JPH0794840B2 - Centrifugal rotating machine - Google Patents

Description

The present invention relates to a centrifugal rotary machine such as a pump or a compressor.

(Prior Art) In a conventional centrifugal pump, for example, a rotating body having an impeller fixed to a shaft is housed in a casing, and a diffuser is arranged on the outer periphery of the impeller concentrically with the impeller. Then, by bringing the wear rings provided on the impeller and the casing close to each other, the suction side and the discharge side of the impeller are sealed in a non-contact state, while the portion where the shaft penetrates the casing has a gland packing and a mechanical seal. The shaft is sealed with a seal or the like. Also,
Both ends of the shaft are supported by bearings fixed to the casing.

In this centrifugal pump, the weight of the rotating body and the load such as the fluid force acting on the rotating body are supported by the bearing portion and the non-contact seal portion. In the bearing portion, as shown in FIG. 5, the rotating body 21 is rotated by the film pressure of the oil film 23 of the wedge-shaped lubricant formed in the gap between the rotating body 21 and the bearing 22.
It is supported eccentrically from the center of e _b . On the other hand, also in the non-contact seal part, the rotating body is supported in the same manner as the bearing part by the film pressure of the handling fluid such as water in the casing.

The supporting force of the film thickness, as shown in FIG. 6, the eccentricity e _b of the rotary member 21 is parabolic manner increases if increased. In other words, if the applied load F _b acting on the rotating body 21 increases, the eccentricity e _b thereof also increases. Incidentally, in FIG. 6, c is up to the radius clearance of the bearing.

(Problems to be Solved by the Invention) In centrifugal pumps that have been speeded up in recent years, the fluid to be handled is a non-contact seal part, that is, an impeller side wear ring due to an increase in the differential pressure between the suction side and the discharge side in the casing accompanying the speeding up. And leaks between the casing-side wear ring and flows in the axial direction, and a force to lift the rotating body acts via the impeller. As a result, the force for supporting the rotating body in the non-contact portion increases, and conversely, the load load on the bearing portion, that is, the bearing load decreases. Therefore, in the bearing portion, the amount of eccentricity of the shaft becomes small and the shaft becomes unstable. Therefore, the excitation force of the fluid acting on the impeller may cause low-order vibration that is not synchronized with the rotational speed of the shaft. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a centrifugal rotating machine in which a sufficient load acts on a bearing portion and vibration is unlikely to occur.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a diffuser having a plurality of stages, in which a diffuser center in any stage is horizontal or higher than the impeller center in the stage. It is eccentric in the direction.

(Operation) As a result of the eccentricity of the diffuser with respect to the impeller, non-uniform pressure is generated around the impeller, and radial thrust acts on the impeller in a direction opposite to the eccentric direction of the diffuser, that is, in a horizontal direction or a lower direction. As a result of this radial thrust being applied to the rotating body via the impeller, the bearing load increases, the eccentric amount of the shaft in the bearing increases, the supporting rigidity of the lubricating oil increases, and vibration of the shaft is suppressed. To be

(Example) Next, one example of the present invention will be described with reference to the drawings.

FIG. 3 shows a 6-stage centrifugal pump according to the present invention. In the figure, a suction side casing 1 and a discharge side casing 2
The casing including the body casing 3 divided into five parts is integrated by stay bolts 4, 4. In this casing, a rotating body in which an impeller 6 having six stages is fixed to a shaft 5 is housed. The wear ring 7 provided on the outer circumference of the inlet of each impeller 6
And the wear ring 8 provided on the casings 1 and 3 are close to each other, so that the suction side and the discharge side of each impeller 6 are sealed in a non-contact state. A diffuser 9 is provided on the outer circumference of each impeller 6.

On the other hand, gland packings 12 and 13 are provided at the portions where the shaft 5 penetrates the casing covers 10 and 11 provided on the suction side casing 1 and the discharge side casing 2, respectively. Both ends of the shaft 5 are supported by journal bearings 16 and 17 fixed to brackets 14 and 15 extending by the suction side and discharge side casings 1 and 2, and
One end on the discharge side is supported by a thrust bearing 18.

Of the diffusers, the third stage diffuser 9a is
As shown in FIG. 1, it is provided eccentric by e _{i with} respect to the center of the impeller 6 in the upward direction. Diffusers 9 other than the third-stage diffuser 9a are provided concentrically with the impeller 6 as shown in FIG.

To make the diffuser 9a eccentric, the diffuser 9a
The blade may be provided at a position displaced from the mounting center by the amount of eccentricity e _i in advance during manufacturing. Alternatively, the inlet side end portions of the vanes located in the eccentric direction of the diffuser 9a manufactured concentrically may be appropriately shaved off by a grinder process or the like, or the diffuser 9a may be shifted and incorporated in the casing 3.

In the centrifugal pump according to this embodiment, the suction side casing 1
The water sucked into the inside is increased in pressure with the rotation of the first-stage impeller 6, is discharged at high speed around the impeller 6, is decelerated while passing through the diffuser 9, and is depressurized in the second stage under high pressure. It is sucked into the impeller 6. In the same manner, the water whose pressure has been increased by the impellers 6 at each stage is discharged from the discharge side casing 2.

As shown in FIG. 1, the third-stage diffuser 9a is eccentric to the impeller 6 upward by e _i , and the impeller 6
Since the gap between the diffuser 9a and the diffuser 9a is not uniform, a pressure difference is generated above and below the impeller 6, and the radial thrust _Fr acts on the impeller 6 in the direction opposite to the eccentric direction of the diffuser 9a, that is, downward.

FIG. 4 shows the relationship between the radial thrust force F _r and the pump flow rate Q / Q _n , where e _o is an arbitrary eccentric amount and Q _n is the design flow rate. As shown in the figure, the radial thrust F _r is the eccentricity e _i
Becomes larger, and the smaller the pump flow rate, the larger.

This radial thrust F _r is transmitted to the shaft 5 via the impeller 6.
Join in. Thus, the bearing load F _b acting on the journal bearing 16 and 17, as shown in FIG. 6, increased by a force corresponding to the radial thrust F _r from the point A to the point B, the eccentricity e _b of the shaft 5 is growing. Then, as the eccentricity e _b increases, the supporting rigidity K ₁ = ΔF _b / Δe _{b of} the journal bearing becomes larger than the supporting rigidity K _{2 at the} point A where the radial thrust F _r does not act, and the shaft 5 becomes stable. Supported by the state. Therefore, the shaft 5 based on the excitation force acting on the impeller 6
Vibration is suppressed.

In the above embodiment, the eccentric direction with respect to impeller 6 of the diffuser 9a was directly above, by the obliquely upward or horizontal direction, the vertical component of force by changing the direction of action of the radial thrust F _r The support rigidity of the journal bearing can be adjusted by adjusting the size. Also, the first
By eccentricizing only the diffusers 9 in the stages or only the diffusers 9 in the final 6 stages, it is possible to increase the axial rigidity of the journal bearing in which vibration is likely to occur.

(Effects of the Invention) As is apparent from the above description, according to the present invention, the support rigidity of the bearing portion can be increased by eccentricizing the diffuser with respect to the impeller, so that the support state of the rotating body is stable, Vibration is less likely to occur, and it is safe.

[Brief description of drawings]

1 is a sectional view of an eccentric diffuser, FIG. 2 is a sectional view of a diffuser without eccentricity, FIG. 3 is a sectional view of a centrifugal pump according to the present invention, and FIG. 4 shows a relation between radial thrust and pump flow rate. 5 and 5 are views showing a shaft support state of a journal bearing, and FIG. 6 is a view showing a relationship between a load applied to a bearing portion or a non-contact seal portion and an eccentric amount. 6 ... Impeller, 9,9a ... Diffuser.

Claims (1)

[Claims] 1. A centrifugal rotating machine, characterized in that, of a diffuser having a plurality of stages, a center of the diffuser in any stage is eccentric in a direction horizontal or above a center of an impeller in the stage.