JPH07110984B2 - How to spray tungsten carbide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a surface of a rolling roller,
The present invention relates to a method for thermal spraying of tungsten carbide which is widely applied to surface hardening of turbine wheel liners for slurries.

[0002]

2. Description of the Related Art Tungsten carbide (WC-Co)
The thermal sprayed coating of (1) has good interparticle bonding force and extremely high hardness, and therefore has excellent wear resistance and impact resistance. Therefore, the thermal spray coating of tungsten carbide (WC-Co) is used for the purpose of abrasion resistance. In order to achieve this purpose, thermal spraying is required with the following points in mind. (1) Cobalt (Co) that is a binder is sprayed on the surface of the base material in a molten state. (2) W2 C of WC showing wear resistance
Suppressing decomposition into W and W. (3) Tungsten carbide is sprayed onto the surface of the base material at high speed in order to form a dense sprayed coating.

In order to satisfy these points, the supersonic flame spraying method has hitherto been mainly used for spraying tungsten carbide. This supersonic flame spraying method is a method characterized in that explosive combustion is used to accelerate the sprayed particles in a short time to reach a high speed, and the WC decomposition is also suppressed and the sprayed coating has wear resistance. Is obtained. However, since the tungsten carbide adheres to the ejection port of the thermal spray torch, the continuous operation time is short and the rate of adhesion of the thermal spray material to the base material, that is, the thermal spray efficiency is low. In addition, noise is remarkably high due to the use of explosive combustion. For example, it is 140 to 160 dB. Therefore, in order to solve such a problem, a new plasma spraying method is required.

In the conventional plasma spraying method, the temperature of the plasma frame is high, and the spraying distance, that is, the distance from the feeding point of the sprayed material to the plasma frame to the base material is long, and Since the enthalpy is high, the WC easily decomposes into W2 C or W, and the wear resistance of the tungsten carbide sprayed coating is inferior to that of the ultra-high speed flame spraying method.

The present invention prevents the decomposition of WC, which is a problem of the conventional spray coating of tungsten carbide by the plasma spraying method, which impairs the wear resistance, and has the problems of the conventional high-speed flame spraying method. It is an object of the present invention to provide a tungsten carbide plasma spraying method capable of prolonging the short continuous operation time and a tungsten carbide sprayed coating obtained by the spraying method.

[0006]

According to the present invention, powdered tungsten carbide is fed and melted in a plasma flame obtained by heating a plasma gas by an arc, and the molten droplets are blown onto a base metal. In the plasma spraying method of tungsten carbide for forming a sprayed coating on a material surface, the arc is formed between a main torch and a sub-torch, a swirling flow of plasma gas is formed around the arc, and the plasma flame is 0.5 to 1.8X10 ⁴ Kj / Kg
Is a method of thermal spraying tungsten carbide, which is characterized by having a low enthalpy, also, in the plasma flame obtained by heating the plasma gas by the arc, the powdered tungsten carbide is fed and melted, In the plasma spraying method of tungsten carbide forming a sprayed coating on the surface of the base material by spraying molten droplets on the base material,
The arc is formed between the main torch and the sub-torch, a swirling flow of plasma gas is formed around the arc, and the plasma flame has a low enthalpy of 0.5 to 1.8 × 10 ⁴ Kj / Kg. The method for thermal spraying of tungsten carbide is characterized in that plasma is separated just before the base material in.

Furthermore, a swirling flow of plasma gas is formed around an arc formed between the main torch and the sub-torch, and the plasma gas is heated by the arc to obtain 0.5 to 1.8 × 10 ⁴ K.
During low enthalpy of the plasma flame of j / Kg, and melted by feeding tungsten carbide particulate, tungsten Carver by spraying the molten droplets in the base material
Spraying methods tungsten carbide which is characterized that you form a thermal spray coating of id is, also, about the arc formed between the main torch and the auxiliary torch, to form a swirling flow of plasma gas, the arc Obtained by heating with.
Powdered tungsten carbide is fed and melted in a low enthalpy plasma flame of ^{5 to} 1.8 × 10 ⁴ Kj / Kg, and the plasma is separated immediately before the base metal in the plasma flame, and then the melting. A sprayed coating of tungsten carbide is formed by spraying drops onto the base material
Spraying side of tungsten carbide and said to Rukoto
Is the law .

[0008]

[Operation] Since a swirling flow of the plasma gas is formed around the arc formed between the main torch and the sub-torch, the arc is focused by the so-called pinch effect, and the plasma frame is formed. Even if it is not in the laminar flow state, it is squeezed and stretched to form a high speed plasma frame. Therefore, it becomes possible to continuously operate for a long time, and at the same time, it is possible to obtain a dense thermal spray coating by colliding the tungsten carbide having a molten Co state with the base material at a high speed. Also, the plasma frame is 0.5 to
Since it has a low enthalpy of 1.8 × 10 ⁴ Kj / kg, it can suppress the thermal decomposition of WC, so that a high quality sprayed coating of tungsten carbide can be obtained.

[0009]

Embodiments of the present invention will be described with reference to the accompanying drawings. In the composite torch-type plasma spraying apparatus P shown in FIG. 1, a main gas inlet 55 having a concentric and same diameter on the axis of the main cathode 53.
The main torch 51 is constituted by the insulator 77 provided with, the main jacket 54 having the discharge port, the insulator 79 provided with the main plasma gas inlet 82, and the main second jacket 81 having the narrowed port. As shown in FIG. 2, the protective gas 56 or the main plasma gas 83 is first introduced into the gas annular chamber 98 from the main gas inlet 55 or the main plasma gas inlet 82 to form one swirl flow forming hole 99 or Through a plurality of swirl flow forming holes 99 arranged in equal parts, it is fed as indicated by an arrow 101 so as to swirl the inner wall of the insulator 77 or the insulator 79.

Next, the auxiliary torch starting electrode 59, which is arranged so as to intersect with the central axis of the main torch 51, has an insulator 78 and a secondary first mantle 60 having an emission port so as to be concentric.
It is attached by the insulator 80 and the sub second outer jacket 86, and further, the insulator 77 or the insulator 7 of the main torch 51.
Insulator 78 having swirling gas forming means 97 similar to
The sub gas 62 is fed from the sub gas inlet 61 provided in the, and the sub second gas 88 is fed through the sub second gas inlet 87 provided in the insulator 80. . The negative terminal of the main power supply 57 is connected to the main cathode 53, and the positive terminal is connected to the main outer jacket 54 and the main second outer jacket 81 via switch means 58 and 84, respectively. Constitutes the main torch 51 as a whole.
The sub power supply 63 has its positive terminal connected to the positive terminal of the main power supply 57 and the sub first outer jacket 60 of the sub torch 52.
The negative terminal of 3 is connected to the auxiliary torch starting electrode 59 via the switch means 64, and these collectively form the auxiliary torch 52. A pair of the sub torches 52 is provided.

The torches shown in FIG. 1 are activated in the following order. That is, the switch 58 is closed, and the main power source 57 first forms the main starting arc 65 between the main cathode 53 and the discharge port of the main outer jacket 54, whereby the protective gas 56 is heated and the main outer jacket 54 is heated from the tip thereof. A conductive plasma is emitted. At this time, when the switch means 84 is closed and then the switch means 58 is opened, the main starting arc 6
The arc emitted from the tip of the main cathode 53 at the same time as 5 is erased forms a main second outer envelope starting arc 85, which heats the protective gas 56 and the main plasma gas 83, and the conductive plasma is generated. 100 is discharged to the outside of the main torch 51. Next, the switch means 64 is closed and the sub power source 6
When the sub starting arc 66 is formed between the sub first outer jacket 60 and the sub torch starting electrode 59 by 3, the sub gas 62 is heated by this arc, and the conductive plasma 68 passes through the constriction opening to cause the conductive plasma 68 of the sub torch 52. It is released to the outside.

When these processes are completed, the main torch 51 and the sub-torch 52 are installed so that their central axes intersect, so that the conductive plasmas 100 and 68 emitted from the main torch 51 and the sub-torch 52 respectively pass through the conductive paths. When the switches 84 and 64 are opened at this stage, a steady hairpin arc 67 is formed by the main power source 57 from the tip of the main cathode 53 toward the outer surface of the constriction mouth of the sub-mantle 60, and is sent to the main torch 51 at this time. By adjusting the amount of gas to be introduced and the amount of gas to be sent to the auxiliary torch 52, respectively, as shown in FIG. 1, a plasma flame 73 is formed which is substantially concentric with the central axis of the main torch 51. To be done. This plasma frame
The film 73 has a high speed, but the enthalpy is set so that Co melts but WC does not decompose, that is, low enthalpy. This specific enthalpy value is 0.5 to
The calculation of this enthalpy is in the range of 1.8 × 10 ⁴ Kj / kg.

[Equation 1] Required by. In order to form such a plasma frame 73, it is effective to increase the thermal spray output of the torches 51 and 52 and increase the amount of plasma gas above the increase rate of the output. . At this time, since the gas is supplied so as to form a strong swirling flow around the arc column of the torches 51 and 52, the arc column is maintained at the axial center position of the torch, and the swirling annular gas sheath is formed concentrically. The heat load exerted on the inner walls of the constriction ports of the positive and secondary outer jackets 54, 60 and the primary and secondary second outer jackets 81, 86 of the secondary torches 51, 52 is uniformly reduced, and the arc current can be increased. As a result, the so-called pinch effect is promoted, the arc is focused more, and high-output, high-temperature and high-speed spraying becomes possible.

A powdery granular tungsten car fed from the material feeding pipe 69 of FIG. 1 toward the plasma frame 73.
The bead 70 is immediately heated to a high temperature by the plasma frame 73 and melted to form a molten droplet 71, which is entrained in the plasma frame 73 and advances toward the base material 75 without spreading much. In the plasma flame 73 containing the molten droplet 71, only the plasma is separated by the plasma decomposition means 72 provided immediately before the base material 75.

As the plasma separating means, for example, a two-fluid nozzle 90 of an atomizer for supplying water and air toward the plasma frame 73 immediately before the base material is used. When the atomizer 90 sprays water, the plasma frame 73 is cut and formed into a conical shape.
The conical plasma frame 73 acts as a tunnel-shaped jacket that minimizes cooling of the molten droplet 71,
The excess heat load on the base material 75 and the thermal spray coating 74 can be removed by the heat of vaporization of the water sprayed by the atomizer, and the adverse effect of the heat load can be prevented. Further, with the explosive expansion of water at this time, the gas is rapidly jetted along the plasma gas to accelerate the molten droplet 71, and as a result, a dense sprayed film is formed.

In this way, the molten droplet 71 separated from the plasma collides with the base material 75 immediately after that and forms the thermal spray coating 74. At this time, by providing a means for supplying gas so as to form a strong swirl flow around the arc column, the arc column is maintained at the axial center position of the torch, and a swirl annular gas sheath is formed concentrically, which results in the conventional laminar flow. In the turbulent flow area that could not be achieved by the plasma spraying device that forms the plasma flame, the plasma flame 73 can be sprayed in a high density and expanded in a stable state, the tungsten carbide melts well, and the mother material is melted at high speed. Since it is sprayed on the material 75, a high quality sprayed coating 74 of tungsten carbide can be obtained with high efficiency. Further, in this practical example, since the spraying distance is short, a dense sprayed coating can be obtained and a tungsten spray can be obtained while the tungsten carbide in which Co is in a molten state is made to collide with the base material at a high speed. The time that the binder stays in the high temperature plasma frame is shortened and the decomposition of WC is suppressed. Furthermore, since the enthalpy of the plasma frame is low, thermal decomposition of WC is suppressed.

The embodiment of the present invention is not limited to the above. For example, if a plasma frame of high speed and low enthalpy can be obtained instead of the compound torch type plasma spraying device as the plasma spraying device, Of course, other plasma spraying devices may be used. In this practical example, only the tungsten carbide was described as the thermal spray material, but the present invention can of course be used for other thermal spray materials that require a high speed, low enthalpy plasma frame. is there. Also, when feeding powdered tungsten carbide into the plasma flame, a gas is used, but instead of this gas, a fluid, for example,
Water may be used.

Next, an experimental example of the present invention will be described. Experimental Example 1 (A) Sample preparation conditions The conditions for forming a tungsten carbide (WC-Co) film were described.

[Table 1] Shown in. As the plasma spraying apparatus, the composite torch type plasma spraying apparatus of the above example was used. The cylindrical base material was used for the adhesion strength test, and the other tests used the sample sprayed on the flat plate base material. (B) X-ray Diffraction Measurement Results An example of the X-ray diffraction measurement results of the conventional atmospheric pressure plasma spray coating A and the high-speed gas flame spray coating B and the X-ray diffraction measurement result of the spray coating C according to the present invention are shown in FIG. . In this figure, ○ (white circle) is WC, ● (black circle) is W2 C, △
(Triangle mark) indicates Co3 C, vertical axis indicates intensity (intensity), and horizontal axis indicates 2θ (deg.). High-speed gas flame spraying has lower enthalpy and lower heat source temperature than conventional plasma spraying, so it is considered that decomposition of WC is less likely to occur. In this example as well, it is clear that the structure of the carbide is higher than that of conventional plasma spraying A. Well left. But,
It can be seen that in the sprayed coating C according to the present invention, the peak of the decomposition product is even smaller and the structure of the carbide is very well left.

(C) Result of measurement of wear loss (wear resistance) FIG. 4 shows the result of wear test of the WC-Co film. In this figure, the vertical axis represents the amount of wear reduction (mg), the horizontal axis represents the number of reciprocating frictions (DS), ○ (white circle) represents the present invention, and ● (black circle) represents high-speed gas frame spraying. The present invention is considered to have a great effect by shortening the residence time by increasing the gas velocity, has a small amount of wear loss, and exceeds the wear resistance of the coating film by high-speed gas frame spraying. (D) Pickers hardness test result The hardness measurement values were in the variation range 1187 to 1453 and the average value Hv = 1284. This value is the value of a coating obtained by high-speed gas frame spraying or explosive spraying (HV = 1200) which is said to be better than plasma spraying.
It can be said that it is comparable to 1300). (F) Adhesive strength test results When the adhesive strength was measured, peeling occurred from the adhesive surface in all the samples. As a result, the adhesion strength of the thermal spray coating exceeds the adhesive strength of 700 Kgf / cm @ 2 and is considered to be practically sufficient. Experimental Example 2 As the plasma spraying apparatus, the composite torch type plasma spraying apparatus of the above example was used.

[Table 2] A thermal spray coating of tungsten carbide was prepared under the thermal spray conditions shown in. As a result, WC was almost decomposed in this sprayed coating, and the wear resistance of the sprayed coating was 370 mg / 3200D.
It became S and was unsatisfactory. That is, it was revealed that a plasma frame having a high enthalpy cannot obtain a desired thermal spray coating.

[0019]

Since the present invention is configured as described above, it has the following remarkable effects. (1) Since the spraying distance can be shortened as compared with the conventional example, it is possible to make the tungsten carbide in which Co is in a molten state collide with the base material at a high speed. In addition, since the time that the tungsten carbide stays in the high temperature plasma frame is shortened, W
The decomposition of C is suppressed. Further, the continuous operation time can be lengthened as compared with the conventional example. Incidentally, in the above-mentioned practical example, continuous operation could be performed for 100 hours or more without maintenance. (2) Since the enthalpy of the plasma flame is low, thermal decomposition of WC can be suppressed. As a result, it is possible to obtain a dense sprayed coating of tungsten carbide having excellent wear resistance.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a diagram showing X-ray diffraction of a thermal spray coating.

FIG. 4 is a diagram showing the results of a wear test of a thermal spray coating.

[Explanation of symbols]

 51 Main torch 52 Sub torch 56 Protective gas 62a Sub gas 62b Sub gas 68 Plasma 70 Chromia 71 Melt droplet 72 Plasma separation means 74 Thermal spray coating 75 Base metal 83 Main plasma gas 88a Sub second gas 88b Sub second gas 97a Swirling gas Forming means 97b Swirling flow gas forming means 99 Swirling flow forming holes

Claims (5)

[Claims] 1. A powder flame-shaped tungsten carbide is fed and melted in a plasma flame obtained by heating a plasma gas by an arc, and the molten droplets are sprayed on a base material to form a sprayed coating on the surface of the base material. In the tungsten carbide plasma spraying method, the arc is formed between a main torch and a sub-torch, a swirl flow of plasma gas is formed around the arc, and the plasma flame is formed.
Spraying method of tungsten carbide characterized by low enthalpy of 0.5-1.8X10 ⁴ Kj / Kg 2. A powder flame-shaped tungsten carbide is fed into a plasma flame obtained by heating a plasma gas by an arc and melted, and the molten droplets are sprayed onto the base material to form a sprayed coating on the surface of the base material. In the tungsten carbide plasma spraying method, the arc is formed between a main torch and a sub-torch, a swirling flow of plasma gas is formed around the arc, and the plasma flame is reduced to 0.
Low enthalpy of 5 to 1.8 × 10 ⁴ Kj / Kg, and method of spraying tungsten carbide, characterized in that plasma is separated just before the base material in the plasma flame 3. The method for thermal spraying of tungsten carbide according to claim 2, wherein the plasma is separated by spraying from an atomizer toward a plasma flame. 4. 0.5 to 1.8 × 10 ⁴ Kj / K obtained by forming a swirling flow of plasma gas around an arc formed between a main torch and a sub-torch and heating by the arc.
Into a low enthalpy plasma flame of g, tungsten powder in the form of particles is fed and melted, and the molten droplets are sprayed on the base material to remove the tungsten carbide.
Spraying methods tungsten carbide which is characterized that you form a thermal spray coating. 5. 0.5 to 1.8 × 10 ⁴ Kj / obtained by forming a swirling flow of plasma gas around an arc formed between a main torch and a sub torch and heating by the arc.
In a low enthalpy plasma flame of Kg, powdered tungsten carbide was fed and melted, and plasma was separated immediately before the base material in the plasma flame.
Tungsten by spraying the molten droplets on the base material
Spraying methods tungsten carbide which is characterized that you form a thermal spray coating of carbide.