A COATING SYSTEM AND METHOD

Field of the Invention

The present invention relates to reduction of passage of the useful heat generated as a result of combustion to the surrounding components and the cooling system, improving fuel consumption by increasing thermal efficiency, and increasing exhaust gas temperatures by means of coating the parts of the diesel engine members, which are exposed to combustion and/or combustion gases, by thermal barrier ceramic based materials.

Background of the Invention The coating technique which is common to apply today mostly in turbine blades is realized as follows;

Roughening the surface that will be coated by processes such as sanding, and performing degreasing,

By means of applying bond layer powder as the lower layer, strengthening the mechanical bond between the main substrate and the ceramic coating, and decreasing the differences in the thermal expansion coefficient,

Spraying the ceramic powder which functions as a thermal barrier layer at high speed and under plasma conditions via a gun by means of the plasma spray method.

The new surface that is produced is used in this form.

The said application is based on coating the powder material by thermal spray method. As a result of both the low wear resistance of the powder material and the porous inner structure, which is the main necessity of thermal barrier coating and heat management applications, there is a risk of detachment of particles and/or powders from the final surface that is obtained. There is a risk of substantial damages if the pollutants generated in the combustion chamber of the diesel engines reach the turbocharger via the exhaust gas. Japanese patent document no. JPS5453628 (A), one of the applications known in the art, discloses about increasing the hardness of the surface of an engine member and enhancing the wear resistance by laser beams. The surfaces of engine members such as a piston ring, valve seat, valve, cam shaft or crank shaft are irradiated with laser beam. Wear resistance of the irradiated portion is enhanced by methods such as hardening, glazing etc.

Chinese patent document no. CN101270970 (A), an application in the state of the art, discloses about coating engine members by the method of thermal atomization. The ring groove of a two-stroke diesel engine is metal coated by atomization. Metal coating is applied to the top and bottom faces (21, 22) of the ring groove.

German patent document no. DE19956622 (Al), an application in the state of the art, discloses about coating piston rings (3) and/or pistons and/or cylinder liners of two-stroke diesel engines. The coating comprises aluminum bronze and is applied to the base material. The coating (4) is applied onto the engine members by means of thermal spray method.

Summary of the Invention The objective of the present invention is to provide a coating system and method which enables to obtain a completely smooth and nonporous coating surface.

Another objective of the present invention is to provide a coating system and method which enables to obtain the top surface smoothening process to be at a very thin wall thickness and enables the coating to be realized without damaging the inner structure and thermal barrier feature of the coating. A further objective of the present invention is to provide a coating system and method which enables to enhance wear resistance of the coating as a result of obtaining a smooth surface, and to prevent the risk of detachment of a powder and/or particle within the combustion chamber and the damages that might occur in the engine members as a result of this risk.

Another objective of the present invention is to provide a coating system and method which enables to prevent fuel and/or oil absorption thanks to the nonporous and smooth surface.

Detailed Description of the Invention

"A coating system and method" developed to fulfill the objective of the present invention is illustrated in the accompanying figure, in which:

Figure 1. is a perspective view where the surfaces to be coated are shown. Figure 2. is a front sectional view of the coating system.

Figure 3. is a schematic view of the coating system.

The components given in the figures are assigned reference numbers as follows:

1. Coating system

2. The surface to be coated

3. Bond layer

4. Top layer

The coating system (1) of the present invention, which is applied to the surfaces of the diesel engines' cylinder head, exhaust/intake valves, exhaust/intake ports and/or pistons that are exposed to combustion gases, basically comprises

- at least one surface (2) on which coating will be applied, - at least one bond layer (3) applied onto the surface to be coated (2), at least one top layer (4) which is applied onto the bond layer (3).

The coating system (1) of the present invention is applied to the surfaces of the diesel engines' cylinder head, exhaust/intake valves, exhaust/intake ports and/or pistons that are exposed to combustion gases.

The bond layer (3) applied onto the surface to be coated (2) facilitates bonding of the ceramic based top layer (4) on the surface.

In order to prevent the risk of powder and/or particles detached from the top surface of the thermal barrier coated material (defined as a technical problem) damaging the engine members, laser glazing step is added to the thermal barrier coating method (100) process.

The coating method (100) developed to fulfill the objective of the invention comprises the steps of

- cleaning and heating the surface to be coated (2) and degreasing (101),

- roughening the surface to be coated (2) by sand blasting, preparing the surface to be coated (2) for mechanical bonding of the coating (102),

- applying a bond layer (3) of a certain thickness onto the sand blasted surface to be coated (2) (103),

- applying the ceramic based powder top layer (4) on the bond layer (3) via thermal spray method (104).

As a result of the high cylinder pressure resulting during combustion throughout operation of a diesel engine, movement of the dynamic members, and the high speed contact of the valve with the valve seat, there is a risk of detachment of powder and/or particle on the coating top layer (4). The top layer (4) obtained in the coating method (100) of the present invention has a very low wear resistance due to the porous inner structure of the thermal barrier coatings and the powder metallurgy that is used. The thermal barrier coated top layer (4) is subjected to laser glazing process in order to prevent potential damages that might occur in the engine members as a result of detachment of powder and/or particles from the coated top layer (4).

Accordingly, the ceramic based top layer (4) is melted by a few microns of wall thickness from the surface by using a laser system. When the molten structure solidifies, it forms an extremely dense and nonporous microstructure. The top layer (4) that is obtained has a completely smooth, nonporous and solid structure. As a result of the increasing wear resistance and rigidness, the risk of detachment of any powder and/or particle from the surface to be coated (2) is prevented. Accordingly, in a diesel engine wherein thermal barrier coating method (100) is used, the damages that may be caused by the particles detached from the coating surface due to high cylinder pressure and mechanical contact on the surrounding components particularly the turbocharger blades are prevented. In the new technique that is developed, a smooth and nonporous coating top layer (4) is obtained by solidifying the top layer (4) upon the laser glazing application after the thermal barrier coating application.

As a result of the laser glazing application, top layer (4) smoothening process is performed at a very thin wall thickness without damaging the inner structure and the thermal barrier feature of the coating.

As a result of obtaining a completely smooth top layer (4), wear resistance of the coating is enhanced and the risk of detachment of a powder and/or particle in the combustion chamber and the damages that might occur in the engine members as a result of this risk are prevented. Furthermore, by means of the nonporous and smooth coating top layer (4), fuel and/or oil absorption through the top layer surface (4) during engine operation is prevented.

The coating system (1) and method (100) of the present invention relates to reduction of passage of the useful heat generated as a result of combustion to the surrounding components and the cooling system, improving fuel consumption by increasing thermal efficiency, and increasing exhaust gas temperatures by means of coating the parts of the cylinder head, exhaust/intake valves, exhaust/intake ports and/or pistons in diesel engines, which are exposed to combustion and/or combustion gases, by thermal barrier ceramic based materials. Thanks to the coating system (1) and method (100) of the present invention, a completely smooth top layer (4) with high wear resistance is obtained as a result of the laser glazing process applied to the coating top layer (4), and thus detachment of powder and/or particles from the surface to be coated (2) (which is a potential problem) and the engine damages that might result especially in parts such as turbochargers are prevented.