CASTING APPARATUS FOR CYLINDER HEAD AND HEAT TREATMENT METHOD FOR CYLINDER HEAD

Abstract

A casting apparatus for a cylinder head and heat treatment method for a cylinder head manufactured by the apparatus is provided. The casting apparatus for a cylinder head is connected with a mold by a pressing unit and a connection pipe and casts a product by pressing and injecting molten metal into the mold. A heat treatment method for the cylinder head manufactured by the apparatus includes: a molten metal supply unit that stores and stabilizes supplied molten metal and a pressing unit that is separately formed from the molten metal supply unit, receives the stabilized molten metal from the molten metal supply unit, and supplies the molten metal to the mold. In addition, a stopper that is soaked in the molten metal in the molten metal supply unit controls the amount of molten metal sent to the pressing unit.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0134727 filed in the Korean Intellectual Property Office on Nov. 26, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Field of the Invention

The present invention relates to a casting apparatus for a cylinder head and a heat treatment method for a cylinder head. More particularly, the present invention relates to a casting apparatus for a cylinder head which separates supplying and pressing of molten metal in casting, and a heat treatment method for a cylinder head.

(b) Description of the Related Art

In general, a low-pressure casting is a casting method used for manufacturing cylinder heads of vehicles and is generally used for manufacturing the cylinder heads of gasoline engines. Cylinder heads having complicated shapes are different in composition and structure because the solidification speed is different according to the portions, such that heat treatment is applied to achieve desired structure.

The heat treatment is usually T7 heat treatment, which is performed in order of solution treatment, quenching, aging, and air cooling. It is possible to reduce manufacturing time by reducing the heat treatment time, thus reducing the time for the solution treatment or the aging.

On the other hand, low-temperature casting is a casting method that presses up molten metal through a connection pipe in the opposite direction of the gravity by pressing the surface of the molten metal in a mode on a closed casting furnace at a low pressure with air or an inert gas to fill the mold, and then providing a riser effect for a predetermined time by applying a low hold pressure to solidify the product in the mold.

FIG. 7 is an exemplary schematic diagram of a casting apparatus for a cylinder head of the related art and a low-pressure casting method of the related art in which when molten metal is supplied through a pouring/pressing portion 20 implemented by integrally forming a pouring portion and a pressing portion, casting is performed right after the molten metal is poured into the pouring/pressing portion 20 by a ladle 10, thus making it may be difficult to ensure safety regarding the molten metal, and the pouring is performed after about 20˜25 shots, allowing oxides to flow into a mold 50 while waiting for the pouring. Reference numeral 40 not stated above indicates a heater.

Further, according to the casting method described above, the cylinder head structure may become coarse after casting and the solution treatment of the cylinder head material may be performed in about 6.5 hours or more.

The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present invention provides a casting apparatus for a cylinder head that reduces heat treatment time by separating supplying and pressing molten metal, and a heat treatment method for a cylinder head.

An exemplary embodiment of the present invention provides a casting apparatus for a cylinder head which is connected with a mold by a pressing unit and a connection pipe and casts a product by pressing and injecting molten metal into the mold. The apparatus may include: a molten metal supply unit that stores and stabilizes supplied molten metal; a pressing unit that is separately formed from the molten metal supply unit receives the stabilized molten metal from the molten metal supply unit, and supplies the molten metal to the mold; and a stopper that is soaked in the molten metal in the molten metal supply unit and controls the amount of molten metal to be sent to the pressing unit.

The stopper may be moved vertically (e.g., in an upward and downward direction) by a driving cylinder and may include a rod formed at one end of the driving cylinder and selectively inserted into a connection aperture that connects the pressing unit and the molten metal supply unit, and a refractory material coated on the rod. The rod may be made of an SUS material and four molten metal gates may be symmetrically formed at the upper portion of the connection pipe. Combustion cooling channels and spark plug pins may be formed at the mold.

Another exemplary embodiment of the present invention provides a heat treatment method of a cylinder head manufactured by a casting apparatus for a cylinder head which may include: a molten metal supply unit that stores and stabilizes supplied molten metal; a pressing unit that is separately formed from the molten metal supply unit, receives the stabilized molten metal from the molten metal supply unit, and supplies the molten metal to the mold; and a stopper that is soaked in the molten metal in the molten metal supply unit and controls the amount of molten metal to be sent to the pressing unit. The method may include: solution treatment of a cylinder head manufactured by the casting apparatus; quenching; and aging. The solution treatment may be performed for about 3.5˜4.5 hours with a temperature range of about 490-510° C. The aging may be performed for about 3.5˜4.5 hours with a temperature range of about 240-260° C. The quenching may be performed to about 70-80° C.

According to an exemplary embodiment of the present invention, since supplying and pressing of molten metal are separated, the structure after casting may be micronized and it may be possible to reduce the time for heat treatment of a cylinder head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic diagram of a casting apparatus according to an exemplary embodiment of the present invention;

FIG. 2 is an exemplary detailed view of a pouring portion and a pressing portion according to an exemplary embodiment of the present invention;

FIG. 3 is an exemplary view showing a portion of a casting apparatus for a cylinder head manufactured by an exemplary embodiment of the present invention;

FIG. 4 is an exemplary graph showing heat treatment time according to an exemplary embodiment of the present invention;

FIG. 5 is an exemplary view showing the shape of a stopper according to an exemplary embodiment of the present invention;

FIG. 6 is an exemplary view showing a side of a cylinder head according to an exemplary embodiment of the present invention;

FIG. 7 is an exemplary schematic diagram of a casting apparatus for a cylinder head of the related art; and

FIGS. 8 to 12 are exemplary graphs showing test results of mechanical properties, heat conductivity, S-DAS, and porosity of a cylinder head manufactured by an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, combustion, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

The advantages and features of the present invention and a method of achieving them will be clear by referring to the exemplary embodiments described in detail below. However, the present invention is not limited to the exemplary embodiments described below and implemented in various ways, the exemplary embodiments are provided to complete the present invention and make the scope of the present invention clear to those skilled in the art, and the present invention is defined only by the range described in claims.

Exemplary embodiments of the present invention relate to a casting apparatus for a cylinder head and a casting method for a cylinder head which reduce solution treatment time by forming four symmetrical gates to reduce the time for heat treatment applied to an aluminum cylinder head manufactured by low-pressure casting, by forming a combustion chamber and a spark plughole cooling channel, and by using a pouring/pressing-separate type of casting furnace having a stopper that prevents inflow of oxides.

FIG. 1 shows an apparatus according to an exemplary embodiment of the present invention and FIG. 2 is an exemplary detailed view of a pouring portion and a pressing portion according to an exemplary embodiment of the present invention.

First, referring to FIG. 1, a casting apparatus for a cylinder head according to an exemplary embodiment of the present invention may include a molten metal supply unit 100 that stores molten metal 20 a pressing unit 200 separated from the molten metal supply unit 100 and supplies the molten metal sent from the molten metal supply unit 100 to a mold 400, and a stopper 300 soaked in the molten metal 20 in the molten metal supply unit 100 and controls the amount of molten 20 to be sent to the pressing unit 200.

The stopper 300 may include a rod 320 formed at the end of a driving cylinder 310, soaked in the molten metal 20, and selectively moved vertically by the driving cylinder 310, and a refractory material 330 coated on the rod 320. The refractory material 330 may be ceramic and the material of the rod 320 may be an SUS material that prevents corrosion.

The rod 320 may control the amount of molten metal 20 sent to the pressing unit 200 from the molten metal supply unit 100 by being selectively inserted into a connection aperture 250 that connects the molten metal supply unit 100 with the pressing unit 200 by the driving cylinder 310. In other words, when the molten metal is supplied to the pressing unit, the stopper 300 may be inserted into the connection aperture 250 and prevents the molten metal 20 from being further sent to the pressing unit 200.

Other than the configuration, in the exemplary embodiment of the present invention, a first level sensor 120 that senses the level of the molten metal poured in the molten metal supply unit 100 may be provided, and similarly in the pressing unit 200, a second level sensor 220 that senses the level of the molten metal to stably supply the molten metal 20 may be provided. First and second heaters 110 and 210 may be disposed in the molten metal supply unit 100 and the pressing unit 200 to prevent the molten metal 20 from decreasing in temperature and a thermometer 230 may be disposed in the molten metal 20 in the pressing unit 200. In addition, a pressing device 270 supplies gas from the exterior to supply the molten metal 20 to the mold 400.

Referring to FIG. 2, the molten metal 20 supplied from a ladle 10 may be stabilized by remaining in the molten metal supply unit 100 by the stopper 300. In other words, the molten metal 20 may cause turbulence while continuously making natural convection due to a temperature difference between the inside and the surface, causing aluminum oxides to exist on the surface of the molten metal 20. Non-uniformity of the structure may be generated by a temperature difference, when the unstable molten metal 20 is supplied to the pressing unit 200. To prevent the non-uniformity, in another exemplary embodiment of the present invention, the amount of the molten metal 20 sent to the pressing unit 200 may be controlled by soaking the stopper 300 into the molten metal supply unit 100. Accordingly, the molten metal 20 may be sent to the pressing unit 200, after stabilization time passes and the molten metal 20 may be stabilized. The stabilization time of the molten metal 20 may be about thirty minutes or more in an exemplary embodiment of the present invention and it may be possible to prevent the aluminum oxides on the surface from flowing into the pressing unit 200 while the stopper 300 is inserted in the connection aperture 250.

Further, the structure may be micronized after casting to reduce the time taken by heat treatment of the material of a cylinder head 460. In particular, it may be important to cool a combustion chamber 450 that has a complicated shape and the portion around. FIG. 3 shows a cylinder head and a portion of a casting apparatus according to an exemplary embodiment of the present invention, in which four molten metal gates 420 may be symmetrically formed in the casting apparatus for a cylinder head, and cooling channels 440 that cool the combustion chamber 450 and spark plug pins 430 that cool a spark plughole (not shown) may be vertically formed. The molten metal gates 420 in the exemplary embodiment of the present invention may be straight gates that allow the molten metal 20 to be from under the mold 400.

The combustion chamber 450 and the portion around may be partially cooled by this configuration, to improve the speed of cooling the combustion chamber 450. In other words, the cylinder head 460 may be cast by receiving the molten metal 20 from the molten metal gates 420 connected with a connection pipe 410, the material of the cylinder head 460 to be cast may be rapidly cooled by the cooling channels 440 and the spark plug pins 430 of the combustion chamber 450 and the portion around the combustion chamber 450 may be partially and rapidly cooled, thereby forming a microstructure. The micronized structure may reduce the solution treatment time in the step of heat treatment.

A heat treatment method of a cylinder head according to an exemplary embodiment of the present invention is described hereafter.

A heat treatment method of a cylinder head according to an exemplary embodiment of the present invention may include supplying stabilized molten metal 20, casting the molten metal 20 by supplying the molten metal 20 to the mold 400 by pressing the molten metal 20, and performing heat treatment on the cast material. In particular, the cylinder head may be made of an AC2B alloy that is Al—Si—Cu-based alloy, the composition of the molten metal may be Si: about 5.0˜7.0, Cu: about 2.0˜4.0, Mg: about 0.5 or less, Zn: about 1.0 or less, Fe: about 1.0 or less, Fe: about 1.0 or less, Mn: about 0.5 or less, Ni: about 0.3 or less, Ti: about 0.2 as a weight percent and the balance may be Al.

A cylinder head may be made of the molten metal by the casting apparatus of a cylinder head, in which the molten metal may be supplied and stabilized in the molten metal supply unit 100, and the molten metal may be supplied to the pressing unit 200 and to the mold 400 after the molten metal 20 is stabilized, thereby producing a casting. Thereafter, heat treatment may be applied to the casting and the heat treatment may include solution treatment, quenching, and aging.

The solution treatment in the exemplary embodiment of the present invention may be a step that heating alloy elements and deposits non-uniformly growing in the material of the cylinder heat after casting to a substantially high temperature to uniformly solidify the heating alloy elements and deposits in a matrix, to form a single phase solid. The solution treatment temperature in the exemplary embodiment of the present invention may be limited in the range of about 490-510° C., which is under a melting point to prevent the cylinder head material from melting and sufficiently solidifying the cylinder head material.

The solution treatment time may be limited to about 3.5-4.5 hours, and when the solution treatment time is less than about 3.5 hours, the deposits etc. may not be sufficiently solidified, and when the time is over about 4.5 hours, complete solidification may be achieved, but the cost may be increased by the increase of the time and the grains may grow, which may deteriorate the properties of the material, thus limiting the solution treatment time to the range described above in the exemplary embodiment of the present invention.

When the non-uniform deposits etc. are solidified in the matrix in the solution treatment step, quenching may be performed to about 70-80° C. Residual stress may be generated by contraction due to cooling in the material of the cylinder head 460 by a rapid temperature change of about 400° C. or more in the quenching process. As the quenching temperature increases, the more the residual stress may be suppressed.

The residual stress may be reduced in the aging process and aging may be performed within the range of about 240-260° C. in the exemplary embodiment of the present invention. Aging may uniformly educe the alloy elements that are uniformly solidified through the solution treatment and may determine the properties of the aluminum cast product. To efficiently achieve the strength and remove the residual stress, aging may be applied to the AC2B cylinder head 460 for about 3.5-4.5 hours in the exemplary embodiment of the present invention.

It may be possible to rapidly grow the deposits in a stable structure by increasing the aging temperature according to the exemplary embodiment of present invention more than the related art, and the aging time may be limited to about 4.5 hours in the exemplary embodiment of the present invention to coarsely grow the deposits and the properties of the material may be decreased when heat treatment is applied for a long time. Further, when the aging time is less than 3.5 hours, the residual stress may not be sufficiently removed, and thus the aging time may be limited to the range described above in the exemplary embodiment of the present invention. Further, since a change in aging temperature has a large influence on eduction, the aging temperature may be limited to about 240-260° C.

In general, dendrite arms grow when molten metal hardens, and the gap between the growing dendrite arms is called DAS (Dendrite Arm Spacing). The dendrite arms may fall into a first dendrite arm that grows in the growing direction of the molten metal and a second dendrite arm perpendicular to the first direction, and the gap between the second dendrite arms is called S-DAS (Secondary Dendrite Arm Spacing). Porosity is a value that indicates the area occupied by pores on a certain surface in a percentage, when the porosity is high, the strength may be reduced.

After heat treatment was applied to the cylinder head manufactured by the exemplary embodiment of the present invention, S-DAS was 45-55 μm and porosity was about 0.12-0.5%. This is equivalent to the value of a cylinder heat that has undergone solution treatment for 6.5 hours.

Further, mechanism properties (e.g., hardness and tensile strength), heat conductivity, S-DAS, and porosity according to the solution treatment on the cylinder head manufactured by the exemplary embodiment of the present invention were measured.

FIGS. 8 to 12 are exemplary graphs showing measurement results and mechanical properties according to solution treatment time are described. As for hardness, a specimen that had undergone aging for 3.5 hours based on an increase in solution treatment time showed higher hardness, as for tensile strength UTS, the tensile strength is proportionate to an increase in solution treatment time and a specimen that had undergone aging for 3.5 hours showed higher tensile strength, and as for heat conductivity, the heat conductivity increased in proportion to the casting status but did not significantly change when solution treatment was applied for 3.5-6.5 hours, and the longer the aging time, the more the heat conductivity increased.

The S-DAS and porosity were 55 μm or less and 0.25% or less, respectively, which are equivalent values to the S-DAS and porosity when solution treatment was applied to a cylinder head manufactured by low-temperature casting of the related art for 6.5 hours.

Consequently, in an exemplary embodiment of the present invention, the accurate temperature and time range were determined for solution treatment and aging in T7 heat treatment that applies heat treatment to an aluminum cylinder head made of an AC2B alloy that is an Al—Si—Cu-based alloy, such that it was possible to achieve tensile strength and yield strength at an equivalent level as those of products manufactured by T7 heat treatment of the related art.

Although exemplary embodiments of the present invention were described above, those skilled in the art would understand that the present invention may be implemented in various ways without changing the spirit or necessary features. Therefore, the exemplary embodiments described above are merely examples and should not be construed as being limitative in all respects.

While this invention has been described in connection with what is presently considered to be exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the accompanying claims.

Claims

1. A casting apparatus for a cylinder head which is connected with a mold by a pressing unit and a connection pipe and casts a product by pressing and injecting molten metal into the mold, the apparatus comprising:

a molten metal supply unit that stores and stabilizes supplied molten metal;

a pressing unit separately formed from the molten metal supply unit, receives the stabilized molten metal from the molten metal supply unit, and supplies the molten metal to the mold; and

a stopper soaked in the molten metal in the molten metal supply unit controls the amount of molten metal sent to the pressing unit.

2. The apparatus of claim 1, wherein the stopper is moved vertically by a driving cylinder, and includes:

a rod formed at one end of the driving cylinder and selectively inserted into a connection aperture that connects the pressing unit and the molten metal supply unit; and

a refractory material coated on the rod.

3. The apparatus of claim 2, wherein the rod is made of an SUS material.

4. The apparatus of claim 1, wherein four molten metal gates are symmetrically formed at the upper portion of the connection pipe.

5. The apparatus of claim 1, wherein combustion cooling channels and spark plug pins are formed at the mold.

6. A heat treatment method of a cylinder head manufactured by a casting apparatus for a cylinder head, comprising:

solution treatment of the cylinder head manufactured by the casting apparatus;

quenching cylinder head materials; and

aging the cylinder head materials, wherein the casting apparatus includes: a molten metal supply unit that stores and stabilizes supplied molten metal; a pressing unit separately formed from the molten metal supply unit, receives the stabilized molten metal from the molten metal supply unit, and supplies the molten metal to the mold; and a stopper soaked in the molten metal in the molten metal supply unit controls the amount of molten metal sent to the pressing unit.

7. The method of claim 6, wherein the solution treatment is performed for about 3.5˜4.5 hours with a temperature range of about 490-510° C.

8. The method of claim 6, wherein the aging is performed for about 3.5˜4.5 hours with a temperature range of about 240-260° C.

9. The method of claim 6, wherein the quenching is performed to about 70-80° C.