JPS62197681A - Screw pump - Google Patents

Abstract

PURPOSE:To prevent the generation of cavitation by installing a tapered screw on the inlet side of the screw rotors of a screw pump, thus preventing a jet stream from being generated from a gap between the screw rotors and a sleeve. CONSTITUTION:The fluid introduced from a suction flange 1 side is sent under pressure to an outlet flange 5 side by each revolution of a main screw rotor 2 and a trailing screw rotor 3. Between the main and trailing screw rotors 2 and 3 and a casing 4, a minute gap 8 is formed by the existence of screw tapered part (a), and said gap 8 is set so as to increase on the inlet flange 1 side in comparison with on the outlet flange 5 side. Therefore, the pressure Pi at a gap outlet edge 9 increases to suppress a jet stream A generated between the screw rotors 2 and 3 and the casing 4, and generation of cavitation is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to the structure of a screw pump, and in particular, a screw rotor structure and a screw rotor support structure suitable for preventing cavitation, reducing axial thrust, and reducing radial thrust. Regarding.

[Conventional technology]

Devices such as conventional screw pumps are known.

1) The device described in Japanese Utility Model Publication No. 44-25107 had a structure in which the incompletely threaded part of the screw rotor inlet was also covered with a sleeve (casing), but the pressure required to prevent the jet flow generated from the gap 1 between the rotor and the sleeve was In other words, no consideration was given to the pressure increase value caused by the incompletely threaded portion.

11) The device described in JP-A-58-197489 had a structure in which the pitch of the screw rotor was changed between the inlet side and the outlet side, but no consideration was given to the fluid force in the axial direction.

The device described in JP-A-51-110703 had a structure in which a balance piston was provided at the discharge 1411 of the screw rotor to make the axial thrust move, but no consideration was given to the balance of the radial thrust. There wasn't.

[Problem that the invention seeks to solve]

Each of the conventional screw pumps described above has the following problems.

1) The technique described in Japanese Utility Model Publication No. 44-25107 does not give sufficient consideration to the increase in liquid pressure due to the fully threaded portion of the screw rotary, and therefore a sufficient pressure increase cannot be expected from the incompletely threaded portion alone. Therefore, the pressure around the gap outlet does not increase due to the gap 1.
There is a problem in that the jet flow generated from the jet does not disappear and the cavitation erosion is not eliminated.

11) The technique described in FMA No. 58-197489 does not take into account the force of the fluid force acting in the axial direction, and suffers from the problem that it is ineffective in reducing the axial thrust.

111°)% The technology described in 110703/1983 does not deal with the fluid force acting in the radial direction of the screw rotor, and the axial surface is designed to improve the axial thread flexibility in order to prevent it. Ta. For this reason, there was a problem of an increase in the number of AM vehicles.

The first object of the present invention is to increase the pressure at the end of the gap formed between the screw rotor inlet and the sleeve.
The purpose is to prevent jet flow due to leakage and to prevent cavitation erosion. Another object of the present invention is to reduce the axial thrust by considering the axial pressure receiving area. Another object of the present invention is to reduce the radial thrust by applying a force opposite the radial thrust.

[Means for solving problems]

The above object can be achieved by the following configuration.

1) To prevent cavitation erosion, either ensure the lead length of a part of the screw that is unrelated to forming a sealed chamber on the inlet side of the screw rotor, or increase the rotor diameter on the inlet side before forming a sealed chamber.

11) To reduce the axial thrust, make the screw lead on the exit side of the screw rotor 2π or more larger than other parts, and reduce the screw height.

111) To reduce radial thrust, provide a notch chamber in a metal bearing or in a part of the sleeve of the balance piston that also serves as a bearing.

[Effect]

1) Securing the lead length of the part unrelated to the formation of a sealed chamber on the inlet side of the screw rotor is to ensure that fluid flows to the end of the gap formed by the screw rotor and sleeve (1) to ensure sufficient pressure rise. is received by the inducer action, so the pressure at the end of the gap increases.As a result, the gap 1 formed by the screw rotor and sleeve
This suppresses the jet flow generated from the air and suppresses cavitation.

11) Change the screw lead and screw height on the exit side by 2π or more with respect to the screw lead and screw height on the inlet side of the screw rotor. In other words, since channel volume = axis-perpendicular channel surface depth x lead, the channel volumes on the inlet side 1 and outlet side should be kept unchanged, the thread lead on the outlet side should be increased, and the thread height should be reduced. Since L reduces the area of the screw rotor's expenditure relative to the discharge pressure, the axial thrust can be reduced.

;rr) Since the discharge side pressure acts on the bearing or the notch provided in a part of the balance piston sleeve, a radial force is generated. Since this direction is opposite to the pressure that the screw rotor receives from the fluid, the radial thrust is canceled and the straddle is reduced by both.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a schematic sectional view of the screw pump.

Here, the fluid entering from the suction flange 1 side is transferred to the main rotor 2.
As the slave rotor 3 meshes and rotates, the outlet 7 flange 5
Forced to the side. A fine/JQ gap 8 is formed between the main and slave screw rotors 2, 3 and the casing 4, and this minute gap 18 has a larger am in the inlet flange 11 rule than the outlet flange 59tlj. First, the outer diameter of the screw in section a is smaller on the inlet 7 flange l side than on the outlet flange 5 side. Note that the shape of this am screw may be different from the following screws in terms of torsion and pitch, but it should be a shape that produces an inducer action.

As a result, the pressure P1 at the outlet end 9 of the plow 1 is the pressure P1 at the outlet end 9 of the plow 1 when the normal screw is not tapered.
Since it becomes larger than i', jet flow is suppressed and cavitation is suppressed. The first figure shows another embodiment for increasing the pressure P1 at the plow 1 outlet end 9, in which the rotor tip diameter Dt of the screw on the inlet side is made larger than the rotor tip diameter Dt of the screw at the outlet 9111. There is a particular thing.

With such a configuration, the dynamic pressure at the outlet end 9 can be increased and the pressure P1 can be increased, so that the jet flow A can be suppressed similarly to the tapered configuration described above.

Figure E is a partially sectional view showing an enlarged main part of the first figure. Here, channel volume = (axis-perpendicular channel area) x (lead)
It is covered with In order to make the flow path performance uniform from the inlet side to the outlet side, in this embodiment, the outlet side thread L is increased and the thread height (Da-Db)/2 is decreased.

The operation of the screw pump configured in this way will be explained.

The axial thrust force Fa is expressed by equation (1).

Fa=-(Pout-Pin)*(Da2-Db")
--(1) Here p out: Discharge pressure, Pin
: Inlet pressure Therefore, as Da-Db becomes smaller, the axial thrust force Fa is reduced. As a result, the life of the bearing can be increased, or the bearing can be made more compact by reducing the size of the bearing.

Still another embodiment of the present invention is shown in FIG. The metal bearings 6 that support the screw rotors 2 and 3 are provided with cutout chambers 10 in the same direction as the force F that the rotor 3 receives from the unbalance between the high pressure chamber and the low pressure chamber formed by the main rotor 2 during boiling. It is. With this configuration, this notch chamber 10
Since the discharge pressure Pout also acts on the rotor, a force F is applied to the rotor in the radial direction as well.

receive. This force P1 is different from the aforementioned force F in the direction of π
Therefore, the forces are canceled at F and IP, and the radial thrust is reduced. As a result, the rigidity of the shaft diameter can be reduced, making it possible to downsize the equipment and increase the fermentation capacity.

〔Effect of the invention〕

The present invention has the following effects.

1) Since cavitation can be prevented, water can be used as a handling liquid. 1. Since cavitation erosion is eliminated, parts life can be extended and reliability can be improved.

11) Since shaft thrust can be reduced, bearing life can be extended. Moreover, there is no need to provide an axial thrust balance device such as a balance piston, and the product can be made more compact.

(2) By reducing the radial thrust, the stiffness of the shaft system is lowered, so the shaft diameter can be reduced, which means the product can be made smaller and lighter.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view of a screw pump according to an embodiment of the present invention, Fig. 2 is a vertical m-plane view showing another embodiment of the present invention, and Fig. 3 is a shaft diagram showing yet another embodiment of the present invention. FIG. 4 is a diagram illustrating a shaft support for reducing radial thrust showing a different embodiment of the present invention, and FIG. 4a is a longitudinal sectional view of the screw rotor, and FIG. 4
The figure is a side view of FIG. 4a, and FIG. 4C is a diagram illustrating the radial thrust force of FIG. 4a. 1... Suction flange, 2... Main rotor, 3... ° slave rotor, 4... Casing (sleeve), 5... Discharge 7 lange, 6... Bearing, 7... Shaft seal Device, 8...
・Gap 1.9...Gap outlet end, 10...Notch chamber, a...Screw taper part No. 2 (Figure 2 Figure 3 Concave 4th surface b a

Claims (1)

[Claims] In a screw pump consisting of several screw rotors and a casing that covers them, there is a tapered screw on the inlet side of the screw rotor, or a tapered screw with a larger lead than other parts, or a screw with a larger lead than other parts. A screw with a large diameter is provided, and a screw with a lead length and screw height that is longer than the lead on the exit side of the screw rotor is provided, and a balance piston cylinder provided at the end of the screw rotor or a part of the bearing part is provided. The structure of a screw pump is characterized by having a notch chamber in the part.