Electric heating – Metal heating – By arc
Reexamination Certificate
2002-07-17
2003-12-02
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S076160, C219S121520, C427S099300
Reexamination Certificate
active
06657152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a torch head for plasma spraying and, more particularly, to a torch head which is inserted into a tube member having a very small diameter to form a film by complete spraying on the inner surface of the tube member.
2. Prior Art
As torch heads for forming coatings by plasma splaying on inner surfaces of tube members, various torch heads have been proposed already. For example, in U.S. Pat. No. 4,877,937, a “plasma spray torch” as shown in
FIG. 4
is proposed. This spray torch, according to the brief of the above publication, is described as follows
“a plasma spray torch comprises a spray nozzle which forms an electrode and which includes a nozzle duct, and a second electrode associated therewith, in a portion of a torch arm, which is electrically insulated from the spray nozzle. The torch arm has flow passages for working gas and for a cooling agent, the latter flowing in one of the flow ducts to the nozzle and being removed after producing its cooling effect from another flow duct. A powder feed conduit opens into the nozzle duct. The working gas flow duct is connected to a duct which passes through the second electrode while at least in the region of its mouth opening, the nozzle duct is inclined relative to the longitudinal axis of the torch arm or the flow duct therein. In a method of internally coating a tube by plasma spraying, the torch is introduced into the tube which is then rotated and moved axially relative to the torch during the spray operation”.
In a conventional torch head as shown in
FIG. 4
, since working gas (changed into a plasma by a discharge arc and heated to such a temperature that a powder can be melted) passage must be formed in a cathode, a cooling agent for cooling the cathode side cannot be formed in the cathode.
In the conventional torch head shown in
FIG. 4
, since the nozzle duct is inclined relative to the longitudinal axis of a flow duct, melted spraying material cannot perpendicularly collide with the inner wall surface of a tube material. For this reason, the spraying material is partially scattered without forming a coating, and it is considered that an excess of material must be used to form a satisfactory coating.
For this reason, for example, a “plasma spray gun” is proposed in Japanese Patent Publication No. 3-57833. This spray gun, according to FIG.
5
and “Claims” in the above publication,
“is a plasma spray gun which is inserted into a pipe or an object to be processed and which includes a cooled electrode
10
and a burner nozzle
12
for coating the inner surface of the object to be processed, and is characterized in that 10 kw can be obtained at the most.”
A satisfactory coating cannot be obtained when a plasma energy is small for the following reason. Since a spraying material is supplied into plasma working gas together with gas, the spraying material is a powder having an average grain diameter of 5 to 45 &mgr;m to make it easy to supply the spraying material. When the spraying material has a grain diameter of 5 &mgr;m or smaller, not only is the spraying material very expensive, but the spraying material may also combine with oxygen and nitrogen in the air and thus fail to form an expected coating. When the spraying material has a grain diameter of 45 &mgr;m or more, the spraying material is not sufficiently melted by the plasma working gas. When the spraying material comprises the powder is to be melted, and an arc is small and short, the working gas is not sufficiently changed into a plasma and a high temperature is not achieved, and the spraying material is not sufficiently melted. In addition, since the injection speed of the working gas cannot be considerably high, the kinetic energy of the spraying material must be small, and a collision energy sufficient to form a coating cannot be obtained.
For this reason, the present inventor investigated a torch head shown in
FIG. 6
or
7
. In the torch head shown in
FIG. 6
, a plasma generation chamber is perpendicular to the longitudinal axis of the torch body, and a cathode is coaxially arranged in the plasma generation chamber. Although a high-energy plasma can be generated, it is difficult to set the diameter of the entire torch head such that the torch head can be inserted into a tube member having an inner diameter of about 50 mm. This is because, when the torch head is to be reduced in size, the distance between the cathode and the anode member must be reduced, and a high voltage cannot be applied across these electrodes. In addition, the cooling passage is limited, and a high-energy plasma cannot be generated.
On the other hand, in the torch head shown in
FIG. 7
, a cathode is coaxially arranged in a torch body, and the distance between the cathode and the anode member can be increased such that a high-energy plasma can be generated. However, since the passage of a plasma gas is bent at an angle of 90°, the anode member is considerably worn. This is because, a high-temperature working gas changed into a plasma by an arc generated between the cathode and the anode member collides with the wall of the passage which is formed in the anode member and which is bent at an angle of 90° to heat the wall portion and to wear the wall portion within a short period of time.
In addition, the present inventor devised a torch head shown in
FIGS. 8 and 9
to improve the above torch head. The torch head shown in
FIGS. 8 and 9
has a plasma gas supply chamber located in an anode member along the longitudinal axis of the anode member. A cathode is coaxially arranged in the plasma gas supply chamber, and a mouth opening to be perpendicular to the longitudinal axis of the plasma gas supply chamber is formed on the side surface of the anode member. In this manner, it is considered that an arc toward the mouth opening is generated. In fact, at the beginning of the use of the torch head, “distorted arcs” indicated by reference numerals
21
in
FIGS. 8 and 9
are generated, and it is understood that the anode member is quickly worn by the distorted arcs.
Therefore, the present inventor evaluated various torch heads configurations of this type in order to:
1) spray a plasma gas into a narrow tube member (diameter of 30 mm to 300 mm),
2) use a powder having an average grain diameter of 5 to 45 m as a spraying material,
3) increase the plasma energy to about 30 kw to 45 kw, and
4) suppress distorted arcs from being generated to elongate the lifetime of a positive electrode (anode).
SUMMARY OF THE INVENTION
The present invention has been made on the basis of the above circumstances. It is an object of the present invention to provide a coating that can be satisfactorily formed in plasma spraying in a narrow tube member to make it possible to elongate the lifetimes of electrodes.
In order to achieve this objective as a means which passes through the orifice
16
at a high speed. Since the plasma generation chamber
17
located at the position of the outlet of the orifice
16
is bent at an angle of 90° with respect to the longitudinal axis of the cathode
12
, the working gas generates a small turbulent flow and has not been sufficiently thinned at this point. The working gas is gradually thinned while forming a stationary flow between the inner bottom of the plasma generation chamber
17
and the mouth opening
18
. This thinning is maximum in the plasma generation chamber
17
located immediately near the mouth opening
18
. This is because the region outside of the mouth opening
18
has the atmospheric pressure, and the atmospheric pressure is remarkably lower than the pressure in the plasma gas supply chamber
15
.
The working gas in the plasma generation chamber
17
which is immediately near the mouth opening
18
is thinned because the orifice
16
exists. In the orifice
16
, the opening area is set to be ⅓ to {fraction (1/10)} the opening area of the mouth opening
18
. This is because when the opening area of the orifice
16
is larger than ⅓ of the opening area of the mouth openin
Cohen Jerry
Paschall Mark
Perkins Smith & Cohen LLP
Shimazu Kogyo Yugengaisha
LandOfFree
Torch head for plasma spraying does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Torch head for plasma spraying, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Torch head for plasma spraying will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3135126