JPWO2017010146A1 - Non-contact annular seal and rotating machine equipped with the same - Google Patents

Abstract

Provided are a non-contact annular seal that reduces the amount of leakage caused when a lead angle is increased in order to increase the pumping effect, and a rotary machine including the same. The non-contact annular seal is a non-contact annular seal for sealing a fluid flowing from the high pressure side to the low pressure side through the gap between the rotating body and the stationary body, and is provided on the surface of the rotating body or the surface of the stationary body forming the gap. A thread groove is provided. The screw groove has a region where the cross-sectional area of the low-pressure side screw groove is smaller than the cross-sectional area of the high-pressure side screw groove. The number of the thread grooves is 4 or more. The rotating machine has this non-contact annular seal.

Description

  The present invention relates to a non-contact annular seal and a rotary machine including the same, and in particular, a fluid between an impeller and a casing in a rotary machine that handles a liquid such as water or oil, in other words, an incompressible fluid. The present invention relates to a non-contact annular seal that reduces the amount of leakage, reduces vibration, and exhibits stable shaft sealing characteristics, and a rotary machine including the same.

  A rotating machine (for example, a pump or the like, hereinafter referred to as a “pump”) for transferring a liquid is widely used in plants or facilities for power generation, chemical processes, sewerage, waterworks, and the like. The pump has a casing and a rotating shaft on which an impeller is mounted. A rotating shaft is arrange | positioned inside a casing and is rotatably supported by a bearing. The liquid sucked from the suction port of the casing is pressurized by the rotation of the impeller and discharged from the discharge port of the casing. That is, in the flow path inside the pump, a high pressure region and a low pressure region are formed, and fluid flows from the high pressure region to the low pressure region. Here, in a slight gap between the casing (fixed portion) and the rotating shaft (rotating portion), if the fluid moves (leaks) from the high pressure region to the low pressure region through this gap, the pump efficiency decreases. For this reason, the clearance gap between a casing and a rotating shaft is sealed by the non-contact annular seal. Thereby, it is suppressed that the pressurized liquid leaks to the low pressure side.

  For example, in the typical multi-stage centrifugal pump shown in FIG. 1 (cited from JIS handbook pump 1st edition, page 74), a non-contact annular seal is used in a portion surrounded by a circle in the figure. That is, it is used between the inlet part of the impeller, between the front stage impeller and the rear stage impeller, between the last stage impeller outlet part and the low pressure side, and the like. In particular, since the differential pressure is large between the impeller outlet and the low pressure side, and fluid leakage is large, the fluid leakage at this portion has a great influence on the pump performance. For this reason, non-contact annular seals of various structures that can reduce the amount of fluid leakage are known.

  A smooth seal is known as the most basic non-contact annular seal. The smooth seal is a seal formed by arranging double cylinders having smooth surfaces. In order to reduce the leakage amount of a non-contact annular seal such as a smooth seal, it is effective to reduce the radial gap between the rotating side and the stationary side of the non-contact annular seal. However, due to practical problems such as vibration and deflection of the rotating shaft, the radial gap cannot be made extremely small. For this reason, a non-contact annular seal that reduces the leakage amount without reducing the radial gap is required. As such a non-contact annular seal, a parallel groove seal, a damper seal, a thread groove seal and the like are known. Hereinafter, an example of a conventional non-contact annular seal will be described.

  FIG. 14 is a partial cross-sectional view of a conventional parallel groove seal. In FIG. 14, the fixed body 131 is shown in a sectional view, and the rotating shaft 121 is shown in a side view. The parallel groove seal 111 includes a rotating shaft 121 that is a rotating body having a smooth outer peripheral surface, and a fixed body 131 in which a plurality of concentric grooves 141 are provided on a surface facing the rotating shaft 121. This parallel groove seal 111 has energy loss due to vortices generated when the fluid flowing through the gap between the rotating shaft 121 and the fixed body 131 passes through the groove 141, pressure loss caused by sudden expansion and contraction of the flow path, and the like. Thus, the leakage amount (movement amount) of the fluid can be reduced.

  15 and 16 are partial cross-sectional views of a conventional damper seal. FIG. 15 shows a damper seal that employs a honeycomb pattern as a damper structure. In FIG. 15, the fixed body 132 is shown in a sectional view, and the rotating shaft 122 is shown in a side view. The damper seal 112 includes a rotating shaft 122 that is a rotating body having a smooth outer peripheral surface, and a fixed body 132 having a plurality of concave portions 142 provided on a surface facing the rotating shaft 122. In the illustrated example, a hexagonal honeycomb pattern is used as the recess 142. The damper seal 112 can reduce the amount of fluid leakage due to the pressure loss of the fluid generated when the fluid flowing through the gap between the rotating shaft 122 and the fixed body 132 flows through the recess 142.

  FIG. 16 shows a damper seal that employs a hole pattern as the damper structure. In FIG. 16, the fixed body 133 is shown in a sectional view, and the rotating shaft 123 is shown in a side view. The damper seal 113 includes a rotating shaft 123 that is a rotating body having a smooth outer peripheral surface, and a fixed body 133 that is provided with a plurality of recesses 143 on a surface facing the rotating shaft 123. In the illustrated example, a circular concave hole pattern is used as the concave portion 143. The damper seal 113 can reduce the amount of fluid leakage due to the pressure loss of the fluid that occurs when the fluid flowing through the gap between the rotating shaft 123 and the fixed body 133 flows through the recess 143.

  FIG. 17 is a partial cross-sectional view of a conventional thread groove seal. In FIG. 17, the fixed body 134 is shown in a sectional view, and the rotating shaft 124 is shown in a side view. The thread groove seal 114 includes a cylindrical fixed body 134 having a smooth inner peripheral surface, and a rotating shaft 124 having a thread groove 144 formed on a surface facing the fixed body 134. When the rotating shaft 124 rotates, the thread groove seal 114 can push the fluid back to the high pressure side by the pumping effect according to the rotation direction, and can greatly reduce the amount of leakage. Since the thread groove seal 114 can push the fluid back to the high pressure side by the pumping effect, the leakage of the fluid can be particularly reduced when sealing an incompressible fluid that is a liquid such as water.

  The pumping effect of the thread groove seal 114 is affected by the size of the lead angle θ of the thread groove 144. That is, if the lead angle θ is small, the pumping effect is small, and if the lead angle θ is large, the pumping effect is large. However, in order to increase the lead angle θ in the rotary shaft 124 having a predetermined diameter, the fixed body 134 having a predetermined inner diameter, and the thread groove seal 114 having a predetermined groove pitch, it is necessary to increase the number of thread grooves. There is.

  FIG. 18 and FIG. 19 are schematic views in which a single thread and a four thread are developed, respectively. The number of screw grooves in the axial direction is eight, and the groove interval (pitch) in the axial direction is δ. When the shaft diameter is D1, the developed lateral length is D1 × π, and the longitudinal length is an arbitrary length L. Therefore, the developed part becomes substantially rectangular.

  FIG. 18 is a schematic diagram of a single thread. When proceeding from the lower left end to the upper side along the screw groove, it reaches A on the right side. However, since the shaft has made one round here, the continuation of the groove moves to A on the left side. By going from A on the left side to B on the right side, the shaft has made one more turn. In the single thread shown in FIG. 18, the interval (pitch) of the grooves in the axial direction is δ and reaches eight times around the upper end H of the thread groove. The lead angle is α.

  FIG. 19 is a schematic view of a four-thread screw. Since there are four starting points of the thread groove every 90 degrees in the radial direction, the flow path is four times as large as the groove of the single thread. Proceeding upward along the screw groove starting from 0 degrees below the left end, it reaches D on the right side, but since it has made one round of the axis here, the continuation of the groove moves to D on the left side. Proceeding further from D on the left side, it reaches the upper end H of the thread groove on the right side. The same is true for the three threaded grooves starting from other angles. In other words, the screw groove reaches the upper end after two rounds. Further, the lead angle of the four-thread screw shown in FIG. 19 is β.

  The pumping performance by the thread groove depends on how much the medium in the thread groove can be moved in the axial direction in one rotation. Therefore, under the same groove width, depth, and pitch conditions, the larger the lead angle, the greater the amount of movement in the axial direction per rotation. As shown in FIGS. 18 and 19, the lead angle α of the single thread is smaller than β of the four thread. And the four-thread screw is superior to the one-thread screw in pumping performance per groove.

  However, the number of screw grooves becomes four times, and in this case, the cross-sectional area of the screw groove 144 increases as the number of thread grooves increases. As the cross-sectional area of the thread groove 144 increases, the amount of leakage flowing from the high pressure side to the low pressure side increases. In some cases, the amount of leakage that increases due to an increase in the cross-sectional area of the screw groove 144 is greater than the amount of leakage that is reduced by the pumping effect, and as a result, the overall amount of leakage increases.

  As described above, increasing the lead angle θ in the thread groove seal 144 improves the pumping effect, but increases the cross-sectional area of the thread groove 144. That is, the thread groove seal 144 has a problem that a trade-off relationship exists between the pumping effect and the cross-sectional area of the thread groove 144.

  The thread groove seal in which the thread groove is formed on the stationary side also has the same problem. FIG. 20 is a schematic partial cross-sectional view of a conventional thread groove seal in which the thread groove is formed on the stationary side. In FIG. 20, the fixed body 134 is shown in a sectional view, and the rotating shaft 124 is shown in a side view. The thread groove seal 115 includes a rotating shaft 124 that is a rotating body having a smooth outer peripheral surface, and a fixed body 134 that has a thread groove 144 formed on a surface facing the rotating shaft 124. The fluid flowing in the direction of the arrow A in the figure through the gap between the rotating shaft 124 and the fixed body 134 receives a force in the rotating direction due to the frictional force of the rotating rotating shaft 124. As a result, a flow from the low pressure side toward the high pressure side along the screw groove 144 (flow in the direction opposite to the arrow A in the figure) occurs, and a so-called pumping effect is generated.

  As in the thread groove seal 114 shown in FIG. 17, the thread groove seal 115 shown in FIG. 20 is improved in pumping effect when the lead angle is increased, but the sectional area of the thread groove 144 is increased. As a result, the overall leakage amount may increase.

  Incidentally, in Japanese Utility Model Publication No. 62-98798 (Patent Document 1) and Japanese Utility Model Application Publication No. 62-101093 (Patent Document 2), in the thread groove seal portion, the screw depth or the screw depth is increased from the high pressure side to the low pressure side. A sealing technique is disclosed in which the thread cross-sectional area depending on the width and width is increased continuously or stepwise. The thread groove seal with such a configuration has a certain sealing effect for fluids under atmospheric pressure such as air, but in the case of incompressible fluid such as water, the cross-sectional area of the seal channel is downstream. As the width becomes larger, the flow in the thread groove seal becomes unstable, which may adversely affect the shaft runout.

Japanese Utility Model Publication No. 62-98798 Japanese Utility Model Publication No. 62-101093

  The present invention has been made in view of the above-described conventional problems, and one of its purposes is to increase the lead angle in order to effectively use the leakage reduction effect due to the pumping effect of the thread groove seal. The purpose is to reduce the influence of the increase in leakage amount. In other words, increasing the lead angle (increasing the number of thread grooves) maximizes the pumping effect of the thread groove seal and reduces the amount of leakage associated therewith.

  Another object of the present invention is to provide a thread groove seal that stabilizes the flow in the thread groove seal and allows the shaft to rotate stably.

  Another object of the present invention is a rotating machine that rotates a rotating shaft to which an impeller is attached to transfer a fluid, and reduces the leakage of fluid pressurized by the impeller to the low pressure side. It is to provide a rotating machine that increases pump efficiency.

  The non-contact annular seal concerning the 1st form of the present invention has a rotating body provided in a rotating part of a rotating machine, and a fixed body provided in a fixing part of the rotating machine, and the rotating body and the fixed A non-contact annular seal configured to seal a fluid flowing through a gap between the body and a screw groove provided on at least one of the surface of the rotating body and the surface of the fixed body that forms the gap. The screw groove has a region in which the cross-sectional area of the screw groove on the high-pressure side is larger than the cross-sectional area of the screw groove on the low-pressure side, and the number of the thread grooves is four or more.

  The non-contact annular seal according to a second aspect of the present invention is the non-contact annular seal according to the first aspect, wherein the region has a continuous cross-sectional area of the thread groove from the high pressure side toward the low pressure side. A reduced region formed to be smaller.

  The non-contact annular seal according to a third aspect of the present invention is the non-contact annular seal according to the second aspect, wherein the reduced region has a depth of the thread groove from the seal inlet side toward the seal outlet side. Has a region formed so as to be continuously reduced.

  A non-contact annular seal according to a fourth aspect of the present invention is the non-contact annular seal according to the second or third aspect, wherein the reduced region has a width of the thread groove from the high pressure side toward the low pressure side. Has a region formed so as to be continuously reduced.

  A non-contact annular seal according to a fifth aspect of the present invention is the non-contact annular seal according to any one of the second to fourth aspects, wherein the reduced area has a constant ratio of the depth and width of the thread groove. It has the area | region formed so that it might become.

  A non-contact annular seal according to a sixth aspect of the present invention is the non-contact annular seal according to the first aspect, wherein the area of the region gradually decreases from the high pressure side toward the low pressure side. Having a reduced region formed on the substrate.

  The non-contact annular seal according to a seventh aspect of the present invention is the non-contact annular seal according to the sixth aspect, wherein the reduced region has a stepped depth of the thread groove from the high pressure side toward the low pressure side. A region formed so as to be smaller.

  A rotating machine according to an eighth aspect of the present invention includes an electric motor, a main shaft that is connected to the electric motor and configured to be rotatable, and an impeller that is fitted to the main shaft and configured to be rotatable together with the main shaft. A casing that houses the impeller, and a bearing that is attached to the casing and rotatably supports the main shaft, the main shaft includes a rotating portion, the casing includes a fixed portion, and the rotation The portion and the fixing portion have the non-contact annular seal described in any one of the first to seventh embodiments.

  According to one aspect of the present invention, in a non-contact annular seal having a thread groove, even if the lead angle of the thread groove is increased (increasing the number of thread grooves) to increase the pumping effect, the screw The cross-sectional area of the groove becomes smaller when considered in the average of the axial direction of the seal, and the leakage amount can be greatly reduced. Thus, according to one aspect of the present invention, a non-contact seal having high shaft sealing performance can be realized without reducing the radial clearance of the non-contact seal.

  Furthermore, as the cross-sectional area of the thread groove decreases continuously or intermittently from the high pressure side toward the low pressure side, the flow in the thread groove seal becomes stable, so that the shaft can rotate stably. became.

  According to another aspect of the present invention, there is provided a rotary machine that rotates a rotating shaft to which an impeller is attached and transfers a fluid, and reduces the leakage of fluid pressurized by the impeller to the low pressure side. A rotating machine that increases efficiency can be provided.

It is sectional drawing of the high pressure pump which can apply the non-contact annular seal which concerns on this embodiment. It is an expanded sectional view of the 1st stage impeller of a high pressure pump. It is a fragmentary sectional view showing the non-contact annular seal of this embodiment. It is a fragmentary sectional view when the non-contact annular seal of FIG. 3 is cut along the rotation axis. It is a figure which shows the thread groove cross section of the high voltage | pressure side of the non-contact annular seal of this embodiment, and the thread groove cross section of a low voltage | pressure side. It is a figure which shows the non-contact annular seal in which the thread groove was provided in the inner surface of a fixed body. It is a figure which shows the cross section of the high voltage | pressure side of a screw groove which has a rectangular cross section, and the cross section of a low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of a screw groove which has a rectangular cross section, and the cross section of a low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of a thread groove which has a triangular cross section, and the cross section of a low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of a thread groove which has a triangular cross section, and the cross section of a low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of a thread groove which has a triangular cross section, and the cross section of a low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of the thread groove which has a U-shaped cross section, and the cross section of the low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of the thread groove which has a U-shaped cross section, and the cross section of the low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of the thread groove which has a U-shaped cross section, and the cross section of the low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of the thread groove which has a semicircular cross section, and the cross section of the low voltage | pressure side. It is a figure which shows the cross section of the high voltage | pressure side of the thread groove which has a semicircular cross section, and the cross section of the low voltage | pressure side. It is a fragmentary sectional view which shows the non-contact annular seal of other embodiment. 6 is a graph showing simulation results of Experimental Example 1 and Comparative Example 1. It is a graph which shows the simulation result of Experimental example 2 and Comparative example 2. FIG. It is a fragmentary sectional view of the conventional parallel groove seal. FIG. 6 is a partial cross-sectional view showing a conventional damper seal that employs a honeycomb pattern. It is a fragmentary sectional view which shows the conventional damper seal which employ | adopted the hole pattern. It is a fragmentary sectional view of the conventional thread groove seal. It is the schematic diagram which expand | deployed the 1 screw | thread. It is the schematic diagram which developed the 4-thread screw. It is a fragmentary sectional view of the conventional thread groove seal in which the thread groove is formed on the stationary side.

  Next, an embodiment of the present invention will be described with reference to the drawings. The following description is merely illustrative of the embodiment, and the technical scope of the present invention is not limited to the following embodiment. Moreover, each component demonstrated below can comprise invention by independent or arbitrary combinations.

  FIG. 1 shows a cross-sectional view of a high-pressure pump (multi-stage centrifugal pump) that is a rotary machine to which the non-contact annular seal according to the present embodiment can be applied. The high-pressure pump 1 includes a main shaft 11 that is connected to an electric motor (not shown) and rotates, impellers 21a, 21b, and 21c fitted to the main shaft 11, a casing 31 that houses the impellers 21a, 21b, and 21c, and a casing. And bearings 45a and 45b attached to 31. The bearings 45a and 45b support the main shaft 11 to be rotatable. An electric motor (not shown) for rotationally driving the high-pressure pump 1 is connected to the main shaft 11 via a coupling 13 fitted to the left end of the main shaft 11.

  The casing 31 has a suction port 33 for sucking a fluid, that is, a liquid such as water from the outside, and a discharge port 37 for discharging the sucked fluid. The first stage impeller 21 a fitted to the main shaft 11 rotates as the main shaft 11 rotates, and sucks fluid into the casing 31 from the suction port 33. The fluid sucked and pressurized by the first stage impeller 21a passes through the first flow path 35a and reaches the second stage impeller 21b. The fluid pressurized by the second stage impeller 21b passes through the second flow path 35b and reaches the third stage impeller 21c. The fluid is further pressurized by the third stage impeller 21c, discharged from the discharge port 37, and transferred through a pipe (not shown). That is, the fluid is pressurized by the first stage impeller 21a, the second stage impeller 21b, and the third stage impeller 21c.

  In the fluid, a pressure difference is generated between the suction side and the discharge side of each impeller 21a, 21b, 21c. That is, the suction side is the low pressure side and the discharge side is the high pressure side. When this pressure difference occurs, a part of the fluid on the high pressure side leaks to the low pressure side through a slight gap. The non-contact annular seal of this embodiment reduces the leakage. In the high-pressure pump 1 shown in FIG. 1, the non-contact annular seal of this embodiment is provided at a site surrounded by a circle. Since the high-pressure pump 1 shown in FIG. 1 is a multi-stage centrifugal pump, the fluid pressure is higher than that of a single-stage centrifugal pump, and the amount of fluid leakage inevitably increases. If the amount of leakage is large, the pump efficiency decreases.

  FIG. 2 is an enlarged cross-sectional view of the first stage impeller 21a of the high-pressure pump 1 shown in FIG. As illustrated, the first stage impeller 21a includes a suction port 23 for sucking fluid and a discharge port 25 for discharging fluid. Here, the pressure of the fluid is low on the suction port 23 side and high on the discharge port 25 side. That is, the suction port 23 is a low pressure part 36, and the discharge port 25 is a high pressure part 38. Here, the fluid leaking portion in the high-pressure pump 1 is mainly a facing portion X between the outer peripheral surface of the suction port 23 and the casing 31a, and a facing portion Y between the outer peripheral surface of the rear surface of the impeller 21a and the casing 31b. Non-contact annular seals 41 and 43 according to the present embodiment are provided in the gaps formed in the facing portions X and Y, respectively.

  In order to reduce the reduction in pump efficiency of the high-pressure pump 1 due to fluid leakage, as shown in FIG. 2, non-contact annular is formed in the gap between the impeller 21a as the rotating part and the casings 31a and 31b as the fixing parts. Seals 41 and 43 are provided to narrow the gap.

  However, in the case of a high pressure pump such as the high pressure pump 1, there is a large difference between the pressure on the back side of the impeller 21a and the pressure on the low pressure side, creating a non-contact annular seal with smooth surfaces facing each other. In such a gap (several hundred μm), the amount of fluid leakage is large. For this reason, in order to reduce the amount of leakage, the gap must be further narrowed to improve the shaft seal characteristics. However, if the gap is narrowed to prevent leakage, problems such as contact between the rotating part and the fixed part occur, so there is a natural limit to narrowing the gap.

  Various devices have been devised in the past regarding the seal structure for preventing this leakage. Specifically, the above-mentioned parallel groove seal, damper seal, thread groove seal, and the like. In these seal structures, grooves and irregularities are provided on the surface of the opposed portion of the seal to increase pressure loss, and the fluid pressure is reduced to reduce the leakage flow rate.

  Among the non-contact seals, the thread groove seal is an excellent seal structure that can reduce the amount of leakage due to the pumping effect of the thread groove, and when the screw groove is provided on the rotating side or the screw groove is provided on the stationary side. There are various forms such as providing screw grooves on both sides.

  In order to increase the pumping effect, which is an advantage of the thread groove seal, it is effective to increase the lead angle of the screw. However, this naturally increases the number of threads. For this reason, the cross-sectional area of the seal gap in the cross section orthogonal to the rotation axis of the seal increases, and the amount of seal leakage increases accordingly, and the effect of reducing the leakage due to the pumping effect is canceled.

  In view of the shaft seal characteristics of the thread groove seal as described above, the shape of the thread groove for maximizing the pumping effect of the thread groove seal has been devised.

  The non-contact annular seals 41 and 43 include rotating bodies 41a and 43a provided on the impeller 21a that is a rotating part of the high-pressure pump 1, and fixed bodies 41b and 43b provided on the casings 31a and 31b that are fixed parts. . In the illustrated example, the rotating bodies 41a and 43a are provided as members different from the impeller 21a, but the rotating bodies 41a and 43a may be formed integrally with the impeller 21a. Similarly, although the fixed bodies 41b and 43b are provided as members different from the casings 31a and 31b in the illustrated example, the fixed bodies 41b and 43b may be formed integrally with the casings 31a and 31b.

  FIG. 3 is a partial cross-sectional view showing the non-contact annular seal of this embodiment applicable to the non-contact annular seals 41 and 43 shown in FIG. In FIG. 3, the fixed body 136 is shown in a sectional view, and the rotating body 126 is shown in a side view.

  As shown in the figure, the non-contact annular seal 116 of the present embodiment is provided on the rotating body 126 provided on the impeller 21a that is the rotating part shown in FIG. 2 and the casings 31a and 31b that are the fixing parts shown in FIG. And a fixed body 136 to be provided. The rotating body 126 is configured to rotate together with the impeller 21a, and includes a screw groove 146 formed in a spiral shape on the surface thereof. That is, the non-contact annular seal 116 of this embodiment is a thread groove seal. The fixed body 136 is formed in a substantially cylindrical shape. The rotating body 126 is a substantially cylindrical member having an outer diameter smaller than the inner diameter of the fixed body 136. The rotating body 126 is disposed inside the fixed body 136 so as to have a predetermined gap with respect to the inner surface of the fixed body 136.

  When the non-contact annular seal 116 is applied to the high pressure pump 1 shown in FIG. 1, the fluid passes through the gap between the fixed body 136 and the rotating body 126 from the high pressure side 155 (seal inlet side) to the low pressure side 156 (seal outlet). Side), that is, in the direction of arrow A in the figure. The rotating body 126 can push the leaking fluid back to the high pressure side by the pumping effect by rotating in a predetermined direction around the rotating shaft 151.

  FIG. 4 is a partial cross-sectional view of the non-contact annular seal 116 of FIG. 3 when cut along the rotating shaft 151. Hereinafter, the thread groove 146 shown in FIG. 3 will be described in detail with reference to FIG. As shown in the figure, the rotating body 126 has a screw groove 146 and a screw thread 157 formed on the surface thereof in a spiral shape with a predetermined lead angle θ. The fixed body 136 and the rotating body 126 are spaced apart so as to have a predetermined gap G. Here, the gap G refers to the shortest distance between the inner surface of the fixed body 136 and the top portion (land portion 157a) of the screw thread 157. The screw groove 146 has a predetermined screw groove width W and screw groove depth D. Here, the thread groove width W is the length of the straight line connecting the adjacent land parts 157a in the shortest, and the screw groove depth D is drawn from the straight line connecting the adjacent land parts 157a to the bottom of the screw groove 146. This is the longest distance of vertical lines. Further, the cross-sectional area 158 (seal gap cross-sectional area) of the screw groove 146 is an area surrounded by the shortest straight line of the adjacent land portions 157a and the outer portion forming the screw groove 146 (a region indicated by a hatched portion in the figure). ). That is, the cross-sectional shape of the thread groove 146 of this embodiment is a rectangular shape.

  In the non-contact annular seal 116 of this embodiment shown in FIGS. 3 and 4, the thread groove width W is constant over the entire length of the thread groove 146, and the thread groove depth D is equal to the high pressure side 155 (seal inlet). Side) toward the low pressure side 156 (seal outlet side). Accordingly, the thread groove depth D of the thread groove 146 on the high-pressure side 155 is the largest, and the thread groove depth D on the low-pressure side 156 is the smallest. That is, the non-contact annular seal 116 is formed so that the cross-sectional area 158 of the thread groove 146 continuously decreases from the high pressure side 155 toward the low pressure side 156.

  FIG. 5 is a diagram showing a cross section of the high-pressure side thread groove and a low-pressure side thread groove of the non-contact annular seal 116 of the present embodiment. As illustrated, the thread groove cross section on the high pressure side of the thread groove 146 is a rectangular cross section having a width a0 and a depth b0. The screw groove cross section on the low pressure side is a rectangular cross section having a width a1 and a depth b1. Here, the width a0 is equal to the width a1, and the depth b0 is greater than the depth b1. That is, the thread groove 146 is formed such that the thread groove depth continuously decreases from the high-pressure side toward the low-pressure side while keeping the thread groove width constant. Thereby, the non-contact annular seal 116 is formed so that the cross-sectional area 158 of the thread groove 146 continuously decreases from the high pressure side toward the low pressure side.

  As shown in FIGS. 3 to 5, the pumping effect is improved by changing the thread groove depth D to continuously reduce the cross-sectional area 158 of the thread groove 146 from the high pressure side 155 toward the low pressure side 156. Therefore, even if the lead angle θ is increased, the average value of the cross-sectional area 158 in the entire length of the thread groove 146 can be reduced as compared with the case where the cross-sectional area of the thread groove is uniformly large. When the cross-sectional area at the beginning of the screw groove on the high-pressure side is A and the cross-sectional area at the end of the low-pressure side is B, if the area ratio B / A is 0 ≦ B / A <1, the result is a non-contact annular seal. The flow rate of fluid leaking from 116 can be reduced. Therefore, according to one aspect of the present invention, a non-contact annular seal having high shaft sealing performance can be realized without reducing the radial clearance of the non-contact annular seal 116. In addition, since the cross-sectional area of the high-pressure side 155 is large and the cross-sectional area of the low-pressure side 156 is small, the flow in the thread groove seal is stabilized, and the shaft can rotate stably.

  In the above embodiment, the cross-sectional area 158 of the thread groove 146 is formed so as to decrease from the high pressure side 155 toward the low pressure side 156 over the entire length of the thread groove 146. However, if the screw groove 146 is formed so that the cross-sectional area 158 has a region that decreases from the high pressure side 155 toward the low pressure side 156 in at least a part of the entire length of the screw groove 146, the same effect can be obtained. Can do.

  In the above embodiment, the screw groove 146 is formed in the rotating body 126, but instead, the screw groove 146 may be provided on the inner surface of the fixed body 136 as shown in FIG.

  FIG. 6 is a view showing a non-contact annular seal 117 in which a thread groove 146 is provided on the inner surface of the fixed body 136. As shown in the figure, the fixed body 136 has a thread groove 146 on its inner surface. The depth of the thread groove 146 is formed so as to decrease from the high pressure side 155 toward the low pressure side 156. That is, the cross-sectional area of the thread groove 146 is formed so as to decrease from the high pressure side 155 toward the low pressure side 156. Thus, since the cross-sectional area of the screw groove 146 is formed so as to decrease from the high-pressure side 155 toward the low-pressure side 156, the average value of the cross-sectional areas in the entire length of the screw groove 146 can be reduced. As a result, the flow rate of fluid leaking from the non-contact annular seal 117 can be reduced. Note that a thread groove 146 may be provided in both the rotating body 126 and the fixed body 136.

  The thread groove 146 of the non-contact annular seal described above has a rectangular cross section, and is formed so that the thread groove depth decreases from the high pressure side 155 toward the low pressure side 156. However, the cross-sectional shape of the thread groove 146 is not limited to this. For example, the cross-sectional shape shown in FIGS. 7 to 10 described below may be used.

  7A and 7B are views showing a cross section on a high pressure side and a cross section on a low pressure side of a thread groove having a rectangular cross section. The screw groove cross section on the high pressure side (seal inlet side) of the screw groove shown in FIG. 7A is a rectangular cross section having a width a0 and a depth b0. The thread groove cross section on the low pressure side (seal outlet side) is a rectangular cross section having a width a1 and a depth b1. Here, the aspect ratio (a0: b0) of the cross section of the thread groove on the high pressure side is the same as the aspect ratio (a1: b1) of the cross section of the thread groove on the low pressure side. Further, the width a0 is larger than the width a1, and the depth b0 is larger than the depth b1. That is, the cross section of the thread groove is formed such that the thread groove width and the thread groove depth are continuously reduced from the high pressure side toward the low pressure side while keeping the aspect ratio constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The screw groove cross section on the high pressure side (seal inlet side) of the screw groove shown in FIG. 7B is a rectangular cross section having a width a0 and a depth b0. The thread groove cross section on the low pressure side (seal outlet side) is a rectangular cross section having a width a1 and a depth b1. Here, the width a0 is larger than the width a1, and the depth b0 is equal to the depth b1. That is, the cross section of the thread groove is formed such that the thread groove width continuously decreases from the high pressure side toward the low pressure side while keeping the thread groove depth constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  8A to 8C are views showing a cross section on a high pressure side and a cross section on a low pressure side of a thread groove having a triangular cross section. The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 8A is a triangular cross section having a width a0 and a depth b0. The thread groove cross section on the low pressure side (seal outlet side) is a triangular cross section having a width a1 and a depth b1. Here, the aspect ratio (a0: b0) of the cross section of the thread groove on the high pressure side is the same as the aspect ratio (a1: b1) of the cross section of the thread groove on the low pressure side. Further, the width a0 is larger than the width a1, and the depth b0 is larger than the depth b1. That is, the cross section of the thread groove is formed such that the thread groove width and the thread groove depth are continuously reduced from the high pressure side toward the low pressure side while keeping the aspect ratio constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 8B is a triangular cross section having a width a0 and a depth b0. The thread groove cross section on the low pressure side (seal outlet side) is a triangular cross section having a width a1 and a depth b1. Here, the width a0 is equal to the width a1, and the depth b0 is greater than the depth b1. That is, the cross section of the thread groove is formed so that the thread groove depth continuously decreases from the high pressure side toward the low pressure side while keeping the thread groove width constant. Thereby, the non-contact annular seal is formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 8C is a triangular cross section having a width a0 and a depth b0. The thread groove cross section on the low pressure side (seal outlet side) is a triangular cross section having a width a1 and a depth b1. Here, the width a0 is larger than the width a1, and the depth b0 is equal to the depth b1. That is, the cross section of the thread groove is formed such that the thread groove width continuously decreases from the high pressure side toward the low pressure side while keeping the thread groove depth constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  9A to 9C are views showing a cross section on the high pressure side and a cross section on the low pressure side of the thread groove having a U-shaped cross section. The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 9A is a U-shaped cross section combining a rectangular cross section having a width a0 and a depth b0 and a semicircular cross section having a radius R0. It is. The screw groove cross section on the low pressure side (seal outlet side) is a U-shaped cross section that combines a rectangular cross section having a width a1 and a depth b1 and a semicircular cross section having a radius R1. Here, the ratio (a0: b0: R0) of the thread groove cross section on the high pressure side is the same as the ratio (a1: b1: R1) of the thread groove cross section on the low pressure side. Further, the width a0 is larger than the width a1, the depth b0 is larger than the depth b1, and the radius R0 is larger than the radius R1. That is, the cross section of the thread groove is formed such that the thread groove width, the thread groove depth, and the thread groove radius are continuously reduced from the high pressure side toward the low pressure side with the ratio being constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 9B is a U-shaped cross section combining a rectangular cross section having a width a0 and a depth b0 and a semicircular cross section having a radius R0. It is. The screw groove cross section on the low pressure side (seal outlet side) is a U-shaped cross section that combines a rectangular cross section having a width a1 and a depth b1 and a semicircular cross section having a radius R1. Here, the width a0 is equal to the width a1, the depth b0 is larger than the depth b1, and the radius R0 is equal to the radius R1. That is, the cross section of the thread groove is formed such that the thread groove depth continuously decreases from the high pressure side toward the low pressure side while keeping the thread groove width and the thread groove radius constant. Thereby, the non-contact annular seal is formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 9C is a U-shaped cross section combining a rectangular cross section having a width a0 and a depth b0 and a semicircular cross section having a radius R0. It is. The screw groove cross section on the low pressure side (seal outlet side) is a U-shaped cross section that combines a rectangular cross section having a width a1 and a depth b1 and a semicircular cross section having a radius R1. Here, the width a0 is larger than the width a1, the depth b0 is equal to the depth b1, and the radius R0 is larger than the radius R1. That is, the cross section of the thread groove is formed such that the thread groove width and the thread groove radius are continuously reduced from the high pressure side toward the low pressure side while keeping the thread groove depth constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  10A and 10B are views showing a cross section on the high pressure side and a cross section on the low pressure side of the thread groove having a semicircular cross section. The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 10A is a semicircular cross section having a width a0, a depth b0, and a radius R0. Here, the width a0 is equal to twice the radius R0, and the depth b0 is equal to the radius R0. The thread groove cross section on the low pressure side (seal outlet side) is a semicircular cross section having a width a1, a depth b1, and a radius R1. Here, the width a1 is equal to twice the radius R1, and the depth b1 is equal to the radius R1. Here, the ratio (a0: b0) of the thread groove cross section on the high pressure side is the same as the ratio (a1: b1) of the thread groove cross section on the low pressure side. Further, the width a0 is larger than the width a1, the depth b0 is larger than the depth b1, and the radius R0 is larger than the radius R1. That is, the cross section of the thread groove is formed such that the thread groove width, the thread groove depth, and the thread groove radius are continuously reduced from the high pressure side toward the low pressure side with the ratio being constant. Thereby, the thread groove can be formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  The thread groove cross section on the high pressure side (seal inlet side) of the thread groove shown in FIG. 10B is a semicircular cross section having a width a0, a depth b0, and a radius R0. The thread groove cross section on the low pressure side (seal outlet side) is an arc-shaped cross section having a radius of curvature R1 and a width a1 and a depth b1. Here, the width a0 is larger than the width a1, and the depth b0 is larger than the depth b1. That is, the cross section of the thread groove is formed such that the thread groove width and the thread groove depth are continuously reduced from the high pressure side toward the low pressure side. Thereby, the non-contact annular seal is formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side.

  7 to 10, the cross-sectional area of the thread groove on the high-pressure side (seal inlet side) is large, the cross-sectional area of the screw groove on the low-pressure side (seal outlet side) is narrow, and Any shape that has a cross-sectional area that continuously changes from the high-pressure side to the low-pressure side can be employed in the non-contact annular seal of this embodiment.

  Further, the thread groove having the cross-sectional shape shown in FIGS. 7 to 10 is formed so as to have a region where the cross-sectional area becomes smaller from the high pressure side toward the low pressure side in at least a part of the entire length of the thread groove. If it is, the effect of this embodiment mentioned above can be show | played.

  Next, a non-contact annular seal according to another embodiment of the present invention in which the cross-sectional area of the thread groove becomes smaller in steps from the high pressure side to the low pressure side will be described. FIG. 11 is a partial cross-sectional view showing a non-contact annular seal of another embodiment applicable to the non-contact annular seals 41 and 43 shown in FIG. In FIG. 11, the fixed body 137 is shown in a sectional view, and the rotating body 127 is shown in a side view. The non-contact annular seal 118 includes a rotating body 127 provided on the impeller 21a which is the rotating part shown in FIG. 2, and a fixed body 137 provided on the casings 31a and 31b which are the fixing parts shown in FIG. The rotating body 127 is configured to be rotatable together with the impeller 21a, and includes a screw groove 147 formed in a spiral shape on the surface thereof. That is, the non-contact annular seal 118 of this embodiment is a thread groove seal. The fixed body 137 is formed in a substantially cylindrical shape. The rotating body 127 is a substantially cylindrical member having an outer diameter smaller than the inner diameter of the fixed body 137. The rotating body 127 is disposed inside the fixed body 137 so as to have a predetermined gap with respect to the inner surface of the fixed body 137.

  The screw groove 147 formed in a spiral shape is formed such that the depth of the screw groove 147 decreases step by step along a predetermined length along the groove traveling direction. The width of the thread groove 147 is constant from the inlet side to the outlet side. The depth of the thread groove 147 is the deepest on the high pressure side 155 (seal inlet side), that is, the bottom diameter of the thread groove 147 is the smallest. The depth of the thread groove 147 is the shallowest at the low pressure side 156 (seal outlet side) (the bottom diameter of the thread groove 147 is the largest).

  Further, the bottom diameter of the screw groove 147 is formed such that d1 <d2 <d3 by several steps (the number of screw grooves) from the high-pressure side 155. In the three stages from the seal inlet side (high pressure side 155), the bottom diameter of the thread groove is d1, and the groove bottom diameter is the smallest (groove depth is deepest). The next four stages are d2, which is an intermediate diameter between d1 and d3. The four-stage groove bottom diameter on the seal outlet side (low pressure side 156) is the largest. That is, a stepped step is formed in one screw groove 147, and the thread groove cross-sectional area is increased so that the cross-sectional area of the seal inlet on the high pressure side 155 is the largest and the cross-sectional area of the seal outlet on the low pressure side is the smallest. The level is changed.

  In other words, the thread groove 147 is formed such that the depth of the thread groove 147 on the high-pressure side 155 is the largest, and the depth of the thread groove 147 decreases step by step toward the low-pressure side 156 every several pitches. . Specifically, the screw groove 147 from the high-pressure side 155 is formed at a first depth over a length of approximately three circumferences (the first stage range in the figure). Continuing to the screw groove 147 formed at the first depth, the screw groove 147 is formed at a second depth smaller than the first depth over a length of approximately four turns (see FIG. Middle second stage range). Subsequently, following the screw groove 147 formed at the second depth, the screw groove 147 is formed at a third depth smaller than the second depth over a length of approximately four turns. (The range of the third level in the figure).

  Accordingly, the thread groove 147 is formed so that the bottom diameter of the thread groove 147 is d1 over three pitches from the high-pressure side 155 (the first stage range in the figure). Subsequently, the screw groove 147 is formed over the next four pitches so that the bottom diameter of the screw groove 147 is d2 which is larger than d1 (in the second stage range in the figure). Finally, the screw groove 147 on the low-pressure side 156 is formed so that the bottom diameter of the screw groove 147 is d3 larger than d2 over four pitches (the range of the third step in the figure).

  Since the thread groove 147 is formed as described above, the non-contact annular seal 118 is formed so that the cross-sectional area of the thread groove 147 gradually decreases from the high pressure side 155 toward the low pressure side 156. Has been. Thus, by reducing the cross-sectional area of the screw groove 147 stepwise, even if the lead angle θ is increased (increasing the number of screw grooves) in order to improve the pumping effect, the entire length of the screw groove 147 is increased. The average value of the cross-sectional areas at can be reduced. As a result, the flow rate of fluid leaking from the non-contact annular seal 118 can be reduced. Therefore, according to the present embodiment, a non-contact annular seal having high shaft sealing performance can be realized without reducing the radial clearance of the non-contact annular seal 116. In addition, since the cross-sectional area of the high-pressure side 155 is large and the cross-sectional area of the low-pressure side 156 is small, the flow in the thread groove seal is stabilized, and the shaft can rotate stably.

  In the non-contact annular seal 118 shown in FIG. 11, the cross-sectional area of the screw groove 147 is formed so as to gradually decrease from the high pressure side 155 toward the low pressure side 156 over the entire length of the screw groove 147. Yes. However, the same effect can be obtained if the thread groove 146 is formed so as to have a region in which the cross-sectional area gradually decreases from the high pressure side 155 toward the low pressure side 156 in at least a part of the entire length of the thread groove 147. Can play.

  Further, in the non-contact annular seal 118 shown in FIG. 11, the cross-sectional area of the screw groove 147 is formed to be small in three stages from the first stage to the third stage in the figure. However, the present invention is not limited to this, and the cross-sectional area may be reduced in two steps or four or more steps according to the specifications of the rotating machine.

  Further, in the non-contact annular seal 118 shown in FIG. 11, the depth of the thread groove 147 is formed so as to decrease step by step every 3 or 4 pitches. However, the present invention is not limited to this, and the thread groove 147 may be formed so that the depth of the screw groove 147 decreases stepwise every two pitches or every five pitches or more according to the specifications of the rotating machine.

  Further, the depth of the thread groove 147 may be formed so as to decrease stepwise not for every pitch but for every predetermined circumferential length of the thread groove 147. That is, the circumferential length of the screw groove 147 may reduce the cross-sectional area step by step for each half of the circumference, or every predetermined length of one or more rounds or every predetermined length of two or more rounds. The cross-sectional area may be reduced stepwise.

  In the non-contact annular seal 118 shown in FIG. 11, the screw groove 147 is formed in the rotating body 127, but the screw groove 147 may be provided on the inner surface of the fixed body 137 instead. Further, both the rotating body 127 and the fixed body 137 may be provided with a thread groove 147.

  The non-contact annular seal 118 shown in FIG. 11 is formed so that the depth of the thread groove 147 decreases step by step along the traveling direction of the thread groove 147 every predetermined length. However, the present invention is not limited thereto, and the width of the screw groove 147 is changed along the traveling direction of the screw groove 147 so that the cross-sectional area of the screw groove 147 gradually decreases from the high pressure side 155 toward the low pressure side 156. May be formed.

  The rotating body and fixed body of the non-contact annular seal shown in FIGS. 3 and 11 are, for example, metal materials such as SUS (stainless steel) material, SS (general structure rolled steel) material, NI-based alloy, and brass. It is formed. A composite material, a ceramic material, a resin material, or the like may be used depending on the required specifications. Further, the optimum thread groove shape (pitch, width, groove depth, etc.) of the thread groove depends on the conditions required for the non-contact annular seal, but may be any shape that can reduce fluid leakage, and is limited to a specific shape. Is not to be done.

  Further, in the non-contact annular seal of the present embodiment shown in FIGS. 3 and 11, the fixed body on the low pressure side or the high pressure side in which the thread groove is not formed is a smooth surface, and in the present embodiment shown in FIG. In the non-contact annular seal, the rotating body on the low-pressure side or the high-pressure side where the thread groove is not formed is a smooth surface. However, the surface on which the thread groove is not formed is not limited to this, and the parallel groove shown in FIG. Alternatively, it may be formed to have the damper structure shown in FIGS. 15 and 16.

  When the non-contact annular seal shown in FIGS. 3 and 11 is applied to the non-contact annular seals 41 and 43 shown in FIG. 2 and the high-pressure pump 1 shown in FIG. 1 is operated, the shaft seal characteristics are improved and the pumping performance is improved. Improved by several percent.

[Experimental Example 1]
When the non-contact annular seal 116 having the thread groove 146 formed on the rotating body 126 shown in FIG. 3 and the non-contact annular seal 117 having the thread groove 146 formed on the fixed body 136 shown in FIG. A leakage flow simulation was performed. The working fluid adopted as the simulation condition is water. The pressure difference between the high pressure side 155 and the low pressure side 156 was 0.6 MPa, and the rotational speed of the rotating body 126 was 3000 rpm. At this time, the number of thread grooves 146 is twelve. The cross-sectional area of the screw groove 146 at the beginning of the high-pressure side screw groove is A, the cross-sectional area is continuously reduced toward the low-pressure side, and the cross-sectional area B of the final screw groove 146 on the low-pressure side is zero. It is.

[Comparative Example 1]
As Comparative Example 1, the non-contact annular seal 114 in which the screw body 144 having a uniform sectional area A is formed in the rotating body 124 shown in FIG. 17 and the uniform sectional area A in the fixed body 134 shown in FIG. A liquid leakage flow simulation was performed when the non-contact annular seal 115 in which the thread groove 144 was formed was used. The working fluid adopted as the simulation condition is water. The pressure difference between the high pressure side and the low pressure side was 0.6 MPa, and the rotational speed of each rotating body was 3000 rpm. In addition, the number of threads of each screw groove 144 at this time is 12.

  FIG. 12 is a graph showing simulation results of Experimental Example 1 and Comparative Example 1. The vertical axis represents the leakage flow rate (× 10 −4 m 3 / s). The leakage amount of the non-contact annular seal 117 (the stationary thread groove seal of this embodiment) shown in FIG. 6 is about 4.7 × 10 −4 m 3 / s, and the non-contact annular seal 115 (prior art) shown in FIG. The leakage amount of the stationary thread groove seal was about 6.7 × 10 −4 m 3 / s. Therefore, the leakage amount of the stationary side thread groove seal of this example is about 70% of the leakage amount of the stationary side thread groove seal of the prior art.

  Further, the leakage amount of the non-contact annular seal 116 (the rotation-side thread groove seal of this embodiment) shown in FIG. 3 is about 4.5 × 10 −4 m 3 / s, and the non-contact annular seal 114 ( The leakage amount of the prior art rotating side thread groove seal was about 6.2 × 10 −4 m 3 / s. Therefore, the leakage amount of the rotation side thread groove seal of this embodiment was about 72% of the leakage amount of the conventional rotation side thread groove seal.

  Based on the simulation results shown in FIG. 12, the leakage amount of the non-contact annular seal of the present embodiment having the thread groove 145 in both the rotating body 126 and the fixed body 136 is the same for both the rotating body 124 and the fixed body 134. It is estimated that it is about 70% with respect to the leakage amount of the conventional non-contact annular seal having the thread groove 144 on the surface.

[Experiment 2]
A liquid leakage flow simulation was performed on the plurality of non-contact annular seals 117 in which the threaded grooves 146 having different numbers of threads were formed on the fixed body 136 shown in FIG. The working fluid adopted as the simulation condition is water. The pressure difference between the high pressure side 155 and the low pressure side 156 was 0.6 MPa, and the rotational speed of the rotating body 126 was 3000 rpm. Note that the number of thread grooves 146 included in each of the plurality of non-contact annular seals 117 is 1, 2, 4, 8, and 12. The cross-sectional area of the screw groove 146 at the beginning of the high-pressure side screw groove is A, the cross-sectional area is continuously reduced toward the low-pressure side, and the cross-sectional area B of the final screw groove 146 on the low-pressure side is zero. It is.

[Comparative Example 2]
As Comparative Example 2, a liquid leakage flow simulation was performed on a plurality of non-contact annular seals 115 in which screw grooves 144 having different numbers of threads were formed on the fixed body 134 shown in FIG. The working fluid adopted as the simulation condition is water. The pressure difference between the high pressure side and the low pressure side was 0.6 MPa, and the rotational speed of each rotating body was 3000 rpm. The number of thread grooves 144 that each of the plurality of non-contact annular seals 117 has is 1, 2, 4, 8, and 12. Further, the screw groove 144 has a uniform cross-sectional area A.

  FIG. 13 is a graph showing simulation results of Experimental Example 2 and Comparative Example 2. The vertical axis represents the leakage amount (m3 / s). In FIG. 13, the amount of leakage reduction due to the thread groove pumping effect (shown as “thread groove pumping effect” in the figure) and the amount of fluid leakage passing through the thread groove as a flow path due to the differential pressure (in the figure, “ The amount of leakage in the thread groove ”and the total leakage amount of the entire non-contacting annular seal (shown as“ seal leakage amount ”in the figure) are shown for each number of threads. The amount of leakage reduction due to the thread groove pumping effect (hereinafter referred to as leakage reduction amount) indicates the amount of liquid movement opposite to the amount of leakage in the thread groove due to differential pressure (hereinafter referred to as leakage amount in the thread groove). It is represented by The total leakage amount of the entire non-contact annular seal (hereinafter referred to as “seal leakage amount”) includes the leakage amount in portions other than the screw groove in addition to the sum of the leakage reduction amount and the leakage amount in the screw groove.

  As shown in the figure, it can be seen that the amount of seal leakage in Experimental Example 2 tends to be smaller when the number of thread grooves is larger. On the other hand, it can be seen that the seal leakage amount of Comparative Example 2 tends to be larger as the number of screws is larger. That is, when the number of thread grooves is 1 and 2, the difference between the seal leakage amount of Experimental Example 2 and the seal leakage amount of Comparative Example 2 is slight, but the number of thread grooves is 4 or more. In this case, the seal leakage amount of Experimental Example 2 is much smaller than the seal leakage amount of Comparative Example 2.

  Further, in both cases of Experimental Example 2 and Comparative Example 2, the amount of leakage reduction increases almost similarly as the number of thread grooves increases (that is, the amount of leakage decreases).

  On the other hand, in Experimental Example 2, even if the number of threads in the thread groove increases, the amount of leakage in the thread groove of one or two threads and the amount of leakage in the thread groove of four or more threads are as follows. You can see that there is almost no change. On the other hand, it can be seen that the leakage amount in the thread groove in Comparative Example 2 significantly increases as the number of thread grooves increases.

  From the above results, in Comparative Example 2, when the number of thread grooves is increased, the lead angle of the thread groove is increased and the leakage reduction amount is increased, but the leakage amount in the thread groove is further increased. It can be seen that the amount of seal leakage cannot be reduced. On the other hand, in Experimental Example 2, an increase in the amount of leakage in the thread groove, which has been caused by increasing the number of thread grooves, can be suppressed. For this reason, in Experimental Example 2, the increase in the amount of leakage reduction caused by increasing the number of thread grooves (increasing the lead angle of the thread groove) exceeds the increase in the amount of leakage in the thread groove, resulting in sealing. The amount of leakage can be reduced.

  From the results shown in the figure, it can be seen that when the number of thread grooves is 4 or more, the difference between the seal leakage amount of Comparative Example 2 and the seal leakage amount of Experimental Example 2 is very large. The reason for this is that when the number of thread grooves is 4 or more, in the non-contact annular seal of Experimental Example 2, the pumping effect of the thread groove is greatly increased and the increase in the leakage amount in the thread groove is effectively suppressed. Because it is possible. Therefore, the effect is remarkable when the thread groove concerning this embodiment is four or more. In other words, when the number of thread grooves is one or two, Experimental Example 2 is not so effective as Comparative Example 2.

  From the above simulation results, it was found that the shaft seal characteristic of the non-contact annular seal according to the present example was better than the shaft seal characteristic of the conventional non-contact annular seal. In addition, the shaft seal characteristics of the non-contact annular seal according to this example are extremely good compared to the shaft seal characteristics of the conventional non-contact annular seal when the number of thread grooves is 4 or more. It was.

  In Experimental Example 2 and Comparative Example 2, a non-contact annular seal in which a thread groove is formed in a fixed body is used. However, a non-contact annular seal or a thread groove in which a thread groove is formed in a rotating body is used as a rotating body and It is presumed that almost the same result is obtained when a non-contact annular seal formed on the fixed body is used.

  The present invention can be used for a non-contact annular seal of a rotary machine such as a pump.

DESCRIPTION OF SYMBOLS 1 ... High pressure pump 11 ... Main shaft 13 ... Coupling 21a ... Impeller 23 ... Suction port 25 ... Discharge port 31 ... Casing 31a ... Casing 31b ... Casing 33 ... Suction port 35a ... 1st flow path 35b ... 2nd flow path 36 ... Low pressure side 37 ... Discharge port 38 ... High pressure side 41 ... Non-contact annular seal 41a ... Rotating body 41b ... Fixed body 45a ... Bearing 45b ... Bearing 114 ... Non-contact annular seal 115 ... Non-contact annular seal 116 ... Non-contact annular seal 117 ... Non-contact annular seal 118 ... Non-contact annular seal 124 ... Rotating body 126 ... Rotating body 127 ... Rotating body 134 ... Fixed body 136 ... Fixed body 137 ... Fixed body 144 ... Groove 145 ... Groove 146 ... Groove 147 ... Groove 151 ... Rotating shaft 155 ... High pressure side 156 ... Low pressure side 157 ... Mountain 157a ... Land part 158 ... Cross sectional area X ... Counter part Y ... Counter part A ... Arrow G ... Gap W ... Groove width a0 ... Width a1 ... Width R0 ... Radius R1 ... Radius

Claims (8)

A rotating body provided in a rotating part of the rotating machine;
A fixed body provided in a fixed portion of the rotating machine,
A non-contact annular seal configured to seal a fluid flowing through a gap between the rotating body and the fixed body,
A screw groove provided on at least one of the surface of the rotating body and the surface of the fixed body forming the gap;
The screw groove has a region where the cross-sectional area of the screw groove on the high-pressure side is larger than the cross-sectional area of the screw groove on the low-pressure side,
The number of threads is 4 or more,
Non-contact annular seal. A non-contact annular seal according to claim 1,
The region has a reduced region formed so that the cross-sectional area of the thread groove continuously decreases from the high pressure side toward the low pressure side,
Non-contact annular seal. A non-contact annular seal according to claim 2,
The reduced region has a region formed such that the depth of the thread groove continuously decreases from the high pressure side toward the low pressure side.
Non-contact annular seal. A non-contact annular seal according to claim 2 or 3,
The reduced region has a region formed such that the width of the thread groove continuously decreases from the high pressure side toward the low pressure side.
Non-contact annular seal. A non-contact annular seal according to claims 2 to 4,
The reduced region has a region formed so that the ratio of the depth and width of the screw groove is constant.
Non-contact annular seal. A non-contact annular seal according to claim 1,
The region has a reduced region formed so that a cross-sectional area gradually decreases from the high pressure side to the low pressure side.
Non-contact annular seal. A non-contact annular seal according to claim 6,
The reduced region has a region formed such that the depth of the thread groove decreases stepwise from the high pressure side toward the low pressure side.
Non-contact annular seal. An electric motor,
A main shaft connected to the electric motor and configured to be rotatable;
An impeller fitted to the main shaft and configured to be rotatable with the main shaft;
A casing for housing the impeller,
A bearing attached to the casing and rotatably supporting the main shaft;
The main shaft has a rotating part,
The casing has a fixed portion;
The rotating machine and the fixed part are rotating machines having a non-contact annular seal according to any one of claims 1 to 7.

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