JP4323070B2 - Valve guide material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to wear resistance and machinability suitable for a valve guide of an internal combustion engine, in particular, the latter excellent sintered alloy.
[0002]
[Prior art]
Special cast irons such as gray cast iron and boron cast iron are sometimes used as valve guides for internal combustion engines, but in the case of cast iron, there are problems with work environment, mass productivity, price, etc., so replacement with sintered alloy Has been promoted. However, general sintered alloys have inadequate wear resistance. On the other hand, if the material is strengthened by adding alloy components, the wear resistance will reach a usable level. (Machinability) decreases. Since the valve guide is assembled to the cylinder head of the engine and the inner diameter is finished by reaming, if the valve guide material is poor in machinability, the time required for machining will be longer and the wear of the tool will be accelerated, resulting in increased production efficiency Be inhibited.
[0003]
[Problems to be solved by the invention]
Previously, the valve guide material developed by the present applicant in order to achieve both wear resistance and machinability (see Japanese Examined Patent Publication No. 55-34858) has a composition of C ... 1.5-4% by mass, Cu ... Sintered alloy of 1-5%, Sn ... 0.1-2%, P ... 0.1-0.3% and Fe balance, but wear resistance is superior to boron cast iron and machinability Although it is harder to cut than cast iron, it is superior to conventional sintered materials and has been widely used by automobile manufacturers. However, in recent years, due to changes in the environment surrounding this field, it has become more necessary than ever to improve productivity as well as improve quality, and a material with better machinability has been demanded for the valve guide material.
[0004]
[Means for Solving the Problems]
Then, when the improvement was aimed at based on the valve guide material which concerns on the above-mentioned prior invention, the result that machinability improved when copper content was increased was obtained. The present invention has been made based on such findings, and one is a copper content of 6 to 20% (mass%; hereinafter,% in this specification is mass% unless otherwise specified. ), And the other one is that together with the increase of copper, a total of less than 4% of enstatite (MgSiO ₃ ) and manganese sulfide (MnS) was added. Is the main point.
[0005]
That is, the valve guide material according to the first invention has a composition of C ... 1.5-4%, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.1-0.3% and Fe. The remaining sintered alloy has a microstructure of Fe-PC-based alloy phase in a matrix mainly composed of pearlite; copper or copper-tin-based alloy phase (this "or" also includes copper and copper-tin based ...) ); Three of free graphite are dispersed. Further, according to the second invention, the alloy composition is C ... 1.5-4%, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.1-0.3%, Fe-PC-C based alloy phase; copper or copper tin based alloy phase; free graphite, pyroxene and manganese sulfide in a base mainly composed of pearlite with a total of less than 4% of dolomite and manganese sulfide and Fe balance The three parties present a distributed organization.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the sintered alloy according to the present invention, carbon is added in the form of graphite powder, and a part (generally 0.8 to 1%) is solid-solved in iron to strengthen the base, or is bonded to phosphorus and relatively A hard particulate Fe-PC-based alloy phase (steadite phase) is generated and dispersed, and the remainder remains in the state of free carbon (graphite) to act as a solid lubricant. The amount of free graphite is about 0.3% when the carbon content (total carbon content) is 1.5%, and about 1.7% when the total carbon content is 3%. When it is less than%, the wear of the valve guide due to sliding with the valve increases. For this reason, the lower limit of the carbon content is 1.5%. On the other hand, if the amount is excessive, the strength of the base material is reduced and segregation or fluidity inhibition is caused during powder molding, so the carbon content is limited to 4%.
[0007]
Copper and tin are usually added in the form of a copper-tin alloy powder having a tin content of about 5 to 20%, and with a required amount of copper powder added thereto. Both promote the progress of sintering and strengthen the base by solid solution, while part remains as a Cu-Sn alloy phase to improve the sliding characteristics and machinability. At this time, when the copper phase is dispersed together with the Cu—Sn alloy phase, this action is further strengthened, but the effect becomes remarkable when the copper content is 6% or more. However, if it exceeds 20%, the wear resistance deteriorates, so the appropriate range of the copper content is 6 to 20%. On the other hand, the above-mentioned action and effect due to the presence of tin occurs when the content is 0.1% or more, but if it exceeds 2%, the base material becomes brittle, so the tin content is suitably 0.1-2%. Range.
[0008]
Phosphorus is added in the form of Fe-P alloy powder or Cu-P alloy powder. The Fe-PC-based alloy phase (steadite phase) produced according to the phosphorus content increases, the rigidity of the base material is increased, and the wear resistance is improved. The steadite phase formed in the matrix can be observed with a microscope when the phosphorus content is approximately 0.05% or more, but 0.1% is necessary to effectively improve the wear resistance. . On the other hand, machinability decreases as phosphorus increases. Therefore, from a practical point of view, the appropriate range of phosphorus is 0.1 to 0.3%.
[0009]
The pyroclasticite in the second invention is a magnesium metasilicate mineral, which is orthorhombic and cleaved, and acts as a solid lubricant like free graphite and further improves machinability. The same applies to manganese sulfide, but it also has the effect of improving the wear resistance of the substrate. Although both are added as powders, the use of campsite and manganese sulfide (preferably 20 to 30% of campsite) can further improve the wear resistance and machinability while maintaining the balance.
[0010]
Although these solid lubricants including free graphite are dispersed in the matrix and exhibit a solid lubricating effect, the material strength decreases as the content (dispersion) increases. In the case of the present invention, if the content exceeds 4%, the material strength necessary for the valve guide material cannot be maintained, so the total amount of the solid lubricant (free graphite, pyroxene and manganese sulfide) is made 4% or less. This means that, for example, when the total carbon content is 1.5% and the free graphite content is 0.7%, the pyroxene and manganese sulfide can be incorporated up to a maximum of 3.3%. The mixing, forming, and sintering of the raw material powder are in accordance with the usual method of powder metallurgy, but the sintering atmosphere is preferably a reducing or carburizing atmosphere. If the sintering temperature is too high, free graphite disappears, so 980-1100 A temperature of about ° C is suitable.
[0011]
(Example 1) First, as raw material powder, carbon is natural graphite powder, phosphorus is Fe-20% P alloy powder, copper and tin are copper powder and Cu-10% Sn alloy powder, iron is reduced iron powder, and powder lubrication. Zinc stearate was prepared as an agent. Next, these are blended in predetermined proportions, and the carbon is uniformly fixed at 2%, phosphorus is 0.1% and 0.3% in the total composition, copper is 2-30%, tin is 0.3%. The mixed powder (reduced iron powder remainder) changed to 1 to 2% was produced. In each mixed powder, the amount of zinc stearate added is uniformly 0.75%.
[0012]
Next, each mixed powder is molded into a predetermined shape at a molding pressure of 490 MPa, and sintered in a reducing gas atmosphere at 1000 ° C. for 60 minutes to obtain a large number of cylindrical samples having a length of 40 mm, an outer diameter of 12 mm, and an inner diameter of 7.4 mm. Produced. The alloy structure of each sample (sintered material) is a pearlite structure with a dense base, white-white Fe-PC system alloy phase (steadite phase), reddish Cu-Sn alloy phase, Samples with a high copper content are interspersed with copper phases.
[0013]
Next, the machinability and wear resistance of each sample thus obtained were tested. Machinability is a sample containing 5% copper and 0.3% phosphorous corresponding to the material of the prior invention. The time required for reaming the inner diameter of the sample and cutting 10 mm in the axial direction is obtained. Comparison was made in terms of an index of 100. Therefore, the smaller the index is, the easier it is to cut and the shorter the processing time, that is, the better the machinability. In addition, the wear resistance is determined by finishing each sample to the specified shape and dimensions of the valve guide and mounting it on the engine simulation test device, and sliding it back and forth for a specified time with a valve loaded with a radial load in the heated state. The difference in the inner diameter of the sample was determined as the amount of wear and compared.
[0014]
The drawing is a graph of these data organized by phosphorus content. Fig. 1 shows the relationship between copper content and machinability, and Fig. 2 shows the relationship between copper content and wear resistance. Show. From the graph, first, regarding the influence of phosphorus, in the range of 0.1 to 0.3% of the phosphorus content, the machinability is less as the phosphorus content is higher, and the wear resistance is higher as the phosphorus content is higher regardless of the copper content You can see that Next, with regard to the influence of copper, the machinability increases sharply as the copper content increases, starting from the time when the content exceeds about 5%. Continue. On the other hand, as for wear resistance, the amount of wear is uniformly small when the copper content is in the range of 6 to 20% and shows excellent wear resistance, but the amount of wear increases in the region before and after that. That is, the wear resistance rapidly deteriorates regardless of the phosphorus content from the time when the copper content exceeds 20%, and even if the copper content is less than 6%, the wear resistance deteriorates more as the phosphorus content increases. Thus, good results are obtained in both machinability and wear resistance at an appropriate range of copper content of 6 to 20%.
[0015]
(Example 2) The raw material powder is the same as that prepared in Example 1, 2% natural graphite powder, 5.5% copper powder, 5% Cu-10% Sn alloy powder, Fe-20% P alloy powder A mixed powder was prepared by adding 1.5% of pyroxenite powder, 0.8% of pyroxene powder, 0.2% of manganese sulfide powder, and 0.75% of zinc stearate to the remaining reduced iron powder. Its total composition is C ... 2%, Cu ... 10%, Sn ... 0.5%, P ... 0.3% (in addition to dolomite, manganese sulfide, and iron balance). For comparison, a mixed powder was prepared by omitting the pyroxene pyroxene powder and manganese sulfide powder from the above composition.
[0016]
Next, these two types of mixed powders were molded and sintered under the same conditions as in Example 1, and the machinability and wear resistance of the obtained samples were tested. As a result, the former data containing pyroxene and manganese sulfide had a machinability index of 38 and a wear amount of 12 μm, whereas in the latter case, the machinability index of 42 and the wear amount of 14 μm. The former is better in both machinability and wear resistance. Looking at the structure of both samples, in the latter case, free graphite, pyroxene and manganese sulfide are dispersed as lubricants in the base, whereas in the latter, only free graphite is present. The difference is considered to have caused the difference in characteristics.
[0017]
【The invention's effect】
The valve guide material according to the present invention has a machinability improved by about twice as compared with the conventional material, and has wear resistance that surpasses that of the conventional material. Therefore, the present invention is extremely useful when the quality as an engine part is solid, and when the workability of the valve guide material is particularly important due to various conditions such as working conditions in the assembly process of the engine, compatibility with the machine tool to be used, etc. Is.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the copper content and machinability of a sample.
FIG. 2 is a graph showing the relationship between copper content and wear resistance of a sample.

Claims (3)

The alloy composition is C ... 1.5-4% by mass ratio, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.1-0.3% and Fe ... the balance, mainly pearlite A sintered valve guide material characterized by exhibiting a structure in which three elements of Fe-PC-C based alloy phase; copper or copper tin based alloy phase; Alloy composition by mass ratio C ... 1.5-4%, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.1-0.3%, in total of pyroxene and manganese sulfide Less than 4% and Fe ... balance, Fe-PC-C based alloy phase; copper or copper tin based alloy phase; free graphite, pyroxene and manganese sulfide dispersed in a base mainly composed of pearlite Sintered valve guide material characterized by presenting. The sintered valve guide material according to claim 2, wherein the total amount of free graphite, dolomite and manganese sulfide dispersed in the matrix is 4% or less.

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