Note: Descriptions are shown in the official language in which they were submitted.
CA 02469461 2004-06-17
A COATING t=OR THE WORtCING SURFACE OF THE CYLINDERS OF
COMBUSTION ENGINES AND A MI'THOD OF APPL~'fNG SUCH A COATING
This is a divisional of application Serial No. 2,296,155 filed January 17,
2000.
Backaround of the Invention
The present invention refers to a ferrous coating applied by a plasma spraying
operation to a substrate serving as a cylinder working surface of a combustion
engine
block. Moreover, the invention also 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 in-
convenient or adverse connection between the cylinder sleeves made of cast
iron end
the engine block made of a light metal alloy must be taken into account.
Alternatively,
also coatings applied by a galvanising process have been used. However, the
applica-
tion of such coating is expensive and, moreover, such coatings may corrode
under the
influence of sulfuric acid and formic acid.
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Furthermore, the application of a coating to bores in gene.rat by means of a
plasma spraying operation is known in the art for a long time. Thereby, a
variety of me-
lallic matenais 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 fnai 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 prop-
erties 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 tribotogic properties of ferrous coatings for the
working sur-
faces of combustion engine cylinder blocks applied by a plasma spraying
operation.
z
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Sumrn_ary of the invention
!n order to meet this and other objects, the invention provides, in a first
aspect, a
ferrous coating applied by a plasma spraying operation to a substrate serving
as a cyl-
finder working surface of a combustion engine block, whereby the coating has a
content
of bound oxygen of between 1 % and 4% by weight.
"fhe inventiøn is based on the surprising observation that a microstructure
can be
created by means of a specially controlled reaction of the powder used far the
coating
and oxygen during a plasma spraying operation, i.e_ a microstructure
comprising out
standing properties as far as machining and processing, respectively, as well
as tri-
boiogy are concerned. Particularly, the coefficient of friction and the
tendency towards
scuffing, i_e. the beginning of adhesive wear, are drastically decreased.
As previously mentioned, the coating of the invention, applied by plasma spray-
ing, has a content of bound oxygen of between 1 and 4% by weight. As a
substrate for
applying such a coating, particularly suitable are:
~ !he cylinder bores of combustion engine cylindEr blocks made of an aluminum
or a mar~nesium alloy or of cast iron;
~ the inner wall of sleeves made of cast iron and inserted into a combustion
cn~
give cylinder block made of an aluminum or a magnesium alloy.
In a preferred embodiment, the bound oxygen forms, together with the iron, Fe0
and Fe304 crystals in the coating. Thereby, if is preferred that the content
of Fez43
amounts to less than 0.2% by weight. The amount of the formed oxides can be
further
controlled by mixing the air with nitrogen or oxygen. if the air is replaced
by pure oxy-
gen, the content of bound oxygen in the coating is reduced by a factor of
about two.
. .... _.. .. .,. ~ -_ . ,~ . _ r , .,. ..,r ~ w.~ .a~.~. .,w ..., .
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In a second aspect, the invention also refers to a method of applying a
ferrous . .
coating to a substrate serving as a cylinder working surface of a combustion
engine
black. The method comprises the steps of providing a plasma spraying
apparatus, pro-
viding 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
cylin-
der working surface; and either
~ supplying air to the plasma spraying apparatus and spraying the air simuita-
neously 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 titers oxy-
gen 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" shat) be understood as "liters
per
minute at an ambient pressure of 1 bar (~ 10' Pa) and a temperature of
20° C. Prefera-
bly, 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°/a by weight
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CA 02469461 2004-06-17
Cr ~ 0_2 to 2.5% by weight
Mn = O.a2 to 3% by weight
i' = O.D1 to 0_ 1 % by weight, if appropriate
S = 0.01 t~ 0.2% by weight, if appropriate
Fe = difference to 100~/o by weight,
in anoti~er preferred ernbadiment, a gas atomized powder is plasma sprayed to
the substrate, whereby the powder has the following composition:
C - 0_1 to 0.8°1° by weight
Cr = ~( 1 to 18% by weight
Mtl = 0.7 to 1 _5% by weight
Mo = 0_1 to 5%, by weight
S ~ O.D1 to 0.2% by weight, if appropriate
P = 0.07 to 0.1 % by weight, if appropriate
he = difference to 100% by weight.
The amount of FeQ and Fe~04 in the coating can be influenced by the distribu,
lion of the size of thc; particies 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 pm, in the
rE:gion of between 10 to 40 frm, or in the region of between 15 to f~0 l.rm.
The size of the
pertic(es can be determined by means of an optical or an electronic
microscope, par-
ticularly by means of a scanning microscope, ar according to the laser
diffraction
mraiiod MICRC~TRAC.'
Preferably, a coating powder is used that has been gas atomized by means of
argon or nitrogen.
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The best results can be obtained if a coating powder is used that is blended
with
a tribofogic oxide ceramics. Preferably, the oxide ceramics consists of TiOz
or A1~03Ti(J~
and/or Afz03Zr02 alloy systems. The portion of the oxide ceramics in the
coating pow,
der can amount to between 5 and 5D% by weight.
It should be noted That the optimum particle size is selected according to the
tri-
bologic properties of the coating to be applied and according to the
mechanical behavior
of the substrate to which the coating has to be applied.
brief Descrit~tion of the Drawin s
In the following; some examples of a coating according to the invention will
be
further described_ In the accompanying drawings:
Fig. 1 shows a diagram illustrating the relation between the particle size of
the
coating powder and the decrease of the coefficient of friction as welt as the
relation be-
tween the particle size of the coating powder and the mechanical
characteristics, ~par-
ticula~iy the adhesive strength of the coating; and
Fig. 2 shows a diagrarr~ illustrating the relation between the amount of bound
oxygen in the coating and the decrease of the coefficient of friction as welt
as the refa-
lion between the amount of bound oxygen in the coating and the mechanical
character-
istics, particularly the adhesive strength of the coating.
Example 1
A coating powder has been applied to the working surface of a cylinder sleeve
of
a combustion engine by means of a plasmatran. The coating powder had the
following
composition-
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C = 9 .1 % by weight .
Cr = i .5°/a by Weight
Mn = '( _5% by weight
Fe = difference to 900% by weight.
If appropriate, the coating powder may also contain S and P in small amounts
(i.e. 0.01 to 0.2% by weight).
TY~e size of the particles of the coating powder was between 5 and 25 lrm. The
powder has been manufactured by a gas atomizing process. The velocity of the
gas
ff~~w Burin c~ the operation of applying the coating was 't t7 rn/s, and the
amount of air fed
to fhe plasmatron for cooling the coating and for the reaction of the powder
was 500
NLIaM (nc~rmaiized liters per minute). This corresponds to about 100 NLPM pure
oxy-
gen. That amount of air was fed through the body of a plasmatron welt known in
the art,
e.g. as described in U.S. Patent No. 5,519,183.
The results of the experiments that have been run have shown that the content
of
oxygen in the applied coating was in the region of 3°/a by weight.
According to a macro
structural analysis performed by means of X-rays, the oxygen is bound
according to the
stoichiometric formulas Fe0 and Fe30~,. Moreover, that analysis has shown that
the
presonce of Fo203 is below the detectable limit.
The coating having been applied, the cylinder sleeve was further processed by
diamond honing. Experiments with a combustion engine provided with such
cylinder
sleeves have clearly confirmed that the coefficient of friction between the
piston rings
and the wall of the cylinder sleeve is substantially reduced, as compared to
well known
cylinder sleeves made of grey cast iron.
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Example 2
A, powder was used having the same composition as in Example 1 herein before;,
but with a particle size of between 10 and 45 ~tm. Moreover, ail other
conditions were
identical to the ones described ire Example 1. Thereby, it was found that the
content of
bound oxygen in the applied coating was in the region of 2% by weight. The
other re-
sults of an analysis of the coating were the same as explained in connection
with Ex-
ample 1.
The coating having been applied, the cylinder sleeve was further processed by
diamond honing. Experiments with a combustion engine provided with such
cylinder
sleeves have clearly confirmed that the coefficient of friction between the
piston rings
and the working surface of the cylinder sleeve again is substantially reduced,
as com-
pared to well known cylinder Sleeves made of grey cast iron, whereby the
reduction of
the coefficient of fr7ction is in relation to the amount of bound oxygen.
~xam~Ie~3
Cylinder sleeves that are to lie used with combustion engines operated with
sul-
phurous fuel ar With methanol, such engines being subject to corrosion when
they are
operated at temperatures below the dew-point at the given conditions, have
been
coated, under the same conditions as described in Example 1, with a powder
having the
following composition:
C = 0_~.°r° by weight
Cr = 13.0% by weight
Mn ~ 1.5% by weight
Mo = 2.0% by weight
.,....m __ ....._ .. ~ .1...<."~ ~..~, x..M~.~. ....._._- ...._.
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.. c~ ...
Fe = difference to 100°la by weight.
ft appropriate, the coating powder may also contain S and P in small amounts
(i.e. 0.01 to 0.2°l° by weight).
The-: size c~f the particles of the coating powder was between 10 and 45 Nm.
The tests that have been run using such a coating yielded substantially the
same
I~-worabla results as explained in Examples '1 and 2.
Example 4
The same procedure was performed as described in Example: 2, except that 30%
by weictht of an ceramics alloy powder was added to the coating powder, the
ceramics
alloy powder having a composition of 60°!° by weight AIZO~ and
40% by weight TiQ2.
The coatings created using such a powder are rtfechanicaliy reinforced due to
the inclu-
lion of the ceramics particles with a size of between ~ and 22 pm.
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_.___-_~_....~.....~___~__.. _ , _ __
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Example r
~i'he same procedure was repeated as described in Example 4, except that 30%
by weight of a ceramics alloy powder was added to the coating powder, the
ceramics
alloy powder having a composition of SO% by weight A1203 and 20% by weight
Ti02.
The coatings created using such a powder are mechanically reinforced due to
the inclu-
sion of the ceramics particles with a size of befween 5 and 22 frm.
Fig. 1 shows a diagram illustrating the relation between the particle size of
the
coating powder and the decrease of the coefficient of friction as well as the
relation be-
tween the particle size of the coating. powder and the mechanical
characteristics, par-
ticularly the adhesive strength of the coating. It Is evident tram the
diagram, on the one
hand, that the coefficient of friction gets lower if the size of the particles
is increased. On
the other hand, the adhesive strength is gradually reduced if the particle
size is in-
creased. A goad compromise may be a particle size in the region of 25 to 30
um,
whereby the adhesive strength amounting to appr. 45-50 MPa should be
sufficient in
most cases while the coefficient of friction is stilt reduced, as compared to
the prior art
coatings, 6y about 22-25%. However, if adhesive strength is the primary goal
and the
reduction of the coefficient of friction is but of secondary importance, one
would chose a
coating powder having particles with a smaller size. In another application,
in which the
reduction of the coeificient of friction is the primary goa! and the adhesive
strength of
tile coating is less important, ono would chose a coating powder having
particles with a
greater size.
Fig. 2 shows a diagram illustrating the relation between the amount of bound
oxygen in the coating and decrease of the coefficient of friction as well as
the rotation
CA 02469461 2004-06-17
..
between the amount of bound oxygen in the coating and mechanical
characteristics,
parCicutariy the adhesive strength of the coating. tt is evident from the
diagram, on the
orro hand, that the coefficient of friction gets lower if the amount of bound
oxygen in the
coating is increased. On the other hand, the adhesive strength is reduced if
the amount
of bound oxygen in the coating is increased. A good compromise may be a
content of
bound oxycden in the region of between 2-2.5% by weight, whereby the adhesive
strength amounting to appr. 40-~t~ MPs should be sufficient in most cases
while the co-
efficient of friction is still reduced, as compared to the prior art coatings,
by about 20-
25%: Correspondingly to what is explained in connection with !=ig. 1, i.e. if
adhesive
strength is the primary goal and the reduction of the coefficient of friction
is but of sec-
ondary importance, one would strive for realizing a tower content of bound
oxygen in the
coating. tn another application, in which the reduction of the coefficient of
friction is the
primary goal and the adhesive strength of the coating is Less important, one
would strive
for realizing a higher content of bound oxygen in the coating.
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