Sliding bearing

Abstract

The present invention pertains to a sliding bearing that is used in a rotary machine such as a pump or a turbine, and particularly to a sliding bearing that is used in an extremely low-temperature environment. The sliding bearing comprises: a sliding contact pad (1) that has a shaft support surface (1a) for supporting the outer circumferential surface of a rotary shaft (100); a shell (2) disposed on the radially outer side of the sliding contact pad (1); and a pad pressing mechanism (3) that presses the sliding contact pad (1) against a pad support surface (2a) of the shell (2) when the sliding contact pad (1) has contracted. The sliding contact pad (1) has a circumferential groove formed in the shaft support surface (1a). The circumferential groove (1a) extends in the circumferential direction of the sliding bearing and extends through a center point (CP) of the shaft support surface (1a).

Description

Sliding bearing

[0001] The present invention relates to a sliding bearing used in rotating machinery such as pumps and turbines, and particularly to a sliding bearing used in an extremely low temperature environment.

[0002] Generally, rotating machinery includes a bearing for supporting a rotating shaft. A sliding bearing may be used in rotating machinery that handles fluids such as pumps and turbines. The sliding bearing has a sliding pad that slidably contacts the rotating shaft and a metal shell disposed outside the sliding pad, and the sliding pad is held by the shell. During the operation of the rotating machinery, the fluid contacts the sliding bearing, and the fluid functions as a lubricant for the sliding bearing.

[0003] A resin material with a low coefficient of kinetic friction is used for the sliding pad. However, when the fluid contacting the sliding bearing is an extremely low temperature fluid such as liquid hydrogen, due to the difference in the linear expansion coefficients of the resin sliding pad, the metal shell, and the fixing member, the sliding pad shrinks significantly more than the shell. As a result, the load pressing the sliding pad against the shell decreases. In the worst case, the sliding pad may separate from the shell.

[0004] Furthermore, during the operation of the rotating machinery, frictional heat is generated due to the sliding contact between the rotating shaft and the sliding pad. The shaft support surface of the sliding pad is heated by the frictional heat, while the outer surface on the opposite side of the shaft support surface becomes extremely low temperature due to contact with the shell. As a result, the sliding pad has a very large temperature gradient in its thickness direction, and the sliding pad may deform. The rotating shaft contacts the deformed sliding pad, and the sliding pad may wear locally.

[0005] Japanese Patent Application Laid-Open No. 2022-188902

[0006] Therefore, the present invention provides a sliding bearing that can eliminate the influence of the difference in the linear expansion coefficients between the sliding pad and the shell and reduce the deformation of the sliding pad caused by frictional heat.

[0007] In one embodiment, a sliding bearing for supporting a rotating shaft is provided, comprising: a sliding pad having a shaft support surface for supporting the outer circumferential surface of the rotating shaft; a shell disposed radially outside the sliding pad; and a pad pressing mechanism for pressing the sliding pad against the pad support surface of the shell when the sliding pad is contracted, wherein the sliding pad has a circumferential groove formed on the shaft support surface, the circumferential groove extends in the circumferential direction of the sliding bearing and extends through the center point of the shaft support surface.

[0008] In one embodiment, if the width of the circumferential groove is W1 and the dimension of the axial support surface along the axial direction of the sliding bearing is D1, then W1 / D1 is in the range of 1 / 30 to 1 / 3. In one embodiment, the sliding pad further has an axial groove formed on the axial support surface, the axial groove extends in the axial direction of the sliding bearing and extends through the center point of the axial support surface. In one embodiment, if the width of the axial groove is W2 and the dimension of the axial support surface along a direction perpendicular to the axial direction of the sliding bearing is D2, then W2 / D2 is in the range of 1 / 20 to 1 / 4. In one embodiment, the circumferential groove intersects with the axial groove.

[0009] In one embodiment, the pad pressing mechanism includes a biasing member that biases the sliding pad toward the shell. In another embodiment, the pad pressing mechanism further includes a pad support member supported by the shell, the sliding pad is supported by the pad support member, and the biasing member biases the sliding pad and the pad support member toward the shell, pressing the sliding pad against the pad support surface of the shell. In yet another embodiment, the pad pressing mechanism includes a pad support member having a tapered shaft portion fixed to the shell, and a tapered hole formed in the sliding pad, the sliding pad is supported by the tapered shaft portion, and the tapered hole is in surface contact with the outer circumferential surface of the tapered shaft portion.

[0010] In one embodiment, the pad pressing mechanism comprises a dovetail groove formed in the sliding pad and a pad retaining rail connected to the pad support surface of the shell, wherein the pad retaining rail has an inverted triangular cross-sectional shape that fits into the dovetail groove. In one embodiment, the dovetail groove and the pad retaining rail extend in an axial direction parallel to the centerline of the sliding bearing. In one embodiment, the sliding bearing further comprises a biasing member that pushes the sliding pad in the axial direction. In one embodiment, the sliding pad contains aromatic polyether ketone, talc, carbon fibers, and unavoidable impurities, wherein the talc content in the sliding pad is 7% by mass or more and 18% by mass or less, and the area ratio of the carbon fibers on the axial support surface of the sliding pad is 27% by more and 35% or less.

[0011] The pad pressing mechanism is configured to press the sliding pad against the pad support surface of the shell when the sliding pad contracts due to contact with an extremely cold fluid (e.g., a liquefied gas such as liquid hydrogen). As a result, the sliding pad is firmly held by the shell, allowing the sliding bearing to maintain stable operation in extremely cold environments.

[0012] The circumferential grooves of the sliding pad guide cryogenic fluids (e.g., liquefied gases such as liquid hydrogen) to the shaft support surface of the sliding pad, suppressing the temperature rise of the shaft support surface caused by frictional heat between the sliding pad and the rotating shaft. As a result, the temperature gradient in the thickness direction of the sliding pad is reduced, and the deformation of the sliding pad can be reduced. Past operating results of sliding bearings show that deformation of the shaft support surface of the sliding pad due to frictional heat is likely to occur in the central region of the shaft support surface. Since the circumferential grooves extend from one side of the shaft support surface to the other, crossing the central region of the shaft support surface, the cryogenic fluid flows through the circumferential grooves and cools the central region of the shaft support surface. As a result, the deformation of the central region of the shaft support surface can be reduced.

[0013] This is a horizontal cross-sectional view showing one embodiment of a sliding bearing. This is a vertical cross-sectional view of the sliding bearing shown in Figure 1. This is an enlarged cross-sectional view showing the sliding pad and pad pressing mechanism. This is a diagram showing an example of the sliding pad in a contracted state. This is a diagram showing one embodiment of the axial support surface of the sliding pad. This is a diagram showing another embodiment of the axial support surface of the sliding pad. This is a horizontal cross-sectional view showing another embodiment of a sliding bearing. This is a diagram showing an example of the sliding pad in a contracted state. This is a horizontal cross-sectional view showing yet another embodiment of a sliding bearing. This is a perspective view showing one embodiment of the sliding pad. This is a perspective view showing a part of one embodiment of the shell. This is a diagram showing an example of the sliding pad in a contracted state. This is a vertical cross-sectional view of the embodiment of the sliding bearing shown in Figure 9. This is a diagram showing an example of the sliding pad in a contracted state.

[0014] Embodiments of the present invention will be described below with reference to the drawings. The embodiments of the sliding bearings described below are suitable for supporting the rotating shafts of rotating machinery (liquid pumps and turbines). In particular, the sliding bearings of the embodiments described below are preferably used as bearings to support the rotating shafts of rotating machinery for transporting cryogenic liquefied gases such as liquefied ammonia, liquid hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas. The sliding bearings of the embodiments described below operate in contact with the liquefied gas.

[0015] Figure 1 is a horizontal cross-sectional view showing one embodiment of a sliding bearing, and Figure 2 is a longitudinal cross-sectional view of the sliding bearing shown in Figure 1. The sliding bearing comprises a plurality of sliding contact pads 1, each having a plurality of shaft support surfaces 1a for supporting the outer circumferential surface of the rotating shaft 100, and a shell 2 arranged radially outward from the plurality of sliding contact pads 1. The plurality of sliding contact pads 1 are arranged around the rotating shaft 100. In the embodiment shown in Figure 1, six sliding contact pads 1 are arranged, but five or fewer or seven or more sliding contact pads 1 may be arranged. In the following description, "radial direction" means the radial direction of the sliding bearing, and "axial direction" means the direction parallel to the center line CL of the sliding bearing and the rotating shaft 100.

[0016] In this embodiment, the shell 2 is a single member that surrounds a plurality of sliding pads 1. In one embodiment, the shell 2 may be an assembly composed of a plurality of members. The shell 2 has a plurality of pad support surfaces 2a that support each of the plurality of sliding pads 1. The pad support surfaces 2a may be flat or curved. The outer surfaces of the plurality of sliding pads 1 are in contact with each of the plurality of pad support surfaces 2a.

[0017] The sliding bearing further comprises multiple pad pressing mechanisms 5 that press multiple sliding pads 1 against multiple pad support surfaces 2a of the shell 2. Each of the multiple pad pressing mechanisms 5 is provided corresponding to each of the multiple sliding pads 1. Since each pad pressing mechanism 5 has the same configuration, the details of the pad pressing mechanisms 5 will be described below with reference to Figure 3.

[0018] Figure 3 is an enlarged cross-sectional view showing the sliding contact pad 1 and the pad pressing mechanism 5. As shown in Figure 3, the pad pressing mechanism 5 includes a spring 7 as a biasing member that biases the sliding contact pad 1 toward the shell 2, and a bolt 8 as a pad support member supported by the shell 2. The sliding contact pad 1 is supported by the bolt 8. The bolt 8 is made of metal.

[0019] The bolt 8 extends radially through the sliding bearing and passes radially through the sliding pad 1 and the shell 2. More specifically, the sliding pad 1 has a through hole 11 through which the threaded portion 8a of the bolt 8 passes, and a recess 12 that accommodates the head 8b of the bolt 8. The head 8b of the bolt 8 is in contact with the bottom of the recess 12. The recess 12 is formed in the axial support surface 1a of the sliding pad 1. The threaded portion 8a of the bolt 8 extends through a through hole 15 formed in the pad support surface 2a of the shell 2. A nut 17 is screwed onto the threaded portion 8a of the bolt 8. The nut 17 is located on the outside of the shell 2.

[0020] In this embodiment, the spring 7, which acts as a biasing member, is an annular disc spring. Disc springs have the advantages of having a high spring constant and being able to be made smaller. In one embodiment, the spring 7 may be a coil spring. The spring 7 is sandwiched between the outer surface of the shell 2 and the nut 17 on the bolt 8. The spring 7 biases the nut 17, the bolt (pad support member) 8, and the sliding contact pad 1 toward the shell 2, pressing the sliding contact pad 1 against the pad support surface 2a of the shell 2.

[0021] The shell 2 has a plurality of guide walls 20 on its inner surface that extend in the axial direction of the sliding bearing. These guide walls 20 are located on both sides of the pad support surface 2a and face both sides of the sliding contact pad 1. When the rotating shaft 100 rotates, the axial support surface 1a of the sliding contact pad 1 slides against the outer circumferential surface of the rotating shaft 100. Therefore, a frictional force acts on the sliding contact pad 1 in the direction of rotation of the rotating shaft 100. The plurality of guide walls 20 on both sides of the sliding contact pad 1 and the bolt 8, which is a pad support member located at the center of the sliding contact pad 1, have the function of maintaining the posture of the sliding contact pad 1.

[0022] As can be seen from Figures 2 and 3, the bolt 8, which serves as the pad support member, is located at the center of the sliding pad 1. In one embodiment, multiple bolts (for example, two bolts) serving as the pad support member may be arranged along the centerline CL of the rotation axis 100. Multiple bolts can further stabilize the position of the sliding pad 1. In another embodiment, multiple bolts serving as the pad support member may be arranged along the circumferential direction of the rotation axis 100.

[0023] The sliding contact pad 1 and the shell 2 are made of different materials. The coefficient of thermal expansion of the sliding contact pad 1 is greater than that of the shell 2. More specifically, the sliding contact pad 1 contains a resin such as PTFE (polytetrafluoroethylene) or PEEK (polyetheretherketone), while the shell 2 is made of a metal such as stainless steel. The material of the sliding contact pad 1 will be described later.

[0024] The sliding bearing of this embodiment is intended to be used while immersed in a liquefied gas such as liquid hydrogen. Therefore, the sliding bearing is required to operate stably at extremely low temperatures. When the sliding pad 1 and shell 2 are cooled by the liquefied gas, the sliding pad 1 and shell 2 contract. As described above, the sliding pad 1, which is made of resin, has a larger coefficient of linear expansion than the shell 2, which is made of metal, so the sliding pad 1 contracts more than the shell 2.

[0025] Figure 4 shows an example of the state in which the sliding contact pad 1 is contracted. When the sliding contact pad 1 contracts, the restoring force of the spring 7 pulls the bolt 8 radially outward, and the sliding contact pad 1 is pressed against the pad support surface 2a of the shell 2 by the bolt 8. Therefore, the contracted sliding contact pad 1 is maintained in contact with the pad support surface 2a of the shell 2. Thus, according to this embodiment, the pad pressing mechanism 5 is configured to further press the sliding contact pad 1 against the pad support surface 2a of the shell 2 as the sliding contact pad 1 contracts due to contact with an extremely cold fluid (for example, liquid hydrogen). As a result, the sliding contact pad 1 is firmly held by the shell 2, and the sliding bearing can maintain stable operation in an extremely cold environment.

[0026] As shown in Figures 1 to 4, the sliding contact pad 1 has a circumferential groove 21 formed on the shaft support surface 1a. The circumferential groove 21 extends in the circumferential direction of the sliding bearing and extends across the central region of the shaft support surface 1a, which is most easily deformed by frictional heat. As shown in Figure 3, the circumferential groove 21 faces the outer circumferential surface of the rotating shaft 100 and is curved along the curved shape of the shaft support surface 1a when viewed from the axial direction. The circumferential groove 21 extends across the entire shaft support surface 1a in the circumferential direction. That is, the circumferential groove 21 extends from one side to the opposite side of the shaft support surface 1a.

[0027] Figure 5 shows one embodiment of the axial support surface 1a of the sliding contact pad 1. In order to increase the area of ​​the axial support surface 1a, the circumferential groove 21 in this embodiment is a single groove. The circumferential groove 21 extends through the center point CP of the axial support surface 1a. In this embodiment, the sliding contact pad 1 has a recess 12 at the position of its center point CP for accommodating the head 8b of the bolt 8, which serves as a pad support member. Therefore, the circumferential groove 21 extends through the recess 12. However, in embodiments where the bolt 8, which serves as a pad support member, and the recess 12 are not located at the center point CP of the sliding contact pad 1, the circumferential groove 21 may not pass through (be connected to) the recess 12.

[0028] During operation of the rotating machine, frictional heat is generated due to the sliding contact between the rotating shaft 100 and the sliding contact pad 1. The shaft support surface 1a of the sliding contact pad 1 is heated by the frictional heat, while the outer surface opposite to the shaft support surface 1a becomes extremely cold due to contact with the shell 2. As a result, the sliding contact pad 1 tends to have an extremely large temperature gradient in its thickness direction. According to this embodiment, the circumferential grooves 21 of the sliding contact pad 1 guide the extremely cold liquefied gas to the central region of the shaft support surface 1a of the sliding contact pad 1, and the temperature rise of the shaft support surface 1a caused by the frictional heat between the sliding contact pad 1 and the rotating shaft 100 can be suppressed. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is reduced, and the deformation of the shaft support surface 1a can be reduced. Furthermore, the circumferential grooves 21 can absorb the deformation of the shaft support surface 1a itself.

[0029] Past operating results of sliding bearings indicate that deformation of the shaft support surface 1a due to frictional heat is most likely to occur in the central region of the shaft support surface 1a. Since the circumferential groove 21 extends from one side of the shaft support surface 1a to the other, crossing the central region of the shaft support surface 1a, cryogenic liquefied gas flows through the circumferential groove 21, cooling the central region of the shaft support surface 1a. As a result, deformation of the central region of the shaft support surface 1a can be reduced.

[0030] From the viewpoint of guiding the liquefied gas to the central region of the shaft support surface 1a, a larger width of the circumferential groove 21 is desirable. On the other hand, from the viewpoint of supporting the outer circumferential surface of the rotating shaft 100 with the shaft support surface 1a, a larger area of ​​the shaft support surface 1a, i.e., a smaller width of the circumferential groove 21, is desirable. Therefore, in one embodiment, if the width of the circumferential groove 21 is W1 and the dimension of the shaft support surface 1a along the axial direction of the sliding bearing is D1, then W1 / D1 is in the range of 1 / 30 to 1 / 3. A circumferential groove 21 with such a width can guide the liquefied gas to the central region of the shaft support surface 1a, and the shaft support surface 1a can stably support the outer circumferential surface of the rotating shaft 100.

[0031] In other embodiments, multiple circumferential grooves 21 may be formed on the axial support surface 1a. In this case, if the sum of the widths of the multiple circumferential grooves 21 is W1, then W1 / D1 is in the range of 1 / 30 to 1 / 3. Since the central region of the axial support surface 1a is the least cooled, one of the multiple circumferential grooves 21 passes through the center point CP of the axial support surface 1a.

[0032] Figure 6 shows another embodiment of the axial support surface 1a of the sliding contact pad 1. In the embodiment shown in Figure 6, the sliding contact pad 1 further has an axial groove 22 formed in the axial support surface 1a. The axial groove 22 extends in the axial direction of the sliding bearing and extends through the center point CP of the axial support surface 1a. To increase the area of ​​the axial support surface 1a, the axial groove 22 is a single groove. The axial groove 22, like the circumferential groove 21, extends across the central region of the axial support surface 1a.

[0033] In this embodiment, the sliding contact pad 1 has a recess 12 at its center point CP for accommodating the head 8b of the bolt 8, which serves as a pad support member. Therefore, the axial groove 22 extends through the recess 12. The circumferential groove 21 intersects with the axial groove 22. More specifically, the circumferential groove 21 and the axial groove 22 intersect at the center point CP of the sliding contact pad 1, where it is most susceptible to deformation due to frictional heat.

[0034] The cryogenic liquefied gas flows through the circumferential grooves 21 and axial grooves 22, cooling the central region of the shaft support surface 1a. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is further reduced, and the deformation of the shaft support surface 1a can be further reduced. Similar to the circumferential grooves 21, the axial grooves 22 can absorb the deformation of the shaft support surface 1a itself. From the viewpoint of guiding the liquefied gas to the central region of the shaft support surface 1a and supporting the outer circumferential surface of the rotating shaft 100 with the shaft support surface 1a, if the width of the axial grooves 22 is W2 and the dimension of the shaft support surface 1a along the direction perpendicular to the axial direction of the sliding bearing is D2, then W2 / D2 is in the range of 1 / 20 to 1 / 4.

[0035] In other embodiments, multiple axial grooves 22 may be formed in the axial support surface 1a. In this case, if the sum of the widths of the multiple axial grooves 22 is W2, then W2 / D2 is in the range of 1 / 20 to 1 / 4. Since the central region of the axial support surface 1a is the least cooled, one of the multiple axial grooves 22 passes through the center point CP of the axial support surface 1a.

[0036] In one embodiment, the sliding contact pad 1 is made of a composite material containing aromatic polyetherketone, talc, carbon fibers, and unavoidable impurities. The axial support surface 1a of the sliding contact pad 1 is made of a material having aromatic polyetherketone, talc, and carbon fibers that provide low friction, high strength, and wear resistance.

[0037] Talc acts as a solid lubricant, reducing the coefficient of friction, while carbon fibers provide wear resistance and a low coefficient of friction. Because carbon fibers are included in the shaft support surface 1a of the sliding pad 1, deformation due to thermal expansion of the shaft support surface 1a can be prevented, improving the seizure resistance of the sliding pad 1.

[0038] Aromatic polyether ketones include at least one of PEK (polyether ketone), PEEK (polyether ether ketone), PEKK (polyether ketone ketone), and PEEKK (polyether ether ketone ketone). In this embodiment, PEEK is used as the aromatic polyether ketone. PEEK can form a transfer film in an extremely low temperature environment.

[0039] The talc content in the sliding pad 1 is 7% by mass or more and 18% by mass or less, preferably 10% by mass or more and 17% by mass or less, and more preferably 12% by mass or more and 15% by mass or less. When the talc content in the sliding pad 1 is within the above range, lubricity is improved and the coefficient of friction of the axial support surface 1a of the sliding pad 1 can be reduced.

[0040] The area ratio of carbon fibers on the axial support surface 1a of the sliding pad 1 is 27% or more and 35% or less, preferably 30% or more and 34%, and more preferably 31% or more and 33% or less. When the area ratio of carbon fibers on the axial support surface 1a of the sliding pad 1 is within the above range, lubricity is improved and the coefficient of friction of the axial support surface 1a of the sliding pad 1 can be reduced.

[0041] When both talc and carbon fiber are included, the talc content in the sliding pad 1 is 7% by mass or more and 18% by mass or less, and the area ratio of carbon fiber on the axial support surface 1a of the sliding pad 1 is 27% or more and 35% or less. Preferably, the talc content is 9% by mass or more and 15% by mass or less, and the area ratio of carbon fiber is 30% or more and 33% or less, and more preferably, the talc content is 10% by mass or more and 12% by mass or less, and the area ratio of carbon fiber is 31% or more and 32% or less. When the talc content and the area ratio of carbon fiber are within the above ranges, the wear resistance is excellent when operating in liquefied gas and the friction coefficient is stably maintained at a low level when operating in air.

[0042] As the shape of the talc, a flaky shape, an ellipse, etc. are preferable. Regarding the diameter of the talc on the shaft support surface 1a of the sliding contact pad 1, the short-axis diameter is preferably 0.1 μm or more, more preferably 0.5 μm or more and 13 μm or less, most preferably 5 μm or more and 11 μm or less. Also, the long-axis diameter is preferably 15 μm or less, more preferably 1 μm or more and 14 μm or less, most preferably 6 μm or more and 12 μm or less. Further, the magnification of the long-axis diameter with respect to the short-axis diameter is preferably greater than 1 times and 15 times or less, more preferably 1 times or more and 10 times or less, most preferably 1 times or more and 5 times or less. When the short-axis diameter, long-axis diameter, and / or the magnification of the long-axis diameter with respect to the short-axis diameter of the talc are within the above ranges, the talc functions as a solid lubricant and the lubricity is improved, and the friction coefficient of the shaft support surface 1a of the sliding contact pad 1 can be reduced.

[0043] The carbon fiber is preferably composed of short fibers. The diameter of the carbon fiber on the shaft support surface 1a of the sliding contact pad 1 is preferably 5 μm or more and 10 μm or less, more preferably 5.5 μm or more and 9 μm or less, most preferably 6 μm or more and 8 μm or less. Also, the length of the carbon fiber on the shaft support surface 1a of the sliding contact pad 1 is preferably 5 μm or more and 1000 μm or less, more preferably 6 μm or more and 500 μm or less, most preferably 7 μm or more and 200 μm or less.

[0044] In one embodiment, the talc, aromatic polyether ketone, and carbon fiber are heated and mixed by a twin-screw kneader to prepare a resin composition, and after compression molding this resin composition, surface processing is performed to manufacture the sliding contact pad 1.

[0045] Next, regarding another embodiment of the sliding bearing, it will be described with reference to FIG. 7. The configuration and operation of this embodiment not particularly described are the same as those of the above-described embodiment described with reference to FIGS. 1 to 5, so the overlapping description is omitted. As shown in FIG. 7, the sliding bearing includes a pad pressing mechanism 5 located at the center of the sliding pad. Although not shown, similar to the embodiment shown in FIG. 1, a plurality of sliding contact pads 1 are arranged around the rotating shaft 100.

[0046] The pad pressing mechanism 5 includes a pad support member 32 having a tapered shaft portion 31 and a tapered hole 35 formed in the sliding contact pad 1. The tapered shaft portion 31 is located inside the shell 2. The pad support member 32 extends in the radial direction of the sliding bearing and penetrates the sliding contact pad 1 and the shell 2 in the radial direction. The sliding contact pad 1 is supported by the pad support member 32. More specifically, the sliding contact pad 1 is supported by the tapered shaft portion 31, and the tapered hole 35 is in surface contact with the outer peripheral surface 31a of the tapered shaft portion 31.

[0047] The sliding contact pad 1 has a recessed portion 37 in which the end portion of the tapered shaft portion 31 of the pad support member 32 is accommodated. The recessed portion 37 is formed on the shaft support surface 1a of the sliding contact pad 1. The pad support member 32 is fixed to the shell 2. More specifically, the pad support member 32 has a threaded portion 32a, and the threaded portion 32a penetrates through a through hole 38 formed in the pad support surface 2a. Double nuts 41 and 42 are screwed onto the threaded portion 32a of the pad support member 32 to fix the radial position of the pad support member 32. The double nuts 41 and 42 are located outside the shell 2. The mechanism for fixing the radial position of the pad support member 32 is not limited to double nuts. For example, a single nut may be screwed onto the threaded portion 32a of the pad support member 32, and further, the nut may be welded to the pad support member 32.

[0048] The pad support member 32 including the tapered shaft portion 31 is made of a material having a smaller linear expansion coefficient than that of the sliding contact pad 1, and is, for example, made of metal. The outer peripheral surface 31a of the tapered shaft portion 31 and the tapered hole 35 have a frustum shape in which the diameter gradually decreases toward the radially outer side (toward the shell 2). The outer peripheral surface 31a of the tapered shaft portion 31 is fitted into the tapered hole 35.

[0049] Figure 8 shows an example of a state in which the sliding contact pad 1 has contracted. When the sliding contact pad 1 contracts due to contact with an extremely cold fluid such as liquefied gas, the tapered hole 35 of the sliding contact pad 1 is pressed more strongly against the outer circumferential surface 31a of the tapered shaft portion 31 compared to when it is at room temperature. The tapered hole 35 of the sliding contact pad 1 slides on the outer circumferential surface 31a of the tapered shaft portion 31, and a force acts on the sliding contact pad 1 that moves it radially outward. As a result, the sliding contact pad 1 is pressed against the pad support surface 2a of the shell 2. Therefore, the contracted sliding contact pad 1 is maintained in contact with the pad support surface 2a of the shell 2.

[0050] Thus, according to this embodiment, the pad pressing mechanism 5 is configured to further press the sliding pad 1 against the pad support surface 2a of the shell 2 as the sliding pad 1 contracts due to contact with an extremely cold fluid (for example, liquid hydrogen). As a result, the sliding pad 1 is firmly held by the shell 2, and the sliding bearing can maintain stable operation in an extremely cold environment.

[0051] The circumferential grooves 21 of the sliding contact pad 1 guide cryogenic liquefied gas to the central region of the shaft support surface 1a of the sliding contact pad 1, thereby suppressing the temperature rise of the shaft support surface 1a caused by frictional heat between the sliding contact pad 1 and the rotating shaft. Since the circumferential grooves 21 extend across the central region of the shaft support surface 1a from one side to the other, the cryogenic liquefied gas flows through the circumferential grooves 21, cooling the central region of the shaft support surface 1a. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is reduced, and the deformation of the shaft support surface 1a can be reduced. Furthermore, the circumferential grooves 21 can absorb the deformation of the shaft support surface 1a itself.

[0052] In addition to the circumferential grooves 21, the sliding contact pad 1 may further include axial grooves 22 as described with reference to Figure 6. Cryogenic liquefied gas flows through the circumferential grooves 21 and axial grooves 22, cooling the central region of the axial support surface 1a. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is further reduced, and the deformation of the axial support surface 1a can be further reduced. Similar to the circumferential grooves 21, the axial grooves 22 can absorb the deformation of the axial support surface 1a itself.

[0053] Next, yet another embodiment of the sliding bearing will be described with reference to Figure 9. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiments described with reference to Figures 1 to 5, so their redundant explanation will be omitted. As shown in Figure 9, the sliding bearing is equipped with a pad pressing mechanism 5 that extends in the axial direction. Although not shown, similar to the embodiment shown in Figure 1, a plurality of sliding pads 1 are arranged around the rotating shaft 100.

[0054] The pad pressing mechanism 5 includes a dovetail groove 50 formed in the sliding pad 1 and a pad holding rail 51 that fits into the dovetail groove 50. The dovetail groove 50 is formed on the outer surface of the sliding pad 1. The pad holding rail 51 has an inverted triangular cross-sectional shape that fits into the dovetail groove 50. The pad holding rail 51 is connected to the pad support surface 2a of the shell 2 and extends axially on the pad support surface 2a. Examples of how the pad holding rail 51 is connected to the pad support surface 2a include a configuration in which the pad holding rail 51 is fixed to the pad support surface 2a by screws or the like, and a configuration in which the pad holding rail 51 and the shell 2 are an integral part. The sliding pad 1 is held by the pad holding rail 51. The dovetail groove 50 has a first tapered side surface 50a, and the pad holding rail 51 has a second tapered side surface 51a that is in surface contact with the first tapered side surface 50a of the dovetail groove 50.

[0055] Figure 10 is a perspective view showing one embodiment of the sliding contact pad 1, and Figure 11 is a perspective view showing a part of one embodiment of the shell 2. As shown in Figures 10 and 11, the dovetail groove 50 and the pad retaining rail 51 extend in an axial direction parallel to the centerline CL of the sliding bearing (see Figure 2). The pad retaining rail 51 is fixed to the shell 2 by screws (not shown). In one embodiment, the pad retaining rail 51 and the shell 2 may be an integral structure.

[0056] Figure 12 shows an example of a state in which the sliding contact pad 1 has contracted. When the sliding contact pad 1 contracts due to contact with an extremely cold fluid such as liquefied gas, the first tapered side surface 50a of the dovetail groove 50 is pressed more strongly against the second tapered side surface 51a of the pad holding rail 51 than at room temperature. The first tapered side surface 50a of the sliding contact pad 1 slides on the second tapered side surface 51a of the pad holding rail 51, and a force acts on the sliding contact pad 1 that moves it radially outward. As a result, the sliding contact pad 1 is pressed against the pad support surface 2a of the shell 2. Therefore, the contracted sliding contact pad 1 is maintained in contact with the pad support surface 2a of the shell 2.

[0057] The sliding contact pad 1 and the pad holding rail 51 are made of different materials. The coefficient of thermal expansion of the sliding contact pad 1 is greater than that of the pad holding rail 51. In particular, in this embodiment, it is preferable to use a combination of materials in which the coefficient of thermal expansion of the sliding contact pad 1 is 50% or more greater than that of the pad holding rail 51. For example, a resin material can be used for the sliding contact pad 1 and a metal such as stainless steel can be used for the pad holding rail 51.

[0058] As described above, according to this embodiment, the pad pressing mechanism 5 is configured to further press the sliding pad 1 against the pad support surface 2a of the shell 2 as the sliding pad 1 contracts due to contact with an extremely cold fluid (for example, liquid hydrogen). As a result, the sliding pad 1 is firmly held by the shell 2, and the sliding bearing can maintain stable operation in an extremely cold environment. In particular, according to this embodiment, since no holes or recesses are formed on the shaft support surface 1a of the sliding pad 1 for passing through the pad support members 8 and 32 as described in the previously described embodiment, the area of ​​the shaft support surface 1a can be increased. Therefore, the sliding pad 1 is less prone to wear, and the sliding bearing can stably support the rotating shaft 100.

[0059] The circumferential grooves 21 of the sliding contact pad 1 guide cryogenic liquefied gas to the central region of the shaft support surface 1a of the sliding contact pad 1, thereby suppressing the temperature rise of the shaft support surface 1a caused by frictional heat between the sliding contact pad 1 and the rotating shaft. Since the circumferential grooves 21 extend across the central region of the shaft support surface 1a from one side to the other, the cryogenic liquefied gas flows through the circumferential grooves 21, cooling the central region of the shaft support surface 1a. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is reduced, and the deformation of the shaft support surface 1a can be reduced. Furthermore, the circumferential grooves 21 can absorb the deformation of the shaft support surface 1a itself.

[0060] In addition to the circumferential grooves 21, the sliding contact pad 1 may further include axial grooves 22 as described with reference to Figure 6. Cryogenic liquefied gas flows through the circumferential grooves 21 and axial grooves 22, cooling the central region of the axial support surface 1a. As a result, the temperature gradient in the thickness direction of the sliding contact pad 1 is further reduced, and the deformation of the axial support surface 1a can be further reduced. Similar to the circumferential grooves 21, the axial grooves 22 can absorb the deformation of the axial support surface 1a itself.

[0061] Figure 13 is a longitudinal cross-sectional view of an embodiment of the sliding bearing shown in Figure 9. The sliding bearing includes an upper leaf spring 55 and a lower leaf spring 56 as biasing members that push the sliding contact pad 1 in the axial direction. The upper leaf spring 55 and the lower leaf spring 56 are in contact with the upper and lower ends of the sliding contact pad 1, respectively. The upper leaf spring 55 and the lower leaf spring 56 are fixed to the upper and lower ends of the shell 2 by retainers 58. The retainers 58 are fixed to the upper and lower ends of the shell 2 by screws 59.

[0062] The upper leaf spring 55 and the lower leaf spring 56 are annular and extend along the circumferential direction of the shell 2. The upper leaf spring 55 and the lower leaf spring 56 protrude radially inward from the shell 2 and contact the sliding contact pad 1. In one embodiment, each of the upper leaf spring 55 and the lower leaf spring 56 may not be annular, but rather composed of multiple leaf spring elements arranged along the circumferential direction of the shell 2.

[0063] The axial length L1 of the sliding contact pad 1 at room temperature is greater than the axial length L2 of the shell 2 at room temperature. Therefore, the sliding contact pad 1 is sandwiched between an upper leaf spring 55 and a lower leaf spring 56 fixed to the shell 2. The upper leaf spring 55 and the lower leaf spring 56 are configured to be elastically bent in the axial direction. With this configuration, the axial position of the sliding contact pad 1 is maintained by the upper leaf spring 55 and the lower leaf spring 56, while allowing for minute changes.

[0064] Figure 14 shows an example of the state in which the sliding contact pad 1 is contracted. When the sliding contact pad 1 contracts due to contact with an extremely cold fluid such as liquefied gas, the axial length L1 of the sliding contact pad 1 approaches the axial length L2 of the shell 2, but the sliding contact pad 1 is located between the upper leaf spring 55 and the lower leaf spring 56. Therefore, the axial position of the sliding contact pad 1 is maintained by the upper leaf spring 55 and the lower leaf spring 56. In other words, the upper leaf spring 55 and the lower leaf spring 56 can absorb the expansion and contraction of the sliding contact pad 1 caused by temperature changes in the sliding contact pad 1.

[0065] The sliding bearing of this embodiment can be assembled as follows. At room temperature, the dovetail groove 50 of the sliding pad 1 and the pad retaining rail 51 of the shell 2 are in a clearance fit. Therefore, first, at room temperature, the dovetail groove 50 of the sliding pad 1 is slid along the pad retaining rail 51 of the shell 2 to fit the dovetail groove 50 of the sliding pad 1 into the pad retaining rail 51. Then, the upper leaf spring 55 and the lower leaf spring 56 are fixed to the shell 2 by the retainer 58 and the screw 59. The circumferential position of the sliding pad 1 is fixed by the engagement of the dovetail groove 50 and the pad retaining rail 51, and the axial position of the sliding pad 1 is fixed by the upper leaf spring 55 and the lower leaf spring 56.

[0066] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims.

[0067] The present invention is applicable to sliding bearings used in rotating machinery such as pumps and turbines, and is particularly applicable to sliding bearings used in cryogenic environments.

[0068] 1. Sliding pad 1a. Axial support surface 2. Shell 2a. Pad support surface 5. Pad pressing mechanism 7. Spring 8. Bolt (pad support member) 8a. Threaded portion 8b. Head 11. Through hole 12. Recessed portion 15. Through hole 17. Nut 20. Guide wall 21. Circumferential groove 22. Axial groove 31. Tapered shaft portion 31a. Outer surface 32. Pad support member 32a. Threaded portion 35. Tapered hole 37. Recessed portion 38. Through holes 41, 42. Nut 50. Dovetail groove 50a. First tapered side surface 51. Pad holding rail 51a. Second tapered side surface 55. Upper leaf spring 56. Lower leaf spring 58. Retainer 59. Screw 100. Rotating shaft

Claims

1. A sliding bearing for supporting a rotating shaft, comprising: a sliding contact pad having a shaft support surface for supporting the outer circumferential surface of the rotating shaft; a shell disposed radially outside the sliding contact pad; and a pad pressing mechanism for pressing the sliding contact pad against the pad support surface of the shell when the sliding contact pad is contracted, wherein the sliding contact pad has a circumferential groove formed on the shaft support surface, and the circumferential groove extends in the circumferential direction of the sliding bearing and extends through the center point of the shaft support surface.

2. The sliding bearing according to claim 1, wherein, if the width of the circumferential groove is W1 and the dimension of the axial support surface along the axial direction of the sliding bearing is D1, then W1 / D1 is in the range of 1 / 30 to 1 / 3.

3. The sliding pad further has an axial groove formed on the shaft support surface, the axial groove extending in the axial direction of the sliding bearing and extending through the center point of the shaft support surface, according to claim 1.

4. The sliding bearing according to claim 3, wherein W2 is the width of the axial groove and D2 is the dimension of the axial support surface along the direction perpendicular to the axial direction of the sliding bearing, and W2 / D2 is in the range of 1 / 20 to 1 / 4.

5. The sliding bearing according to claim 3, wherein the circumferential groove intersects with the axial groove.

6. The sliding bearing according to claim 1, wherein the pad pressing mechanism includes a biasing member that biases the sliding pad toward the shell.

7. The sliding bearing according to claim 6, wherein the pad pressing mechanism further comprises a pad support member supported on the shell, the sliding pad is supported on the pad support member, and the biasing member biases the sliding pad and the pad support member toward the shell, thereby pressing the sliding pad against the pad support surface of the shell.

8. The sliding bearing according to claim 1, wherein the pad pressing mechanism comprises a pad support member having a tapered shaft portion fixed to the shell, and a tapered hole formed in the sliding pad, the sliding pad being supported by the tapered shaft portion, and the tapered hole being in surface contact with the outer circumferential surface of the tapered shaft portion.

9. The sliding bearing according to claim 1, wherein the pad pressing mechanism comprises a dovetail groove formed in the sliding pad and a pad retaining rail connected to the pad support surface of the shell, the pad retaining rail having an inverted triangular cross-sectional shape that fits into the dovetail groove.

10. The sliding bearing according to claim 9, wherein the dovetail groove and the pad retaining rail extend in an axial direction parallel to the centerline of the sliding bearing.

11. The sliding bearing according to claim 10, further comprising a biasing member for pressing the sliding contact pad in the axial direction.

12. The sliding bearing according to claim 1, wherein the sliding pad comprises an aromatic polyether ketone, talc, carbon fibers, and unavoidable impurities, the talc content relative to the sliding pad is 7% by mass or more and 18% by mass or less, and the area ratio of the carbon fibers on the axial support surface of the sliding pad is 27% by more and 35% or less.

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