Screw vacuum pump unit

Abstract: The present invention provides a screw vacuum pump unit in which both a screw block and a driving motor are mounted on one side surface of a casing of a speed change gear, both axes of a male rotor and a female rotor in the screw block are arranged in vertical adjacency within a substantially perpendicular virtual plane, and suction ports and discharge ports are arranged on both sides with the vertical plane inter­ vening therebetween, whereby maintaining can be facilita­ ted.

Description: The present invention relates to a screw vacuum pump unit comprising a screw casing which defines a working chamber and which has suction ports and discharge ports communicating with the working chamber, a screw block which has a male rotor and a female rotor that are rotatably received in the working chamber and that are rotated meshing with each other, a motor which drives the rotors, and a speed change gear which has transmission means for transmitting rotation of the motor to the rotors and a casing for receiving the transmission means therein. As disclosed in the offical gazette of Japanese Patent Application Laid-open No. 60-216089 (corresponding to EP-A-166851), a prior-art screw vacuum pump is such that a pair of male and female rotors which rotate meshing with each other are received in the working chamber of a casing which has suction ports and discharge ports, and that the rotors are driven by a driver, whereby a gas is imbibed from a space to have its pressure lowered, into the interstice between both the rollers, and it has its pressure raised and is exhausted into the atmosphere. In the prior-art unit, the axes of the male rotor and female rotor are arranged within a horizontal plane, and both the rotors are arrayed within the horizontal plane, so that a floor area required for installation enlarges. Moreover, on account of the structure in which the suction ports and discharge ports of the casing are arranged on both the sides of the horizontal plane (in the upper surface of the casing and lower surface thereof), either the suction ports or the discharge ports are lying in the lower surface of the casing. Therefore, the job of connecting pipes to the suction ports or the discharge ports lying in the lower surface of the casing must be carried out at the lower surface of the casing, and the job efficiency is very inferior. Further, in a case where reaction products have been deposited in the vacuum pump as in use for the evacuation of a semiconductor manufacturing plant, it is not easy to eliminate the products or to routinely inspect the situation of deposition. In performing these operations, there are the problems that pipes need to be detached and that special tools are required. US-A 2880676 describes a sanitary type pump comprising a casing which defines a working chamber and which has a suction port and a discharge port communicating with the working chamber. The pump unit further comprises a pump block which has a first impeller and a second impeller that are rotatably received in the working chamber and that are rotated meshing with each other. With the pump impellers of the gear type or of the lobe type are used. For driving the impellers a motor is provided coupled with a speed change gear which has transmission means for transmitting rotation of the motor to the impellers and a casing for receiving the transmission means therein. On the one side of said casing of the speed change gear the motor is mounted, while on the opposite side the pump block is provided. The axes of the two impellers are arranged in vertical adjacency within a substantial perpendicular virtual plane. The suction port and the discharge port are arranged on both sides with the perpendicular plane intervening therebetween. This prior art impeller pump unit needs space, as in spite of the vertical arrangement of the impellers in the pump block which reduces widths, the unit is very lengthy because of arranging the pump block in the one side of the speed gear casing and the motor on the other side. Furthermore, by arranging the suction port and the discharge port only on a horizontal axis, maintenance can become difficult. The object of the present invention is to provide a screw vacuum pump unit which can decrease a floor area for installation and can simultaneously facilitate maintenance. The present invention for accomplishing the objects is characterized in that both a screw block and a motor are mounted on one side surface of said casing of said speed change gear, in that the axes of both said male and female rotors in said screw block and of said motor are contained in a virtual vertical plane, in that said suction ports are arranged on the one side of said virtual vertical plane while the said discharge ports are arranged on the other side of said plane, in that the suction ports extend one in the horizontal direction and another from above in the vertical direction communicating with the said one, and in that the discharge ports are three and extend one horizontally and two vertically to the horizontally extending discharge port. Since, as described above, the male rotor and the female rotor are arrayed in the perpendicular (vertical) direction, the floor area suffices with an extent for receiving a single rotor and can be made smaller than in the prior art. Simultaneously, since the suction ports and the discharge ports are respectively located on the right side and left side of both the rotors and are prevented from lying at the lower surface of the casing, a job for connecting pipes to the suction and discharge ports and jobs for maintenance, such as the clearing and inspection of deposits, can be readily conducted. Preferably, a silencer cartridge is inserted in the discharge port. Advantageously, said silencer cartridge is inserted in at least the vertical discharge ports. Said silencer cartridge can be constructed of an outer cylinder, an inner cylinder which is formed with a large number of pores, and a sound-absorbing material which is interposed between said inner cylinder and said outer cylinder. It is convenient that the speed change gear has a gearing for transmitting rotation of the motor to the rotors and a casing for enveloping the gearing that both said screw block and said motor are coupled to one side surface of said casing of said speed change gear by flanges, and that the axes of both said rotors of said screw block and an axis of said motor are arranged in vertical adjacency within the said substantially perpendicular virtual plane. It is preferred that the said male rotor, said female rotor and said motor are arranged in this order within the virtual perpendicular plane, particularly in this order from above. Usually, the said discharge ports are arranged near said casing of said speed change gear, while said suction ports are arranged at positions remote from said casing of said speed change gear. The invention is further explained by means of drawings. Fig. 1 is an exterior view of a screw vacuum pump showing an embodiment of the present invention; Fig. 2 is a sectional view taken along line II-II in Fig. 1; Fig. 3 is a sectional view taken along line III-III in Fig. 1; Fig. 4 is a sectional view showing an embodiment of the present invention in which only one horizontal suction port is provided; Fig. 5 is a sectional view showing an embodiment of the present invention in the case where the whole vacuum pump is enveloped in a sound-insulating cover; Fig. 6 is a sectional view of the essential portions of an embodiment in which a silencer cartridge is arranged in a discharge port; and Fig. 7 is a sectional view of the silencer cartridge. A male rotor 1 has a plurality of twisted lands and grooves, while a female rotor 2 has a plurality of twisted grooves and lands. The lands of the male rotor 1 are shaped so as to mesh with the grooves of the female rotor 2, and the grooves of the male rotor 1 so as to mesh with the lands of the female rotor 2. A screw casing is constructed of a main casing 3, and an end casing 4 which is coupled to one end face of the main casing 3 by bolts. The main casing 3 defines therein a working chamber 30, which is surrounded with a water jacket 27. A cover 5 is coupled to the end face to the end casing 4 remote from the main casing 3. The male rotor 1 and female rotor 2 mentioned above are received in the working chamber 30 of the main casing 3. Bearings 7, 8 and shaft seals 23, 24 are arranged between both the rotors 1, 2 and the main casing 3. Likewise, bearings 9, 10 and shaft seals 25, 26 are arranged between both the rotors 1, 2 and the end casing 4. The two rotors 1 and 2 are rotatably supported by the bearings 7, 8, 9 and 10. Gears 11 and 12 are coupled to one end side of both the rotors 1, 2, and they mesh with each other. The gear 12 meshes with a drive gear 13 which is coupled to the shaft of a motor 14. The gears 11, 12 and the drive gear 13 are received in the gear casing 6 of a speed change gear. Herein, the male rotor 1, female rotor 2 and motor 14 are arranged in this order from above in such a manner that the respective axes of both the rotors 1, 2 and the motor 14 are horizontal and are parallel to one another and that the axes as viewed from the gear side are aligned within a plane extending in the perpendicular (vertical) direction. The motor 14 and the screw casing, which receives the male rotor 1 and the female rotor 2 therein, are arranged on one side of the gear casing 6, and the flange 3f of the main casing 3 is coupled to the gear casing 6 by bolts. The main casing 3 is provided with suction ports 3a, 3b on one side thereof, and with discharge ports 3c, 3d, 3e on the other side thereof. The suction ports 3a and 3b are held in communication with the working chamber 30 by the suction port 3a, while the discharge ports 3c, 3d and 3e are held in communication with the same by the discharge port 3d. The suction port 3a extends in the horizontal direction, and the suction port 3b communicates therewith orthogonally from above. On the other hand, the discharge port 3d can discharge gases in the horizontal direction, the discharge port 3c communicates with the port 3d orthogonally from above, and the discharge port 3e communicates with the port 3d orthogonally from below. Numeral 16 designates a suction side stop collar, and symbols 17a and 17b denote discharge side stop collars. The details of the shaft seals 23, 24, 25 and 26 are described in US-A-4,487,563. Besides, the embodiment comprises an oil pump (not shown) which feeds oil 29 to the meshing parts of the bearings 7, 8, 9 and 10 and the gears 11, 12 and 13. When the motor 14 is driven, the rotors 1 and 2 are rotated through the drive gear 13 and the gears 11 and 12, and the fluid of a chamber to be evacuated is imbibed from the suction port 3b into the working chamber 30 (in Fig. 3, the suction port 3a is held closed by the stop collar 16) and is emitted from the discharge port 3c through discharge openings 15a and 15b (in Fig. 3, the discharge ports 3d and 3e are held closed by the respective stop collars 17a and 17b). In a case where the fluid is to be imbibed from the suction port 3a for the convenience of piping, it is easy that the suction side stop collar 16 is detached to open the suction port 3a and that the suction port 3b is closed. Likewise, on the discharge side, it is easy to select a necessary one from among the discharge ports 3c, 3d and 3e and to connect a pipe thereto. In addition, in such a case where deposits having adhered to the interior of the vacuum pump unit due to reaction gases are to be cleared, a vertically penetrating passage extending from the discharge port (a passage extending from the discharge port 3c in communication therewith) makes it possible to sweep away the deposits with a brush or the like from the upper discharge port 3c and to put them out from the lower discharge port 3e. Therefore, operations for maintenance can be readily performed. According to the present embodiment, the rotors 1, 2 and the motor 14 are so arranged that their axes are horizontal and are parallel to one another and that the axes viewed from the axial end side are aligned on the perpendicular plane. Moreover, the screw casing which receives the male rotor 1 and female rotor 2 therein, and the motor 14 are arranged on one side of the gear casing 6. Therefore, the widthwise and lengthwise dimensions of the pump proper can be sharply reduced to make the installation area smaller, and suction and discharge pipes can be readily connected to facilitate operations for maintenance such as the clearing of deposits at the discharge ports. Fig. 4 is a sectional view corresponding to Fig. 3, of a screw vacuum pump unit which shows an embodiment of the present invention and which is provided with a single horizontal suction port. Fig. 5 is a sectional view showing an embodiment in which the present invention is applied to a case of enveloping the whole vacuum pump in a sound-insulating cover in order to reduce noise (this figure corresponds to a section III-III in the case of enveloping the whole vacuum pump of Fig. 1 in a sound-insulating cover). Referring to Fig. 5, symbols 18 and 18b denote suction pipes which connect the sound-insulating cover 21 and the suction ports of the pump proper, symbols 19a, 19b and 19c denote discharge pipes which connect the sound-insulating cover and the discharge ports of the pump proper, and numeral 20 denotes a sound-absorbing material which is stuck to the inner surface of the sound-insulating cover. As illustrated in the figure, a plurality of piping ports are provided in the upper parts and sideward parts of the sound-insulating cover. This brings forth the effect that piping is very easy. Moreover, the discharge ports 3c, 3d and 3e are provided in three directions, so that when reaction products have deposited at the discharge ports, the deposits can be readily cleared from the upper port 3c or the horizontal port 3d and put out from the lower port 3e. This brings forth the effect that the maintenance of the pump unit is very easy. Fig. 6 shows an embodiment in which silencer cartridges 22 are inserted in the discharge ports 3c, 3d and 3e in order to facilitate the clearing and simultaneously to silence the pump unit. As shown in Fig. 7, the silencer cartridge 22 is constructed of an outer cylinder 22c, an inner cylinder 22b which is formed of a punching metal plate (porous steel plate), and a sound-absorbing material 22a which is packed between the inner and outer cylinders 22b, 22c. When the silencer cartridges 22 are inserted in the discharge ports in this manner, reaction products deposit on the inner surface of these silencer cartridges. When a predetermined period of time has lapsed or when the pump unit is to be inspected, the stop collars 17a and 17b are detached, and the silencer cartridges 22 are replaced with new ones, whereby the reaction products having deposited at the discharge ports or in discharge regions can be eliminated.

Claims: A screw vacuum pump unit comprising a screw casing (3, 4) which defines a working chamber (30) and which has suction ports (3a, 3b) and discharge ports (3c, 3d, 3e) communicating with the working chamber (30), a screw block which has a male rotor (1) and a female rotor (2) that are rotatably received in the working chamber (30) and that are rotated meshing with each other, a motor (14) which drives the rotors (1, 2), a speed change gear which has transmission means (11, 12, 13) for transmitting rotation of the motor (14) to the rotors (1, 2) and a casing (6) for receiving the transmission means (11, 12, 13) therein, characterized in that both said screw block and said motor (14) are mounted on one side surface of said casing (6) of said speed change gear, in that the axes of both said male and female rotors (1, 2) in said screw block and of said motor (14) are contained in a virtual vertical plane, in that said suction ports (3a, 3b) are arranged on the one side of said virtual vertical plane while the said discharge ports (3c, 3d, 3e) are arranged on the other side of said plane, in that the suction ports (3a, 3b) extend one (3a) in the horizontal direction and another (3b) from above in the vertical direction communicating with the said one (3a), and in that the discharge ports (3c, 3d, 3e) are three and extend one horizontally and two vertically to the horizontally extending discharge port (3d). A screw vacuum pump unit according to claim 1, wherein a silencer cartridge (22) is inserted in the discharge ports (3c, 3d, 3e). A screw vacuum pump unit according to claim 2, wherein said silencer cartridge (22) is inserted in at least the vertical discharge ports (3c, 3e). A screw vacuum pump unit according to claim 2 or 3, wherein said silencer cartridge (22) is constructed of an outer cylinder (22c), an inner cylinder (22b) which is formed with a large number of pores, and a sound-absorbing material (22a) which is interposed between said inner cylinder (22b) and said outer cylinder (22c). A screw vacuum pump unit according to one of the preceding claims, wherein the speed change gear has a gearing (11, 12, 13) for transmitting rotation of the motor (14) to the rotors (1, 2) and a casing (6) for enveloping the gearing (11, 12, 13), wherein both said screw block and said motor (14) are coupled to one side surface of said casing (6) of said speed change gear by flanges (3f), and wherein the axes of both said rotors (1, 2) of said screw block and an axis of said motor (14) are arranged in vertical adjacency within the said substantially perpendicular virtual plane. A screw vacuum pump unit according to one of the claims 1 to 5, wherein said male rotor (1), said female rotor (2) and said motor (14) are arranged in this order within the virtual perpendicular plane. A screw vacuum pump unit according to one of the claims 1 to 6, wherein said male rotor (1), said female rotor (2) and said motor (14) are arrayed in this order from above within the virtual perpendicular plane. A screw vacuum pump unit according to one of the claims 1 to 7, wherein said discharge ports (3c, 3d, 3e) are arranged near said casing (6) of said speed change gear, while said suction ports (3a, 3b) are arranged at positions remote from said casing (6) of said speed change gear.

Inventors: HAYAKAWA TADASHI, MITSUHASHI SHINJI, NAYA KOUTAROU, SHIINOKI KAZUAKI, UCHIDA RIICHI, HAYAKAWA, TADASHI, MITSUHASHI, SHINJI, NAYA, KOUTAROU, SHIINOKI, KAZUAKI, UCHIDA, RIICHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1987
Main classification: F04C23
IPC codes: F04C18, F04C29, F04C25, F04C23