US3020102A - Molecular pumps - Google Patents

Description

Feb. 6, 1962 w. BECKER MOLECULAR PUMPS Filed March 9, 1960 5 3 7 2 T m w w 7 1 7 9 7 7 mi 6 .I\ 7 .I

Z x F Jlv 5 I G I F INVENTOR M ILA. I BECKE )2 W M //7 W70 10 I'KXSV/D A m Attorneys rates Patented Feb. 6, 1962 3,020,102 MOLECULAR PUMPS Willi Becker, Ehringshausen, Kreis Wetzlar, Germany,

assignor to Arthur Pfeiifer G.m.b.H., Wetzlar, Germany Filed Mar. 9, 1960, Ser. No. 13,895 4 Claims. (#Cl. 308-77) This invention relates to pumps for producing high vacua, which are known in various forms under the name of molecular pumps. The operation of these pumps is based on the fact that the gas or the gas molecules have a movement impulse imparted thereto in the direction from high vacuum to a preliminary vacuum by external friction against a rotary member.

One known and particularly advantageous embodiment of a molecular pump of this nature is illustrated in FIGS. 1 and 2 of the drawing. 'In this pump the co-operating parts of the rotary member and the casing comprise discs having slot-like recesses, which alternate in the direction of the axis of the rotary member, and at least the slots of the discs of one part have two lateral bounding faces, which are inclined in relation to the axis of the rotary member and form with the end face of the discs of the other part a wedge-shaped chamber tapering in the direction of movement of the rotary member.

In molecular pumps of the kind referred to the bearing plates accommodating the bearings for the pump shaft bound the pressure chamber or chambers of the pump communicating with the backing pump. Accordingly in the pressure chambers themselves there is merely a very low pressure. In pumps of this nature there is the danger that the oil or grease serving to lubricate the bearings becomes heated by the friction in the bearings, that oil or grease vapours reach the pressure chambers and condense against the cooler parts of the pump to form a film, and that the film creeps along the walls of the pump and reaches the suction side of the pump, i.e., the high vacuum side, vaporises there and by reason of its vapour pressure causes deterioration of the vacuum. This danger is avoided by the bearing arrangement according to the invention.

According to the invention, there is secured to the inner side or" each bearing plate bounding the pressure side of a molecular pump a casing which encloses the opening in the bearing plate, surrounds the shaft with slight clearance, and is furnished with cooling chambers, and which is provided with a return pipe for the oil passing out of the bearing. The casing is preferably divided by means of a wall which is disposed vertically to the shaft of the pump, possesses an opening for the passage of the shaft, and leaves at the lowest point of the casing a connection between the two chambers. The shaft is preferably stepped twice within the casing in order to prevent a creeping of the oil along the shaft. At the lowest point of the casing there is provided a discharge pipe for the oil, which is forced by a pump in circulation through the bearing.

By means of the bearing arrangement according to the invention it is accomplished that oil vapours formed upon the passage of oil into the pressure chamber of the pump condense substantially in the first chamber of the casing, the condensate being discharged together with the oil accumulating on the bottom of the chamber. So far as vapours reach the second chamber, these finally condense in that chamber and the condensate is likewise discharged together with the oil accumulating on the bottom of the chamber.

Furthermore, according to the invention, the cooling chamber is so constructed that it surrounds the casing, and the connecting sockets of the molecular pump for motor or carries a suitable driving element.

connection of the backing pump are so arranged on the pump casing that they are located at the lowermost point of the pump casing below the cooling chamber. There is thus also obtained at the same time a cooled surface directed towards the pressure chamber of the pump, which surface in conjunction with the arrangement of the sockets provides the advantage that vapours sucked up from the container condense against the surface of the cooling chamber and the condensate dropping off therefrom passes directly into the suction pipe of the backing pump. It is thus avoided that the sucked up vapours condense at any other points of the pump and pass as a film to the suction side of the pump.

An embodiment of the invention is described by way of example in the following in conjunction with the accompanying drawing, in which I FIG. 1 is a longitudinal section through a molecular pump of the kind initially referred to above.

FIG. 2 is a cross-section through the development of the slotted discs of the two pump parts.

FIG. 3 shows to enlarged scale a longitudinal section similar to FIG. 1, with omission of the middle portion, of a pump furnished witha bearing arrangement according to the invention.

The cylindrical casing 1 of the molecular pump is closed at the ends by the bearing plates 2 and 3, and carries in its middle portion a socket 4 for connection of the suction pipe leading to the apparatus to be evacuated. Other sockets shown at 5 serve for connection of the pressure pipe leading to a backing pump. In the bearing plate 2 and 3- there is mounted the shaft 6 of the rotary portion of the pump. The shaft journal 7 passes through the plate 3 and is either directly coupled to the driving A seal 8 prevents gases from entering the pump.

The shaft 6 carries a plurality of discs 9, in the example shown eight discs, which are connected to the shaft to be rigidly rotatable therewith. These discs are located with slight clearance between the discs shown at 10, which are firmly mounted in the shell 1 of the casing and have at their centre an opening for the passage of the shaft 6. The fixed discs 10 are so arranged in the pump casing that at the centre of the pump there is formed a suction chamber 11 and at each end a pressure chamber 12. As shown by FIG. 2, the discs 9 possess on the outer periphery recesses or slots shown at 13. The individual slots are separated from each other by the tooth-like portions 14. Similar slots 15 are provided on the outer periphery of the discs 10 fixed to the casing. The teeth separating the same are shown at 16 (FIG. 2).

The new bearing arrangement in respect of a pump of this nature is shown in FIG. 3. To the inner side of the two bearing plates 2 and 3 there is secured a cylindrical casing 17, which comprises a shell 18 and a bottom 19 having an opening 2%) for the passage of the shaft 6. The shaft itself is stepped in diameter twice. The part shown at 21 is mounted by way of a bush 22 in the annular abutment 23 of the two plates 2 and 3. The stepped portion 24 is likewise located within the casing 17. The casing itself, by means of a wall 25, which is secured therein, is disposed vertically to the shaft 6 and possesses an opening 26 for the shaft portion 24, is divided into two chambers shown at 27 and 28. The wall 25 terminates closely above the lowermost point of the casing, so that the two chambers communicate with one another. The opening 26 surrounds the shaft portion 24- with slight clearance.

The shell 18 is surrounded by a second shell 29 having a flange 30; the annular space between the shells 18 and 29 is shown at 3-1. For attachment of the casing 13 there are employed screws 32, and for sealing purposes the sealing rings shown at 33 and 34. The outer chamber 31 possesses a supply pipe 35 and a discharge pipe 36 for the cooling agent, for example water. For the supply of oil there is employed a pipe 37 and for discharge of the oil from the chambers 27 and 28 a pipe 3'5. The pipe 35 is connected to a cold water pipe, the pipe 36 leads to a discharge. The pipe 37 is connected to a pump 39, which forces oil through the bearing, and the pipe 38 to the reservoir of the pump 39.

In the drawing there are shown for the sake of better comprehension two pumps, one for each bearing. In the practical embodiment there will be employed only one pump, which will supply both bearings with oil. The oil supplied to the bearings 22 by the pump 39 accumulates in the chamber 23 and again flows off through the pipe 38. Any oil vapours formed in the chamber 28 condense therein, as the shell 18 is maintained at a low temperature by the cooling water in the annular chamber 3i. So far as oil vapours should still pass through the gap 26 into the chamber 27, they will condense in that chamber and the condensate will flow back into the chamber 28 and be discharged through the pipe 38.

Oil vapours which are sucked up from the vessel to be evacuated and reach the pressure chamber 12 condense against the surface of the shell 29. The condensate runs along the surface to the lowest point of the shell 29 and there drips off. Below the lowest point of the shell there are provided in contradistinction to FIG. 1 the sockets for connection of the backing pump, so that the condensate dripping off passes directly into the sockets 5 and from there to the backing pump.

I claim:

1. In a bearing arrangement for molecular pumps, pressure chambers in a pump which are subjected to a preliminary vacuum, a pump shaft for the pump, bearing plates bounding the said pressure chambers and each plate having an opening therein, a casing secured to the inner side of each bearing plate, each casing enclosing the opening in the respective bearing plate and surrounding the pump shaft with slight clearance, cooling chambers in association with said casing, and a return pipe for oil passing out of the bearing plates.

2. In a bearing arrangement for molecular pumps, pressure chambers in a pump which are Subjected to a preliminary vacuum, a pump shaft for the pump, bearing plates bounding the said pressure chambers and each plate having an opening therein, a casing secured to the innerside of each bearing plate, each casing enclosing the opening in the respective bearing plate and surrounding the pump shaft with slight clearance, a wall in each casing disposed vertically to the said shaft and traversed thereby, the said wall dividing the said casing into two axially adjacent chambers, each wall having an opening therein surrounding the shaft with slight clearance, and the said two chambers being connected together at the lowest point of the said casing by means of a passage in the said well, and a return pipe for oil passing out of the bearing.

In a bearing arrangement for molecular pumps, pressure chambers in a pump which are subjected to a preliminary vacuum, a pump shaft for the pump, bearing plates bounding the said pressure chambers and each plate having an opening therein, a casing secured to the inner side of each bearing plate, each casing enclosing the opening in the respective bearing plate and surrounding the pump shaft with slight clearance, the said shaft having two stepped sections within the said casing, cooling chambers in association with each casing, and a return pipe for oil passing out of the bearing.

4. In a bearing arrangement for molecular pumps, pressure chambers in a pump which are subjected to a preliminary vacuum, a pump shaft for the pump, bearing plates bounding the said pressure chambers and each plate having an opening therein, a casing secured to the inner side of each bearing plate, each casing enclosing the opening in the respective bearing plate and surrounding the pump shaft with slight clearance, a shell surrounding said casing and forming together with said casing an external annular cooling chamber, intake and discharge means in association with said cooling chamber, sockets for a connection of pipes leading to a backing pump, said sockets being located at the lowest point of the said casing below the said shell, and a return pipe for oil passing out of the bearing.

References Cited in the file of this patent UNITED STATES PATENTS 802,453 Johnson Oct. 24, 1905

Images