JPS6030592A - Production of composite valve seat - Google Patents

Abstract

PURPOSE:To form a good composite valve seat with uniform adhesion without microcracks by subjecting a base material for the valve seat formed by molding powder and sintering the molding and a working face material to grasping under pressure or rolling pressurizing in dies to a specific density or above and subjecting the same further to resintering. CONSTITUTION:A powder-molded base material for a valve seat having heat resistance and high crushing strength and a working face material consisting of heat- and wear resistant powder are both subjected to preliminary sintering. Both materials are superposed and are inserted into dies, by which the materials are subjected to uniaxial compression or rolling pressurization permitting strong compression to >=90% true density. The compressed body obtd. in such a way is resintered in a vacuum furnace kept at >=1,100 deg.C to form the composite valve seat having uniform quality without microcracks.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a valve seat that exhibits excellent characteristics by combining two types of sintered bodies into one body. As a valve seat is press-fitted into a cylinder head and repeatedly struck by the valve face, it must have not only wear resistance but also heat resistance and high radial crushing strength to prevent it from falling off.

By the way, sintered metals are widely used because they can easily produce mechanical parts with excellent wear resistance, but the
Since it has 20% pores, its strength is low. Therefore, in order to manufacture valve seats from sintered metal, raw material powders for the contact surface and the base are filled into a mold, formed, and sintered to form an integrated sintered valve seat, which improves wear resistance. The applicant has already proposed a valve seat that maintains a high contributing porosity in the abutting surface and has a low porosity on the base side to increase engineering strength (Japanese Patent Application No. 55-7788 and Japanese Patent Application No. 55 -25722).

This has made it possible to provide a sintered metal valve seat with wear resistance and heat resistance on the contact surface and strength on the base, but wear resistance is required only in narrow spaces. Even though it is only the contact surface, the amount of raw material powder for the contact surface is 172 to 1/3 of the entire valve seat during molding.If you try to reduce this amount and reduce costs, you will end up with a complicated press mechanism, which will increase the cost. Becomes high.

In addition, since the raw material powder for the contact surface and the raw material powder for the base are filled in two layers in the mold and molded to form a single green compact, two powders with different characteristics are used.
For example, when sintering a green compact consisting of 2N raw material powder in which two layers with different alloy components coexist, if the appropriate sintering conditions are set for one of the layers, there is no excess or deficiency for the other layer. arise,
They have problems such as different deformations and dimensional changes, or inability to exhibit appropriate characteristics.

The purpose of the present invention is to provide a method for manufacturing a composite valve seat that solves the above-mentioned problems. In a method for manufacturing a composite valve seat, a valve seat having a desired shape is divided into a first member that constitutes the valve contact surface and a second member that constitutes the base of the valve seat, which are molded and sintered separately, and then both members are combined. The parts are stacked and inserted into a mold, pressed together to make the density of each part 90 to 98% of the true density, and then pressed together, and then resintered to eliminate the micro Tarawak and bond both parts together. A method of manufacturing a composite valve seat made of iron-based sintered metal is characterized in that the valve seat is divided into two parts, a contact surface part and a base part, and a first member and a second member each exhibiting the required properties separately. After blending the raw material powder, shaping and sintering, each sintered body is stacked and re-compressed in a forging gui to increase its strength, and then re-sintered and bonded together to manufacture a composite valve seat. Regarding the method.

The present invention will now be described with reference to the accompanying drawings.

As shown in Fig. 1, a valve seat 2 is fitted into a valve head 1 of a cylinder, and a valve 3 moves up and down and comes into contact with and separates from the contact surface 4 of the valve seat 2 to cut off the gas and pass through the valve. I do things. At this time, the valve contact surface 4 is the valve 3
In addition to being hit hard by the contact surface, it is also heated by high-temperature combustion gas, so high wear resistance and heat resistance are required, but only the contact surface 4 is required to have such properties. The other part of the valve seat, that is, the base 5, is press-fitted into the cylinder head 1 and is subjected to compression force.The valve seat 2 is subjected to permanent deformation due to the difference in thermal expansion coefficient due to repeated heating and cooling, and deformation due to the impact of the valve 3. It is sufficient that the strength, particularly the radial crushing strength, is large enough to prevent the cylinder head 1 from falling.

In the present invention, for example, as shown in FIG. 2, the first member 6 includes a contact surface, and the second member 7 forms a base and becomes a holding part when fitted into a cylinder head.
Separately form a sintered body. Instead of dividing the first and second members into two stages as shown in Figure 2, they can be divided so that the first member is fitted into the second member as shown in Figure 3, or for other purposes. It can be divided into various shapes depending on the situation.

The raw material powder for the first member is blended to provide high wear resistance and heat resistance, if necessary. Both parts are first mixed, shaped and then sintered in the same manner as in the usual sintered metal manufacturing method. These are stacked and inserted into a mold and cold pressed. It is necessary to apply a sufficient forging effect to the entire valve seat, especially the base, to reduce the porosity and increase the density. The density after forging must be 90% or more of the true density; if it is less than this, the mechanical strength of the valve seat will be insufficient.

To recompress the sintered body, uniaxial compression such as conventional forging or forging may be used, but it is also possible to compress the sintered body locally and sequentially by pressing the conical surface of a right circular cone against the top surface of the sintered body and rolling it. According to the method of rolling and pressing (hereinafter referred to as rolling pressing), plastic deformation easily occurs inside the sintered body, and the recompression effect is large. This forging by rolling pressure is known as so-called rotary forging. Rotation suitable for rolling and pressurizing annular bodies such as valve seats.

An example of a forging machine is shown in Fig. 4. In the figure, a first member sintered body 15 and a second member sintered body 16 are inserted into a cavity 14 of a mold formed by a die 11, a core 12, and a lower punch 13, and both sintered bodies are The second member is rolled and pressurized from the bottom surface between the lower punch 13 that is pushed up by the cylinder and the conical surface 18 of the conical body 17 that swings around the central axis OA at an angle α.

The first and second members that have been forged in this way are temporarily forge-welded and have been plastically deformed and hardened, and small cracks have formed starting from the remaining pores. In order to improve the diffusion bonding of both parts, it is necessary to resinter them by heating them to the sintering temperature in a non-oxidizing atmosphere. It is sufficient for this temperature to be 1050°C or higher; for example, if the first member has a structure in which hard particles that contribute to wear resistance are dispersed, the temperature should be set to such a high temperature that this will diffuse into the base and disappear. That is inappropriate.

If oxides are formed during resintering, this will inhibit the disappearance and diffusion of the crank, so heating should be carried out in a reducing or inert gas atmosphere or in a vacuum.

After the above-mentioned treatment, the product is machined to a predetermined size as usual. Furthermore, depending on the application, heat treatment may be applied to fully demonstrate the characteristics of the metal material.

Next, an example will be described.

A first member and a second member having the shapes shown in FIG. 2 were manufactured as shown in Table 1.

Note to Table 1: The numbers in parentheses for density are the ratios St and Zn to the true density.
For comparison, zinc stearate was filled in the mold in two layers as in the conventional method using the same raw material powder as in the above case for the contact surface (first member) and base (second member). te8 T on
/ ca! Press molded at a pressure of 1/100
The sintered body was sintered at 1250°C for 90 minutes in T o r r ) to a density of 7.0 g/c+l1 (90%), and then rotary forged (23 Ton) L to a density of 7.4 g/cd (95%).
) and then re-sintered in AX gas at 1120°C for 90 minutes to give a density of 7.4 g/cd (95%). Table 2 shows the hardness and radial crushing strength of both.

From Table 2, the composite valve seat produced by the method of the present invention clearly has superior hardness and radial crushing strength compared to those produced by the conventional method.
It can be seen that the wear resistance and the strength against deformation during use are high.

As explained above, according to the method of the present invention, two members having different molding and sintering conditions can be manufactured under optimal conditions, and these can be combined to form a composite valve seat. Furthermore, a composite valve seat can be made by combining members made of materials containing elements that are not desired to be diffused into each other.

As a result, the second member, which can be molded and sintered at low cost, can be molded and sintered separately, and only the first member can be molded and sintered under special conditions, which reduces manufacturing costs. If a raw material powder having wear resistance and heat resistance is used, a valve seat with excellent wear resistance and heat resistance can be easily manufactured at a low cost, and the practical effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the relationship between a valve seat and a valve, FIG. 2 is a cross-sectional view showing an example of a valve seat comprising a first member and a second member according to the present invention, and FIG. FIG. 4 is a sectional view showing an example of a rotary forging machine suitable for implementing the present invention. 1... Cylinder head, 2... Valve seat, 3.
... Valve, 4... Contact surface, 5... Valve seat base, 6... First member, 7... Second member Patent attorney Kamoshi 1) Second son! Figure 2

Claims (1)

[Scope of Claim] A method for manufacturing a composite valve seat made of iron-based sintered metal, in which the contact surface of a valve seat for an internal combustion engine is made of a heat-resistant and wear-resistant sintered metal, wherein a valve seat having a desired shape constitutes a pulp contact surface. The first member that constitutes the base of the valve seat and the second member that constitutes the base of the valve seat are separately molded and sintered, and then both members are inserted into a mold in an overlapping manner and pressed to reduce the density of each member to the true density. 90-98y6
A method for manufacturing a composite valve seat made of iron-based sintered metal, characterized by bonding and press-welding the parts, followed by re-sintering to eliminate the microcrank and bonding both parts together.