JPH11287329A - Sliding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhibit stable slidability even under the condition that temperature and viscosity of sealed fluid are varied. SOLUTION: A plurality of dimples 3a, 3b having different depths d0, d1 (d0<d1) are formed on a sliding surface 1. When a clearance hA between the sliding surfaces 1 and 2 is decreased to a value hA0 due to lowering of fluid viscosity accompanied with temperature rise, decrease of load capacity in the dimple 3b having the depth d1 is compensated by the increase of the load capacity of the dimple 3a having the depth d0. To the contrary, when the clearance hA between the sliding surfaces 1 and 2 is increased to a value hA1, the decrease of the load capacity in the dimple 3a having the depth d0 is compensated by the increase of the load capacity of the dimple 3b having the depth d1. Stable slidability is thus exhibited.

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 sealing element on a stationary side sliding on the rotating shaft side in a shaft sealing device for sealing a fluid around a rotating shaft of an apparatus. is there.

[0002]

2. Description of the Related Art A mechanical seal includes 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 perpendicular to an axis. The sliding members are required to have excellent abrasion resistance and sliding characteristics because the end surfaces of the sliding members closely slide against each other to prevent fluid leakage around the shaft. 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.

[0005] In recent years, in order to improve the sliding characteristics, a sliding material having a large number of dimples formed on a sliding surface in a regular array pattern has been developed. According to this type of sliding material, the occurrence of blisters and the like on the sliding surface described above can be effectively prevented. This is because a large number of dimples formed on the sliding surface function as a lubricating liquid pool, forming a stable lubricating liquid film even under severe sliding conditions, and a dimple having a spiral directionality. By giving a pumping action to the lubricating fluid that intervenes on the sliding surface,
This is because the thickness of the lubricating liquid film and the amount of leakage of the liquid to be sealed are appropriately controlled, and lubrication and cooling of the sliding surface are promoted.

[0006]

However, in the sliding material having a large number of dimples formed on the sliding surface in the prior art, the depth of all dimples is substantially constant, for example, about 10 μm, and the liquid to be sealed is Is constant temperature (constant viscosity)
It is assumed that Therefore, a problem is pointed out that under a condition in which the temperature of the liquid to be sealed fluctuates, a change in friction coefficient is large due to a change in viscosity of the lubricating liquid film interposed between the sliding surfaces.

The present invention has been made under the above circumstances, and a technical problem thereof is that a stable sliding can be performed even under a condition in which the temperature (viscosity) of the liquid to be sealed changes. An object of the present invention is to provide a sliding material capable of exhibiting a property.

[0008]

Means for Solving the Problems The technical problems described above are:
This can be effectively solved by the present invention. That is, the sliding member according to the present invention is characterized in that a large number of dimples having different depths are formed on a flat sliding surface. Preferably, the minimum depth of the dimple is 0.2
μm and the maximum depth is 60 μm.

A large number of dimples formed on the sliding surface hold the liquid to be sealed which intervenes as a hydrodynamic lubricating liquid film between the sliding surface and the other dimple. Each dimple can be regarded as constituting a Rayleigh step as shown in FIG.

In FIG. 1, one sliding surface 1 is formed with a Rayleigh step 1a extending in a direction perpendicular to the cross section of the drawing, and the other sliding surface 2 is formed flat.
When the sliding surfaces 1 and 2 relatively move in a direction perpendicular to the Rayleigh step 1a, that is, when the sliding surface 1 moves in the direction of arrow A or the sliding surface 2 moves in the direction of arrow B, both sliding surfaces The fluid interposed between the surfaces 1 and 2 tends to follow the sliding direction of the sliding surface 1 or 2 due to the viscosity thereof. At that time, the presence of the Rayleigh step 1a generates a fluid bearing pressure (dynamic pressure). . The load capacity due to this bearing pressure is
The size of the gap between the sliding surface 1, 2 _{h A,} when the size of the gap between the bottom and the sliding surface 2 of the Rayleigh steps 1a and _{h B,} the value of _{h B} / _{h A} is 1.866 It is well known that the maximum is obtained by the analysis in the case of (for example, "Trilogy" published by Modern Science Co .; see page 232).

Here, assuming that the portion 3 whose gap with the sliding surface 2 is enlarged by the Rayleigh step 1a is a dimple, the depth d of the dimple 3 is
Load capacity by the dynamic pressure of the fluid is maximized at a concentration of from about about 90% of the gap h _A between the sliding resistance of the sliding surface 1 is expected to most stable. The value type of the fluid in the gap h _A, the viscosity of the fluid is a function of temperature and pressure, are those determined by the load or the like for pressing the sliding surface 2 each other, the type and the load or the like of the fluid does not change , Especially when operating under controlled temperature conditions
The gap _{h A} is constant. Therefore, in this case, a stable load capacity can be obtained with the dimples 3 having the same depth d, and constant slidability can be obtained.

[0012] However, for example, when, as the temperature of the fluid changes greatly depending change of the process fluid temperature and sliding conditions, it also varies the gap h _A between the sliding surface 1 by a change in viscosity of the fluid become. Especially like oils and fats,
For the temperature dependency is large fluid viscosity, since the large variation of the gap h _A due to temperature changes, as described above, the dimple depth d of the gap h _A between the sliding surface 1 When the load capacity is about 90%, the condition greatly deviates from the condition where the load capacity is maximized, that is, a situation occurs in which good liquid lubrication with sufficient load capacity is not exhibited.

In that respect, as shown in FIG.
_{0, d 1 (d 0 <} d 1) a plurality of kinds of dimples 3
When a and 3b are formed, the clearance h _A between the sliding surfaces 1 and 2 becomes h _A0 due to a decrease in fluid viscosity due to a rise in temperature, for example.
If narrowed, although in the dimple 3b depth d ₁ will deviate from the condition, in the dimple 3a depth d ₀ is the load capacitance is increased by approximating the condition, sliding by an increase in fluid viscosity conversely If the gap h _a between the surface 1 and 2 spreads h _A1, but in the dimple 3a depth d ₀ to deviate from the condition, the load capacitance approximates the conditions in the dimple 3b depth d ₁ is increased I do. Therefore, the decrease in the load capacity of some of the dimples due to the temperature change is compensated for by the increase in the load capacity of the other dimples, and stable slidability is always exhibited.

The reason why the minimum value of the dimple depth is 0.2 μm and the maximum value thereof is 60 μm is as follows. For example in the case of a low viscosity fluid like water, since the minimum value of the clearance h _A between the sliding surface 1 is assumed to be about 0.3 [mu] m, the minimum dimple depth 0 By setting the thickness to 0.2 μm, it is possible to sufficiently cope with a decrease in viscosity. Further, in the case of low-temperature oil, it is assumed that the viscosity increases to about 200 times that of water. Therefore, if the maximum value of the dimple depth is 60 μm, it is possible to sufficiently cope with the increase in viscosity.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, when the temperature (viscosity) of a fluid to be sealed generally changes in two levels, a binary discrete distribution of dimple depth is sufficient. . FIG. 3 shows, as an example, an enlarged view of a case where dimples 3a and 3b having two kinds of depths are alternately formed on the sliding surface 2 in a lattice point shape at a ratio of 1: 1.

In the case where the temperature (viscosity) of the fluid to be sealed changes randomly, it is desirable to have a continuous distribution having a very large value of the dimple depth.
The dimple depth is a discrete distribution having 3 to 5 values. this is,
This is because it is difficult to perform dimple processing with a continuous distribution of dimple depths, and a sufficient effect can be obtained even with a discrete distribution of 3 to 5 values. That is, even if the fluid temperature changes randomly due to a change in the sliding conditions during operation or the like, the change in the gap between the sliding surfaces accompanying the change in the fluid temperature causes any one of the dimple depths of 3 to 5 values. However, this is because the load capacity due to the hydrodynamic bearing pressure is approximated to a depth at which the load capacity becomes substantially maximum.

[0017]

EXAMPLES A sliding test was performed on the following examples and comparative examples using a mechanical seal tester under the test conditions described below. As shown in FIG. 4, a mechanical seal tester includes a casing 13 for supporting a stationary ring 11 as a sample in a non-rotating state via a gasket 12, and a rotating shaft rotatably inserted through the inner periphery of the casing 13. 14 and
A rotating ring 15 supported on the outer periphery of the rotating shaft 14 via a packing 16 so as to be movable in the axial direction, and opposed to the fixed ring 11 in the axial direction; A spring 17 for bringing the surface into close contact with the sliding surface of the fixed ring 11
Fixed ring 11, gasket 12, casing 1
3. A liquid L to be sealed is sealed in a sealed space surrounded by the rotating shaft 14, the rotating ring 15, and the packing 16.

As the stationary ring 11, a ring made of a high-density silicon carbide sliding material and having circular dimples having a diameter of 120 μm formed on the sliding surface 11a with a dimple area ratio of 8% was used. In the embodiment, the dimple depth is 10 μm and 3
As shown in FIG. 3, two types of 0 μm were formed, and the ratio was 1: 1. In the comparative example, a circular dimple having a diameter of 120 μm was formed at a dimple area ratio of 8%, and all the dimples had a uniform depth of 10 μm.

In this sliding test, a rotating ring 15 made of fired carbon impregnated with resin and having a sliding surface formed into a smooth surface free of dimples was used, and other conditions were as follows. Test conditions (1) Liquid L to be sealed Non-viscous neutral oil (2) Peripheral speed of sliding surface 1.1 m / s (3) Surface pressure of sliding surface 1.5 MPa (4) Temperature of liquid L to be sealed Two conditions of 310K and 290K

FIG. 5 shows the results of the above-mentioned tests evaluated in terms of the coefficient of friction. According to the test results, when the oil temperature of the non-viscous neutral oil to be sealed is 310 K, the friction coefficient in the example is slightly larger than the friction coefficient in the comparative example, but the oil temperature is 290 K. In the comparative example, the friction coefficient in the comparative example is increased by 0.09 compared to the level of the oil temperature of 310K, whereas the increase in the friction coefficient in the example is suppressed to only 0.03. That is, in the comparative example, the fluctuation of the friction coefficient due to the oil temperature change was large, but in the example, the fluctuation of the friction coefficient due to the oil temperature change was small, and it was confirmed that stable sliding performance was obtained.

The present invention is not construed as being limited to the illustrated embodiment. For example, the opening shape of the dimple is not limited to a circular shape as shown in the figure, but may be another shape such as an elliptical shape or a rectangular shape.

[0022]

According to the sliding material of the present invention, since a large number of dimples having different depths are formed on the sliding surface, it is possible to reduce the fluid interposed between the sliding material and the sliding surface during sliding. The load capacity due to the generated fluid bearing pressure decreases with some dimples due to changes in fluid temperature, but increases with other dimples, so the load capacity is stable, and good sliding properties are always maintained regardless of temperature changes. Is achieved.

[Brief description of the drawings]

FIG. 1 is a view for explaining the function of a dimple formed on a sliding surface in a sliding material of the present invention.

FIG. 2 is a view for explaining the operation of dimples having different depths formed on a sliding surface in the sliding material of the present invention.

FIG. 3 is a perspective view showing a partial cross section showing an embodiment of the sliding member of the present invention in an enlarged manner.

FIG. 4 is a schematic half-sectional view of a mechanical seal tester used for a sliding test of a sliding member, cut along a plane passing through an axis.

FIG. 5 is an explanatory diagram showing test results.

[Explanation of symbols]

 1,2 sliding surface 3,3a, 3b dimple

Claims (2)

[Claims] 1. A sliding material comprising a plurality of dimples of different depths formed on a flat sliding surface. 2. The method according to claim 1, wherein the dimple has a minimum depth of 0.2 μm and a maximum depth of 60 μm.
m, a sliding material for a mechanical seal.