U.S. patent application number 10/788129 was filed with the patent office on 2004-09-09 for mechanical seal.
Invention is credited to Kudari, Mitsuru, Ninomiya, Masanobu.
Application Number | 20040173971 10/788129 |
Document ID | / |
Family ID | 32821151 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040173971 |
Kind Code |
A1 |
Kudari, Mitsuru ; et
al. |
September 9, 2004 |
Mechanical seal
Abstract
A balance ratio for a stationary seal ring is designed to allow
a seal face to be opened when, with a rotary seal ring at
standstill, steam of a predetermined pressure is supplied to an
endo-fluid region while a sealing-fluid region is brought into an
exhausting state. On the other hand, an O-ring constituting a
secondary seal portion is retained by a groove formed in a flange
portion of a seal case, thereby preventing a force on the O-ring
from affecting the stationary seal ring even when the steam is
supplied to the endo-fluid region.
Inventors: |
Kudari, Mitsuru; (Hyogo,
JP) ; Ninomiya, Masanobu; (Hyogo, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
SUITE 3100, PROMENADE II
1230 PEACHTREE STREET, N.E.
ATLANTA
GA
30309-3592
US
|
Family ID: |
32821151 |
Appl. No.: |
10/788129 |
Filed: |
February 26, 2004 |
Current U.S.
Class: |
277/361 |
Current CPC
Class: |
F16J 15/3484 20130101;
F16J 15/3404 20130101 |
Class at
Publication: |
277/361 |
International
Class: |
F16J 015/34; F16J
015/43 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2003 |
JP |
55870/2003 |
Claims
What is claimed is:
1. A mechanical seal interposed between a housing of an apparatus
having a rotary shaft and the rotary shaft, and operative to seal
an endo-fluid region against an exo-fluid region, the mechanical
seal comprising: a rotary seal ring mounted to said rotary shaft; a
stationary seal ring in axially opposing relation with said rotary
seal ring for cooperatively defining therebetween a seal face
constituting a primary seal portion for establishing a fluid seal
between said endo-fluid region and said exo-fluid region, the
stationary seal ring having a balance ratio designed to permit said
seal face to be opened by supplying steam of a predetermined
pressure to said endo-fluid region and by bringing said exo-fluid
region into an exhausting state when said rotary seal ring is at
standstill; a seal case mounted to said housing for axially movably
retaining said stationary seal ring, and including a groove
extended circumferentially of a portion thereof in close proximity
of and opposing relation with said stationary seal ring; an elastic
member retained by said seal case and urging said stationary seal
ring into movement toward said rotary seal ring; and a seal member
mounted in said groove and interposed between said stationary seal
ring and said seal case for constituting a secondary seal portion
for establishing a fluid seal between said endo-fluid region and
exo-fluid region.
2. A mechanical seal according to claim 1, wherein an exhaust hole
extended through said seal case has one open end located near a
place where droplets fall, the droplets being formed by
condensation on a surface of said stationary seal ring exposed to
said exo-fluid region.
Description
FIELD OF THE INVENITON
[0001] The present invention relates to a mechanical seal for
sealing a shaft and more particularly, to a mechanical seal for use
in apparatuses requiring periodical sterilization.
DESCRIPTION OF THE PRIOR ART
[0002] Apparatuses used for producing food, drug or the like
require periodical sterilization for hygienic reasons. In this
case, a mechanical seal used for sealing a rotary shaft of the
apparatus is also subjected to the sterilization. Since such a
mechanical seal has a structure including a sealing portion, it is
difficult to pass a sterilizing fluid therethrough. Hence, the
mechanical seal is disassembled before subjected to the
sterilization. On the other hand, there has also been proposed a
mechanical seal adapted for a so-called Sterilization-In-Place
which permits the sterilization to be carried out in a
non-disassembled state (see, for example, Japanese Unexamined
Patent Publication No. 2001-21045). Specifically, a support member
for supporting a stationary seal ring is retreated by means of a
cylinder piston for producing a gap between the stationary seal
ring and a rotary seal ring, and hot steam is passed through the
gap thereby sterilizing the interior of the mechanical seal. The
device is provided with a shield, such as bellows, between the
support member and a casing, the shield preventing the fluid from
entering a cylinder side.
[0003] The conventional mechanical seal, as described above,
involves a disassembly operation each time the sterilization is
carried out. Hence, the sterilizing operation suffers quite a poor
efficiency. In a case where the mechanical seal adopts the
arrangement as disclosed in the above-mentioned Patent Publication,
on the other hand, the cylinder and associated members thereof are
necessary, so that the mechanical seal as a whole has a large and
complicated construction.
OBJECT AND SUMMARY OF THE INVENTION
[0004] In view of the foregoing, it is an object of the present
invention to provide a mechanical seal which permits the
sterilization to be carried out in the non-disassembled state and
features a simple and compact construction.
[0005] According to the present invention, a mechanical seal
interposed between a housing of an apparatus having a rotary shaft
and the rotary shaft, and operative to seal an endo-fluid region
against an exo-fluid region, the mechanical seal comprises: a
rotary seal ring mounted to the rotary shaft; a stationary seal
ring in axially opposing relation with the rotary seal ring for
cooperatively defining therebetween a seal face constituting a
primary seal portion for establishing a fluid seal between the
endo-fluid region and the exo-fluid region, the stationary seal
ring having a balance ratio designed to permit the seal face to be
opened by supplying steam of a predetermined pressure to the
endo-fluid region and by bringing the exo-fluid region into an
exhausting state when the rotary seal ring is at standstill; a seal
case mounted to the housing for axially movably retaining the
stationary seal ring, and including a groove extended
circumferentially of a portion thereof in close proximity of and
opposing relation with the stationary seal ring; an elastic member
retained by the seal case and urging the stationary seal ring into
movement toward the rotary seal ring; and a seal member mounted in
the groove and interposed between the stationary seal ring and the
seal case for constituting a secondary seal portion for
establishing a fluid seal between the endo-fluid region and
exo-fluid region.
[0006] In the mechanical seal of the above arrangement, the balance
ratio is so designed as to permit the seal face to be opened by
supplying the steam. At this time, the seal member is subjected to
the pressure of the steam but is received by an axial end face of
the groove. Accordingly, the seal member does not affect the
balance ratio for the stationary seal ring. It is therefore ensured
that the seal face is positively opened to allow the steam to pass
through the mechanical seal for sterilization. Thus is provided the
mechanical seal permitting the sterilization to be carried out in
the non-disassembled state. In addition, the mechanical seal does
not require the cylinder for opening the seal face and hence, the
mechanical seal featuring the simple and compact construction can
be provided.
[0007] The above mechanical seal may have an exhaust hole extended
through the seal case and having one open end located near a place
where droplets fall, the droplets being formed by condensation on a
surface of the stationary seal ring exposed to the exo-fluid
region. In this case, the droplets are discharged via the exhaust
hole and hence, the interior of the mechanical seal may be quickly
dried by ventilating dry air therethrough after the ventilation of
the steam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a sectional view showing a mechanical seal
according to one embodiment of the present invention;
[0009] FIG. 2 is an enlarged view showing a right-half portion of
FIG. 1;
[0010] FIG.3 is a fragmentary enlarged view showing a part of a
flange portion of the above mechanical seal;
[0011] FIG. 4 is a view as viewed along the arrow IV of FIG. 3;
[0012] FIG.5 is an enlarged view showing a portion around a rotary
seal ring and a stationary seal ring during a normal operation of
the above mechanical seal;
[0013] FIG. 6 is an enlarged view showing the portion around the
rotary seal ring and the stationary seal ring of the above
mechanical seal during a sterilizing operation; and
[0014] FIG. 7 is a sectional view showing a mechanical seal of a
structure having a different exhaust system from that of FIG.
1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] FIG. 1 is a sectional view showing a mechanical seal
according to one embodiment of the present invention. The
mechanical seal 1 is interposed between a housing 51 of an
apparatus containing a sealed fluid therein and a rotary shaft 52
of the apparatus. The mechanical seal 1 includes in a seal case 2
two sets of rotary seal structures constituted by a rotary seal
ring 3 in combination with a first stationary seal ring 4 and a
second stationary seal ring 5. A first rotary seal structure is
constituted by the rotary seal ring 3 and the first stationary seal
ring 4. The first rotary seal structure provides a fluid seal
between an endo-fluid region H within the housing 51 and a
sealing-fluid region (exo-fluid region) S where a fluid such as a
sealing gas is present. On the other hand, a second rotary seal
structure is constituted by the rotary seal ring 3 and the second
stationary seal ring 5. The second rotary seal structure provides a
fluid seal between the sealing-fluid region S and an atmosphere
region L opened into the atmosphere. The above apparatus is an
agitator for food, drug or the like, for instance. The mechanical
seal 1 is mounted substantially in a position shown in the
figure.
[0016] FIG. 2 is an enlarged view showing a right half portion of
FIG. 1. Referring to FIG. 2 (also to FIG. 1), the seal case 2
includes a cylindrical case body 21, and flange portions
(retainers) 22, 23 fastened to axially opposite ends of the case
body 21 via bolts 24, 25. On the other hand, a first sleeve 6 is
fitted on the rotary shaft 52 of the agitator, and the annular
rotary seal ring 3 is fitted on a cylindrical portion 6a formed at
a distal end of the first sleeve 6. Upper and lower sealing
end-faces 3s of the rotary seal ring 3 define flat faces orthogonal
to an axis of the rotary shaft 52. It is noted that the sealing
end-face 3s is formed with a plurality of shallow grooves 3g (depth
of several micrometers) near an outer circumference thereof. The
grooves 3g are radially extended and arranged in a radial fashion,
for example.
[0017] A second sleeve 8, at the upper position, is fitted on the
rotary shaft 52 after the rotary seal ring 3 is fitted on the
cylindrical portion 6a. The second sleeve 8 is fitted with the
first sleeve 6 at the lower position and fastened thereto by means
of a bolt 9. The aforesaid rotary seal ring 3 is clamped between
support portions 6b, 8b of the sleeves 6, 8 via O-rings 10, 11. The
support portions 6b, 8b are protruded outwardly from respective
outer peripheries of the sleeves 6, 8. An O-ring 12 is fitted in a
groove 6a1 formed in the cylindrical portion 6a. The O-ring 12 is
in contact with the rotary seal ring 3. The second sleeve 8 is
fixed to the rotary shaft 52 by means of a plurality of screws 13
(only one of which is shown in FIG. 1).
[0018] On the other hand, the first stationary seal ring 4 and the
second stationary seal ring 5, as annular members, have sealing
end-faces 4s, 5s orthogonal to the axis of the rotary shaft 52,
respectively. The first and second stationary seal rings 4, 5
oppose axially opposite sides of the rotary seal ring 3. Respective
seal faces defined between the rotary seal ring 3 and the
individual stationary seal rings 4, 5 constitute respective primary
seal portions between the endo-fluid region H and the sealing-fluid
region S, and between the sealing-fluid region S and the atmosphere
region L.
[0019] The stationary seal rings 4, 5 have cylindrical base
portions 4a, 5a extended in the opposite directions from the
respective sealing end-faces 4s, 5s thereof. The cylindrical base
portions 4a, 5a are axially movably inserted in the respective
flange portions 22, 23. The flange portions 22, 23 are formed with
U-shaped grooves 22a, 23a circumferentially of respective portions
thereof which are in close proximity of and opposing relation with
the respective base portions 4a, 5a. The grooves 22a, 23a receives
therein O-rings 14, 15, respectively. Thus, secondary seal portions
are defined between the endo-fluid region H and the sealing-fluid
region S and between the sealing-fluid region S and the atmosphere
region L.
[0020] The first and second stationary seal rings 4, 5 are formed
with a plurality of notches 4c (FIG. 1), 5c (2 places in this
embodiment) at outer peripheral corners thereof, and the notches
are arranged with a predetermined circumferential spacing. In
correspondence to the individual notches 4c, 5c, a plurality of
pins (2 pins) 16 (FIG. 1), 17 are implanted in the flange portions
22, 23. These pins 16, 17 are engaged with the notches 4c, 5c in a
manner to provide axial and radial clearances such as to permit
some degrees of axial and radial movement of the stationary seal
rings 4, 5. The flange portions 22, 23 are further formed with
spring holding holes 22b, 23b (FIG. 1) at plural circumferential
places thereof (6 places in the embodiment) where the pins 16, 17
are not implanted. The stationary seal rings 4, 5 are urged into
movement toward the rotary seal ring 3 by means of the springs 18,
19 (FIG. 1) mounted in these holes 22b, 23b.
[0021] The case body 21 is provided with a passage hole 21p, with
which an external pipe line 101 (FIG. 1) and a valve 102 (FIG. 1)
are connected. The sealing gas is introduced into the sealing-fluid
region S by opening the valve 102. The pressure of the sealing gas
is controlled such as to provide a higher pressure in the
sealing-fluid region S than those of the endo-fluid region H and
the atmosphere region L. During the operation of the agitator, the
sealing gas of a predetermined pressure is constantly supplied to
the sealing-fluid region S.
[0022] A vertical hole 22v and a horizontal hole 22h communicated
therewith are extended through the flange portion 22. The vertical
hole 22v and horizontal hole 22h constitute a steam ventilation
hole to be described hereinlater. An upper end of the vertical hole
22v opens into a spring seat face 22c facing the sealing-fluid
region S. The horizontal hole 22h is connected with an external
pipe line 103 (FIG. 1) and a valve 104 (FIG. 1). When the valve 104
is opened, the external pipe line 103 is opened into the
atmosphere.
[0023] FIG. 3 is an enlarged sectional view showing an upper end of
the flange portion 22 (the figure showing a portion of a different
circumferential phase from that of the spring holding hole 22b).
FIG. 4 is a view as viewed along an arrow IV in FIG. 3. Referring
to the figures, the flange portion 22 is formed with a slit 22e cut
down vertically from its top side 22d and radially extended to its
outer periphery. The bottom of the slit 22e is inclined downwardly
toward the outside (the right-hand side as seen in FIG. 3). The
slit 22e is provided for discharging water accumulated in the
groove 22a to the vertical hole 22v (specifically described
hereinlater). The slits 22e are formed at plural circumferential
places of the flange portion 22, and each of slits 22e is located
at position of a different circumferential phase from that of the
spring holding hole 22b.
[0024] Next, description will be made on how the mechanical seal of
the above construction operates during normal operation. First,
when the rotary shaft 52 is at standstill, both the first and
second stationary seal rings 4, 5 are in contact with the rotary
seal ring 3. When the rotary shaft 52 and the rotary seal ring 3
are rotated in a state where the sealing gas of the predetermined
pressure is supplied to the sealing-fluid region S by opening the
valve 102 and closing the valve 104, the sealing gas produces a
dynamic pressure in the grooves 3g of the rotary seal ring 3. The
dynamic pressure axially moves the stationary seal rings 4, 5 away
from the rotary seal ring 3 (of the order of several micrometers),
so that the rotary seal ring 3 and the stationary seal rings 4, 5
are maintained in non-contact relation via the sealing gas. Thus,
fluid layers of the sealing gas are formed between the sealing
end-face 3s of the rotary seal ring 3 and that 4s of the stationary
seal ring 4, and between the sealing end-face 3s of the rotary seal
ring 3 and that 5s of the stationary seal ring 5. Hence, fluid seal
is provided between the endo-fluid region H and the sealing-fluid
region S and between the sealing-fluid region S and the atmosphere
region L. At this time, a minor amount of the sealing gas leaks
into the endo-fluid region H and the atmosphere region L of
relatively lower pressures. The amount of leaked gas constitutes a
consumption of the sealing gas during the operation.
[0025] FIG. 5 is an enlarged view showing a portion around the
rotary seal ring 3 and the first stationary seal ring 4 during the
above normal operation. At this time, the O-ring 14 is located at a
lower end of the groove 22a as subjected to the pressure of the
sealing gas. A balance ratio K1 for the first stationary seal ring
4 is expressed as K1=S2/S1, where S1 denotes an area of seal face
defined by the seal ring 4 (representing an annular area, and the
following S2 and S3 also representing annular areas), and where S2
denotes a pressure receiving area subjected to a pressure for
pressing the first stationary seal ring 4 in a direction to close
the seal face. The value of the balance ratio is so designed as to
cause the aforementioned separation of the first stationary seal
ring 4 from the rotary seal ring 3, taking into consideration the
spring force of the spring 18, the weight of the first stationary
seal ring 4 and the like. Normally, the value of the balance ratio
is preferably in the range of 0.6 to 1.6. The selection of such a
value provides a seal arrangement which basically retains an
intrinsic nature of the seal to inhibit the seal face from being
opened and which permits the dynamic pressure to slightly open the
seal face for bringing the stationary seal ring into the
non-contact state.
[0026] It is noted that the second stationary seal ring 5 is also
designed the same way.
[0027] Next, in a state where the agitator is deactivated to bring
the rotary shaft 52 to standstill, the agitator is sterilized. In
this sterilization operation, the valve 102 of FIG. 1 is closed,
whereas the valve 104 is opened. This brings the sealing-fluid
region S into an exhausting state. On the other hand, hot steam (at
about 130.degree. C.) of a predetermined pressure is supplied to
the interior of the agitator or the endo-fluid region H. The steam
sterilizes the interior of the agitator and also enters space
between the rotary seal ring 3 and the first stationary seal ring
4. Thus, the first stationary seal ring 4 is moved away from the
rotary seal ring 3, as shown in FIG. 6, so that a gap G (of dozens
micrometers) is formed therebetween. The hot steam passes through
the gap G and then through the vertical hole 22v and the horizontal
hole 22h to be exhausted outside. In this manner, the sterilizing
operation for the agitator also accomplishes the sterilization of
the mechanical seal. In some cases, a pipe for discharging the
steam may be added to the external pipe line 101 (FIG. 1) in order
to promote the temperature rise of the mechanical seal portion
during the sterilizing operation.
[0028] In the above sterilizing operation, the pressure of the
steam moves the O-ring 14 in the groove 22a to make the O-ring 14
abut on an axially upper end of the groove, as shown in FIG. 6. At
this time, the pressing force on the O-ring 14 is received by the
flange portion 22 and hence, the pressing force does not act on the
first stationary seal ring 4. Therefore, a balance ratio K2 for the
first stationary seal ring 4 is expressed as K2=S3/S1, where S1
denotes the area of seal face defined by the seal ring, and where
S3 (=S1-S2) denotes a pressure receiving area subjected to a
pressure for pressing the first stationary seal ring 4 in the
direction to close the seal face. The balance ratio K2 is rewritten
as K2=1-K1. Conversely to the normal operation, the mechanical seal
has a basic nature prone to open the seal face. Thus is provided a
seal arrangement wherein the seal face is opened to a greater
degree than in the normal operation by the supplied steam, thereby
allowing for ventilation.
[0029] If, at this time, the force on the O-ring 14 is also applied
to the first stationary seal ring 4, the force of closing the seal
face is increased so that the balance ratio exceeds the above value
K2. Accordingly, the first stationary seal ring 4 is less prone to
move away from the rotary seal ring. However, the O-ring 14 is
received by the flange portion 22, as described above, whereby the
increase of the pressure receiving area S3 is avoided to thereby
prevent the balance ratio from being affected. Consequently, it is
ensured that the first stationary seal ring 4 is positively moved
away to a degree required for the ventilation.
[0030] Because of the passage of the steam, condensation forms on
the outside of the first stationary seal ring 4. However, the
resultant droplets fall to be discharged via the vertical hole 22v
and the horizontal hole 22h. In addition, droplets built up on the
O-ring 14 are also discharged via the slits 22e. Subsequently, dry
air in place of the steam is ventilated for quick removal of
moisture adhered to the mechanical seal.
[0031] The foregoing embodiment is arranged such that the steam is
exhausted via the vertical hole 22v and the horizontal hole 22h.
However, in a case where the mechanical seal is mounted in an
apparatus with the rotary shaft 52 positioned horizontally, as
shown in FIG. 7, the flange portion 22 may obviate the hole for
discharging gas/water while the valve 104 may be connected with the
external pipe line 101. In this case, the normal operation may be
carried out with the valve 102 opened and the valve 104 closed.
When the steam or dry air is ventilated, the valve 102 may be
closed while the valve 104 may be opened.
[0032] While the foregoing embodiment illustrates the non-contact
type mechanical seal, the sterilization may also be performed by
the same arrangement using a contact type mechanical seal.
[0033] The O-rings 14, 15 may be replaced by other sealing
members.
[0034] The spring 18 is not limited to the helical spring used in
the foregoing embodiment but may be other elastic member. For
instance, a leaf spring or metal bellows may be used. In a specific
case, there may be used an O-ring.
* * * * *