JPS6379901A - Production of cylinder liner - Google Patents

Abstract

PURPOSE:To improve wear resistance and lubricating oil holdability while maintaining strength by molding a green compact of quickly cooled Al alloy powder contg. hypereutectic Si to a cylindrical body and forming blowholes to the inside peripheral surface thereof by heat rays, then grinding the cylindrical body to form recesses. CONSTITUTION:The quickly cooled Al alloy powder contg. the hypereutectic Si in order to improve the wear resistance is compacted to form the green compact which is then extrusion-molded by hot extrusion. The Al alloy is thereby molded to the cylindrical body and is made into a sintered body. The gaseous components incorporated in supersaturation in the cylindrical body gasify to generate gas bubbles in the molten part when the inside peripheral surface of such cylindrical body is partially remelted by the high-density energy heat rays. The molten metal solidifies quickly to confine the gas bubbles and to form the blowholes when the heat rays are annihilated. The inside peripheral surface is machined to a prescribed shape by which the recesses functioning as oil pools are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a cylinder liner made of sintered aluminum alloy, and more particularly to a method for manufacturing a cylinder liner having a recess for a lubricating oil reservoir on its inner peripheral surface. .

(Prior Art) In general, press-fitting of cast iron or processing technology of cast iron is used for the liner of an aluminum cylinder block for the purpose of improving wear resistance. However, since this processing technique uses cast iron, there is a problem in that thermal dimensional changes occur due to the difference in coefficient of thermal expansion between the aluminum cylinder block and the aluminum cylinder block.

For this reason, among aluminum alloys with similar coefficients of thermal expansion, A with good wear resistance and containing silicon in the hypereutectic
390 alloy (A-17% St) is used as a cylinder liner material or as an integral block.

(Problem to be solved by the invention) Increasing the amount of silicon in the aluminum alloy in this way does improve wear resistance, but the problem is that castability and especially machinability deteriorate. There is. For this reason, A3
Aluminum alloys with a silicon content of 90 alloy or higher have problems that make them unsuitable for practical use, despite their excellent wear resistance.

On the other hand, in order to improve the ability of the cylinder liner to retain lubricating oil, appropriate irregularities are formed on the inner circumferential surface of the cylinder liner during grinding. For example, in the case of silicon-containing aluminum alloys, NaOH
A method has been proposed in which the base structure of an aluminum alloy is etched in an aqueous solution to form irregularities. but,
In this etching, the unevenness formed is extremely small, and there is a problem in that the lubricant cannot be sufficiently retained.

Furthermore, as shown in Japanese Patent Application Laid-Open No. 57-35653, there is a method in which hydrogen is added to an aluminum alloy in a supersaturated state and a large number of pinholes are formed inside the aluminum alloy during solidification. However, in this method, a large number of pinholes are randomly formed in the aluminum alloy, resulting in insufficient strength as a cylinder liner, resulting in problems such as pressure leakage.

This invention was made in view of the above-mentioned problems, and the purpose of this invention is to provide a cylinder liner that not only has improved wear resistance but also improves lubricating oil retention while maintaining strength. The purpose is to provide a manufacturing method.

(Means for Solving the Problems) In order to solve the above-mentioned problems and achieve the purpose, a method for manufacturing a cylinder liner according to the present invention involves compacting rapidly solidified aluminum alloy powder containing hypereutectic silicon. a process of making a green compact by hot extrusion, a process of extrusion molding this compact by hot extrusion to form a cylindrical body, and a process of irradiating the inner peripheral surface of this cylindrical body with high-density energy hot rays to melt the irradiated part. The method is characterized by comprising a step of forming a blowhole therein, and a step of grinding the inner circumferential surface of the cylindrical body to form a recess.

(Function) In the cylinder liner manufacturing method according to the present invention configured as described above, an aluminum alloy is used as the material of the cylinder liner for the purpose of improving wear resistance. This aluminum alloy is compacted from quenched aluminum alloy powder containing hypereutectic silicon, and this aluminum alloy is extruded into a cylindrical body by hot extrusion to become a sintered body. Although this sintered body contains supersaturated gas components, its sintered density is set close to the theoretical density, and it has excellent strength and toughness.

The surface of a predetermined portion of the inner peripheral surface of this cylindrical body is partially remelted by the high-density energy hot wire. Due to this remelting, the supersaturated gas component is gasified, so that bubbles are generated in the melted portion. After this, when the high-density energy hot ray leaves, the molten metal rapidly solidifies due to heat conduction, which traps air bubbles in the re-melting zone and creates blowholes.

By cutting the inner peripheral surface of such a cylindrical body into a predetermined shape, a recess that functions as an oil reservoir is formed on the inner peripheral surface.

(Example) Hereinafter, an example of the method for manufacturing a cylinder liner according to the present invention will be described in detail with reference to the accompanying drawings.

First, an aluminum alloy containing hypereutectic silicon (AM-
The molten metal (25% Si) is gas atomized and rapidly cooled to form a powder, which is classified to have an average particle size of 100 to 150 (μm).
) to create aluminum alloy powder. This aluminum alloy is preliminarily compacted to have a porosity of about 24 (%). This preform was stored in an aluminum can and 5x
In a vacuum of 10-a (mmHg) and at 400 (℃)
After degassing for 1 hour in a high temperature atmosphere, it is sealed. This step is performed to remove moisture, oxygen, etc. adsorbed at the same time as gas atomization, so as not to interfere with the subsequent sintering step.

The preformed body enclosed in this manner is hot extruded at a temperature of 400 (° C.) to extrude and mold a cylindrical sintered body. Here, the density of the extruded sintered body is the theoretical density of 98
．． 5 (%), which is set to a state with almost no pores.

The inner and outer peripheral surfaces of this sintered body are cut and machined into a predetermined cylindrical shape to form a cylinder liner. Then, this cylinder liner is press-fitted into the cylinder block. The thus press-fitted cylinder liner is locally remelted by irradiating a predetermined portion of the inner peripheral surface of the cylinder liner with a laser beam in the form of a high-density energy hot ray under the following conditions.

Processing equipment Co2 laser device Processing conditions Output: 800 (W) Processing speed: o, 2 (m/min) Focal length;
5 (jncl+) defocus; 3 (mm) upper melting range; width
1 (mm) Processing gas: N2 Pressure: 1, 5 (kg/cm2) Remelting is performed under these conditions to produce blowholes with an average size of about 100 (μm). The state of the metallographic structure of the portion of the inner peripheral surface of the cylinder liner where the blowhole was formed in this manner is as shown in the photograph in FIG. As is clear from the right half of the photograph in FIG. 1, blowholes are formed only in the remelted portion. Incidentally, the left half of the photograph in FIG. 1 shows a state in which it has not been remelted by the laser beam, in other words, it remains sintered.

After generating the blowhole in this way, the inner circumferential surface of the cylindrical liner is ground, and a concave opening ratio (recess opening area ratio) based on the blowhole is developed on this inner circumferential surface at 20%. . The recesses developed in this way function as oil reservoirs for lubricating oil.

The following tests were conducted to confirm the effectiveness of the cylinder liner produced through the process described above.

First, a portion of the cylinder liner formed in the above process was cut out to create a disk as a test piece, and a wear test was conducted using this disk.

In order to compare the effects of this example with those of the others, the following two test pieces were formed in the same shape as the test piece of the example and used as a comparative example.

Comparative Example (1) Disc made from A390 <2> / Disc made from 1-25% St sintered material but not laser processed This wear experiment was conducted using a bottle-on-disk type testing machine. l0W
-30 engine oil was used as the lubricating oil.

The sliding body used was a rust-resistant bottle whose sliding surface was plated with hard chrome.

The test was run-in for 10 minutes at a sliding speed of 7.2 (m/min) and an initial surface pressure of 60 (kgf/cm'), and then the surface pressure was increased by 10 (kgf/cm2). Each step was continued for 5 minutes, and the critical surface pressure at which seizure occurred was measured. The measurement results are shown in the table below.

As is clear from this table, the conventional A390 (comparative example
It is confirmed that the anti-seizure performance is significantly improved compared to 1>). In particular, comparative example <2> using sintered material of the same material.
It is understood that the disk formed according to this embodiment, in which a recess is formed as an oil reservoir, has a better seizure limit when compared to the above.

As described above, according to this embodiment, the following effects can be achieved.

That is, in the casting method, as the silicon content increases, the fluidity of the molten metal decreases, making it difficult to obtain a liner material shape with a small processing allowance. In addition, as the number of hard Si particles increases, the primary crystal Si becomes coarser, so that the wear of the cutting tool increases during cutting, and the cut surface also becomes rougher.

On the other hand, in the powder metallurgy method, the diameter of the primary crystal St can be reduced by rapid cooling during powder production, and as a result, extrusion processing after sintering becomes possible, making it possible to easily produce hollow materials with small processing allowances. At the same time, machinability is also improved. In addition, since the molten metal is rapidly cooled and turned into powder, it is confirmed that it contains supersaturated H2, which is the source of blowholes.

Furthermore, since the melted portion is locally formed using a high-density energy hot ray such as a laser, thermal deformation is small and the liner can be easily heat-processed even after being press-fitted.

By controlling the amount of heat input during thermal processing and the amount of supersaturated gas contained in the sintered body, it becomes possible to control the amount of blow poles produced. In this way, the depression obtained in the above process becomes a pool of lubricating oil, and the hypereutectic S 1
- The sliding properties of the A1 alloy can be improved.

Note that this invention is not limited to the configuration and steps of the embodiment described above, and can be modified in various ways without departing from the elements of this invention.

For example, in the above-mentioned embodiment, it was explained that An-25%St was used as the aluminum alloy containing hypereutectic silicon, but the value is not limited to this value and may be within the range described below. .

That is, in order to investigate the appropriate range of 5 itL, in the above-mentioned test, the specific wear amount of the test piece was measured at a sliding speed of 3 (m/sec). As a result, as shown in FIG. 2, as the Si content increases, the specific wear amount decreases. In particular, when the Si content is 20% or more, this specific wear amount becomes stable.

Therefore, the lower limit of the Si content is 20 (wt!k). In addition, the upper limit value is set to 40 (wt! 6) in consideration of the fact that extrusion processability decreases as the Si content increases. In this way, the Si content ranges from 20 (wt zero) to 40 (wt)
It is sufficient if it is within the range of wH).

Further, in the above-mentioned embodiment, the high temperature atmosphere during degassing was set to 400 ('tl:), but it is not limited to this value and may be within the range described below.

That is, the higher the degassing temperature, the greater the degree of degassing, and the smaller the amount of blowholes produced in the remelting process. Furthermore, if degassing and extrusion are performed at a temperature of 500 (°C) or higher, the strength will decrease. On the other hand, if degassing is performed on the low temperature side, blowholes will be excessively generated during remelting. Therefore, the contact area during sliding decreases, the surface pressure per unit area becomes excessive, and sliding performance deteriorates. Furthermore, if degassing and extrusion are performed at a temperature of 350 ('C) or lower, cracks will occur during extrusion, making processing difficult. In this way, the temperature atmosphere is 350 (
'C) to 500 (°C) is sufficient.

Furthermore, in the above embodiment, the degree of vacuum during degassing was explained to be 5 x 10-5 (mm0-5), but it is not limited to this value and may be within the range described below. Good.

That is, as the degree of vacuum during degassing increases, the degree of degassing increases and the rate of blowhole formation during remelting decreases. On the other hand, as the degree of vacuum decreases, the blowhole generation rate increases. Therefore, the degree of vacuum for degassing is between 1 x 10-2 and I x 10-5 (mm0-5), which is obtained industrially.
It is appropriate that it be within the range of 5.

In addition, in the above-mentioned embodiment, the frontage ratio of the recess is set to 2.
Although it has been explained that it is 0%, it is not limited to this value and may be within the range described below.

That is, at the temperature during degassing, when the aperture ratio increases as described above, the contact area during sliding decreases,
The surface pressure per unit area becomes excessive, and sliding performance deteriorates.
The pressure generated during seizure is reduced. Furthermore, as the aperture ratio decreases, lubricating oil retention deteriorates, and the pressure at which burnout occurs also decreases. When the relationship between this frontage ratio and the pressure at which scorching occurs is measured, the correlation shown in FIG. 3 is obtained. As is clear from the results shown in FIG. 3, the aperture ratio is preferably within the range of 10 to 50 (%).

(Effects of the Invention) As described in detail above, the method for manufacturing a cylinder liner according to the present invention includes a step of compacting a hypereutectic silicon-containing quenched aluminum alloy powder to form a green compact, and a step of compacting the compacted powder. a step of extrusion molding the body by hot extrusion to form a cylindrical body; a step of irradiating the inner circumferential surface of the cylindrical body with high-density energetic heat rays to melt the irradiated part and generate a blow pole there; The method is characterized by comprising a step of grinding the inner circumferential surface of the cylindrical body to form a recess.

Accordingly, the present invention provides a method for manufacturing a cylinder liner that can not only improve wear resistance but also improve lubricating oil retention while maintaining strength.

[Brief explanation of the drawing]

FIG. 1 is a top view photographing the state of the metal structure in which blowholes are formed on the inner circumferential surface of the cylinder liner by an embodiment of the cylinder liner manufacturing method according to the present invention, and FIG. 2 shows the silicon content and the state of the metal structure. FIG. 3 is a diagram showing the relationship between the specific wear amount of the cylinder liner, and FIG. 3 is a diagram showing the relationship between the aperture ratio and the seizure occurrence pressure. ”2J

Claims (4)

[Claims] (1) A step of compacting rapidly-cooled aluminum alloy powder containing hypereutectic silicon to form a compact; a step of extruding this compact by hot extrusion to form a cylindrical body; It includes a step of irradiating the inner circumferential surface of the body with high-density energy heat rays to melt the irradiated part and creating a blowhole there, and a step of grinding the inner circumferential surface of this cylindrical body to form a recess. A method for manufacturing a cylinder liner, characterized in that: (2) The quenched aluminum alloy powder contains 2 silicon
The method for producing a cylinder liner according to claim 1, characterized in that the cylinder liner is contained in a proportion of 0 weight percent or more and 40 weight percent or less. (3) The method for manufacturing a cylinder liner according to claim 1, wherein the green compact is vacuum degassed in a high-temperature atmosphere before being extruded. (4) The method for manufacturing a cylinder liner according to claim 1, wherein the extruded cylindrical body is press-fitted into a cylinder block after its inner and outer peripheral surfaces are cut. .