SCREW PUMP

Abstract: Screw pump of the type which comprises a rotatable screw (16) in a housing (11), the threads (20, 21) of which are partially in engagement with a rotatable sealing device (19). The screw area of the screw (16), that is, the thread groove (20) and thread root (21) of which are generated by a generatrix (22), which is a part of a circle arch, the circle of which is rotatable about an eccentric rotation axis (23), when the generatrix rotates about the shaft of the screw (24) and displaced along this with a velocity which is proportional to the rotational velocity of the screw. The sealing device (19) comprises at least one circular disc (25), the eccentric rotation axis (26) of which, being arranged transverse to the axis (24) of the screw, coincides with the rotation axis of the generatrix.

Description: SCREW PUMP The present invention refers to a screw pump of the type which comprises a rotatable screw in a house, the threads of which are in engagement with a rotatable sealing device. Background of the invention Industrial waste products, such as waste chemicals, waste oil and so on are often of very high viscosity and heavily contaminated with wearing particles in varying size. When pumping these media it is important to use a low speed pump as possible, which can swallow large particles and to give the high viscous medium good time to flow up. Today among others so called modified archimedes screw pumps are used, with a multiple toothed radially positioned sea¬ ling and pressure build-up disc, which is in engagement with the screw. An example on such screw pump is described in SE-B-8101863. Because of the geometry of the sealing disc the meshing part of the screw can not simply be machined, which implies bad sealing and high wear on included parts. The displacement is limited by screw flanks during one screw turn and the cylinder wall and two successive teeth on the sealing disc. In practice the whole screw diameter cannot be used, since the screw must have a supporting center shaft, which steals a part of the displacement of the pump. More¬ over the relatively large sealing disc demands large space, which results in the pump being bulky. Object of the invention and most essential features The object of the invention is to provide a screw pump of the type stated by way of introduction, the pump screw of which can be machined, which has a very large displacement, which can swallow large particles in respect to its diame- ter, which has small build in dimensions and which is cha¬ racterized in low wear between the pump screw and the sea- ling discs, which results in long life and long periods between the services. Morever a change of the wearing parts such as the gaskets of the sealing discs should be possible to be carried out rapidly and in some simple operations. These tasks have been solved by the screw area of the screw, that is the thread groove and the thread root is generated by a generatrix, which is a part of a circular arc, the circle of which can rotate around an eccentric rotation axis, when the generatrix rotates around the axis of the screw and is moved along this with a velocity which is proportional to the rotation velocity of the screw, and that the sealing device comprises at least one circular disc, the eccentric rotation axis of which, is arranged crosswise towards the axis of the screw, coincides with the rotation axis of the generatrix. Description of the drawings The invention will be described in closer detail with refe¬ rence to the drawings, which describe an embodiment. Fig. 1 shows the screw pump according to the invention in a lateral view. Fig. 2 shows a section along the line II - II in fig.*-'1 and with the sealing discs shown in an initial position. Fig. 3 shows a view analogous with Fig. 2 of the screw pump with the sealing discs rotated 90° relatively the sealing discs in fig. 2. Fig. 4 is a section along the line IV - IV in Fig. 3. Fig. 5 shows an end view of the screw pump according to the invention with the output opening. __ scription of embodiments T screw pump according to the invention consists of a pump hoii. ng 11, which comprises an input section 12, a compres- sion action 13 and an output section 14. The input section 12 is rovided with an input opening 15 at one end of a screw 1 which extends throughout the whole pump housing 11 and the periphery of which is cylindric in the same way as the inside of the pump housing. At one side of pump housing a motor 17 is fixed by screws, which preferably can be a hydraulic motor, the drive shaft of which is nonrotateably connected to the screw 16. At the opposite end of the screw pump in the output section an output opening 18, such as shown in figures 2 and 5. The compressing section 13 of the screw pump comprises partly a specially designed portion of the screw and partly with this cooperating sealing device 19, which cooperates with the screw 16. The compressing section of the screw 16 is formed as a screw surface, that is a thread groove 20 and a thread root 21, which is generated by a generatrix, which is a part of a circular arch 22, the circle of which is rotateable about an eccentric rotation axis 23, when the generatrix rotates about the shaft 24 of the screw 16 and simultaneously is moved along this with a velocity which is proportional to the rotation velocity of the screw. The thread groove 20 and the thread root 21 within the compressing section 13 has obtained the form showr in the figures 6 to 11, b^ is, the screw 16 has a df recessed portion withs.. rt where the operation is positioned, while the par :>f the screw which is -ised by its return phase to a ,-__at extent is, ' absorbed by the supporting cross section of the screw. The sealing device situated within the compressing section 13 in the embodiment shown is constituted by two sealing discs 25, which are rotateable about an eccentrically ar¬ ranged shaft 26, which coincides with the geometric axis 23. Each sealing disc 25 is provided with a periferal sealing means 39. The sealing discs 25 are arranged radially relati¬ vely the screw 16 and are situated just opposite each other whereby the size of the sealing discs and the position of the eccentric shaft 26 has been chosen such, that the sea¬ ling disc 25 which is active for the present, in one of its end positions extends almost up to the center axis 24 of the screw. The two shafts 25 and 26 of the sealing discs are connected by means of a transmission 27, which in the em¬ bodiment shown in fig. 4 is constituted by double cardan joints 28 connected to each other by means of a shaft 29. The sealing discs 25 obtain their rotating driving power from the screw 16. The sealing discs 25 are 180° are displaced in phase, which means that it is only one sealing disc at at time, that lies in working position during respectively the half operation revolution of the screw. The sealing disc 25 which is not operative, that is, which has only sealing function, is returned to the initial position by it being connected by the cardan joints 28 with the other, for the present active sealing disc, until it comes to the position where the operation cycle starts. This means that only 180° of the pump screw operates actively. It is then possible to use the non active half to physically support the screw and let the operating disc run all_way down to the center of the screw and there by_ btain maximum displacement. The working phase —32 ~ is thus used two times per revolution. In order to obtain a soft tϊaτ_-si_-___ι_JErojι_the working phase 32 along the whole return phase 33, the threadT^r©<_cz^_20 passes over into a partly circular return path 30, which r tn ns ^ -^^spective sealing disc 25 to the active part of the thread groove In order to prevent internal leakage between the screw 16 ^nd the sealing disc 25 on the side, where it is positioned the operation phase, the cylindrical thread crests 34 of ti screw have been designed with an axial extension 35, whi. * is so large, that it during the whole operation phase seal, the recess 36, in which the sealing disc 25 is mo¬ vable The screw 16 can be divided into a compression screw 37 siti_ *ed within the compression sector 13 and a feeding screw 38 provided within the input section 12. The axial extension 35 of the compression screw 37 at the thread roots is successively narrowing in the feeder screw 38. To sum up the following advantages may be quoted: 1. Sealing disc which extends all way down to the center of the screw implies maximum displacement in reference to the diameter of the screw and that large particles can be pum¬ ped. 2. 180° s operating phase which can be used 2 times per revolution. 3. Supporting screw shaft which lies in the return phase and does not contribute to dead volume. 4. The screw pump can also be made with 4 discs and 90° operation phase which then will be completely self sealing. 5. Wide thread crest which gives a self sealing screw again¬ st the return path of the disc. 6. Circular sealing discs (wear detail) which will be inex¬ pensive to manufacture. 7. Rounded outer diameter on the sealing disc which "rolls" • over screw shaft for exact sealing. 8. Circular sealing discs make the screw machineable and thereby tighter and less wear. 9. The sealing discs are linked together with 180° phase displacement by means of double cardan joints so that the operating disc returns the resting one. 10. Alternating wear and seal surface on the sealing discs which gives lower wear.

Claims: CLAIMS 1. Screw pump of the type which comprises a rotateable screw (16) in a housing (11), the threads (20,21) of which are partially in engagement with a rotateable sealing device (19), c h a r a c t e r i z e d t h e r e i n, that the screw area of the screw (16), that is, the thread groove (20) and thread root (21) of which are generated by a generatrix (22), which is a part of a circle arch, the circle of which is rotateable about an eccentric rotation axis (23), when the generatrix rotates about the shaft of the screw (24) and displaced along this with a velocity which is proportional to the rotational velocity of the screw, and that the sealing device (19) comprises at least one circular disc (25), the eccentric rotation axis (26) of which, being arranged transverse to the axis (24) of the screw, coincides with the rotation axis of the generatrix. 2. Screw pump according to claim 1, c h a r a c t e r i z e d t h e r e i n, that the sealing device (19) comprises at least two circular sealing discs (25) provided diametrically opposed to each other. 3. Screw pump according to claim 2, c h a r a c t e r i z e d t h e r e i n, that the thread grooves (20) of the screw (16), in the portion which comprises the operation phase (32) of the screw, is designed to extend substantially to the center of * _e screw and that the supporting cross section portion of ti screw is situated in that part of the screw which is coκ> rised by its return phase (33). 4. Screw pump according to claim 2 or 3, c h a r a c t e r i z e d t h e r e i n, that the thread grooves (20) of the screw (16), in that part which is comprised by its return phase (33), is formed with a partly circular return path (30) for the sealing discs (25). 5. Screw pump according to claim 2, c h a r a c t e r i z e d t h e r e i n, that the sealing discs (25) are nonrotateably connected to each other by means of a transmission (27) with 180° phase displacement. 6. Screw pump according to claim 5, c h a r a c t e r i z e d t h e r e i n that the sealing discs (25) are provided with a periferal sealing means (37). 7. Screw pump according to claim 3, c h a r a c t e r i z e d t h e r e i n, that the periphery of the screw (16) is cylindrical and that the cylindrical thread crests (34) of thread roots (21) on both sides of the sealing device (19) has an axial exten¬ sion, which is so large that it at least during the opera- tion phase of a screw revolution preserves its sealing function against the inside of the pump housing (11) and against a recess (36) in which the sealing disc (25) of the sealing device (19) is movable. 8. Screw pump according to claim 7, h a r a c t e r i z e d t h e r e i n, at the axial extension (35) of the thread roots (21) on OΪ side of the sealing device (19) successively narrows and bee τιes a feeder screw.

Inventors: JOHANSSON ANDERS, JOHANSSON, ANDERS
Applicants: JOHANSSON ANDERS, JOHANSSON, ANDERS
Application year: 1991
Main classification: F04C3
IPC codes: F04C3