JPS6356347A - Casting method for light alloy cylinder head - Google Patents

Abstract

PURPOSE:To cast a cylinder head and valve seats with one time of operation and to improve productivity by mounting fiber moldings to valve hole forming parts of sand cores for forming intake and exhaust ports having pressure-resistant coating layers, installing the same into a casting mold, then pouring a molten metal into the mold and pressurizing the molten metal to pack the molten metal into the fiber moldings. CONSTITUTION:After the fiber moldings f1, f2 are mounted to the outside peripheral faces of the valve hole forming parts 51, 52 of the sand cores 31, 32, the sand cores 31, 32 are disposed in the cavity 7 of a metallic mold 6. The installation of the moldings f1, f2 to the mold 6 is facilitated and the positional deviation and deformation of the fiber moldings f1, f2 during casting are prevented if the fiber moldings are mounted in the cavity in the above-mentioned manner. Since the light alloy constituting the cylinder head and the light alloy of the valve seats are the same material and are continuous with each other without having joints, the joint strength increases and the wall thickness around the valve seats can be reduced. Coolability is thereby improved. Since the pressure resistant coating layers are provided on the surfaces of the cores 31, 32 the destruction of the cores 31, 32 is prevented and the penetration of the molten metal to the cores 31, 32 is prevented. Casting defects, etc., are thus averted.

Description

Detailed Description of the Invention A1 Objective of the Invention (1) Industrial Field of Application The present invention relates to a light alloy cylinder head used in an internal combustion engine, particularly a light alloy cylinder head body, and a cylinder head body integrated with the cylinder head body. The present invention relates to a method for casting a valve seat comprising an annular fiber molded body and a light alloy matrix.

(2) Conventional technology Conventionally, when casting this type of cylinder head, the valve seat obtained through casting and machining is installed in a mold using a core, and then molten light alloy is added to the mold. A method is used in which the valve seat is cast into the cylinder head body at the same time as the cylinder head body is injected under pressure (see Japanese Patent Laid-Open No. 59-224-409).

(3) Problems to be solved by the invention However, in the conventional method, casting operations such as casting of the valve seat and casting of the cylinder head body must be performed twice, and the valve seat is cast before the casting of the cylinder head body. Since the cylinder head must be machined, many steps are required to cast the cylinder head, resulting in poor productivity.

In addition, in order to firmly hold the valve seat to the cylinder head body by casting, it is necessary to
The wall thickness of the part surrounding the valve seat must be increased, and as a result, there is also the problem that cooling performance deteriorates as the wall thickness around the valve seat increases.

An object of the present invention is to provide a method for casting the cylinder head that can solve the above problems.

B0 Structure of the Invention (1) Means for Solving the Problems The first invention is characterized in that the fiber molded bodies are respectively attached to the valve hole molding portions of a sand core for molding suction and exhaust ports having a pressure-resistant coating layer on the surface. and placing both sand cores in the mold;
Injecting the light alloy molten metal into the mold, pressurizing the molten metal to obtain the cylinder head body, and filling the side fiber molded body with the molten metal to obtain both valve seats. shall be.

Further, the second invention provides a method for applying a coating agent for obtaining a pressure-resistant coating layer to the surface of the sand core for forming suction and exhaust ports, and when the coating agent is in a semi-dry state, the valves of both sand cores are each of the fiber molded bodies is installed in the hole molded part,
Next, the coating agent is completely dried to obtain the coating layer, and the side fiber molded bodies are respectively joined to both valve hole molding parts via the coating layer; the step of installing both sand cores in a mold; Injecting the light alloy molten metal into the mold, pressurizing the molten metal to obtain the cylinder head body, and filling the side fiber molded body with the molten metal to obtain both valve seats. shall be.

(2) Effects According to the first invention, a cylinder head can be obtained by one casting operation using a fiber molded body.

Furthermore, since the light alloy that makes up the cylinder head body and the light alloy matrix of both valve seats are made of the same material and are continuous without any seams, the joint strength between the cylinder head body and both valve seats is high. This makes it possible to reduce the wall thickness of the area around both valve seats in the cylinder head body and improve the cooling performance thereof.

Furthermore, since a pressure-resistant coating layer is provided on the surface of the sand core, it is possible to prevent the sand core from being destroyed by pressurized molten metal. By preventing the insertion of the valve seat, it is possible to avoid defects such as poor casting surface on the inner circumferential surface of the valve seat.

Moreover, since the fiber molded bodies are attached to the sand core, the fiber molded bodies can be easily installed in the mold, and it is possible to prevent the positional shift and deformation of each fiber molded body during casting.

According to the second invention, each fiber molded body is joined to each valve hole molded part through a pressure-resistant coating layer, and this prevents the fiber molded body from falling off and being damaged when the sand core is installed in the mold. Furthermore, it is possible to more reliably prevent misalignment, deformation, etc. of each fiber molded body during casting.

(3) Embodiment FIG. 1 shows a cylinder head 1 made of a light alloy, and the cylinder head 1 includes a cylinder head main body 1a made of a light alloy, and valve seats 2I on the intake and exhaust sides integrated with the cylinder head main body 1a.
, 2□, and both valve seats 21.2□ are composed of an annular fiber molded body and a light alloy matrix.

The fiber molded article is made by partially bonding reinforcing fibers with an inorganic binder. The reinforcing fibers have excellent adhesion to the light alloy matrix, and have various effects such as improving wear resistance, improving strength, and suppressing the coefficient of thermal expansion, such as alumina fibers, silica fibers, and silicon carbide fibers. Single fibers and mixed fibers thereof are applicable, and it is also possible to use ceramic fibers such as whiskers and silicon nitride fibers.

The fiber volume ratio (vr) of each fiber molded body is 10 on the intake side.
~20%, and 20% or more on the exhaust side is appropriate. The reason why the fiber volume fraction on the exhaust side is set high is that the heat load on the valve seat 2□ on the exhaust side is large.

Examples of light alloys include aluminum alloys and magnesium alloys.

Next, the casting operation of the cylinder head 1 will be explained.

First, we will discuss the production of the fiber molded body used for the valve seat 21 on the intake side.
A molding material is prepared by dispersing a material manufactured by IC1 (trade name: Safil, average diameter: 3 μm, average length: 0.2 n) in a 5% aqueous solution of colloidal silica as an inorganic binder.

A porous cylindrical mold is manufactured using shell sand with an average particle size of AFS34 and a resin addition rate of 2.2%.

The mold is immersed in the molding material, and while the mold is being rotated, a suction action is applied to the inside of the mold to cause the molding material to adhere to the outer peripheral surface of the mold to a predetermined thickness.

Using a rubber press, apply 10k of molding material to the outer peripheral surface of the mold.
Press with a pressure of gf/d, then dry in a drying oven for 4 hours.
A drying operation was performed at 00° C. for 2 hours to obtain a circular fiber molded material.

Using a vacuum furnace, the fiber molded material was fired at 800°C for 30 minutes, and the outer diameter was 31.5++n and the inner diameter was 24.5.
mm, height 4. Q vs, fiber volume percentage approximately 15%
(Bulk density: approximately 0.51 g/cc) A fiber molded body on the intake side is obtained.

The valve seat 2 on the exhaust side was made using the same method using the molding material. Obtain a fiber molded body used for. This fiber molded body on the exhaust side has an outer diameter of 30 mm, an inner diameter of 21 mm, and a height of 4.0 mm.
Basket, t@ fiber rod volume ratio approx. 21% (umbrella density approx. 0.68
g/cc).

As shown in FIG. 2, in sand cores 33, 32 for forming suction and exhaust ports having a pressure-resistant coating layer on the surface, valve holes 4. ．． After attaching the fiber molded bodies f, f2 on the intake and exhaust sides to the outer circumferential surface of the valve hole molding portions 58, 5□ that form 4□,
Those sand cores3. .

3□ is the intake and exhaust port of the cavity 7 in the mold 6 used as the cylinder head casting mold)8. ．． 82 respectively. In this way, both fiber molded bodies f,
, f2 are attached to both sand cores 31, 3□, it becomes easy to install both fiber molded bodies f,, f2 in the mold 6, and also prevents misalignment of both fiber molded bodies f,, f2 during casting. Deformation etc. can be prevented.

Also, in cavity 7, both valve guides 91.9□
Press-fit hole 10. ．． Place the core metal 111 in the part corresponding to 10□.
．． 11° and these mandrels 111. A cylindrical body 12. which is integrally formed using core sand on the outer peripheral surface of the 11° and has a pressure-resistant coating layer on its surface. .

13. A core for press-fit hole forming having an angle of 12°. ．． 132,
Furthermore, a sand core 15 for forming a rain space has a pressure-resistant coating layer on its surface at a portion corresponding to the spaces 141 and 142 for accommodating both valve mechanisms. , 152, and water jacket 1
A sand core 17 for water jacket molding having a pressure-resistant coating layer on its surface is disposed at a position corresponding to 6.

A reservoir 20 communicates with the lower part of the cavity 7 via a gate 18 and a runner 19, and a plunger 22 is slid into a cylinder hole 21 communicating with the lower part of the reservoir 20.

A plurality of gas vent holes 23 are formed in the mold 6 and communicate with the upper part of the cavity 7, and each gas vent hole 23 is provided with a closing pin 2.
4 is inserted. Each gas vent hole 23 has a small diameter part 23a on the side of the cavity 7 and a large diameter part 23b on the atmosphere side communicating with the small diameter part 23a.
Therefore, when each closing pin 24 fits into each small diameter portion 23a, communication with the atmosphere is cut off from the cavity 7, and when each closing pin 24 is located within each large diameter portion 23b, the cavity 7
communicates with the atmosphere.

With the cavity 7 communicating with the atmosphere and the plunger 22 being lowered, molten aluminum alloy (JIS, AC2B) at 720°C is supplied to the molten metal sump 20,
The plunger 22 is raised and the cavity 7 is opened under atmospheric pressure.
Inject molten metal into.

During the pouring operation under atmospheric pressure, the pressure of the molten metal is low and both the fibrous molded bodies f, f2 have a predetermined fiber volume ratio, so the molten metal does not penetrate into each of the fibrous molded bodies f, f2. Further, the gas in the cavity 7 is pushed up by the molten metal and escapes into the atmosphere through each gas vent hole 23.

After the cavity 7 is filled with molten metal, each closing pin 2
4 cuts off the communication between the cavity 7 and the atmosphere. Then, the plunger 22 pumps the molten metal in the cavity 7 to 5 Q k
The cylinder head body 1a is obtained by pressurizing with a pressure of gf/cA, and the molten metal is filled into each of the fiber molded bodies f, , f, and the valve seats 2 on the intake and exhaust sides are filled. .

Get 2□.

During pressurization of the molten metal, since a pressure-resistant coating layer is formed on each sand core 3I, 32, etc., the sand cores 31, 3□, etc. do not break, and the sand core 33
, 3□ can be prevented from being inserted into the valve seats 28, 2□, thereby avoiding defects such as poor casting surfaces on the inner circumferential surfaces of the valve seats 28 and 2□.

Also, the aluminum alloy that constitutes the cylinder head body 1a and both valve seats 2. ．． Since the aluminum alloy matrix No. 22 is made of the same material and is seamlessly continuous, the cylinder head body 1a and both valve seats 2I,
2□ becomes stronger, and this increases the wall thickness around both valve seats 2I, 2□ in the cylinder head body 1a, that is, the distance d between the water jacket 16 and both valve seats 21, 2□, −
d4 can be reduced to improve their cooling properties.

Figure 3 is a micrograph (100x magnification) showing the metal structure of the valve seat 2 on the exhaust side, in which short alumina fibers a are dispersed in the aluminum alloy matrix m, and casting defects such as gas holes occur. It can be seen that there is no

Next, a method for forming the pressure-resistant coating layer will be explained.

The pressure-resistant coating layer has a two-layer structure, and the first and second coating agents shown in Tables (1) and (2) are used to form them.

Table I Table ■ In Tables ■ and ■, sodium dialkyl sulfosuccinate (trade name: Perex 5% aqueous solution) is used as a wetting agent, and Formasta B (trade name) is used as an antifoaming agent. In Table ■, the product name A-PAX is used as zircon powder, and the product name GCl is used as phlogopite.
ooO are used respectively. In Table ■, the trade name Lubricate is used as the aggregate.

Hereinafter, as an example, the formation of a pressure-resistant coating layer on the sand core 31 for forming an intake port will be described.

(a) Sand core 3. is immersed in the first coating agent for 3 seconds.

(bl) The sand core 31 is taken out from the first coating chamber, and the first coating agent applied to the surface of the sand core 31 is naturally dried for 8 minutes or more to a semi-dry state.

(C1 sand core 31 was placed in a drying oven and heated to 180℃ for 15 minutes.
A drying process is performed for 1 minute to completely dry the first coating agent to obtain a first coating layer.

(dl Take out the sand core 31 from the drying oven and air cool it for 10 minutes or more.

(e) Dip the sand core 3 into the second coating agent for 3 seconds.

(f) Sand core 3. is taken out from the second coating agent, and the second coating agent applied to the surface of the first coating layer is air-dried for 3 minutes or more to a semi-dry state.

(g) l Sand core 3. Place it in the drying oven and heat it at 150°.
C1 A drying process is performed for 15 minutes to completely dry the second coating agent to obtain a second coating layer.

(h) Take out the sand core 31 from the drying oven and cool it in air.

The fiber molded body f1 on the intake side has the sand core 3 as described above.
．． After forming the first and second coating layers on the surface of the sand core 3. Valve hole molding part 5. The device 8 is installed.

In this case, the fiber molded body f is placed in a sand core 3. In order to reliably hold the fiber molded body f1 after the above (fl process, that is, when the second coating agent is in a semi-dry state
is attached to the sand core 31, and then step (g) is performed, the fiber molded body f1 is attached to the sand core 3I through the second coating layer.
It is securely bonded to the

As a result, the sand core 3. The fiber molded body f will not fall off and be damaged during installation, and displacement, deformation, etc. of the fiber molded body f during casting can be more reliably prevented.

C6 Effects of the Invention According to the first invention, a cylinder head can be obtained in one casting operation using a fiber molded body, and the conventional machining process can be eliminated, thereby improving the productivity of the cylinder head. can.

Furthermore, since the joint strength between the cylinder head body and both valve seats can be increased, the wall thickness around both valve seats in the cylinder head body can be reduced and cooling performance thereof can be improved.

Furthermore, the pressure-resistant coating layer can prevent each sand core from being destroyed by the pressurized molten metal, and the pressure-resistant coating layer can prevent the molten metal from being inserted into each sand core while filling each fiber molded body with the molten metal. This makes it possible to avoid defects such as poor casting surfaces on the inner circumferential surface of each valve seat.

Furthermore, each fiber molded body can be easily installed in a mold via each sand core, and each sand core can prevent misalignment, deformation, etc. of each fiber molded body during casting. can.

According to the second invention, since each fiber molded body is bonded to each sand core through a pressure-resistant coating layer, in addition to the above-mentioned effects, the fiber molded body is prevented from falling off when the sand core is installed in the mold. It is possible to more reliably prevent problems such as breakage and misalignment of the fiber molded body during casting.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view of a cylinder head, FIG. 2 is a longitudinal sectional front view of a cylinder head casting mold, and FIG. 3 is a microscopic photograph showing the metal structure of a valve seat. f,, f2...Fiber molded body, 1...Cylinder head, 1a...Cylinder head body, 21,2□...Valve seat, 31,3゜...Sand core,
56,5°... Valve hole forming part, 6... When used as a mold Applicant: Honda Motor Co., Ltd. Agent, Patent Attorney Ken Ochiai Figure 1

Claims (2)

[Claims] (1) When casting a light alloy cylinder head comprising a light alloy cylinder head body and a valve seat integrated with the cylinder head body, the valve seat is composed of an annular fiber molded body and a light alloy matrix. , mounting the fiber molded bodies on the valve hole molding portions of a sand core for forming suction and exhaust ports having a pressure-resistant coating layer on the surface, and installing both sand cores in a mold; A light alloy product characterized by using the following steps: injecting a molten alloy, pressurizing the molten metal to obtain the cylinder head body, and filling both fiber molded bodies with the molten metal to obtain both valve seats. Cylinder head casting method. (2) When casting a light alloy cylinder head comprising a light alloy cylinder head body and a valve seat integrated with the cylinder head body, the valve seat is composed of an annular fiber molded body and a light alloy matrix. A coating agent for obtaining a pressure-resistant coating layer is applied to the surface of the sand core for forming suction and exhaust ports, and when the coating agent is in a semi-dry state, the valve hole forming portions of both sand cores are coated with the above coating agent. a step of respectively mounting the fiber molded bodies, then completely drying the coating agent to obtain the coating layer, and joining both the fiber molded bodies to both valve hole molding parts through the coating layer; both sand cores; After pouring the light alloy molten metal into the mold, the molten metal is pressurized to obtain the cylinder head body, and the molten metal is filled into both fiber molded bodies to obtain both valve seats. A method for casting a light alloy cylinder head, comprising the steps of;