JPS5827952A - Composite valve sheet - Google Patents

Abstract

PURPOSE:To obtain a composite valve sheet with high fatigue strength and heat conductivity by forming a sliding surface to a valve and a part fitting in a cylinder head from 2 kinds of solid phase sintered iron alloys different from each other in average size and volume percentage of pores after sintering. CONSTITUTION:This composite valve sheet is composed of the 1st sintered alloy 1 having a sliding surface 3 to the valve and the 2nd sintered alloy 2 fitting in a cylinder head 5. The alloy 1 is a solid-phase sintered iron alloy having 11- 19vol% pores after sintering, and the alloy 2 is a solid-phase sintered iron alloy having 4-10vol% pores having 5-30mum average size after sintering. The preferred alloy 2 is formed with powder consisting of 0.2-1.0% Co and the balance essentially Fe as the final components. The composite valve sheet has said characteristics and a moderate coefft. of thermal expansion when applied to an engine which is exposed to high temp. and high load.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a valve seat 1 used in an internal combustion engine, particularly a composite valve seat 1 made of two different types of sintered alloys.

Valve seals for internal combustion engines have been most commonly used since they were first used for unleaded gasoline engines, but they have been difficult to use in high-temperature, high-load engines and high-speed engines.

One of the reasons for this is the presence of pores in the sintered alloy, which reduces the strength and surface 1 thermal fatigue strength of the sintered alloy, causing valve seat 1 to fall off or break in high-temperature, high-load engines. It's easy. l: Ru. Another reason is that there is a difference in coefficient of thermal expansion between the valve seat 1 and the cylinder head, which are normally press-fitted into the cylinder head, and this is why sintered alloys, in particular, tend to come off easily when assembled to a cast iron cylinder head. by.

On the other hand, although many composite valve seats that combine different types of valve seats have been devised, only one in which the valve seat is made of steel and the pulp contact surface is made of sintered alloy (Japanese Patent Application Laid-Open No. 147326/1989) is the only one that can be used for high-temperature, high-load engines. could not be used. The reason for this is that there are problems with the coefficient of thermal expansion and strength of sintered alloys such as I7. Therefore, a valve seat 1 which is a composite of sintered alloys, for example, JP-A-49-93 '109, JP-A-53-79911,
JP-A No. 49-88112 and the like are only used for the purpose of reducing raw material costs by combining a relatively low-performance sintered alloy in addition to the nine valve faces. On the other hand, it is possible to improve the thermal conductivity and strength of the sintered alloy by applying a sealing treatment using an infiltration method, but even such a sealing treatment does not result in a significant improvement in strength. It is unlikely that the coefficient of thermal expansion will be significantly improved.

The present invention aims to obtain a valve seat having high fatigue strength, thermal conductivity, and an appropriate coefficient of thermal expansion, which is applicable to high-temperature, high-load engines, and is described below. .

First, the gist of the present invention resides in a composite valve seat having the following three configurations as described in the claims.

(1) It consists of a first sintered metal that forms the sliding surface of the valve and a second sintered metal that mainly forms the fitting part with the cylinder head.

(2) The second sintered alloy is a solid phase iron-based sintered alloy having 4-10% by volume of sintered pores with an average particle size of 5-30 μm.

(3) Such a composite valve seat, in which the first sintered alloy is a solid-phase iron-based sintered alloy having sintered pores of 11 to 19% in terms of volume % of pores, is as shown in Fig. 1. This is a composite valve seat consisting of a first sintered alloy 1 having a sliding surface 3 and a second sintered alloy 2 that fits into the cylinder throat 5. each! The composite valve seat of the present invention has the following characteristics and is effective as a composite valve seat by arranging a special sintered alloy.

1. For the second sintered alloy, there is a special surface l in this part.
Although abrasion resistance is not required, as will be described later, the strength of the first sintered alloy cannot be obtained, so the second sintered alloy is required to have extremely high strength, low thermal fatigue strength, and an appropriate coefficient of thermal expansion. be done.

The second sintered alloy of the present invention satisfies these requirements, and first of all, because it is a sintered alloy, it has the following advantages.

In general, the joining of two parts is broadly classified into welding/brazing and diffusion joining, but in the case of small-volume parts such as valve seats, the effect of thermal distortion caused by welding is significant, impairing physical properties. Furthermore, brazing cannot provide sufficient bonding strength under high temperature and high load conditions.

Furthermore, diffusion bonding between steel or cast iron and sintered alloys is a special material that cannot be obtained without liquid phase sintering. Because it is possible to utilize the progression of the bonding process for bonding between members, extremely strong bonding strength can be obtained.

Furthermore, in the present invention, the following effects can be obtained by making the second sintered alloy a solid-phase iron-based sintered alloy in which pores with an average diameter of 5 to 30 μ are 4 to 10% by volume. .

First, in the case of pores with an average particle size of 30 μ or more, the notch effect due to the pores is large, which can prevent the growth of minute cracks generated from the pores especially against thermal fatigue, and the thermal fatigue strength decreases. do. On the other hand, when trying to reduce the average diameter to 5μ or less, there is a limit to the miniaturization of iron-based powders, and unless liquid phase sintering is used, liquid phase sintering will not be possible. The average diameter can only be set to 5μ or more because the generated particles undergo significant dimensional changes and have poor product stability.

More preferably, pores with a diameter of 250 μm or less occupy 40% or more by volume of the entire pores. This is 250
This is because when there are many coarse pores larger than μ, the strength decreases significantly.

On the other hand, if the number of pores exceeds 10% by volume, the strength and thermal fatigue strength will decrease in proportion to the amount of pores.This is the limit point where the coefficient of thermal expansion will further decrease, so the amount of pores should be 1096 or less. is selected. Furthermore, when attempting to produce a sintered alloy by solid-phase sintering without producing a liquid phase, the amount of pores that can be obtained is only υ4% or more due to the limit of miniaturization of iron-based powder as described above.

Furthermore, the second sintered alloy of the present invention must be solid-phase sintered. This is because when dimensional changes occur, the shape of the composite sheet becomes severely distorted, making it impossible to manufacture.

In order to obtain such a second sintered alloy, it is necessary to use a fine powder with an average particle size of less than 100μ, which is usually called an atomized powder, and when a powder with an average particle size of 100μ or more is used, pores are more likely to be formed. Moreover, the press formability deteriorated significantly, and it was difficult to obtain pores in the second sintered alloy of the present invention.

The second sintered alloy of the present invention as described below is preferably a powder containing SJ powder, specifically, C002 to 1.0% by weight of the final component, with the balance substantially consisting of Fe.

Powders containing such a small amount of added elements not only can be easily formed into a particle size of 1007i or less, but also have excellent press moldability. If the amount of C is less than 1.0%, a large amount of ferrite will occur, and the sintered alloy will soften, resulting in insufficient strength.On the other hand, if it exceeds 1.0%, the liquid phase generation temperature will decrease. It is preferable to select a CO of 12 to 1.0% because there is a risk of not only a liquid phase forming easily and causing gagginess but also cementite forming depending on the cooling rate and embrittlement.

Furthermore, as a second sintered alloy, (CrsNi
s Mo, Cu) at 0.5 to 3
．． It is desirable to add 0%. These (Cr %Ni
Although XMo, C1) is a solid solution in the matrix and is effective against thermal properties, etc., when it exceeds 3.0%, press formability decreases and a liquid phase tends to occur, causing potash, on the other hand. 0.
If 5% is not vortexed, the effect of addition will be longer, so 0.5-3.
Selected at 0%. Although the addition of such alloying elements is particularly effective in EGR diesel engines, etc., which are subjected to extremely high temperature conditions, addition of these alloying elements is not necessary in ordinary diesel engines, gasoline engines, etc. from the viewpoint of press formability.

The second sintered alloy of the present invention has been explained above, but since the first sintered alloy of the present invention is strongly bonded to the second sintered alloy, the strength of the composite valve seat and the second sintered alloy are lower than those of the second sintered alloy. The purpose of the first sintered alloy is only to obtain the abrasion resistance necessary for the pulp sliding surface.

As such a first sintered alloy, a solid phase sintered alloy with a pore content of 11 to 19% is required.

The pores in the sintered alloy improve wear resistance by forming an oxide film.1 This is due to the high hardness of the oxide film, low coefficient of friction, and excellent corrosion resistance. Due to synergy.

Therefore, if the amount of pores is less than 11% by volume, the effect of such pores cannot be obtained.On the other hand, if the amount of pores is more than 19% by volume, the strength will be insufficient against the impact with the valve. In order to achieve this, the pore content must be selected within the range of -11 to 19% by volume.

Furthermore, regarding the necessity of solid-phase sintering, when a liquid phase is generated, in materials with a relatively large amount of pores such as the first sintered alloy, the amount of pores decreases, but Japanese pores are likely to occur, and coarse pores are likely to occur. Solid phase sintering is necessary because various defects occur due to pores, and because dimensional changes become significant when liquid phase sintering occurs.

Specifically, the first sintered alloy contains C0.8-2.5% by weight of the final components, (Crs W % Ti, Nb
, C01iAo) for table use of 5 to 5
It is preferable that the sintered alloy contains 30% and the balance is substantially equal to 1:17'e. C is added to form carbides and adjust the matrix structure, but if it is less than 0.8%, the amount of carbide will be insufficient and the necessary surface abrasiveness will not be obtained, and if it exceeds 2.5%, the cooling rate will decrease. In addition to the formation of cementite, an excessive amount of carbide also causes significant embrittlement of 0.8 to 2.
Selected at 5%.

On the other hand, (Crs W % Tl, Nb
Although it improves the effect of corrosion resistance, if it is less than 596, the amount of hard particles is too small, resulting in poor surface abrasion resistance.
If it exceeds 096, not only will there be too many hard particles, but
The embrittlement of the base was remarkable, and (CrXMO% Tj-s Nb
X0% MO) must be selected at 5 to 30% in the river.

In addition, for products that require heat resistance and monofacial corrosion resistance (N
J, Crs Cu) at 1°0~
Adding 3.0% is also effective in some cases.

As such a first sintered alloy, for example, Japanese Patent Publication No. 51-1
No. 3093, Japanese Patent Publication No. 1983-44483, Japanese Patent Publication No. 1983-
No. 98610, JP-A-53-81410, JP-A-55
The valve seat according to the prior art such as No. 164057 can be adjusted and used, and it is also desirable to perform an infiltration treatment for the purpose of improving thermal conductivity.

As described above, the composite valve seat of the present invention has a first sintered alloy that has a large pore volume and is inferior in strength but has excellent wear resistance, and a first sintered alloy that has a large pore volume and is inferior in strength, but has an extremely high porosity that has excellent strength, thermal fatigue strength, and thermal conductivity. By solid-phase sintering a special secondary sintered alloy with reduced And the bonding strength of the first and second sintered alloys is also strong.

In manufacturing the present invention, since both the first and second sintered alloys are solid-phase sintered, the first and second sintered alloys are prepared by pressing compacts having the same inner and outer diameters in advance. Although it is possible to assemble the composite valve seat after molding, in the present invention, filling the powder of the first and second sintered alloys in two layers and integrally press-forming the composite valve seat of the present invention is sufficient. It is possible to obtain pores in a bisintered alloy.

This is because the second sintered alloy has less one alloying element and uses fine powder, so even with the same compacting pressure, it can produce a green compact with significantly higher density than the first sintered alloy. Depends on what you can get.

More preferably, by press forming as shown in FIG. 2, the composite pulp of the present invention can be more easily produced and the density of the second sintered alloy can be increased.

First, in a normal press machine, the lower punch 6 is fixed, so if we explain it as a fixed lower punch (of course, in a die fixed type, the relative movement of the die and lower punch is reversed), the die and the lower punch After gradually filling the four-fold space at 6 with the first sintered alloy powder 11 and the second sintered alloy powder 2, the earth punch 9 is lowered with the diamond fixed 17, and the diamond is then lowered into the upper punch 9. After descending at approximately half the speed of the descending speed and completing the compaction of powder 1, the diamond descends at approximately the same speed as the lower punch 9, completing the compaction of powder 2. do. According to such press forming, the desired density of the upper part of the powder 2, which requires high-density compacting, is first obtained by compacting only with the upper punch, and then the die is lowered at half the speed of the upper punch. ,
Since Powder 1 and Powder 2 are compacted with substantially the same force from above and below, compacting of Powder 1 with a uniform density is achieved. Powder 1 has a limit in compaction density due to the fact that the powder itself is a high alloy as described above, and after being compacted uniformly as described above, the die and lower punch descend at the same speed. The underside of the L powder 2 is strongly compacted, and the powder 1 is homogeneous and compacted to a significantly higher density. Furthermore, if a high degree of powder compaction is desired, it is possible to finally lower only the upper punch and perform powder compaction.

In addition, in the case where powder 1 and powder 2 are filled in the reverse order, after forming a space 17 on powder 2, the die and upper punch are lowered at the same speed, and then the die is lowered at approximately half the speed of the upper punch. The key point is that the relative movement of the die, the lower punch, and the lower punch is such that the powder is first compacted by the punch on the powder 2 side, and then both the upper and lower punches are pressed down. This is achieved by compacting the powder at the same speed and finally compacting the powder with a punch on the powder 1 side.

The distribution of this powder 1\2 is determined by whether the punch that shaped the sliding surface of the valve seat is placed on the punch side. It is desirable to fill the two sides with ivy powder I because it has excellent properties.

The core rod 8 moves in the same way as the diamond.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention. Fig. 2 is a cross-sectional view showing the manufacturing method of the present invention 6 Explanation of Jungetsu 1: First sintered alloy 2: Second sintered alloy 6: Lower bunch 7: Die 9: Upper punch Patent applicant Nippon Pist Schilling Co., Ltd. Company 3 Figure

Claims (2)

[Claims] (1) In a composite valve seat made of two types of anisotropic sintered alloys, a first sintered alloy forms the valve sliding surface, and a second sintered alloy mainly forms the fitting part with the cylinder head. Furthermore, the second sintered alloy is a solid phase iron-based sintered alloy having sintered pores of 4 to 10% by volume of pores with an average diameter of 5 to 30μ, and A composite valve seat characterized in that the alloy is a solid phase iron-based sintered alloy having sintered pores of 11 to 19% in terms of volume % of pores. (2) A patent characterized in that the second sintered alloy is formed by compacting powder with an average particle size of 100 μm or less