Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02069020 2001-07-30
P
1
The present invention relates to a seal assembly for a
shaft comprising a stuffing box.
A seal assembly of the type mentioned .above is known from EP-
0 242 699. This seal is specially designed to withstand high
pressure and is based on attaining a high contact pressure
between the annular sealing elements secured against rotation
and the rotating shaft. This is achieved through reduction
of the sealing elements' inner diameter -- which is initially
greater than the shaft diameter -- by the backup rings on
each side of the sealing elements having been provided with
opposed, parallel undulating side faces, whereby on contrac-
ts tion of said backup rings toward one another, the annular
elastic sealing elements are urged to assume a corresponding
undulated form. This causes reduction of the inner diameter
of the sealing elements such that these are pressed against
the shaft for sealing, gliding engagemernt therewith. Sealing
zo against high pressure is thus achieved. This seal assembly
does not permit eccentricity in the shaft during its
rotation.
The purpose of the present invention is to provide a shaft
as seal for use for a shaft passing from a room having a
contaminated atmosphere, e.g., dust-filled air, through an
opening in a wall to another room which is to be protected
from said contaminated atmosphere.
3o Seal assemblies for this purpose are known, for example, from
US-patent no. 3,434,727. Similar seal assemblies are also
known from, for example, US-patent no. 3,194,571. The known
solutions, however, have a very short functional lifetime
(about 3-4 weeks) when used in heavily dust filled surround-
35 ings. Frequent replacement of the seal assemblies involves
considerable maintenance costs for installations having many
such shaft seal assemblies, at the same time as stopping the
2
system for the replacement is often disadvantageous.
Furthermore, the known seal assemblies are poorly suited for
or unable to absorb eccentricity or irregularities in a
rotating shaft.
The present invention therefore proposes to solve 'the
problems recognized thus far in a simple and inexpensive
manner, rendering annual maintenance more reasonable and
affording a seal assembly having a considerably longer
functional life than the known devices.
The seal assembly for a shaft according to the invention is
particularly well suited for use with feed screws in the
chamber of a smoke purification plaint in the smelting
~5 industry, but it will also be immediately understood that
the shaft seal assembly shown and described herein may be
used in other industrial areas where shaft sealing is a
problem.
2o In workshop halls the working environment is often poor due
to excessive leakages, particularly of dust. This necessi-
tates frequent cleaning of the work area floor, as large
quantities of dust can accumulate there. Such dust may also
entail a considerable risk to health.
There are several causes of this type of leakage including,
for example, the problem of eccen'trici'ty in 'the shaft,
whereby -the sealing ring becomes deformed when standing in
the housing of the stuffing box. Such eccentricity could
3o cause severe wear to the shaft if the stuffing box material
were to come into contact with the shaft. Another reason
the leakage may be considerable is because fans in the work
premises draw in dust Pram chimney flues with great force and
cause an overpressure. Filter bags intended for purifica-
lion of the smoke become coated with dust on the outside and
lose their effectiveness. Shaft eccentricity will occur when
excessive moisture forms within a chamber. The dust has a
CA 02069020 2001-07-30
3
tendency to become packed, whereby the shaft begins to run
untrue and could suffer permanent damage.
The wearability for the previously known shaft seal
assemblies for use in the smelting ind'.ustry is brief, and
the consumption rate for bearings is also increased as a
result of dust being blown into the actual bearing house.
According to one aspect of the invention, there is
provided a seal assembly for a shaft, the assembly
comprising a stuffing box having an inner circular
cylindrical wall surface, for attachment to a wall having
an opening for passage of a shaft therethrough, and at
least one annular sealing lip of elastic material secured
at each end section of the stuffing box to close and bear
resiliently against the shaft and form acute angles
therewith. Each of the at least one annular sealing lip
defines therebetween an annular chamber in the stuffing
box. The annular chamber encloses at least one annular
elastic sealing member disposed between the shaft and an
inner circular cylindrical wall surface of the stuffing
box. The sealing member is releasably and resiliently
retained on the shaft for rotation therewith, and extends
obliquely outward toward the inner wall surface of the
stuffing box and forms an acute angle with the shaft. A
vertex of the acute angle is turned toward a shaft passage
opening in the wall which bounds a room having an
atmosphere to be contained.
The purpose of the invention is thus to provide a simple
solution for the problems known thus far, with the
CA 02069020 2001-07-30
3a
characterizing features for the invention being disclosed
in the following specification and the subsequent patent
claims, in addition to the references to the enclosed
drawings which show an embodiment example of the present
invention.
Figure 1 shows a stuffing box 1 according to the invention
in cooperation with a shaft,
Figure 2 shows an elastic sealing lip to be placed at the
ends of the stuffing box, seen from the side in flat
state,
Figure 3 shows an elastic sealing lip adapted for
positioning between the respective end. sealing lips, seen
from the side and in flat state,
Figure 4 shows a rigid annular member adapted to be placed
between the aforementioned end sealing lips, seen from the
side.
A clamping ring designed for forming a wall of the
stuffing box has the same circumferential form as the
annular member, and
Figure 5 shows the same as Figure l, with the exception
that the stuffing box circumference is inserted in an
opening in a wall and sealed thereagainst with an annular
packing.
4
As shown in Figure 1, the shaft seal assembly comprises
stuffing box A having an inner circular cylindrical wall
surface a1 for mounting on or in a wall 9 having an opening
9a ~therethrough for the passage of shaft 10. At least one
annular sealing lip 1 o.f elastic mater:lal, e.g., rubber or
the like, is secured at each end section of stuffing box A
and encloses and bears resiliently against shaft 10, farming
acute angles therewith.
Sealing lips 1 define between them an annular chamber a in
stuffing box A for at least one annular elastic sealing
member disposed between shaft 10 and the inner circular
cylindrical wall surface a1 of stuffing box A. This sealing
member is composed of an annular sealing lip 2 of elastic
y5 material similar to the material in sealing lips 1. Sealing
lips 2 are releasably and resiliently retained on shaft 10
for rotation therewith, and extend obliquely outward toward
the inner wall surface a1 of stuffing box A, forming an acute
angle with shaft 10. The acute angles formed by sealing
zo lips 1,2 with shaft 10 are turned with the vertexes -thereof
toward the shaft passage opening 9a in wall 9, which bounds
on a room having a dust- or particle--filled atmosphere and/or
a fluid-filled chamber.
z5 The annular sealing lip 2 in non-assembled state as shown in
Figure 3 has an inner diameter for its central opening 2a
which is smaller than the diameter of shaft 1Ø and an outer
diameter greater than -the inner diameter of annular chamber
a. Thus, upon exertion of inward axial pressure on shaft 10,
3o central opening 2a of sealing lip 2 will be expanded and wil3
effect the aforementioned resilient retention, and will cause
the tilting of the side surfaces of sealing lip 2 toward
shaft 10, thereby also reducing the effective outer diameter
of sealing lip 2 for adaptation to the inner diameter of
35 annular chamber a.
20~~020
In the embodiment form shown in Figures 1 and 5, three
annular sealing lips 2 are arranged in spaced relationship
within chamber a.
The inner wall surface al of stuffing box A is composed of
-the inner circular cylindrical wall surface of a rigid
cylindrical annular member 3 provided with at least two axial
through-going bores 3b for engagement with stud bolts 5
disposed around the shaft passage opening 9a in wall 9. A
clamping ring 4 with central opening 4a and mounting hole 4b
aligned with a corresponding central opening 3a and bores 3b
in annular member 3 is also adapted fox engagement with stud
bolts 5. The annular sealing lips l are adapted for retention
between annular member 3, and clamping ring 4 and wall '9,
respectively, said components being clamped -together with the
aid of nuts 6 on the ends of stud bolts 5 opposite wall 9.
Stud bolts 5 run with a clearance in bores 3b through annular
member 3, which enables 'thereby the radial adaptation/ad~ust
ao went of stuffing box A to shaft 10.
The annular sealing lip 1 extends outwardly to the exterior
cylindrical surface of annular member 3 and is provided with
insertion holes 1b aligned with the bores 3b in annular
member 3 and thereby with stud bolts 5. The annular sealing
lips 1 are thus retained against annular member 3, as
mentioned above.
Ln an embodiment form of the shaft seal as shown in Figure
30 5, clamping rings 4 and 4' define annular chamber a of the
stuffing box. In other words; wall 9 which constitutes one
of the walls of annular chamber a in the embodiment form
indicated in Figure 1 is replaced by aforementioned clamping
ring 4'. Thus -there is provided a complete, removable
stuffing box A' for non-rota~table positioning at or in a
shaft passage opening 9a' in wall 9' with the aid of
appropriate mounting and sealing means.
,~a6~~~0
6
Figure 5 thus shows a sealing ring having a If-shaped cross~-
section and outwardly opening grooves, which grooves are
placed against the edges of shaft passage opening 9a', -the
inner surface of said sealing ring bearing an the outer
circular surface of annular member 3 in sealing engagement
therewith. Annular member 3 is provided with a lubricant
supply inlet 7 to annular chamber a for the supply of
lubricant 8 to the interstices between sealing lips 1 and 2.
0
In one embodiment form of the sealing lip, inner edge surface
2b on annular sealing lip ~ may form an acute angle with one
of the side surfaces of sealing lip 2 facing toward shaft
passage opening 9a. Similarly, the outer edge surface 2c of
sealing lip 2 may form an acute angle with the other side
surface of sealing lip 2 facing away from said shaft passage
opening 9a. In this way, a better surface contact is attained
between, respectively, shaft 10 and inner edge surface 2b of
sealing lips 2, and the outer edge surface of sealing lips 2
ao and the inner wall surface ag of annular member 3.
The shaft seal described hereinabove is mounted on an
existing shaft 10 and chamber wall 9 with cable passage
opening 9a therethrough by means of, for example, four stud
z5 bolts 5 secured in corresponding threaded holes in chamber
wall 9, which holes and thus said stud bolts 5 are aligned
with the aforementioned holes in, respectively, cylindrical
annular member 3, clamping rings 4 and annular sealing lips
1. Twa rubber rings or annular sealing lips 1 are slid first
30 onto shaft 10 and then, With their holes 1b onto aforemen-
tioned stud bolts 5. The fact that central opening la of
sealing lips 1 has a diameter slightly smaller than the
diameter of shaft 10, as mentioned above, enables the
achievement of the desired curved configuration of the lips.
35 It may be expedient, for example, to have an opening diameter
that is 10 mm smaller than the diameter of shaft 10.
Cylindrical annular member 3, preferably of steel, is then
7
slid by means of its bores 3b onto the aforementioned stud
bolts 5.
As is apparent from figure 1, central opening 3a of annular
member 3 has a diameter 'that is substantially greater than
the diameter of shaft 10. Rings or lips 2 of elastic
material, e.g., rubber, are inserted onto shaft 10 and into
central opening 3a of said annular member 3. Central opening
~a of lips 2 has a diameter slightly smaller than that of the
shaft and preferably greater than the diameter of the opening
of aforementioned lips 1. The opening diameter for lips 2
may suitably be 5 mm smaller than the diameter of shaft 10.
An additional two rings or annular lips 1 may then be slid
onto shaft 10, these being of -the same configuration as the
first said lips 1. After that, clamping ring 4 -- suitably
of steel -- is placed on stud bolts 5 at holes 4b 'thereof,
whereafter nuts 6 are screwed onto stud bolts 5. Tightening
of the screws for secure interconnection of the previously
ao mentioned components may take place after the bearing and
bearing house (not shown) for shaft 20 are securely mounted
in the desired position. The described stuffing box A will
self-center automatically relative to shaft 10 because stud
bolts 5, as mentioned previously,.run with a clearance in
bores 3b through annular member 3 and because nuts 6 have not
yet been tightened, enabling the sealing lips and, with them,
annular member 3 t o move radially and adapt to the position
of shaft 10. Nuts 6 are then tightened arid 'the stuffing box
is ready for use. While shaft 1.0 rotates, heat resistant
3o grease 8 is fed into the annular chamber a of stuffing box A
through lubricant supply inlet '7.
It is important that an equal number of lips 1 be disposed on
either side of annular member 3. If there are used only one
35 lip 1 on one side thereof (the outside) and two lips 1 toward
chamber wall 9, the one lip situated on the outside will turn
itself outwards when grease is pumped in.
CA 02069020 2001-07-30
g
It is expedient to provide lips 1 and 2 with a thin film of
oil at the edge of the central opening forming the seal
around shaft 10 in order thereby to facilitate the assembly
task. Lips 1 are slid onto shaft 10 with the bend of the lip
opposite to the position the lips are. to have, said lips in
their final position being drawn back slightly to reverse
their curve into the opposite position, i.e., with the tip of
the lip turned toward wall 9. Lips 1 and 2 shall have a bend
0 or inclination directed the same way so that the lip edges
bearing on shaft 10 will point in the .direction of the dust-
filled room, which in Figure 1 is located outside wall 9.
When lips 1 are mounted, they are slid onto shaft 10 with
their tilt or inclination opposite to that of their final
position for use. The change in the tilt is achieved by
drawing lips 1 back slightly, enabling the lip to reverse
itself into the correct position.
o A feature of the shaft seal assembly a<~cording to
the invention is that the stuffing box incorporated therein
is substantially easier to mount on the shaft since the
seals, i.e., lips 1 and 2, center themselves automatically in
relation to shaft 10, as mentioned above. Thus, there is no
25 need for adjustment, which previously has been an exacting
and time-consuming operation. The problem of shaft eccentri-
city which deforms and wears out known shaft seal assemblies
has now been solved in the present invE~ntion by means of the
inward-turned lips 1, which yield resi:Liently and thus allow
3o shaft 10 to rotate with eccentricity. 'This feature, combined
with the fact that lips 2 are mounted fixedly on shaft 10 and
rotate together therewith within annular chamber a of
stuffing box A, thus forming a type of labyrinth seal, and
the fact that lubricant 11 is introduced through lubricant
35 supply inlet 7 to the interstice between lips 1 and 2,
further contributes toward attainment of an effective seal.
At the same time, the lips are subjected to very little wear.
20UUU~U
9
There is provided by means of the present invention a shaft
seal having a long operational lifetime, which may readily be
adapted without significant difficulties to shafts having
poor 'tolerance or irregularities.
The shaft seal is constructed such that the rigid clamping
ring 4 situated outermost will in no way come into contact
with shaft 10, due to the fact that axial opening 4a in
clamping ring 4 has a substantially greater diameter than
shaft 10. Thus all danger of shaft wear against clamping
ring 4 is avoided.
According to tests undertaken, the shaft seal according to
the present invention tolerates about 5 bar of overpressure
within the dust-filled chamber/room into which shaft 10 runs
and is connected, for example, to a feed screw. The seal
assembly has also been sub;Jected to temperatures up to 150oC
without negative effects on the shaft seal.
2O
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