JP4323071B2 - 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]
Therefore, when the improvement was attempted while based on the valve guide material according to the above-mentioned prior invention, the result that the machinability is significantly improved by increasing the copper content and reducing the phosphorus content together. Obtained. The present invention has been made based on such findings, and one of them is a copper content of 6 to 20% (mass%; hereinafter,% in this specification is mass% unless otherwise specified). And the phosphorus content within the range of 0.01 to less than 0.1%, and the other is to increase the amount of copper and phosphorus. In addition to the suppression of the above, the main point is that less than 4% in total is added of enstatite (MgSiO ₃ ) and manganese sulfide (MnS).
[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 ... 0.01-0.1%, A sintered alloy of the balance of Fe and Fe, the metal structure of which is based on pearlite in a copper or copper tin-based alloy phase (this “or” also includes copper and copper-tin based ...); and free graphite Is distributed. Further, according to the second invention, the alloy composition is C ... 1.5-4%, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.01-0.1%, A total of less than 4% of pyroxene and manganese sulfide, and a remaining Fe alloy, and a structure in which copper or copper-tin alloy phase is dispersed in a base mainly composed of pearlite; free graphite, pyroxene and manganese sulfide are dispersed. Presented. In addition, in the base of these alloys, the production | generation of a Fe-PC system alloy phase is recognized according to phosphorus content. Therefore, such a case is also included in the above-mentioned base mainly composed of perlite.
[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. Therefore, the upper limit of the carbon content is 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. Depending on the phosphorus content, the steadite phase produced increases, the rigidity of the substrate increases and the wear resistance improves, but the machinability decreases. Therefore, since the object of the present invention is to improve machinability as compared with the prior invention material, the phosphorus content is less than the prior invention material and less than 0.1% (however, 0.01%). Increases free graphite and improves machinability. Although the wear resistance decreases as the amount of phosphorus decreases, the wear amount is still 1/3 or less compared to gray cast iron, which is far superior.
[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 total composition is fixed to 4 types of carbon: 2% uniformly, phosphorus: 0.01%, 0.03%, 0.1%, 0.3%. Was mixed powder (reduced iron powder balance) with 2-30% and tin 0.1-2%. 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 having a dense base, and a reddish Cu-Sn alloy phase and a sample having a high copper content are dotted with a copper phase. In addition, a sample with a high phosphorus content is dotted with a lot of white Fe-PC-based alloy phases (steadite phases), but a sample with a low phosphorus content has a decrease in it. Yes. By the way, when the amount of free graphite of the sample with high phosphorus content (0.3%) and the sample with low content (0.03%) was measured from the insoluble residue obtained by dissolving the chips of each sample in acid, the latter was compared. In this sample, free graphite is increased by about 0.2 to 0.3%.
[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 this graph, first, regarding the influence of phosphorus, when the phosphorus content is in the range of 0.01 to 0.3%, the machinability is less and the wear resistance is more phosphorus regardless of the copper content. You can see that it is superior. Next, with regard to the influence of copper, machinability shows a rapid improvement from the time when the copper content exceeds about 5%, and it is slow even at 10% or more, but continues to improve to a content of 30%. Yes.
[0015]
On the other hand, the wear resistance is uniformly small in the range of about 6 to 20% of copper, and shows excellent wear resistance, but the wear amount increases before and after that. That is, the wear resistance deteriorates rapidly 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 markedly with less phosphorus. By the way, even within the scope of the present invention, the amount of wear is slightly increased as a result of the suppression of phosphorus as compared with the material of the prior invention, but for example, the wear amount of 56 μm of copper ... 6%, phosphorus ... 0.01% is practically acceptable. It is in a range that is possible, and is far superior to the wear amount of 170 μm of gray cast iron valve guides under the same test conditions.
[0016]
(Example 2) The raw material powder prepared in Example 1 was used, natural graphite powder 2%, copper powder 5.5%, Cu-10% Sn alloy powder 5%, Fe-20% P alloy powder. A mixed powder in which 0.15%, pyroxene pyroxene powder 0.8%, manganese sulfide powder 0.2%, and the balance reduced iron powder with 0.75% zinc stearate was prepared. Its total composition is C ... 2%, Cu ... 10%, Sn ... 0.5%, P ... 0.03% (along with pyroclastic pyroxene, manganese sulfide, and iron balance). For comparison, a mixed powder was prepared by omitting the pyroclastic powder and manganese sulfide powder from the above composition.
[0017]
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 17 and a wear amount of 35 μm, whereas in the latter case, the machinability index of 19 and the wear amount of 38 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.
[0018]
【The invention's effect】
The valve guide material according to the present invention has improved machinability by about 4 times compared to the conventional material while maintaining the wear resistance which is not much different from the conventional material. Therefore, the present invention is extremely useful when the workability of the valve guide material is particularly emphasized from the working conditions in the assembly process of the engine, compatibility with the machine tool to be used, and various other relationships.
[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, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.01-less than 0.1%, and Fe ... remainder, pearlite A sintered valve guide material characterized by exhibiting a structure in which a copper or copper-tin alloy phase; and free graphite are dispersed in a base mainly composed of. Alloy composition by mass ratio: C ... 1.5-4%, Cu ... 6-20%, Sn ... 0.1-2%, P ... 0.01-less than 0.1%, Sum of pyroxene and manganese sulfide Sintered valve guide material characterized by exhibiting a structure in which copper or copper-tin alloy phase; free graphite, pyroxene and manganese sulfide are dispersed in a base mainly composed of pearlite, with less than 4%, and Fe ... balance . The sintered valve guide material according to claim 2, wherein a total amount of free graphite, pyroxene and manganese sulfide dispersed in the base is 4% or less.

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