JP2011111923A - Method for estimating life of centrifugal compressor impeller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately recognize the creep strain of an impeller of a centrifugal compressor used for a supercharger and the like by a simple method and accurately estimate the life of the impeller thereby. <P>SOLUTION: A labyrinth packing 30 is disposed between a back surface 28 of the impeller 12 of the centrifugal compressor 10 and a bearing housing 20 and prevents part of compressed air from flowing in a seal space s through a radial clearance C1. An opposing surface 36 opposing to an outer circumference surface 34 of the impeller 12 right in front is disposed at an upper end part 31 of the labyrinth packing 30. Creep strain of the impeller 12 is measured by measuring the radial clearance C1 by a vernier caliper, a clearance gauge or the like. Creep characteristics causing creep fracture is recognized beforehand from creep strain of the impeller 12. Operation limit timing of the impeller 12 is determined from the creep strain of the impeller 12 and the creep characteristics. A lower limit value Cm of the radial clearance C1 is set and it is defined as impeller use limit timing when the radial clearance C1 reaches the lower limit value Cm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a life prediction method capable of accurately predicting the life of an impeller of a centrifugal compressor used for a supercharger of an internal combustion engine such as a marine diesel engine by a simple means.

In recent years, centrifugal compressors used for superchargers of marine diesel engines are required to have higher pressure ratios (for example, 4 to 5 times) and higher efficiency. In order to satisfy these conflicting requirements, generally, the rotational peripheral speed of the impeller is increased.
On the other hand, an impeller having a high rotational peripheral speed generates high stress inside due to centrifugal force acting on itself. Furthermore, the compressed air becomes high temperature, and a part of the high temperature air becomes a leakage flow and goes around the rear surface of the impeller from the gap with the housing, and overheats the impeller from the rear surface. Since the compressed air has a higher temperature as the pressure ratio becomes higher, the impeller exposed to high stress and high temperature has a risk of creep destruction.

  Patent Document 1 discloses a centrifugal compressor applied to an engine supercharger or the like. Hereinafter, taking this centrifugal compressor as an example, the configuration of the centrifugal compressor for the supercharger will be described. In FIG. 5, the centrifugal compressor 100 has an impeller 104 fixed to the outer peripheral surface of a rotor shaft 102, and a plurality of blades 105 projecting radially on a hub surface 14 b of the impeller 104. The outer peripheral side of the impeller 104 is hermetically sealed with a housing 106 of the compression portion and a bearing housing 108 except for the flow path of the compressed air. A labyrinth packing 110 is provided on the back surface 104a of the impeller 104 and the wall surface of the bearing housing 108 facing the back surface, and seals the seal space s between the back surface of the impeller and the bearing housing 108.

  The seal space s communicates with the outside through the air discharge hole 112, and a small amount of leaked air entering the seal space s is released to the outside through the labyrinth packing 110. A thrust collar 114 is fixed to the rotor shaft 102, and a main thrust bearing 116 and an anti-thrust bearing 118 are provided on the bearing housing 108 with the thrust collar 114 interposed therebetween. The rotor shaft 102 is supported in the axial direction by the main thrust bearing 116 and the anti-thrust bearing 118.

When the impeller 104 rotates, the compressed air flows into the flow path formed between the blades 105 from the direction of the arrow a and is accelerated by the blades 105. The compressed air accelerated by the blade 105 is decelerated in the diffuser region d, and the static pressure is increased and pressurized.
Compressed air reaches a high temperature of 200 to 250 ° C. at the outlet of the impeller 104, and a part of the compressed air passes through the labyrinth packing 110 to become a leakage flow l and flows into the seal space s. This leakage flow l overheats the impeller 104 from the back side.

  Usually, an aluminum alloy or the like is used as the material of the impeller 104. When the impeller 104 is overheated from the back side, the strength decreases, and creep distortion occurs in an atmosphere of high stress and high temperature. If this creep strain is left unattended, there is a risk of creep rupture.

  In Patent Document 1, in order to prevent overheating of the impeller 104 due to the leakage flow l, an annular space 120 is provided in the labyrinth packing 110, and an air passage 122 communicating with the annular space 120 is provided in the bearing housing 108. Then, low-temperature air is introduced into the seal space s through the air passage 122 and the annular space 120 from the outside to prevent the impeller 104 from being overheated.

  Patent Document 2 also discloses means for preventing the impeller 104 from being overheated by the leakage flow l and preventing the impeller 104 from being destroyed by creep. In this means, an annular deflector protrudes from the back surface 104a of the impeller 104, and the leakage flow l that has entered the seal space s is applied to the annular deflector so that the flow path of the leakage flow l is deflected and separated from the back surface 104a. Thus, overheating of the impeller 104 is prevented.

JP-A-4-365997 JP 2008-25576 A

  Even with the means disclosed in Patent Document 1 or Patent Document 2, it is difficult to eliminate the creep distortion of the impeller. Although creep strain develops from places where load stress and temperature are locally severe, it is difficult to find out the occurrence of local creep strain. The creep distortion in the impeller gradually increases the outer diameter of the impeller due to the centrifugal force applied to the impeller. The strain changes abruptly just before finally reaching a large break, but before that, the growth of the strain is slight, so in order to grasp the strain change, a small strain change is detected. There is a need to.

  Thus, in order to operate the centrifugal compressor safely, it is possible to detect the extension of the impeller creep, predict the impeller life, and replace the impeller before a large-scale breakage occurs. It is necessary to take measures. For this purpose, there is also a method of setting an operation limit time of the impeller and exchanging before the time is exceeded. However, since the actual creep extension state of the impeller depends on the operating load of the engine and the supercharger, the set operation limit time does not match the actual creep extension state. Therefore, since the impeller is replaced at a stage where continuous use is sufficiently possible, there is a lot of waste. In addition, frequent checking of the impeller will increase the burden on the operation manager.

  In view of the problems of the prior art, the present invention accurately grasps the creep distortion of the impeller of the centrifugal compressor by a simple method, thereby accurately predicting the life of the impeller and before creep breaking. An object is to enable replacement and to eliminate unnecessary replacement of the impeller.

In order to achieve this object, the impeller life evaluation method of the centrifugal compressor of the present invention is:
In the method for predicting the life of a centrifugal compressor impeller, which detects the creep distortion of the impeller mounted on the rotary shaft of the centrifugal compressor and predicts the life of the impeller from the detected value of the creep distortion.
A pre-process for grasping creep characteristics from creep distortion of the impeller at high temperature during operation of the centrifugal compressor to creep fracture;
A gap grasping step for grasping in advance a radial gap between the outer peripheral surface of the impeller and the wall surface of the stationary part facing the outer peripheral surface of the impeller before operation of the centrifugal compressor;
A creep strain measuring step of measuring the radial gap after operation of the centrifugal compressor, and obtaining a creep strain of the impeller from a difference between the radial gap and the radial gap measured in the gap grasping step;
A life prediction step of comparing the creep strain with the creep characteristics to determine the impeller operating limit time.

  In a centrifugal compressor used for a supercharger or the like, air of 30 to 40 ° C. is usually supplied to an impeller, and the compressed air is compressed by the impeller to increase the temperature. Therefore, the outer peripheral end side becomes higher in temperature, and the region close to the back side becomes higher due to leakage flow. Accordingly, the creep distortion on the outer peripheral end side increases. When the creep distortion is extended, the outer diameter of the impeller is increased, so that the radial gap between the outer peripheral surface of the impeller and the stationary portion wall surface facing the outer peripheral surface is reduced.

  In the method of the present invention, since the radial gap between the outer peripheral surface of the impeller and the stationary part wall surface facing this outer peripheral surface is measured, even if the creep distortion is minute, it can be measured with high sensitivity. By measuring the radial clearance periodically, it is possible to grasp the progress of creep distortion of the impeller, so it is not necessary to remove the impeller or collect a sample from the impeller, and to accurately replace the impeller. Can be judged. Therefore, the impeller can be surely replaced before the impeller creeps, and the impeller can be used to the operating limit.

  For example, four measurement points may be measured around the impeller, and an average of these measurement values may be taken. The measurement of the outer diameter of the impeller may be performed when the centrifugal compressor is stopped and cooled so as not to be affected by the centrifugal force applied to the impeller and the thermal expansion of the impeller.

  In the method of the present invention, it is preferable to set a lower limit value of the radial clearance and set the lower limit value as the impeller usage limit value. As a result, the radial clearance is periodically measured, and if the measured value is smaller than the lower limit value or is expected to be smaller than the lower limit value by the next measurement, the impeller is Try to exchange. As a result, it is possible to accurately grasp when the impeller needs to be replaced.

In the method of the present invention, the radial gap may be a radial gap between the outer peripheral surface of the impeller and a protrusion formed on the stationary part wall surface so as to protrude toward the outer peripheral surface of the impeller.
As described above, since the protrusion is provided on the wall surface of the stationary part directly facing the outer peripheral surface of the impeller, the gap between the outer peripheral surface of the impeller and the wall surface of the stationary part can be minimized. Leakage flow entering the space can be minimized.

  In this case, a lead wire is interposed between the outer peripheral surface of the impeller and the protrusion before the operation of the centrifugal compressor, and the lead wire formed by the creep strain of the impeller after the centrifugal compressor is operated in the creep strain measurement process. The radial gap may be obtained from the amount of the dent. Thereby, the creep distortion amount of the impeller can be easily and accurately measured from the dent amount of the lead wire.

  In the method of the present invention, a labyrinth packing is provided between the rear surface of the impeller and the stationary portion wall surface facing the rear surface, and a radial clearance is provided between the rear surface of the impeller and the convex piece of the labyrinth packing fixed to the stationary portion wall surface. It is good that it is a radial direction gap.

In a centrifugal compressor in which a labyrinth packing is provided between the rear surface of the impeller and the stationary part wall facing the rear surface, the life of the impeller, the outer diameter of the impeller, and The relationship with the radial clearance between the convex pieces of the labyrinth packing is grasped.
After the operation of the centrifugal compressor, the life of the impeller can be determined by measuring the radial clearance.
Since the gap between the convex pieces of the labyrinth packing is originally very small, it is possible to grasp a small distortion of the impeller that occurs in the early stage of creep by grasping the change with time.

  In this case, the radial gap may be the average value of the radial gaps between the convex pieces of the labyrinth packing, but if possible, the radial gap on the outer peripheral side where the radial distortion of the impeller appears greatly. It is good to measure.

According to the method of the present invention, in the method for predicting the lifetime of a centrifugal compressor, the creep distortion of the impeller mounted on the rotary shaft of the centrifugal compressor is detected and the life of the impeller is predicted from the detected value of the creep distortion. , A pre-process for grasping creep characteristics from creep distortion to creep fracture of the impeller at high temperature during operation of the centrifugal compressor, and stationary against the outer peripheral surface of the impeller and the outer peripheral surface of the impeller before the centrifugal compressor is operated A gap grasping process for grasping in advance the radial gap with the wall of the section, and measuring the radial gap after the operation of the centrifugal compressor, and the difference between the radial gap and the radial gap measured in the gap grasping process The creep strain measurement step for obtaining the creep strain of the impeller and the life prediction step for obtaining the operation limit time of the impeller by comparing the creep strain with the creep characteristics. Even if it is small, it can be measured with high sensitivity, and by measuring the radial clearance periodically, it is possible to grasp the progress of creep distortion of the impeller, so it is necessary to remove the impeller and collect samples from the impeller Instead, it is possible to accurately determine when to replace the impeller.
Therefore, the impeller can be surely replaced before the impeller is creep-destructed, and the impeller can be used to the operating limit.

It is a front view sectional view concerning a 1st embodiment which applied the method of the present invention to a centrifugal compressor used for a supercharger for a marine diesel engine. It is front view sectional drawing concerning 2nd Embodiment which applied this invention method to the centrifugal compressor used for the supercharger for marine diesel engines. FIG. 3 is a partially enlarged view of FIG. 2. It is front view sectional drawing concerning 3rd Embodiment which applied this invention method to the centrifugal compressor used for the supercharger for marine diesel engines. It is front sectional drawing of the conventional centrifugal compressor used for the supercharger for marine diesel engines.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

(Embodiment 1)
A first embodiment in which the method of the present invention is applied to a centrifugal compressor used in a turbocharger for a marine diesel engine will be described with reference to FIG. FIG. 1 shows an impeller 12 of the centrifugal compressor 10 and its peripheral region. In FIG. 1, a plurality of blades 16 are fixed radially to the hub surface 14 of the impeller 12. The outer peripheral side of the impeller 12 is hermetically sealed with the housing 18 of the compression portion and the bearing housing 20.

  Above the housing 18, a partition wall 22 that forms a diffuser region d, and a housing 24 in which the partition wall 22 is mounted with bolts 25 are provided. A sealing O-ring 26 is interposed between the housing 18 and the housing 24. A labyrinth packing 30 is provided facing the back surface 28 of the impeller 12. The labyrinth packing 30 is fixed to the wall surface of the bearing housing 20 with bolts 32. The labyrinth packing 30 and the impeller back surface 28 are provided with a plurality of convex pieces 42 and 44. These convex pieces 42 and 44 are alternately arranged to form a labyrinth and seal the seal space s.

When the impeller 12 rotates, the compressed air flows into the flow path formed between the blades 16 from the direction of the arrow a and is accelerated by the blades 16. The compressed air accelerated by the blade 16 is decelerated in the diffuser region d, and the static pressure is increased and pressurized.
The compressed air at the outlet of the impeller 12 becomes as high as 200 to 250 ° C., part of which becomes a leakage flow l and flows into the seal space s through the labyrinth packing 30. This leakage flow l overheats the impeller 104 from the back side.

In the present embodiment, the outer peripheral surface 34 of the impeller 12 and the facing surface 36 provided on the upper end portion 31 of the labyrinth packing 30 are opposed to each other, and the diameter between the impeller outer peripheral surface 34 and the facing surface 36 is set. direction gap C ₁ is configured such that the following dimensions 1 mm. When the creep of the impeller 12 is extended, since the outer diameter of the impeller 12 increases, the radial clearance C ₁ is reduced. Therefore, the relationship between the creep characteristics of the impeller 12 and the outer diameter of the impeller 12 is grasped in advance by a method such as creep analysis, and the limit value of the outer diameter of the impeller corresponding to the limit life of the impeller 12 is set. deep. This limit value, to set the lower limit C _m of radial clearance C _1.

During operation of the centrifugal compressor 10, periodically measure the radial clearance C _1. Its measuring method is, for example, to measure the radial clearance C ₂ with calipers or feeler gauge. If the radial clearance C ₁ is either smaller than the lower limit value C _m, or radial clearance C ₁ is expected that less than the lower limit value C _m before the next inspection time, to replace the impeller 12 Like that.
The measurement of the outer diameter of the impeller is performed at normal temperature (20 to 30 ° C.) when the operation of the centrifugal compressor 10 is stopped and cooled so as not to be affected by the centrifugal force and thermal expansion caused by the rotation of the impeller 12. ). Since creep strain remains as permanent strain, accurate measurement results can be obtained by measuring at room temperature. Moreover, the measurement method employ | adopts the method of measuring four places around the impeller 12 and taking the average value of these measured values, for example.

According to this embodiment, the radial clearance C ₁ by periodically measuring, can grasp the extension conditions of creep strain of the impeller 28. Accordingly, it is possible to determine the creep destruction time of the impeller 12 without requiring removal of the impeller 12 or sampling from the impeller 12. Therefore, it is possible to accurately determine the replacement time of the impeller 12. Accordingly, the impeller 12 can be surely replaced before the impeller 12 creep-breaks, and the impeller 12 can be used to near the creep rupture limit.

(Embodiment 2)
Next, a second embodiment of the method of the present invention will be described with reference to FIG. The present embodiment is an example applied to a centrifugal compressor used in a turbocharger for a marine diesel engine, as in the first embodiment. In the present embodiment, in the upper end portion 31 of the labyrinth packing 30 that faces the impeller outer peripheral surface 34, an annular portion that protrudes toward the impeller outer peripheral surface 34 at the inlet portion facing the diffuser region d of the facing surface 36. A protrusion 40 is provided. Other configurations of the centrifugal compressor 10 are the same as those in the first embodiment.

In the present embodiment, by measuring the radial clearance C ₂ between the impeller outer peripheral surface 34 and the protrusion 40, it can grasp the creep extended state of the impeller 12. The measurement method, it is also possible to measure the radial clearance C ₂ with calipers and feeler gauge, as another measurement method, as shown in FIG. 3 and fixes the Namarisen member 46 to the projections 40 Like that. Since the lead wire 46 is recessed due to the creep distortion (34 → 34 ′) of the impeller 12, the creep distortion of the impeller 12 can be accurately measured by measuring the amount of the depression δ.
Then, it is determined as in the first embodiment, to set the lower limit value C _m in the radial clearance C ₂ corresponding to the limit the life of the impeller 12, the replacement timing of the impeller 12 relative to the lower limit value Cm.

According to this embodiment, by providing the projections 40 on the opposing surface 36 of the upper end portion 31 of the labyrinth seal 30 may take a radial clearance C ₂ smaller than the radial clearance C ₁ of the first embodiment . Since Therefore, it is possible to reduce the leakage flow l leaking into the seal space s from the radial clearance C ₂ through the labyrinth packing 30, thereby reducing the degree of superheating of the impeller 12.
Moreover, the creep distortion of the impeller 12 can be easily and accurately measured by fixing the lead wire to the protrusion 40 and measuring the dent amount δ of the lead wire 46.

(Embodiment 3)
Next, a third embodiment of the method of the present invention will be described with reference to FIG. The configuration of this embodiment is the same as that of the first embodiment. In this embodiment, grasp the protruding piece 42 of the labyrinth packing 30, to measure the radial clearance C ₃ between the convex pieces 44 provided on the back 28 of the impeller 12, the creep compliance status of the impeller 12 To do.
In the present embodiment, it is difficult to measure the radial clearance C ₃ while wearing the impeller 12 to the rotor shaft. Therefore, in the measurement method, the impeller 12 is once removed from the rotor shaft, and the lead wire 46 is fixed to the convex piece 42 of the labyrinth packing 30 as shown in FIG. Next, the impeller 12 is mounted on the rotor shaft, and the centrifugal compressor 10 is operated. After the operation of the centrifugal compressor 10, the creep distortion of the impeller 12 can be measured by measuring the dent amount δ of the lead wire 46.

The measurement of the radial clearance C ₃ is a radial gap C ₃ convex pieces of each stage of the labyrinth packing 30 is measured and may calculate the average value of those measurement values. However, if possible, because creep strain appears larger on the outer peripheral side of the impeller 12, it may measure the radial clearance C ₃ convex pieces located as much as possible the outer peripheral side.

Since the gap of the projecting pieces of the labyrinth packing 30 is originally very small dimensions, according to this embodiment, by measuring the radial clearance C _3, also a small distortion generated creep initial impeller 12 Accurate measurement.
Each of the above embodiments is an example of a centrifugal compressor applied to a turbocharger for a marine diesel engine. However, the present invention is not limited to these applications, and is applied to other internal combustion engines and the like. It can also be applied to a compressor.

  According to the present invention, the life of the impeller of the centrifugal compressor can be accurately grasped by simple means, the creep destruction can be avoided, and the impeller can be used to the maximum.

DESCRIPTION OF SYMBOLS 10 Centrifugal compressor 12 Impeller 14 Hub surface 16 Blade 18, 24 Housing 20 Bearing housing 22 Bulkhead 25, 32 Bolt 26 Sealing O-ring 28 Impeller back surface 30 Labyrinth packing 34 Impeller outer peripheral surface 36 Opposing surface 40 Protruding part 42, 44 convex piece 46 lead wire C ₁ , C ₂ , C ₃ radial clearance C _m lower limit d diffuser region l leakage flow s seal space δ dent amount

Claims (6)

In the method for predicting the life of a centrifugal compressor impeller, which detects the creep distortion of the impeller mounted on the rotary shaft of the centrifugal compressor and predicts the life of the impeller from the detected value of the creep distortion.
A pre-process for grasping creep characteristics from creep distortion of the impeller at high temperature during operation of the centrifugal compressor to creep fracture;
A gap grasping step for grasping in advance a radial gap between the outer peripheral surface of the impeller and the wall surface of the stationary part facing the outer peripheral surface of the impeller before operation of the centrifugal compressor;
A creep strain measuring step of measuring the radial gap after operation of the centrifugal compressor, and obtaining a creep strain of the impeller from a difference between the radial gap and the radial gap measured in the gap grasping step;
A method for predicting the life of a centrifugal compressor impeller, comprising: a life prediction step for obtaining an operation limit time of the impeller by comparing the creep strain with the creep characteristics.   The method for predicting the lifetime of a centrifugal compressor impeller according to claim 1, wherein a lower limit value of the radial gap is set, and the lower limit value is set as an impeller use limit value.   The radial direction gap is a radial direction gap between an outer peripheral surface of an impeller and a protruding portion formed to protrude toward the outer peripheral surface side of the impeller on the stationary part wall surface. The lifetime prediction method of the described centrifugal compressor impeller.   Before the operation of the centrifugal compressor, a lead wire is interposed between the outer peripheral surface of the impeller and the protrusion, and in the creep strain measurement step, the lead wire formed by the creep strain of the impeller after the centrifugal compressor is operated. 4. The method for predicting the lifetime of a centrifugal compressor impeller according to claim 3, wherein the radial clearance is obtained from a dent amount.   A labyrinth packing is provided between the rear face of the impeller and the stationary part wall surface facing the rear face, and the radial gap is a radial gap between the convex pieces of the labyrinth packing fixed to the rear face of the impeller and the stationary part wall surface. The method for predicting the lifetime of a centrifugal compressor impeller according to claim 1 or 2, wherein the method is a method for predicting the lifetime of the centrifugal compressor impeller.   A lead wire is interposed between the convex pieces, and the radial clearance is obtained from the dent amount of the lead wire formed by the creep strain of the impeller after the centrifugal compressor is operated in the creep strain measurement step. The lifetime prediction method of the centrifugal compressor impeller of Claim 5 characterized by these.

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