Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD AND AN APPARATUS FOR PLASMA TREATING
THE SURFACE OF SUBSTRATES
Background of the Invention
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The present invention refers to a method and an apparatus for plasma treating
the surface of substrates.
In order to get an optimum quality of a coating that has been applied to the
sur-
face of a substrate by means of a plasma spraying apparatus, on the one hand,
the
surface of the substrate must be as clean as possible and, on the other hand,
the sub-
strate to be coated has to be heated to a certain temperature. Both of these
require-
ments contribute to a perfect adhesion of the coating to the surface of the
substrate.
Prior Art
In most cases, the coating operation of the surface of substrates takes place
in a
treatment chamber in which usually a subatmospheric pressure is created in
order to
avoid that the surface of the substrate to be coated oxidizes. In the methods
known in
the prior art, the substrate to be coated is inserted into the treatment
chamber in the in-
terior of which it is first cleaned, then heated and finally coated. The
result is that the du-
ration of the entire treatment operation not only depends on the time it takes
to coat the
surface of the substrate, but that duration is substantially increased by the
cleaning and
heating steps.
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Objects of the Invention
24429P1.doc
Thus, it is an object of the invention to provide a method for plasma treating
the
surface of substrates by means of which the duration of the entire treatment
operation
of the substrate can be substantially decreased and, thereby, the throughput
substan-
tially increased without impairing the high quality of the coating applied to
the surface of
the substrate.
It is a further object of the invention to provide an apparatus for plasma
treating
the surface of substrates by means of which the duration of the entire
treatment opera-
tion of the substrate can be substantially decreased and, thereby, the
throughput sub-
stantially increased without impairing the high quality of the coating applied
to the sur-
face of the substrate.
Summary of the Invention
In order to meet these and other objects, the invention provides, according to
a
first aspect, a method for plasma treating the surface of substrates in which
a first sub-
strate is coated by a plasma coating apparatus in the interior of a treatment
chamber
while, simultaneously, a second substrate to be subsequently coated is pre-
treated out-
side of that treatment chamber.
According to a second aspect, the invention provides an apparatus for plasma
treating the surface of substrates, comprising a treatment chamber, a device
for creat-
ing a subatmospheric pressure in the treatment chamber, and a plasma spraying
appa-
ratus located in the interior of the treatment chamber.
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The apparatus further comprises at least one pre-treatment chamber, a device
for creating a subatmospheric pressure in the pre-treatment chamber, and a
plasmatron
located in the interior of the pre-treatment chamber.
Due to the fact that the time consuming pre-treatment operation of the
substrate,
that has to be done before the real coating operation of the surface of the
substrate, is
performed outside of the treatment chamber, a first substrate can be plasma
coated in
the interior of the treatment chamber, while simultaneously a second substrate
to be
subsequently coated can be pre-treated outside of the treatment chamber. The
result is
that the dwell time of the substrate in the treatment chamber can be shortened
and the
throughput substantially increased. It should be noted that the expression
"simultane-
ously" shall be understood in a sense that the pre-treatment operation and the
coating
operation take place simultaneously at least during a portion of the required
time, i.e. at
least partially overlap. On no account the expression "simultaneously" should
be inter-
preted such that both operations have to be started at the same moment or have
to end
at the same moment.
Experience has shown that the time required for the pre-treatment, i.e. for
clean-
ing and heating the substrate, can vary between 50% and 200% of the time
required to
plasma coat the surface of the substrate. In other words, using the method and
the ap-
paratus according to the present invention in which the pre-treatment of a
substrate is
performed outside the treatment chamber, the throughput can be increased by
appr.
50% to 100%.
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Brief Description of the Drawings
24429P1.doc
In the following, the method and an embodiment of the apparatus according to
the invention will be further described, with reference to the accompanying
drawings, in
which:
Fig. 1 shows the apparatus in a first phase of operation;
Fig. 2 shows the apparatus in a second phase of operation;
Fig. 3 shows the apparatus in a third phase of operation;
Fig. 4 shows the apparatus in a fourth phase of operation;
Fig. 5 shows the apparatus in a fifth phase of operation.
Detailed Description of the Method and of a preferred Embodiment of the
Apparatus
First, the general layout of the apparatus of the invention will be described
in
more detail with the aid of Figs. 1 and 2 showing the apparatus during two
different
phases of operation. Since the basic principle of pre-treating and coating of
a substrate
by means of a plasmatron is well known to any person skilled in the art, in
the following,
only the characteristics will be further discussed that are essential in
connection with the
present invention. Moreover, in the present example, it is assumed that the
substrates
that have to undergo a surface treatment by means of a plasma torch are made
of me-
tallic material.
The apparatus according to the invention comprises a central treating chamber
1
in which a plasma spraying apparatus 10 is received. The plasma spraying
apparatus
is mounted on a first swiveling supporting apparatus 11 that can be moved
along
three orthogonal axes within a Cartesian coordinate system. At the left side
next to the
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central treating chamber 1, a first pre-treating chamber 2 is provided, while
a second
pre-treating chamber 3 is located at the right side next to the central
treating chamber 1.
The first pre-treating chamber 2 is provided with a first removable cover 4,
and the sec-
and pre-treating chamber 3 is provided with a second removable cover 5. The
covers 4,
being removed, a substrate S1 and S2, respectively, can be inserted into the
pre-
treating chambers 2, 3 and removed therefrom, respectively.
The first pre-treating chamber 2 comprises a plasmatron 20 mounted in its inte-
rior by means of a second swiveling supporting apparatus 21, and the second
pre-
treating chamber 3 comprises a plasmatron 30 mounted in its interior by means
of a
third swiveling supporting apparatus 31. Moreover, the first pre-treating
chamber 2 is
provided with a first supporting member 23 adapted to receive the substrate
S2, while
the second pre-treating chamber 3 is provided with a second supporting member
33
adapted to receive the substrate S1. At the end of the first supporting member
23, a first
clamping member 24 is attached by means of which the substrate S2 can be
clamped
to the supporting member 23, and at the end of the second supporting member
33, a
second clamping member 34 is attached by means of which the substrate S1 can
be
clamped to the supporting member 33. Each of the first and second covers 4 and
5, re-
spectively, is provided with an opening 6 and 7, respectively, through which
the first and
second supporting members 23 and 33, respectively, extend.
The first and second supporting members 23 and 33, respectively, are movable
along their longitudinal axes to such an extent that the particular substrate
S2 and S1,
respectively, can be fixed to the first and second supporting members 23 and
33, re-
spectively, and clamped by the first and second clamping members 24 and 34,
respec-
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tively, outside of the first and second pre-treatment chambers 2 and 3,
respectively, and
that the substrates S2 and S1, respectively, can be displaced into the central
treatment
chamber 1 by means of the supporting members 23 and 24, respectively.
Moreover, the
supporting members 23 and 24, respectively, are rotatable around their
longitudinal
axes such that the substrates S2 and S1, respectively, can be rotated into an
optimal
position both during the pre-treatment as well as during the coating operation
in order to
realize an even pre-treatment and coating, respectively.
Between the central treatment chamber 1 and the first pre-treatment chamber 2,
a first slide member 27 is provided, and between the central treatment chamber
1 and
the second pre-treatment chamber 3, a second slide member 37 is provided.
Thus, the
central treatment chamber 1 can be tightly closed with regard to the first and
second
pre-treatment chambers 2 and 3. The first and second slide members 27 and 37,
re-
spectively, are of essential circular shape and are received in first and
second guide
members 28 and 38, respectively.
As can be seen from Figs. 1 and 2, the first slide member 27 is in its closed
posi-
tion such that the central treatment chamber 1 is separated from the first pre-
treatment
chamber 2. In order to avoid an exchange of gas between the first pre-
treatment cham-
ber 2 and the central treatment chamber 1, as well as between the first and
second pre-
treatment chambers 2 and 3, respectively, and the ambient atmosphere, the
first and
second guide members 28 and 38, respectively, are provided with sealing
members 29
and 39, respectively. It is understood that also the first and second covers 4
and 5, re-
spectively, are provided with sealing members; however, for the sake of
clarity, that
sealing members are not shown in the drawings.
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In order to evacuate the central treatment chamber 1 as well as the first and
sec-
and pre-treatment chambers 2 and 3, there is provided an evacuation apparatus
that is,
again for the sake of clarity, not shown in the drawings as well. Moreover,
such evacua-
tion apparatuses being well known to every person skilled in the art removes
the need
to further discuss them here.
In the following, the method of the invention as well as the mode of operation
of
the apparatus will be further explained with reference to Figs. 1-5.
Fig. 1 shows a first phase of operation; thereby, the second slide member 37
lo-
Gated between the central treatment chamber 1 and the second pre-treatment
chamber
3 is in its open position, while the first slide member 27 located between the
central
treatment chamber 1 and the first pre-treatment chamber 2 is in its closed
position. By
this measure, both in the central treatment chamber 1 and in the first pre-
treatment
chamber 2, in each case a gaseous atmosphere can be created that is best
suited to
the particular operation to be performed; thus, a mutual influencing of or an
interference
between the different operations, - coating the substrate S1 in the central
treatment
chamber 1 and pre-treating the substrate S2 in the first pre-treatment chamber
2 -, can
be avoided. Anyway, in the present example, both in the central treatment
chamber 1
and in the first pre-treatment chamber 2, a subatmospheric pressure in the
order of
appr. 10 to 50 mbar is maintained.
The first substrate S1 clamped to the second supporting member 33 is coated by
means of the plasma spraying apparatus 10 located in the central treatment
chamber 1.
The coating jet escaping from the plasma spraying apparatus 10 is designated
by refer-
ence numeral 12. Simultaneously, as the substrate S1 is coated, the second
substrate
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S2 is pre-treated by means of the plasmatron 20 located in the first pre-
treatment
chamber 2. The expression "pre-treating" shall be understood, in the present
case, as
an operation comprising cleaning and heating the substrate S2. In Fig. 1, the
heating
operation is shown; this is accomplished by means of a plasma torch 25
generated by
the plasmatron 20; in Fig. 2, the cleaning operation is illustrated; this is
realized by gen-
erating an electric arc 25A between the plasmatron 20 and the substrate S2.
Due to the
fact that the substrate S2 is connected as the cathode, and further by the
presence of
the electric arc 25A, a flow of electrons takes place from the substrate S2 to
the plas-
matron 20, with the result that the surface of the substrate S2 is freed from
contamina-
tion and oxides. That operation is well known to the person skilled in the art
under the
expression "sputtering". In certain cases, it may be advantageous that the
substrate S2
alternately is cleaned and heated. It is understood that the first substrate
S1 has under-
gone a cleaning and heating process as well in a mode as explained herein
before prior
to being coated.
Once the first substrate S1 has been coated and the second substrate S2 has
been cleaned and heated, the second supporting member 33 is moved to the
right. As
soon as the first substrate is in the interior of the second pre-treatment
chamber 3, the
second slide member 37 is moved from its open to its closed position (cf. Fig.
3) and,
thereafter, the first slide member 27 is moved from its closed to its open
position. In or-
der to enable the second cover 5 of the second pre-treatment chamber 3 to be
removed
and the finally coated substrate S1 to be removed from the second pre-
treatment
chamber 3, the second pre-treatment chamber 3 is vented until its pressure
corre-
sponds to ambient atmospheric pressure. After the second cover 5 has been
removed,
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the second supporting member 33 is further moved to the right to such an
extent that
the finished substrate S1 can be removed from the second clamping member 34
and
replaced by another one (cf. Fig. 4). Simultaneously, the second substrate S2
now can
be displaced from the first pre-treatment chamber 2 into the central treatment
chamber
1. Once the second supporting member 33, together with the new substrate, has
been
moved into the second pretreatment chamber 3, the second cover 5 is axed to
seal the
second pre-treating chamber 3 and the latter one can be evacuated again.
Thereafter, the second substrate S2 now located in the central treatment cham-
ber 1 can be coated by means of the plasma spraying apparatus 10, while the
further
substrate S3 is cleaned and heated by means of the plasmatron 30 located in
the sec-
and pre-treatment chamber 3 in a kind as has been explained herein before.
Due to the fact that not only the first and second pre-treatment chambers 2
and
3, respectively, but also the central treatment chamber 1 can be evacuated, a
particular
substrate can be transported, after having been pre-treated, from the
particular pre-
treatment chamber 2 and 3, respectively, into the central treatment chamber 1
without
the danger that the cleaned surface of the substrate is oxidizing again.
It is understood that the example described herein before represents only one
of
the possible variants of the method of the invention and of the apparatus of
the inven-
tion, respectively. Particularly, within the scope of the appended claims,
modified meth-
ods and apparatuses could be used as well. For example, instead of providing
two pre-
treatment chambers, onle one thereof or even three or more of them could be
provided.
Similarly, also the design and the arrangement of the supporting members could
be
constructed in a different manner.
