GB2224321A

GB2224321A - Mechanical shaft-end seal assembly

Info

Publication number: GB2224321A
Application number: GB8924526A
Authority: GB
Inventors: Alexandr Mikhailovich Nasonov; Alexandr Vasili Velikorechanin; Valery Alexandrovich Veligin; Andrei Alexandrovich Yanovsky; Valery Valiakhme Shagiakhmetov; Leonid Andreevich Kaluzhsky; Valentin Petrovich Moiseev
Original assignee: VNI PI ALJUMINIEVOI MAGNIEVOI
Current assignee: VNI PI ALJUMINIEVOI MAGNIEVOI
Priority date: 1988-10-31
Filing date: 1989-10-31
Publication date: 1990-05-02
Also published as: HU206146B; DD297865A5; YU210189A; CN1023576C; CN1042403A; FR2638501B1; GB8924526D0; RU2083899C1; GR890100703A; DE3934752A1; HUT55886A; HU895611D0; FR2638501A1

Description

t MECHA1,1MAL SHAFT-BI',D SEAL ASSEIMBLY #1 Z.224321 The present

invention'is in the field.of equipment used in hydrometallurgy, relating more particularly to shaft-end seal assemblies. The invention can be most ad- vantageously used for sealing pump shafts to be employed at large differential pressures in abrasive suspensions and solutions tending to crystallize, such as are typical of suspensions and solutions to be found in alumina-processing industries.

According to the invention three is provided a me- chanical shaft-end seal assembly to seal a shaft against a housing, comprising a support ring secured to thshaft and forming a hermetically tight joint therewith, an annular thrust member installed between the shaft and the housing, with a radial clearance relative to these, displaced along the shaft relative to the support ring, held by means of an elastic member relative to the housing in the direction of said support ring, and forming a friction pair therewith, a means to lock the annular thrust member to prevent rotation relative to the housing, and a sealing ring installed between the housing and the annular thrust member, made of flexible elastic material and having, in radial section, an U-shaped form consisting of two interconnected branches, one attached to the hou.-ing, the other to the annular thrust member, wherein circular recesses are provided in the annular thrust member, on the side of its outer surface, and in the housing, on the sifte of its inner surface, said cir- cular recesses being open on the support ring side, with I the sealing ring branches being tightly set in said circular recesses, one of the sealing :, ring branches, acco.m modated in the circular recess in the annular thrust mem ber being held to the housing so as to be capable of mov ing relative thereto when acted upon by the elastic for ce produced by said elastic member, and the sealing ring segment interconnecting the two branches being on the support ring side.

The provision of the sealing ring U-shaped in radial section and made of flexible elastic material, with one of the ring branches tightly set in the circular recess made in the housing, and the other tightly set in a circular recess made in the annular thrust member, having its free end portion secured therein and held in contact with the housing while being capable of displacement relative thereto, and the location of the sealing ring segment interconnecting the two branches on the support ring side, enable protection from fouling by abrasive suspension particles of the segment which has the sealing rinE; branch set in the circular recess in the annular thrust member sliding over it in the process of the friction pair being increasingly worn out, affording, in consequence thereof, comparatively constant resistance to the displacement of the annular thrust member over the sliding segment whose size is defined by the length of the mobile branch and is prac- tically unlimited, i.e. ensuring high reliability to, and long useful life for, CD I -c-sed mechan4-:,l sha-Pt-end seal assembl-r.

% he P_:71- - 11 In one of the embodiments of the invention, the sealing ring branch accommodated in the circular recess made in the annular thrust member may be hold against the housing through the sealing ring branch accommodated in the circular recess made in the housing.

In this embodiment, the sealing ring branch set in the circular recess made in the annular thrust member slides over the surface of the other sealing ring branch as the friction pair (support ring - annular thrust mem- ber) is being gradually worn out.

It is advisable that'. the free end of the sealing ring branch accommodated in the circular recess made in the annular thrust member be displaced relative to the circular recess made in the housing, in the direction away from the support ring, by a value not less than the pre-specified maximum allowable wear for the friction pair, said sealing ring branch being held directly to the housing within said displacement zone.

In this'design, as the friction pair (support ring - annular thrust member) is being gradually worn out, the sealing ring branch accommodated in the circular recess made in the annular thrust member will slide over the surface of the metallic housing, this allowing for lower resistance to the displacement of the annular thrust member, as compared to the resistance incident to one sealing ring branch sliding over the other. The decrease in said resistance makes it less probable for the annular thrust member to bind in the process of seal operation.

It is also advisable that in the case where the free end of the sealing ring branch accommodated in the circular recess of the annular thrust member is displaced as stated Lbove, circular grooves be provided in the annular thrust member, open on the circular recess base side, while the sealing ring branch be provided with circular projections to fit into said circular grooves.

This type of construction permits of substantially reducing the force arising from the high pressure cavity side to hold the sealing ring branch accommodated in the circular recess of the annular thrust member to the wall of said circular recess,. hence of-preventing this branch from being squeezed out through the clearance between the.housing and the holder ring when the seal is operat- ed under high pressure conditions, and thereby avoiding possible increases in resistance to the displacement of the annular thrust member, the result being a still more reliable shaft-end seal performance. The reduced sealing ring branch-to-circular recess wall holding force is due to the side walls of the circular grooves on the low pressure cavity side interacting with the circular projections of the sealing ring branch to take up much of the force acting upon the sealing ring from the high pressure cavity side.

In the following the invention will be made fully apparent by a detailed description of its embodiments with due references to the accompanying drawings wherein:

FIG.1 is a sectional view taken longitudinally and illustrating a mechanical shaft-end seal assembly according to the invention; FIG.2 is an enlarged view of the assembly 1 of FIG.

FIG.3 is the assembly 1 of FIG.1, less sealing ring; and FIG.4 is another version of sealing ring installation, different from that shown in FIG.2.

The mechanical shaft-end seal assembly (FIG.1) desig- ned to seal a shaft 1 relative to a housing 2, comprises a support ring 3 fitted into an intermediate ring 4 connected to the shaft 1 at its tail Part 5 by means of, e.g., scre,.,is (not shown). Installed between the intermediate ring 4 and shaft 1 is a circular gasket 6 designed to provide hermetically tight connection for the support ring 3 via the intermediate ring 4 to the shaft 1. In one of the embodiments of this invention, there may be no intermediate ring, the circular gasket being installed in this case directly between the support ring and the shaft. Other versions are also possible for installing the support ring over the shaft. Mounted between the shaft 1 and the housing 2, with a radial clearance relative to these, is an annular thrust member 7 consisting of a holder ring 8 and a thrust ring 9 fitted into said holder ring. Other versions of annular thrust member design are also possible, thus having the holder ring 8 made integral with the thrust ring 9. The annular thrust member 7 is displaced along the shaft 1 relCa- tive to the - 6 support ring 3 and held tightly in contact with the support ring 3, via the thrust ring 9, by means of an elastic member 10, thus, for example, by means of a spring acting upon the holder ring 8. The support ring 3 and the thrust ring 9 form a friction pair, dividing the cavity between the shaft 1 and the housing 2 into a high pressure cavity 11 and a low pressure cavity 12. Secured in the housing 2 is a radially oriented pin 13 whose tail end enters a longitudinal slot 14 in the holder ring B. The pin 13 and the slot 14 form a means adapted for locking the annular thrust member 7 to prevent rotation relative to the housing 2. In the holder ring 8, on the side of its outer surface, and in the housing 2, on the side of its inner surface, there are provided, res- pectively, circular recesses 15 and 16 (FIG-3) open on the side of the support ring 3. In one of the embodiments of this invention, the circular recess 16 may be provided in an intermediate ring attached to, and forming a hermetically tight joint with, the inner surface of the housing 2, rather than directly in the housing 2. The end of the circular recess 15 in the holder ring 8 is displaced relative to the end of the circular recess 16 in the housing 2 by a distance "All which must be equal to at least the pre-specified maximum allowable wear on the friction pair 3 - 9. In the holder ring'S of the annular thrust member 7, there are provided circular grooves 17 open from the base side of the circular recess 15 and distributed along its length. The grooves 17 are formed as depressions in the base of the circular recess 15, which has a wavy form, in radial section. Radially, the circular grooves may also have some other - e.g. rectangular - form. Also, a version is possible, in which the holder ring 8 has no circular grooves 17 at all. The circular recesses 15 and 16 terminate, respectively, in circular grooves 18 and 19 having a dovetail form in radial section. Installed between the housing 2 and the holder ring 8 is a sealing ring 20 (FIG.2) made of flexible elastic - e.g. rubber - material and having an U-shaped form in radial section. One of the branches, 20-a, of the sealing ring 20 is tightly set in the circular recess 16 in the housing 2. The other branch 20-b is tightly set in the circular recess 15 in the holder ring 8, this branch having circular projections 21 to tightly fit the circular grooves 17. The segment 20-c of the sealing ring 20, interconnecting the sealing ring branches 20-a and 20-b, is on the support ring side. The sealing ring branch 20-a has its tail part attached to the housing 2, this tail part tightly fitting the cir- cular groove 19. The sealing ring branch 20-b has its tail part attached to the holder ring 8, this tail part tightly fitting the circular groove 18, and is held tightly in contact with the housing at the displacement segment "All with a force that permits the holder ring 8 complete with the thrust ring 9 of being displaced when acted upon by the elastic force produced by the member 10. Based on the condition of the holder ring 8 remaining mobile, the maximum force to hold the sealing ring branch 20-b to the housing 2 may be determined by a known computational method accounting for the materials of the housing 2 and the sealing ring 20, as well as the elastic force produced by the member 10, and, where there is lubricant to be present between housing and sealing ring, also for the characteristics of said lubricant. The minimum force to hold the sealing ring branch 20-b to the housing 2 is selected experimentally, based on the condition of reliable sealing to be ensured at the displacement segment "A". Depending on their geometrical form, the sealing ring branches 20-a and 20-b may either be held together one against the other with a relatively low force such that would avoid the holder ring 8 from binding when displaced relative to the housing 2, or be arranged with a clearance in between. The manner of mu- tual arrangement of the sealing ring branches 20-a and 20-b, their interaction, as well as the dimensions and geometrical form of said branches may easily be selected experimentally, based on the conditions o; design simplicity and ease of fabrication, as well as reliably seal- ing the clearance between the housing 2 and the holder ring 8 from the high pressure cavity side.

In one of the embodiments of this invention (FIG.4), the end of the circular recess provided in the holder ring 8 coincides, which reference to the length of the shaft, with the end of the circular recess provided in the housing 2. In this embodiment, the sealing ring branch 20-b is held to the housing 2 via the sealing ring branch 20-a and has a length exceeding the magnitude of the pre-specified maximum allowable wear on the friction pair. The maximum force to hold the sealing ring branch 20-b to the housing is determined in this case taking account of the material of the sealing ring 20 and the elastic force produced by the member 10.

With the shaft-end seal assembly in operation, the face of the support ring 3 (FIG.1) rotating with the shaft 1 slides over the face of the thrust ring 9 secured in the holder ring 8 prevented from rotation by means of the pin 13 fitted into the slot 14. The high pressure cavity 11 is isolated from the low pressure cavity 12 by the friction pair 3 - 9 and the sealing ring 20. In the process of shaft-end seal operation, the friction pair 3 - 9 is being gradually worn out, with the holder ring 8 gradually displaced in the direction of the support ring 3 by the action of the elastic member 10, ensuring constantpressure to bear upon the thrust ring 9 to hold it to the support ring 3. As the holder ring 8 is being displaced. so is the pin 13, along the slot 14, while the branch 20-b (FIG.2) of the sealing ring 20 is slid- ing along the surface of the housing 2 over the displacement segment "All. Since the displacement length "All is equal to at least the pre- specified maximum allowable wear on the friction pair 3 - 99 arid the contacting surfaces of the housing 2 and the sealing ring branch 20-b are protected within this area from being fouled by abrasive suspension particles, the magnitude of the friction force and the force of resistance to the displacement of the annular thrust member 7, related thereto, will not increhse to any substantial extent throughout the service life of the shaft-end seal assembly, which affords a longer useful life and higher performance reliability for the proposed mechanical shaft-end seal assemb- ly. - In the process of shaft-end seal operation, the sealing ring is affected by a pressure from the side of the high pressure cavity 11, whose resulting force has a horizontal component P tending to hold the sealing ring branch 20-b to the wall of the circular recess 15 and squeeze it out through the clearance between the housing 2 and the holder ring 8. The side walls of the circular grooves 17 located on the side of. the low pressure cavity, interact with the circular projections 21 to take up much of the force F, the result being that the force F, which holds in fact the sealing ring branch 20-b to the wall of the circular recess 15, is found to be considerably less than the force F. The number of circular grooves 17 and, accordingly, that of circular projections 21, their form, and their dimensions are selected experi- mentally, with due account taken of the working pressures. the material of the sealing ring 20. and some other characteristics, based on the condition of preventing the sealing ring branch 20-b from being squeezed out into the clearance between the housing 2 and the holder ring 8. Preventing the sealing ring branch 20-b from being squeezed out into said clearance between the housing 2 and the holder ring 8, avoid, in its turn, possible inereases in resistance to the displacement of the annular thrust member, enhancing, as a result, the performance -- 11 - reliability of the shaft-end seal assembly still further. Besides, the form of the circular grooves 17 and circular projections 21 are selected such as to prevent the possibility of such sections of the branch 20-b of the sealing ring 20 as project from the circular recess 15 catching the. holder ring in the process of its displacement.

In the embodiment of the invention (FIG.4) where the end of the circular recess provided in the holder ring 8 coincides, with reference to the shaft length, with the end of the circular recess provided in the housing 2, the branch 20-b of the sealing ring 20 slides over the surface of the branch 20-a in the process of the friction pair 3 - 9 being gradually worn out.

12 - 1

Claims

Claims:

1. A mechanical shaft-end seal assembly to seal a shaft against a housing, comprising a --upport ring secured to the shaft and forming a hermetically tight-joint therewith, an annular thrust member installed between the shaft and the housing, with a relative clearance relative to these, displaced along the shaft relative to the support ring, held by means of an elastic member to this support ring and forming a friction pair therewith, a means adapted for locking the annular thrust member to prevent rotation relative to the housing, and a sealing ring installed between the housing and the annular thrust member, made of flexible elastic material, and having, in radial section, an U-shaped form consisting of two interconnected branches, one branch being attached to the housing, the other branch having its tail part attached to the Rnnular thrust member, with circular recesses, open on the support ring side, being provided in the annular thrust member, on the side of its outer surface, and in the housing, on the side of its inner surface, the sealing ring branches being tightly set in said circular recesses, one of these sealing ring branches, accommodated in the circular recess in the annular thrust member, being held to the housing so as to be capable of moving relative to the housing when acted upon by the elastic force produced by said elastic member, and the sealing ring segment interconnecting the two sealing ring branches being on the support ring side.

C) k 1

2. A mechanical shaft-end seal assembly as defined in Claim 1, wherein the sealing ring branch accommodated in the circular recess in the annular thrust member is held to the housing via the sealing ring branch accom5 modated in the circular recess in the housing.

3. A mechanical shaft-end seal assembly as defined in Claim 1, wherein the free end of the sealing ring branch accommodated in the circular recess in the annular thrust member is displaced relative to the circular re- cess in the housing in the direction away from the support ring by a distance equal to at least the pre-specified maximum allowable wear on the friction pair, said sealing ring branch being held directly to the housing within said displacement zone.

4. A mechanical shaft-end seal assembly as defined in Claim 3, wherein circular grooves are provided in the annular thrust member, open on the base side of its circular recess, while the sealing ring branch accommodated in this circular recess has circular projections fitting 20 said circular grooves.

5. A mechanical shaft-end seal assembly substantially as hereinbefore described with reference to the accompanying drawings.

1 14

6. A mechanical shaft-end seal assembly to seal a shaft against a housing. comprising a support ring secured to the shaft and forming a hermetically tight joint therewith, an annular thrust member installed between the shaft and the housing held by means of an elastic member to the support ring and forming a friction pair therewith, means adapted for locking the annular thrust member to prevent rotation relative to the housing, and a sealing ring installed between the housing and the annular thrust member.

1 1.

Published 1990 at The Patent Offlee, State House, 6871 High HoIbora, LondonWC1R4TP.Further copies maybe obtained from The Patent Office. Sales Branch. St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con. 1187