JPS5846526B2 - Manufacturing method of sintered metal piston ring - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a piston ring made of a sintered alloy.

In general, sintered alloys provide materials with excellent sliding properties and are widely used as various sliding members.

Therefore, attempts have been made for a long time to manufacture piston rings, which require excellent sliding properties, from sintered alloys.

However, in the conventional method of manufacturing piston rings using powder metallurgy, the piston rings are formed into a ring-shaped powder molding that has an extremely thin wall thickness relative to the outer diameter, has a small weight relative to the outer diameter, and has a small heat capacity. body (hereinafter referred to as green compact).

), and then put it in a normal heating furnace and heat it up to sinter it. Therefore, it is difficult to heat the green compact uniformly during the sintering process, so Did the sintered ring material become deformed and lose its dimensional accuracy? It is inevitable that this will happen.

In general, sintered alloys are materials with poor machinability, so
If the sintered ring material is deformed and dimensional accuracy is impaired, the number of post-processing steps will increase, and piston rings in particular are thin, so if the material is deformed, polishing will be required. However, it is difficult to obtain piston rings with sufficient flatness.

On the other hand, piston rings are used under conditions where stress is applied, particularly under conditions where repeated stress is applied.

Therefore, the piston ring needs to be made of a material that is unlikely to undergo permanent deformation due to the effects of stress or heat, that is, a material that is unlikely to cause thermal deformation and has high fatigue strength. Ordinary iron-carbon based sintered alloy piston rings are more prone to thermal damage than conventional cast iron piston rings, and have lower fatigue strength, making them sufficient for piston rings used in a wide range of applications. Instead, improvements in material quality are desired.

As a method for reducing thermal damage of piston rings made of iron-carbon based sintered alloy, the present inventors added a small amount of P and B in addition to C to Fe to reduce Fe3P during sintering.
-By melting the liquid phase corresponding to the ternary eutectic composition of Fe3C-Fe or Fe2B-Fe5C-Fe, the pores in the sintered alloy can be changed from irregularly pointed to rounded. We first proposed a method to increase the resistance to thermal damage and improve the transverse rupture strength, fatigue strength, and impact value (Japanese Patent Application Nos. 48-38057 and 1977-110223). did.

If this method is used, thermal deformation of the piston ring is considerably improved, but since a liquid phase is generated during sintering, shape deformation will occur unless the entire green compact is heated uniformly. When a conventional sintering method using an industrial furnace is used, shape deformation becomes particularly significant.

For the above reasons, piston rings made of sintered alloy have only been put into practical use for some small-diameter rings.

It is an object of the present invention to provide a method for manufacturing a sintered alloy piston ring that eliminates the drawbacks of the prior art described above, that is, reduces the occurrence of deformation during sintering, and improves thermal cracking resistance and fatigue strength. It was done for the purpose of
In the method of the present invention, the piston ring material is formed by compression molding an annular green compact into an annular shape with continuous abutments in the free state of the piston ring, that is, in the state before insertion into the cylinder. An induction coil surrounding the compact is concentric with the powder compact, and the
It is sintered by induction heating using alternating current of 0 KHz or less.

According to the method of the present invention, the annular powder compact is inductively heated by an induction coil installed concentrically with the annular powder compact, so that the temperature is raised uniformly over the entire circumference of the compact. A sintered alloy piston ring material with good dimensional accuracy with little deformation can be obtained, and since the compact is heated and sintered by an induced current, the contact points between the metal powder particles that make up the compact are Made of a sintered alloy that generates a large amount of heat and therefore has sufficient and strong diffusion sintering between particles, which has improved resistance to heat damage and fatigue strength, which is especially necessary for piston rings. Piston rings are obtained.

Here, when using high-frequency alternating current, there is an advantage that the temperature of the powder compact can be raised in a short time.

On the other hand, powder compacts usually contain lubricant, and in the case of powder compacts with dimensions such as piston rings, it takes 20 to 40 seconds to remove this, so avoid excessively rapid heating. In addition, when the frequency is high, the penetration depth of the induced current becomes shallow, and there is a difference in temperature rise between the outer and inner circumferences. It has the disadvantage of being easily deformed and cracked.

Therefore, the frequency should not be too high, and in the case of the present invention, the upper limit is 50 KHz.

Furthermore, if the frequency is too low, sintering takes a long time and oxidation of the material increases, so it is not desirable to use an excessively low frequency.
It is desirable to set it to Hz or more.

Examples of the present invention will be described below.

Sprayed iron powder of 1100 mesh as raw material powder, average particle size 1
Using 0 micron natural graphite powder and -325 mesh electrolytic copper powder, the composition was mixed to become 1.3%C, 13%Cu, balance Fe, and 0.75% zinc stearate was added as a mold lubricant. After mixing for 30 minutes with a V-type mixer, 73
5t, using a mold shaped like a piston ring for
Molded with a molding pressure of <- to create an annular green compact with continuous openings, and! Sintered piston ring materials were obtained using the following two methods.

(1) Using a conventional industrial furnace, 20 molecules were pre-sintered at 700°C, and then main sintering was performed at 1,120°C for 25 minutes using an endothermic gas (average composition: 24% CO, 131% H2,45 %H2
, 0.30% CO2) atmosphere.

(2) 5K using a frequency of 30KHz by the method of the present invention
Heating is performed in argon gas with an output of W, heating time to 700°C is 30 seconds, heating time to 1,150°C is 5Q.
The temperature was raised with SeC, held at 1,150°C for 20 seconds, and then cooled naturally.

The two types of piston ring materials obtained in this way were
Processed into a rectangular piston ring with dimensions of 3g x 2 x 3,
In addition to comparing the elastic modulus, thermal fatigue, and fatigue strength,
A flatness test was conducted after processing, and Table 1 shows the number of defects per 50 rings, based on the criteria that the non-contact portion should be % or more of the top and bottom surfaces of the ring as defective.

Here, regarding thermal deterioration, it indicates the rate of decrease in tension when the temperature is 350°C and the holding time is 3 hours, in accordance with the method for measuring heat resistance of piston rings specified in JIS B2O33. be.

The fatigue test was conducted by repeatedly opening and closing the joint, and the stress was calculated from the dimensions of the piston ring, the elastic modulus, and the opening and closing dimensions of the joint, and the stress amplitude was sufficient to withstand 107 repetitions.

As shown above, the method of the present invention is effective in improving the thermal damage of sintered alloy piston rings, improving fatigue strength, and reducing flatness defects, and also because it can be sintered in a short time. There is less reaction between the compacted powder and the atmosphere, and it is possible to use a lower grade atmosphere than before.In addition to short sintering time, it has industrial value such as being able to manufacture sintered alloy piston rings at low cost. It is a big thing.

Claims (1)

[Claims] 1. An annular powder compact formed by compression molding into a circular ring shape with continuous joints in the free state of the piston ring, and an induction coil surrounding the powder compact in a concentric manner with the annular powder compact. 1. A method for producing a piston ring made of a sintered alloy, which comprises sintering the piston ring by induction heating using an alternating current of I KHz or more and less than 50 kHz, and then forming a joint.