaction between the oxide film of the metal tubular body and the ceramic layer. Therefore, the present invention was conceived.

That is, the method for manufacturing a ceramic tubular body of the present invention is as follows:
(a) forming an oxide film on the inner surface of the metal tubular body; (b) applying an inorganic binder solution to the inner surface of the tubular body; and (c) immediately adhering ceramic powder to the layer of the inorganic binder solution. A ceramic layer is formed, and (d) small particles having a coefficient of thermal expansion larger than that of the tubular body are filled and sealed and heated and fired, whereby the ceramic layer is densified by the expansion of the small particles and is firmly attached to the inner surface. The inorganic binder used to impart adhesiveness in the method of the present invention, which is characterized in that it adheres closely to Phosphate binders such as aluminum, monobasic calcium phosphate, monobasic magnesium phosphate, bound sodium phosphate, phosphoric acid, sol binders such as colloidal silica, colloidal alumina, and colloidal zirconia, and ethyl silicate are suitable.

The binder is used in the form of an aqueous solution, and its concentration is between 20 and 4
5% by weight is preferred. If it is less than 20% by weight, the contact force will be small and peeling will occur easily. Further, if the content is higher than 45% by weight, the coating operation becomes difficult. More preferably, it is 25 to 40% by weight.

Appropriate amounts of curing agents can also be added to the binder solution. Although the curing agent differs depending on the type of binder, any known curing agent can be used. For example, silicate binders include sodium silicate, calcined aluminum phosphate, dicalcium silicate, carbon dioxide, and the like. For aluminum phosphate, there are basic oxides such as magnesia and lime, calcium aluminate, ammonium fluoride, and the like.

As the ceramic powder, both a refractory heat insulating material powder that provides heat insulation properties and a refractory material powder that specifically provides fire resistance can be used. Preferably, first, a section iWIm made of a refractory heat insulating material is formed, and then a refractory layer made of a refractory material is formed.

As the fireproof heat insulating material, inorganic heat insulating materials such as glass balloons, foamed silica, and perlite can be used. The particle size of the powder is suitably in the range of 10 to 500 μm. 1
If it is smaller than 0 μm, there is a high risk of cracking or peeling due to shrinkage, and if it is larger than 500 μm, it will be difficult to form a smooth film layer. A more preferable particle size range is 20 to 200
It is μm.

As the refractory material, commonly used materials such as chamotte, heat-resistant glass (Pyrex glass), fused silica, cordierite, mullite, alumina, zircon, and zirconia may be used, but zirconia is particularly preferred because of its low thermal conductivity. The average particle size of refractory material powder is generally 10-500μ
m range.

If it is smaller than 10 μm, agglomeration between particles tends to occur, making it difficult to form a smooth film layer, and easily shrinking under the influence of high heat. Moreover, if it is larger than 500 μm, it is difficult to form a smooth film. The preferred particle size range is 20-200 μm.

Small particles with a larger coefficient of thermal expansion than the tubular body include steel, copper,
Small balls of metal such as aluminum, silica sand, zirconia, etc. can be used. Since cast iron such as vermicular is usually used as the tubular body forming the ceramic coating layer, a comparison of the thermal expansion coefficients of these materials is shown below.

Vermicular cast iron: 10.2X10'/'C steel Ball: 13.0X10'/'C copper
Ball: 33. 0X10-6/"C Zirconia: 8.0X10'/"C The difference in thermal expansion coefficient between the small particles to be filled and the metal tubular body is O ~ 20x10'/
'C is preferred.

Further, if the difference in thermal expansion coefficient is smaller than 6×10 −6 /″C, the effect of compressing the ceramic layer due to the thermal expansion of the small particles will not be sufficient.

The particle size of the small particles should be relatively small so that the pressing force on the ceramic VW layer due to thermal expansion can be as uniform as possible, and so that it can be densely packed into a tubular body with a complicated shape such as an exhaust manifold. is desirable, specifically 0.
5-2. It is desirable that it is about Orm.

Next, the procedure of the method of the present invention will be explained.

First, an inorganic binder solution is applied to the inner surface of the tubular body by spraying or the like. Ceramic powder is applied to the resulting uniformly thick layer of inorganic binder solution.

Although any method can be used as long as the ceramic powder is uniformly deposited on the solution layer, a particularly preferred method is to spray the ceramic powder onto the inorganic binder solution layer. Alternatively, a tubular body with a coated inner surface may be filled with ceramic powder so that the solution is sufficiently coated with the ceramic powder.
There is also a method of forming a ceramic powder layer impregnated with a binder solution by removing only the ceramic powder that does not adhere after 3i. In either method, air blowing is preferably performed in order to completely remove unimpregnated ceramic powder. The thickness of the ceramic layer thus obtained depends on the concentration and thickness of the inorganic binder solution, but is generally on the order of 100 to 1500 microns per cycle.

Next, perform humidification as necessary. Humidification regimen is 50-80
℃ temperature, 40-80% relative temperature 30-120
This is done by holding it for a minute. As a result, the ceramic layer is completely impregnated and solidified with the inorganic binder solution.

After curing, it is dried by heating and holding at 270-300''C for 30-60 hours.

Generally, it is preferable that the ceramic coating layer is composed of a refractory insulation layer and a refractory layer, and the refractory insulation layer should have a thickness of 0.5 to 3.0 mm, and the refractory layer should have a thickness of 0.5 to 3.0 mm. It is necessary to have a thickness of 0 glume.

Therefore, in this case, first, the cycle of the above steps is repeated a plurality of times to form a fireproof heat insulating layer, and then a fireproof layer is formed by the same procedure.

The step of heating and firing the small particles filled and sealed is carried out when the fireproof heat insulating layer and the fireproof layer are completed, but it may be carried out last after the ceramic coating layer is formed.

The small particles are filled after the lower opening of the tubular body is sealed, but since it is necessary to apply compressive stress to the ceramic layer due to thermal expansion of the small particles during heating and firing, the small particles are filled as densely as possible. Therefore, it is desirable to fill the tubular body while vibrating it. It also benefits the upper opening after filling. The lid is designed so that it can sufficiently withstand the suppression caused by the thermal expansion of the small particles.
Firmly adheres to the tubular body.

In this state, it is then heated and fired. In general, the metamorphosis of castings is 78
Since this occurs at around 0°C, it is necessary to bake at a lower temperature. Additionally, if fired at too high a temperature, cracks may occur due to shrinkage. Therefore, it is best to bake at a temperature of 775°C. The firing temperature is maintained for a certain period of time, generally 30 to 60 minutes.

During firing, the tubular body, ceramic powder, and small granules all undergo thermal expansion, but the coefficient of thermal expansion of the small granules is sufficiently larger than that of the tubular body, so the ceramic layer sandwiched between them is strongly attached to the inner surface of the tubular body. You will be under pressure. After heating and firing, the tubular body is cooled in a furnace and the small particles are taken out.

[Function] In the method of the present invention, the small particles have a sufficiently larger coefficient of thermal expansion than the tubular body, and can be packed densely into a tubular body of any shape. Sufficient compressive stress can be applied during heating and firing of the layer.

Therefore, the ceramic coating layer after firing is sufficiently dense and has strong adhesion to the inner surface of the tubular body.

[Example] The present invention will be explained in more detail by the following example.
The present invention is not limited thereto.

Example 1 A cast iron manifold that was previously degreased with an alkaline solution of P l-110 to 11 (coefficient of thermal expansion = 10°2 x 1
0-6/℃), silica ratio 2.9 as a first step,
Calcined aluminum phosphate (H, B hardener manufactured by Hoechst) as a hardening agent in a sodium silicate aqueous solution with a concentration of 30% by weight.
A coating containing 10% by weight of Immediately, as a heat insulating material, use shirasu balloons with a bulk specific gravity of 0°2) and a particle size of 44 to 150 μm (coefficient of thermal expansion: 10.OXl 0'/”C).
was scattered.

After Shirasu balloon is fully attached, 75℃, 70%R
It was cured in H for 60 minutes and then dried by heating to 120° C. for 30 minutes.

After drying, steel grains with a diameter of 1 to 1.5 a (thermal expansion coefficient: 13,
The inside was filled with OXl 0'/'C), the opening was closed, the tube was inserted into the furnace, and the firing operation was performed. The heating temperature and heating time were as follows.

The temperature was increased to 20-50° C. for 1 hour, 50-100° C. for 1 hour, 100-200'C1T-1 hour, increased to 200-300° C. for 1 hour, and held at 300° C. for 1 hour to complete the firing process, thereby forming a heat insulating layer.

As a second step, the same inorganic binder solution as above was applied on the heat insulating layer, and stabilized zirconia particles (thermal expansion coefficient near, OX 10-6) with a particle size of 44 to 150 μm were applied.
/” After spraying C), curing and drying, the average diameter is 1.5
The inside was filled with M steel grains, the opening was closed, the steel was inserted into the furnace, and the same firing operation as above was performed to form a refractory layer.

Substantially no blisters or cracks were observed in the obtained heat insulating layer and fireproof layer. Further, this fireproof/insulating manifold was repeatedly heated with 1000° C. firing gas and allowed to cool, but virtually no cracks or peeling of the coating layer was observed.

Example 2 As a first step, a curing agent was added to an aqueous sodium silicate solution with a silica ratio of 2.9 and a concentration of 40% by weight on the inner surface of the same iron manifold as in Example 1, which had been previously degreased with an alkaline solution with a pH of 10 to 11. As a coating material, 10% by weight of calcined aluminum phosphate (To1.B hardener manufactured by Hoechst) was added. Immediately, as a heat insulating material, bulk specific gravity 0.2) particle size 4
Shirasu balloons with a size of 4 to 150μ were sprayed.

After the whitebait balloon has fully adhered, 75
It was cured for 60 minutes at 70% RH and then dried by heating at 120°C for 30 minutes.

As a second step, the same inorganic binder solution as above was applied onto the above-mentioned adiabatic pattern, and stabilized zirconia particles having a particle size of 44 to 150 μm were further sprinkled on the surface, followed by curing and drying.

Thereafter, the inside was filled with steel grains having a diameter of 1 to 1.5 B, the frontage was closed, and the tube was inserted into a furnace. The firing conditions were the same as in Example 1. In this way, a fireproof layer was formed on the heat insulating layer.

Substantially no blisters or cracks were observed in the obtained heat insulating layer and fireproof layer. Further, this fireproof/insulated manifold was repeatedly heated with combustion gas at 1000°C and allowed to cool, but virtually no cracks or peeling of the coating layer was observed.

Example 3 A ceramic coating layer consisting of a heat insulating layer and a refractory layer in a cast iron manifold was formed in exactly the same manner as in Example 1 except that silica sand having an average diameter of 1 mm was used instead of the 14 balls.

Substantially no cracks were observed in the resulting heat insulating layer and fireproof layer. Also, 10% for this fireproof and insulated manifold.
Although heating with combustion gas at 00°C and cooling were repeated, virtually no cracks or peeling of the coating layer was observed.

Comparative Example 1 A heat insulating layer and a fireproof layer were formed under the same conditions as in Example 1 except that small particles were not used. Significant blisters, cracks, and peeling were observed in these layers.

[Effects of the Invention] As is clear from the above, the method for manufacturing a ceramic WI tubular body according to the present invention includes the step of heating and firing a ceramic coating layer by inserting small particles having a sufficiently larger coefficient of thermal expansion than the tubular body into the tubular body. Since it is filled and sealed, its thermal expansion can be used to compress and press the ceramic coating layer. Therefore, the ceramic coating layer of the ceramic coated tubular body coated by the method of the present invention is substantially free of bubbles and peeling from the inner surface of the tubular body. Further, since small particles are used, there is an advantage that a strong ceramic layer can be easily formed even on a tubular body having a complicated internal shape.

Claims (4)

[Claims] (1) In a method for manufacturing a metal tubular body having a ceramic coating layer on the inner surface, (a) forming an oxide film on the inner surface of the metal tubular body, (b) applying an inorganic binder solution to the inner surface, and ( c) Immediately adhering ceramic powder to the layer of the inorganic binder solution to form a ceramic layer; (d) filling the tubular body with small particles having a larger thermal expansion coefficient than the tubular body and heating and firing the sealed state; A method characterized by densifying the ceramic layer and firmly adhering it to the inner surface by expanding the small particles. (2) In the method according to claim 1, the tubular body is made of cast iron, and the small particles are one or more types of metal balls such as iron balls, steel balls, copper balls, and aluminum balls. A method characterized by being a combination of. (3) A method according to claim 1 or 2, characterized in that steps (b) to (d) are repeated two or more times. (4) In the method according to claim 3, 1
A method characterized in that an inner layer made of one or more of the ceramic layers is used as a heat insulating layer, and a surface layer made of one or more of the ceramic layers is used as a refractory layer.