JP2008523994A - Article casting method - Google Patents

Abstract

  A method of casting an article using a mold including a mold cavity, the method comprising providing a halogen-containing compound on at least a portion of the mold surface adjacent to the mold cavity, and introducing molten metal into the mold cavity. Pouring, cooling and solidifying the metal, and removing the article from the mold.

Description

  The present invention relates to a method for casting an article, and more particularly, but not exclusively, to a method for sand casting an aluminum alloy engine block.

  The engine block is usually made by sand casting an aluminum alloy. It is known to line the surface of each cylinder in the engine block to which the piston reciprocates with a cast iron liner to provide a reciprocating surface with suitable low friction and good wear resistance. Yes. Such liners increase the weight of the engine and the use of such liners is a disadvantage for removing heat from the engine cylinders because cast iron has a lower thermal conductivity than aluminum-based alloys.

  Thus, in order to remove the cast iron liner, various processes have been developed to coat the inner surface of each cylinder with a metal harder than aluminum, providing a reciprocating surface with low friction and wear resistance, These processes include electrical coating, plasma transfer wire arc coating, and laser alloying. For example, an iron-based alloy-coated plasma spray is described in Patent Document 1, and the use of laser alloying is described in Patent Document 2 and Patent Document 3. Unfortunately, such a process produces a satisfactory coating only when applied to a relatively smooth substrate, and even after machining, the sand-molded engine block surface is very porous. It is quality.

  This problem is taken up in Patent Document 4, which inserts a cylindrical brass insert into the sand mold, and this brass insert forms a cylinder in the engine block. A method for casting an aluminum engine block is disclosed. As a result of the use of an insert member having such a high thermal conductivity, the cooling rate of the aluminum alloy around the insert member is much faster than the cooling rate of the aluminum alloy elsewhere in the mold cavity. Thus, the porosity in the resulting casting is greatly reduced in the volume around the insert, and once the insert is removed, machining inside each cylinder is performed using the method described above. Produce a surface that is suitable for.

This method, however, has a number of drawbacks. Removal of brass inserts can be difficult, especially in V-engines where the cylinder is tilted with respect to the engine block, requiring extra and relatively laborious steps in the manufacturing process. . In addition, brass inserts are susceptible to mechanical damage, especially after repeated exposure to molten aluminum alloy, the brass inserts are annealed and soft and need to be replaced over a period of time. Increase the cost of the casting process.
US Pat. No. 6,548,195 US Pat. No. 6,39,0050 European Patent Application No. 1041173 US Pat. No. 5,931,213

  According to a first aspect of the present invention, we provide a method of casting an article using a mold that includes a mold cavity, the method including a halogen on at least a portion of the surface of the mold adjacent to the mold cavity. Providing a compound; injecting molten metal into the mold cavity; cooling and solidifying the metal; and removing the article from the mold.

  By using such compounds, the porosity formed by the reaction at the surface of the casting adjacent to the appropriate part of the mold is reduced, and once machined, this surface can be electrocoated, plasma transfer. It provides a suitable substrate for wire arc coating and the like, and produces a wear resistant surface with low friction.

  Preferably the halogen is fluorine. The coating can be, for example, dipotassium fluorotitanate. Alternatively, the halogen can be chlorine, for example, a potassium chloride-magnesium chloride eutectic.

  Preferably, the halogen comprising the compound is provided in a coating applied to at least a portion of the mold surface that forms at least a portion of the mold cavity.

  Preferably, the method further comprises the step of applying hydrostatic pressure to the article. In this case, preferably the method further comprises heating the article to a temperature at which the entire article is solid while applying hydrostatic pressure.

  Applying hydrostatic pressure to the article at a particularly high pressure usually removes internal vacancies in the cast article, improves the mechanical integrity of the article, and such cavities during machining of the article Reduces the risk of exposure to the surface of the article.

  The metal is preferably mainly aluminum. The metal can be an aluminum-silicon alloy, preferably a hypoeutectic aluminum-silicon alloy.

Preferably, the coating is sprayed on the surface of the mold.
Preferably, the mold is made exclusively from sand.
The article can be an engine block. In this case, preferably, the portion of the mold covered with the coating material is a cylinder in the engine block.

  According to a second aspect of the invention, we provide a casting of an article using the method consisting of the first aspect of the invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings, which show a schematic diagram of a method of making an article according to the present invention.

  In this example, the method is applied to sand casting the engine block 10 from a conventional hypoeutectic aluminum-silicon alloy, such as the 356 or 354 alloy detailed below.

  However, it should be understood that this method applies equally to the manufacture of any cast article using any metal or alloy, such as an aluminum-magnesium alloy or magnesium-based alloy.

  The mold 12 is formed from a first mold part 12a and a second mold part 12b made from zircon sand or silicon sand using conventional sand mold technology. The cylindrical portion of the upper mold part 12a that forms a cylindrical cavity, such as for an engine block cylinder, is then coated with a coating 14 containing a halogen such as fluorine. In this example, the halogen is fluorine, and the coating material contains a powder of dipotassium fluorotitanate (K2TiF6). Other halogen-containing compounds can alternatively be used, such as a potassium chloride-magnesium chloride eutectic, potassium borofluoride, or a mixture of aluminum chloride.

  K2TiF6 powder is mixed with a solvent, a filler material such as zircon powder, and a gelling agent. The covering material includes, for example, 60% by weight of powder (the powder includes 25% by weight of zircon powder and 75% by weight of dry milled powder of K2TiF6) and 40% of IPA solvent.

  The dressing is usually sprayed on the surface of the mold, but can also be applied on the mold. Alternatively, dry K2TiF6 powder may be rubbed onto the surface of the mold, or added directly to the sand used to form the mold at a rate of about 0.5 wt% K2TiF6. good.

  The mold parts 12a, 12b are then clamped together to form a mold cavity, a molten aluminum-silicon alloy is injected into the mold cavity, and the mold is cooled until the alloy solidifies. The as-cast engine block 10 is then removed from the mold 12.

  Typically, during sand casting of an alloy such as an aluminum-silicon (Al-Si) hypoeutectic alloy, hydrogen ions migrate from the mold 12 into the liquid metal adjacent to the mold surface. As the molten metal solidifies, the dissolved hydrogen exits from the solidification zone into the liquid metal that is still molten and extends approximately perpendicular to the surface of the casting to a depth of 3-4 mm. A plurality of subsurface elongated microvoids are formed. It is believed that strontium inclusions in the alloy facilitate the formation of this microvoid. Traditionally, during machining of a cast article, less than 3 mm of material is removed from the surface of the article, and thus such machining exposes these voids to the surface of the article, and plasma transfer wire arc coating, It has been formed on surfaces that are unsuitable for electrical coatings and coatings of that kind.

  However, in the presence of a K2TiF6 coating, the coating mitigates the migration of hydrogen ions into the molten metal, thus greatly reducing the surface and subsurface microvoids of the casting. This is believed to be caused by the fluorine in the coating reacting with the hydrogen ions before the hydrogen ions can be dissolved in the molten metal. As a result, the surface of the casting adjacent to the coating, i.e., the inner surface of the cylinder in the engine block in this example, does not have surface microvoids that adversely affect the completeness of the coating, as described above. Can be machined and coated.

  However, even when a K2TiF6 coating is used, such castings are not as a result of reaction with the mold as described above, but as a result of the relatively slow cooling rate associated with sand casting. May include internal voids that are formed. Internal vacancies may be exposed on the surface of the article during casting machining, and it is therefore desirable to remove these vacancies in addition to fine vacancies on the surface.

  Thus, the as-cast engine block is subjected to a hydrostatic compression molding using a conventional, eg, commercially available AIHIPPING process or Bodycott Densai® II process. In such a process, the engine block is housed in a fluid container and heated to a temperature close to the melting temperature of the alloy but the alloy remains solid, for example, 40 degrees below the solidus temperature of the alloy. For example, a pressure of 1000 atoms is applied. The engine block is usually pressurized and held in a heated fluid for 45 minutes to 1 hour.

  The combination of fluid pressure and temperature rise causes the internal cavities to sink, and the material surrounding each vacancy is diffusion bonded. Thus, the internal voids are substantially removed, and the mechanical perfection of the casting is improved. In this way, the casting can be machined with substantially reduced risk of exposure of internal vacancies on the surface of the casting.

  HIPPING cannot be used to improve surface microvoids because the pressurized fluid provides internal support that fills the surface voids and prevents the voids from sinking Should be understood. In addition, the aluminum alloy layer that separates each void from the surface of the article is relatively thin and can be easily destroyed under the pressure of the pressurized fluid, thus allowing the fluid to be pressurized inside the void. HIPPING is not effective in removing subsurface fine vacancies because it exposes to and prevents coalescence of materials around the vacancies. Therefore, in order to solve the problem of surface / surface vacancies and internal vacancies, it is necessary to use a template coated with a compound containing halogen or a template containing a compound containing halogen in addition to HIPPINNG It is.

  After HIPPING, the casting is then machined to the required dimensions and surface roughness. In this example, the inner surface of the cylinder is machined in preparation for the application of a plasma transfer wire coating, an electrical coating, or a coating that has low friction using this type and is excellent in wear resistance. The

  As used in this specification and the claims, the terms “comprising” and “comprising” and variations of these terms mean that the particular feature, step, or completeness is included. The term should not be considered as excluding the presence of another feature, step or element.

  The features disclosed in the foregoing description, or the appended claims, or the accompanying drawings showing the specific forms or means for performing the disclosed functions, or methods or steps for achieving the disclosed results Are used to implement the present invention in its various forms, either separately or in combination of these features, as the case may be.

1 is a schematic diagram of a method of making an article according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Engine block 12 ... Mold 12a, 12b ... Mold component 14 ... Coating material

Claims (19)

Providing a halogen containing compound to at least a portion of the surface of the mold adjacent to the mold cavity;
Injecting molten metal into the mold cavity;
Cooling and solidifying the metal;
Removing the article from the mold;
A method of casting an article using a mold that includes a mold cavity.   The method of claim 1, wherein the halogen is fluorine.   The method according to claim 2, wherein the coating material is dipotassium fluorotitanate.   The method of claim 1, wherein the halogen is chlorine.   The method of claim 4, wherein the coating comprises a potassium chloride-magnesium chloride eutectic.   6. The halogen-containing compound is provided in a coating applied to at least a portion of the mold surface that forms at least a portion of the mold cavity. The method described.   The method according to any one of claims 1 to 6, further comprising the step of applying hydrostatic pressure to the article.   The method of claim 7, further comprising maintaining the article at an elevated temperature that maintains a solid state while the entire article is applying hydrostatic pressure.   The method according to claim 1, wherein the metal is mainly aluminum.   The method of claim 9, wherein the metal is an aluminum-silicon alloy.   11. The method of claim 10, wherein the metal is a hypoeutectic aluminum-silicon alloy.   12. A method according to any one of the preceding claims, wherein the coating is sprayed onto the mold.   The method according to claim 1, wherein the mold is mainly made of sand.   The method according to claim 1, wherein the article is an engine block.   The method of claim 14, wherein a portion of the surface of the mold cavity that is coated with the dressing forms a cylinder in an engine block. An article cast using the method of any one of claims 1-15.   A method of making an article substantially as herein described with reference to the accompanying drawings.   Article substantially as herein described with reference to and / or shown in the accompanying drawings.   Any novel feature or combination of features substantially as herein described with reference to the accompanying drawings and / or substantially as shown in the accompanying drawings.

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