US2963884A

US2963884A - Screw-rotor compressors or motors

Info

Publication number: US2963884A
Application number: US728861A
Authority: US
Inventors: Rosenschold John Rutger Mun Af; Trulsson Sven Ivar
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1957-04-17
Filing date: 1958-04-16
Publication date: 1960-12-13
Anticipated expiration: 1977-12-13

Description

Dec. 13, 1960 J. R. MUNCK AF ROSENSCHLD ETAL SCREW-ROTOR COMPRESSORS OR MOTORS Filed .Aprill 16. 1958 Fig. 2

Fig.

3 Sheets-Sheet l Dec. 13, 1960 2,963,884

J. R. MUNcK AF Rosx-:NscHLD ET AL SCREW-ROTOR COMPRESSORS OR MOTORS Filed April 16. 1958 3 3 Sheets-Sheet 2 6 Fig. [+V 2O Illa.' Y i /\f////// /f/ f 7 Ill HNI

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Dec. 13, 1960 2,963,884

J. R. MUNCK AF RosENscHLD ETA.

SCREW-ROTOR COMPRESSORS OR MOTORS Filed April 16, 1958 3 SheeS-Shee'l'l 3 ATTORNEY SCREW-KOTOR COMPRESSRS R MOTORS John Rutger Munck af Rosenschld, Saltsjobaden, and Sven Ivar Trulsson, Nacka, Sweden, assignors to Atlas sCopco Aktiebolag, Nacka, Sweden, a corporation of weden Filed Apr. 16, 1958, Ser. No. 728,861 Claims priority, application Sweden Apr. 17, 1957 3 Claims. (Cl. 62-331) This invention relates to screw-rotor compressors or motors operating on an elastic working fluid and comprising a casing and two or more screw-type rotors mounted in bearings in said casing and intermeshing to form working chambers for said working uid which working chambers move from registry with an inlet port at the casing in which one uid pressure prevails to register with an outlet port at the casing in which another uid pressure prevails, as the rotors revolve. Machines of the above type are most commonly used as compressors but may also be operated as motors. For the sake of simplicity, the following etailed description of apparatus embodying the invention describes such apparatus only when used as a compressor, which fact, however, should not be considered as a limitation of the scope of the invention as set forth in the claims.

.aired States Patent In apparatus of the kind under consideration, for small pressure differences, i.e. less than 2 kilogrammes per square eentimetre, it has been possible to use ball bearings for the mounting of the rotor shafts and it has also been possible to arrange the rotors in the casing in any convenient manner. In such compressors operating with a pressure difference in excess of 2 kgs./sq.cm. between the inlet and the outlet of the compressor it has been common practice to use only plain bearings for the rotor shafts since the bearing loads have been considered too high for ball or roller bearings at the speeds at which said compressors are normally operated. Compressors of the kind under consideration have the disadvantage that they produce an intense and irritating noise. Such compressors have, further, the disadvantage that the ediciency drops very quickly if the clearance between the rotors and between the rotors and the casing is larger than absolutely necessary. One object of this invention is to reduce the above mentioned deficiencies and to provide a compressor which emits as little disturbing noise as possible in the room Iwhere the compressor is mounted and which simultaneously shows a good eciency and has small bearing loads.

By locating the rotor shafts in a common horizontal plane with the port communicating with the working chambers in which the high pressure prevails disposed at the underside of the rotors and with the port communicating with the working chambers in which the low pressure prevails disposed at the upper side of the rotors the pressure difference between the upper and the under sides thereof during operation `of the compressor or motor helps to lift the rotors and the weight of the rotors is consequently partially compensated for, so that a portion of the radial pressure on the radial bearings of the rotor shafts is counterbalanced by fluid pressure. The provision of radial roller bearings for the rotor shafts makes it possible to reduce the clearance between the rotors and between the rotors and the casing to a veiy small value so that leakage through the machine is reduced to a minimum and the eihciency is increased which is also a result of the reduced bearing loads and of the reduction of the frictional resistance produced thereby.

2,953,884 Patented Dec. 13, 196() are The invention has, furthermore, the advantage that the casing enclosing the rotors may be divided horizontally along the common rotor shaft plane so that the upper half `of the casing may be `removed for inspection without moving other parts of the machine or of the pipe connections. The provision of noise-emitting pipes and conduits below the door of the room in which the compressor or motor is mounted reduces the disturbing noise in said room materially so that the noise in said room is on an acceptable level and, furthermore, the forces originating from the system of pipes and conduits is transmitted directly to the foundation of the compressor or motor without stressing the compressor or motor casing. By providing the opening in which the high pressure prevails at the underside of the casing, said casing may without inconvenience be provided with stiffening ribs or the like at the portion which has the greatest load. Conduits to an intermediate cooler of a compressor which may preferably be disposed below the door level may in accordance with the invention be made with reduced length which also helps to maintain good ediciency and to lreduce the disturbing noise.

The above and other `detailed objects of the invention and the advantages to be derived from its use will appear as the ensuing portion of this specification proceeds.

In the accompanying drawings one embodiment of a compressor plant and a screw compressor embodying the invention is illustrated by way of example.

Fig. l isa side view and partial section of a compressor plant embodying the invention. Fig. 2 is an end view of the plant according to Fig. l. Fig. 3 is a longitudinal section through yone of the screw compressors shown in Figs. l and 2. Fig. 4 is a plan View of the compressor shown in Fig. 3. Fig. 5 is a section yon line V-V in Fig. 3, and Fig. 6 is a section on line VI--V I in Fig. 3.

The compressor plant illustrated in Figs. l and 2 consists of a low-pressure compressor 1, a high-pressure compressor 2 and an electric motor 3 which drives the compressors. The motor and the compressors are mounted in a machine room on a concrete foundation 4. The compressors 1 and 2 are essentially of the same design and in order to disclose the invention the high pressure compressor 2 only is described in detail. Said compressor consists of a casing which comprises a lower portion 5 and an upper portion 6 providing two horizontally extending intersecting bores for the reception of the rotors, a two-piece intake end closure structure 7, S, and an end closure structure 9 at the outlet end. Air is supplied to the compressor '2 through a conduit 10 which at the opening 11 is connected to the underside of the casing portion 7, S, and the air compressed in the compress-or 2 is discharged from the compressor through a pipe 12 which at the opening 13 is connected to the underside of the compressor casing portion 5. In the compressor casing two screw-

type rotors

14 and 15 are mounted with their shafts in radial Iroller bearings 16 and 17, respec tively, with the shafts disposed in a single horizontal plane 31. The rotors are, furthermore, provided with plain thrust bearings 13 at one end to take care of the axial forces. From the opening 11 the passage 19 in the inlet

end closure structure

7, 8 leads to an inlet port 2G at one end of the upper end portion of the bores in which the rotors are situated and from an outlet port 21 at the lower end portion of the bores in which the rotors are situated a passage 22 runs from the underside of the rotors to the pipe 12 and further through an aftercooler 23 to a pipe line 24. From the drawings it will be evident that the inlet and outlet ports may be said to be disposed, respectively, at the diagonally opposite upper and lower end portions of the bores in the casing. Air from the atmosphere is admitted -at 25 and conducted through a pipe 26, an admission valve 27 and a pipe 28 to the lowpressure compressor 1. From the low-pressure compressor the air is conducted through a pipe 29 and an intermedi-ate cooler 30 to the pipe 10 and the highpressure compressor 2 as described hereinabove. All pipes and coolers are disposed below the floor 32 of the machine roorn.

The compressor described hereinabove and illustrated on the accompanying drawings should be considered only as an example and the details of the invention may be modified in several different ways within the scope of the claims` In order to unload the rotors from axial pressure the rotors of the highand low-pressure stage may, for instance, be connected. The invention may, as stated in the preamble of this specification, also be employed in screw motors which are driven by compressed air or hot gas. The invention may naturally be used in connection with twoor multiple-stage com pressors as well as in single-stage compressors.

What we claim is:

l. A rotary device of the character described for operation with an elastic uid working medium comprising a casing having two horizontally extending intersecting bores and closure structure at the ends of said bores and said casing further having a low pressure port and a high pressure port located, respectively, at the diagonally opposite upper and lower end portions of said bores, two screw-type rotors mounted for rotation in said bores and intermeshing to form working chambers for said working medium, which chambers register with different ones of said ports in different positions of rotation of the rotors and progressively decrease in length toward the highY pressure port as therotors revolve, said rotors having shafts located in a common horizontal plane in said casing, radial roller bearings mounted in said closure structure for supporting said rotor shafts in said casing, a first passage for low pressure working medium extending from a first opening on the underside of said Y y casing to said low pressure port, and a second passage for high pressure working medium extending from said high pressure port to a second opening on the underside of said casing.

2. A device as defined in claim l, in `which said first passage comprises two branches extending respectively on opposite sides of the mountings for said bearings to connect said first opening with said low pressure port.

3. A rotary compressorplant of the character de scribed for compressing an elastic Huid Working medium comprising a oor structure, a foundation structure, a compressor casing having two horizontally extending intersecting bores and closure structure at the ends of said bores and said'oasing further 'having a low pressure inlet port and a high pressure outlet port located, respectively, at the diagonally opposite upper and lower end portions of said bores, two screw-type rotors mounted for rotation in said bores and intermeshing to form working chambers for said working medium, which chambers register with different ones of said ports in different positions of rotation of said rotors and progressively decrease in length toward the high pressure port as the rotors revolve, said rotors having shafts located in a common horizontal plane in said casing, radial roller bearings mounted in said closure structure for supporting said rotor shafts in said casing, a rst passage for low pressure working medium extending from a rst opening on the underside of the casing to sm'd low pressure inlet port, a second passage for high pressure working fluid extending from said high pressure port to a second opening on the underside of said casing, a cooler mounted in said foundation structure, a fluid intake passage in said foundation structure, a first conduit disposed substantially in said foundation structure and leading from said intake passage to said rst passage in the casing, a second conduit disposed substantially in said foundation structure and leading to said cooler from said second passage in said casing, and means carried by said foundaton structure and Adisposed substantially above the level of said door structure for driving said rotors.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,653 Boestad inne 28, 1949 2,727,364 Perez Dec. 20, 1955 FOREIGN PATENTS 384,355 Great Britain Dec. 8, 1932