Note: Descriptions are shown in the official language in which they were submitted.
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PLASMA SPRAYING APPARATUS
Background of the Invention
The present invention refers to a plasma spraying apparatus,
comprising a plasma torch head, an outlet nozzle having a central
longitudinal axis that is provided in the plasma torch head and
serves as an anode, and a coating powder feeding channel provided
in the plasma torch head and running substantially perpendicular
to the central longitudinal axis of the outlet nozzle.
Under the expression "plasma spraying apparatus", a coating
apparatus shall be understood, both generally an in the present
case, that is provided with a so-called plasmatron, whereby the
coating material is fed to the plasma jet in the form of powder.
That coating powder is molten in the plasma jet and applied to the
substrate as a homogenous layer.
Prior Art
In nearly all plasma spraying apparatuses used nowadays, the
coating powder is fed to the plasma jet laterally, i.e. in radial
direction. Examinations of substrates that have been coated using
such plasma spraying apparatuses have shown that inhomogenous por-
tions in the form of inclusions can occur from time to time in the
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applied coating layer. The reason for the occurrence of such in-
clusion most probably lies in the fact that coating powder parti-
cles adhere to the outlet nozzle, serving as an anode, of the
plasma torch head, whereby such powder agglomerates are entrained
by the plasma jet from time to time. The powder agglomerates en-
trained by the plasma jet usually are heavily oxidized and con-
taminated, respectively, with the result that they impair the
quality of the applied coating.
It is supposed that particularly aerodynamic conditions are
responsible for the occurrence of such powder particle agglomer-
ates.
Obiects of the Invention
Thus, it is an object of the invention to provide a plasma
spraying apparatus having a plasma torch head by means of which
coatings can be applied that show an improved quality. Particu-
larly, it is an object of the invention to provide a plasma spray-
ing apparatus having a plasma torch head in which the occurrence
of such agglomerates of coating powder particles in the applied
coating is avoided.
Summary of the Invention
In order to meet these and other objects, the present inven-
tion provides a plasma spraying apparatus, comprising a plasma
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torch head, an outlet nozzle provided in plasma the torch head and
adapted to serve as an anode, and a coating powder feeding channel
provided in the plasma torch head that runs substantially perpen-
dicular to a central longitudinal axis of the outlet nozzle.
The plasma torch head is provided with at least one gas outlet
aperture adapted to feed a gaseous medium to the outlet nozzle
such that an accumulation of coating powder particles in the re-
gion of the outlet nozzle is substantially avoided.
In a preferred embodiment, the plasma torch head comprises a
supporting member defining a cavity that is located between the
gas outlet aperture and the coating powder feeding channel,
whereby the gaseous medium is fed into that cavity.
In this way, the afore mentioned problems can be solved and
the occurrence of accumulations of coating powder particles in the
region between the coating powder channel and the outlet nozzle
can be avoided.
Brief Description of the Drawings
In the following, an embodiment of the apparatus according to
the invention will be further described, with reference to the ac-
companying drawings, in which:
Fig. 1 shows a schematic side view of a conventional plasma
torch head;
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Fig. 2 shows a schematic side view of a plasma torch head ac-
cording to the invention;
Fig. 3 shows a top view of the plasma torch head of Fig. 2;
Fig. 4 shows a front view of the plasma torch head of Fig. 2;
Fig. 5 shows a top view of the anode base body member of the
plasma torch head of Fig. 2; and
Fig. 6 shows a longitudinal sectional view of the anode base
body member of the plasma torch head of Fig. 2.
Detailed Description of a Preferred Embodiment
Fig. 1 shows a schematic side view of a conventional plasma
torch head 1. As can be seen from this drawing, the plasma torch
head 1 comprises an anode base body member 2, a cathode base body
member 4 as well as an insulating body member 3 inserted between
the anode base body member 2 and the cathode base body member 4
and electrically insulating the anode base body member 2 from the
cathode base body member 4.
The anode base body member 2 is provided with an anode nozzle
6, and the cathode base body member 4 is provided with a cathode
member 7. The plasma torch head 1 has a longitudinal central axis
L-1, and it can be seen from Fig. 1 that the afore mentioned anode
nozzle 6 as well as the afore mentioned cathode member 7 are lo-
Gated along an axis L-2 running perpendicular to the central lon-
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gitudinal axis L-1 of the plasma torch head 1. Thus, a plasma jet
created by the plasma torch head 1 escapes laterally out of the
plasma torch head 1, in the direction of the axis L-2.
Both the anode base member 2 and the cathode base member 4 are
manufactured of a material having a good electrical conductivity,
for example of brass. Thereby, the anode nozzle 6 is electrically
connected to the anode base member 2, and the cathode member 7 is
electrically connected to the cathode base member 4. The supply of
the coating powder is accomplished by means of a tube member 9
that is provided at the outside of the plasma torch head 1. Since
this tube member 9 runs perpendicular to the afore mentioned lon-
gitudinal axis L-2, the coating material is fed to the plasma jet
10 in a substantially radial direction. The plasma torch head 1 is
of very compact design. Thus a plasma spraying apparatus incorpo-
rating such a plasma torch head 1 is particularly suitable for
coating the inner walls of tubes and pipes.
It is understood that the plasma torch head 1 further com-
prises a number of channels provided for feeding cooling media and
other media required for the operation thereof. However, since
these channels are not relevant in connection with the present in-
vention, they are not shown in the drawings.
Fig. 2 shows a schematic side view of the plasma torch head 1
according to the invention, while Fig. 3 shows a top view of the
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plasma torch head 1 of Fig. 2 and Fig. 4 shows a front view of the
plasma torch head 1 of Fig. 2. In the following, the design of the
plasma torch head 1 will be further explained, whereby the same
parts and elements are designated with the same reference numerals
as in Fig. 1.
The plasma torch head 1 according to the invention is provided
with a gas supply channel 12 (Fig. 2) that is located in the inte-
rior of the anode base body member 2. Moreover, the anode base
body member 2 is provided with a recess 13 having essentially
conical shape. The gas supply channel 12 has an outlet aperture
12a opening into that recess 13. The tube member 9 provided for
supplying coating material is fixed to a supporting member 14 hav-
ing a cavity 15 extending between the recess 13 and the coating
powder supply tube member 9. This cavity 15 can be flooded with a
gas 16 supplied via the channel 12, as it is symbolized in Fig. 2.
The gas 16 escapes from the cavity 15 at the side that is directed
towards the plasma jet 10. In this way, it is avoided that an ac-
cumulation of coating powder can occur in the aerodynamically
critical region between the outlet edge of the anode nozzle 6 and
the mouth of the powder supply tube member 9.
Fig. 5 shows a top view of the anode base body member 2 and
Fig. 6 shows a longitudinal sectional view of the anode base body
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member 2. From these two figures, particularly the design of the
anode nozzle 6 and the shape of the recess 13 can be seen.
According to the desired effect and depending on the kind of
the coating powder, both a reactive or an inert gas can be fed via
the channel 12. In most cases, it is sufficient to feed the gas
through the channel 12 in a rate of 10 to 20 liters per minute.
