JPS58124568A - Plasma spray method - Google Patents

Abstract

PURPOSE:To contrive to improve the efficiencies of spraying and working and the quality of a spray coating film, in the formation of a coating film layer by a spray method, by using plasma arc reformed by the action of electromagnetic force. CONSTITUTION:By using plasma arc reformed into a configuration widen toward the surface 8 of a workpiece to be spray-coated from the opening of a nozzle, a coating layer having large width is formed by only one spray even when the powder of a spray material is ejected from the nozzle with a substantially large angle. In order to obtain the plasma arc having said configuration, annular coils 14, 15 are arranged approximately symmetrically with respect to the workpiece 9 to be spray-coated, and exciting currents each flowing to the opposite direction are applied to the coils, so that a cusped magnetic field directing outwards is formed in the space of the plasma arc above the workpiece 9 to be spray-coated. Since the charged particles in the plasma arc have the feature difficult to move across the line of magnetic force, coned plasma arc being widened toward the periphery similar to the configuration of the line of magnetic force is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma spraying method for spray coating or spray forming using plasma.

1. Materials such as metals, alloys, metal compounds, ceramics, and cermets. A surface modification method in which a material is heated to a melted or nearly melted state and bombarded with particulates against the material surface to form a new coating layer on the material surface is called a thermal spray coating method.

Further, a method of forming a thermal spray coating layer on a mold surface that has been previously processed into a predetermined shape and then removing the mold material to obtain a desired shape is called a thermal spray molding method. These thermal spray coating methods and thermal spray molding methods are often collectively referred to simply as thermal spraying. The coating layer formed by thermal spraying provides insulation and heat resistance to the material in a small amount.

Furthermore, it is possible to impart various properties not found in other materials, such as low friction characteristics, wear resistance, and corrosion resistance, so it has become one of the basic industrial technologies that is needed in a wide range of fields.

Thermal spraying methods include gas spraying, arc spraying, wire blast spraying,
There are plasma spraying methods, among others, the plasma spraying method has a high energy density obtained by the plasma generator, can spray even difficult-to-melt materials, has high work efficiency, and the sprayed material collides with the material surface at a high speed. Therefore, it has been making great progress in recent years because of its characteristics such as adhesion and the ability to obtain a coating layer of good quality.

By the way, although the performance of the coating layer has been improved with the advent of plasma spraying, conventional thermal spraying generally has low spray processing speed, high porosity of the sprayed coating layer, and problems with the sprayed coating and the sprayed coating. It has problems such as poor adhesion to the material and easy peeling.

The present invention aims to improve thermal spraying efficiency and work efficiency in thermal spraying,
This is to measure the improvement of thermal/sprayed coating properties.

Next, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows the principle of conventional plasma spraying.

A power supply l is connected to the cathode 2 and the anode nozzle 3 having the cooling water passage 4.
is connected, a DC arc 5 is generated during this time, and the rear Fl
Working gas fed from the direction shown is heated by an arc and ejected from the nozzle 3 as an ultra-high temperature plasma jet 6. Thermal spray material is usually powdered and blown into the nozzle from the direction indicated by F2, heated and accelerated by the plasma jet, and becomes a molten or semi-molten powder 7 that collides with the surface of the material 9, forming a coating 8. Form. Argon or nitrogen is generally used as the working gas, but hydrogen, helium, or other gases may also be used. In the method shown in FIG. 1, most of the input power is generated within the nozzle, so the high temperature region of the plasma jet is narrow.

Energy utilization efficiency is low because heat exchange between the thermal spray powder material and the plasma jet is not sufficient.

FIG. 2 is a diagram showing the principle of plasma arc thermal spraying, which is currently being used in some areas to increase energy efficiency and improve adhesion. In the plasma jet spraying method shown in Figure 1, most of the power is consumed inside the nozzle, whereas in the plasma arc spraying method shown in Figure 2, a large proportion of the power is consumed by the plasma arc drawn outside the plasma torch. Consumed in lO. For this purpose, the cathode 2 and the material to be sprayed 9
An electric circuit is also formed between them. Figure 2 shows cathode 2
An example is shown in which the power supplies 1 and 11 are connected between the cathode 2 and the nozzle 3, and between the nozzle 3 and the material 9 to be sprayed, respectively. You can create an electric circuit just between them. Other polarity combinations than those shown are also available. By drawing out the plasma arc to the outside of the nozzle, the contact time between the plasma gas and the sprayed material 7 is increased, increasing heating efficiency, and the material to be sprayed is also heated, improving the adhesion between the sprayed coating and the material surface. It has been recognized that there are benefits such as:

In the case of either plasma jet spraying or plasma arc spraying, the width of the coating obtained by - times of spraying is 15
It's about 25 cods, which isn't that big.

This is the biggest reason why the processing area speed cannot be increased. Additionally, there is a considerable amount of thermal spray powder material that is delivered toward the plasma gas and is not heated sufficiently because it spreads over an area larger than the plasma jet or plasma arc diameter. This is the cause of lowering the yield of thermal spray material.

FIG. 3(a) shows the principle of the thermal spraying method of the present invention. The present invention is characterized by the use of a plasma arc 10 that is deformed into a shape that diverges from the nozzle exit toward the surface of the material to be thermally sprayed by the action of electromagnetic force. By using such a divergent plasma arc, even if the spray material powder is ejected from the nozzle at a considerably large angle, it can fly without coming off the plasma arc, and as a result, a wide coating layer can be produced with one spray. This results in a significant improvement in the yield of thermal spray material and the speed of thermal spray processing.

There are various methods that can be used to make the plasma arc divergent, based on the electromagnetic knowledge currently available.
An example thereof is shown in FIG. 3(b). When circular coils 14 and 15 are arranged almost symmetrically across the material 9 to be thermally sprayed, and excitation currents directed in opposite directions are passed through each coil, lines of magnetic force as shown by 16 pointing outward on the surface of the material 9 are formed. A so-called cusp-shaped distributed magnetic field is created in the plasma arc space. Since the charged particles in the plasma arc have a property of being difficult to move across the lines of magnetic force, the shape of the plasma arc is close to the shape of the lines of magnetic force. In other words, a cone plasma arc that spreads toward the end is formed. This is an example of a method for spreading a plasma arc two-dimensionally symmetrically around the arc axis, but depending on how the magnetic field is created, it is also possible to create a fan-shaped plasma arc that spreads flatly in one dimension. For example, Arata, Maruo: Technology Report
so the 08AKA UniversityV
ol, 22. Zui 1039 (1972) p 13
Cusp magnetic fields such as those shown in Figures 5-153 can be used.

Although the advantage of using a diverging plasma arc created by a steady cusp magnetic field is significant, it has the problem that it is difficult to deform the plasma arc without the application of a fairly strong magnetic field. FIG. 4 shows a method of the present invention devised to address this drawback. This method is characterized in that an alternating magnetic field is applied to the plasma arc to cause the plasma arc to undergo reciprocating vibrational motion in synchronization with an alternating frequency, and this plasma arc is used as a heat source for heating the thermal spray material powder. In FIG. 4, it is assumed that the plasma arc is carrying a current from the material 9 to be sprayed toward the internal cathode 2 of the spraying torch 30, and when a magnetic field that is perpendicular to the plane of the paper and directed from the back to the front of the paper is applied to this current,
Since the plasma arc is subjected to a force represented by the vector product of current and magnetic field strength, the plasma arc takes on a curved shape as shown, for example, by l○. If the magnetic field is an alternating magnetic field, the direction of the electromagnetic force acting on the plasma arc will reverse every half cycle, so the plasma arc will eventually
It will make a reciprocating oscillating motion between the distances shown in '. If the frequency of the alternating magnetic field is increased to a certain extent, it will actually be 10
A fan-shaped plasma arc that spreads toward the end with both ends at and l O' is obtained. Various methods are possible for generating a magnetic field to make the plasma arc vibrate with electromagnetic force. The method described in ``Magnetic field generation method for magnetic field generation method'' can be used. Furthermore, in order to obtain a plasma arc that oscillates with a two-dimensional spread,
1 "Method for magnetically driving plasma arc" can be used.

The advantage of deforming the plasma arc by the action of electromagnetic force is that the shape of the arc can be precisely controlled by changing the magnetic field distribution. For example, even when creating a substantially wide plasma arc by applying an alternating magnetic field to the plasma arc and causing it to vibrate at high speed, the plane of vibration can be changed by changing the direction of the magnetic field vector, and by changing the magnetic field strength. You can change the width. Furthermore, by appropriately selecting the alternating magnetic field waveform, it is possible to shape the heat distribution into a desired shape. By superimposing a direct current component on the alternating magnetic field, it is also possible to create an asymmetrical shape that is biased to one side. As shown in the figure, the material to be thermally sprayed A
Assuming that there is a BOD, consider a model in which the material is moved in the direction shown by F5 relative to the plasma spraying torch 30 to create a sprayed layer gradually from side AB to side CD. Here, the description will proceed assuming that the direction parallel to side AC or BO is the X direction, the direction parallel to side AB or CD is the y direction, and the direction perpendicular to ABOD is the second direction. FIG. 6 shows several modes of the plasma arc deformed by the action of electromagnetic forces. Although it is in oscillatory motion, it is so fast that it can essentially be regarded as a spread plasma arc.
It is treated without making any particular distinction from a plasma arc that is constantly expanding. Figures (a) (b) (c)
(d) is the mode projected onto the x-z plane, and (e)
, (f), (ω and (h) are the modes projected onto the 7-2 plane.The actual modes are (a) to (d)
It is a combination of any one of (e) to (h). We will take up some typical combinations and explain in some detail the advantages of each combination. The combination of (a) and (e) is a thermal spraying method in which no modification is made to the conventional plasma arc. (b) and (
Combination e) is one in which the plasma arc is spread one-dimensionally in a plane perpendicular to the direction of thermal spraying progress, which reduces the proportion of the thermal spray powder that flies out of the plasma arc without being heated and increases the yield. The width that can be sprayed while traveling is large, increasing work efficiency. In the combination of (C) and (,), the spread of the plasma arc in the X direction is made asymmetrical, and the plasma arc is provided in the direction where the thermal spraying has already been completed. The main aim of this combination is to reheat already formed sprayed coating layers. In recent years, self-fusing alloy thermal spraying materials have been developed, which are used by impregnating a fluxing agent in the thermal spraying material and heating and melting it after spraying, in order to more completely bond the substrate and thermal spray coating layer and to create a porosity-free homogeneous alloy coating. It has become commonly used. In this case, basically, after thermal spraying is completed, the coating layer must be reheated using an appropriate heat source to melt the coating layer. However, according to the method of the present invention, the plasma arc that spreads over the area that has already been thermally sprayed becomes the heat source for reheating and melting, so the heating and melting process proceeds at the same time as thermal spraying, making it possible to significantly simplify one process. . A similar effect can also be achieved by a combination of (a) and ()1).

Next, the combination of (a) and (g) spreads the plasma arc in the spraying progress direction and biases the spread toward the front of the spraying.

Such a plasma arc deformation makes it possible to perform thermal spraying without heating the material surface immediately before thermal spraying. Since the sprayed material collides with the heated material surface, the bonding force between the material and the sprayed coating layer increases.

As is clear from the explanation of the several examples above, the yield of thermal sprayed material is improved by the method of deformation, the work efficiency is improved by expanding the thermal spraying width,
It is possible to improve coating performance by pre-heating the thermal spray material and post-heating the thermal spray coating, and to omit post-treatment steps. Many combinations other than those described above are possible, but what kind of effects can be expected from each combination can be easily inferred from the examples described above.

FIG. 7 is for explaining a method of using a plasma arc curved in one direction in order to more effectively perform the above-mentioned pre-heating or post-heating.

Three typical shapes of the plasma arc projected on the XZ plane when the coordinate system is adopted for the model in Figure 5 are (a),
Shown in (b) and (C). (a) is a case where the curve is not curved on the X2 plane, (b) is a curve in the direction where thermal spraying has already been completed, and (C) is a curve in the direction where thermal spraying has not yet been performed. On the other hand, (a), (e),
(f) similarly shows three mortar-like shapes of the plasma arc projected onto the yz plane. The plasma arc shown in the combination of projections (a) and (d) is that used in conventional thermal spraying without deformation. (a), (
In the combination e), the plasma arc is curved forward in the spraying direction, and when spraying is performed using this plasma arc, the spraying material powder flies inside the nozzle and within the plasma arc for a certain period of time after leaving the nozzle. During this time, it is heated and becomes molten or semi-molten, after which it exits the plasma arc region and collides with the surface of the material, forming a thermally sprayed coating. On the other hand, since the plasma arc is bent in the spraying direction, a portion of the energy input to the plasma arc is effectively used for preheating the spraying material. It is also possible to melt the surface layer of the material to be thermally sprayed into a very thin layer and allow all of the thermal spraying material to collide with it, thereby making it possible to obtain a coating with strong bonding strength. In thermal spraying using a plasma arc using a combination of (b) and (d), since the plasma arc is bent over the area where the spraying has already been completed (2), most of the input power is used for post-heating and melting of the sprayed coating. Can be used effectively. Extremely effective (= can be used) as a plasma arc for simultaneous thermal spraying of self-fusing alloys and post-remelting treatment. The same post-heating is possible with the combination of (a) and (, f). is clear.

Various combinations other than those described above are possible, and the effects of each combination can be easily inferred from the above explanation. In order to bend the plasma arc in one direction, in the method for vibrating the plasma arc described above, it is sufficient to make the external magnetic field acting on the plasma arc a constant magnetic field instead of an alternating magnetic field, and by changing the magnetic field strength. The degree of curvature can be controlled.

Next, an example will be described. Table 1 summarizes the results of the conventional plasma arc spraying method and the method of the present invention, which was implemented to increase spray material utilization efficiency and spray width.

1 is the conventional method, and the plasma arc current value is 350 A, and thermal spraying is performed without applying an external magnetic field.

2 is a case in which a steady cusp-shaped magnetic field as shown in FIG. 3(b) is applied and a cone-shaped plasma arc expanding toward the end is used. At the bottom, the cross-sectional area of the plasma arc becomes larger, which reduces the energy density. Therefore, the plasma arc current value is slightly larger than that of the conventional method.
Must be set.

In this example, when the plasma arc current was set to 50OA, a good sprayed coating was obtained.

As shown in FIG. 3(b), the orisp magnetic field is created through direct current flowing in two rings in opposite directions. The magnetic field strength measured on the axis of symmetry was 800 Gauss at the exit of the plasma torch nozzle and 7 Gauss at the surface of the material to be sprayed. Item (3) in the table is an example of thermal spraying using an alternating magnetic field orthogonal to the plasma arc to cause one-dimensional oscillating motion, which can be essentially regarded as a fan-shaped plasma arc that spreads toward the end. In this case, the plasma arc current was 4"5-OA, the external magnetic field strength acting on the bra woman arc was 120 Gauss r, p, m in the space where the plasma arc existed, and the alternating frequency was 400 Hz. In case,
The thermal spray powder used was alumina with a particle size of 250 mesh or less. The distance between the plasma spraying torch and the material to be sprayed was 7 om. The thermal spray material utilization efficiency is expressed as a percentage of the thermal spray coating formation rate divided by the thermal spray powder supply rate.

Table 1 From the above, in the method of the present invention, the thermal spraying material utilization efficiency can be improved.

It was confirmed that the thermal spray coating width was considerably higher than that of the conventional method.

Table 2 is an example showing that the adhesion of the coating is improved by implementing the method of the invention which allows pre-heating of the sprayed area. (1) shows the results of thermal spraying using a conventional method with a plasma arc current of 350A. In (2), a DC magnetic field equal to the amplitude value is superimposed on an alternating magnetic field that oscillates in a sine wave, and thermal spraying is performed without applying a magnetic field so that the plasma arc oscillates from directly below the torch to the area in front of the sprayed area. In this example, the vibration frequency was 400 Hz, the magnetic field strength was 180 Gauss r, p, m, and the plasma arc current was 450 A.

In Example (3), the results were obtained by performing thermal spraying by constantly curving the plasma arc in front of the thermal spraying. 45 OA' in a steady magnetic field of 180 Gauss perpendicular to the plasma arc
The arc is generated.

In all cases in Table 2, the distance between the plasma torch and the surface of the material to be thermally sprayed is 7011111, and the material to be thermally sprayed is a 4-thick iron plate, degreased and blasted with nickel-chromium alloy powder (80% Ni- 20% cr) was used as the thermal spraying material.

The following examples relate to the case where a self-fusing alloy is thermally sprayed using the method of the present invention which allows for post-spray heating. The distance between the plasma torch and the iron plate material was kept at 70 fins, the plasma arc current was set at 35 OA, and the nickel base was 17% chromium, 4% silicon, 3.5 tiboron, 1% carbon,
Self-fusing alloy powder with a composition containing 4% iron is shown in Fig. 6 (C), (
Thermal spraying was carried out using an oscillating plasma arc having the shape shown in e).

In this case, a direct current magnetic field equal to the amplitude value is further superimposed on the sinusoidal oscillating magnetic field to cause asymmetric vibration of the plasma arc. The magnetic field strength is 180 Gauss (r, p, m
, ) and the vibration period is 400 H2.

The plasma arc moving in the already sprayed area heats the coating layer in this area and melts it. In the conventional thermal spraying process for melting alloys, it was necessary to carry out the subsequent remelting process as an independent process, but in the method of the present invention, this process is no longer necessary. When we observed the cross section of the sprayed layer made by the method of the present invention, we found that the flux component contained as a raw material incorporated metal oxides, floated to the surface, and solidified, and the sprayed layer was formed in a uniform, pore-free state. It was confirmed that the method was inferior to the conventional method.

The above explanation has been given using a thermal spray coating as an example, but the present invention uses a plasma arc whose shape or motion is controlled by a magnetic field to enable thermal spraying with pre-heating or post-heating, improve the yield of thermal sprayed material, and improve workability. This invention makes it possible to increase efficiency, and the present invention is also extremely useful in thermal spray molding.

[Brief explanation of the drawing]

FIG. 1 shows the principle of a conventional thermal spraying method using a plasma jet, and FIG. 2 is an explanatory diagram showing the principle of a conventional thermal spraying method using a plasma arc. Fig. 3(a) is an explanatory diagram of the thermal spraying method using a cone-shaped plasma arc with a diverging end according to the present invention, and Fig. 3(b) is an illustration of the magnetic field generation method and magnetic field line distribution for creating a diverging recone-like plasma arc. FIG. Figure 4 is a principle diagram showing an example of a thermal spraying method using an oscillating plasma arc.
Figure 5 is an explanatory diagram showing the coordinate system in a model of thermal spraying on a flat plate, and Figure 6 is a typical deformation pattern of a plasma arc that can be considered to be a widened plasma arc or a plasma arc whose width has been substantially expanded due to high-speed oscillation motion. Figures (a) to (d) are plasma arc diagrams seen from the spraying direction, and (e) to (h) are plasma arc diagrams seen from the side perpendicular to the spraying direction. figure. Figure 7 is a classification diagram of the curve pattern of a plasma arc curved in one direction. Figures 1 (a) to (c) are plasma arc diagrams viewed from the direction of progress of thermal spraying, and (d) to (f) 1 are plasma arc diagrams viewed from the side perpendicular to the direction of progression of thermal spraying. 1.11...Power source 2...Cathode 3...Anode nozzle 4...Cooling channel 5...DC arc 6...Ultra high temperature plasma shift...Powder
Et 8... Film 9...
・Material 10...Arc 14.15...Inner ring coil 16...Magnetic force line distribution broom 3h≧ko" 3rd Shintb) 6 times (9)' (A)
'b) Surface q rcノ

Claims (1)

[Claims] (1) When a new coating layer is formed on the surface of the material by colliding particles of the material that have been heated to a molten or near-molten state with the surface of the material, deformation is caused by the action of electromagnetic force. (2) Plasma spraying method according to claim 1, characterized in that a plasma arc whose width is widened by the action of electromagnetic force is used. Method (3) A plasma spraying method according to claim 1, characterized in that a plasma arc that vibrates back and forth at high speed due to the action of an electromagnetic force (4) A plasma spraying method that uses a plasma arc that reciprocates at high speed due to the action of an electromagnetic force. The plasma spraying method according to claim 1, characterized in that a plasma arc having a curved shape is used.