Mixed powder thermal spraying method

Details Mixed powder thermal spraying method Mixed powder thermal spraying method

2001-06-19

2003-04-08

Bareford, Katherine A. (Department: 1762)

Coating processes

Spray coating utilizing flame or plasma heat

Silicon containing coating

C427S446000, C427S455000, C427S456000

Reexamination Certificate

active

06544597

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to Japanese Patent Application No. 2000-185541 filed Jun. 21, 2000, the disclosure of which is incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a mixed powder thermal spraying method, specifically to a mixed powder thermal spraying method in which a plasma jet is bent to carry out thermal spraying.
Techniques such as thermal spraying are widely used for sliding parts of cars as a method for providing sliding faces thereof with an abrasion resistance, and materials used for thermal spraying range over various fields from single materials to mixed (or combined) materials according to uses. Among them, a plasma thermal spraying gun for a bore is used when carrying out bore plasma thermal spraying as is the case with a bore internal surface for a cylinder block, and a structure of the plasma thermal spraying gun includes a system in which a plasma jet generated between an anode and a cathode is bent to an extension direction of the gun and thermally sprayed (
FIG. 11
) and a system in which a plasma jet is generated vertically to an extension direction of the gun according to arrangement of an anode and a cathode (FIG.
12
).
An internal feeding method (a method in which powder is fed in the inside of a thermal spraying electrode) in which as shown in
FIG. 11
, powder
108
fed from a powder-feeding tube
106
passes through a powder-feeding passage
107
(pore) disposed in a copper alloy-made anode
102
and is fed to a plasma jet
104
from a feeding port
107
a
has so far been carried out as a method for feeding a powder material to a thermal spraying gun
101
having a system of bending a plasma jet.
When feeding a powder material by the system of
FIG. 11
, particles molten by the plasma jet
104
pass through the anode in the form of a thermal spraying flame
105
, so that the molten particles
109
adhere to the inside of the anode (particularly the vicinity of a plasma jet injection port) in passing. If continuing thermal spraying as it is, adhesion of the molten particles
109
is expanded and comes to fill up the feeding port
107
a,
and the problem of clogging with the powder is brought about. Further, thermal spraying over a long period of time causes abrasion and deformation
107
b
of the powder-feeding passage
107
by virtue of flow of the powder. This causes turbulent flow in the powder-feeding passage
107
to reduce an injection speed of the powder, and therefore brought about is the problem that the molten particles
109
are liable to further adhere to the anode.
Accordingly, in such thermal spraying method, a frequency of maintenance of the thermal spraying gun against adhesion and clogging of the molten particles grows large, and the productivity is deteriorated. Further, when abrasion of the powder-feeding passage
107
is accelerated, the anode
102
has to be exchanged even if the anode
102
does not reach an intrinsic life. The anode
102
has a special shape and therefore is expensive, which has led to an increase in the product cost.
On the other hand, an external feeding method (a method in which powder is fed in the outside of the thermal spraying electrode) in which as shown in
FIG. 12
, powder
108
is fed to a resulting plasma jet
124
from a powder-feeding port
126
a
which is an outlet of a powder-feeding tube
126
has so far been carried out as a method for feeding a powder material to a thermal spraying gun
121
having a system in which a plasma jet is generated vertically to an extension direction of the gun.
In the system shown in
FIG. 12
, not only the thermal spraying distance is short as compared with the system shown in
FIG. 11
, but also the plasma output has had to be suppressed so that a heat effect is not exerted on an article to be processed. Accordingly, the plasma has a low output, and a very fine powder material has to be used in order to sufficiently melt and accelerate the powder material at a short thermal spraying distance, so that there have been the problems that the powder is increased in a cost and it is difficult to manage the powder. Further, the finer the powder is, the more the fluidity thereof is deteriorated, and therefore it is concerned that it becomes difficult to stably feed the powder.
In addition thereto, two kinds of the bore thermal spraying guns described above each have one powder-feeding port, and particularly when preparing a mixed thermal spraying film comprising two or more kinds of components, there has so far been employed, (1) a method in which plural powders to be used are mixed in advance and fed or (2) a method in which plural powders to be used are alloyed or combined (combination by mechanical alloy) in advance and fed.
In the method (1), it is difficult to continue feeding the mixed powders in an always fixed proportion. Further, there have been the problems that among the mixed powders, the powder having a lower melting point is molten before coming out from the powder-feeding port and liable to cause clogging and that if the plasma output is reduced in order to avoid it, the powder having a higher melting point is not sufficiently molten to reduce a quality of the thermal spraying film.
Further, in the method (2), there have so far been the problems that not only the powder cost is elevated but also alloying or combining is difficult because of the nature of the components of the material.
SUMMARY OF THE INVENTION
The present invention has been made in light of such existing situations, and an object thereof is to provide a mixed powder thermal spraying method in which an anode having a high durability and a low price can be used and a thermal spraying powder is easily managed and in which a thermal spraying film having a high quality is obtained.
In accordance with the present invention, there is provided a mixed powder thermal spraying method in which: a plasma jet is bent to carry out thermal spraying; in forming a mixed thermal spraying film comprising two kinds of materials having different melting points by bore thermal spraying, powder-feeding ports are provided for each material; and each powder-feeding port is controlled respectively to externally feed each material.
According to the method, the fed powder and the particles molten by a plasma jet do not pass through the inside of the anode, and therefore solved are the problems of adhesion of the molten particles to the anode, clogging of the fed powder caused by it and abrasion of a powder-feeding passage in the anode which have so far been brought about in conventional techniques. Accordingly, maintenance of the anode can be freed, and a life of the anode is extended. Further, the structure of the anode is simplified, so that the anode is decreased in a cost. Thus, the thermal spraying method which is excellent in a mass productivity and a maintenance can be provided at a low cost.
Further, the powder-feeding tube is a separate member, so that the feeding conditions are separately controlled in such a manner that the position of the feeding port can freely be set up, whereby the feeding conditions suited to the respective materials can be set up. A mixed proportion in the thermal spraying film can always constantly be maintained, and therefore a quality of the thermal spraying film is stabilized and elevated. Further, even if the powder-feeding tube is clogged, only the feeding tube can readily be exchanged.
To perform the mixed powder thermal spraying method in accordance with the present invention, it is advantageous to feed externally a material having a higher melting point from a thermal spraying flame high temperature part side and to feed externally a material having a lower melting point from a thermal spraying flame low temperature part side.
The plasma jet generated between the anode and the cathode in plasma thermal spraying stays in a very high temperature area. The powder is molten by the plasma jet, and the molten particles thereof form a thermal spraying flame. In

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