UNI-AXIAL SCREW PUMP

Abstract

The present invention describes a uni-axial screw pump to convey viscous fluids with high pump efficiency wherein restraining devices restrain the fluid's tendency to rotate around the axis as the rotor rotates. As a result, all the fluid trapped between the helical thread and inner surface of inner cylindrical casing is forced in the axial direction towards the discharge end. It can also be employed as hydraulic turbine, thermo motor, liquid motor, extruder, molder and etc. The screw pump includes a thread disconnected perpendicularly to the axis to make a plurality of thread sections, a plurality of annular restraining devices being inserted in the annular gaps formed between disconnected thread sections. The annular restraining devices have restraining elements and openings for the fluid to be conveyed through, inner cylindrical sections being axially disposed between the inserted annular restraining devices to enclose the screw rotor.

Description

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a uni-axial screw pump that conveys various liquids with different viscosities with a high pump efficiency and also to a motor with large output.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.

In 300 BC, an ancient Greek scientist Archimedes invented a so-called “screw pump” with bamboo to pump water, having a helical blade mounted on a shaft, which rotated inside a cylindrical hollow stem of bamboo. A screw pump attracts concerns as a promising pump due to its simple structure, its mechanically strong rotor and its capability of operating in a wide range of flow and compression in comparison with other types of screw pumps.

Screw pumps whose entrance ends and discharge ends are bounded by sealing lines are called enclosed screw pumps. And those without such sealing line are called open screw pumps. Depending on the number of shafts carrying the threaded rotor, the enclosed screw pumps are categorized into one-shaft screw pumps (or uni-axial screw pump), two-shaft screw pumps and three-shaft screw pumps.

An example of the one-shaft screw pump is the Moineau pump which comprises an externally threaded rotor mounted in an internally threaded resilient casing, each carrying thread winding in the opposite direction to be intermeshed each other.

When the screw rotor rotates relative to the outer casing, the fluid trapped in the compartments formed in each pitch of the screw is continuously conveyed in the axial direction. Thus, the Moineau pump is capable of quantitatively transferring various viscous fluids with high pump efficiency. The intermeshing of the external thread of screw rotor and internal thread of the outer casing is realized by two modes of movement of a complicated motoring device. Eccentric rotating and rocking movement results in complication of the motoring device and unfavorable vibration by the dynamic load. Besides, the outer casing should be made of resilient nonmetallic material with good endurance. For this purpose, endurable synthetic rubber is generally used, but its service life is one month or less. Recent introduction of the ceramic outer casing considerably increases service life, whereas the obtained pressure at the discharge end decreased to half that of the synthetic rubber screw pump.

Due to the unbalanced rotational movement of its motoring device that provides two movement modes of eccentric rotating and rocking, the speed of rotation should be limited, which makes mass transfer by Moineau pump impossible. Moreover, a lot of mechanical friction loss is produced owing to the intermeshing of the threads that enables formation of seal and forced conveyance of the fluid to the outlet with high pump efficiency. In an effort to overcome such factional losses and limitation of rotation speed, screw pumps with two shafts were invented.

A two-shaft screw pump comprises two parallel spaced shafts, each carrying externally threaded rotors, the shafts being mounted in a pump body so that the threads of the rotors intermesh. Volumes of liquid trapped in each pitch between the threads of the rotors and the internal surface of casing are urged towards an outlet of the pump as the rotors rotate. During rotation, the threads intermesh, the gaps inevitably being formed at the points of intermeshing. By precisely differentiating the external diameters of the two screw rotors, it is theoretically possible to avoid the formation of a gap, which enables operation of the screw pump under high pressure. An ideal gap should be kept in the formation of seal, and it is necessary to synchronize the rotating speed of the two rotors. Therefore, two-shaft and three-shaft screw pumps necessarily have the intermediary motoring device comprising a pair of synchronous gears.

And thus the production of these screw pumps raises various technical problems in the processing of intermeshing propellers. Moreover, enclosed two-shaft and three-shaft screw pumps are only capable of conveying lubricant fluids without foreign matters. Open two-shaft screw pumps were developed to widen the limited range of applicable fluids, improve conveying conditions of screw pumps and lower production cost.

As for the open two-shaft screw pump, the sealing line is not formed even theoretically, which makes it possible to convey non-lubricant fluids in a wide range of flow and conveying compression. However, the manufacturing process of these open screw pumps is still complicated and their weight is much heavier, since axial movement of fluid is realized necessarily by motoring device comprising a pair of synchronous gears.

Many studies have been carried out to avoid complexity in structure and manufacturing problems caused by the intermediary motoring device and to realize the axially forced conveyance of fluid by means of a uni-axial screw pump.

As a screw rotor rotates in an outer cylinder with a linear central axis, the viscous fluid trapped in the groove of the screw, for its viscosity, rotates around the axis of the screw and thus does not move in the axial direction as the screw rotor rotates. In the structure of a screw pump for conveying powder material with high deformation resistance, the linear and grate-shaped grooves on the internal surface of the cylindrical casing restrain the material from moving in a direction around the axis and force it in an axial direction, wherein the material adjacent to the inner surface of casing rather than that adjacent to the axis is more restrained against movement in a direction around its axis to thereby be urged in the axial direction.

To realize forced conveyance of fluid in the axial direction in a cylindrical casing with smooth inner surface, as realized in multi-axial screw pump, it is necessary to restrain the liquid's tendency to move in a direction around the axis of the screw rotor. It is based on the principle of bolt and nut. In order to ensure axial movement of a nut, the nut should be restrained from moving around the axis when rotating the bolt.

BRIEF SUMMARY OF THE INVENTION

The first object of this invention is to provide a screw pump with high pump efficiency by inventing a new structure for a uni-axial screw pump, wherein, by restraining the liquid's tendency to rotate around the axis as the rotor rotates, the entire volume of conveyed fluid trapped between the helical blade and inner surface of cylindrical casing is forced in the axial direction towards the discharge end.

The second object of this invention is to provide a uni-axial screw pump, which is simple to manufacture, small in external dimensions and capable of conveying fluids with various viscosities.

The third object of this invention is to provide a uni-axial screw pump having a continuous motion mode, short conveyance channel and well-balanced state of rotation resulting in a high speed of pumping. The above objects could be achieved by the present invention that discloses a uni-axial screw pump mainly comprising: an outer cylindrical casing with entrance end and discharge end; a screw rotor mounted in the casing which conveys the fluid from the entrance end to the discharge end as it rotates; and a motor directly connected to the rotor to drive the rotor. The thread extended on the rotor axis is disconnected perpendicular to the axis to make a plurality of thread sections. A plurality of annular restraining devices are inserted in the annular gaps formed between said disconnected thread sections, the annular restraining devices having restraining elements and openings for the fluid to be conveyed through. Inner cylindrical sections are axially disposed between the inserted annular restraining devices to enclose the screw rotor, as a result of which the fluid is restrained by the restraining elements from moving in a direction around the axis as the axis rotates and is forced in the axial direction to the discharge end.

In a preferred embodiment of the present invention, the thread is disconnected at intervals of a screw pitch vertical to the axis to make a plurality of thread sections, a plurality of ring shaped spaces being formed between thread sections. A plurality of restraining devices are inserted into the spaces. The number of thread sections equals that of the screw pitches in this embodiment.

According to the present invention, the restraining devices are annular discs that fit the annular gaps. The annular discs comprise alternately restraining elements and openings that the fluid may pass through in the axial direction. By the restraining elements, the fluid is restrained against the movement in a direction around the axis to thereby be forced in the axial direction.

In a preferred embodiment of the present invention, the annular restraining devices are diametrically halved for the convenience of fabrication and radially inserted into the annular spaces between the thread sections to be assembled as a unit.

According to the present invention, the internal diameter of the annular restraining devices is smaller than that of the axis, whereby the devices are plunged into the axis resulting in thorough sealing.

The part of the disconnected surface of the thread at which the openings of the restraining devices intersect with the thread is round shaped to thereby decrease resistance to the fluid.

If the screw pumps are employed as extruders or molders, restraining elements of the restraining devices are bar shaped.

The axis of the screw pump is tapering from the entrance end to the discharge end, the taper of which is 1/2-1/40 towards the discharge end.

The outer cylindrical casing is in the form of jacket so that the halved restraining devices and inner cylindrical sections, can be conveniently and accurately assembled.

The uni-axial screw pump according to the present invention further comprises a liquid-cushion equalizer to equalize the thrust of the screw pump, wherein a rotating liquid-cushion equalizing disc is fixed to the axis of the screw rotor and a stationary liquid-cushion equalizing disc is mounted inside the covering of medal. The two equalizing discs are contacted by means of the eccentric ring.

The uni-axial screw pump further comprises the structure of bearings wherein fibrous non-metallic medals are inserted in 3-6 borings radially disposed in steel (or cast iron) bushing. The structure makes it possible for the bearings to be safely immersed in the fluid and also for them to be closely located from each other.

The external dimension of the uni-axial screw pump according to the present invention is less than one half that of the open two-shaft screw pump which has the same discharge capacity.

In comparison with the Moineau pump with identical diameter of the screw, the flow of the screw pump of the present invention is increased by ten times, the external dimension is 40%, the production cost is less than one seventh. Due to its simple motoring device and no friction surface, its service life is increased by 20 times more than that of the Moineau pump and causes less vibration and sound during operation.

If the screw pump according to the present invention is employed as a hydraulic turbine, its efficiency, for its reaction rate of nearly 1, is higher than that of the existing hydraulic turbine by 10-15%. Its weight per horsepower is decreased to 1/8-1/10 that of existing hydraulic turbine with the same output and its service life is increased by 5 times as compared with that of the existing turbine.

Owing to the above advantages of the present invention, it can effectively serve for various purposes, for example, as hydraulic turbine, thermo motor, liquid motor, hydraulic coupling, extruder, food-processing machine.

The above objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of examples.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of the uni-axial screw pump according to a preferred embodiment of the present invention wherein a plurality of restraining devices are interposed between disconnected thread sections to restrain the fluid from moving around the axis and force all the fluid in the axial direction.

FIG. 2 (a) is a sectional view of liquid-cushion equalizer according to a preferred embodiment of the present invention.

FIG. 2 (b) is a sectional view of the said liquid-cushion equalizer that shows the contact surface wherein rotating disc and stationary disc are contacted by means of an eccentric ring.

FIG. 3 (a) is a sectional view of nonmetallic medal of the bearing according to the present invention.

FIG. 3 (b) is a sectional view that shows a nonmetallic medal and its covering.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, the screw pump (1) made in accordance with the present invention is illustrated comprising an outer cylindrical casing (2) having an entrance end (1a) and a discharge end (1b).

The screw rotor (3) is a mold unit or welded unit is directly connected with the motor (4) and rotatably mounted in the outer casing (2). The thread (5) extended on the screw rotor (3) is disconnected at intervals of a pitch to make a plurality of thread sections (5) as many as screw pitches. The axis (6) of the screw is not disconnected, as a result of which a plurality of annular spaces is formed as the rotor (3) rotates between said disconnected thread sections (5). A plurality of annular restraining devices (7) that fit the annular spaces are inserted therein. The devices (7) restrain the conveyed fluid from moving in a direction around the axis (6) as the screw rotor (3) rotates and urges it to axially move towards the discharge end (1b). An annular restraining device (7) is disposed at the start of the screw in order to restrain the conveyed fluid from the beginning and thus the number of the annular restraining devices (7) is one more than that of the pitches of the screw.

As shown in FIG. 1, the annular restraining device comprises alternately restraining elements (9) and the trapezoid-shaped openings (8) for the fluid to pass through.

If the screw pump is employed as an extruder and molder, the restraining element is bar-shaped.

The annular restraining devices (7) are diametrically divided into two, as shown in FIG. 1 for the convenience of fabrication. The screw rotor (3), inner cylindrical sections (10) and the two-divided thread sections (7) are fabricated in proper sequence. The two-divided thread sections (7) are respectively inserted in the annular spaces in the radial direction to be assembled as a unit.

The internal diameter of the annular devices (7) is a little shorter than that of the axis (6) and thus a groove is formed on the axis (6) where the annular devices (7) and the axis (6) intersect with each other. And the annular devices (7) are inserted therein. Therefore, the annular devices (7) are plunged into the axis (6) resulting in thorough sealing structure to prevent the leakage of the fluid in the gaps between the said devices (7) and the axis (6).

The axis (6) of the screw rotor (3) is tapering toward the discharge end (1b) to increase the filling co-efficient in each thread sections (5), whose taper ranges from 1/2-1/40 according to the kind of the conveyed fluid.

A plurality of inner cylindrical sections (10) are disposed between the annular restraining devices (7) to encompass the screw rotor (3).

The part of the severed surface of the thread (5) at which the openings of the restraining devices (7) intersect with the severed surface of the thread is round shaped to thereby decrease resistance to the fluid.

The outer cylindrical casing (2) is in the form of jacket so that the halved restraining devices (7) and inner cylindrical sections (10) can be conveniently and accurately assembled. As shown in FIGS. 2 (a) and (b), the device to equalize the thrust of the screw rotor (3) is disposed at discharge end (1b), which comprises stationary liquid cushion disc (11) and rotating liquid cushion disc (12) contacted by means of eccentric ring (13b).

As shown in FIGS. 3 (a) and (b), fibrous non-metallic medals (16a) and (16b) in their coverings (15a) and (15b) are inserted in 3-6 borings radially disposed in steel (or cast iron) bushing (14a) and (14b) which makes the bearing structure that can be safely immersed and lubricated in the fluid.

The operation of the above-mentioned screw pump (1) is described hereinafter in detail.

First of all, the operation of a screw pump with a connected thread is explained. As the screw rotor rotates, the fluid around the screw rotor receives rotation moment and moment against rotation from the work surface of the thread and inner surface of cylinder. The fluid with viscosity has the tendency to rotate around the axis as the rotor rotates, while the inner surface of cylinder gives anti-rotating moment to the fluid and force it to move in the axial direction towards the discharge end. Since most of the fluid trapped in the groove of the screw tends to move around the axis as the rotor rotates, the relative speed difference between the work surface of the thread and the fluid is nearly 0. Therefore, geometric flow and compression is not formed and the rotating fluid causes heat inside the cylinder. The operation of the screw pump (1) with disconnected thread sections (5) and annular restraining devices (7) between them provided by the present invention is described hereinafter. As the rotor (3) rotates, the fluid trapped in the grooves of the screw receives energy by the restraining element that resists it from moving around the axis (6). As the resisted surface area increased, most of the fluid is urged to flow horizontally in the axial direction towards the discharge end (1b). As a result, geometric flow is formed and the compression energy is obtained that is in proportion to the square of relative speed. The annular restraining devices (7) have restraining elements (9) and alternated openings (8) that provide a restraining effect and conveying effect at the same time, the mechanical energy and compression energy being continuously exchanged.

Therefore, the compression energy at the discharge end (1b) gets equal to compression in one thread sections (5) multiplied by the number of the thread sections (5).

In the uni-axial screw pump (1) according to the present invention, axial thrust occurs by compression energy of the fluid. FIGS. 2 (a) and (b) shows a liquid cushion equalizing device employed in an embodiment of the present invention to equalize axial thrust of the screw pump (1) of the present invention. The operation of the equalizer (11) is described in more detail hereinafter. The front surfaces of rotating cushion disc (12) and stationary disc (11) are influenced by the compressed fluid through the gap between the axis (6) and the bushing (14b) at the discharge end (1b), the two discs being fixed to the axis (6) and prevented from axial movement. On the annular surface of the rotating cushion disc (12), pressure is given corresponding to its total area, which is equalized to the axial thrust by controlling the diameter of the disc (11). As shown in FIGS. 2 (a) and (b), the rotating cushion disc (12) and stationary cushion disc (11) are ideally contacting each other at their sides by a nonmetallic ring (13b), which is eccentrically fixed to the stationary disc (11). The nonmetallic ring (13b) involves rotating and rocking movement, as a result of which it is constantly lubricated and cooled to thereby increase its service life by 20 times that of concentric ring where heat is accumulated. In case that additional contacts may occur between the axis (6) at the entrance end and the covering (15a) of the medal (16a) by the unbalanced thrust, nonmetallic contact ring (13b) is inserted at the side of the covering (15a) to thereby decrease the friction.

Due to its axial parallel flow from the entrance end (1a) to the discharge end (1b), the uni-axial screw pump (1) with restraining devices (7) according to the present invention has a short conveyance route and is not influenced by the radial load. The bearings of the screw pump are mounted on both ends of the axis wherein fibrous non-metallic (wooden or plywood) medals are inserted in 3-6 borings radially disposed in steel (or cast iron) bushings (14). The structure makes it possible for the bearings to be safely immersed and lubricated in the fluid and also for them to be closely located to each other. The vertical contact between steel and fabric nonmetal has a low abrasion co-efficient resulting in increased service life by 3-5 times that of the metal ball bearing.

The present invention is not limited to the above-mentioned embodiments.

Claims

1. A uni-axial screw pump comprising: an outer cylindrical casing with entrance end and discharge end;a screw rotor mounted in said outer cylindrical casing, the rotor conveying fluid from said entrance end to said discharge end as said screw rotor rotates; anda motor directly and drivingly connected to said screw rotor, said motor having a rotor axis with thread extended on said rotor axis, said thread being disconnected perpendicularly to said rotor axis to form a plurality of thread sections, said rotor axis having a plurality of annular restraining devices being inserted in annular gaps formed between the disconnected thread sections, said annular restraining devices having restraining elements and openings for the fluid to be conveyed through, inner cylindrical sections being axially disposed between the inserted annular restraining devices, enclosing said screw rotor, wherein fluid is restrained by said restraining elements from moving in a direction around an axis of said screw rotor as the axis rotates, forcing the fluid in an axial direction to said discharge end.

2. A uni-axial screw pump according to claim 1, wherein said thread disconnects at intervals of a screw pitch vertical to said rotor axis.

3. A uni-axial screw pump according to claim 1, wherein the restraining devices are annular discs fitted into the annular spaces

4. A uni-axial screw pump according to claim 3, wherein said annular discs are diametrically halved and radially inserted into the annular spaces.

5. A uni-axial screw pump according to claim 3, wherein an internal diameter of each annular restraining disc is smaller than a diameter of said rotor axis, the restraining disc being plunged into said rotor axis to form a sealing structure.

6. A uni-axial screw pump according to claim 1, wherein said disconnected thread sections are round shaped.

7. A uni-axial screw pump according to claim 1, wherein said annular restraining devices are bar shaped.

8. A uni-axial screw pump according to claim 1, wherein said screw rotor has an axis tapering from said entrance end to said discharge end, an amount of taper having a range of 1/2-1/40 towards said discharge end.

9. A uni-axial screw pump according to claim 1, wherein said outer cylindrical casing is a jacket, the restraining devices and inner cylindrical sections being halved for convenient and accurate assembly.

10. A uni-axial screw pump according to claim 1, further comprising: a liquid-cushion equalizer comprising equalizing discs, wherein a rotating liquid-cushion equalizing disc is fixed to the axis of the screw rotor, and wherein a stationary liquid-cushion equalizing disc is mounted inside a metal covering, the two equalizing discs being in contract by an eccentric ring.

11. The uni-axial screw pump further comprising: a plurality of bearings, wherein fibrous non-metallic medals are inserted in 3-6 borings radially disposed in a bushing, said bearings being immersed and lubricated by the fluid.