JPH0645856B2 - Spray coating for gap control - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is formed to control a clearance between a rotating mating member such as a clearance between an impeller and a compressor housing of a turbocharger for an automobile as small as possible. Thermal spray coating.

2. Description of the Related Art As shown in FIG.
The exhaust gas from the exhaust manifold of the engine is guided to the turbine housing 1 to rotate the turbine wheel 2, and the rotation of the impeller 4 connected to the turbine wheel 2 via the shaft 3 compresses the intake air in the compressor housing 5. It sends compressed intake air to the engine. An aluminum alloy casting is generally used as the compressor housing 5 in such an automobile turbocharger, and a material obtained by quenching and tempering a heat-resistant aluminum alloy casting is generally used as the impeller 4.

By the way, in the automobile turbocharger, it is advantageous to improve the turbo efficiency (compressor efficiency) by reducing the gap H between the tip of the impeller 4 and the inner wall surface of the compressor housing 5 facing it. It has been known. However, this gap H
If is too small, the tip of the impeller 4 may come into contact with the compressor housing 5 due to slight eccentricity or vibration of the shaft 3 during rotation, and the impeller 4 may be damaged. Therefore, the gap H between the compressor housing 5 and the impeller 4 of the conventional automobile turbocharger is required to be at least 0.3 to 0.5 mm, although it depends on the size of the turbocharger. It was a big cause that could not be improved.

On the other hand, also in the gas turbine engine, it is preferable to minimize the gap between the turbine casing and the turbine blades in order to minimize the power loss, but in this case as well, there was a problem similar to that of the automobile turbocharger. Therefore, regarding gas turbine engines, Japanese Patent Publication No. 50
No. 690, it has been proposed that the turbine casing be made of a softer ceramic than the turbine blade to prevent damage to the turbine blade.

Further, regarding a gas turbine engine for an aircraft, JP-A-52-72335 or JP-A-52-85031.
As shown in No. 2, a mixed powder of an alloy powder such as Ni—Cr alloy powder or Al—Cu alloy and Ni graphite powder in which graphite is coated with Ni is sprayed on the surface of the casing of the compressor, and the spraying is performed. A technique has been proposed in which the film is cut by a rotary blade as a mating member to adjust the gap between the casing and the rotary blade.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As shown in Japanese Patent Publication No. 50-690, the construction of a material that is softer than the entire rotating member of the turbine casing (in this case, the turbine blade) is a significant material. This is costly and unrealistic. Therefore, as disclosed in JP-A-52-72335 and JP-A-52-85031, a method of forming a sprayed coating and cutting it with a rotating member as a mating member to adjust the gap is effective. It is believed that there is. This method is sufficient for a general-purpose automobile turbocharger, but in reality, it is not yet satisfactory when a higher rotational speed is given such as for racing.

That is, the thermal spray material as described above, for example (Ni-Cr
Alloy) -Ni coated graphite or (Al-Cu alloy) -N
When the i-coated graphite or the like is directly sprayed onto the turbine casing or the compressor housing, the structure of the sprayed coating is almost uniform over the entire area by the conventional method, and the surface roughness of the sprayed coating is 60 to 200 μmRz. Therefore, for example, when cutting the sprayed coating formed on the compressor housing with an impeller to adjust the clearance, when trying to rotate the impeller at an ultra-high speed from the initial stage such as for racing, the cutting resistance becomes large in the initial stage. The rotation speed of the impeller may not increase smoothly. Further, when trying to rotate at an ultra-high speed, even if the impeller or the like is rotated in the initial stage, the hardness of the mating material (impeller, etc.) may change in the structure of the sprayed coating such as Al-Cu alloy or Ni-Cr alloy. Since there is a base metal layer having a hardness close to that of the impeller, there is a risk that the tip contact portion of the impeller or the like will be locally scratched or worn. If a sprayed coating having a regular uniform structure is formed in a race turbocharger or the like that requires ultra-high speed rotation, problems such as cutting of the coating and wear of the impeller may occur. It was

Further, if a sprayed coating having a uniform structure as described above is used when ultra-high speed rotation is required such as a turbocharger for racing, the adhesion to the base material such as the compressor housing is often insufficient. In this case, peeling may occur due to shear stress at the interface between the base material and the thermal spray coating, which occurs when the thermal spray coating is cut with an impeller or the like. In order to improve the adhesion, a Ni-based alloy or the like may be sprayed on the surface of the base material in advance to form a base layer (bond layer), and a spray coating for gap adjustment may be formed on the base layer. Although conventionally performed, there is a problem in that the formation of the underlayer hinders the productivity and raises the cost.

The present invention has been made in view of the above circumstances, and a gap between a mating member that rotates at an ultra-high speed, such as a portion facing an impeller in a compressor housing of a turbocharger for automobiles for racing, is made as small as possible. As a thermal spray coating formed for adjusting the gap at a desired portion, it is necessary to provide a thermal spray coating that has a small work resistance at the initial stage of ultra-high speed rotation and at the same time has a sufficiently high adhesion to the base material. It is intended.

Means for Solving the Problems The thermal sprayed coating of the present invention basically comprises dispersing soft non-metallic material particles in a soft metallic material, and determining the diameter or flatness of the soft non-metallic material particles as the thickness of the thermal sprayed coating. Both the initial machinability and the adhesion to the base material are simultaneously improved by changing the thickness direction.

Specifically, the invention of claim 1 is a soft thermal spray coating formed on a surface of a base material at a portion facing a rotating mating member, and the mating member is formed by cutting the surface layer by rotating the mating member. In the spray coating for gap control for adjusting the gap with the member, the soft non-metal material particles are dispersed in the soft metal material, and the particle size of the soft non-metal material particles is the side of the interface with the base material. It is characterized in that it is configured so as to increase toward the surface of the film.

The invention according to claim 2 is a soft thermal spray coating formed on the surface of the base material at a portion facing the rotating mating member, and the gap between the mating member is formed by cutting the surface layer by rotating the mating member. In the spray coating for gap control to adjust the, the non-metallic material particles are dispersed in the soft metal material, and the flatness of the soft non-metallic material particles from the surface side of the coating to the interface with the base material. It is characterized in that it is configured so as to become larger toward it.

Here, the flatness of the soft non-metallic material particles means that the maximum diameter in the direction orthogonal to the thickness direction of the thermal spray coating is a and the maximum diameter in the thickness direction of the thermal spray coating is b, as shown in FIG. , Flatness rate F (%) Use the indicated value.

When a mating member, such as an impeller, is rotated with a sprayed coating consisting of soft non-metallic material particles dispersed in a soft metallic material formed on the surface of a compressor housing of an automobile turbocharger, its rotation In the initial stage of, the tip of the mating member rotates while contacting the sprayed coating, and the portion of the contacted thickness in the sprayed coating is scraped off,
The gap with the mating member is adjusted to substantially zero.

Here, the thermal spray coating according to the invention of claim 1 is configured such that the particle diameter of the soft non-metallic material particles increases from the interface side with the base material toward the surface. Therefore, since the particles of the soft non-metallic material dispersed in the surface layer of the thermal spray coating, that is, the layer that is initially cut by the mating member, are coarse, the surface layer is soft and brittle as a whole, and has a good machinability. Has become. Further, in order to form a surface layer in which coarse soft non-metal material particles are dispersed in this way, it is necessary to use coarse thermal spray particles during thermal spraying of the surface layer portion, but coarse thermal spray particles are completely Since the particles collide with the surface of the base material before they melt, the particles are less likely to be crushed during the collision, which reduces the bonding force between particles and facilitates the formation of pores between particles, which also makes the surface layer brittle and machinable. Contributes to being good. Therefore, when the surface layer of the thermal spray coating is scraped off in the initial stage of rotation of the mating material, the brittle and good machinability surface layer is easily scraped off, and the machining resistance becomes a small value.

On the other hand, in the layer (base layer) on the side of the thermal spray coating that is in contact with the base material, since the diameter of the dispersed soft non-metallic material particles is small, it is a dense and relatively hard layer as a whole. High adhesion. Further, in order to form a base layer in which such fine soft non-metal material particles are dispersed, it is necessary to use fine spray particles at the time of spraying the base layer portion, but the fine spray particles are sufficient to the central portion of the particles. Since the particles collide with the surface of the base material in the molten state, the particles are easily crushed at the time of collision, resulting in a dense layer, and since the particle temperature is kept high, the wettability with the base material is also good. Contributes to the improvement of the adhesion to the base material.

Thus, in the invention of claim 1, by changing the particle size of the soft non-metallic material particles dispersed in the thermal spray coating in the thickness direction, the initial cutting resistance when the mating material rotates can be reduced. At the same time, the adhesion to the base material can be improved.

Next, in the thermal spray coating according to the invention of claim 2, the flatness of the soft non-metallic material particles is increased from the surface toward the base material. Therefore, the soft non-metal particles dispersed in the surface layer of the thermal spray coating cut by the rotation of the mating material have a small flatness and are spherical or lumpy. It is easy to fall off when cut by a material, and therefore the surface layer has a good machinability. Further, in order to form a surface layer in which soft non-metallic material particles having a small flatness ratio are dispersed as described above, it is necessary to prevent the particles from being crushed when the spray particles collide with the base material surface during spraying. , For that purpose, it is necessary to reduce the energy given at the time of thermal spraying so that the thermal spray particles do not completely melt,
In that case, as described above, the bonding force between the particles becomes small and pores are easily generated between the particles, so that the machinability becomes good.

On the other hand, in the layer (base layer) on the side of the thermal spray coating that is in contact with the interface with the base material, the flatness of the dispersed soft non-metal particles is large, and such a base layer has high adhesion to the base material. That is, in order to form a base layer in which particles of a soft non-metallic material having a large flatness ratio are dispersed, it is necessary to flatten the particles when the sprayed particles collide with the surface of the base material during spraying. The particles to be collided with the surface of the base material during thermal spraying are sufficiently melted and it is necessary to make the particles collide at a high thermal spraying rate. In this case, the base layer becomes a dense layer and the adhesion to the base material becomes high, Further, in this case, since the sprayed particles are kept at a high temperature, the wettability with the base material becomes good, which also contributes to the improvement of the adhesion with the base material.

As described above, according to the second aspect of the invention, the flattening ratio of the soft non-metallic material particles dispersed in the thermal spray coating is changed in the thickness direction to reduce the initial cutting resistance when the mating material rotates. At the same time, the adhesion to the base material can be improved.

Here, as the soft non-metallic material particles dispersed in the thermal spray coating, a resin such as polyester or graphite can be used. Further, as the soft metal material serving as the base, an Al alloy, a Ni alloy, or the like can be used.

In order to change the particle size of the soft non-metallic material particles in the thickness direction of the thermal spray coating in the invention of claim 1, the particle size of the thermal spray particles at the time of thermal spraying may be changed. The particle size of soft non-metallic material particles in the layer is 150 to 2
It is preferable that the soft nonmetallic material particles in the base layer near the interface with the base material have a diameter of about 10 to 50 μm, and the particle diameter changes stepwise or continuously between them.

On the other hand, in the invention of claim 2, in order to change the flatness of the soft non-metallic material particles in the thickness direction of the sprayed coating, in the case of plasma spraying, the spraying current and / or the amount of plasma gas may be changed. That is, the spray current and / or plasma gas amount is increased in the initial stage of the spraying start, and the spray current and / or plasma gas amount is reduced in the final stage, while the spray current and / or plasma gas amount is increased stepwise or continuously. You can reduce it.

Examples Examples and comparative examples in which the present invention is applied to a compressor housing of an automobile turbocharger will be described below. In each of the examples and comparative examples, polyester was used as the soft non-metal material and aluminum-silicon alloy (Al-12 wt% Si) was used as the soft metal material.

[Embodiment 1] As shown in FIGS. 1 to 3, among the air flow portions of the compressor housing 5 made of an aluminum alloy casting, particularly the portion facing the tip of the impeller 4 as a mating member (the gap between the impeller and the impeller 4). Is 0.4mm) and Al-
Polyester particles 8 are dispersed in the 12 wt% Si alloy phase 7.
The sprayed coating 6 having a thickness of 0.5 mm was formed so that the particle size of the polyester particles 8 changed in the thickness direction as shown in FIG.
The detailed process conditions are as follows.

First, the compressor housing 5 which is the base material is washed with trichlene, and then the surface of the portion where the sprayed coating 6 is to be formed is shot blasted using an Al ₂ O ₃ sintering grid, and the surface roughness is about 25 to 60 μmRz. And
Next, using a plasma spraying apparatus, preheat to about 100 to 150 ° C. at a current of 400 A, an Ar gas flow rate of 69 / min, and an H ₂ gas flow rate of 2 / min, and subsequently 60 wt% (Al-12 wt.
% Si) -40 wt% polyester was used for thermal spraying, the particle size of the thermal spraying material powder was changed as follows. That is, at the start of thermal spraying, use a powder with a particle size within the range of 10 to 50 μm, and then increase the particle size with time, and at the end of thermal spraying, that is, when the thickness of the sprayed coating is close to 0.5 mm, The diameter was set to 150 to 200 μm. The current during spraying was 400 A, Ar gas flow rate 90 / min, H ₂
The gas flow rate was 2 / min.

When the obtained thermal spray coating was examined, the size of the polyester particles dispersed in the thermal spray coating was 150-150 near the surface.
It was found to be 200 μm, and the grain size gradually decreased toward the base metal side, and it became clear that it was 10 to 50 μm near the interface with the base metal.

[Example 2] In the same manner as in Example 1, in forming the thermal spray coating 6 on the compressor housing 5, cleaning, shot blasting, and preheating were performed in the same manner as in Example 1, and then 60 wt% (Al-12wt) as a thermal spray material. % Si) -40 wt% Polyester having a particle diameter of 50 to 150 μm and having a constant spray powder, a spray coating 6 in which the flatness of the polyester particles 8 changes in the thickness direction was formed by plasma spray as shown in FIG. The conditions for thermal spraying are as follows.

At the initial stage of thermal spraying, that is, at the stage of forming the thermal spray coating on the side close to the base metal, the current is 600 A and the Ar gas flow rate is 100
/ Min, H ₂ gas flow rate is 2.5 / min, and then the current and gas flow rates are gradually reduced, and the current is 350 A, A at the final stage of spraying, that is, the step of forming the outermost surface layer of the sprayed layer
The r gas flow rate was 85 / min and the H ₂ gas flow rate was 1.5 / min.
The control of the spraying conditions is performed for the purpose of gradually reducing the energy given to the sprayed powder particles and the velocity during flight.

Examination of the obtained thermal spray coating revealed that the flatness of the polyester particles 8 dispersed in the thermal spray coating 6 is small on the surface and large on the base material interface side as shown in FIG. . Here, if the flatness ratio F is expressed as F = {(a−b) / a} × 100 (%) using a and b of FIG. 5, the flatness ratio F is about 20 to 30% on the surface, Near the interface with the material,
It was confirmed that it was close to 100%.

[Comparative Example 1] In the same manner as in Example 1, when forming a thermal spray coating on the compressor housing, the particle size of the thermal spray powder was 50 to 150.
A thermal spray coating was formed under the same conditions as in Example 1 except that a film having a constant μm was used. In this case, the diameter of the polyester particles in the thermal spray coating was about 50 to 150 μm, which was almost constant.

[Comparative Example 2] In the same manner as in Example 2, in forming the thermal spray coating on the compressor housing, the thermal spray conditions were set to a current value of 500 A, A
A thermal spray coating was formed under the same conditions as in Example 2 except that the flow rate of r gas was 90 / min and the flow rate of H ₂ gas was 2 / min. In this case, the flatness F of the polyester particles in the thermal spray coating was about 40 to 50%, which was almost constant.

[Performance Evaluation 1] The compressor housings having the sprayed coatings formed in Examples 1 and 2 and Comparative Examples 1 and 2 were incorporated into actual turbochargers, and the impeller speed was 150,000r.
After operating for 180 minutes at pm, the degree of improvement in turbo efficiency (compressor efficiency) (the degree of improvement compared to the case where no sprayed coating was formed) was examined.

As a result, in each of the compressor housings of Example 1 and Example 2, it was confirmed that the turbo efficiency was improved by 3 to 4%. On the other hand, in the compressor housings of Comparative Example 1 and Comparative Example 2, it was found that the impeller was difficult to rotate in the initial stage and the turbo efficiency was reduced by 0.5 to 1.0% during the initial 50 hours.
After that, in the compressor housings of Comparative Examples 1 and 2,
It was observed that the turbo efficiency was improved by 2 to 3% with the decrease rate.

After the above-mentioned operation test, the surface of the sprayed coating and the surface of the impeller were observed, and in Examples 1 and 2, there was some abnormal normal wear surface, but in Comparative Examples 1 and 2, some sliding scratches were found on the impeller. Admitted.

Here, in any of the Examples and Comparative Examples, the clearance between the compressor housing and the impeller is
A sprayed coating with a thickness of 0.5 mm is formed with respect to the design value of 0.4 mm, and proper clearance can be obtained by scraping the surface layer of the sprayed coating in the initial stage of rotation of the impeller. Therefore, the load on the rotation of the impeller is the maximum at the initial stage, and if the clearance is gradually secured and the impeller contacts the sprayed coating only locally, the load becomes smaller. The thermal spray coating of Comparative Example 1 is in a state where the diameter of the polyester particles in the surface layer, that is, the portion to be initially shaved, is relatively small, that is, in a dense state. The flatness ratio is relatively large, that is, the binding force to the polyester particles is large.Therefore, the cutting resistance is large because the machinability of the surface layer is poor, and an excessive load is applied to the impeller at the initial stage of rotation, which causes rotation. It is probable that it was difficult to do so, the turbo efficiency became low, and that the impeller suffered sliding damage. On the other hand, in the thermal spray coating of Example 1, the particle size of the polyester particles of the surface layer that was initially shaved was large, and in Example 2
In the case of the thermal spray coating, the surface layer has a small flatness of the polyester particles, that is, the polyester particles are in an unmelted state and are not sufficiently fixed to the surrounding Al-12 wt% Si alloy. Is brittle and has good machinability, it is considered that, as described above, high turbo efficiency was obtained without impeding the rotation of the impeller even at the initial stage of rotation of the impeller, and sliding scratches did not occur.

[Comparative Example 3] In the same manner as in Example 1, when forming a thermal spray coating on the compressor housing, a particle size of 150 to 250 was obtained as the thermal spray powder.
A thermal spray coating was formed under the same conditions as in Example 1 except that a film having a constant μm was used. In this case, the diameter of the polyester particles in the thermal spray coating is about 150 to 250 μm, and the entire thermal spray coating is in a brittle state.

[Comparative Example 4] In the same manner as in Example 2, in forming the thermal spray coating on the compressor housing, the thermal spray conditions were set to a current of 350 A and Ar.
A thermal spray coating was formed under the same conditions as in Example 1 except that the gas flow rate was 85 / min and the H ₂ gas flow rate was 1.5 / min. In this case, the flatness F of the polyester particles in the thermal spray coating is approximately constant at about 10 to 20%, and the structure is brittle as a whole.

[Performance Evaluation 2] The compressor housings of Examples 1 and 2 and Comparative Examples 3 and 4 were subjected to an operation test using the same actual turbocharger as in Performance Evaluation 1.

As a result, in the cases of Comparative Examples 3 and 4, the initial 1 to 2
Since the compressor efficiency drastically decreased in time, the operation was stopped and the compressor housing was examined. As a result, it was confirmed that there was a part where the sprayed coating was peeled off. On the other hand, in the case of Examples 1 and 2, such peeling did not occur until the end of the operation for 180 hours, and the turbo efficiency did not decrease.

Adhesion to the base material of the sprayed coating of Comparative Examples 3 and 4 reduced the 0.2~0.5kgf / mm ² were examined by the shear test, the thermal spray coating of Examples 1 and 2 In contrast to this,. 1 to 2 kgf / mm ² It was confirmed to be big. From this, Comparative Examples 3 and 4
If the entire thermal spray coating has a fragile structure as described above, the adhesion with the base material will deteriorate, and local peeling will occur during operation, and the air flow will be disturbed from that part as the starting point and the compressor efficiency will drop sharply. found. On the other hand, in Examples 1 and 2, the portion of the thermal spray coating that is in contact with the base material is dense and has high adhesion to the base material. Therefore, the thermal spray coating does not peel during operation, and the compressor efficiency does not drop sharply.

[Example 3] In the same manner as in Example 1, in forming the thermal spray coating on the compressor housing, the initial particle size at the start of thermal spray was set to 0 to 10µ.
The particle size was changed in the thickness direction in the same manner as in Example 1 except that the particle size was less than m.

[Performance Evaluation 3] The compressor housings of Example 1 and Example 3 were each incorporated in an actual turbocharger, and a long-term durability evaluation test was performed at an impeller rotation speed of 150,000 rpm for 2000 hours. In this case, as a messy evaluation, a test was conducted with play between the impeller shaft and the bearing during assembly.

As a result, in Example 3, a slight decrease in efficiency was observed after 1500 hours. This is because in the evaluation test in this case, the amount of the thermal spray coating scraped off is large because it gives play to the impeller, so after 1500 hours, the base layer portion on the side close to the base metal of the thermal spray coating, that is, the initial thermal spray portion However, in the case of Example 3, the diameter of the polyester particles in the initial sprayed portion (base layer) is remarkably small, and since that portion is a remarkably dense and hard layer, the work resistance is high and the spraying is high. It was found that the coating was in a state in which it was difficult to scrape, and the efficiency fell due to deformation of the impeller when the base layer portion was cut after 1500 hours. In the case of Example 1, no abnormality occurred until the end of the test.

From such an evaluation test, even when changing the diameter of the polyester particles in the thickness direction of the thermal spray coating, in order to obtain a stable and high efficiency for a long period of time, it seems that the cutting resistance does not become excessively large even in the initial thermal spray portion. In addition, it is understood that it is preferable that the diameter of the dispersed soft non-metal particles is at least 10 μm or more.

EFFECTS OF THE INVENTION As is clear from the above-mentioned examples, the spray coating for gap control of the present invention has good machinability of the surface layer and does not give an unreasonable load to cutting by the mating member. Moreover, it has excellent adhesion to the base material. Therefore, even in applications such as racing turbochargers where the mating member rotates at an ultra-high speed, the mating member may not rotate smoothly due to the cutting resistance at the initial stage of the mating member rotating at an ultra-high speed, or the mating member may not rotate smoothly. It does not cause local damage, and there is very little risk that the thermal spray coating will peel off due to the shearing force of the mating member.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an example in which the thermal spray coating of the present invention is applied to a compressor housing of a turbocharger for automobiles, and FIG. 2 is the thermal spray coating of the present invention cut by a mating member (in this case, an impeller). An enlarged cross-sectional view schematically showing the situation, FIG. 3 is an enlarged cross-sectional view schematically showing an example of the structure of the sprayed coating of the invention of claim 1, and FIG. 4 is a schematic example of the structure of the invention of claim 2. 5 is an enlarged sectional view schematically showing
FIG. 6 is a schematic diagram for explaining the aspect ratio in the invention of claim 2, and FIG. 6 is a sectional view showing an example of a turbocharger for an automobile to which the invention is applied. 4 ... Impeller (counterpart member), 5 ... Compressor housing (base material), 6 ... Thermal spray coating, 7 ... Al-12
wt% Si alloy phase (soft metal material), 8 ... Polyester particles (soft non-metal material particles).

Claims (2)

[Claims] Claim: What is claimed is: 1. A soft thermal spray coating formed on the surface of a base material at a portion facing a rotating mating member, wherein the gap between the mating member is adjusted by cutting the surface layer by rotating the mating member. In the spray coating for gap control, the soft non-metallic material particles are dispersed in the soft metal material, and the particle size of the soft non-metallic material particles increases from the interface side with the base metal toward the coating surface. A spray coating for gap control, which is characterized in that 2. A soft thermal spray coating formed on the surface of a base material at a portion facing a rotating mating member, and the clearance between the mating member is adjusted by cutting the surface layer by rotating the mating member. In the spray coating for gap control, the soft non-metallic material particles are dispersed in the soft metallic material.
A spray coating for gap control, characterized in that the flatness of the soft non-metallic material particles is increased from the surface of the coating toward the interface with the base material.