US3623826A

US3623826A - Turbine pump with improved rotor and seal constructions

Info

Publication number: US3623826A
Application number: US869842A
Authority: US
Inventors: Arman Mandell; Gordon Osterstrom
Original assignee: Sargent Welch Scientific Co
Current assignee: Sargent Welch Scientific Co
Priority date: 1969-10-27
Filing date: 1969-10-27
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30

Abstract

A high-vacuum axial flow turbine pump having novel oil seal and rotor constructions. The rotors are machined from a single blank of material and include a row of inclined blades divided into a plurality of segments each defined by a pair of inclined faces, offset from but parallel to the inclined faces on an adjacent segment of the blade. The improved oil seal closely surrounds an end portion of the impeller shaft containing a plurality of the rotors, and includes a pair of seal elements having inwardly directed annular faces, and a pair of oil collector grooves, one associated with each seal element, with the axially innermost groove having a foam or like insert therein for picking up oil and transferring it by capillary action and gravitational force to an outlet in a lower portion of the seal.

Description

United States Patent lnventors Arman Mandel] Chicago; Gordon Osterstrom, Winnetka, both of 111. App]. No. 869,842 Filed Oct. 27, 1969 Patented Nov. 30, 1971 Assignee Sargent-Welch Scientific Company Skokie,1l1.

TURBINE PUMP WITH IMPROVED ROTOR AND 8/1935 Barker 416/237 Primary Examiner-Henry F. Raduazo Alrurne vGreist Lockwood. Greenawalt & Dewey ABSTRACT: A high-vacuum axial flow turbine pump having novel oil seal and rotor constructions. The rotors are machined from a single blank of material and include a row of inclined blades divided into a plurality of segments each defined by a pair of inclined faces, offset from but parallel to the inclined faces on an adjacent segment of the blade. The improved oil seal closely surrounds an end portion of the impeller shaft containing a plurality of the rotors. and includes a pair of seal elements having inwardly directed annular faces, and a pair of oil collector grooves one associated with each seal element. with the axially innermost groove having a foam or like insert therein for picking up oil and transferring it by capillary action and gravitational force to an outlet in a lower portion of the seal.

PATENTED nnvao :97:

SHEET 2 BF 2 /00 B 98 A /////I//' IN VE N TORS GORDON E. OSTERSTROM TURBINE PUMP WITH IMPROVED ROTOR AND SEAL CONSTRUCTIONS BACKGROUND AND DESCRIPTION OF THE INVENTION Until recently, it had been generally believed that turbinetype pumps were not able to be used advantageously in highvacuum systems. However, as a result of new theories and recent improvements in the technology of turbine pumps, it has become apparent that, with a properly designed pump, a number of advantages can be obtained. Following the discovery that suitable pumps may be used for this purpose, a number of pump designs have been proposed, some of which have actually been manufactured and sold.

These pumps, while offering a number of advantages, and being operative to produce good results, are nonetheless capable of being further improved. Two areas in which such improvements have been needed are those of producing suitable impellers and of insuring that the advantages of the high vacuum levels attainable in the improved pumps will not be nullified by reason of poor oil control in the pump units. Referring now to the first problem area, namely, that of impeller production, it is common to fabricate a single, build-up impeller by fastening together a large number of disclike rotor elements in an axially aligned relation, with a turbine pump impeller typically comprising at total of to or more rotor elements, arranged into several groups, with the rotors in each group being substantially identical with one another, but different from the rotors in another rotor group. In particular, according to recently developed theories which have apparently been proved in practice to be substantially correct, it is desired to produce an axially thin rotor element having thin, fairly long span blades thereon, spaced apart from each other by a distance which is a multiple of several times the blade thickness. Such blades, according to the prior art, might be made by casting, machining or forging. Since the rotor elements in question may be rotated at rotor speeds of 10,000 to 20,000 r.p.m. or more, high strength and nearly perfect dynamic balance are essential.

It is fairly well established that unless very exotic materials are used, castings will lack at least one of these properties. Forgings of complex blade shapes is difficult, expensive, and time consuming. Machining blades on the peripheral portions of a rotor blank is a satisfactory method of forming turbine rotor blades; however, the shapes indicated by theoretical and experimental considerations are not easy to machine by known methods. Accordingly, there has been a need for a rotor element of a configuration which maybe easily machined by conventional apparatus and techniques, and which will nevertheless provide blade shapes capable of producing the vacuum levels desired.

Referring again to the problem of oil control, seal designs which are satisfactory in use have been made, but these designs are also of a construction which makes them difficult to manufacture and install, with the result that vacuum pumps incorporating efi'ective seals have heretofore been troubled by the problem of excessive cost of seal assemblies therefor.

In view of the foregoing problems, an object of the invention is to provide a vacuum pump including an improved oil seal and an improved rotor construction.

Another object is to provide a rotor assembly which can be simply, rapidly and accurately machined by existing techniques and apparatus.

A still further object is the provision of a rotor element having segmented blades with the blade segments being defined in part by face portions which are parallel to, but offset from, one another.

Another object is the provision of a rotor assembly having blades thereon which have increased effective working spaces between blades near a radially outer portion of the blades, and decreased working spaces between blade segments near the inner portions of the blade.

A still further object is to provide a rotor element in which the faces of the blades are comprised entirely of planar surfaces.

Another object is the provision of a one-piece rotor assembly which may be manufactured by a simple method.

Still another object is the provision of an improved turbine pump oil seal assembly.

Another object is the provision of an oil seal assembly having two elements, each having an oil return groove associated therewith, with the grooves being axially offset from each other, and with at least one groove having means therein for directing oil flow to the grooves by capillary action as well as by gravity.

Another object is to provide an oil seal for a turbine pump of the type just described, which is easy to manufacture and which is readily adapted to be manufactured in a one-piece construction.

These objects and advantages of the invention, and other, including those inherent in the invention, are accomplished by providing a turbine pump having a plurality of rotor elements, each with a row of blades disposed about the periphery of the hub thereof, and in which each blade is segmented blade having the segments thereof defined in part thereof by pairs of angularly disposed front and rear blade face portions forming each segment, which are parallel to the pairs of faces in an adjacent segment but are offset relative thereto, and by providing a seal construction which includes two seal members an oil return groove associated with each of said seal members, as well as means in at least one of the grooves for collecting and retaining oil therein at least partially by capillary action.

The manner in which these objects and advantages are achieved will be more clearly understood when reference is made to the following detailed description of the preferred embodiments of the invention, and to the accompanying drawings forming a part hereof, in which like reference numerals indicate corresponding parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partially in elevation and partially in section, showing a vacuum pump including the oil seal of the invention;

FIG. 2 is a vertical sectional view on an enlarged scale, showing the oil seal assembly of the invention;

FIG. 3 is a perspective view, partially diagrammatic, showing a rotor and a cutting tool used in the manufacture thereof;

FIG. 4 is an enlarged fragmentary front elevational view of a portion of the rotor element of the invention; and

FIG. 5 is a sectional view of one segmented rotor blade of the invention; and,

FIG. 6 is a view of some of the rotor blades of FIG. 4, taken looking radially inwardly along the line 6-6 of FIG. 4.

Referring now to the drawing in greater detail, the invention will be described with reference to a vacuum pump 20 embodying the novel oil seal arrangement 22 and the novel rotor construction 24 of the invention.

Referring particularly to FIGS. 1 and 2, it can be seen that the pump 20 includes a connector flange 26 for attachment to a region to be evacuated, a cylindrical casing 28 and an impeller 30 disposed centrally therein. The impeller 30 consists of a plurality of rotor elements 24, to be described in further detail herein, with each rotor element 24 being disposed adjacent an associated stator 32 fixed in place by support rings 34 disposed within the casing 28. An end portion of the impeller 30 includes a driven gear 36, an enlarged diameter first bearing surface 38, and a second bearing surface 40, each having a fixed bearing unit 42, 44 associated therewith. Axially inwardly of the bearing surface 40 is a reduced diameter shaft portion 46, and axially inwardly thereof are a pair of

slinger surfaces

48, 50 separated by a shaft groove 52 disposed therebetween. By a slinger surface is meant one which is adapted to throw off oil falling thereon by reason of centrifugal force attendant to high speed rotation.

Surrounding the parts just named is a seal body 54 which includes one or more openings 56 extending axially thereof for reception of mounting fasteners 58 or the like. The body 54 also comprises a first, axially outer seal element 60 defined in part by a radially inwardly facing, annularly extending surface 62, which is spaced apart from the slinger surface 48 by a working clearance of 0.005 up to 0.015 inches. A first oil groove 64 lies radially outwardly of the surface 62 and the radially innermost portion of the groove lies substantially in a plane extending through the axial center of the opening in the body 54 defined by the surface 62. A collector surface 66 lies radially outwardly of and is joined to groove 64 by a transition surface 68. A second, axially inner seal element 70 is partially defined by a radially inwardly facing annularly extending surface 72 which is of enlarged diameter in respect to surface 62 and is spaced apart from slinger surface 50 by a working clearance of the order of 0.005 to 0.0l5 inches. The element 70 is also partially defined by a wall section 74 terminating in a second oil collector groove 76 having an insert 78 of a porous material, such as a synthetic resin foam, snugly disposed therein. In use, liquid oil or oil vapors are fed through line 80 and passage 82 into the space between the bearings 42, 44, where the major portion thereof is retained for a relatively long period. Oil passing axially inwardly of the impeller 30

contacts surfaces

46, 48 and 50, but is thrown therefrom by centrifugal force and collected in

grooves

64, 74. Oil appearing in grooves 64 flows down by gravity into the discharge area 84 of element 60, while oil thrown into the groove 76 is trapped by capillaryaction within the insert 78 and between the insert 78 and the walls defining the groove. Oil thus trapped in this groove collects in the outlet 86 disposed at the bottom portion of the seal body 54. A sea] constructed as set forth above is effective to prevent axial flow of liquid oil along the axially outer parts of the impeller shaft 30 and is also suitable for collecting substantial amounts of condensed oil vapors.

Referring now to the construction of a novel rotor unit, a rotor assembly 24 is shown in FIG. 3 to include a hub portion 88 and a plurality of blades 90, each comprising, in the illustrated embodiment, three segments, A, B, and C. Segment A is the radially outermost segment, segment B lies just inwardly thereof, and segment C is the innermost segment and terminates at a blade root portion 92 adjacent the hub 88. Each blade includes a flat front face portion 94 which, in the embodiment illustrated, lies in a single plane. A rear face portion 96 is disposed parallel to the front face portion 94, and also lies in a single plane, the planes of both

faces

94, 96 being parallel to the plane of rotation of the rotor assembly 24.

As may be noted by particular reference to FIG. 6, segment A comprises a leading, inclined face portion 98, and segment B includes an inclined working face 100 which is parallel to but offset from the plane occupied by face 98. Segment C includes a front working face 102, which is also parallel to the planes of

faces

98, 100 but is offset therefrom along a line perpendicular t the planes of the other faces. By further reference to FIG. 6, it will be noted that trailing edge faces 104, 106, 108 are provided on segments A, B, and C, and that these faces are parallel to but offset from one another, so that the spacing between any one trailing edge 104 and its counterpart leading edge 98 on an adjacent blade is greatest on the radially outwardly disposed segments, and that this interblade spacing is somewhat less in respect to faces 100, I06 and still less in regard to

faces

102, 108, although the spacing therebetween is still significant in relation to the thickness of the blade. That is, the ratio of the thickness of a blade 90 measured at segment A of the blade, to the distance to a face of an adjacent blade is on the order of about 4 or to 1, although it may be about 2 or 3 to I measured between the

inclined faces

102, 108 on segment C, for example.

In the embodiment illustrated, it may be seen, by reference to FIG. 4, that particularly in the areas segments A and B, there is a line of sight through the rotor element 24 between blades 90, the line of sight being taken parallel to the rotor axis of the impeller shaft. It will be understood that this interblade space is a function of blade thickness, blade angle, and interblade spacing.

Rotors made according to the present invention are used in turbopumps, not only in the inlet stages of the pumps, but also in the intermediate stages, and in some cases, the outlet stages. In some of these stages, particularly the intermediate stages, it is desired that the angle of blade inclination be considerably flatter than the angle of inclination of such blades on inlet stage rotors, with the result that there may be reduced thickness lines of sight axially through the rotors, or even no axial line of sight at all, because of overlap between a trailing edge of one rotor blade and a leading edge of the next following blade. However, the advantages of strength, economy and simplicity without noticeable sacrifice of performance are still present in such rotors.

It will be further understood that a turbopump may be made which incorporates stator blades formed in the manner described. Although stators are not subjected to centrifugal force, balancing stresses, and the like, stators which have the same blade configuration as that shown herein for rotor blades are nonetheless operative and perform excellently. In fact, one advantage of making stator blades having the configuration shown is that such blades will, when made in the same manner with the same tooling, inherently be formed in substantially a mirror image relation to the rotors with which they are associated in use, which is desireable for achieving uniform gas flow. Thus, the invention is operative and advantageous as applied to both rotors and stators.-

Referring now to FIG. 3, there is shown somewhat diagrammatically a method of making the rotors 24. FIG. 3 shows a milling cutter 110 rotatably mounted on a shaft 1 12, and comprising a central, large diameter disc 114, a pair of smaller diameter discs disposed concentrically of and on either side of disc 114 (only one disc 116 being shown), and still further reduced diameter discs 118 (only one shown) lying outwardly of disc 116. Each

disc

114, 116, 118 includes a cutter element 120 thereon. Accordingly, it will be seen that a rotor or stator may be made by rigidly supporting the rotor or stator element in a suitable jig, and, with the rotor disc 24 disposed in a given plane, the disposition of the milling cutter is arranged relative thereto so that it is directed inwardly toward the center of the rotor 24 along a radius thereof, and lies in a plane which is inclined so as to be disposed at an acute angle with respect to the rotational plane of the disc 24. Thereupon, the cutter 110 may be moved inwardly, and sidewalls 102, 108 are formed by the cutter disposed on disc 114, while

walls

100, 106 and 98, 104 are formed by the cutters disposed on

discs

116 and 118, respectively.

In the illustrated embodiments, three blade segments are shown, but it will be understood that it is not necessary to the invention that any particularly number of segments are provided. Likewise, the exact angle or depth of cut is not critical, nor is the fact that the segments are of equal radial extent of controlling importance. It is, however, an advantage of the invention that maximum strength consistent with maximum interblade spacing and minimum blade thickness be provided. In this connection, it will be understood that the problem of supporting the rotor during blade formation is a prior art problem which has been very significant, but which is substantially overcome by providing the construction and method shown herein. It will be further noted by reference to FIG. 3, for example, that the cutting elements 120 of the cutter 110 have the sharpened edge portions thereof lying along the radially outward portion of the cutter 110 which lies in the direction of tool advance, and accordingly, the cutting action takes place along such surface as the cutter is moved radially inwardly of the rotor. This does away with the need for cutters which would engage inclined faces of the blades along the plane thereof, which would be necessary if a blade with parallel edges and constantly decreasing interblade spacing adjacent the hub were attempted to be formed by conventional techniques.

Accordingly, it will be seen that the present invention provides a turbopump having an improved rotor construction and an improved oil seal construction, and accordingly a pump which possesses a number of advantages and characteristics, including those referred to herein and others which are inherent in the invention.

We claim:

I. A rotor element for use in a high vacuum, axial flow turbine-type pump, said element being integrally formed of a single piece of material and including a hub portion disposed generally centrally thereof for association with a rotatable portion of a shaft to provide rotary motion for said element, and multiplicity of blades disposed about the periphery of said hub, each blade including a plurality of blade segments, said blades being defined in part by front and rear planar blade surface portions which are generally parallel to each other and to the plane of rotation of the rotor element, and further defined by a plurality of pairs of angularly inclined working face portions, one pair of said face portions being provided for each of said segments of said blade, said working face portions extending between said front and rear surface portions, all of said pairs of working face portions being parallel to one another, with each pair comprising one blade segment being offset from the pairs of faces comprising other segments of said blade, the faces comprising one of said pairs of working faces on a radially relatively more outwardly disposed segment being more closely spaced apart from each other than are the faces defining a segment of the same blade lying radially inwardly of said relatively more outwardly disposed segment, the innermost segments of said blades exhibiting overlap when viewed in a plane non'nal to the frontal faces thereof so as to obstruct a line of sight therethrough.

Claims

1. A rotor element for use in a high vacuum, axial flow turbinetype pump, said element being integrally formed of a single piece of material and including a hub portion disposed generally centrally thereof for association with a rotatable portion of a shaft to provide rotary motion for said element, and a multiplicity of blades disposed about the periphery of said hub, each blade including a plurality of blade segments, said blades being defined in part by front and rear planar blade surface portions which are generally parallel to each other and to the plane of rotation of the rotor element, and further defined by a plurality of pairs of angularly inclined working face portions, one pair of said face portions being provided for each of said segments of said blade, said working face portions extending between said front and rear surface portions, all of said pairs of working face portions being parallel to one another, with each pair comprising one blade segment being offset from the pairs of faces comprising other segments of said blade, the faces comprising one of said pairs of working faces on a radially relatively more outwardly disposed segment being more closely spaced apart from each other than are the faces defining a segment of the same blade lying radially inwardly of said relatively more outwardly disposed segment, the innermost segments of said blades exhibiting overlap when viewed in a plane normal to the frontal faces thereof so as to obstruct a line of sight therethrough.