U.S. patent application number 09/281281 was filed with the patent office on 2001-12-20 for shaft seal apparatus.
Invention is credited to FUJIWARA, SATOSHI, FUSE, TOSHIHIKO, OKUMACHI, EIJI.
Application Number | 20010052673 09/281281 |
Document ID | / |
Family ID | 26430489 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052673 |
Kind Code |
A1 |
OKUMACHI, EIJI ; et
al. |
December 20, 2001 |
SHAFT SEAL APPARATUS
Abstract
A shaft sealing apparatus 109 comprising a seal case 1 mounted
on a tank shell 102 of rotary equipment, a rotary seal ring 3 fixed
to the rotary shaft 106 of the rotary equipment, a stationary seal
ring 4 held in the seal case 1 opposite to the rotary seal ring 3
and movable in the axial direction, a coil spring 5 to thrust the
stationary seal ring 4 against the rotary seal ring 3, a gas
feeding channel 6 formed out of a series of gas passages running
through the seal case 1 and the stationary seal ring 4 and opening
between the two seal end faces 31, 41 of the two seal rings 3, 4,
and a gas jetting mechanism to jet, selectively, a seal gas 71 such
as nitrogen and a sterilization gas 72 such as steam through the
gas feeding channel 6 into between the seal end faces 31, 41. In
normal operation, the shaft seal apparatus 109 functions to seal at
the relatively rotating portions of the end faces 31, 41 of the
seal rings 3, 4, while holding the seal ends 31, 41 in a
non-contact state, by jetting a seal gas 71 such as nitrogen into
between the two seal end faces 31, 41. In sterilization mode, a
sterilization gas 72 such as steam is jetted into between the two
seal end faces 31, 41 instead of the seal gas 71, sterilizing at
least the gas feeding channel 6 and the seal end faces 31, 41.
Inventors: |
OKUMACHI, EIJI; (HYOGO-KEN,
JP) ; FUJIWARA, SATOSHI; (HYOGO-KEN, JP) ;
FUSE, TOSHIHIKO; (HYOGO-KEN, JP) |
Correspondence
Address: |
GRIFFIN BUTLER WHISENHUNT & SZIPL LLP
SUITE PH-1
2300 NINTH STREET SOUTH
ARLINGTON
VA
222042396
|
Family ID: |
26430489 |
Appl. No.: |
09/281281 |
Filed: |
March 30, 1999 |
Current U.S.
Class: |
277/348 |
Current CPC
Class: |
F16J 15/342 20130101;
B01F 2035/351 20220101 |
Class at
Publication: |
277/348 |
International
Class: |
F16J 009/00 |
Claims
What is claimed is:
1. A shaft seal apparatus that comprises: a seal case mounted in a
rotary shaft penetrating position of a tank shell of rotary
equipment; a rotary seal ring fixed to a rotary shaft of the rotary
equipment; a stationary seal ring held in the seal case opposite to
the rotary seal ring and movable in the direction of the shaft
axis; a thrusting member mounted between the seal case and the
stationary seal ring and thrusting the stationary seal ring against
the rotary seal ring; and a gas feeding channel comprising a series
of gas passages running through the seal case and the stationary
seal ring and opening between the opposing seal end faces of the
two seal rings and a gas jetting mechanism to jet a seal gas or a
sterilization gas selectively into between the seal end face
through the gas passages, wherein, in normal operation, the shaft
seal apparatus functions to seal at the relatively rotating
portions of the end faces of the seal rings while holding the seal
end faces in a non-contact state by jetting the seal gas into
between the two seal end faces, and, in sterilization mode, the
sterilization gas is jetted into between the two seal end faces
instead of the seal gas, sterilizing at least the gas passage and
the seal end faces.
2. The shaft seal apparatus of claim 1, wherein the seal gas
comprises nitrogen gas at a pressure higher than a pressure in the
rotary equipment.
3. The shaft seal apparatus of claim 1, wherein the sterilization
gas comprises steam at a pressure equal to a pressure of the seal
gas.
4. The shaft seal apparatus of claim 1, wherein the seal case and
the rotary shaft are engaged with each other such that the seal
case and the rotary shaft are rotatable relative to one another and
are non-movable relative to one another in the radial direction.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a shaft seal apparatus. The shaft
seal apparatus of the present invention is employed in rotary
equipment such as stirrers and mixers that are intended for use in
the manufacture of pharmaceuticals, foodstuffs, and the like.
BACKGROUND OF THE INVENTION
[0002] A vertical type stirrer or agitator 101 as shown in FIG. 5
is used in the production of fermented products such as, for
instance, fermented drinks. This stirrer 101 has a motor-supporting
frame 103 set up on a tank shell 102 forming a fermentation tank, a
motor (with a reducer, etc.) 104 mounted on the top of the
motor-supporting frame 103, and a rotary shaft or stirrer shaft 106
connected to the motor 104. Shaft 104 is supported in a
free-rotating state by motor-supporting frame 103 by means of a
bearing 105. Shaft 104 extends down inside tank shell 102 and is
held vertically in the fermentation tank inner space 107. Shaft 104
is constituted so that agitation propellers 108, 108 mounted at the
lower end thereof agitate a treatment material to enhance
fermentation in tank inner space 107.
[0003] This type of fermentation stirrer 101 is designed so as to
prevent fermentation gases generated in tank 107 from leaking out
by providing an appropriate shaft seal apparatus 109 between rotary
shaft 106 and a rotary shaft penetrating portion 102a of tank shell
102.
[0004] Some known types of shaft seal apparatus 109 installed on
this type of stirrer 101 are equipped with a single or double
end-face contact mechanical seal while others are provided with
grand-packings.
[0005] The type of shaft seal apparatus equipped with a single
mechanical seal (hereinafter referred to as "the first prior art
apparatus") has a seal case in the rotary shaft penetrating portion
102a in which a stationary seal ring on the seal case is pressed
against a rotary seal ring on the rotary shaft 5. Thus, in the
first prior art apparatus, tank inner space 107 is sealed by a
sliding contact between the two seal rings rotating relative to one
another.
[0006] The end-face contact type shaft seal apparatus provided with
a double mechanical seal (hereinafter called "the second prior art
apparatus") has a pair of mechanical seals, of the same type of the
first prior art apparatus, arranged side by side. A sealing fluid
region is thus formed between the pair of mechanical seals and
keeps the tank inner space 107 air-tight. The sealing fluids used
in this type of apparatus include oils and liquids that would cause
no problems if they leak into the tank. The type of shaft seal
apparatus using oil as sealing fluid is additionally provided with
an oil unit where the oil is circulated so as to keep the oil from
leaking into the tank inner space from the seal region. This type
of shaft seal apparatus is also designed so that the pressure of
the oils and liquids (that would cause no problems if they leak
into the tank) can be held higher than that inside the tank, to
prevent the gas inside the tank (i.e., the fermentation gas) from
leaking out into the seal region.
[0007] The type of apparatus using a grand-packing (hereinafter
name "the third prior art apparatus") has a stuffing box installed
in the rotary shaft penetrating position 102a and a number of grand
packings, generally braided packings, are arranged side by side in
the space between the stuffing box and the rotary shaft 106 to seal
the tank inner space 107. Also, a lantern ring is usually provided
in the middle of the group of grand-packings, where nitrogen gas is
fed.
[0008] Rotary equipment such as the aforesaid fermentation stirrers
101, when used with pharmaceuticals, foodstuffs, raw materials to
be processed into pharmaceuticals and foodstuffs, and other such
materials, require strict hygienic control. They are subjected to
sterilization treatment periodically or as necessary by the
injection of a sterilization gas, usually high-temperature steam,
into the tank inner space 107. In this sterilization treatment,
parts of the shaft seal apparatus that face the tank inner space
107 cannot be cleaned well by the sterilization gas which is jetted
into the tank alone. Therefore, the same gas is directly jetted
onto those parts of the shaft seal apparatus.
[0009] In the first and second prior art apparatuses, however, the
seal end faces on both sides which are in contact with each other
cannot be well sterilized by the jetting of the sterilization gas.
Especially in the second prior art apparatus, which is of
complicated construction, the sterilization gas cannot reach many
parts of the apparatus, which results in grossly insufficient
sterilization. Another problem is that since those prior art
apparatuses are based on end-face contact type mechanical seals,
dust will arise from the contact wearing of the two end faces in
operation, which can fall into the tank inner space 107. It is
difficult, therefore, to achieve sufficient hygienic control in the
tank. The problem with the first prior art apparatus is that the
gas in the tank cannot be shut out completely. Toxic or odiferous
gases in the tank could contaminate or otherwise damage the
environment.
[0010] The third prior art apparatus also presents the following
problems. The grand-packings cannot be cleaned enough even by
jetting a sterilization gas directly at them. Furthermore, the
grand-packings produce dust from contact with the rotary shaft 106
in operation, and that dust can fall into the tank inner space 107.
For those reasons, sufficient hygienic control in the tank inner
space 107 is difficult to effect, as with the first and second
prior art apparatuses.
[0011] As set forth above, the first through third prior art
apparatuses cannot be well-sterilized by hygienic procedures
including treatment by jetting sterilization gas. They are
accordingly not suitable for use in rotary equipment where strict
sanitation is required. The industry would benefit if those
problems were addressed.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide a shaft
seal apparatus which can completely seal off fermentation gas in a
fermentation tank without causing dusting (such as from wearing)
and which is fully sterilizable by sterilization gas. A shaft seal
apparatus having these attributes is quite suitable for use in
rotary equipment where vigorous hygienic control must be
exercised.
[0013] It is another object of the present invention to provide a
shaft seal apparatus the construction of which is simplified to the
maximum possible extent by using gas feeding passages formed in a
seal case and a stationary seal ring not only as means for
generating static pressure by seal gas but also as means for
sterilizing a tank by sterilization gas.
[0014] It is a further object of the present invention to provide a
shaft seal apparatus which affords excellent sealing even in rotary
equipment in which a seal case is difficult to mount with precision
or in which the shaft vibrates because of the construction or
function of the machine.
[0015] These objects are achieved by a shaft seal apparatus which
comprises a seal case mounted in a rotary shaft penetrating portion
of a tank shell of rotary equipment, a rotary seal ring fixed to
the rotary shaft of the rotary equipment, a stationary seal ring
held in the seal case opposite to the rotary seal ring and movable
in the direction of the shaft axis, a thrusting member mounted
between the seal case and the stationary seal ring and thrusting
the stationary seal ring against the rotary seal ring, a gas
feeding channel comprising a series of gas passages running through
the seal case and the stationary seal ring and opening between two
opposing seal end faces of the two seal rings, and a gas jetting
mechanism to jet seal gas or sterilization gas selectively to
between the seal end faces from the gas feeding channel.
[0016] In normal operation, the shaft seal apparatus functions as
sealing at the relatively rotating portion of the end faces of the
seal rings while holding the seal ends in a non-contact state by
jetting a seal gas into between the two seal end faces. In
sterilization mode, a sterilization gas is jetted into between the
two seal end faces instead of the seal gas, sterilizing at least
the gas feeding channel and the seal end faces.
[0017] In a preferred embodiment, the seal gas used is nitrogen
compressed to a higher pressure than the pressure in the rotary
equipment, and the sterilization gas is steam at the same pressure
as the seal gas.
[0018] It is also noted that deterioration or loss of sealing
performance due to vibration of the rotary shaft is avoided by
engaging the seal case and the rotary shaft by means of a bearing
or a similar coupling member such that the two are rotatable
relative to one another but unchangeable in position relative to
each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a vertical, sectional view of a shaft seal
apparatus of the present invention.
[0020] FIG. 2 is an enlarged view of the core part of FIG. 1.
[0021] FIG. 3 is a front view of the seal end face of the
stationary seal ring of the shaft seal apparatus.
[0022] FIG. 4 is a vertical, sectional view of a variation example
which view corresponds to FIG. 2.
[0023] FIG. 5 is a vertical, sectional schematic view of an example
of rotary equipment on which the shaft seal apparatus is
mounted.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIGS. 1 to 3 show an example of the present invention
applied to the shaft seal apparatus 109 of the agitator 101 for
fermentation treatment shown in FIG. 5.
[0025] The shaft seal apparatus 109 in this example is an
externally pressing type non-contacting seal comprising, as
illustrated in FIGS. 1 and 2, a seal case 1 mounted in a rotary
shaft penetrating portion 102a of a tank shell 102 forming a
fermentation tank 107; a connecting means 2 which connects the seal
case 1 and an agitator shaft or rotary shaft 106 extending down
through the seal case 1 and the rotary shaft penetrating portion
102a such that the shaft 106 and the seal case 1 are rotatable
relative to one another but unmovable relative to one another
radially; a rotary seal ring 3 provided inside the seal case 1 and
fixed to the rotary shaft 106; a stationary seal ring 4 provided in
the seal case 1 opposite to the rotary seal ring 3 and freely
movable in the direction of the shaft axis; a thrusting member 5
mounted between the seal case 1 and the stationary seal ring 4 so
as to press the stationary seal ring 4 against the rotary seal ring
3; a gas feeding channel 6 comprising a series of gas passages
running through the seal case 1 and the stationary seal ring 3 and
opening between the opposing seal end faces 31 and 41 of the two
seal rings 3 and 4; a gas jetting mechanism 7 to jet a seal gas 71
or a sterilization gas 72 selectively into between seal end faces
31 and 41 from gas feeding channel 6; and a draining mechanism to
discharge gases 71 and 72. Shaft seal apparatus 109 is arranged to
seal the tank inner space 107, that is, the peripheral region
outside of the seal rings 3 and 4 and the relatively rotating
portion of the seal rings 3 and 4 while holding the two seal ends
31 and 41 in a non-contact state by jetting seal gas 71 into
between the two seal end faces.
[0026] The seal case 1, as shown in FIG. 1, comprises a cylindrical
main body 11; a retainer portion formed out of three parts 12, 13,
and 14 provided at the lower end section of main body 11; and a
circular flange portion 15 provide at the lower end of main body
11. Seal case 1 is mounted on the rotary shaft penetrating portion
102a of the tank shell 102 by means of the flange portion 15 such
that seal case 1 surrounds rotary shaft 106 concentrically. The
retainer portion is of a double cylindrical construction opening
downward with cylindrical outer retainer 12 and inner retainer 13
connected by circular back wall 14.
[0027] Coupling member 2 comprises, as shown in FIG. 1, a bearing
mounted between the upper section of the main body 11 of seal case
1 and the cylindrical sleeve 106a mounted on the rotary shaft 106.
Coupling member 2 connects the seal case 1 and the rotary shaft 106
such that the two are rotatable relative to one another and
non-movable relative to one another in the radial direction and the
axial direction. Lubrication spaces 23, 23 kept air-tight by oil
seals 21, 21 provided above and under the coupling member bearing 2
are formed between the main body 11 of seal case 1 and the sleeve
106a of rotary shaft 106. It is designed so that a lubricant (such
as grease) 25 injected in to the lubrication spaces 23, 23 from a
lubricant path 24 lubricates bearing 2.
[0028] Rotary seal ring 3 as illustrated in FIGS. 1 and 2 is fit
into the lower part of sleeve 106a and clamped non-movable in the
axial direction and relatively non-rotatable between a circular jaw
portion 106b formed integrally on the lower part of the sleeve 106a
and a cylindrical clamping sleeve 106c fit into the lower section
thereof.
[0029] The stationary seal ring 4, which is shown in FIGS. 1 and 2,
is held in the seal case with the lower end face, that is, the end
face 41 of the stationary seal ring 4, opposite to and
concentrically with the upper end face of the rotary seal ring 3,
that is, the rotary seal end face 31, such that the ring 14 is
slidable in the axial direction and relatively non-rotatable. To
further illustrate, a pair of first O rings 91 and 91, placed a
specific distance apart in the vertical direction from each other
are provided as a secondary seal on the periphery of the stationary
seal ring 4 in such a way that the stationary seal ring 4 is held
by the inner cylindrical surface of the outer retainer 12 of the
retainer portion and is slidable in the vertical direction. On the
inner cylindrical surface of the stationary seal ring 4 a second O
ring 92 is provided as a secondary seal in such a way that the
stationary seal ring 4 is held by the outer circumferential surface
of the inner retainer 13 of the retainer portion and is slidable in
the vertical direction. The stationary seal ring 4 has engaging
holes 42 on its upper end face or the back side as shown in FIG. 1.
Rotation stopper pins 43 embedded in the back wall 14 are engaged
with these holes. In this manner, the stationary seal ring 4 is
kept from rotating in relation to the seal case 1 while being
allowed to move in the axial or vertical direction within a
specific distance.
[0030] The thrusting member 5 is formed of one or a plurality of
coil springs (a single coil spring is shown in the drawings) placed
between the back side of the stationary seal ring 4 and the back
wall 14 of the retainer portion to thrust the stationary seal ring
4 against the rotary seal ring 3 as shown in FIGS. 1 and 2.
[0031] Gas feeding channel 6 comprises, as shown in FIGS. 1 to 3, a
circular interconnecting space 61, formed between the outer
circumferential surface of the stationary seal ring 4 and the inner
cylindrical surface of the outer retainer 12 as shown in FIGS. 1 to
3, and sealed by the upper and lower first O rings 91 and 91; a
passage 62 on the seal case side extending from the outer
circumferential surface of seal case 1 to the interconnecting space
61 through the outer retainer 12; a plurality of static pressure
generating grooves 63 formed on the stationary seal ring end
surface 41; and a passage 64 on the seal ring side penetrating the
stationary seal ring 4 and extending from the interconnecting space
61 to the static pressure generating grooves 63. Each of the static
pressure generating grooves 63 is a circular arc-formed recess and
forms a circle concentric with the stationary seal end face 41 as
shown in FIG. 3. It is noted that the downstream end of the passage
64 on the seal ring side is branched out, with each branch terminal
64a opened at each static pressure generating groove 63.
[0032] The gas jetting mechanism 7, as shown in FIG. 1, comprises a
seal gas supply pipe 74 led from a seal gas supply source 73 and
having its downstream end connected to the passage 62 on the seal
case side; a seal gas supply valve 74a, a pressure control valve
74b, a filter 74c, and a check valve 74d all provided in the seal
gas supply pipe 74; a sterilization gas supply pipe 76 led from a
sterilization gas supply source 75 and having its downstream end
connected to the seal gas supply pipe 74 at the downstream side of
the check valve 74d; and a sterilization gas supply valve 76a and a
check valve 76b provided in the sterilization gas supply pipe 76.
Gas jetting mechanism 7 is arranged to feed the seal gas 71 or the
sterilization gas 72, as desired, into the gas feeding channel 6 at
a higher pressure than the pressure level of tank inner space
107.
[0033] In normal operation, where the shaft needs to be sealed by
the shaft seal apparatus 109, the seal gas supply valve 74a is
opened while the sterilization gas supply valve 76a is kept closed.
Thus the seal gas 71 is supplied to the static pressure generating
grooves 63 at a higher pressure than the pressure level of the tank
inner space from the seal gas supply pipe 74 through passage 62 on
the seal case side, interconnecting space 61, and passage 64 on the
seal ring side, so as to generate static pressure between the two
seal end faces 31 and 41 and keep them in a non-contacting state.
One uses as seal gas 71 gas of a type which would cause no problems
even if it were to leak into tank inner space 107. Nitrogen gas is
employed in the present embodiment.
[0034] Tank inner space 107 may be sterilized with the machine put
out of operation and no sealing by the shaft seal apparatus 109 is
needed. In the sterilization procedure, the sterilization gas
supply valve 76a is opened with the seal gas supply valve 74a kept
closed so that the sterilization gas 72 at a suitable pressure
(e.g., at the same pressure as that of the seal gas 71) may be fed
to the static pressure generating grooves 63 from the sterilization
gas supply pipe 76 through the downstream portion of the seal gas
supply pipe 74 (a portion of the seal gas supply pipe 74 downstream
of a location at which the pipe 76 is connected to the pipe 74),
the passage 62 on the seal case side, the interconnecting space 61,
and the passage 64 on the seal ring side. The sterilization gas 72
is the same gas as is used for sterilization of the tank inner
space 107. In the present embodiment, high temperature steam is
used.
[0035] It is noted that sterilization gas 72 is led from the same
sterilization gas supply source 75 for sterilization of the tank
inner space 107. In the present embodiment, furthermore, a
sterilization gas passage 76c is formed through the outer retainer
12 of seal case 1 and this sterilization gas passage 76c is
connected to the sterilization gas supply pipe 76 so as to jet a
part of the sterilization gas or steam 72 supplied from the
sterilization gas supply pipe 76 onto the outer circumferential
surface of the opposing portion of the seal rings 3 and 4.
[0036] The draining mechanism 8 includes, as shown in FIGS. 1 and
2, a drain space 81 or an inner space of the seal case 1 shielded
from the tank inner space 107 and the lubrication space 23 by the
seal end faces 31 and 41 and the lower oil seal 21; a slinger 82
provided in the drain space 81 and fixed to the sleeve 106a; and a
discharge channel 83 leading through the main body 11 of the seal
case 1 and opening at the lower end side of the drain space 81. The
slinger 82 is provided with a circular protrusion 82a on the
peripheral edge thereof. The upper end of a circular protrusion 14a
extending from the inner circumferential edge of the back wall 14
projects inside the inner circumferential surface of this circular
protrusion 82a. The discharge channel 83 is opened at a level
matching, in the vertical direction, the circular protrusions 14a
and 82a. In the draining mechanism 8, gases 71 and 72 flow out into
the drain space 81 through space between the seal end faces 31 and
41 and flow through space between the two protrusions 14a and 82a
and are discharged from the discharge channel 83. The gases 71 and
72 are guided by the circular protrusion 82a to flow into the
discharge channel 83, from where the gases are discharged quickly
and smoothly. There is little possibility that the gases will flow
upward instead of being discharged through discharge channel 83.
Therefore, there is no concern that the high temperature steam 72,
for example, will rise to a level higher than discharge channel 83.
Oil seal 2, therefore, will not be exposed to high temperature
deterioration.
[0037] The component parts of the shaft seal apparatus 109
(including the sleeves 106a and 106c) may be made from stainless
steel (e.g., JIS designation SUS 316), taking into consideration
fermentation temperature and the necessity for freedom from
contamination.
[0038] When a seal gas is provided between a rotary seal ring 3 and
a stationary seal ring 4, a fluid film (static pressure) of seal
gas is formed between the seal rings 3 and 4 for keeping the seal
rings 3 and 4 in a non-contact state, with the seal rings 3 and 4
spaced from each other by a small distance. At the area where the
fluid film is formed, that is, the area between seal ring end faces
31 and 41, the region outside of the apparatus and the region
inside the apparatus are separated and sealed from one another.
[0039] In order to avoid contamination, the seal rings 3 and 4 are
made of materials, for example, respectively, stainless steel and
carbon, that neither decompose nor produce dust. Seal end faces 31
and 41 may wear as a result of contact between them that occurs
during, e.g., cessation of operation. Hence, the surface (seal end
face 31) of the rotary ring 3 made of stainless steel is provided
with a wear-resistant ceramic coating layer made of, for example,
CrO.sub.2. Since stationary ring 4 is made from carbon which is
high in lubricating effect, such as sintered carbon, that is,
powdered carbon formed into the shape of the ring and then
sintered, the surface (seal end face 41) of stationary seal ring 4
needs no coating. Where one seal end face (in this case, seal end
face 41) is high in lubrication, increased rotational torque and
lessened wear are obtained when starting and stopping relative
rotation of the seal end faces.
[0040] Because seal rings 3 and 4 are made of different materials
as described, any contact wear which does occur will occur at the
carbon seal. This facilitates maintenance of the apparatus, because
it will be necessary to change only one of the two seal rings.
[0041] The shaft seal apparatus thus prepared according to the
present invention can seal the tank inner space 107 perfectly
without causing such problems as encountered with the prior art
which was discussed earlier in this specification.
[0042] To illustrate further, in normal operation of fermentation
treatment by the stirrer 101, seal gas supply valve 74a is opened
with sterilization gas supply valve 76a kept closed so that the
seal gas 71 is fed into between seal end faces 31 and 41 through
seal gas feeding channel 6 to generate an end face opening force
therebetween. This opening force is generated by a static pressure
produced by the seal gas 71 led to the static pressure generating
grooves 63. Therefore, seal end faces 31 and 41 are held in a
non-contact state wherein an equilibrium is established between the
opening force and the closing force (produced by spring 5 pressing
stationary seal ring 4 toward rotary seal ring 3). Since the
pressure of the seal gas 71 is higher than that in tank inner space
107, the fluid (fermentation gas, etc.) in the tank is not allowed
to enter between the seal end faces 31 and 41. Thus, the tank inner
space 107 is completely sealed, precluding the possibility of
contaminating the environment.
[0043] That arrangement exhibits a hygienic seal function, because
tank inner space 107 is sealed with seal end faces 31 and 41 kept
in a non-contact state. Thus no wear dust produced by contact
between faces 31, 41 finds its way into tank inner space 107. It is
also noted that while the seal gas 71 may be led into tank inner
space 107 through between seal end faces 31 and 41, the seal gas 71
is nitrogen gas, which would not cause problems even if it might
leak into tank inner space 107. That is, possible leakage of the
seal gas 71 into tank inner space 107 would not constitute a
problem. It is further noted that although the seal gas 71 is
continuously fed while stirrer 101 is in operation, the operation
is started and ended this way: stirrer 101 is started (with the
rotary shaft driven) only after the seal gas 71 is fed and the seal
end faces 31 and 41 are held in a right non-contact state. The
supply of the seal gas 71 is cut off only after the stirrer is
stopped with the rotary shaft 106 coming to a complete
standstill.
[0044] As mentioned earlier, tank inner space 107 of stirrer 101 is
sterilized by jetting steam periodically or as necessary. In this
sterilization operation, the parts of the shaft seal apparatus
which face the tank inner space 107 can be well sterilized by
feeding steam 72 through gas feeding channel 6.
[0045] That is, if with the rotary shaft at a standstill the
sterilization gas supply valve 76a is opened with the seal gas
supply valve kept closed and then steam 72 is supplied through gas
feeding channel 6, steam 72 reaches static pressure generating
grooves 63 through gas feeding channel 6, passes through between
seal end faces 31 and 41, and flows into tank inner space 107 and
drain space 81. In the initial stage, seal end faces 31 and 41 are
in contact with each other, but steam 72, which is at the same high
pressure as the seal gas 71, opens and separates seal end faces 31
and 41 just as the seal gas 71 does and jets into tank inner space
107 and drain space 81.
[0046] Therefore, the steam 72 evenly reaches not only the inside
of gas feeding channel 6 but also seal end faces 31 and 41 in a
contact state, to effect through sterilization. The steam 72, which
jets into tank inner space 107 through between seal end faces 31
and 41, comes into contact with the parts of the shaft seal
apparatus which face tank inner space 107 (including the outer
circumferential surfaces of seal rings 3 and 4) and flows into tank
inner pace 107. Thus those parts of the apparatus are sterilized
sufficiently. Those parts of the apparatus are additionally treated
by the steam 72 which is jetted from sterilization gas channel 76c
toward the outer circumferential surface of the contact area
between seal rings 3 and 4.
[0047] When producing a static pressure with the seal gas 71 led to
static pressure generating grooves 63 to hold seal end faces 31 and
41 in a non-contact state, in order to provide for good sealing
function it is necessary to keep seal end faces 31 and 41 parallel
to each other and concentric with each other. Where the mounting of
seal case 1 on tank shell 102 is imprecise, or if rotary shaft 106
vibrates, parallelism and concentricity of the seal end faces will
be lost, resulting in poor sealing function. Especially with a type
of stirrer 101 as aforesaid in which the rotary shaft 106 is
supported by means of the bearing 105 at the upper part alone, the
shaft tends to vibrate and it is difficult to obtain a satisfactory
sealing function.
[0048] In the aforesaid shaft seal apparatus 109 of the present
invention, however, the seal case 1 and the rotary shaft 106 are
engaged via a coupling member bearing 2 such that the seal case 1
and the rotary shaft 106 are relatively rotatable but are
relatively non-movable in the radial direction. Even if the shaft
vibrates there will be no change in relative position, therefore,
between the rotary seal ring 3 provided on the rotary shaft 106 and
the stationary seal ring 4 mounted in the seal case 1. That is, the
seal rings 3 and 4 are held in a relatively constant relation of
position. Thus the seal end faces 31 and 41 are kept in proper
parallelism and concentricity, and they exhibit good sealing
function.
[0049] In addition, the rotary shaft 106 is also held by means of
seal case 1 and bearing 2 mounted in the rotary shaft penetrating
portion 102a of tank shell 102. That is, rotary shaft 106 is
supported by two bearings, bearing 105 at a point apart from the
tank shell 102 and also bearing 2 at a point close to tank shell
102. Thus the shaft vibration caused by the stirring resistance
acting on the agitation propellers 108, 108 can be controlled to
the maximum possible extent, with the stirring effect improved. It
is noted also that seal case 1 is engaged with rotary shaft 106 via
bearing 2. Thus the relation of position between seal case 1 and
rotary shaft 106 is kept constant by bearing 2, and it is easy to
install the seal case 1 on the tank shell 102 with precision.
[0050] As set forth above, shaft seal apparatus 109 seals tank
inner space 107 by feeding the seal gas 71 at a pressure higher
than that in the tank into between the seal end faces 31 and 41,
keeping those seal end faces in a non-contact state. Thus leakage
from tank inner space 107 can be completely shut off. Also, there
is no contact wear dusting between the seal end faces 31 and 41,
and thus there is no concern that wear dust will fall into tank
inner space 107. In addition, a sterilization gas 72 such as steam
is jetted from between the seal end faces 31 and 41 to the outer
and inner circumferential surfaces of those seal end faces.
Therefore, the parts of the shaft seal apparatus difficult to
sterilize, especially the seal end faces 31 and 41 which face tank
inner space 107, can be sterilized well. Thus it is possible
according to the present invention to exercise hygienic control
effectively and sufficiently on tank inner space 107 and the
aforesaid parts of the shaft seal apparatus.
[0051] While there has been described a preferred form of the
present invention, it is understood that the invention is not
limited thereto, and that changes and variations may be made
without departing from the basic principle of the invention.
[0052] For example, a squeezer such as an orifice, capillary tube,
or porous member may be provided at a suitable place of the channel
6 (as at the gas passage 64 on the seal ring side) as shown in FIG.
4, so that the gap between the seal end faces 31 and 41 will be
automatically adjusted. In this arrangement, when the gap between
the seal end faces 31 and 41 increases because of vibration of the
rotary equipment (stirrer 101) or the like, the flow rate of the
seal gas flowing from the static pressure generating grooves 63 to
between the seal end faces 31 and 41 and the flow rate of the seal
gas flowing to the static pressure generating grooves 63 through
the squeezer 69 will be out of balance. Then the pressure within
the static pressure generating grooves 63 decreases, and the
opening force will be smaller than the closing force. As a result,
the gap between the seal end faces 31 and 41 will decrease to a
proper size. On the other hand, when the gap between the seal end
faces 31 and 41 is too small, the pressure in the static pressure
generating grooves 63 will rise in the same mechanism, the opening
force will be greater than the closing force, and the gap between
the seal end faces 31 and 41 will increase to a proper size.
[0053] In another variation, the static pressure generating groove
63 can be in any form. For example, a groove may be formed so that
the groove is in the form of a circle concentric with the seal end
face 41.
[0054] The shaft seal apparatus 109 of the present invention is
applicable as means for shaft sealing not only in a vertical type
fermentation stirrer 101 but also in a variety of other kinds of
rotary equipment which require vigorous sterilization by a
sterilization gas such as steam. Such equipment includes, e.g.,
agitators and mixers for use in the production of pharmaceuticals,
foodstuffs, and the like. Unlike the dynamic pressure type
non-contact seals in which the seal end faces are held in a
non-contact state by dynamic pressure generated by the relative
rotation thereof, a shaft seal apparatus of the present invention
is suitable for use in rotary equipment in which the revolution of
the rotary shaft is not fast enough to generate the required
dynamic pressure. A shaft seal apparatus of the present invention
is also suitable for use in rotary equipment for the treatment of
toxic substances whose leakage from a tank inner space must be
prevented completely. Whichever the type of rotary equipment to be
sealed, the properties and pressure of the seal gas and
sterilization gas to be jetted between the seal end faces 31 and 41
will be selected according to the purpose of the application and
the nature of the rotary equipment.
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