JPS6260967A - Piston with ceramic ring and manufacture thereof - Google Patents

Abstract

PURPOSE:To secure such a piston ring that is excellent in wearproofness, heat resistance and heat insulatability, besides very good in lubricatability, by using a sintered body made up of a polycrystal substance consisting in partially stabilized zirconia inclusive of a tetragonal system at normal temperature and having the fine crystal grains. CONSTITUTION:For example, zirconia powder containing YzO3 as much as mol% is heated and sintered, thereby securing a sintered body of 0.3mum in mean crystal grain diameter containing tetragonal system zirconis crystal of 70% by volumetric percentage. Then, this sintered body is molded into a blank 2 for piston ring use. Next, this blank 2 is placed on a mold part of a lower mold 5 of a device as in illustration and a part of a ring groove of a piston 1 is adjusted to it. And, under this state, with heating within the specified temperature range, a push rod 6 and upper molds 3 and 4 are moved at the specified deformation rate, and the blank 2 is thrust in the ring groove of the piston 1. With this constitution, mirror finishing takes place on an inner surface of the mold whereby a surface of the piston ring is mirror-finished, thus excellent lubricatability and wearproofness are securable.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a piston whose piston ring is made of ceramics and a method for manufacturing the same.

b. Prior Art Conventionally, ceramics have been used for various purposes because of their excellent heat resistance, heat insulation, and wear resistance. However, it has no elasticity, is hard and brittle, and is difficult to be plastically deformed, so its use is limited to specific applications.

Furthermore, piston rings of pistons used in engines are made of metal that can be plastically deformed.

C1 Problems to be Solved by the Invention As mentioned above, conventional ceramics have excellent heat resistance, heat insulation, and wear resistance, so it would be very convenient if they could be used as a substitute for metal parts.

In other words, the metal piston rings used in engine pistons are used for sliding parts and are required to have heat resistance, wear resistance, and dimensional accuracy.After precision molding, the piston rings are made using elastic deformation. It's stuck in the groove. However, when trying to use this piston ring as a substitute for ceramic piston rings, as mentioned above, ceramics are hard and brittle, making it difficult to mold, and after molding, they must be attached to the piston ring groove in the same way as metal piston rings. The problem is that even if you try, it will be damaged.

On the other hand, ceramics are extremely hard, and when grinding them, they are usually processed using a diamond grindstone, which increases processing costs. Furthermore, it is substantially difficult to manufacture a member such as a piston ring, which has a complicated curved surface and requires strict dimensional accuracy, by grinding. In other words, it has been almost impossible to produce a piston ring by plastically deforming ceramics and to fit it onto a piston.

The present invention has been made in view of the above circumstances, and solves the problems of the prior art, and provides a piston with a ceramic ring that is molded using ceramics and that is fitted into the piston at the same time as the molding. In order to solve the above-mentioned problems, the present invention aims to provide a method for producing the same, which is a partially stabilized zirconia containing tetragonal crystals at room temperature, and which has fine crystals. The piston ring is made of a sintered body made of a polycrystalline body containing grains, and is made of partially stabilized zirconia containing tetragonal crystals at room temperature, using a polycrystalline body containing fine crystal grains. After sintering into a predetermined shape, the temperature is 1200℃~16
00'C1 It is designed to be wrapped around the piston at a deformation speed of IQm/sec or less.

The present invention will be explained in detail below.

First, in the present invention, among ceramic materials, a polycrystalline body containing fine crystal grains of tetragonal zirconia at room temperature is processed by applying stress such as tensile or compressive stress at a certain appropriate temperature range and strain rate. It was discovered that this material produces superplastic deformation reaching 120% or more and can be used with various molding methods, and this was applied to the molding and installation of piston rings used in engine pistons.

That is, the polycrystalline body used to obtain the superplastic deformation must contain at least 20% by volume of tetragonal zirconia crystals, and the grain size must be 2 μm or less. is desirable, and 1 μm or less is more preferable.

In addition, the appropriate temperature range for performing the processing is 1200°C ~
The temperature is 1600°C, preferably 1400°C to 1500°C.

At temperatures below 1200°C, the deformation rate (processing speed) becomes extremely slow, making it impractical; at temperatures above 1600°C, zirconia grains grow significantly and exceed the critical grain size, becoming monoclinic at room temperature. A strengthening mechanism based on stress-induced transformation cannot be expected.

Therefore, deformation becomes easy, but the strength of the molded product is significantly reduced.

Further, the strain rate may be, for example, 1X10-' to 6X10-'/sec at a temperature of 1450°C, and can be increased as the temperature increases; This is preferably 10 m/sec or less in terms of deformation speed (processing speed). In a speed range higher than this, the formation and growth of cavities (gaps) at grain boundaries becomes significant, leading to destruction during processing or a decrease in strength.

In addition, in order to obtain a polycrystalline body of tetragonal zirconia at room temperature, for example, Y z O3+ M g O+ C
A zirconia solid solution may be created by adding a O+ Ce O2 or the like. The concentration range of the solid solution varies depending on the type of compound, and the production rate of tetragonal zirconia is determined by the equilibrium diagram with ZrO□. For example, YtO3 contains tetragonal zirconia in a range of 2 mol % to 6 mol %.

Next, a method for manufacturing a piston according to the present invention will be specifically explained.

FIGS. 1 to 3 illustrate the procedure for carrying out the method according to the present invention, in which numeral 2 indicates a piston into which a piston ring is fitted, 2 a piston ring material using the ceramics according to the present invention, and 3 4 is the left upper mold that reciprocates left and right; 4 is the right upper mold that also reciprocates left and right; 5
1' is the lower molding part, 6 is a push rod that reciprocates in the vertical direction,
7 is a semicircular mold part recessed on the lower mold part 5, 8 and 9 are arc-shaped mold parts provided in the upper mold parts 3 and 4, respectively, and 10 is a mold part on both sides of the mold part 7. This is a guide roller provided.

As shown in FIG. 4, the piston 1 is provided with a ring groove 11 for fitting a piston ring therearound. Since this piston 1 is heated as described below when a piston ring is fitted by carrying out the method according to the present invention, it is necessary to use a material or a method that can withstand this heating temperature. In other words, the light alloy pistons used in ordinary gasoline engines cannot be used because they may soften and melt when heated. Therefore, it is necessary to prevent the temperature from rising by using, for example, a cast iron piston with a slightly high melting temperature, and by abutting a cold metal on the inside, or by cooling with water. Or silicon carbide in the piston itself,
Using ceramics made of silicon nitride, alumina, etc.
Preferably, the piston itself is made of a heat-resistant material.

The material 2 of the piston ring is, for example, Y2O.

Using zirconia powder containing 3 mol% of Heat sintered and contain 70% by volume of tetragonal zirconia crystals with an average grain size of 0.3
Obtain a μm sintered body. Next, this sintered material 2 is processed into the piston 1 using a grinding machine using a diamond grindstone.
This ring is finished to a size corresponding to ring a11.

Each of the molds 3, 4, and 5 is made of a heat-resistant material, such as alumina, silicon carbide, mullite, etc., so as not to cause a reaction between the piston ring and the material 2 during processing. Select the appropriate material according to the processing temperature. The surface of each mold that comes into contact with the material 2 is given a mirror finish (.

e. Operation As shown in Figure 1, open the upper molds 3 and 4 to the left and right,
The material 2 is placed on the mold part 7 of the lower mold 5. Next, as shown in FIG. 4, a part of the ring a11 of the piston l is aligned with this material 2, and the centers of the piston 1 and the mold part 7 are aligned, and this position is held by an appropriate holding means. Hold.

Next, in this state, the material 2 to be processed is
C to 1600°C, preferably 1400°C to 1500°C, and while maintaining this temperature range, lower the pushpiece 6 to deform the piston ring l at a predetermined deformation speed, that is, 10 m/see or less. It is pushed down and pushed together with the material 2 into the mold part 7 of the lower mold 5 as shown in FIG. Due to the presence of the rollers 10, the material 2 is smoothly guided and formed into a U-shape as shown.

Next, move the left and right upper molds 3 and 4 toward the center piston 1 as shown in FIG. What is necessary is to push the material 2 into the mold portions 8 and 9 while maintaining a predetermined deformation speed.

In this way, the piston ring is formed and the piston is installed in the groove at the same time, and a piston equipped with a ceramic piston ring is manufactured.

By applying a mirror finish to the inner surface of the mold, the piston ring manufactured by the above method has a mirror finish on the product surface after processing, that is, the piston ring surface, and has excellent lubricity and wear resistance. . Note that a plurality of piston rings may be installed at once using the method described above.

f, using zirconia powder containing 3 mol% of Example YtOy, 1
Sintered by heating at 300°C to 1500°C, containing 70% by volume of tetragonal zirconia crystals with an average grain size of 0.3 μm
A sintered body is obtained. Using this], 87n, width 4 dragons.

A material for a long and narrow piston ring with a thickness of 2N was molded.

Next, this was set in the device shown in Fig. 1 (made of silicon carbide) together with a silicon carbide piston with a diameter of 60 mm, and the deformation rate of each of the pressing molds and upper molds was set at a temperature of 1450 to 1500 °C. Processing was performed with the ratio of 6u/lll1n.

The time required for processing was about 10 minutes.

As a result, the surface roughness of the piston material made of the zirconia sintered body before molding was 1 μm, but the surface roughness of the piston ring after being processed using the mirror-finished silicon carbide mold was 0.0 μm. It was less than 1 μm, and a product with extremely high precision was replaced.

g. Effects of the Invention As described above, according to the present invention, by superplastic processing of ceramics, piston ring forming, surface finishing, and attachment to the piston can be done simultaneously, and the piston ring has wear resistance and heat resistance that cannot be obtained with metal members. The piston can be replaced with a ceramic ring that has excellent properties such as heat resistance, heat insulation, and good lubricity, and can greatly contribute to higher efficiency of the engine.

Furthermore, by increasing the dimensional accuracy of the mold, it is possible to increase the accuracy of the piston ring of the present invention,
Even complex curved surfaces and minute properties of the mold are easily transferred to the product, i.e. the piston ring.

It became possible to reproduce it.

Furthermore, the piston ring deformation processing speed is within a practical range, making it suitable for mass production.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining the procedure for carrying out the method according to the present invention, and FIG. 4 is an enlarged perspective explanatory view showing the piston portion in FIG. 1. ■... Piston, 2... Piston ring material, 3, 4... Upper mold, 5... Lower mold, 6... Push rod, 8, 9, 10... Mold section , 11...Piston ring groove.

Claims (2)

[Claims] (1) A piston with a ceramic ring, characterized in that the piston ring is a sintered body made of partially stabilized zirconia containing tetragonal crystals at room temperature and a polycrystalline body containing fine crystal grains. (2) Partially stabilized zirconia containing tetragonal crystals at room temperature, polycrystalline material containing fine crystal grains is used, and after sintering it into a predetermined shape, the temperature is 1200°C to 1600°C, and the deformation rate is 10mm/ A method for manufacturing a piston with a ceramic ring, characterized by wrapping the piston around the piston in less than sec.