JPH07174136A - Journal bearing - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent the bearing metal temperature from rising due to higher bearing load and higher peripheral speed of steam turbine / generator. [Composition] A journal bearing supporting a rotating shaft, in the vicinity of the minimum oil film position 12 where the temperature of the bearing metal 3 is maximum,
A turbulent flow transition layer 17 is provided for changing the flow state of the lubricating oil 4 from laminar flow to turbulent flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a journal bearing for supporting a rotary shaft of a large rotating machine such as a steam turbine or a generator, and particularly to a bearing metal which is heated to a high temperature due to heat generated by frictional force of a lubricating oil film of the bearing. The present invention relates to a journal bearing whose temperature is kept low.

[0002]

2. Description of the Related Art A journal bearing for supporting a rotary shaft of a large rotating machine such as a steam turbine or a generator is divided into an elliptical bearing in which the bearing metal is formed in an elliptical shape and a pad in which the bearing metal receives a load. Pad bearings are commonly used because of their high reliability. here,
A conventional technique will be described by taking the elliptical bearing as an example.

As shown in FIG. 9, a conventional journal bearing has a bearing inner ring 2 divided into upper and lower halves for supporting a journal 1 which is a bearing portion of a rotating shaft in a large rotating machine such as a steam turbine or a generator. A bearing metal 3 made of a bearing alloy such as white metal is welded to the inner peripheral surface of the bearing inner ring 2 in order to enhance lubrication characteristics.

The lubricating oil 4 is supplied from the oil supply hole 5 into the bearing inner ring 2 and flows through the gap between the journal 1 and the bearing surface 7 of the bearing metal 3, and then the oil drain hole 6 and the side flow 8 are provided.
Are discharged to the outside of the bearing. When the journal 1 rotates, the lubricating oil 4 flowing in the gap with the bearing surface 7 forms a wedge oil film to generate the pressure of the oil film 9, and the rotary shaft is supported via the oil film 9. At this time, the geometrical relationship between the journal 1 and the bearing surface 7 is as shown in FIG.

That is, the center O _j of the journal 1 is displaced in the same direction as the rotation direction by the rotation of the journal 1, and with respect to the vertical axis 10 passing through the center O _l of the arc of the bearing surface 7 of the lower half of the bearing,
A line connecting the center O _l and the center O _{j of the} journal 1,
That is, the journal eccentric shaft 11 moves to the position of the angle φ. At this time, the minimum oil film position 12 is formed on the extension line of the journal eccentric shaft 11. In a large steam turbine / generator, this angle is around φ = 35 degrees in the rated state.

By forming this minimum oil film position 12, a wedge oil film of the lubricating oil 4 is formed, and the pressure of the oil film 9 is generated as shown in FIG. A value obtained by integrating the pressure distribution of the oil film 9 in the bearing becomes equal to the bearing load applied to the bearing, and the bearing supports the load applied to the journal 1.

The maximum oil film pressure position 13 of the pressure distribution of the oil film 9 generally occurs upstream of the minimum oil film position 12, and in a large steam turbine / generator, φ = 25 in the rated state.
It is near. Since this maximum oil film pressure usually reaches several times the average bearing surface pressure (bearing load / bearing projected area), compressive stress is generated in the bearing metal 3.

Further, since the journal bearing for supporting the rotary shaft of a large rotating machine such as a steam turbine / generator has a large diameter and a high rotational speed, its peripheral speed becomes a considerably high speed of 50 m / sec or more. Therefore, a shearing force is generated in the lubricating oil film due to the speed difference between the journal 1 and the bearing metal 3, and this causes friction loss of the bearing, which in turn causes heat generation to raise the temperature of the bearing lubricating oil. Instead, the temperature of the bearing metal 3 is also increased.

As described above, the lubricating oil 4 is always supplied with a low temperature lubricating oil from the oil supply hole 5 as shown in FIG. 9, and the high temperature lubricating oil is discharged from the oil discharge hole 6 and both sides of the bearing. It However, although the heat transferred to the bearing metal 3 is transferred to the outside through the bearing inner ring 2, the heat generated by the frictional force generated in the lubricating oil causes a high temperature near the bearing surface,
Especially in the vicinity of the minimum oil film thickness where the maximum oil film pressure occurs, the temperature becomes considerably high.

Therefore, in order to enable stable operation of the actual plant for a long period of time, a thermocouple is buried in the bearing inner ring 2 near the minimum oil film position 12 of the bearing, and the bearing temperature is constantly monitored. Further, in order to prevent seizure of the bearing and outflow due to melting of the bearing metal 3, an alarm value and a machine stop value are set for the measured value of the bearing temperature. Figure 10 shows the strength of the bearing metal that is the background of this.
Shown in.

In FIG. 10, the horizontal axis represents the bearing metal temperature, and the vertical axis represents the bearing local surface pressure. The limit value regarding the bearing temperature currently adopted for the journal bearings of large-scale steam turbines / generators for commercial use is the bearing metal strength (contact pressure 15
Considering the design margin and the limit temperature of 0 kg / cm ² ), the warning value is set to 107 ° C and the stop value is set to 121 ° C for the elliptical bearing. This value was determined in consideration of the fact that the actual bearing metal temperature is higher because the position where the thermocouple is embedded is about 30 mm from the bearing surface.

[0012]

However, since recent steam turbines / generators have a large capacity, the output generated by a single rotor is also large, and the rotor itself is also large and large. Since the journal bearing causes a loss due to the friction of the oil film, it is desirable to design the journal diameter to be as small as possible in order to reduce the friction loss as much as possible and improve the efficiency of the entire plant. Since it needs to be transmitted to the generator side, the diameter of the journal bearing is designed according to its torque.

Therefore, the larger the output of the rotor, the larger the diameter of the bearing and the higher the peripheral speed thereof. Currently, the maximum diameter of a bearing used in a tandem steam turbine / generator with a rated output of 700 MW is 533 mm, its peripheral speed is about 100 m / sec, and the bearing load reaches 30 to 35 tons.

Here, when the peripheral speed is increased, the shearing force generated in the lubricating oil film is further increased, the frictional force is large and the amount of heat generation is also large. Further, when the bearing load increases, the minimum oil film thickness shown in FIG. 9 decreases, the wedge effect of the lubricating oil 4 due to the rotation of the journal 1 increases, the maximum oil film pressure increases, and the amount of heat generation naturally increases. Therefore, the journal bearings used in large steam turbines / generators are used under conditions in which the bearing metal temperature is extremely strict in terms of temperature as compared with the bearings of ordinary rotary machines.

FIG. 11 shows an example in which the bearing metal temperature of an elliptical bearing having a diameter of about 500 mm was measured by burying dozens of thermocouples at a position about 10 mm from the bearing surface. In FIG.
The curve shows the isotherms obtained from the measurement results at the position of 10 mm from the bearing surface of the bearing metal on the developed surface of the lower half of the journal bearing surface. These values are the data at rated speed and rated bearing load. .

As can be seen from this figure, the maximum temperature generation position 15 of the bearing metal is in the vicinity of θ = 40 degrees, and as shown in FIG. 9, the minimum oil film position 12 due to the rotational deviation of the journal center is at the rated speed. Since θ = 35 degrees, it can be seen that the maximum occurrence position of the bearing metal 3 occurs slightly behind the minimum oil film position 12.

The maximum temperature is 110 ° C. or higher, which is a very high temperature. Further, it can be seen that the intervals between the isotherms near the maximum temperature generation position 15 of the bearing metal are very close, and the temperature gradient is very high in a narrow range. This indicates that the flow condition is laminar, the thermal conductivity is lower than that of turbulent flow, and that there is a large thermal gradient in a narrow range, and the local flow in the vicinity is laminar. Is. In rotary machines that use high-temperature working fluids such as steam turbines and generators, the bearing metal temperature may rise or fall depending on the thermal conditions of the working fluid.
Although there is a margin in design, under certain conditions, there is a possibility that the bearing temperature measurement value for monitoring will reach an alarm value and operation will not be possible. In addition, when the capacity and performance of steam turbines and generators will increase in the future, and bearings will have higher loads and higher peripheral speeds, the bearing metal temperature will rise further due to the reasons described above, and in conventional usage, It may not be possible to use the journal bearing safely.

The present invention has been made in consideration of the above-mentioned circumstances, and provides a journal bearing which can prevent the bearing metal temperature from rising due to the increased load and the increased peripheral speed of the bearing of the steam turbine / generator. The purpose is to do.

[0019]

In order to solve the above-mentioned problems, a first aspect of the present invention is a journal bearing for supporting a rotating shaft, wherein a journal oil bearing a maximum bearing metal temperature is provided near a minimum oil film position. It is characterized in that a turbulent flow transition layer for transitioning the flow state of the lubricating oil from laminar flow to turbulent flow is provided.

A second aspect of the present invention is characterized in that the turbulent flow transition layer according to the first aspect is provided in a range from the maximum oil film pressure position of the lubricating oil to the vicinity of the minimum oil film pressure position.

A third aspect of the present invention is characterized in that the turbulent flow transition layer according to the first or second aspect is a portion having a rough surface roughness provided near the minimum oil film position.

A fourth aspect of the present invention is characterized in that the turbulent flow transition layer according to the first or second aspect is a recess formed near the minimum oil film position.

According to a fifth aspect of the present invention, a suction hole is provided at the maximum oil film pressure position of the lubricating oil according to the first or second aspect, and a blowout hole is provided near the minimum oil film pressure position, and these holes are made to communicate with each other by a communication hole. It is characterized by that.

[0024]

According to the first aspect of the present invention having the above-mentioned structure, in the vicinity of the minimum oil film position where the bearing metal temperature becomes maximum,
Since a turbulent transition layer that transitions the flow state of the lubricating oil from laminar flow to turbulent flow is provided, the heat transfer coefficient between the lubricating oil and the bearing metal is increased, the bearing metal temperature is prevented from rising, and rotation is improved. The shaft system can be operated stably.

In the second aspect, the turbulent flow transition layer is provided in the range from the maximum oil film pressure position of the lubricating oil to the vicinity of the minimum oil film pressure position, so that the load capacity of the bearing is not reduced.

In the third aspect, the turbulent flow transition layer is a rough surface portion provided near the minimum oil film position, and in the fourth aspect, the turbulent transition layer is a recess formed near the minimum oil film position. Therefore, in both cases, the flow state of the lubricating oil can be made turbulent.

According to the present invention, the suction hole is provided at the maximum oil film pressure position of the lubricating oil, and the blowout hole is provided in the vicinity of the minimum oil film pressure position. Part of the lubricating oil at the pressure position passes through the communication hole and is blown out from the blowout hole. The jet flow can disturb the laminar flow and make the lubricating oil flow turbulent.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the lower half of the bearing inner ring in one embodiment of the journal bearing according to the present invention. It should be noted that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals as those in FIG.

As shown in FIG. 1, in the journal bearing of the present embodiment, a normal bearing surface finish roughness (normal design value is 1.
The turbulent transition layer 17 having a rough finish (for example, about 6.3 s) that is rougher than about 6 s is formed.
It is desirable that the turbulent flow transition layer 17 be installed upstream from the vicinity of the minimum oil film position in the rotation direction under the rated operating conditions of the bearing.

Next, the operation of this embodiment will be described.

In FIG. 2, the horizontal axis represents the surface roughness, and the vertical axis represents the transition Reynolds number and the surface finish at which the lubricating oil flow changes from the laminar flow to the turbulent flow in the case of the normal surface finish roughness. The effect is represented by taking the ratio with the transition Reynolds number in the case of roughening. As can be seen from FIG. 2, as the surface roughness is increased, the Reynolds number that transitions to turbulence becomes smaller, and the state of the flow in that portion easily transitions to turbulence.

In the journal bearing of this embodiment, as shown in FIG. 1, a turbulent transition layer 17 having a rough surface finish is formed in the vicinity of the minimum oil film position. Although a laminar flow state occurs, the use of the bearing as described above causes the flow state of the lubricating oil to be turbulent near the minimum oil film position.

By the way, it is known that the heat transfer coefficient becomes extremely high when the flow state of the lubricating oil changes from laminar flow to turbulent flow. The same can be said for the state of the flow of lubricating oil in the journal bearing. In other words, in the turbulent flow state as compared to the laminar flow state, heat exchange between the lubricating oil 4 and the bearing metal 3 is facilitated, the temperature of the lubricating oil 4 does not rise locally, and further, the temperature of the bearing metal 3 increases. It is expected that the maximum value of will not rise so much.

Generally, the state of the lubricating oil flow in the journal bearing is evaluated by the friction coefficient of the bearing. In FIG. 3, the horizontal axis represents the average Reynolds number of the bearing, and the vertical axis represents the friction coefficient.・ It shows the characteristics of the general friction coefficient of bearings used in generators. The average Reynolds number Re and the bearing friction coefficient f shown here are defined as follows.

[0036]

## EQU1 ## Re = U · Cr / ν In this equation, U is the journal peripheral speed, Cr is the bearing radius average gap, and ν is the kinematic viscosity coefficient of the lubricating oil.

[0037]

F = F / A / (γ · U ² / g) In this equation, F is the bearing shear force, A is the bearing wetted area,
γ is the specific gravity of lubricating oil, and g is gravity.

As shown in FIG. 3, the bearing friction coefficient f is a straight line that steeply descends to the right where the average Reynolds number Re is low (low rotational speed and small bearing diameter). After the flow transition point 18, the slope of the straight line becomes gentle. This is the point that the state of the flow of the bearing lubricating oil transits from laminar flow to turbulent flow on average.

Large-diameter bearings used in large-scale steam turbines and generators of 500 MW class or higher have average Reynolds numbers in the range of about 5000 to 7000. Judging from the friction loss, they are already on average. It can be seen that it is used in the region of turbulence.

However, in the bearing as shown in FIG.
Due to the movement of the journal 1, the oil film thickness becomes non-uniform on the circumference of the journal 1, and the bearing radius gap is not constant.
Therefore, it is understood that the flow of the lubricating oil 4 in the bearing is not considered to be average, and the temperature distribution characteristic of the bearing metal 3 cannot be discussed unless the local flow is evaluated. To evaluate the flow at various points on the circumference of the bearing, the local Reynolds number R _el is defined as follows.

[0041]

R _el = U · C _rl / ν In this equation, U is the journal peripheral speed, C _rl is the local bearing radius gap, and ν is the kinematic viscosity coefficient of the lubricating oil.

That is, the local Reynolds number R _el can be evaluated by using the local bearing radial clearance C _rl as a radial clearance determined by the geometrical relationship between the journal and the bearing surface. When evaluated by this, the local Reynolds number R _el near the minimum oil film is 7
The bearing used in large steam turbines / generators of 00MW class has R _el = 2000, which is considerably lower than the transition point 3000 as shown in FIG. The flow condition near the oil film can be evaluated as laminar flow.

As described above, when the flow is a laminar flow, the heat transfer coefficient is lower than that of the turbulent flow, the heat gradient is large in a narrow range, and the maximum bearing metal temperature generated near the minimum oil film position is The condition is much higher than that of turbulence.

In this embodiment, this local laminar flow state is controlled by the surface roughness to make a transition to a turbulent flow. That is, in the vicinity of the minimum oil film position where the maximum metal temperature of the bearing metal temperature distribution is generated, the flow state is changed to turbulent flow. When the flow becomes turbulent, the heat transfer coefficient becomes much higher than that in the laminar flow, the bearing metal temperature decreases, and a large thermal gradient is not obtained in a narrow range.

FIG. 4 shows an isotherm similar to the bearing metal temperature distribution shown in FIG. 11, which is the measured value when the rotational speed is increased with the same bearing. By increasing the rotation speed, the Reynolds number also increases, the bearing metal temperature decreases,
It can be seen that the thermal gradient is gentler than in FIG. 11, and the maximum bearing metal temperature is also lowered by 100 ° C and 10 ° C.

In the bearing of this embodiment, as shown in FIG. 1, since the turbulent transition layer 17 having a rough surface finish as compared with other portions of the bearing surface is provided in the vicinity of the minimum oil film, as described above. In addition, even if that portion is locally laminar under normal use conditions, by using the bearing in which the turbulent transition layer 17 is formed, the flow of the lubricating oil 4 near the minimum oil film position is made turbulent, and the lubrication at that portion is performed. The heat transfer coefficient between the oil 4 and the bearing metal 3 is made extremely high, and the temperature of the lubricating oil 4 does not rise.
It is possible to increase the maximum value of the temperature of.

Next, modifications of the journal bearing of the above embodiment will be described with reference to FIGS.

Generally, if the surface of the bearing is rough, the load capacity of the bearing will be reduced. Therefore, it is desirable to effectively form the turbulent transition layer in a narrow range. As described above, the maximum temperature generation position of the bearing metal occurs immediately after the bearing minimum oil film position. Therefore, in order to effectively arrange the turbulent flow transition layer without reducing the load capacity of the bearing, the turbulent flow transition layer 19 is provided immediately after the bearing maximum oil film pressure position as in the first modification shown in FIG. It is installed in a narrow range from (for example, θ = 25 degrees) to the downstream side of the bearing minimum oil film position (for example, θ = 45 degrees).

Since the load capacity of the bearing is determined at a large bearing oil film pressure, by limiting the installation position of the turbulent flow transition layer 19 as in the first modification, the load capacity of the bearing is not lowered, It is possible to provide a journal bearing in which the bearing metal temperature does not rise similarly to the effect of the local turbulent flow state described above.

As means for accelerating the turbulent flow transition region, in addition to the means for controlling the surface roughness as described above, the second means shown in FIG.
A dent formed like a modification or the third one shown in FIG.
There are those in which grooves are formed as in the modified example, and further, those in which the flow in the laminar flow state is disturbed by the jet flow as in the fourth modified example shown in FIG. Even in these modified examples, the same effect as that of the above-described embodiment can be obtained.

That is, in the second modified example shown in FIG. 6, a plurality of depressions 20 are formed in the axial direction in the vicinity of the minimum oil film as concave portions that disturb the flow of lubricating oil in the laminar flow state. Under normal use conditions, even in a locally laminar flow state, the depression 20 can make the flow state of the lubricating oil turbulent. Also,
In the third modification shown in FIG. 7, the groove 21 as a recess is formed in the axial direction in the vicinity of the minimum oil film, and in this case also, the same effect as the second modification shown in FIG. 6 can be obtained.

In the fourth modification shown in FIG. 8, a suction hole 22 is provided near the maximum oil film pressure generating position, and a blowout hole 23 is provided near the minimum oil film pressure, and these holes 22 and 23 are connected to each other (bypass line). ) 24, and since the pressure of the lubricating oil in the blowing hole 23 is smaller than that in the suction hole 22, a part of the maximum oil film pressure generation position passes through the communication hole 24 and the blowing hole 23 near the minimum oil film. Blown out from. The jet flow can disturb the flow in the laminar flow state and make the flow of the lubricating oil 4 turbulent.

According to each of these modifications, the flow of the lubricating oil 4 is controlled in the vicinity of the bearing minimum oil film position to make it turbulent, and heat transfer between the lubricating oil 4 and the bearing metal 3 is carried out, as in the above-described embodiments. It is possible to raise the temperature and lower the temperature of the bearing metal 3.

[0054]

As described above, according to claim 1 of the journal bearing according to the present invention, the state of the lubricating oil flow is changed from laminar flow to turbulent flow in the vicinity of the minimum oil film position where the bearing metal temperature is maximum. Since a turbulent transition layer is formed to make the transition to the turbulent flow state, the flow state near the minimum oil film position can be made turbulent, the heat transfer coefficient between the lubricating oil and the bearing metal can be improved, and the bearing metal temperature can be kept low. it can. As a result, the reliability of the bearings used in the steam turbine / generator with high peripheral speed and high load is improved, and the entire plant can be operated stably for a long period of time.

According to the second aspect, the turbulent flow transition layer is provided in the range from the maximum oil film pressure position of the lubricating oil to the vicinity of the minimum oil film pressure position, so that the load capacity of the bearing is not lowered, and the turbulent transition layer is provided. The same effect as can be obtained.

In the third aspect, the turbulent transition layer is a portion having a rough surface, and in the fourth aspect, the turbulent transition layer is a concave portion. By providing such a portion on the bearing, both can make the flow state of the lubricating oil turbulent, and the same effect as in claim 1 can be obtained.

According to the fifth aspect, a part of the lubricating oil at the maximum oil film pressure position passes through the communication hole and is blown out from the blowing hole. Therefore, the jet flow disturbs the laminar flow state and the lubricating oil flow state. Can be made to be a turbulent flow, and the same effect as that of claim 1 can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of essential parts showing an embodiment of a journal bearing according to the present invention.

FIG. 2 is a diagram showing a relationship between surface roughness and turbulent transition Reynolds number ratio.

FIG. 3 is a diagram showing a relationship between a bearing average Reynolds number and a shaft friction coefficient.

FIG. 4 is a temperature distribution diagram of the bearing metal of the bearing according to the present embodiment.

5 is a perspective view of a main part showing a first modified example of the journal bearing of the embodiment of FIG.

6 is a perspective view of a main part showing a second modification of the journal bearing of the embodiment of FIG.

7 is a perspective view of a main part showing a third modified example of the journal bearing of the embodiment of FIG.

8 is a cross-sectional view of a main part showing a fourth modified example of the journal bearing of the embodiment of FIG.

FIG. 9 is a sectional view showing a conventional journal bearing.

FIG. 10 is a diagram showing the strength of bearing metal in a conventional example.

FIG. 11 is a temperature distribution diagram of bearing metal of a conventional journal bearing.

[Explanation of symbols]

 1 Journal 2 Bearing Inner Ring 3 Bearing Metal 4 Lubricating Oil 7 Bearing Surface 9 Oil Film 12 Minimum Oil Film Position 13 Maximum Oil Film Pressure Position 17 Turbulent Transition Layer 19 Turbulent Transition Layer 20 Cavity (Concave) 21 Groove (Concave) 22 Suction Hole 23 Blowout Hole 24 communication hole

Claims (5)

[Claims] 1. A journal bearing for supporting a rotating shaft, comprising: a bearing near a minimum oil film position where the bearing metal temperature is maximum.
A journal bearing, comprising a turbulent transition layer that transitions the flow state of lubricating oil from laminar flow to turbulent flow. 2. The journal bearing according to claim 1, wherein the turbulent flow transition layer is provided in a range from a maximum oil film pressure position of lubricating oil to a vicinity of a minimum oil film pressure position. 3. The journal bearing according to claim 1, wherein the turbulent flow transition layer is a portion having a rough surface provided near the minimum oil film position. 4. The journal bearing according to claim 1, wherein the turbulent flow transition layer is a recess formed near the minimum oil film position. 5. A suction hole is provided at the maximum oil film pressure position of the lubricating oil, and a blowout hole is provided near the minimum oil film pressure position, and these holes are communicated by a communication hole. Or the journal bearing described in 2.