JPH0263645A - Method for casting cylinder head - Google Patents

Abstract

PURPOSE:To quicken cooling velocity of molten metal and to improve service life with heat fatigue resistance at intermediate part of valve seats by pouring molten Al metal into a die forming groove for cooling at position of a die facing to cavity at the intermediate part of the valve seats and rapidly cooling the molten metal at the intermediate part of the valve seats. CONSTITUTION:In the die 1, plural port cores 3, 3 are fitted to form cavity 4. The groove 2 for cooling is formed at the position facing to the intermediate part of the port cores in the die 1. The die 1 fitting core assembly is preheated and the molten Al metal having the prescribed temp. is poured into the cavity 4. The molten metal is flowed into the intermediate part 9 of the valve seats and also into the groove 2 for cooling. The molten metal is rapidly cooled and a cylinder head casting 6 having small dendritic arm spacing value in the material structure at the intermediate part 9 of the valve seats is obtd. by removing the material flowing into the groove 2 for cooling from the casting after casting the cylinder head casting 6. By this method, the service life with the heat fatigue resistance is improved and the development of crack at the time of operating the engine can be prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for casting cylinder heads for internal combustion engines, and more particularly, to a method for casting cylinder heads that prevents the occurrence of cracks between intake and exhaust valve seats. .

[Conventional technology]

In currently mass-produced automobile engines, cracks sometimes occur between the intake and exhaust valve seats of the cylinder head.Recently, with the advent of turbocharged engines, four-hartz engines, etc., automobile engines are becoming increasingly high-output. As a result, accidents tend to occur frequently where cracks occur between the intake and exhaust valve seats.

FIG. 4 shows a bottom view of the cylinder head of a conventional four-cylinder engine. Inlet valve seats 7. Cracks may occur in the exhaust half seat 8 or in the space 9 between the valve seats. This is due to the fact that this part 9 is exposed to very high combustion heat during engine operation, and the installation of cooling water passages is restricted due to the installation of the Harutsu, nozzle, etc., and the part 9 between the valve seats becomes high temperature, causing thermal fatigue. This is to wake up.

Japanese Patent Application Laid-open No. 56-6045 discloses that in casting a cast iron cylinder head, a spheroidizing agent is placed in the mold for the C1 valve gap, and during casting, the molten metal comes into contact with the spheroidizing agent, and the valve area becomes spheroidized. A method of manufacturing a cylinder head has been proposed in which the mechanical strength is improved by spheroidal graphitization or incomplete spheroidal graphitization of the cylinder head and the vicinity thereof, thereby preventing cracks between the valves that occur during operation.

[Invention or problem to be solved]

It is unavoidable that the area between the intake and exhaust valve seats in the cylinder head will reach high temperatures during engine operation, and cracks will form in this area due to thermal fatigue. Furthermore, although the manufacturing method described in the above-mentioned publication has been applied to the casting of cast iron cylinder heads, it has not been applied to the casting of aluminum cylinder heads.

An object of the present invention is to solve the above-mentioned problems and provide a cylinder head casting method that prevents cracks between the intake and exhaust valve seats that occur during operation in an aluminum cylinder spatula. .

(Means and Effects for Solving the Problems) The present invention involves pouring molten aluminum into a mold in which a cooling groove is formed in the part of the mold that faces the cavity between the valve seats of the cylinder head, and This is a cylinder head casting method in which molten metal is rapidly cooled and cast.

It is shown in cross section.

A plurality of boat cores 3, 3 are attached to the mold 1, and a cavity 4 is formed. Mold 1 contains boat cores 3, 3.
A cooling groove 2 is formed at a position opposite to the intermediate portion where the cooling groove 2 is installed. This method of cooling groove 2 is shown in Fig. 2 (A) (
As shown in B), the width is W, the length is W, and the depth is D. An example of casting an aluminum cylinder head for a diesel engine using this mold will be described.

Approximately 440-450 mm for mold 1 with core assembly installed
Preheat to 690°C and pour the 690°C molten aluminum into Ki\Vitai 4. The dimensions of the cooling grooves 2 provided in the mold 1 are as shown in Fig. 2 (when the center spacing of the boat cores 3 is 24 mm).
A) Width W = 5 mm, length L = 20 + nn + shown in (B)
, the depth d = 15 mm, the draft angle 0 = 3 degrees, and the radius R of the groove tip = 2 m + i.

The molten metal injected into the cavity 4 enters the valve seat space 9 between the boat cores 3 and also flows into the cooling grooves 2. The molten metal that has flowed into the space between the valve seats 9 at this time is
The molten aluminum poured into the casting mold releases heat from the contact surface with the mold l, or the heat is radiated from the mold, or cooling grooves are formed in the part of the mold facing the area between the valve seats. The molten metal flowing into the cooling groove is rapidly cooled by the mold, and the molten metal between the valve seats connected to it also cools at a similar rate.

As the cooling rate of molten aluminum increases, the value of dendrite, arm, and subesink of the material structure decreases. After casting the cylinder head casting in this way,
By removing the material that has flowed into the cooling grooves from the casting, a cylinder head casting is obtained that has a smaller tentrite, arm, and sink value for the material structure between the valve seats.

Cracks that occur between valve seats are caused by thermal load, and the thermal fatigue life is closely related to the value of tent light arm spay sink of the cylinder head material structure, and the smaller the value, the lower the thermal fatigue life. Extends lifespan.

(Example) As shown in FIG. 1, a part of a casting mold for a cylinder head is heated, and the heat is removed from the mold through the molten metal flowing into the cooling groove 2, and the mold is rapidly cooled.

After the cylinder head casting is cast in this way, by removing the material that has flowed into the cooling groove 2 from the casting, a cylinder head casting with a smaller value of dendrite arm subay sink of the material structure of the space 9 between the valve seats can be obtained. .

The crystal structure of the aluminum alloy has a dendritic crystal structure 5 having a large number of secondary arms 12 in a direction perpendicular to a negative order arm 11, as shown in an enlarged model of a micrograph in FIG. The spacing between the secondary arms 12 is similar to that of a dendroid arm sp.
acing), and its value decreases as the cooling rate during casting becomes faster.

In the above embodiment, the value of the dendrite arm spay sink in the space 9 between the valve seats was 57 to 58 gm, which was previously 60 gm.

The cracks that occur in the space between the valve seats 9 are caused by thermal load, and the thermal fatigue life is closely related to the value of the punch line arm space sink of the cylinder material structure. The smaller the value, the longer the life.

According to the experimental results using Death 1-Piece, the value of the dendrite arm subay sink in the above example became 57 to 58 gm from the conventional 60 gm.
Thermal fatigue life is improved by about 1.2 times.

〔Effect of the invention〕

By accelerating the cooling rate of the molten metal in the area between the valve seats during cylinder head casting, the present invention reduces the value of dendrite arm spay sink in the material structure and improves the thermal fatigue life in this area. Therefore, it is possible to prevent cracks from occurring during engine operation.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view of a casting mold for a cylinder head used in the present invention, Figures 2 (A) and (B) are diagrams showing the dimensions of cooling grooves provided in the mold, and Figure 3 is a diagram showing the material structure. The enlarged model diagram, FIG. 4, is a bottom view of the cylinder head. l Mold 2. Cooling groove 3: Boat core 4: Cavity 5: Dendritic structure model 6: Cylinder head 9: Valve seat space D: Dendrite arm subay sink Patent attorney Kazuo Furukawa

Claims (1)

[Claims] A cylinder head characterized in that molten aluminum is poured into a mold in which cooling grooves are formed in the part of the mold facing the cavity between the valve seats of the cylinder head, and the molten metal between the valve seats is rapidly cooled and cast. casting method.