Development of plasma spray-coated cylinders 2000-05-0069
In recent years, one of the most important issues in the
automotive industry is the improvement of fuel economy started from
the environmental problem. Making cars lighter and reducing the
coefficient of friction are two ways to improve fuel economy.
Reducing the weight of a cylinder, an engine component, is a
typical example. The traditional, mainstream method to reduce
cylinder weight has been to convert cast iron cylinder blocks into
aluminum cylinder blocks by using cast iron sleeves. To further
make engines lighter and more compact, however, it is desirable
that cast iron sleeves be abolished, or, in other words, making
cylinder blocks sleeveless.
A typical technology to make cylinder blocks sleeveless is
applying anti- wear coating on a bore wall. Electroplating is
currently the mainstream method used for this technology. It must
be noted, however, electroplating is used primarily for
low-pressure cast cylinders. It is not applied to die-cast
cylinders because of the porosity in the bore walls in the die-cast
cylinders. Application of this technique to die-cast cylinders,
therefore, is extremely important for the purpose of increasing
casting productivity and realizing lightweight and compact designs
through reduction of the wall thickness.
We chose to look into the plasma-spraying technology as a
candidate for solving this problem. Since this technique allows
high-speed formation of coatings as thick as several hundred
microns regardless of the work material, the plasma-spraying
technology sheds light to sealing of the porosity. The abundance of
the raw material for making the coating also leads to easy
formation of cheap, composite coating by combining various raw
This paper reports the process of developing low-cost,
sleeveless spray- coated cylinders by the plasma-spraying
technology taking advantage of the above-mentioned properties. Use
of the technique with die-cast material is also reported.