JPH0533601A - Method for manufacturing ceramic turbo rotor - Google Patents

Abstract

(57) [Summary] [Purpose] To enhance the strength of the blade part and the root part of the gas outlet side of the hub part, which is the high stress part of the ceramic turbo rotor, the defect due to falling out and the low density due to defective air release in the cavity The part of is processed and removed so that it can withstand high rotation. [Structure] Wing portion 3 and hub portion 2 of ceramic turbo rotor
After firing the molded body, the root portion 5 of the gas outlet side is processed and removed from the root of the burr generated by the mold matching surface to a depth of more than half of the width of the burr, and the surface roughness is 5 μmRm.
It is set to ax or less. Further, 200 μm or more is removed from the root of the burr generated by the chamfered shape of the mold matching portion, and the surface roughness is set to 5 μm Rmax or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbocharger (hereinafter abbreviated as "turbo") used by connecting to an exhaust system of an internal combustion engine.
The present invention relates to a method for manufacturing a ceramic turbo rotor, and more particularly to a ceramic turbo rotor having high strength capable of withstanding high speed rotation.

[0002]

2. Description of the Related Art Ceramic materials such as silicon nitride, sialon, and silicon carbide have excellent heat resistance and thermal shock resistance, and ceramic turbo rotors using them have been actively developed. Since the turbo rotor rotates at high speed, it is known that high stress due to centrifugal force acts on the shaft root.
The shaft root refers to a joint between the shaft and the hub. Therefore, in Japanese Unexamined Patent Publication No. Sho 61-226501, the R shape of the shaft root portion and the surface roughness of the shaft root portion and the shaft portion are regulated to alleviate stress concentration on this portion and withstand high speed rotation. Disclosed is a technique for obtaining the information. That is,
The stress can be reduced by the shape.

[0003]

The present inventor conducted a stress analysis by the finite element method (FEM) in order to develop a ceramic turbo rotor capable of withstanding higher speed rotation. The result is shown in FIG. The thick lines in the figure are iso-stress lines. The number is an index showing the magnitude of stress due to centrifugal force,
The larger the number is, the higher the stress is. From this figure, it was found that the root portion of the blade (here, the joint portion between the blade portion and the hub portion refers to the root portion on the gas outlet side) is subjected to a higher stress than the shaft root portion. Therefore, it has been recognized that it is necessary to make the shaft root part capable of withstanding high stress.

For example, a method of reducing the stress by reducing the blade thickness to reduce the centrifugal force can be considered.
However, with this method, since the blade thickness is thin, the chipping resistance due to foreign matter collision is poor, and reliability cannot be ensured.

It is also conceivable to increase the R shape in the same manner as in the shaft root of the prior art to reduce the stress concentration at the root. But for the wing root,
A large R shape cannot withstand high stress for the reasons described below. That is, the blade shape of the ceramic turbo rotor is complicated, and it is manufactured by dividing the mold into a number corresponding to the number of blades. Therefore, a parting surface of the mold is required at the root of the blade, and burrs are generated from this parting surface. Then, the burrs are dropped or chipped to become defects, which serve as the starting points of cracks and reduce the strength. Further, although the air in the cavity escapes from the parting surface, if the air is not sufficiently escaped, the air remains in the powder compact near the burr, resulting in a non-dense portion. Since this low-density portion has low strength, it also causes a decrease in strength. For these reasons, even if the R shape is made large, it is not possible to withstand high stress as long as there is burr and its influence.

There is also a method of eliminating the influence of the burr by removing the burr and the vicinity of the burr by processing at the stage of the molded body.
However, since it is not as strong as the sintered body at the stage of the molded body, even if it is possible to eliminate the influence of burrs, conversely, notch scratches due to processing are likely to occur. Therefore, due to stress concentration, the processing scratch becomes a starting point of a crack, and it is still impossible to endure high stress.

Therefore, an object of the present invention is to increase the strength of the ceramic turbo rotor by eliminating the factor of lowering the strength of the blade root.

[0008]

In order to obtain a ceramic turbo rotor capable of withstanding a high rotation speed, the present inventor considers that it is necessary to increase the strength of the blade root.
The present invention has been completed by studying the effects of burrs on the blade roots and the vicinity of the burrs.

That is, according to the first invention, a ceramic turbo rotor comprising a shaft portion, an umbrella-shaped hub portion connected to the shaft portion, and a blade portion connected to the hub portion is divided into a plurality of parts.
At least a joining portion of the wing portion and the umbrella-shaped hub portion is molded into a turbo rotor-shaped molded body by molding powder with a mold having a parting surface at the base portion on the side where the diameter of the umbrella becomes smaller, and the molded body is fired. In the method for manufacturing a ceramic turbo rotor according to claim 1, after firing the molded body, the root portion is at least half the width of the burr from the root portion of the first burr generated by the joining part of the parting surfaces of the mold. The problem described above is solved by a method for manufacturing a ceramic turbo rotor, which is characterized in that the surface roughness is Rmax of 5 μm or less by processing and removing to the depth of.

In a second aspect of the present invention, a ceramic turbo rotor comprising a shaft portion, an umbrella-shaped hub portion connected to the shaft portion, and a blade portion connected to the hub portion is divided into a plurality of parts, and at least the ceramic turbo rotor is divided into a plurality of parts. Among the joints of the blade portion and the umbrella-shaped hub portion, powder is molded with a mold having a parting surface at the base portion on the side where the diameter of the umbrella becomes smaller to form a turbo rotor-shaped molded body, and the molded body is fired. In the manufacturing method of the ceramic turbo rotor
After firing the molded body, the root portion is generated by at least the chamfered shape of the intersection between the surface defining the product shape of the mold and the parting surface of the mold, and the base portion of the second burr protruding from the product shape. It is intended to solve the above-mentioned problems by a method for manufacturing a ceramic turbo rotor, characterized in that the surface roughness is Rmax 5 μm or less by processing and removing to a depth of 200 μm or more.

The burr includes a first burr and a second burr.
Explaining with reference to FIG. 2, as shown in FIG. 2A, the first burr 6 is generated by the ceramic powder to be molded entering the mating portion of the parting surface of the mold. . The second burr 7 has a shape of the ridge line at the intersection of the cavity surface forming the product shape and the parting surface of the mold, and the intentional chamfering process at the time of manufacturing the mold and the molding of the ceramic powder are repeated. The chamfered shape is formed by rounding due to wear and the like. When the molds having such a shape are matched, a mountain-shaped recess is formed. The second burr 7 is generated by the ceramic powder entering this portion.

The first burr 6 has a width of about 20 μm in a normal die manufacturing accuracy. The width of the second burr 7 is usually larger than that of the first burr 6, and the second burr 7
The first burr 6 is further formed on the top of the normal molded body. If the first burr 6 falls off, a recess is formed to a depth of about half the width of the first burr 6, and this can be the starting point of a crack. Therefore, it is necessary to remove from the root portion of the first burr 6 to at least a depth equal to or greater than the depth of the depression. Therefore, in the first invention, it is decided to process and remove from the root portion of the first burr to a depth of at least half the width of the burr.

As described above, the vicinity of the second burr 7 has a non-dense portion, but according to the research by the present inventor, the depth is about 200 μm from the base 9 of the second burr 7. is there. And, in the case of a usual method for manufacturing a molded body, this depth does not increase any more even if the size of the product or the size of the second burr 7 changes. This is because when the product or the burr is large, the air easily escapes, and the proportion of the air left in the mold is small. On the other hand, when the product or the burr is small, the air is difficult to escape and a large proportion is left. However, there is no big difference in the absolute amount regardless of the size of the product or the burr, and as a result, the depth of the non-dense portion is the same from the base 9 of the second burr 7 to about 200 μm. It becomes. Therefore,
By processing and removing 200 μm or more, the non-dense portion having weak strength is removed. The second burr 7 may fall off as shown in FIG. 2B, and the larger the burr, the larger the depression. However, the larger the size, the more difficult it is to drop off. Therefore, at least 200 μm or more is sufficient to eliminate the influence of the falling off part.

Further, even if a crack is generated in the root portion 9 of the second burr 7, it is effective to remove it by processing, but a large crack having a depth of 200 μm or more can be visually observed and a defective product. Can be removed as On the other hand, in the case of a crack smaller than this, it cannot be found without using inspection means such as fluorescent flaw detection. Therefore, since it is only necessary to perform processing removal for a product in which cracks cannot be observed with the naked eye, it was decided to perform processing removal of 200 μm or more in the second invention.

The reason why the surface roughness of the machined portion is set to 5 μm Rmax or less is that if the surface roughness is less than 5 μm, stress will be concentrated on the processing scratches, which will cause a crack to start, and even if the effect of burrs is removed by the processing, the strength of This is because no improvement is seen and the strength is rather reduced. If the surface roughness is preferably 3 μmRmax or less, the strength is further improved.

[0016]

In the vicinity of the burr generated at the blade root portion of the ceramic turbo rotor molding, a notch defect occurs due to the burr falling off. Further, even if it does not fall off, the air in the cavity near the burr does not completely escape and tends to remain in the molded body, so that it is not dense and has low strength, which is a starting point of fracture. The root of the wing is a part where high stress acts, so its influence is great. Therefore, in the first invention, the vicinity of the burr is processed and removed after firing, and the surface roughness is regulated to 5 μmRmax or less, thereby removing the dent caused by the first burr detachment which becomes the starting point of the fracture and stress concentration due to the processing scratch. Has a high strength. Further, in the second invention, even higher strength can be obtained by removing a portion which is not dense and has low strength in the vicinity of the burr, removal of the dent due to the second burr dropping, and reduction of stress concentration due to processing scratches. .

[0017]

EXAMPLES The present invention will be described in more detail with reference to examples. 3 wt% each of yttria and spinel was added to the silicon nitride powder as a sintering aid, and wet mixing was performed for 24 hours in a ball mill. Next, after drying at 150 ° C., 16 wt% of an organic binder was added to the ceramic powder, and kneading was performed at 150 ° C. with a kneader to form injection molding pellets.
Next, the pellets were used to form a turbine rotor shape by injection molding. 1 in the oven
Degreasing was performed by heating to 500 ° C. at a temperature rising rate of ˜5 ° C./H. Next, it was set in a silicon nitride sheath (cylindrical case) and sintered at 1800 ° C. for 4 hours in a nitrogen atmosphere. A cross-sectional view of the ceramic turbo rotor thus obtained is shown in FIG. In this ceramic turbo rotor, the large diameter side of the shaft portion 1 and the umbrella-shaped hub portion 2 are connected. A plurality of blades 3 are connected to the tapered surface of the umbrella-shaped hub 2. Although not shown, the tip of the wing portion 3 is usually twisted. The connecting portion between the large diameter side of the umbrella-shaped hub portion 2 and the shaft portion 1 is the shaft root portion 4. In addition, the connecting portion between the small diameter side of the umbrella-shaped hub portion 2 and the blade portion 3 is the shaft root portion 5.

Observing the cross section of the blade root after firing,
As shown in FIGS. 2 (a) and 2 (b), there were a portion where burr was generated and remained, and a portion where the burr fell off and became a depression. FIG. 4 is a photograph showing a crystal structure of a blade section of a rotor, which was destroyed by cracking from the second burr drop-off portion without machining and removing the vicinity of the burr as in the present invention. It is shown that there are minute cavities in the vicinity of the burr due to defective air removal in the cavity, and it is not dense.

Therefore, the blade root portion 5 on which high stress acts
Then, a super finishing process was performed by pressing a grindstone as shown in FIG. In this embodiment, since the # 2000 grindstone was used for superfinishing, the surface roughness after processing was 1 μm.
It was Rmax. A schematic view of the cross-sectional shape of the root portion of the blade after processing is shown in FIG. In this embodiment, t = 70 μm from the root portion 9 of the second burr (90 μm from the first burr root).
m) Processing removal was performed to remove the effect of burrs.

The strength of the blade root portion of the fired body thus obtained after processing was determined by a method of pressing the load pin 13 against the blade and applying a load to examine the breaking load as shown in FIG. The relationship between the surface roughness of the machined surface and the blade breaking load was examined by this evaluation method, and the results are shown in FIG. When the surface roughness is 6 μmRmax, the strength is lower than the unmachined strength when the vicinity of the burr is not processed and removed, and the strength is improved by setting the surface roughness to 5 μmRmax or less. In this embodiment, since the surface roughness is 1 μmRmax,
A blade breaking load of 175 kgf and a raw strength of 75 k
The strength was greatly improved compared to gf. Also, t = 220
When the processing removal of μm was performed, the variation in strength decreased and the average strength increased to 180 kgf.

As described above, a large strength improving effect was obtained under static load. Therefore, in order to investigate the dynamic strength when actually rotating, a hot spin test (forced under severe conditions) was performed at 950 ° C. Destruction test) was performed and the number of revolutions of destruction was examined. As a result, 20
While destroyed in × 10 ⁴ rpm, the present example was a 24 × 10 ⁴ rpm. That is, according to the present invention, the improvement in strength capable of withstanding a high rotation speed was recognized.

By the way, when a fired body is manufactured, a layer called a fired alteration layer may occur near the surface of the fired body depending on the firing atmosphere. This is because the concentration of the auxiliary component in the surface layer of the burned surface of the fired body changed depending on the magnitude of the vapor pressure of the sintering auxiliary component in the atmosphere. When the concentration of the auxiliary component in the atmosphere is low, the auxiliary component evaporates from the surface layer of the burnt skin to lower the component concentration. Conversely, when the concentration of the auxiliary component in the atmosphere is high, the concentration of the component of the burnt surface layer is high. Goes up. When the amount of the auxiliary component is small as in the former case, the densification of the surface layer does not proceed sufficiently and the room temperature strength decreases. On the other hand, when the amount of the auxiliary component is large, the amount of the grain boundary phase is large and the high temperature strength is lowered.

In the present embodiment, the molded body is housed in a cylindrical cylinder made of silicon nitride, called a sheath, and fired. By changing the material of this sheath, one of the auxiliary component elements, Al
The element distribution in the blade cross section of No. 1 was investigated by EPMA line analysis. The result is shown in FIG. FIG. 8A shows the case where a pressureless sintered silicon nitride sintered body containing a large amount of an auxiliary agent is used as a sheath.
FIG. 8B shows the case where the reaction-sintered silicon nitride sintered body containing less auxiliary agent is used. In the former, the amount of the auxiliary component is increased up to about 200 μm from the surface, and in the latter, on the contrary, about 10 μm.
It is reduced to about 0 μm. In this example, since the reaction-sintered silicon nitride was used, the auxiliary component concentration in the burnt surface layer was low as shown in FIG. 8 (b).

These abnormal layers with altered firing can be prevented to some extent by strictly controlling the firing atmosphere.
However, the equipment and conditions therefor become extremely strict, which makes it practically difficult. Therefore, although the formation of the abnormal layer by firing is unavoidable to some extent, the depth thereof is up to about 200 μm under the usual firing equipment and conditions. Therefore, by processing removal for removing the effect of burrs as in the second invention, it is possible to simultaneously process and remove the fired altered layer.
It can greatly contribute to the improvement of strength.

As described in the above embodiments, in this embodiment, the factors that reduce the strength near the burr are removed by machining, so the blade breaking load is improved and the dynamic strength by the hot spin test is also improved. Improved. In addition, the abnormal layer with altered calcination generated under normal calcination conditions can be removed at the same time, which further has the effect of improving strength.

[0026]

As described above, the present invention processes and removes notch defects due to burrs falling off at the blade roots, which are high stress parts of ceramic turbo rotors, and low density parts due to defective air removal from the burrs into the cavity. By doing so, the starting point of destruction can be removed. Further, by defining the surface roughness of the machined surface to be 5 μmRmax or less, it is possible to reduce the stress concentration on the machining scratches. From the above,
The strength of the blade root of the ceramic turbo rotor is improved to withstand high rotation, and the turbo performance is improved. Further, the performance of the turbo can be improved without changing the shape of the ceramic turbo rotor. Further, it is possible to obtain a product having a constant strength regardless of variations in quality of the molded product, particularly defects near the burr.

[Brief description of drawings]

FIG. 1 is a sectional view showing the shape of an embodiment of a ceramic turbo rotor of the present invention.

FIG. 2 is a schematic view of a partial cross section showing a burr shape of a blade root portion of the example.

FIG. 3 is a schematic view of a partial cross section showing a shape after processing and removing a burr-affected portion of a blade root portion of an example.

FIG. 4 is a photomicrograph (600 times) showing a crystal structure of a conventional second flash dropout portion.

FIG. 5 is an explanatory view showing a method of processing a wing root portion of the embodiment.

FIG. 6 is an explanatory view showing a method of measuring the strength of the wing root portion of the example.

FIG. 7 is a graph showing the relationship between the surface roughness of the machined surface and the breaking load of the blade root portion of the example.

FIG. 8 is a graph showing the results of examining the element distribution on the blade section of the example by EPMA line analysis.

FIG. 9 shows a ceramic turbo rotor having the shape of the embodiment
It is a graph which shows the result of having stress-analyzed by EM.

[Explanation of symbols]

1 ... Shaft 2 ... Hub 3 ... Wing 4 ... Root of shaft 5: Wing root 6 ... the first burr 7 ... second burr 8: First burr base 9 ... Second burr base 10-Second burr dropout part 11 ... Whetstone 12-chuck 13 ... Load pins

Claims (2)

[Claims] 1. A ceramic turbo rotor comprising a shaft portion, an umbrella-shaped hub portion connected to the shaft portion, and a blade portion connected to the hub portion is divided into a plurality of parts, and at least the blade portion and the umbrella-shaped rotor portion are provided. Of the joined portion of the hub portion, the powder is molded with a mold having a parting surface at the base portion on the side where the diameter of the umbrella becomes smaller to form a turbo rotor-shaped molded body, and the molded body is fired to produce a ceramic turbo rotor. In the manufacturing method, after firing the molded body, the root portion, at least from the root portion of the first burr generated by the mating portion of the parting surface of the mold, processed and removed to a depth of half or more of the width of the burr,
A method for manufacturing a ceramic turbo rotor, characterized in that the surface roughness is set to Rmax 5 μm or less. 2. A ceramic turbo rotor composed of a shaft portion, an umbrella-shaped hub portion connected to the shaft portion, and a blade portion connected to the hub portion is divided into a plurality of parts, and at least the blade portion and the umbrella-shaped rotor portion are formed. Of the joined portion of the hub portion, the powder is molded with a mold having a parting surface at the base portion on the side where the diameter of the umbrella becomes smaller to form a turbo rotor-shaped molded body, and the molded body is fired to produce a ceramic turbo rotor. In the manufacturing method, after the molded body is fired, the root is formed by at least the chamfered shape of the intersection of the surface defining the product shape of the mold and the parting surface of the mold. A method for manufacturing a ceramic turbo rotor, characterized in that the surface roughness is Rmax 5 μm or less by processing and removing from the root of the burr to a depth of 200 μm or more.