JP2001020003A - Sliding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive sliding material excellent in lubricity, wear resistance and mechanical strength. SOLUTION: The powder of a raw metal selected from stainless steel, heat resistant steel, copper, copper alloy, aluminum, aluminum alloy, etc., is sintered by powder metallurgy to produce an annular sintered metal 11 having a lot of dispersed pores 11a. A lot of recessed parts 10b, each being a part of an exposed one among the dispersed pores 11a, are present at random at the end face 10a which is to be a sliding surface of the sintered metal 11, and a hardened layer 12 is formed by a hardening treatment method selected from nitriding treatment, carbonization treatment, and ion implantation treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member used as a sealing element on a rotating shaft side or a stationary sealing element sliding on the rotating shaft in a mechanical seal or the like for sealing a fluid around a rotating shaft of an apparatus. is there.

[0002]

2. Description of the Related Art A mechanical seal is an end face in which a sliding member provided on a rotating shaft side and rotating with the rotating shaft and a stationary sliding member provided on a non-rotating housing side are orthogonal to the axis. The close sliding between the members prevents leakage of fluid around the shaft, and the sliding material is required to have excellent wear resistance and sliding characteristics. For this reason, as a material of the sliding material, a hard material such as silicon carbide or alumina having excellent wear resistance, or carbon having excellent self-lubricating properties is used.

When sliding between flat surfaces under lubrication with an isothermal incompressible fluid, if the flat surfaces are extremely smooth, a lubricating liquid film is theoretically not formed between the sliding surfaces in a steady state. In an actual mechanical seal, a lubricating liquid film is formed due to factors such as minute undulations generated on the sliding surface and surface roughness. However, during sliding, the waviness and surface roughness change due to frictional heat and the like, and a change in the thickness of the lubricating liquid film accompanying this change causes a change in the coefficient of friction and the amount of heat generated on the sliding surface. When the sliding material is used under severe conditions, such as a PV value, which is extremely high, the average value and the maximum value of the friction coefficient and the amount of heat generated by the sliding increase, so that minute deterioration or breakage of the sliding surface progresses.

For example, when a hard sliding material such as silicon carbide is used in combination with a sliding material made of carbon having self-lubricating properties, frictional heat causes a blister called blister on a sliding surface on the carbon side. It is known that worm-like abnormal wear often occurs. Such destruction of the sliding surface occurs because the liquid lubricating film between the sliding surfaces has completely disappeared.

Therefore, in recent years, a pore-dispersed sliding material having a large number of pores at a predetermined ratio has been developed in order to improve the sliding characteristics. As a typical example, a pore-dispersion sliding material made of, for example, a silicon carbide sintered body is disclosed in Japanese Patent Publication No. 5-69.
066, etc. According to this kind of pore-dispersed sliding material, it is possible to effectively prevent the occurrence of blisters and the like on the sliding surface described above. This is because the lubricating liquid film is stabilized even under severe sliding conditions in which the lubricating liquid film tends to disappear, because a large number of concave portions due to pores exposed on the sliding surface function as a lubricating liquid pool. This is because lubrication and cooling are promoted.

[0006]

However, according to the above prior art, the silicon carbide sintered body is expensive, and moreover,
During the sintering process of silicon carbide, the synthetic resin powder to be added to the sintering material to form pores therein is decomposed by heating, which causes a problem that the sintering furnace is contaminated. Also, the silicon carbide sintered body has a small fracture toughness value,
That is, because of its high brittleness, cracks are easily generated by impact, and the strength is further reduced by forming pores inside.

[0007] Although the above-mentioned problem has been described with respect to a sliding material made of a silicon carbide sintered body, a similar problem has been pointed out with respect to a sintered body of titanium carbide, titanium nitride, titanium carbonitride, silicon nitride and the like. You.

The present invention has been made in view of the above problems, and its main technical problem is to provide an inexpensive sliding material having excellent lubricity, abrasion resistance and mechanical strength. To provide.

[0009]

In order to effectively solve the above-mentioned technical problems, a sliding material according to the present invention is made of a sintered metal having a large number of pores dispersed therein and has a sliding surface. A hardened layer formed by a hardening process is formed on the surface layer portion of the end face to be formed. That is, the sliding surface is formed of a hardened layer, thereby improving the wear resistance, and the concave portion formed by the pores appearing on the sliding surface functions as a lubricating liquid reservoir, thereby improving the liquid lubricity. The fracture toughness value is increased by using a binder metal.

As the sintered metal, stainless steel, heat-resistant steel, copper, copper alloy, aluminum,
Selected from aluminum alloys. In the sintering process by powder metallurgy, since the dispersed pores are inevitably formed by bonding the metal particles together in a solid state, there is no need to intentionally perform a pore forming operation by previously mixing a synthetic resin powder or the like. Thus, contamination of the sintering furnace by the thermally decomposed synthetic resin can be prevented. The dispersed pores formed by the powder metallurgy generally have an average pore diameter of 5
Although the porosity is 3 to 20% at 100 μm, it is determined in consideration of the usage conditions of the sliding material.

The hardening treatment for forming the hardened layer is selected from nitriding, carbonization and ion implantation methods in consideration of the type of sintered metal, sliding conditions, characteristics of the fluid to be sealed, temperature, and the like. You. The thickness of the layer is determined in consideration of sliding conditions, target life, and the like, but is generally several μm to several tens μm. The hardened layer formed in this way is free from the risk of peeling off when a hard layer made of another material is coated, and has a kind of gradient in which the element distribution due to the hardening process changes continuously in the layer thickness direction. Because it is a functional material, it also has excellent thermal shock resistance.

On the surface of the sintered metal, the pores appear as depressions. A large number of recesses appearing on the sliding surface hold a part of the liquid that intervenes as a hydrodynamic lubricating liquid film between this sliding surface and the sliding surface of the mating material to stabilize the lubricating liquid film. Has the function of

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic enlarged sectional view near a sliding surface showing an embodiment of a sliding member according to the present invention. The sliding member 10 is made of a sintered metal 11 having a shape as a sliding ring of a mechanical seal, and has a hardened layer 12 formed on a surface layer of an end surface 10a serving as a sliding surface with a mating member. A large number of concave portions 10b are formed at random on the end face 10a.

FIG. 2 is a flowchart showing a manufacturing process of the sliding member 10. That is, first, in step S1, a raw metal powder selected from stainless steel, heat-resistant steel, copper, copper alloy, aluminum, aluminum alloy and the like is mixed,
In the next step S2, the raw metal powder is filled into an annular molding space of a compression molding die apparatus, and compression molded at a predetermined pressure. Thereby, a powder compact having the shape of the sliding ring of the mechanical seal is preformed.

Next, in step S3, the powder compact taken out of the compression molding die apparatus is heated in a sintering furnace at a predetermined sintering temperature lower than the melting temperature of the raw metal for a predetermined time, thereby forming an annular shape. Is sintered. In step S4, recompression molding is performed to increase the dimensional accuracy of the sintered annular sintered metal 11 and to increase the bonding strength of the metal particles. In step S5, the end face serving as a sliding surface is formed. 10a is machined flat by polishing or the like. As described above, since the sintered metal 11 obtained by sintering the metal powder is a porous sintered metal having a large number of dispersed pores 11a therein,
A large number of recesses 10b are randomly present on the machined end face 10a by exposing a part of the dispersed pores 11a.

Next, in step S6, a hardened layer 12 is formed on the end surface of the machined sintered metal 11 by a method selected from nitriding, carbonizing and ion implantation. FIG. 3 shows the relationship between the depth from the surface, the nitrogen concentration and the hardness when a hardened layer is formed on the surface layer of the sintered metal by nitriding. The “hardened layer” in the present invention is a range (a region indicated by a in the figure) in which a certain degree of hardening is recognized with respect to the original hardness of the sintered metal.

[0017]

FIG. 4 is a diagram showing an example in which SUS316 stainless steel powder is sintered by powder metallurgy to obtain an average pore diameter of 50 μm.
m, an annular body made of a pore-dispersed sintered metal having a porosity of 8% and having a Vickers hardness Hv of a sliding material having a hardened layer formed by nitriding on the surface of an end surface serving as a sliding surface. Is shown together with the result of measurement of the pore-dispersed sintered metal before the nitriding treatment as a comparative example.

As is apparent from the measurement results, in the comparative example, a slight increase in hardness, which is considered to be work hardening caused by cutting or polishing, is recognized in the surface layer portion, but is not significant. On the other hand, in the case after the nitriding treatment, a remarkable increase in hardness is observed in the surface layer.

[Sliding Test 1] The sliding material of the above embodiment was subjected to a sliding test using a mechanical seal tester. The mating sliding member was made of a high-strength carbon material and had a flat sliding surface without intentionally formed concave portions. Other conditions were as follows. Test conditions (1) Liquid to be sealed High viscosity oil (2) Sliding speed 15m / s (3) Surface pressure of sliding surface 0.35MPa (4) Temperature of liquid to be sealed -10 ° C (5) Sliding time 2 time

After sliding for 2 hours, the carbon sliding surface of the mating material was observed. As a result, no blisters, which are forms of carbon damage, were generated. Therefore, it was confirmed that the sliding material according to this example provided excellent lubricity.

[Sliding Test 2] Next, a sliding test was performed by a mechanical seal tester on the sliding material according to the above embodiment and a sliding material of a pore-dispersed sintered metal not subjected to nitriding treatment. Carried out. The mating sliding material arranged on the rotating side is made of a high-strength carbon material and has no intentionally formed concave portion, and has a flat sliding surface, and other conditions are as follows. And Test conditions (1) Liquid to be sealed Water (2) Sliding speed 4.5m / s (3) Sealing pressure 0.5MPa (4) Temperature of liquid to be sealed 80 ° C (5) Sliding time 100 hours (6) Test Previous sliding surface roughness In both Examples and Comparative Examples, 0.1 μm except for the concave portion. Opposite sliding material (carbon) 0.2 μm

According to the above-mentioned sliding test, in the case of the sliding material of the comparative example not subjected to nitriding treatment, leakage of the liquid to be sealed (water) was recognized from 40 minutes after the start of the test, and up to 100 hours. Total leakage reached 25cc. In addition, the wear amount of the sliding surface of the sliding material of the comparative example was 14 μm, and the surface roughness was 1.
The sliding surface wear amount of the mating sliding material was 21 μm, and the surface roughness was 1.8 μm.

On the other hand, in the case of the sliding material of the embodiment, no leakage was observed until the end of the test. Also,
The wear amount of the sliding surface in the sliding material of the example is 0.2 μm,
Surface roughness is 0.3μm, sliding surface wear of mating sliding material is 5μ
m, and the surface roughness was 0.5 μm. That is, as compared with the case of using the sliding material of the comparative example made of a pore-dispersed sintered metal that does not form a hardened layer by nitriding, the amount of wear and surface roughness is significantly reduced, and excellent sealing performance can be realized. confirmed.

[0024]

According to the sliding material of the present invention, the thickness of the lubricating liquid film and the amount of leakage of the liquid to be sealed can be appropriately controlled by the concave portion formed on the sliding surface, and the surface of the sliding surface can be provided. The formation of the hardened layer results in a sliding material having excellent wear resistance. Also, since the base material is made of sintered metal by powder metallurgy,
The fracture toughness value is higher than when made of ceramics.

Further, since a large number of concave portions due to dispersed pores formed in the sintering process are present on the surface of the sliding material, it is not necessary to perform processing for forming the concave portions on the sliding surface. The pores are inevitably formed during the sintering process, and there is no need to add synthetic resin powder for forming pores to the raw metal powder. Moreover, the metal powder material itself is cheaper than the ceramic material, so that the raw material cost and the processing cost can be reduced to provide an inexpensive product, and the sintering furnace is not contaminated.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional perspective view of the vicinity of a sliding surface of a sliding material according to the present invention.

FIG. 2 is a flowchart showing a manufacturing process of the sliding material.

FIG. 3 is an explanatory view showing an example of physical properties of a cured layer in the present invention.

FIG. 4 is an explanatory diagram showing the results of measuring Vickers hardness of the sliding materials of the example and the comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Sliding material 10a End face used as a sliding surface 10b Depression 11 Sintered metal 11a Pores 12 Hardened layer

Claims (3)

[Claims] 1. A sliding material comprising a sintered metal having a large number of pores dispersed therein and having a hardened layer formed by a hardening treatment on a surface layer of an end surface serving as a sliding surface. 2. A sliding material, wherein the sintered metal according to claim 1 is selected from stainless steel, heat resistant steel, copper, copper alloy, aluminum, and aluminum alloy sintered by powder metallurgy. . 3. The sliding material according to claim 1, wherein the hardening treatment is selected from nitriding treatment, carbonizing treatment, and ion implantation treatment.