TRANSPLANTED THERMAL BARRIER COATING SYSTEM

Abstract

Method for forming a molded part and the molded part. The method includes applying a thermal barrier coating (TBC) system to a sand core; inserting the TBC coated sand core into a mold; and forming a cast iron part in the mold with the inserted TBC coated sand core.

Description

BACKGROUND

1. Field of the Invention

Embodiments are directed to applying a thermal barrier coating system to a sand core in a molding process.

2. Discussion of Background Information

Regeneration is a process used, e.g., in diesel engine manifolds, to remove accumulated soot from filters, such as diesel particulate filters. Regeneration can be performed passively, e.g., from exhaust heat or by adding a catalyst to the filter, or by actively adding heat into the exhaust system. These manifolds, which can be produced, e.g., by a die casting and/or injection molding process, can be exposed to heat extremes, e.g., about 760° C., that can result in thermo-mechanical fatigue, e.g., cracking, in the part, which can allow gases and heat to escape. FIG. 7 shows critical areas in the exhaust manifold and turbo manifold in which this cracking is likely to occur. The existence of these cracks prevent the exhaust and/or turbo manifolds from keeping heat inside the manifold, which prevents the regeneration process from adequately removing accumulated soot.

Thermal barrier coatings (TBCs) are applied on components such as combustors, high-pressure turbine blades, vanes, shrouds, and the like. TBCs are applied to components to increase the operating temperature of hot gas path components which can result in higher energy output and improved engine efficiencies. TBCs provide thermal insulation that enables TBC coated components to survive at higher operating temperatures, to increase component durability and to improve engine reliability. Moreover, when TBCs are applied to manifolds, the following advantages have been attained:

Benefit                    Percentage change (%)
Fuel savings               11
Engine life extension      20
Power output increase      10
Reduction of emission      20-50
Reductions of particulate  52
Lubricating oil savings    15
Maintenance cost reduction 20

SUMMARY

Embodiments are directed to molding products using sand cores. In the particular, the molded products can be parts specially designed to retain high heat, e.g., in an engine, but which avoid the formation of cracks.

A transplanted thermal barrier coating (TBC) system is applied to a sand core prior to the casting or molding process. The TBC system can include a ceramic layer as a top coat applied on the sand core and a metallic layer as a bond coat applied on the top coat. Preferably, the TBC system can also include an abradable layer as an adhesion coat applied on the sand core and the top coat is then applied on the adhesion layer.

The TBC can be applied to the sand core using a thermal spraying process. Preferably, the same thermal spray process is used for each component of the TBC system.

Embodiments are directed to a method for forming a molded part that includes applying a thermal barrier coating (TBC) system to a sand core; inserting the TBC coated sand core into a mold; and forming a cast iron part in the mold with the inserted TBC coated sand core.

In embodiments, the TBC system may include a ceramic layer and a metallic layer. The method can further include applying the ceramic layer over the sand core with an air plasma spray thermal spray process; and applying the metallic layer onto the ceramic layer with the air plasma spray thermal spray process. The ceramic layer can include yttria stabilized zirconia and the metallic layer can comprise a low-alloyed carbon steel that forms a bond coat for the cast iron. Further, before the ceramic layer is applied, the method further may also include preheating the sand core with the air plasma spray thermal spray process.

According to other embodiments, the TBC system can further include an adhesion layer. Moreover, before the ceramic layer is applied, the method can also include applying the adhesion layer onto the sand core with an air plasma spray thermal spray process, wherein the ceramic layer is applied onto the adhesion layer. The adhesion layer can include NiC (Nickel Graphite) or mixtures of metal and polymer, such as metal-based polymer composites, in particular an Al based polymer, preferably at least one of a MCrAlY based polymer (wherein M for example equals Co, Ni or Co/Ni), a NiCrAl based polymer, a NiAl based polymer, an Al-bronze based polymer or an AlSi polyester. Preferably, the polymer in the adhesion layer includes a thermoplastic polymer such as Polytetrafluoroethylene (PFTE).

In accordance with other embodiments, the sand core can include one of silica sand, chromite sand, or zircon sand; bentonite; water; and inert sludge. The sand core can also include anthracite. Further, the one of silica sand, chromite sand or zircon sand may further include olivine, staurolite, or graphite.

Embodiments are directed to a molded part that includes a cast iron body; and a TBC system integrally molded with an interior surface of the cast iron body. Preferably, the TBC system is applied according to the method for forming the molded part.

In accordance with still yet other embodiments, the TBC system comprises a ceramic layer and a metallic layer. The ceramic layer can include yttria stabilized zirconia and the metallic layer can comprise a low-alloyed carbon steel. The TBC system may further include an adhesion layer, and the adhesion layer can comprise NiC (Nickel Graphite) or mixtures of metal and polymer, such as metal-based polymer composites, preferably an Al based polymer, more preferably at least one of a MCrAlY based polymer (wherein M for example equals Co, Ni or Co/Ni), a NiCrAl based polymer, a NiAl based polymer, an Al-bronze based polymer or an AlSi polyester.

Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 shows a sand core for an exemplary embodiment;

FIGS. 2A-2F illustrate a process by which a transplanted TBC system is applied to the sand core;

FIGS. 3A-3E illustrate an alternative to the process depicted in FIGS. 2A-2F to by which a transplanted TBC system is applied to the sand core without a bond coat;

FIGS. 4A-4G illustrate another process by which a transplanted TBC system is applied to the sand core;

FIGS. 5A-5F illustrate an alternative to the process depicted in FIGS. 4A-4G to by which a transplanted TBC system is applied to the sand core without a bond coat;

FIG. 6 shows a cross-section of the sand core with transplanted TBC system in a mold; and

FIG. 7 shows critical areas for cracks in known engine manifolds.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

Cores are used for producing interior surfaces of a component, in particular a component with complex shapes, in a die casting and/or injection molding process. FIG. 1 shows an exemplary core 10 for an engine manifold, but it is understood that cores can be used for any number of casting and/or molding processes forming components for gasoline or diesel engines such as turbocharger parts and components, e.g., for automobiles, sport-utility vehicles, light-weight and heavy-duty trucks, farming equipment, marine vehicles, commercial and non-commercial vehicles, etc. In the exemplary embodiment, core 10 is made of a sand composition, in which the sand composition is a mixture of: 75-85 wt. % of silica sand (SiO2), chromite sand (FeCr2O4), or zircon sand (ZrSiO4); 5-11 wt. % bentonite (clay); 2-4 wt. % water; and 3-5 wt. % inert sludge 3 to 5%. In embodiments, the silica sand, chromite sand or zircon sand can include a proportion of olivine, staurolite, or graphite and/or the composition can include up to 1 wt. % (>0-1 wt. %) anthracite.

Casted and/or molded parts, e.g., those parts utilized in an engine, can be exposed to heat extremes, e.g., about 760° C., which can result in thermo-mechanical fatigue, e.g., cracking, in the part, which can allow gases and heat to escape. Further, in components that are designed to keep or retain heat, e.g., manifolds, it is desired that component is formed so that heat transfer through the component housing or walls is avoid to the greatest extent possible. To address these issues, embodiments are directed to forming a thermal barrier coating (TBC) system on the inside surface of the casted and/or molded part. The TBC system can include plural layers or coatings formed by thermal spraying, e.g., plasma spraying, high velocity oxygen fuel (HVOF) spraying, or other suitable spraying processes, for depositing powder products to form at least a ceramic layer and a metallic layer. By the presently described solution, full, crack free, coverage of the interior surface of casted and/or molded parts is achieved using a thermal spraying process of a TBC in combination with a sand core.

FIGS. 2A-2F show an exemplary process for forming a transported TBC on a casted and/or molded part. As shown in FIG. 2A, a sand core 20, such as the core shown in FIG. 1, is formed for an interior of a part to be formed. In FIG. 2B, a TBC 21 (or ceramic layer) is applied to sand core 20 via a thermal spraying process. Prior to applying TBC 21, it can be advantageous to preheat sand core 20, particularly a sand core comprising bentonite, to avoid evaporation of water or binding chemicals in the sand during the TBC application, which can disadvantageously lead to poor adhesion, cracking and spallation. By way of non-limiting example, the preheating of core 20 can be achieved with a plasma torch or plum without feeding powder, e.g., by air plasma spraying from a cascaded plasma torch such as the SINPLEXPRO-90 from OERLIKON METCO (US) INC.

Thermal barrier coating 21 functions to protect part to be produced from thermo-mechanical fatigue (cracking) and to keep heat inside the part. By way of non-limiting example, when the part to be produced is an engine manifold, the applied TBC 21 increases the heat management efficiency for fuel consumption reduction. Preferably, TBC 21 has a porosity lower than 15-25% to avoid penetration of liquid metal during the casting process, e.g., as discussed below with reference to FIG. 2E, which can result in the unintended creation of deposits inside the casted parts after solidification (scabbing effect). Alternatively, the TBC 21 can be applied as a dual layer system with a porous TBC layer applied to sand core 20 and a non-porous (dense) TBC layer applied to the porous TBC layer, in particular the porous TBC layer having a porosity of 15-25% and the non-porous TBC layer having a porosity of 1% to lower than 15%, more preferably 5% to 10% in order to avoid penetration of liquid metal during the casting process. Furthermore, the TBC 21 can be applied as a gradient layer with a porosity decreasing from the sand core 20 to avoid penetration of liquid metal during the casting process. In order to adjust the porosity of the TBC, the coating parameters can be adjusted, i.e. the power of the plasma and optionally the flow of a secondary gas, the velocity and/or temperature of the deposition particles can be controlled accordingly. In the exemplary embodiment, TBC 21 is formed by the thermal spraying of powder products, e.g., yttria stabilized zirconia (YSZ), such as METCO 204NS powders by OERLIKON METCO (US) INC., onto sand core 20 with a thickness between 100 and 1000 microns, preferably 200-800, and more preferably between 400-500 microns.

After application of TBC 21, a bond coat 22 or metallic layer is applied, as in FIG. 2C. Bond coat 22 ensures adhesion of TBC 21 to the casted part in FIG. 2E. In embodiments, bond coat 22 can be a low-alloyed carbon steel applied to TBC 21 by thermal spraying of powder products, e.g., FeCrMnC (Fe 1.4-1.6Cr 1.4-1.6Mn 1.0-1.3C), such as METCO XPT 512 powder from OERLIKON METCO (US) INC. or CoCrAlY (Co 29Cr 6Al 2Si 0.3Y), such as AMDRY 920) powder from OERLIKON METCO (US) INC., and can be applied up 100 microns, and preferably up to 50 microns, and more preferably between about 15 and 30 microns. However, in order to avoid penetration of liquid metal during the casting process a thicker bond coat 22 can be applied, having a thickness of up to 500 microns, preferably a thickness between about 100 and 500 microns, more preferably between about 100 and 350 microns. Preferably, bond coat 22 is applied in the same manner as used in applying TBC 21, i.e., air plasma spraying from a cascaded plasma torch such as the SINPLEXPRO-90 from OERLIKON METCO (US) INC.

Coated sand core 20 is then inserted into a mold 24, e.g., a sand mold, as shown in FIG. 2D, so that an opening 23 is formed within mold 24 to receive a casting material. In FIG. 2E, a casting material 25 suitable for the part to be cast, e.g., gray cast iron, such as ferritic cast iron SiMo51, austenitic cast iron D5S and austenitic cast stainless steel HK30, is deposited into opening 23 to cast the part. In a conventional manner, the transplanted TBC coated casted part is removed from sand mold 24 and sand core 20 is likewise removed.

In an alternative embodiment to that shown in FIGS. 2A-2F, the process can be performed without FIG. 2C, i.e., without applying a bond coat after TBC 21. In this alternative embodiment, which is illustrated in FIGS. 3A-3E, after the application of TBC 31 in FIG. 3B, the coated sand core 30 is inserted to the mold 34 in FIG. 3C and casting material 35 is deposited into opening 33 of mold 34 in FIG. 3D. In a conventional manner, the transplanted TBC coated casting part is removed from mold 34 and sand core 30 is likewise removed in FIG. 3E.

To ensure that the casted and/or molded part is protected from cracks and that the produced part will maintain heat within the part, the TBC and bond coat layers should be applied to all parts of the sand mold that will form inner surfaces of the part so that the liquid cast iron does not directly contact the sand mold. However, spraying of functional areas of the sand mold, e.g., areas for positioning the core in the mold or assembling the mold, should be avoided.

FIGS. 4A-4G show another exemplary process for forming a transported TBC on a casted and/or molded part. As shown in FIG. 4A, a sand core 40, such as the core shown in FIG. 1, is formed for an interior of a part to be formed. In contrast to the exemplary embodiment of FIGS. 2A-2F, the TBC system additionally includes an adhesion (adhesive) layer 46 or abradable layer that is applied to sand core 40 via a thermal spraying process, e.g., air plasma spraying from a cascaded plasma torch such as the SINPLEXPRO-90 from OERLIKON METCO (US) INC. Adhesion layer 46, which can be an aluminum silicate abradable layer that includes various polymers (AlSiPolyester), is applied to sand core 40 by thermal spraying of powder products, e.g., METCO 1606, METCO 601, AMDRY 2010, AMDRY XPT 268, or AMDRY 2000, all from OERLIKON METCO (US) INC., to a thickness between 20 and 500 microns, preferably between about 100 to 400 microns, and more preferably between about 200 and 350 microns. Applying adhesion layer 36 on sand core 40 ensures easy deposition as a first layer, as it has good affinity to sand core 46 and less sensitivity to heat effect. Advantageously, in contrast to the previously described embodiments, preheating of sand core 40 is not required before applying adhesive layer 40 or subsequent layers.

In FIG. 4C, a TBC 41 or ceramic layer is applied to adhesion layer 46 via a thermal spraying process, and preferably the same thermal spraying process utilized in applying adhesion layer 46, i.e., air plasma spraying from a cascaded plasma torch such as the SINPLEXPRO-90 from OERLIKON METCO (US) INC. As in the previously described embodiment, TBC 41 functions to protect the part to be produced from thermo-mechanical fatigue (cracking) and to keep heat inside the part. As described previous, TBC 41 preferably has a porosity lower than 15-25% to avoid penetration of liquid metal during the casting process, e.g., as discussed below with reference to FIG. 4E, which can result in the unintended creation of deposits inside the casted parts after solidification (scabbing effect). Alternatively, the TBC 41 can be deposited as the dual layer system or the gradient layer (with the porous TBC layer or TBC layer with the higher porosity applied to the adhesion layer 46). In the exemplary embodiment, TBC 41 is formed by applying the thermal spraying of powder products, e.g., yttria stabilized zirconia (YSZ), such as METCO™ 204NS powders by OERLIKON METCO (US) INC., onto sand core 40 with a thickness between 100 and 1000 microns, preferably 200-800, and more preferably between 400-500 microns.

After application of TBC 41, a bond coat 42 or metallic layer is applied, as in FIG. 4D. Bond coat 42 ensures adhesion of TBC 41 to the casted part in FIG. 4F. In embodiments, bond coat 42 can be a low-alloyed carbon steel applied to TBC 41 by thermally spraying, e.g., FeCrMnC (Fe 1.4-1.6Cr 1.4-1.6Mn 1.0-1.3C), such as METCO XPT 512 powder from OERLIKON METCO (US) INC. or CoCrAlY (Co 29Cr 6Al 2Si 0.3Y), such as AMDRY 920) powder from OERLIKON METCO (US) INC. and can be applied up 100 microns, and preferably up to 50 microns, and more preferably between about 15 and 30 microns. However, in order to avoid penetration of liquid metal during the casting process a thicker bond coat 42 can be applied, having a higher thickness as described above. Again, bond coat 42 is preferably applied in the same manner as used in applying TBC 41, i.e., air plasma spraying from a cascaded plasma torch such as the SINPLEXPRO-90 from OERLIKON METCO (US) INC.

Coated sand core 40 is then inserted into a mold 43, e.g., a sand mold, as shown in FIG. 4E, so that an opening 44 is formed within mold 43 to receive a casting material. In FIG. 4F, a casting material 45 suitable for the part to be cast, e.g., gray cast iron, such as ferritic cast iron SiMo51, austenitic cast iron D5S and austenitic cast stainless steel HK30 is deposited into opening 44 to cast the part. In a conventional manner, the transplanted TBC coated casted part is removed from sand mold 44 and sand core 40 is likewise removed. However, in this embodiment, adhesion layer 46 functions to ensure integrity of TBC 41 during mechanical removal of the sand core 40 after the casting process by enhancing the breaking zone between sand core 40 and adhesion layer 46. Without adhesion layer 46, the risk of TBC 41 breaking is high.

In an alternative embodiment to that shown in FIGS. 4A-4G, the process can be performed without FIG. 4D, i.e., without applying a bond coat after TBC 41. In this alternative embodiment, which is illustrated in FIGS. 5A-5F after the application of TBC 51, the coated sand core 50 is inserted to the mold 54 and casting material 55 is deposited into opening 53 of mold 54. In a conventional manner, the transplanted TBC coated casting part is removed from mold 54 and sand core 50 is likewise removed.

To ensure that the casted and/or molded part is protected from cracks and that the produced part will maintain heat within the part, the adhesion layer, TBC and bond coat layers should be applied to all parts of the sand mold that will form inner surfaces of the part so that the liquid cast iron does not directly contact the sand mold. However, spraying of functional areas of the sand mold, e.g., areas for positioning the core in the mold or assembling the mold, should be avoided.

The above exemplary processes are advantageous in that pre-processing, like grit blasting, is not necessary because core 20 provides a rough surface for coating, and in that parts for coating are used in as-sprayed conditions, i.e., after processing, such as machining, is not necessary.

FIG. 6 shows a cross-section of the part still in the mold. In this example, adhesion coat 66 (abradable-based material layer) having a thickness between 264 and 300 microns is applied onto sand core 60, TBC 61 (top coat—ceramic layer) having a thickness between 435 and 438 microns is applied onto adhesion coat 66, and bond coat 62 (metallic layer) having a thickness between 19 and 23 microns is applied onto TBC 61. Casting material 65 is shown cast onto bond coat 62.

When the cast and/or molded part with a transplanted TBC system is an engine manifold for a heavy-duty truck, engine efficiency has been found to be improved by 0.5%. Fuel consumption was improved by reducing heat dissipation to the cooling system by 4-12% and by a higher temperature in the after treatment (turbo) system of about 2%, providing more efficient conversion and a more efficient turbo system. This savings can be significant. For example, based on a simple calculation, the cost saving per vehicle over a lifetime of 10 years while saving 0.2% fuel is approximately 1000 Euro. In particular, conservatively assuming 0.2% fuel saving reveals, for an average fuel consumption of 50,000 liters of diesel per year for a heavy-duty truck, savings can be as much as 1,000 liters. However, as test have shown fuel reductions of 0.5%, savings over the lifetime of the vehicle can be up to 2,500 liters.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

1. A method for forming a molded part, comprising: applying a thermal barrier coating (TBC) system to a sand core;inserting the TBC coated sand core into a mold; andforming a cast iron part in the mold with the inserted TBC coated sand core.

2. The method according to claim 1, wherein the TBC system comprises a ceramic layer and a metallic layer.

3. The method according to claim 2, further comprising: applying the ceramic layer over the sand core with an air plasma spray thermal spray process; andapplying the metallic layer onto the ceramic layer with the air plasma spray thermal spray process.

4. The method according to claim 2, wherein the ceramic layer is applied as dual layer system with a porous TBC layer applied over the sand core and a non-porous TBC layer applied onto the porous TBC layer.

5. The method according to claim 2, wherein the ceramic layer is applied as a gradient layer with a porosity decreasing from the sand core.

6. The method according to claim 2, wherein the ceramic layer is applied with a thickness between 100 and 1000 microns, preferably between 200 and 800, more preferably between 400 and 500 microns.

7. The method according to claim 2, wherein the metallic layer is applied with a thickness between 100 and 500 microns, preferably between 100 and 350 microns.

8. The method according to claim 2, wherein the metallic layer is applied with a thickness up to 100 microns, preferably up to 50 microns, more preferably between 15 and 30 microns.

9. The method according to claim 2, wherein the ceramic layer comprises yttria stabilized zirconia and the metallic layer comprises a low-alloyed carbon steel that forms a bond coat for the cast iron.

10. The method according to claim 3, wherein, before the ceramic layer is applied, the method further comprises: preheating the sand core with the air plasma spray thermal spray process.

11. The method according to claim 1, wherein the TBC system further comprises an adhesion layer.

12. The method according to claim 11, wherein the adhesion layer is applied with a thickness between 20 and 500 microns, preferably between 100 and 400 microns, more preferably between 200 and 350 microns.

13. The method according to claim 11, wherein, before the ceramic layer is applied, the method further comprises: applying the adhesion layer onto the sand core with an air plasma spray thermal spray process, wherein the ceramic layer is applied onto the adhesion layer.

14. The method according to claim 11, wherein the adhesion layer comprises at least one of NiC or a mixture of metal and polymer, such as a metal-based polymer composite, preferably an Al based polymer, more preferably at least one of: a MCrAlY based polymer, a NiCrAl based polymer, a NiAl based polymer, an Al-bronze based polymer or an AlSi polyester.

15. The method according to claim 1, wherein the sand core comprises: one of silica sand, chromite sand, or zircon sand;bentonite;water; andinert sludge.

16. The method according to claim 15, wherein the sand core further comprises anthracite.

17. The method according to claim 15, wherein the one of silica sand, chromite sand or zircon sand further includes olivine, staurolite, or graphite.

18. A molded part comprising: a cast iron body; anda TBC system integrally molded with an interior surface of the cast iron body.

19. The molded part formed by a method according to claim 1, the molded part comprising: a cast iron body; anda TBC system integrally molded with an interior surface of the cast iron body.

20. The molded part according to claim 18, wherein the TBC system comprises a ceramic layer and a metallic layer.

21. The molded part according to claim 18, wherein the ceramic layer comprises yttria stabilized zirconia and the metallic layer comprises a low-alloyed carbon steel.

22. The molded part according to claim 18, wherein the TBC system further comprises an adhesion layer.

23. The molded part according to claim 22, wherein the adhesion layer comprises at least one of NiC or a mixture of metal and polymer, such as a metal-based polymer composite, preferably an Al based polymer, more preferably at least one of: a MCrAlY based polymer, a NiCrAl based polymer, a NiAl based polymer, an Al-bronze based polymer or an AlSi polyester.

24. The molded part according to claim 18, wherein the molded part is one of a turbocharger component, an exhaust manifold or a turbo manifold.