JP4596537B2 - Exhaust system turbine housing manufacturing method and exhaust system turbine housing using the same - Google Patents

Description

  The present invention relates to an exhaust system turbine housing such as a turbocharger having an aerodynamic spiral scroll portion that uses exhaust gas from an internal combustion engine, and a method for manufacturing the same.

Regulations on the emission of particulate matter (PM) or nitrogen oxides (NOx) that cause air pollution and the emission of CO ₂ directly linked to global warming are expected to become increasingly severe in the future. In order to cope with such regulations, for example, in an internal combustion engine such as an automobile engine, in connection with purifying exhaust gas and improving fuel efficiency, further increase in combustion efficiency, lower heat capacity, or weight reduction of exhaust system parts. Such technical improvements are desired.

  For example, a turbocharger incorporated in an engine of an automobile or the like applies exhaust gas discharged from an exhaust pipe to a turbine blade and rotates the turbine blade at a high speed of about 200,000 revolutions per minute, thereby increasing the intake pressure to the engine. This is an exhaust system component that dramatically improves the combustion efficiency and output of the engine. The turbocharger includes a turbine housing that contains turbine blades. The turbine housing has a scroll portion having an aerodynamic spiral for ejecting exhaust gas uniformly and at high speed. The scroll portion of the turbine housing is a flow path for flowing exhaust gas from the intake port to the exhaust port of the turbine housing, and the surface shape such as the surface roughness and unevenness of the inner wall of the scroll portion affects the flow of the exhaust gas. Will be affected. In particular, the smaller the surface roughness of the inner wall of the scroll portion, the lower the flow resistance of the exhaust gas, thereby suppressing a decrease in the flow rate of the exhaust gas passing through the scroll portion, and promoting higher combustion efficiency of the turbocharger.

  In order to clean the exhaust gas, it is important to quickly bring the temperature of the turbine housing to the catalyst activation temperature of 300 ° C., that is, to increase the temperature rise rate of the turbine housing. In order to improve the temperature raising rate, it is effective to reduce the heat capacity. For this purpose, it is preferable to reduce the weight of the turbine housing. In particular, reducing the thickness of the scroll portion, which is a flow path for the exhaust gas, is effective because the heat capacity of the scroll portion itself can be reduced and heat removal from the exhaust gas can be suppressed. And the weight reduction of the turbine housing which is a heavy article among turbocharger parts leads to an improvement in fuel consumption.

  As one of the means for solving the above-mentioned problems, the applicant of this patent proposed a manufacturing technique by the lost wax casting method shown in Patent Document 1, and impregnated the surface with colloidal silica or the like as a specific preferable technique. A special fireproof core is proposed as a casting core. As described in Patent Document 1, the method of using this special refractory core as a casting core is excellent in shape retention and removability after casting, and there is a problem in manufacturability for the vanishing model itself. It has been considered to be an advantageous means for a method using a water-soluble core, which is considered to be, or a method using a ceramic core having a problem in removability after casting as a casting core.

JP 2003-56354 A

The present inventor has studied an exhaust system turbine housing effective for further lowering heat capacity and higher combustion efficiency using the above-described casting core disclosed in Patent Document 1. In the examination process, when the casting core proposed in Patent Document 1 is used, it is difficult to make the surface shape a smooth curved surface and reduce the surface roughness on the inner wall of the scroll portion of the exhaust system turbine housing. There has occurred.
In pursuit of the cause, in Patent Document 1, it was considered that the most important scroll inner wall transferred the impregnated surface of the casting core. In the casting core in which the surface is impregnated with a refractory, it is difficult to smooth the surface of the casting core itself with high accuracy.

  The object of the present invention is to effectively reduce the heat capacity and increase the combustion efficiency by providing a surface shape with a small surface roughness and a smooth curved surface on the inner wall of the scroll portion, which is the casting surface of the exhaust system turbine housing. A novel exhaust system turbine housing and a method of manufacturing the same.

  As a result of studying the manufacturing technology of the exhaust system turbine housing in view of the above problems, the present inventor has previously used a water-soluble core or the like that has been considered to have a problem in manufacturability without using a casting core. By optimizing the method to obtain a highly accurate vanishing model, the surface roughness of the inner wall of the scroll part, which is the casting surface, can be reduced, and the surface shape can be made a smooth curved surface. I came up with the invention.

That is, the method of manufacturing an exhaust system turbine housing according to the present invention includes a scroll part having an aerodynamic spiral continuing from an intake port, and an exhaust port arranged at the center of the spiral of the scroll part. A method of manufacturing an exhaust system turbine housing in which the surface roughness of the inner wall of the scroll portion is 5 μm or less in Ra,
(1) A step of forming a turbine housing vanishing model having substantially the same shape as the exhaust system turbine housing;
(2) Mold forming step for eliminating and removing the turbine housing disappearance model after coating the turbine housing disappearance model with a refractory;
(3) a casting process for casting into the mold;
The turbine housing vanishing model has a shape corresponding to the space inside the scroll part, and after forming a core having a surface roughness Ra of 1 μm or less with a core-forming vanishing material, By placing the core in a mold and injecting a vanishing material for forming a turbine housing to obtain a molded body containing the core, and then removing the core-forming vanishing material from the molded body by removing the core. An exhaust system turbine housing manufacturing method obtained by removing a core.

  In the production method of the present invention, it is preferable to use a mold having a surface roughness Ra of 4 μm or less corresponding to the inner wall of the scroll portion. The mold can be formed by coating a plurality of laminated refractory layers with a slurry having an average particle size of 350 μm or less and a stucco having an average particle size of 1500 μm or less.

  By the above-described method for manufacturing an exhaust system turbine housing, a scroll portion having an aerodynamic vortex continuing from an intake port and an exhaust port disposed at the vortex center of the scroll portion, and an inner wall of the scroll portion which is a casting surface A new exhaust system turbine housing having a surface roughness Ra of 5 μm or less can be obtained.

  In the exhaust system turbine housing of the present invention, the minimum thickness of the scroll portion is preferably 2 mm or less, and more preferably the minimum thickness of the scroll portion is 1.5 mm or less.

According to the exhaust system turbine housing manufacturing method of the present invention, the inner surface of the scroll part, which is the casting surface of the exhaust system turbine housing, can be provided with a surface shape having a small surface roughness and a smooth curved surface. The combustion efficiency of the turbocharger can be increased by suppressing the decrease in the flow rate of the exhaust gas passing through the. Further, the scroll portion can be thinned, and the exhaust gas turbine housing can be made lighter and the exhaust gas can be purified by reducing the heat capacity.

  An important feature of the method for manufacturing an exhaust system turbine housing according to the present invention lies in a molding process of a turbine housing vanishing model having substantially the same shape as the exhaust system turbine housing. One of the features is that in forming the turbine housing vanishing model, a core made of a vanishing material for forming a core, having a shape corresponding to the space inside the scroll portion, and having a surface roughness Ra of 1 μm or less is used. It was. In other words, the present invention adopts a technique of first manufacturing a highly accurate turbine housing disappearance model, not a technique of a casting core that remains until casting and becomes a part of a mold cavity. .

  Then, the surface corresponding to the inner wall of the scroll part, which is important in the highly accurate turbine housing vanishing model, is molded with a smooth core formed of the core-forming vanishing material. Specifically, the core is placed in a mold, and the vanishing material for forming the turbine housing is injected to obtain a molded body containing the above-described core. The core is removed by eliminating and removing the conductive material, and the surface corresponding to the inner wall of the scroll portion of the turbine housing vanishing model is a surface onto which the surface of the removed core is transferred.

  As described above, the core in the present invention is not a part of the mold cavity at the time of casting, so it is not necessary to use a refractory material whose surface roughness is difficult to control. The surface of the turbine housing vanishing model transferred by the core can be smoothed.

  The core-destructible material in the present invention is a material that can be eliminated as described above in the process of forming the turbine housing vanishable model. For example, it is easily melted or semi-molten by heating at about 70 ° C. A material that can be made to flow or a material that can be dissolved in a solvent such as water, specifically, a disappearing material such as a resin or wax can be used.

In addition, as described above, the core in the present invention has a shape corresponding to the space in the scroll portion, and the core has a surface roughness Ra of 1 μm or less.
The surface of the core is transferred to the turbine housing vanishing model as described above. Then, the surface of the turbine housing disappearance model onto which the smooth surface of the core is transferred is transferred to the mold. Further, the surface of the mold is transferred to the cast exhaust system turbine housing, and a casting surface based on the surface of the core is formed on the inner wall of the scroll portion.

  In this way, the surface of the core repeats transfer three times to the turbine housing vanishing model, mold, and cast exhaust turbine housing, so the smoothness of the transferred surface relative to the surface of the group to be transferred is to degrade. Considering the deterioration of the smoothness of the surface due to this transfer, the surface roughness of the inner wall of the scroll part, which is the casting surface, can be set to 5 μm or less by Ra by setting the surface roughness of the core to 1 μm or less by Ra. . More preferably, a core having a surface roughness Ra of 0.5 μm or less is used.

  In addition, the shape of the core is a shape corresponding to the space in the scroll unit. A shape corresponding to the scroll portion is formed in the turbine housing disappearance model formed by including the core, and a shape corresponding to the space in the scroll portion is formed in the mold formed using the turbine housing disappearance model. It is formed. In the exhaust system turbine housing formed by casting the mold, a scroll portion having substantially the same shape of the scroll portion inner space as the above-described core is formed. In other words, by forming the core in a shape corresponding to the space in the scroll portion, the cast exhaust system turbine housing can be provided with the scroll portion without any special processing or the like.

  In addition, as described above, the surface corresponding to the inner wall of the scroll portion of the mold according to the present invention is a surface onto which the surface of the turbine housing disappearance model based on the surface of the core is transferred. For this reason, it is preferable to use a mold whose surface roughness corresponding to the inner wall of the scroll part of the mold is 4 μm or less in Ra, and thereby the surface roughness of the inner wall of the scroll part which is the casting surface is 5 μm or less in Ra. be able to. More preferably, a mold having a surface roughness Ra of 3 μm or less is used.

  Although the important features in the method of manufacturing the exhaust system turbine housing of the present invention have been described above, in the turbine housing, the flow velocity of the passing fluid can be suppressed by smoothing the inner wall of the scroll portion, and by reducing the thickness of the scroll portion. Low heat capacity and light weight are possible. In particular, the exhaust system turbine housing of the present invention can achieve higher combustion efficiency of the turbocharger and cleaner exhaust gas by smoothing the inner wall of the scroll part and thinning the scroll part in the exhaust system turbine housing. This manufacturing method is suitable.

  In addition, an exhaust system turbine housing which is a target in the manufacturing method of the present invention includes a scroll portion having an aerodynamic spiral continuing from an intake port, and an exhaust port disposed at the spiral center of the scroll portion. This is because it is a feature of an exhaust system turbine housing widely used for a turbocharger having an aerodynamic spiral scroll portion that uses exhaust gas from an internal combustion engine.

  The exhaust turbine housing obtained by the manufacturing method described above has a small surface roughness of the inner wall of the scroll part, which is a casting surface, and a smooth curved surface. By using a core with a roughness Ra of 1 μm or less, a novel exhaust system turbine housing can be obtained in which the surface roughness of the inner wall of the scroll portion, which is the casting surface, is 5 μm or less.

Hereinafter, the exhaust system turbine housing and the manufacturing method thereof according to the present invention will be described in detail with reference to the drawings.
A typical shape of an exhaust system turbine housing (hereinafter referred to as a turbine housing) is shown in FIG. In FIG. 1, the turbine housing 1 includes a scroll portion 3 having an aerodynamic spiral continuing from an intake port 2 and an exhaust port 4 disposed at the center of the scroll of the scroll portion 3. In this example, the housing joint 5 is provided on the substantially opposite side of the exhaust port 4 to the compressor (not shown) side.

  In such a turbine housing 1, a turbine impeller (not shown) is arranged inside the spiral of the scroll portion 3, and the turbine impeller is rotated by exhaust gas flowing from the intake port 2 to the scroll portion 3, The intake pressure can be increased by facilitating the rotation of a compressor impeller (not shown) connected coaxially. Furthermore, a variable nozzle (not shown) can be disposed between the turbine impeller and the scroll portion 3, and the amount of exhaust gas flowing into the exhaust port 4 can be variably controlled by the opening of the variable nozzle.

Hereinafter, an example of the manufacturing method of the present invention for manufacturing the turbine housing 1 shown in FIG. 1 will be described in detail according to the required steps.
(1) Molding process of vanishing model In the manufacturing method of the exhaust system turbine housing of the present invention, the molding process of the turbine housing vanishing model is the most important process as described above. As an example, a core made of a vanishing material for forming a core is disposed at a location corresponding to the scroll portion of the turbine housing in the mold, and the vanishing material for forming the turbine housing is placed in the mold after the mold is clamped. Is removed from the mold, and the core made of the above-described core-forming vanishing material is removed, thereby removing the turbine housing vanishable model having substantially the same shape as the turbine housing. The process of obtaining is described below.

First, a configuration example in a mold for producing a turbine housing vanishing model having substantially the same shape as the turbine housing 1 will be described.
The shape of the turbine housing vanishing model in the present invention is substantially the same as that of the turbine housing. The shape of the cast turbine housing is shaped by the space shape of the mold cavity used for casting, and the space shape of the mold cavity is shaped by the turbine housing vanishing model. That is, the shape of the turbine housing can be formed by making the shape of the turbine housing vanishing model substantially the same as that of the turbine housing.

  As an example, as shown in FIG. 2, the mold may have a configuration in which middle molds 13 to 16 are combined with the upper mold 11 and the lower mold 12. The middle dies 13 and 14 are configured by combining a plurality of placement cores 13a to 16a, or are configured to be openable and closable in a substantially radial direction with respect to the spiral center of the scroll portion 3 and rotatable about the spiral center. It is preferable to configure by combining a plurality of slide cores. With such a mold configuration, the mold can be easily opened after the turbine housing 1 is molded.

  Then, the core 10 having a shape corresponding to the space in the scroll portion 3 and having a surface roughness Ra of 1 μm or less is positioned and disposed in the mold configured as described above. When the core 10 is disposed, the position of the spiral center of the scroll portion 3 and the phase of the spiral with respect to the intake port 2 are accurately positioned, and the core 10 is injected when the vanishing material for forming the turbine housing is injected into the mold. It is important to arrange them so that they do not move.

  As a means for arranging the core 10, for example, as shown in FIG. 2, the placement cores 17 and 18 having recesses are disposed with respect to the upper mold 11 and the lower mold 12. , 18 to form a convex portion 10a that can be fitted. Then, when the mold is clamped, the concave portions of the placing cores 17 and 18 and the convex portions 10a of the core 10 are fitted together so that the core 10 is held by the placing cores 17 and 18 so that the inside of the mold is The core 10 can be accurately positioned and arranged. It is also possible to form a convex portion with respect to the placement cores 17 and 18 and a concave portion with respect to the core 10. The placing core 17 and the placing die 18 can be integrally formed with the upper die 11 and the lower die 12, respectively.

Further, as another means for arranging the core 10, for example, a core support member made of a vanishing material for forming a turbine housing is prepared, and this core support member is arranged between the core 10 and the mold. By supporting the core 10 in this way, the core 10 can also be positioned and arranged with high accuracy in the mold. However, even if the same vanishing material for forming the turbine housing is used, a fusing mark which is a boundary line with the core support member remains, which is disadvantageous in that it is necessary to remove the fusing mark. In addition, if a fusing mark is generated on the inner wall 3a of the scroll portion 3, it is difficult to remove it, and the surface shape may become minute as it is and the smoothness of the surface shape may be impaired.

  As described above, the upper mold 11, the middle molds 13 to 16, and the lower mold 12 are clamped so that the core 10 is positioned and disposed, whereby the intake port 2, the scroll portion 3, and the exhaust port 4 of the turbine housing 1. And a cavity 20 corresponding to the housing joint 5 and having substantially the same spatial shape as the turbine housing 1 can be formed in the mold.

  Next, a melted or semi-melted vanishing material for forming a turbine housing is injected into the cavity in the above-described mold, thereby forming a molded body including the core 10. Then, the mold is opened and the molded body is taken out, and the core-forming vanishing material is removed from the molded body, and only the core 10 contained is removed. The molded body from which the core 10 is removed has a shape corresponding to the inner space of the scroll portion 3, so that the space from which the core 10 is removed is substantially the same as the inner space of the scroll portion 3. The shape of the space is modeled. That is, the configuration in which the core 10 having a shape corresponding to the space in the scroll portion 3 is disposed in the cavity in the mold having the substantially same space shape as that of the turbine housing 1 is substantially the same as the turbine housing 1. A turbine housing disappearance model having the following shape can be obtained.

  In the production method of the present invention, the core-forming disappearance material for forming the core can be formed using a disappearance material such as a resin or wax that is dissolved or semi-melted by heating at about 70 ° C., It is preferably formed using a solvent-soluble wax. The core formed using the solvent-soluble wax can be removed by elution by simple means of immersing in the solvent without being particularly heated, and the core can be easily removed from the molded body.

  As the solvent, for example, an aqueous acidic solution such as water or 5% hydrochloric acid can be used, but a solvent that does not easily react with the vanishing material for forming a turbine housing that forms the molded body is preferable. As the wax, for example, a wax that is soluble in the above-described water or acidic aqueous solution that is a solvent may be used. Preferably, water that is easy to handle is used as a solvent, and a water-soluble wax that is eluted in water is used. More preferably, the core is first immersed in warm water to substantially dissolve and remove the water-soluble wax, and then immersed in dilute hydrochloric acid to completely dissolve and remove the water-soluble wax.

  In addition, as the vanishing material for forming the turbine housing described above, a resin that can be easily flowed by being melted or semi-melted at a temperature higher than, for example, 150 ° C. or higher, than the vanishing material for forming a core. Dissolvable materials such as wax can be used. Further, when the core is eluted and removed with a solvent, a material that dissolves or semi-melts at a temperature equivalent to the core-forming vanishing material such as 70 ° C. can be used as long as the material does not elute in the solvent. Such a vanishing material for forming a turbine housing can be easily removed by elution and the like, and by using this to form a vanishing model of the turbine housing, the vanishing model of the turbine housing can be easily removed from the mold. Can do. Moreover, you may use evanescent materials, such as a plastic which carbonizes at about 1000 degreeC high temperature, such as styrene and an epoxy resin.

  Through the procedure described above, the core 10 having a shape corresponding to the space in the scroll portion 3 of the turbine housing 1 and having a surface roughness Ra of 1 μm or less is used, and the shape is substantially the same as that of the turbine housing 1. The turbine housing disappearance model which has can be obtained. The turbine housing vanishing model can be provided with a surface having a small surface roughness and a smooth surface at a portion corresponding to the inner wall 3a of the scroll portion 3 of the turbine housing 1.

(2) Mold molding step The mold molding step in the method for manufacturing an exhaust system turbine housing of the present invention is, as an example, for the turbine housing vanishing model obtained by the above-described turbine housing vanishing model molding step. An exhaust system is provided by providing a feeder or runway made of a vanishing material for forming the turbine housing similar to the turbine housing vanishing model, coating it with a refractory, and removing the turbine housing vanishing model after coating. This is a step of forming a mold having a cavity having substantially the same spatial shape as the turbine housing.

  For example, first, to the turbine housing vanishable model, a hot water or a runner made of the same vanishing material for forming the turbine housing is adhered to form a tree shape. A turbine housing disappearance model having a tree shape is coated with a refractory so as to have a predetermined mold thickness. At this time, it is also preferable to assemble a plurality of turbine housing disappearance models in one tree shape and coat the plurality of disappearance models simultaneously with a refractory because the production efficiency is improved.

  In the manufacturing method of the present invention, an appropriate mold thickness and mold strength are provided at locations corresponding to the inside of the scroll portion 3 of the turbine housing 1 of the above-described turbine housing vanishing model, thereby preventing mold cracking and molten metal leakage during casting. It is also important to plan. For this reason, when the mold has a predetermined mold thickness, it is preferable to divide the refractory coating on the turbine housing vanishing model into a plurality of times and to stack a plurality of refractory layers. For example, a slurry having an average particle size of 350 μm or less It is preferable to form a mold in which a plurality of refractory layers are laminated by alternately coating stucco having an average particle size of 1500 μm or less. By providing a plurality of refractory layers in the mold in this way, a strong bond is obtained between the refractory layers, the strength of the mold is improved, and even if cracks occur in the mold during casting, It can stop and prevent molten metal leakage.

As an example of the formation of a refractory layer, first, a refractory slurry is coated, then a refractory stucco is coated, and after sufficient drying, excess stucco is removed, and this is repeated to form a refractory layer. It is formed by laminating. As the refractory to be coated, zircon, silica, alumina, mullite, etc., which are materials that can withstand the molten metal cast in the casting process can be used. For example, ZrO ₂ , SiO ₂ , Al ₂ O ₃ or the like can be used singly or as a mixture as the above-mentioned slurry and stucco particulate components.

Further, in the formation of the refractory layer, it is preferable that 50% or more of ZrO ₂ having good fire resistance is blended particularly from the first layer to about four layers. In the first layer, it is important that fine refractory grains are densely arranged on the surface of the turbine housing vanishing model, and the surface to be a cavity in the mold is formed so that the surface roughness becomes small. . For this purpose, it is preferable to use a slurry containing a large number of refractory grains having a small average particle size and a relatively high viscosity. Specifically, refractory particles such as SiO ₂ and Al ₂ O ₃ are blended with ZrO _{2 having} good fire resistance as a granular component, and further, an antifoaming agent, a surfactant and the like are added, and the average particle size is 50 μm or less. A mixture slurry in which the viscosity of Zahn cup # 4 is about 30 to 50 seconds can be used, and the surface to be a cavity in the mold formed thereby can have a surface roughness Ra of 4 μm or less. As the stucco to impart strength to the refractory layer by coating is then slurried in initial layer, a mixture of SiO ₂ or the like to be ZrO ₂ of refractory, refractory was about 100~150μm an average particle size Grain can be used.

  And as a slurry used for the second and subsequent layers to be laminated on the first layer, it is possible to provide the mold thickness and strength by increasing the average particle size and decreasing the viscosity as compared with the previous layer. preferable. For example, the same refractory particles as the first layer can be used, the average particle size can be about 250 to 350 μm, and the viscosity by Zahn Cup # 4 can be about 10 to 20 seconds. On the outer layer side of the mold, in order to improve the packing density in each layer, it is also preferable to use a mixture of fine particles having an average particle size of 20 μm or less and coarse particles of about 50 to 100 μm. As the stucco used in the second and subsequent layers, the above-mentioned refractory grains having an average particle size of about 100 to 150 μm and an average particle size of about 500 to 1500 μm can be used on the outer layer side of the mold.

  Next, after the mold formed as described above is sufficiently dried, the vanishing material for forming the turbine housing is removed by elution or the like, thereby removing the vanishing model of the turbine housing from the mold. As a means for removing the vanishing material for forming the turbine housing, there is a means for removing it by heating and melting it with a high-temperature steam autoclave, for example. Furthermore, the obtained mold is preferably fired at a high temperature of, for example, 1000 ° C. or more, and sufficient strength can be imparted to the mold.

  By the procedure described above, a mold having substantially the same space shape as the turbine housing 1 can be obtained. The surface corresponding to the inner wall 3a of the scroll part 3 in the mold has a small surface roughness and a smooth surface shape based on the smooth surface of the core 10 having a surface roughness Ra of 1 μm or less. Thus, a surface having a surface roughness Ra of 4 μm or less can be obtained.

(3) Casting process The casting process in the method for manufacturing an exhaust system turbine housing of the present invention is performed by casting a molten metal obtained by melting a metal material into a mold obtained by the above-described mold molding process and cooling the mold. This is a step of obtaining an exhaust system turbine housing having substantially the same shape as that of the above-described turbine housing vanishing model by removing the casting mold.

  The exhaust system turbine housing in the present invention is required to have high temperature strength and corrosion resistance as an exhaust system part that uses exhaust gas from an internal combustion engine. Therefore, the above-mentioned metal materials include austenitic stainless steel, various heat resistant steels and heat resistant steels. An alloy, a Ni-based or Co-based super heat-resistant alloy, or the like can be used. Further, there are cases where machining and welding joining with other members are performed in the subsequent process, and for example, Fe-0.45C-0.15Si-20Ni-25Cr-3W-2Nb (mass%) which is excellent in machinability and weldability. Fe-0.45C-0.15Si-10Ni-20Cr-3W-2Nb (mass%) is particularly suitable.

And the above-mentioned metal material is melt | dissolved in the atmosphere suitable for the characteristic in an inert gas or a vacuum, and it is set as a molten metal, and this molten metal is supplied to a casting_mold | template.
Casting to the mold can be performed under reduced pressure, suction or vacuum in consideration of various conditions such as the characteristics of the molten metal and the amount of hot water in the mold. Preferably, suction casting is employed to improve the hot water supply property, and the thin scroll portion 3 is surely filled with molten metal. Then, after casting, the mold is removed after cooling, and unnecessary runners and hot water are removed from the cast product. Furthermore, mold scraps, scales, etc. adhering to the casting can be removed by shot blasting, sand blasting, water blasting, or the like.

  By the procedure described above, the scroll portion 3 having an aerodynamic spiral continuing from the intake port 2 and the exhaust port 4 arranged at the spiral center of the scroll portion 3 are provided, and the inner wall of the scroll portion 3 which is a casting surface is provided. An exhaust system turbine housing having a surface roughness 3a of Ra of 5 μm or less can be obtained. Moreover, you may perform a machining etc. with respect to the obtained turbine housing 1 as needed.

  As described above, in the production method of the present invention, the surface of the inner wall of the scroll portion, which is the casting surface, is controlled by controlling the surface of the core made of the core-forming vanishing material. Although the core used in the present invention can be formed by machining such as cutting, the core-forming vanishing material is injected into a mold having a cavity having substantially the same shape as the scroll portion. It is preferable to form. This is because, according to a conventional NC processing machine or the like, it is easy to reduce the surface roughness of the surface constituting the cavity of the mold and to form the surface shape into a smooth surface.

  In addition, when the core-forming vanishing material is injected into the mold to form the core, if the injection pressure of the core-forming vanishing material is sufficiently high, the surface of the mold cavity is formed. It is transferred directly to the surface of the core. For this reason, the surface roughness of the core can be set to 1 μm or less by Ra by setting the surface roughness of the surface constituting the cavity of the mold to 1 μm or less by Ra. Even if wrinkles or burrs are generated on the surface of the core when the core is molded, the core made of the disappearing material for core molding is relatively flexible, so by repairing the surface of the core It is easy to make the surface roughness Ra 1 μm or less.

  Further, in the present invention, a core having a shape corresponding to the space in the scroll portion and having a surface roughness Ra of 1 μm or less is injected, and a core-forming vanishing material is injected into a cavity with good dimensional accuracy in the mold. Thus, a core with good dimensional accuracy can be obtained. The scroll part cast by applying the turbine housing vanishing model having a shape corresponding to the inner space of the scroll part obtained by the core is improved in dimensional accuracy, and the thickness of the scroll part is reduced. Thus, an exhaust system turbine housing effective in reducing the heat capacity and weight can be obtained. Preferably, the minimum thickness of the scroll portion is 2 mm or less, and more preferably the minimum thickness is 1.5 mm or less.

A turbine housing 1 having a shape shown in FIG. 1 and having an interval of 80 mm between the end face of the exhaust port 4 and the end face of the housing joint 5 and a weight of 1.6 kg, which is an embodiment of the present invention, is cast by the lost wax precision casting method. Molded.
First, a mold for defining a space shape corresponding to the core 10 included in the turbine housing vanishing model was processed by an NC processing machine and further polished to prepare a core forming mold. The surface roughness of the surface constituting the cavity in this core forming mold was 0.317 μm in Ra (shown in FIG. 5). Next, a water-soluble wax (Solibble # 70, Precision Metalsmiths, Inc.), which is a core-destructible material, is injected into the core-forming mold and has a shape corresponding to the space inside the scroll portion 3. Then, the core 10 included in the turbine housing disappearance model was obtained. The core 10 had a surface roughness Ra of 0.461 μm (shown in Table 1).

(1) Turbine housing vanishing model forming process Next, a mold for defining a space shape corresponding to the turbine housing vanishing model is processed by an NC processing machine and further polished to form a turbine housing vanishing model. The upper mold 11, the lower mold 12, the middle molds 13 to 16, and the placement cores 13a to 16a, 17, and 18 shown in FIG. In addition, the surface roughness of the surface constituting the cavity in the mold for forming the turbine housing vanishable model was 0.357 μm in Ra (shown in FIG. 5). Next, as shown in FIG. 2, the middle molds 15 and 16 and the placement cores 15 a, 16 a, and 18 are placed on the lower mold 12, and the middle molds 13 and 14 and the placement cores 13 a, 14 a, 17 were each assembled separately. Furthermore, after fitting the convex part 10a of the core 10 to the concave part of the placing core 18, the core 10 is clamped and the core 10 is gripped by the placing cores 17 and 18, and positioned. A turbine housing vanishing model forming mold having a turbine housing corresponding cavity 20 having substantially the same space shape as the turbine housing 1 was configured.

  Then, a wax insoluble in water (pattern wax A7-TCF / RR, Bryson Japan Co., Ltd.), which is the vanishing material for forming the turbine housing, is injected into the mold for forming the vanishing model for the turbine housing. A molded body containing the child 10 was obtained. Next, the molded body is immersed in water and further immersed in a 5% hydrochloric acid aqueous solution to completely elute and remove the core 10 from the molded body, and the turbine housing disappearance model having substantially the same shape as the turbine housing 1 is obtained. Got. In addition, the surface roughness of the location corresponding to the scroll part inner wall 3a of a turbine housing evanescent model was 1.399 micrometers in Ra (shown in Table 1).

  Next, a hot water or runway made of the same wax as the turbine housing disappearance model described above is bonded to the turbine housing disappearance model to form a tree model, and refractory slurry and stucco are repeatedly applied to the tree model. Coating was performed to obtain a mold having nine refractory layers. In the first layer, colloidal silica, zircon sand, silicon emulsion, and dioctyl sodium sulfosuccinate solution were blended, and a slurry having an average particle size of 45 μm and a viscosity of 40 seconds with Zahn Cup # 4 was coated. Next, a stucco mixed with zircon sand having an average particle size of 100 μm and 150 μm and different particle sizes was coated. For the 2nd to 4th layers, a stucco prepared by mixing the slurry used in the first layer with a viscosity adjusted to 15 seconds by Zahn cup # 4 and alumina having an average particle size of 250 μm and 350 μm having different particle sizes was used. For the 5th to 8th layers, a slurry in which fine particles having an average particle size of 20 μm mainly composed of silica and zircon sand and coarse particles of 50 μm and 75 μm were mixed and the viscosity of Zahn cup # 5 was adjusted to 30 seconds was used. The stucco used was a mixture of silica and alumina mainly having an average particle size of 300 μm, 400 μm, 850 μm, and 1200 μm. In each layer, after drying, the excess stucco was blown away, and then the 9 layers, which are the outer layers of the mold, were immersed in the slurry used for the 8 layers and dried sufficiently.

  Next, after the mold containing the turbine housing disappearance model is sufficiently dried as described above, a tree-shaped model made of the above-mentioned water-insoluble wax by a high-temperature steam autoclave from the mold, that is, the turbine housing A casting mold for casting was obtained by heating and melting a turbine housing disappearance model having substantially the same shape as No. 1 and a hot water or runner and completely removing it by elution. The surface roughness of the part corresponding to the inner wall 3a of the scroll portion of the mold was obtained by dividing the mold formed by the same manufacturing method as described above. As a result, the surface roughness was 2.195 μm in Ra (shown in Table 1). Met.

  Then, Fe-0.45C-0.1Si-0.7Mn-10Ni-20Cr-3W-2Nb (mass%) is melted in the atmosphere to form a molten metal, sucked and cast into a mold, cooled, disassembled, and then shot into sand. After removing mold waste and the like, blow cleaning was performed to obtain a turbine housing 1 as an example of the present invention. In the example, casting was performed with the target value of the minimum thickness of the scroll portion set to 1.5 mm, and at this time, the turbine housing 1 having a minimum thickness of 1.5 mm and having no casting defects was obtained.

  Moreover, although the turbine housing 1 used as a comparative example was manufactured by the same manufacturing method as the turbine housing 1 used as the above-mentioned Example, exceptional surface roughness with respect to the core 10 used for forming the turbine housing vanishing model. No control was performed.

Regarding the surface roughness of the inner wall of the scroll part 3 which is an important feature in the exhaust system turbine housing of the present invention and the manufacturing method thereof using the turbine housing 1 which is the embodiment and the comparative example manufactured as described above, JISB0601: 2001 Based on this, arithmetic average height roughness Ra, maximum height roughness Rz, and ten-point average roughness _RZJIS were measured. An example of the measured surface roughness is summarized in Table 1. 3 and 4, (i) core 10, (ii) turbine housing vanishing model, (iii) mold, and cast molding (iv) surface of turbine housing 1 used in the examples and comparative examples are shown. An example of a roughness curve is shown. In addition, the measurement location of surface roughness is a location corresponding to the scroll part inner wall 3a which is a casting surface, or the scroll part inner wall 3a in any case. FIG. 5 shows an example of the surface roughness curve measured in the cavity of (i) the core forming mold and (ii) the turbine housing vanishing forming mold used in the examples.

As is apparent from Table 1, FIG. 3, and FIG. 4, in the exhaust turbine housing 1 of the present invention shown in the examples, the surface roughness of the scroll portion inner wall 3a, which is the casting surface, was 5 μm or less in terms of Ra. In addition, the surface roughness of the surface corresponding to the core 10 and the scroll portion inner wall 3a in the mold shown in the examples was 1 μm or less for Ra of the core 10 and 4 μm or less for Ra of the mold. On the other hand, in the conventional exhaust system turbine housing 1 shown in the comparative example, the surface roughness of the scroll portion inner wall 3a is as large as about 7 μm in Ra compared to the embodiment of the present invention. As for other maximum height roughness Rz and ten-point average roughness _RZJIS , Rz is about 20 μm, _RZJIS is about 14 μm in the example, Rz is about 40 μm, and _RZJIS is about 30 μm in the comparative example. Met.

  From the measurement results of the surface roughness described above, even if the turbine housing 1 is manufactured using the core 10 made of the same core-forming vanishing material, the core 10 whose surface roughness is controlled to 1 μm or less by Ra The used turbine housing 1 of the present invention has a smaller surface roughness of the inner wall 3a of the scroll portion, which is a cast surface, and is smoother than the conventional turbine housing 1 using the core 10 that does not perform special surface roughness control. In that respect, it was confirmed that it was excellent.

  As described above, according to the method for manufacturing an exhaust system turbine housing of the present invention, the scroll portion 3 having an aerodynamic spiral continuing from the intake port 2 and the exhaust port 4 arranged at the spiral center of the scroll portion 3 are provided. Thus, it was confirmed that the exhaust system turbine housing 1 in which the surface roughness of the scroll portion inner wall 3a, which is the casting surface, is 5 μm or less in Ra can be obtained. Moreover, the exhaust system turbine housing 1 whose minimum thickness of the scroll part 3 is 2 mm or less was able to be obtained.

It is a block diagram containing the partial cross section which shows the specific example of the exhaust system turbine housing of this invention. It is a mimetic diagram showing an example of metallic mold composition in a manufacturing method of an exhaust system turbine housing of the present invention. It is an example of the surface roughness curve of the core used in the Example of this invention, the turbine housing disappearance model, the location corresponding to the scroll part inner wall of a casting_mold | template, and a scroll part inner wall. It is an example of the surface roughness curve of the core used in the comparative example, the turbine housing disappearance model, the part corresponding to the scroll part inner wall of a casting_mold | template, and a scroll part inner wall. It is an example of the surface roughness curve of the cavity of the mold for core formation used in the Example of this invention, and the mold for turbine housing disappearance model formation.

Explanation of symbols

  1. Turbine housing, 2. 2. intake port; Scroll part, 3a. Inner wall, 4. 4. exhaust port; Housing joint, 10. Core, 10a. Convex part, 11. Upper mold, 12. Lower mold, 13-16. Medium size, 13a-16a. Place core, 17, 18. Place core, 20. Cavity for turbine housing

Claims (5)

A scroll portion having an aerodynamic spiral that continues from the intake port, and an exhaust port disposed at the center of the scroll of the scroll portion, the surface roughness of the inner wall of the scroll portion that is the casting surface is 5 μm or less Ra An exhaust system turbine housing manufacturing method comprising:
(1) A step of forming a turbine housing vanishing model having substantially the same shape as the exhaust system turbine housing;
(2) Mold forming step for eliminating and removing the turbine housing disappearance model after coating the turbine housing disappearance model with a refractory;
(3) a casting process for casting into the mold;
The turbine housing vanishing model has a shape corresponding to the space inside the scroll part, and after forming a core having a surface roughness Ra of 1 μm or less with a core-forming vanishing material, By placing the core in a mold and injecting a vanishing material for forming a turbine housing to obtain a molded body containing the core, and then removing the core-forming vanishing material from the molded body by removing the core. An exhaust system turbine housing manufacturing method obtained by removing a core . 2. The method of manufacturing an exhaust system turbine housing according to claim 1, wherein a mold having a surface roughness Ra of 4 [mu] m or less corresponding to the inner wall of the scroll portion is used . The mold has a plurality of laminated refractory layers, and the refractory layer is formed by alternately coating a slurry having an average particle size of 350 μm or less and a stucco having an average particle size of 1500 μm or less. The manufacturing method of the exhaust system turbine housing of Claim 1 or 2 . Exhaust system turbine Pillow grayed characterized by comprising using the manufacturing method of the exhaust system turbine housing according to any one of claims 1 to 3. Exhaust system turbine Pillow grayed according to claim 4, the minimum thickness of the scroll portion is equal to or is 2mm or less.

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