JP2006002578A - Two layer structure valve seat made of iron-base sintered alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that shrinkage occurs when raw powder of a two layer structure sintered iron-base valve seat is press-formed and the green compact is sintered, the shrinkage of the sintered body increases with use of highly-alloyed raw material, dimensional shrinkage of the sintered body (product blank) with respect to a die dimension increases, and a dimension of a highly-alloyed seat layer having large shrinkage and a dimension of an inexpensive material support layer having small shrinkage become different except joint surfaces if the support layer not contacting a valve is made of inexpensive material. <P>SOLUTION: The support layer 2 made of Fe-based material not contacting the valve has one or more of nonmetal powder particles and high hardness metal particles dispersed in an iron-based base consisting primarily of Fe. Powder particles for reducing compressibility at the time of press forming are added into the iron-base low alloy base of the support layer to increase springback and lower a density of the compact. This technique increases the dimensional shrinkage percentage of the compact at the time of sintering and the dimensional shrinkage percentage almost equal to a seat layer 1 is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an iron-based sintered alloy valve seat having a two-layer structure particularly suitable for high-power automobile engines and gas engines such as LPG and CNG.

  Conventionally, as a means for producing an iron-based sintered alloy valve seat at a low cost, a part requiring wear resistance including a contact surface repeatedly hit and slid by a valve face (hereinafter referred to as “seat layer”); For example, Patent Document 1 (Japanese Patent Application Laid-Open No. Hei 9) discloses a two-layer structure of a portion (hereinafter referred to as “support layer”) that is made of a relatively inexpensive component different from the above-described sheet layer and abuts against the bottom surface of the cylinder head press-fitting hole. -151712) and Non-Patent Document 1 ("Easy Automotive Materials for Design Engineers", Nikkei Business Publications, Inc., September 6, 1993, pp. 63-65). In the method disclosed in Patent Document 1, the raw material powder of each of the sheet layer and the support layer is filled in a mold, compression-molded into an integrated green compact consisting of two upper and lower layers, and then sintered. ing.

On the other hand, with the increase in the output of automobile engines and the use of clean fuels for pollution prevention such as LPG and CNG, the thermal load and mechanical load that the engine valve seat receives tend to increase more and more. In order to cope with such an increase in thermal load and mechanical load on the valve seat, an alloying element is added by a pre-alloy method as described in Patent Document 2 (Japanese Patent Laid-Open No. 2002-220645) by the present inventor, for example. A high alloying method that adds a large amount of alloying elements, such as a method of dispersing hard particles or solid lubricants with a composition of Fe-60 to 70% Mo-0.1% or less to a base using iron powder. Has been used for valve seats.
JP-A-9-151712 JP 2002-220645 A "Easy automotive materials for design engineers", Nikkei BP, September 6, 1993, pages 63-65

However, due to the high alloying of the iron base alloy base and the combination of the iron base alloy base and the solid lubricant, the formability at the time of press forming the sintered alloy raw material is lowered. In addition, shrinkage occurs due to the sintering of the green compact, but the amount varies depending on the composition and particle size of the powder. In the sintered body of the high alloying raw material as described above, the shrinkage increases, and the dimensional shrinkage of the sintered body (product material) tends to increase with respect to the mold size.
When trying to manufacture a valve seat having a two-layer structure using a support layer that does not contact the valve as a low-cost material, the dimensions of the highly alloyed sheet layer with large shrinkage and the low-cost material support layer with small shrinkage are as follows: There arises a problem that it is different except for the joint surface.

It is known that the dimensional change of the Fe-based sintered material is greatly affected by the composition. That is, C acts on shrinkage, Ni acts on shrinkage, and Cu acts on expansion. Therefore, it is possible to adjust the dimension of the support layer in the state of the sintered body (product material) to the dimension of the sheet layer by adjusting the amount of these additive elements. However, due to the recent increase in the heat load of valve seats and other measures such as high alloying, large dispersion of hard particles, and dispersion of solid lubricants, etc. have been taken in the seat layer, the sintered sheet layer (product material) There is a tendency that the dimensional change rate with respect to the metal mold is extremely large at about 0.7% or more, and it is not possible to cope with the adjustment of the components of these additive element amounts. For this reason, the generation of cracks due to a significant difference in the dimensional change rate between the sheet layer and the support layer during sintering, and the finishing cost increase, resulting in a decrease in the productivity of the valve seat.
On the other hand, by limiting the powder particle size of the iron-based alloy particles used for the Fe-based material support layer to a large one, the density of the compact is reduced, the shrinkage during sintering is increased, and the sheet layer and the support layer Although it was considered that the dimensional change rate was close, if the powder particle size was limited to a certain size or more, the cost of the powder itself increased significantly due to an increase in the process of powder production, and the original purpose of forming a two-layer structure. A certain cost reduction cannot be achieved.

As a result of diligent research in view of the above problems, powder particles that reduce the compressibility during press molding are added to the iron-based low alloy base of the support layer, and the density of the compact is reduced by increasing the spring back. The inventors have found that by increasing the dimensional shrinkage rate of the formed body at the time of ligation, a shrinkage rate substantially equal to that of the sheet layer can be obtained.
The springback focused on by the present invention is that the distance between particles of the powder material temporarily deformed during press molding is reduced and the density is increased, and then the particle shape is restored when the press pressure is released, and the distance between particles Is a phenomenon in which the density increases and the density decreases.

  The present invention proposes to increase the spring back amount of the support layer so that the mold reference shrinkage rate of the support layer matches the mold reference shrinkage rate of the sheet layer. That is, since the spring back naturally occurring in the seat layer is difficult to adjust due to the hard particles and the solid lubricant, the present invention proposes to adjust the spring back of the support layer to increase the shrinkage.

That is, the iron-based sintered alloy valve seat of the present invention comprises a sheet layer made of an Fe-based material containing a solid lubricant and hard particles on the surface of the valve seat that is press-fitted into the cylinder head of the internal combustion engine. In the two-layer structure sintered iron-based valve seat comprising a Fe-based material support layer having a component structure different from that of the Fe-based material sheet layer in contact with the bottom surface of the cylinder head hole, the Fe-based material support layer is One or more kinds of non-metallic powder particles and high-hardness metal particles are dispersed in an iron-based matrix mainly composed of Fe.
The feature of the present invention is to uniformly disperse non-metallic powder particles and / or high-hardness metal particles that lower the compressibility of the support layer in order to make the dimensional change between the sheet layer and the support layer uniform during production, and press The spring back at the time of molding is enlarged, and the dimensional shrinkage rate characteristic of the sheet layer at the time of sintering is almost equal to the shrinkage characteristic. That is, repeatedly measuring the dimensional change of the molded body and sintered body of the iron-based sintered alloy valve seat of the present invention and the conventional one, in the iron-based sintered alloy valve seat of the present invention (FIG. 3), Compared to the conventional iron-based sintered alloy valve seat (FIG. 2), the outer diameter of the molded body 11 spring-backed against the mold 10 is larger, and the shrinkage of the sintered body 12 is larger. The step between the sheet layer and the support layer is exaggerated.

Non-metallic powder particles to be blended in the support layer of the iron-based sintered alloy valve seat of the present invention include Al ₂ O ₃ , oxides such as talc, nitrides such as TiN, sulfides such as MnS, CaF Fluoride such as ₂ (fluorite) and high-hardness metal particles are high-hardness metal powders such as stellite, FeMo, and FeCr. When the average particle size of the non-metallic powder and the high-hardness metal particles is larger than 150 μm, the strength of the sintered alloy is lowered, so that it is preferably 150 μm or less.

The base composition of the support layer of the valve seat made of the two-layer structure iron-based sintered alloy according to the present invention is an iron base in consideration of the high temperature strength, thermal conductivity, and low cost which are originally required characteristics of the valve seat, C, Any one or more of Ni, Cu, Cr, and Mo is contained as an alloy with 3 to 8 wt% Fe or as a component combined with Fe. Among these components, C, Cr, Mo, Ni are alloyed in iron, while Cu may be alloyed in Fe by using fine Cu, etc., but in an elemental form, it is compounded with an Fe-based alloy in an iron-based matrix. Even if it is done, there exists an effect, such as a heat conductivity improvement. Moreover, as powder particles that reduce the compressibility at the time of molding in order to equalize the dimensional change between the sheet layer and the support layer at the time of manufacture, high-hardness metal powder such as stellite, FeMo, FeCr, or Al ₂ O ₃ Non-metallic powder particles such as oxides such as talc, nitrides such as TiN, sulfides such as MnS, fluorides such as CaF ₂ (fluorite), or a combination of two or more thereof Is contained in an amount of 0.5 to 5% by weight. If the high hardness metal powder and nonmetal powder particles to be blended are less than 0.5% by weight, a sufficient effect on the dimensional change rate during sintering cannot be obtained. On the other hand, when the amount is more than 5% by weight, the strength of the support layer is greatly reduced. Therefore, the blending amount of the high-hardness metal powder and non-metal powder particles is 0.5 to 5% by weight.

The sheet layer of the double-layer iron-based sintered alloy valve seat according to the present invention is heated by dispersing hard particles and solid lubricant in a base to which a large amount of alloy elements such as high-speed steel powder is added. Any iron-based sintered alloy that can cope with an increase in mechanical load and mechanical load can be used without particular limitation.
In the method for producing a valve seat made of a two-layer structure iron-based sintered alloy according to the present invention, conditions such as preparation, molding, dewaxing, and sintering of mixed powder are as described in Patent Document 2 (Japanese Patent Laid-Open No. 2002-220645). According to the conditions described in paragraph numbers 0033 to 0036.

EXAMPLES The two-layer structure iron-based sintered alloy valve seat according to the present invention will be described in more detail with reference to the following examples. The unit “%” used in the examples is “% by weight” unless otherwise specified.
The powders used for the sheet layers used in Examples and Comparative Examples were as follows. (1) Prealloy powder made of iron powder containing Mo: 3%, Cr: 0.8% and V: 3% having a peak in a particle size distribution of 150 to 200 mesh; (2) Carbonyl nickel powder under 325 mesh; 3) Metal Mo powder with 325 mesh under; (4) Graphite powder with 325 mesh under; (5) Containing 61.33% Mo and 0.03% C as hard particles, the balance being substantially Fe and unavoidable impurities 150 Ferromolybdenum (Fe-Mo) powder having a peak at ˜200 mesh; (6) Calcium fluoride (CaF ₂ ) powder having a peak at 325 to 400 mesh as a solid lubricant. These raw material powders were blended in the composition shown in Table 1, and 0.5% zinc stearate for improving mold release during pressing was further added to obtain a mixed powder of the sheet layer. The above (1) to (4) react to form an iron-based alloy base.

The powder used for the support layer of the examples was as follows. (1) Prealloy powder made of iron powder containing 3% of Cr having a peak in a particle size distribution of 150 to 200 mesh; (2) Ni powder for maintaining strength: 2.5%; (3) C (graphite) Powder: 0.8%; (4) Zinc stearate 0.5% to improve mold release during pressing; (5) Reduced compressibility during press molding to equalize dimensional change between sheet layer and support layer. As powder particles to be used, FeMo, FeCr, Al ₂ O ₃ , and talc are used alone or in combination, and 1 to 5%. These powders were blended to form a mixed powder of the support layer as shown in Table 1.

  Further, in the support layer of the comparative example, the same iron powder as in the examples, Ni for maintaining the strength: 2.5% and C: 0.8%, zinc stearate 0.5% for improving the mold release during pressing The amount of Ni added as an alloying element for adjusting the dimensional change to the iron powder similar to that of the example without adding high-hardness metal particles and non-metal powder particles (Comparative Example 1), Hard metal particles and non-metal powder particles were not added (Comparative Example 2).

Combining the sheet layer shown in Table 1 with the support layers of Examples and Comparative Examples, the mixed powder was molded so that the relative ratio of the sheet layer and the support layer was sheet layer / support layer = 4/6 in the thickness ratio. And press molded at a pressure of 637 MPa to produce a molded product for a valve seat. The dimensions were measured immediately after the molded body was extracted from the press.
The molded body was dewaxed by heating at 650 ° C. for 1 hour, sintered in a vacuum atmosphere at 1180 ° C. for 1 hour, quenched by gas cooling, and finally tempered at 500 ° C. The dimensions were measured after tempering. Thus, the valve seat test piece of the Example of the structure shown in FIG. 1 and a comparative example was obtained.

  The outer diameter dimensions of the sheet layer and the support layer of each test piece were measured in the above-described stage, and the difference (change rate) in dimensional shrinkage between the sheet layer and the support layer due to sintering was investigated. Table 2 shows the ratio of shrinkage of the outer diameter at the part farthest from the joint of the sintered product when the outer diameter of the molding die is 1.

  As is apparent from Table 2, by adding powder particles that reduce the compressibility during press forming to the Fe—Cr alloy of the support layer, the shrinkage ratio against the mold can be adjusted to 0.7 to 0.9%. It can be made substantially equivalent to a sheet layer having a large mold shrinkage ratio. On the other hand, simply increasing the alloy component Ni does not provide the same mold shrinkage ratio as the sheet layer, and increasing the alloy components such as Ni, Mo, and C equalizes the dimensional change between the sheet layer and the support layer. It can be seen that it cannot be converted.

  As described above, the valve seat made of the two-layer structure iron-based sintered alloy according to the present invention is a low-cost iron-base alloy having a small amount of alloy elements with respect to the sheet layer and having a different component composition from the sheet layer in the support layer, and By equalizing the rate of dimensional change between the sheet layer and the support layer during sintering, it is possible to reduce the influence on productivity due to the occurrence of cracks in the sintering process and the increase in processing allowance. Thus, the two-layer structure iron-based sintered alloy valve seat according to the present invention is excellent in manufacturability and inexpensively while maintaining excellent wear resistance in the seat layer.

It is sectional drawing of the valve seat test piece created in the Example and comparative example of this invention. It is a schematic diagram explaining the dimensional change of the molded object for conventional valve seats made from an iron base sintered alloy, and a sintered compact. It is a schematic diagram explaining the dimensional change of the molded object for valve seats made from an iron-based sintered alloy of this invention, and a sintered compact.

Explanation of symbols

1 Sheet layer 2 Support layer 10-Mold 11-Molded body 12-Sintered body

Claims (6)

The surface of the valve seat that is press-fitted into the cylinder head of the internal combustion engine is made of a Fe-based material sheet layer containing solid lubricant and hard particles, and the surface that contacts the bottom surface of the cylinder head is the Fe-based material. In a two-layer structure sintered iron-based valve seat comprising a Fe-based material support layer having a component composition different from that of the sheet-made sheet layer, the Fe-based material support layer is formed on a ferrous base containing non-metallic powder as a main component. An iron-based sintered alloy valve seat in which one or more of particles and high-hardness metal particles are dispersed. 2. The iron-based sintered alloy valve according to claim 1, wherein the Fe iron-based base contains 3 to 8 wt% of one or more of C, Ni, Cu, Cr and Mo. Sheet. The content of one or more of the non-metallic powder particles and the high-hardness metal particles contained in the Fe-based material support layer is 0.5 to 5% by weight. The iron-based sintered alloy valve seat as described. Non-metallic powder particles contained in the support layer made of the Fe-based material are Al ₂ O ₃ , oxides such as talc, nitrides such as TiN, sulfides such as MnS, CaF ₂ (fluorite), etc. The iron-based sintered alloy valve seat according to any one of claims 1 to 3, wherein the valve seat is one or more of fluorides. 5. The high hardness metal particles contained in the Fe-based material support layer are any one or two or more of stellite, FeMo, FeCr, and the like. 6. This is a valve seat made of an iron-based sintered alloy. The iron-based sintered alloy valve seat according to any one of claims 1 to 5, wherein the Fe-based material sheet layer includes high-speed steel powder particles.

Images