Coating processes – Spray coating utilizing flame or plasma heat – Metal oxide containing coating
Reexamination Certificate
2001-10-23
2003-06-03
Bareford, Katherine A. (Department: 1762)
Coating processes
Spray coating utilizing flame or plasma heat
Metal oxide containing coating
C427S456000, C427S451000
Reexamination Certificate
active
06572931
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention refers to a method of applying a ferrous coating to a substrate serving as a cylinder working surface of a combustion engine block.
PRIOR ART
In the prior art, the traditional material for the working surfaces of the cylinders of combustion engine blocks that are made of aluminum or magnesium alloy is constituted by grey cast iron or cast iron blended with compacted graphite. Thereby, cylinder sleeves made of such cast iron are pressed or cast into these combustion engine blocks.
By providing such cylinder sleeves, however, on the one hand the size and the weight of the engine block is influenced in a negative sense. On the other hand, an inconvenient or adverse connection between the cylinder sleeves made of cast iron and the engine block made of a light metal alloy must be taken into account. Alternatively, also coatings applied by a galvanizing process have been used. However, the application of such coating is expensive and, moreover, such coatings may corrode under the influence of sulfuric acid and formic acid.
Furthermore, the application of a coating to bores in general by means of a plasma spraying operation is known in the art for a long time. Thereby, a variety of metallic materials can be applied to the substrate. Once the coating has been applied by means of the plasma spraying operation, the bores are further processed by diamond honing to reach their desired final diameter and provided with the desired topography. The ability of the coating to be processed and machined, respectively, and the tribologic properties are depending to a high degree on the microstructure and the physical properties of the particular coating.
OBJECTS OF THE INVENTION
It is an object of the present invention to improve the machining and processing, respectively, as well as the tribologic properties of ferrous coatings for the working surfaces of combustion engine cylinder blocks applied by a plasma spraying operation.
SUMMARY OF THE INVENTION
In order to meet this and other objects, the invention provides a method of applying a ferrous coating to a substrate serving as a cylinder working surface of a combustion engine block. The method comprises the steps of providing a plasma spraying apparatus, providing a coating powder constituting the raw material of the coating to be applied, spraying the coating powder by means of the plasma spraying apparatus onto the cylinder working surface; and either
supplying air to the plasma spraying apparatus and spraying the air simultaneously with the coating powder onto the substrate in an amount of between 200 and 1000 normalized liters per minute; or
supplying an oxygen containing gas to the plasma spraying apparatus and spraying the oxygen containing gas simultaneously with the coating powder onto the substrate in an amount of between 40 and 200 normalized liters oxygen per minute; or
supplying oxygen to the plasma spraying apparatus and spraying the oxygen simultaneously with the coating powder onto the substrate in an amount of between 40 and 200 normalized liters per minute.
The expression “normalized liters per minute” shall be understood as “liters per minute at an ambient pressure of 1 bar (=10
5
Pa) and a temperature of 20° C. Preferably, the velocity of the gas flow in the interior of the sleeve or cylinder bore amounts to between 7 and 12 m/s during the plasma spraying operation.
In a preferred embodiment, a gas atomized powder is plasma sprayed to the substrate, whereby the powder has the following composition:
C=0.4 to 1.5% by weight
Cr=0.2 to 2.5% by weight
Mn=0.02 to 3% by weight
P=0.01 to 0.1% by weight, if appropriate
S=0.01 to 0.2% by weight, if appropriate
Fe=difference to 100% by weight.
In another preferred embodiment, a gas atomized powder is plasma sprayed to the substrate, whereby the powder has the following composition:
C=0.1 to 0.8% by weight
Cr=11 to 18% by weight
Mn=0.1 to 1.5% by weight
Mo=0.1 to 5% by weight
S=0.01 to 0.2% by weight, if appropriate
P=0.01 to 0.1% by weight, if appropriate
Fe=difference to 100% by weight.
The amount of FeO and Fe
3
O
4
in the coating can be influenced by the distribution of the size of the particles of the powder. Depending on the coating to be realized, the size of the particles of the powder can be in the region of between 5 to 25 &mgr;m, in the region of between 10 to 40 &mgr;m, or in the region of between 15 to 60 &mgr;m. The size of the particles can be determined by means of an optical or an electronic microscope, particularly by means of a scanning microscope, or according to the laser diffraction method MICROTRAC.
Preferably, a coating powder is used that has been gas atomized by means of argon or nitrogen.
The best results can be obtained if a coating powder is used that is blended with a tribologic oxide ceramics. Preferably, the oxide ceramics consists of TiO
2
or Al
2
O
3
TiO
2
and/or Al
2
O
3
ZrO
2
alloy systems. The portion of the oxide ceramics in the coating powder can amount to between 5 and 50% by weight.
It should be noted that the optimum particle size is selected according to the tribologic properties of the coating to be applied and according to the mechanical behavior of the substrate to which the coating has to be applied.
REFERENCES:
patent: 3935797 (1976-02-01), Niimi et al.
patent: 4060653 (1977-11-01), O'Day et al.
patent: 5466906 (1995-11-01), McCune, Jr. et al.
patent: 5592927 (1997-01-01), Zaluzec et al.
patent: 5622753 (1997-04-01), Shepley et al.
patent: 5649994 (1997-07-01), Holko
patent: 5663124 (1997-09-01), Rao et al.
patent: 5723187 (1998-03-01), Popoola et al.
patent: 5766693 (1998-06-01), Rao
patent: 940082 (1956-03-01), None
patent: 735928 (1932-11-01), None
Thermal Spraying: Practice, Theory, and Application, American Welding Society, Inc., 1985, p. 57.
Bareford Katherine A.
Sulzer Metco AG
Tarolli, Sundheim Covell & Tummino L.L.P.
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