JPH05320856A - Plasma thermal spraying method - Google Patents

Abstract

(57) [Summary] [Purpose] To easily produce high-performance coatings. [Structure] The plasma jet J is shielded by a gas flame B to widen the high temperature portion of the plasma jet J. The gas flame B is deflected outward by the flow straightening vanes 9 on the way to prevent the gas flame B from hitting the base material 5. Preheating and cooling of the spray base material 5 are unnecessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma welding method for forming a film on the surface of a member by using a plasma jet as a heat source.

[0002]

2. Description of the Related Art For the purpose of imparting heat resistance and abrasion resistance to the surface of a member such as an iron making facility, a film is formed on the surface thereof. There is a thermal spraying method as the film forming means, and among the thermal spraying methods, the plasma thermal spraying method uses thermal plasma as a heat source, and therefore has an advantage that a high melting point material such as ceramics can be used. The principle is that the thermal spraying powder is fed into the plasma jet, the thermal spraying powder is melted by the heat of the plasma, and the powder is accelerated by the pressure of the plasma and jetted from the nozzle toward the base material. acceleration·
The heated particles are deposited on the surface of the base material to form a film.

Although there are many problems that must be solved by plasma spraying, the shield of the plasma jet is important. With respect to this shield, the present inventors have previously proposed a method of surrounding the plasma jet with a gas flame (Japanese Patent Laid-Open No. 2-217457). According to this method, by enclosing the plasma jet, it is possible to prevent the entrainment of the atmosphere and to suppress the temperature drop of the velocity of the plasma jet due to the entrainment. This effect can be expected more by using a flame flame as the shield gas, and the high-speed part and high-temperature part of the plasma jet are enlarged, and the acceleration and heating conditions of the thermal spray powder are improved, which has the advantage of improving the coating properties. is there.

[0004]

The present inventors have used this method for forming various films since the development of this method.
In the process, it was also found that there are points to be improved as described below.

One is that the base material is overheated. This occurs because the gas flame used for the shield has less attenuation of the temperature field than the plasma jet and heats the base material. Therefore, some kind of base material cooling is necessary to obtain a good thermal spray coating. Secondly, when the initial base material temperature is lower than about 15 ° C., the interface between the base material and the coating film contains a large amount of water, which causes deterioration over time after the coating film is formed. This occurs because water vapor generated by combustion of a gas flame condenses on the surface of the base material, and the water content is confined by the deposition of spray particles, and oxidation progresses with the lapse of time after the film is formed, resulting in deterioration of the film characteristics. cause. Therefore, it is necessary to preheat the base material before the start of thermal spraying.

As described above, in the plasma spraying method in which the plasma jet is shielded by the gas flame, the base material is preheated and then the film formation is started to perform the spraying while cooling so that the base material is not overheated. This is necessary to obtain a good film, and workability is not good. Also, preheat
It is necessary to control the temperature in association with cooling, which further reduces workability.

An object of the present invention is to provide a plasma spraying method for improving workability by eliminating the need for preheating / cooling of the base material without impairing the advantage of the plasma shield by the gas flame.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have studied a method of shielding a thermal spray base material from a gas flame. As a result, if the plasma jet is surrounded by the gas flame in the upstream portion of the flame near the crater of the gas flame, the high temperature portion of the plasma jet will be generated in the downstream portion of the flame even if the gas flame is diffused outward. It was found that the effect of enlarging was hardly reduced, and that the shield property against the plasma jet was hardly reduced.

The present invention has been made on the basis of the above findings. A gas flame is ejected around a plasma jet containing sprayed particles along the jet, and a gas flow is provided by a straightening vane provided midway along the ejection path of the gas flame. The gist is a plasma spraying method characterized in that a flame is deflected from the middle to the outside.

[0010]

FIG. 1 is an elevational view schematically showing an embodiment of the present invention.

A plasma gas G is placed inside the plasma torch 1.
Is supplied, the electrode 2 inside the torch and the nozzle 3 at the tip of the torch
The plasma gas G is turned into plasma by an arc generated between the and, and a plasma jet J is jetted downward from the outlet of the nozzle 3. The thermal spray powder P is supplied to the plasma jet J through the powder supply pipe 4. Thermal spray powder P
Is accelerated and heated by the plasma jet J, and is sprayed onto the thermal spray base material 5 below to form a film 6 on the surface thereof.

An annular gas burner 7 is concentrically attached to the tip of the plasma torch 1. The gas burner 7 has a plurality of craters 8 arranged around the nozzle 3 at equal intervals in the circumferential direction. Then, the fuel F is supplied to the gas burner 7 to shield the periphery of the plasma jet J,
Gas flame B is ejected downward from each crater 8.

Below the gas burner 7, a cylindrical straightening vane 9 is provided.
Are provided concentrically with the plasma torch 1. The rectifying blade 9 is a tapered cylindrical body that spreads outwards downward, and the plasma jet J and the accelerated / heated powder pass through the inside thereof, and the gas flame B collides with the outer peripheral surface. .. A sufficient gap is secured between the gas burner 7 and the flow straightening blade 9.

The gas flame B ejected from each crater 8 of the gas burner 7 shields the periphery of the upstream portion of the plasma jet J ejected from the nozzle 3 of the plasma torch 1 and expands its high temperature portion. Then, it collides with the outer peripheral surface of the flow straightening blade 9 and is deflected outward. This prevents the gas flame B from being sprinkled on the base material 5.

In the structure of the flow straightening blade 9, the gas flame B is the spray base material 5
However, the structure is not particularly limited, but the following conditions must be satisfied. Do not be damaged by the heat of plasma jet J and gas flame B. For this purpose, it is preferable to cool the flow straightening blade 9. The straightening vanes 9 do not obstruct the flight path of the sprayed powder P. Since it moves with the plasma torch 1, it should be as light as possible.

Regarding the installation position of the flow straightening blade 9, the gas flame B
Can be prevented from hitting the thermal spray base material 5, the thermal spray powder P
In addition to not hindering the flight path of the plasma torch 1
It is necessary that the nozzle 3 is not too close. When the flow straightening blade 9 is brought too close to the plasma torch 1, the gas flame B is not sufficiently superposed on the plasma jet J, and the effect of enlarging the high temperature portion of the plasma jet J is reduced.

Desirable dimensions and installation positions of the flow straightening blade 9 in consideration of such conditions are as follows. In addition,
The straightening vanes 9 are assumed to be the tapered cylindrical body shown in FIG.

The arranging diameter D of the craters 8 in the gas burner 7 is preferably 25 to 40 mm. If D is too small, there is no shield effect and it becomes an integral heat source, and if D is too large, the effect of the gas flame does not affect the plasma. The inlet diameter d of the straightening vanes 9 is preferably 20 to 35 mm in order to be smaller than the array circle diameter D of the craters 8 and to satisfy the above condition. The inclination angle θ with respect to the central axis is preferably 30 to 45 °. This is because it is larger than the spread angle of the powder flight path. If the angle is made larger than this, the rectifying blade 9
The flow of the gas flame after passing is not smooth, which in turn adversely affects the flow of the gas flame B. The distance L from the nozzle outlet of the plasma torch 1 to the flow rectifying blade 9 is 20 to
40 mm is desirable. If the flow straightening blade 9 is too close to the nozzle outlet, there is a problem in heat resistance, and if it is too far away, the distance between the thermal spray torch 1 and the base material 5 is constant at about 100 to 140 mm, and it is difficult to secure the installation space. The height h of the flow straightening blade 9 is preferably 50 to 80 mm. If it is too low, the rectifying effect will be insufficient, and if it is too high, the installation space will be difficult.

[0019]

EXAMPLES Examples of the present invention will be described below.

The flow straightening blade used is shown in FIG. Straightening vane 9
Is a cooling pipe 10 that is a tapered cylinder and also serves as a support portion.
The cooling water was circulated inside. Table 1 shows the material and dimensions of the flow straightening blade 9. The installation position was on the central axis of the nozzle 3 of the plasma torch 1, and the distance from the outlet of the nozzle 3 was 40 mm. Table 2 shows the basic conditions and evaluation method of plasma spraying.

[0021]

[Table 1]

[0022]

[Table 2]

FIG. 3 shows the results of film formation by gas flame shield thermal spraying without the use of flow straightening blades.
The bond strength test results after the elapse of time are shown in relation to the initial base material temperature. When the initial base material temperature is 15 ° C. or lower, the film strength deteriorates with time. This indicates that preheating of the base material is necessary when using the base material at a temperature of 15 ° C. or lower. It becomes a problem at low temperatures such as winter.

FIG. 4 shows the result of coating film formation by gas flame shield thermal spraying without straightening vanes, in which the base material temperature at the end of coating film formation was controlled by adjusting the cooling of the base material. The initial base material temperature was 20 ° C. The base material temperature is 200 at the end of film formation.
When the temperature is set to be ° C, the film strength becomes maximum. Therefore, when the test piece is small and overheated, the base material needs to be cooled. Under the conditions of the present study, the base material temperature after the film production was completed was 450 ° C. without cooling, and the base material was overheated.

FIG. 5 shows the results of joint strength tests of coatings produced under various thermal spraying conditions including the present invention 7 after 5 hours and 72 hours after the coating was produced. Table 3 shows the detailed conditions. The coatings A and B are coatings produced by normal plasma spraying without using a gas flame or a rectifying blade, C to F are coatings produced by gas flame shield spraying without using a rectifying blade, and G and H.
Is a coating produced by gas flame shield thermal spraying using the flow straightening blade of the present invention.

In the coating strength test after 5 hours, the coating produced by gas flame shield thermal spraying has a uniformly higher bonding strength of the coating than that produced by ordinary plasma spraying. However, the base material initial temperature is low and the C and D coatings containing water at the interface of the base material coating deteriorate with time. Other than the coatings G and H produced by using the flow straightening blades, only the coatings of E and F at the initial temperature of the base material of 20 ° C. keep the bonding strength high. However, the coatings of E and F are inferior to those produced by using the flow straightening blade even if the base material is cooled during the thermal spraying. Further, in the thermal spraying method using the straightening vanes, even if the initial base material temperature is 5 ° C, the gas flame is prevented from spattering on the base material, so that no condensation occurs at the interface between the base material and the coating, and the coating characteristics change over time. No deterioration is observed and good film formation is possible. In addition, the film surface temperature is almost 2 at the end of film production.
The temperature is 00 ° C, which is a condition under which a high-strength coating can be produced.

[0027]

[Table 3]

[0028]

As is clear from the above description, in the plasma spraying method of the present invention, by shielding the plasma jet with a gas flame, the high temperature portion effective for melting the sprayed powder is expanded and a dense sprayed coating is formed. Enable formation of. Moreover, the problem of overheating of the coating and dew condensation on the sprayed surface when the temperature of the base material is low are prevented without cooling and preheating of the base material, and there is no adverse effect on the spraying of the shield by the gas flame. Therefore, a high-performance film can be easily produced.

[Brief description of drawings]

FIG. 1 is an elevational view schematically showing an embodiment of the present invention.

FIG. 2 is an elevation view and a bottom view of a flow straightening blade used in an embodiment of the present invention.

FIG. 3 is a table showing the relationship between the initial base material temperature and the joint strength when a flow straightening blade is not used in gas flame shield thermal spraying.

FIG. 4 is a chart showing the relationship between the coating surface temperature and the joint strength at the end of thermal spraying when a flow straightening blade is not used in gas flame shield thermal spraying.

FIG. 5 is a table showing coating bond strengths 5 hours and 72 hours after the coating is produced when the coating is produced under various thermal spraying conditions including the present invention.

[Explanation of symbols]

 1 Plasma torch 3 Nozzle 5 Thermal spray base material 6 Coating 7 Gas burner 8 Crater 9 Straightening vane J Plasma jet B Gas flame

Claims (1)

[Claims] 1. A gas flame is ejected around a plasma jet containing thermal spray particles along the jet, and the gas flame is deflected outward from the midpoint by a straightening vane provided in the ejection path of the gas flame. And a plasma spraying method.