Rubber bearing

Abstract

To provide a rubber bearing excellent in economical efficiency, productivity and repairability by utilizing the characteristics of a rubber layer.SOLUTION: A rubber bearing according to the present invention is a water lubrication type rubber bearing in which a horizontal rotary shaft is supported by a rubber layer disposed on an inner circumferential surface of a shell, wherein the rubber layer has a pair of upper water grooves and lower water grooves facing each other with respect to a bearing center O in a cross section of the rubber bearing, and the upper water grooves are provided at an angle θ1 in a range of 140° to 170°. Here, in a right-handed XYZ rectangular coordinate system in which the bearing center O of the rubber bearing is the origin and the direction of the rotating shaft is the X-axis, the cross section of the rubber bearing is a YZ plane, the Z value of the upper water groove is on the positive side, and the Z value of the lower water groove is on the negative side. The turning angle refers to a rotation angle (θ) from the nine o'clock direction when the rotation axis rotates clockwise in the cross section of the rubber bearing (turning direction).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-lubricated rubber bearing for supporting horizontal rotating shafts such as the propulsion shaft of a ship or the power shaft of a generator or pump. [Background technology]

[0002] Rubber bearings have excellent wear resistance and other properties, such as averaging the local load from the rotating shaft, absorbing shaft vibration, and discharging slurry that has flowed into the sliding surface. However, water-lubricated rubber bearings have a problem in that their coefficient of friction is very low when a water film is formed, but high when dry. Various proposals have been made to improve this problem.

[0003] For example, Patent Document 1 proposes a water-lubricated rubber bearing that is integrally mounted with a rubber bearing body inside a metal outer cylinder. The inner cross-sectional shape of the rubber bearing body is configured to provide at least linear contact with the rotating shaft. The rubber constituting the rubber bearing body contains 40 to 70 weight percent inorganic lubricant, and the rubber bearing body has a hardness of 80 to 90 degrees on the JIS hardness scale. The inner cross-sectional shape of the rubber bearing body Ea of this rubber bearing is not limited to a regular octagon in plan view; regular polygons such as a regular hexagon or regular decagon are also acceptable. However, excessive polygonal shapes are undesirable because they increase the contact area with the rotating shaft M. The invention also describes a water-lubricated rubber bearing with a coefficient of friction that is several times to one-tenth of that of conventional rubber bearings, eliminating the need for a forced lubricating water supply device, which was previously used to supply water when starting a pump.

[0004] Patent Document 2 proposes a rubber composition for use in sliding components such as bearings and shaft seals. Specifically, the proposed rubber composition contains ethylene-propylene-diene rubber and porous carbon particles produced from plant raw materials, with the porous carbon particles contained in an amount of 160 to 340 parts by mass per 100 parts by mass of the ethylene-propylene-diene rubber. This rubber composition has a low coefficient of friction and excellent wear resistance, with a coefficient of friction in water of 0.05 at a sliding speed of 1 m / s and 0.11 at a sliding speed of 0.001 m / s.

[0005] Patent Document 3 proposes a rubber bearing for a rotating shaft used underwater, using foamed rubber with a void ratio of 1 to 60 vol % as the rubber material. This rubber bearing can obtain sufficient lubrication because the lubricating water is retained in the voids of the foamed rubber. As a result, it is said to be able to solve the problem of insufficient lubrication due to the contact area with the propeller shaft being pressed against the propeller shaft, which causes abnormal noise, particularly when the propeller shaft is started, due to the lack of seawater.

[0006] Non-Patent Document 1 proposes a two-layer structure bearing, consisting of a rubber layer on the inner circumferential surface of the shell and a fluororesin layer on the surface where the propeller shaft slides, and includes a full-molded, barrel-type, or segmented bearing. This bearing is said to utilize the advantages of rubber bearings while compensating for their weaknesses. Specifically, it is said to have a low coefficient of friction, self-lubrication, high reliability against unexpected accidents such as water shortages, good seizure resistance under high loads, and low localized and average wear. However, it is more expensive than single-layer rubber bearings, and is said to experience greater wear than rubber bearings when used in locations with a high amount of slurry. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Utility Model Application Publication No. 59-35727 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-60846 [Patent Document 3] Japanese Patent Application Publication No. 8-303465 [Non-Patent Document 1] High Reliability Technology for Seawater-Lubricated Stern Tube Bearings, Fumitaka Yoshikawa, Journal of the Japan Society of Marine Engineers, Vol. 27, No. 9 (1992-6), pp. 735-741 Summary of the Invention [Problem to be solved by the invention]

[0008] Water-lubricated rubber bearings have the problem that their coefficient of friction is very low when a water film is formed, but high when dry. To address this problem, Patent Documents 1 and 2 propose rubber materials containing activators such as inorganic lubricants, while Patent Document 3 proposes a water-absorbing rubber material using foamed rubber. Non-Patent Document 1 proposes a rubber material with a two-layer structure consisting of a rubber layer and a surface layer of fluororesin that has a low coefficient of friction and self-lubricating properties.

[0009] The rubber bearing with a fluororesin layer on the surface, as described in Non-Patent Document 1, is a bearing that makes use of the advantages of rubber bearings while compensating for their weaknesses, and is excellent as a water-lubricated rubber bearing. However, because it has a two-layer structure of a rubber layer and a fluororesin layer, it is not easy to further improve productivity, repairability, or economy, and there is also the problem that the slurry discharge function that utilizes the elasticity of the rubber is reduced.

[0010] In view of the problems and demands of conventional rubber bearings, the present invention aims to provide a rubber bearing that utilizes the characteristics of the rubber layer and is excellent in economy, productivity, and repairability. [Means for solving the problem]

[0011] The rubber bearing according to the present invention is a water-lubricated rubber bearing in which a horizontal rotating shaft is supported by a rubber layer disposed on the inner peripheral surface of the shell, the rubber layer having a pair of upper and lower water grooves facing each other with respect to the bearing center O in the cross section of the rubber bearing, the upper water grooves being arranged at an angle θ1 in the range of 140° to 170°. Here, in a right-handed XYZ Cartesian coordinate system with the bearing center O of the rubber bearing as the origin and the direction of the rotating shaft as the X axis, the cross section of the rubber bearing is the YZ plane, the upper water groove is on the +Z side and the lower water groove is on the -Z side. The rotation angle refers to the rotation angle (θ) from the nine o'clock direction when the rotating shaft rotates clockwise (rotation direction) in the cross section of the rubber bearing.

[0012] In the above invention, it is preferable that the thickness of the rubber layer from the position of the water supply channel (rotation angle θ1) to angle θ2, which is further rotated at a rotation angle in the range of 160° to 220°, is 15% to 25% thicker than the thickness (t) of other parts.

[0013] The rubber layer may also have a plurality of cooling water grooves on its circumferential upper surface between the upper and lower water grooves, where the circumferential upper surface refers to the upper portion of the rubber bearing bisected by a straight line connecting the upper and lower water grooves in a cross section.

[0014] The rubber layer may be made of a natural rubber (NR), nitrile rubber (NBR), chloropropane rubber (CR) or chlorosulfonated polyethylene rubber (CSM) composition and have a uniform thickness (t). [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a rubber bearing that utilizes the characteristics of the rubber layer and is excellent in economy, productivity, and repairability. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an explanatory diagram showing a cross section of a rubber bearing according to the present invention. [Figure 2] FIG. 2 is an explanatory diagram of the rubber bearing shown in FIG. 1 when a cooling water groove is further provided. [Figure 3] FIG. 1 is an explanatory diagram showing the configuration of a rubber bearing used in a friction test to examine the effect of the positioning of the rubber bearing between the water supply and sewerage channels. [Figure 4] FIG. 1 is an explanatory diagram showing the configuration of a friction tester. [Figure 5] FIG. 2 is an explanatory diagram showing the configuration of bearings (FFB, MRB) of comparative examples. [Figure 6] 1 is a graph showing the relationship between the peripheral speed and the wet friction coefficient of each bearing obtained by a friction test. [Figure 7] 7 is a graph showing the relationship between the peripheral speed of a bearing and the wet friction coefficient, extracted from the friction coefficient curves of FIG. 6. [Figure 8] 10 is a graph showing the relationship between the rotation angle and the friction coefficient of each bearing obtained by a friction test. [Figure 9] 1 is a graph showing the relationship between the circumferential speed and the wet friction coefficient of a rubber bearing having a convex portion in which the thickness of the rubber layer according to the present invention is increased. [Figure 10] 9 is a graph showing the relationship between the width of the convex portion (back groove angle) and the friction coefficient for the friction coefficient curve shown in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described. The rubber bearing according to the present invention relates to a water-lubricated rubber bearing in which a horizontal rotating shaft is supported by a rubber layer disposed on the inner peripheral surface of a shell, and the rubber layer has a pair of upper and lower water grooves that face each other with respect to the bearing center O in the cross section of the rubber bearing. That is, the rubber bearing has a pair of water grooves that face each other with respect to the bearing center O in the cross section of the rubber bearing. Of the pair of water grooves, the upper water groove is disposed at an angle θ1 in the range of a rotation angle of 140° to 170°. Here, in a right-handed XYZ Cartesian coordinate system with the bearing center O of the rubber bearing as the origin and the direction of the rotating shaft as the X axis, the cross section of the rubber bearing is the YZ plane, the upper water groove is on the positive Z side, and the lower water groove is on the negative Z side. The rotation angle refers to the rotation angle (θ) from the nine o'clock direction when the rotating shaft rotates clockwise (in the direction of rotation) in the cross section of the rubber bearing.

[0018] An example of a rubber bearing according to the present invention is shown in Figure 1. Figure 1 shows a cross section (YZ plane) of this rubber bearing. This rubber bearing 10 has a rubber layer 13 provided on the inner surface of a shell 11, and this rubber layer 13 has a pair of upper water grooves 14 and lower water grooves 15 that face each other relative to the bearing center O. A rotating shaft 20 is supported by the rubber layer 13 of the rubber bearing 10, and a bearing gap 18 is provided on the upper surface of the circumference of the rotating shaft 20. Water or seawater is introduced into this wedge-shaped bearing gap 18 to provide water lubrication. When this rubber bearing is used as a rubber bearing for a ship's propeller shaft, the X axis is the direction of the propeller shaft (horizontal rotating shaft, clockwise as indicated by the arrow), and the XY plane is a horizontal plane. In the YZ cross section of the rubber bearing, the Y axis is a horizontal axis, and the Z axis is a vertical axis. The arrow shown on the rotating shaft 20 indicates its direction of rotation (clockwise).

[0019] The rubber bearing 10 is located at a position where the water channel has a rotation angle θ1 in the range of 140° to 170°. This allows for the construction of a rubber bearing with a low coefficient of friction, as explained below. The rubber bearing 10 may further include a convex portion 135 that protrudes in the rotation direction from the back surface of the water channel 14, as shown in FIG. 1. This convex portion 135 is 15% to 25% thicker than the constant thickness t of the main body 130 of the rubber layer 13. Therefore, a back groove is provided in the shell 11 to accommodate this convex portion 135. Furthermore, for cooling purposes, the rubber bearing 10 may include multiple cooling water grooves 16 between the water channel 15 and the water channel 14 in the upper portion (upper peripheral surface) of the cross section of the rubber bearing, which is bisected by a straight line connecting the water channel 15 and the water channel 14, as shown in FIG. 2. The number (spacing) of the cooling water grooves 16 can be determined depending on the required cooling performance of the rubber bearing. [Example]

[0020] Water-lubricated rubber bearings have an extremely low coefficient of friction when a water film is formed, making them desirable as water-lubricated bearings. However, their high coefficient of friction in dry conditions is problematic. To address this issue, we focused on the location of the rubber bearing's water grooves, particularly the upper and lower water grooves, and conducted friction tests to examine the effect of their location. Figure 3 shows the rubber bearing used in this test. This rubber bearing 10 has a rubber layer 13 on the inner surface of a shell 11 and has upper and lower water grooves 14 and 15. Friction tests were conducted on several types of bearings with different positions of the upper water groove 14, i.e., different rotation angles θ of the upper water groove 14. The friction tester used in the tests is shown in Figure 4. The test results are shown in Figure 6. The test in Figure 6 was performed under a surface pressure of 0.25 MPa.

[0021] In the friction tester shown in Figure 4, the temperature of the water tank is maintained at 20°C, and no forced convection of water is used. The bearing is lifted by a pneumatic cylinder, and a specified load is applied to the lower side of the bearing via the sleeve of the propeller shaft. The required sleeve can be attached to the propeller shaft.

[0022] In Figure 6, the horizontal axis represents peripheral speed and the vertical axis represents friction coefficient, and the parameters represent the various bearings tested. In Figure 6, the friction coefficient curves for MRB0° to MRB160° represent test results for rubber bearings with rotation angles of 0° to 160°, respectively. The friction coefficient curves for FFB and MRB represent test results for comparative bearings. In both cases, the rubber layer is divided into eight sections via water grooves. As shown in Figure 5(a), the FFB has a rubber layer 2 on the inner surface of the shell 1, and a sliding member 3 made of synthetic resin PTFE is arranged on the surface periphery of the rubber layer 2 via water grooves 4. This corresponds to the two-layer fully molded bearing described in Non-Patent Document 1, in which a rubber layer on the inner surface of the shell and a fluororesin layer are provided on the surface where the propeller shaft slides. As shown in Figure 5(b), the MRB has a rubber layer 2 on the inner surface of the shell 1, and water grooves 4 are provided at equal intervals on the surface of the rubber layer 2.

[0023] Figure 6 shows that for all friction coefficient curves, the friction coefficient drops rapidly in the peripheral speed range of 0.1 m / s to 0.5 m / s, gradually decreases in the peripheral speed range of 0.5 m / s to 1.0 m / s, and remains approximately constant at higher peripheral speeds. Comparing the friction coefficient curves for the MRB and MRB20°, the friction coefficient curve for MRB20° is slightly lower (low friction coefficient side), but they nearly overlap. Comparing the friction coefficient curves for MRB0° to MRB160°, the friction coefficient curve decreases as the rotation angle θ increases. Bearings with friction coefficient curves parallel to the horizontal axis are considered to have an adequate lubricant film. For rubber bearings, it is important to determine how to form a lubricant film at low peripheral speeds of 0.5 m / s, especially at peripheral speeds of 0.25 m / s or less. Figure 7 shows bearings exhibiting characteristic trends from the friction coefficient curves shown in Figure 6.

[0024] According to Figure 7, the friction coefficient curve for the MRB0° is unique; the friction coefficient drops sharply in the peripheral speed range from 0.1 m / s to 0.25 m / s and then remains approximately constant. The friction coefficient for peripheral speeds of 0.25 m / s or more overlaps with the friction coefficient curve for the FFB. The friction coefficient curve for the MRB160° is very low, and the friction coefficient at a peripheral speed of 0.1 m / s is also very low. The low friction coefficient of the FFB at a peripheral speed of 0.1 m / s is thought to be due to the effect of the fluororesin used as the sliding material, but the friction coefficient of the MRB160° is lower than that of the FFB.

[0025] On the other hand, when comparing the cross-sectional shapes of the MRB0° and MRB160° rubber bearings, the only difference is the position of the water grooves. However, this change in the water groove position significantly lowered the friction coefficient of the rubber bearing in the low peripheral speed range (0.1 to 0.5 m / s), which is understood to have enabled water lubrication. Also, as shown in Figure 7, when comparing the friction coefficient curves of the MRB and MRB0°, the friction coefficient curve of the MRB0° is significantly lower. Furthermore, when comparing the friction coefficient curves of the FFB and MRB160°, the friction coefficient curve of the MRB160° is significantly lower, especially at peripheral speeds of 0.5 m / s or less. The unexpectedly high friction coefficient of the MRB or FFB bearings is likely related to the presence of water grooves around the entire rubber layer, as shown in Figure 5, particularly in the load-bearing portion below the horizontal axis in the cross-section of the rubber bearing.

[0026] Figure 8 shows a graph that determines the relationship between the rotation angle of the water supply channel for the rubber bearing and the friction coefficient, based on the results in Figure 6. The horizontal axis represents the rotation angle, the vertical axis represents the friction coefficient, and the parameter represents the peripheral speed. Figure 8 shows that the friction coefficient for each peripheral speed decreases linearly as the rotation angle increases, and that the friction coefficient reaches nearly zero at rotation angles between 140° and 170°. The slope of the friction coefficient line also decreases as the peripheral speed increases, and the friction coefficient lines overlap at peripheral speeds between 0.5 m / s and 2 m / s. Judging from the characteristics of these friction coefficient lines, it appears as if the inflow water from the water supply channel is acting as a brake, resisting the rotation of the rotating shaft.

[0027] Furthermore, in the graph of Figure 8, the friction coefficient at a turning angle of 0° is unrelated to the above-mentioned friction coefficient curve, showing peculiarities. The friction coefficient at a peripheral speed of 0.1 m / s at a turning angle of 0° is close to the friction coefficient line at a peripheral speed of 0.1 m / s, and can be said to be within the range of data variation. However, at other peripheral speeds, the friction coefficient is clearly much lower than the friction coefficient line. [Example]

[0028] As described above, the rubber bearing 10 according to the present invention, in which the water supply channel 14 has a rotation angle of 160° (θ1), has a low coefficient of friction, and a lubricating film is properly formed even at low peripheral speeds, which is understood to be due to the wedge effect of a sliding bearing. Incidentally, a stretching effect based on the elasticity of the rubber is also expected in rubber bearings. Friction tests were conducted on bearings with a rubber layer that had a convex portion by changing the thickness of a portion of the rubber layer of the rubber bearing. The same friction tester as above was used. However, because the rubber bearing 10 with a rotation angle of 160° (θ1) has an extremely low coefficient of friction, the surface pressure was set to 0.6 MPa to make it easier to observe the effect.

[0029] For this friction test, a rubber bearing 10 was used that had a convex portion 135 that protruded in the rotation direction from the back surface of the water supply groove 14 shown in Figure 1. The rotation angle of the convex portion 135 further rotated from the position of the water supply groove 14 (rotation angle θ1 = 160°) was defined as α, and tests were conducted using rubber bearings with various different α. The convex portion 135 of the rubber layer 13 was about 15% to 25% thicker than the main body 130, which had a thickness t.

[0030] The test results are shown in Figures 9 and 10. In Figure 9, the horizontal axis represents the circumferential speed, the vertical axis represents the coefficient of friction, and the parameter is the turning angle (back groove angle) α. Since the convex portion 135 is housed in a back groove provided in the shell 11, the back groove angle α, which indicates the size of the back groove, was used. The back groove angle α represents the width of the convex portion. Figure 10 is a graph showing the relationship between the back groove angle and the coefficient of friction based on the results of Figure 9. In Figure 9, the horizontal axis represents the circumferential speed, the vertical axis represents the coefficient of friction, and the parameter is the back groove angle α.

[0031] 9, in all of the friction coefficient curves, the friction coefficient reducing effect of the convex portions 135 of the rubber layer 13 is observed when the peripheral speed is 1 m / s or less, particularly 0.5 m / s or less, and further 0.1 m / s. In particular, a significant friction reducing effect is observed in the case of the MRB160° friction coefficient curve (back groove angle α is 0°, turning angle is 160°).

[0032] FIG. 10 clearly shows the friction coefficient reduction effect of the convex ridge portions 135. It can be seen that the friction reduction effect of a rubber bearing having the convex ridge portions 135 decreases in proportion to the back groove angle α. It can also be seen that all of the friction coefficient lines become nearly parallel to the horizontal axis when the back groove angle α is between 40° and 60°, and the friction coefficient reduction effect of the convex ridge portions 135 disappears. The inclination angle of the friction coefficient lines is greatest at a peripheral speed of 0.1 m / s and slightly smaller at 0.25 m / s than at 0.1 m / s. The friction coefficient lines at peripheral speeds of 0.5 m / s and 0.75 m / s overlap, have a small inclination angle, and are nearly parallel to the horizontal axis. As described above, the friction coefficient reduction effect of the convex ridge portions 135 of the rubber layer 13 is significant at low peripheral speeds, and the size (width) of the convex ridge portions 135 is preferably such that the back groove angle α is between 20° and 50° (angle θ2 when the turning angle is between 160° and 220°). In addition to forming the convex portions 135, a method of locally increasing rubber elasticity may also be a method of locally decreasing rubber hardness.

[0033] As described above, the rubber bearing according to the present invention consists of a single layer, a rubber layer, and utilizes the properties of rubber to provide a low coefficient of friction at low peripheral speeds, a coefficient of friction lower than that of FFT bearings. By utilizing the characteristics of the rubber layer, it is possible to provide a rubber bearing that is economical, productive, and easy to repair. This rubber bearing solves the problem that two-layer structure bearings, such as FFT bearings, which have a rubber layer on the inner circumferential surface of the shell and a fluororesin layer on the surface where the propeller shaft slides, are expensive and suffer greater wear than rubber bearings when used in places with a lot of slurry. [Explanation of symbols]

[0034] 10 Rubber bearings 11 Shell 13 Rubber layer 130 Main body 135 Convex part 14 Water Supply Ditch 15 Sewer 16 Cooling water groove 18 Gap 20 Rotation axis

Claims

1. A water-lubricated rubber bearing in which a horizontal rotating shaft is supported by a rubber layer disposed on the inner peripheral surface of a shell, The rubber layer has a pair of upper and lower water grooves that face each other relative to the bearing center O in the cross section of the rubber bearing, and the upper water grooves are arranged at an angle θ1 with a rotation angle in the range of 140° to 170°. Here, in a right-handed XYZ rectangular coordinate system with the bearing center O of the rubber bearing as the origin and the direction of the rotation axis as the X axis, the cross section of the rubber bearing is the YZ plane, with the Z value for the upper water groove on the + side and the Z value for the lower water groove on the - side. The rotation angle is the rotation angle (θ) from the nine o'clock direction when the rotation axis rotates clockwise (rotation direction) on the cross section of the rubber bearing.

2. The rubber bearing according to claim 1, characterized in that the thickness of the rubber layer from the position of the water supply channel (rotation angle θ1) to an angle θ2, which is a further rotation angle in the range of 160° to 220°, is 15% to 25% thicker than the thickness (t) of other portions.

3. 3. The rubber bearing according to claim 1, wherein the rubber layer has a plurality of cooling water grooves formed on the circumferential upper surface between the sewer water groove and the upper water groove. Here, the upper peripheral surface refers to the upper portion of the cross section of the rubber bearing that is bisected by a straight line connecting the sewer groove and the water groove.

4. 3. The rubber bearing according to claim 1, wherein the rubber layer is made of a natural rubber (NR), nitrile rubber (NBR), chloropropyl rubber (CR), or chlorosulfonated polyethylene rubber (CSM) composition and has a uniform thickness (t).

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