Sealing Assembly With Pump Device

Abstract

A sealing assembly for a rotatable shaft, wherein a cooling, lubricating, or buffer medium is circulated by means of an external thread on a rotatable member and an internal thread in a non-rotatable member. The internal thread has a hand opposite to that of the external thread and surrounds the latter with a small radial clearance.

Description

This invention relates to sealing assemblies or mechanical seals of the kind having at least one pump device arranged adjacent to the slide surfaces within the shaft-receiving bore containing the seal, said pump device serving to circulate a cooling, lubricating, buffer or sealing medium, the part of said pump rotating with the shaft having an external thread coaxially surrounding the shaft and intended to convey the medium. Such seals will be referred to hereinafter as seals of the type stated.

In a known seal of such type, the pump device serves as a rule to convey a fluid coolant to a heat-exchanger arranged outside of the seal, and back to the seal. A disadvantage in pump devices in which the external thread rotating with the shaft is surrounded by a smooth, stationary, cylindrical bore, is that the necessary circulating quantity and thus adequate cooling can be achieved only at high numbers of revolution. This is attributable to the fact that the known conveying thread results only at high circumferential speeds in a pressure which is sufficient to overcome the flow resistance of the circulatory path in which magnetic filters, separators and the like may be arranged.

Other pump devices known in seal assemblies have a relatively large radial dimension and, therefore, cannot be arranged in the shaft-receiving bore containing the seal assembly, or are very inefficient, which, in itself, is disadvantageous on account of the additional heating thereby generated in the coolant.

An object of the present invention is to provide a seal of the kind stated whose pump device has a small radial dimension, but produces a high conveying pressure and output of the conveyed medium, even at relatively low numbers of revolution.

According to the invention we provide a seal of the kind stated, in which an internal thread stationary in relation to the casing containing the shaft-receiving bore surrounds the external thread with a small radial clearance, the hand of said internal thread being opposite to that of the outer thread. Tests have established that the pressure generated by such a pump device is up to eight times higher than by one wherein a conveyor thread rotates in a smooth bore, and thus a very high degree of hydraulic efficiency can be attained.

The internal thread is preferably formed in a separate, immovable bush set in the shaft-receiving bore.

The external thread may be formed on a component adapted to rotate with the shaft but axially movable relative thereto. The component may be a rotating slide-ring itself. The axial reactive thrust generated by the conveyance of the medium on the external thread may be used to modify the pressure force exerted by the slide-ring on the counter-ring, depending on the direction of rotation and on the number of revolutions.

Embodiments of the invention will now be described by way of example, with reference to the drawings, in which:

FIG. 1 is a fractional axial section through a first embodiment of a seal assembly according to the invention, in which the outer thread serving for conveyance is arranged on a sleeve carrying the rotating counter-ring member;

FIG. 2 is a fractional axial section through a second embodiment of a seal assembly according to the invention, in which the outer thread is arranged in a sleeve carrying the rotating slide-ring member and a guide-plate is provided to direct the flow of fluid to the sealing surfaces;

FIG. 3 is a fractional axial section through a third embodiment showing a double seal according to the invention, wherein the outer thread is formed in a bush which is separate from and surrounds carrier-sleeve means;

FIG. 4 is a fractional axial section through a fourth embodiment showing a double seal according to the invention, in which two pairs of outer and inner threads are provided;

FIG. 5 is a fractional axial section through a fifth embodiment of a seal according to the invention, in which the pressure spring of the slide-ring forms the conveyor thread;

FIGS. 6 and 7 show details.

Identical or identically-acting components are designated with corresponding reference numerals throughout the drawings. The suffixed letters a and b indicate whether certain sealing elements are non-rotatable or rotatable, respectively.

In the embodiment of FIG. 1, a shaft sleeve 2 is rigidly mounted about a shaft 1 in a fluid-tight manner, a carrier sleeve 3b being mounted on the shaft sleeve 2 and held in place by a screw 4. An O-ring 6 in an annular groove 5 of the carrier sleeve 3b serves as a seal between the sleeves 2 and 3b. A counter-ring member 7b is rigidly seated in carrier sleeve 3b, a non-rotatable slide-ring member 8a bearing against said counter-ring member 7b and being rigidly seated in a carrier sleeve 9a which is in turn seated non-rotatably but in the axial direction movably in an annular groove 10 of a cover 13 closing off the stepped, shaft-receiving through-bore 11 of a casing 12. Cover 13 is secured in a fluid-tight manner to casing 12 which is stationary relative to shaft 1 and may be mounted on a support (not shown). Casing 12 and cover 13 together form the housing of the sealing assembly. The carrier sleeve 9a and slide-ring 8a are urged towards the counter-ring 7b by a plurality of springs 14a, one of which is shown in FIG.1 An O-ring 10 R is positioned between carrier sleeve 9a and cover 13.

A multiple external thread 15 is tapped in the outer circumference of carrier sleeve 3b, said thread, in axial section, having a rectangular shape. It should be noted that thread 15 is positioned within bore 11 in spaced relationship to the wall of the bore.

The carrier sleeve 3b, whose bounding surface envelope is cylindrical, is surrounded with slight radial clearance by a bush or bushing 16 of approximately the same axial length, which is immovably set in the stepped bore 11. A thread 17 is tapped in the cylindrical bore of bush 16, the thread 17 being similar to the thread 15 in carrier sleeve 3b, but the hands of the threads being opposite to each other. Thus, a left-hand thread 15 will be associated with a right-hand thread 17, and vice versa.

The two threads 15 and 17 form the active parts of a pump device which, when shaft 1 rotates, sucks in a cooling, lubricating, buffer or sealing medium by way of an inlet bore 18 provided in casing 12, and conveys or propels it from there above counter-and slide-ring members 7b and 8a to an outlet bore 19 passing through cover 13. The inlet bore 18 and outlet bore 19 are connected by way of conduits with a heat-exchanger (not shown in FIG. 1) which cools the medium before it enters the seal again.

Screw 4 is preferably provided in the vicinity of the axial end region of thread 15, and then only a small reduction in the hydraulic efficiency occurs because of the disturbance in the contour of the conveying threads. The required pump capacity and pressure can be obtained by changing the number of threads, the thread pitch and the groove dimensions.

It will be clear that the arrangement shown is adapted to prevent leakage from the casing interior at the left hand side of FIG. 1 to the outside in the direction towards cover 13 while effectively circulating a cooling, lubricating or buffer medium through the casing.

The embodiment according to FIG. 2 differs from that just described in that slide-ring member 8b, which is set into carrier sleeve 9b and is strutted in the axial direction by a spring 14b, rotates with the shaft, whereas the counter-ring member 7a is arranged to be stationary and is supported by two O-rings 6b in a two-part cover 13',13" . An annular guide-plate 20, which directs the coolant flow into the immediate vicinity of the contacting faces of slide-ring member 8b and counter-ring member 7a, is provided apporoximately in the radial plane containing said contacting faces which form a seal.

The internal thread serving to convey the medium as in the first embodiment, is formed in a bush 16 mounted in the shaft bore 11, while the external thread 15 is formed in the cylindrical circumference of carrier sleeve 9b. The external coolant circuit may be the same as that described for FIG. 1.

FIG. 3 shows a double seal constructed according to the invention, such as is used, for example, in rendering a nuclear reactor fluid-tight or a pump intended therefor. The sealing medium is in this case active in the space or chamber between the two pairs of slide- and counter-ring members 7'a, 8'b and 7"a, 8"b and circulates through a high-pressure heat-exchanger 21 which is connected to the chamber. According to the invention, a supply container 22 adpated to replenish the circulating medium and charged with gas keeps the sealing medium at a pressure a few atmospheres above the highest pressure to be sealed off and thus augments the sealing effect. A further feature is that the external thread 15 is cut into a separate sleeve 23 which is mounted independently of the sealing means and surrounds the carrier-sleeves 9'b and 9"b over a part of the axial length, and which is prevented from substantially moving axially and circumferentially relative to shaft 1 by a grub-screw or setscrew 24. An internal shoulder 25 on an extension of the bush 16 which has the internal thread, at the same time provides a support for the stationary counter-ring member 7"a.

In the present embodiment it is possible to use units comprising slide-and counter-ring members and carrier sleeves of normal construction such as are employed for seals which do not have circulation of a sealing medium.

In the further embodiment according to FIG. 4, which corresponds in some essential details of construction and arrangement of the slide- and counter-ring units to the double seal of FIG. 3, no separate sleeve is provided for the external thread 15. On the contrary, in a manner partly similar to that shown in FIG. 2, two external threads 15' and 15" are provided on two rotating slide-ring members 9'b and 9"b, while two internal threads 17' and 17" cooperating with the two external threads are provided in separate bushes 16', 16". Each of the internal threads 17' and 17" has a hand opposite to that of the external thread 15' or 15" with which it is associated, the hands of the external threads in turn being opposite to each other. It follows that the internal threads likewise are of opposite hands. As a result, a conveyance of the medium takes place in a direction depending on the direction of rotation of the shaft, the medium passing through the space or chamber remaining between the two bushes 16', 16". A bore 19 connected to the heat-exchanger 21 opens into said chamber while two bores 18' and 18" which are likewise connected to the heat exchanger terminate at opposite ends of the bushes 16' and 16" which ends are disposed axially at opposite sides of bore 19. In a certain direction of rotation of the shaft as assumed in the embodiment of FIG. 4, the bores 18', 18" will serve as the inlet openings and bore 19 as the outlet opening, but the functions of the bores would be reversed if the shaft rotates in the opposite direction.

According to the embodiment shown in FIG. 5, the pressure-spring 26 for the rotating slide-ring member 8b which spring preferably has multiple coils of rectangular cross-sections, can at the same time be used as an external thread for conveying the enclosed medium, resulting in a saving in manufacturing costs and radial height. Spring 26 is connected to shaft sleeve 2 for rotation therewith.

In all embodiments of the invention it is preferable, in particular in the case of highly loaded seals, to form groove means in the sliding surfaces of the slide- or counter-ring units. This is indicated, by way of example, at 27 in FIG. 1 where the rotatable counter-ring 7b is provided with groove means, and at 28 in FIGS. 3 and 4 where the stationary counter-rings 7'a and 7"a are provided with such groove means.

FIG. 6 shows the grooved end face of the rotatable counter-ring 7b of FIG. 1 in elevation and illustrates the shape of grooves 27, each of which starts at one point of the outer circumference of the ring and leads back to another point of the same circumference so that each groove communicates with the medium under pressure, the medium surrounding the ring, see FIG. 1. Preferably, the grooves are symmetrically arranged on the respective end face as shown in FIG. 6, and each groove has the shape of a circular arc, but other forms may likewise be used, for example, a straight chord-like shape or a polygonal shape.

FIG. 7 shows an elevational view of the grooved end of stationary counter-ring 7'a as provided in FIGS. 3 and 4. It will be apparent that the grooves 28 of FIG. 7 correspond in principle to grooves 27 of FIG. 6.

The described arrangement of grooves results in an intended irregularity in the cooling of at least one of the rings which both slide upon each other and tend to heat up due to friction. This in turn will result in warping of the irregularly cooled ring. Though the extent of such warping will be very small, particules of the cooling and lubricating medium to be sealed will then wedge into the interstices formed between the cooperating end faces of the sealing rings; thus, beneficial hydrodynamic lubrication will be obtained in a manner similar to that observed in the case of thrust bearings. Accordingly, metal to metal contact will be minimized at the cooperating end faces of the sealing rings so that the amount of friction and resulting wear will be reduced. Small losses of cooling and lubricating medium may occur due to slight leakage caused by warping, but this is inconsequential in view of the great advantages obtained by hydrodynamic behavior. When rotation of shaft 1 is stopped, the development of heat will cease and the warping will disappear so that both cooperating end faces of the rings will again be plane and full contact of these end faces will be reestablished.

Claims

What is claimed is:

1. A shaft sealing assembly with a pump device for circulating a liquid medium around a rotatable shaft, a housing stationary relative to said shaft and provided with a wall having a bore, said housing provided with openings for admission and discharge of said medium, said shaft extending through said bore; sealing means comprising a slide-ring unit coaxially surrounding said shaft within said bore and arranged for movement axially of said shaft under resilient pressure; a counter-ring unit similar to said slide ring unit but prevented from axial movement relative to said shaft when in operating position; one of said ring units being mounted for rotation with said shaft, and each of said ring units having an end face for mutual contact under said resilient pressure to form a seal; an external thread of a predetermined hand on said one ring unit; and means stationary relative to said housing and forming an internal thread within said bore, said internal thread having a hand opposite to said hand of the external thread and surrounding the latter with a radial clearance so small that upon rotation of the shaft said external and internal threads are adpated to cooperate for propelling said medium over said end faces and through said openings in the housing, each of said internal and external threads having thread length and thread spacing essentially equal to one-half pitch.

2. A sealing assembly according to claim 1, wherein said sealing means includes groove means formed in said end faces, said groove means starting and terminating at the circumference of one end face for communication with said medium.

3. A sealing assembly according to claim 2, wherein said groove means has the shape of a circular arc.

4. A sealing assembly according to claim 2, wherein said groove means comprises a plurality of grooves symmetrically arranged on one end face.