JPH0517283B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a cast iron rocker arm, and more specifically, it is suitable not only for use in unleaded gasoline engines but also for high lead gasoline engines, and has excellent wear resistance and scuffing resistance, and is capable of preventing damage to sliding mating materials. This invention relates to a method of manufacturing a cast iron locking arm that has less corrosion resistance. In the engine valve mechanism, the rocker arm that converts the rotational movement of the cam into the vertical movement of the valve must have sufficient mechanical properties to withstand complex stresses such as bending, tension, and compression. Of course, in sliding parts with other parts (cams, valves, etc.), especially wear resistance, characteristics that can withstand scratching and abrasion, so-called scuffing resistance, and damage to the sliding counterpart material are particularly important. Less sexuality is needed. By the way, depending on the type of gasoline used,
Rocker arm materials that have conventionally shown good sliding performance with unleaded gasoline may cause significant wear and scuffing when used with high lead gasoline. This is because when high-leaded gasoline is used, combustion products unique to high-leaded gasoline that are not generated when burning unleaded gasoline are generated by the combustion of gasoline, and these are mixed into the lubricating oil and cause the sliding of the rocker arm to occur. It is thought that this impedes the sliding performance of the moving parts. Next, in a method for manufacturing a rocker arm, it is generally performed to pour molten cast iron into a sand mold and cast a rocker arm rough material. However, in the casting method using a sand mold, the temperature of the sand mold cannot be increased, and as a result, the flowability of molten cast iron deteriorates. In this case, the flowability of the metal can be improved by increasing the wall thickness of the rocker arm, but the weight of the rocker arm increases more than necessary. Therefore, as a method to improve the flowability of molten cast iron, it has been considered to improve the flowability by adding 1.5 to 2% Si to the molten cast iron, and to perform casting molding of small parts using a sand mold. There is. However, in the manufacturing method of the Rocker arm by adding Si, although it is possible to improve the flowability, the addition of Si makes it easier for graphite with low hardness to precipitate in the texture of the dough, and as a result, this graphite causes the Rocker arm itself to deteriorate. Another problem arises in that the wear resistance of the material decreases. Therefore, in the conventional manufacturing method of rocker arms, even if the composition of molten cast iron is adjusted, it is difficult to manufacture rocker arms with excellent wear resistance without graphite precipitation while improving flowability. There is. In view of the above, the present invention solves the drawbacks of the conventional rocker arm manufacturing method and provides a cast iron rocker arm with excellent sliding performance. The present invention provides a cast iron rocker arm that has excellent wear resistance and scuffing resistance, and is less likely to damage sliding mating materials, not only when using unleaded gasoline but also when using high lead gasoline. According to the present invention, such a purpose is achieved by using a weight ratio of C: 0.5 to 4%, Mn: 5 to 20%, and the balance substantially
Molten cast iron made of Fe is poured into a lost wax mold, held at a temperature of 950 to 1300°C for 0.5 to 5 hours, and then cooled as-cast or at a faster rate than as-cast.
This is achieved by a method for manufacturing a cast iron rocker arm, which is characterized in that rocker arm rough material is cast and formed. Here, if the weight ratio of C is less than 0.5%, the abrasion resistance will be poor, and if it exceeds 4.0%, graphite will be produced and the abrasion resistance will be poor. Furthermore, if the weight ratio of Mn is less than 5.0%, it is difficult to turn into austenite, and if it exceeds 20%, the aggressiveness toward the mating material becomes strong and the amount of wear of the mating material increases, so the content was set at 5 to 20%. The structure that is maintained at a temperature of 950 to 1300℃ for 0.5 to 5 hours is a structure in which carbide is dispersed and crystallized in an austenite base, or a structure in which austenite, martensite, pearlite, and bainite are minutely mixed. If this condition is not met, pearlite and bainite will increase, making it impossible to obtain a cast iron rocker arm with excellent wear resistance. Cooling as-cast or at a faster rate than as-cast is carried out in order to prevent a large amount of pearlite and bainite from precipitating in the base structure, and is a common cooling method using the lost wax method. As for the method of cooling at a faster rate than as-cast, cooling can be performed by blowing air or the like, as is generally practiced. If necessary, the molten cast iron of the present invention may contain Cr; 15% or less by weight as an element for improving wear resistance;
At least one element selected from Mo: 20% or less and V: 10% or less can be added. Cr,
When Mo and V are added in a weight ratio exceeding each weight ratio, they become more aggressive toward the other material and increase the amount of wear on the mating material, so they must be added within a range below each weight ratio. Embodiments of the present invention will be described below based on the accompanying drawings. Using the lost wax method at a mold temperature of 800°C, a raw rock arm material with the composition shown in the table below was cast. In addition, the tapping temperature is 1600 to 1700℃, and the casting temperature is
The temperature is 1550-1650℃.

[Table] In the table, samples No. 1, No. 3 to No. 5 are representative of the materials of the present invention, and after pouring molten cast iron into a lost wax mold, the temperature of 0.5 ~5
After holding for a period of time, the rough material of the rock arm was cast and formed in an as-cast state. Sample No. 2 was not subjected to heat treatment, that is, after pouring,
The rough material of the rock arm was cast and formed in an as-cast state without being held at a temperature of 950 to 1300°C for 0.5 to 5 hours. Sample No. 6 to Sample No. 9 are test solutions for determining the upper and lower limits of the composition of the material of the present invention, and were subjected to the same treatment as the material of the present invention. Sample No. 10 is a so-called high chromium cast iron, which is the material used for the Rotsuka arm, which is also commonly used in unleaded gasoline. After machining and finishing each Rotsuka arm raw material cast and formed as described above, high lead and high octane gasoline are used to remove the rough material, which significantly deteriorates the sliding performance.
Using degraded oil B containing 0.256 wt.% Zn and 0.048 wt.% P, a low-speed scuffing test was conducted by motoring at 1000 rpm. The test results are shown in the figure. The test time was 200 hours, and the water temperature was 60℃. In addition, including Zn; 0.16wt.%, P; 0.12wt.%,
A low-speed scuffing test similar to that described above was also conducted using degraded oil A, but the results were almost the same as when degraded oil B was used. In the above test, the judgment criteria were cam wear amount of 100μ or less and rocker arm wear amount of 100μ or less. From the results, the present invention material samples No. 1, No. 3 to No. 5
It was judged that the sliding properties were good, although there were some variations. For sample No. 2, the wear amount was within the criteria, but a large amount of pearlite and bainite were likely to be formed in the base structure, making it difficult to manufacture a rocker arm with excellent wear resistance that was stable for each casting. It was something I couldn't do. As can be seen from the results of Sample No. 6 to Sample No. 9, which are test melt materials, when the amount of each added element is large, the amount of wear on the cam, which is the sliding mating material, is large, and it is not suitable as a rocker arm material. However, if the mating cam material has excellent wear resistance, it may be possible to increase the amount of wear resistance improving elements such as Cr, Mo, V, etc. As described above, compared to sample No. 10, which is conventionally used for unleaded gasoline, the material of the present invention has all the characteristics such as wear resistance, scuffing resistance, and damage to sliding mating materials. The sliding properties were good. As is clear from the above, according to the method for manufacturing a cast iron rocker arm according to the present invention, the mold temperature of the lost wax mold can be increased, thereby eliminating the need to supplement the flowability of molten cast iron with elements such as Si. Therefore, it is possible to easily cast a rocker arm with excellent wear resistance and no graphite precipitation while improving flowability. The cast iron rocker arm manufactured by the manufacturing method according to the present invention can be used not only when using unleaded gasoline but also when using high lead gasoline.
It has the advantage of having excellent wear resistance and scuffing resistance, and less damage to the mating material it slides on, so-called excellent sliding performance.

[Brief explanation of the drawing]

The figure is a graph showing the results of a low-speed motoring test performed by motoring various test materials.

Claims (1)

[Claims] 1 Weight ratio: C: 0.5-4%, Mn: 5-20%,
Molten cast iron, the remainder of which is essentially Fe, is poured into a lost wax mold and heated to a temperature of 950 to 1300°C to form a melt of 0.5 to 5.
1. A method for manufacturing a cast iron rocker arm, which comprises maintaining it for a period of time, cooling it as-cast or at a faster rate than the as-cast, and then casting and forming a raw material of the rocker arm.