Note: Descriptions are shown in the official language in which they were submitted.
STI~TEMENT OF THE INVENTTON
This invention provides apparatus which comprises
a rotatable rotor for processing viscous liquid material
and having a cylindrical surface adjacent a portion of
the rotor containing viscous ]iquid material under
pressure, and a housing having a stationary cylindrical
surface coaxial with and spaced apart from said rotor
surface by a narrow clearance. According to the invention
dynamic sealing means are provided for preventing
leakage of the pressurized material past the clearance.
The dynamic sealing means includes a plurality of
helical sealing channels carried by one of the surfaces,
arranged so that the liquid material can penetrate $ e
channels. The width of the surface carrying the sealing
channels and the number, angle and geometry of the
sealing channels are selected so that outward penetration
of the clearance and the channels by the pressurized
liquid is opposed by the inward force applied to the
liquid in the sealing channels as the surfaces are
relatively rotated to resist the extent of outward
penetration of pressurized liquid in any of the sealing
channels.
~4~7~5
THE FIELD OF THE INVENTION
This invention relates to novel, improved sealing means for
rotary processors particularly those for processing viscous or
particula~e plastic or polymeric materials.
i7~5
--2--
DESCRIPTION OF THE PRIOR ART
U.S. Patent No. 4,142,805 and U.S. Patent ~o.
4,194,841 by Zehev Tadmor - one of the inventors of this
Application - disclose processes and apparatus for processing
plastic or polymeric materials.
The essential elements of the basic, individual,
~ ate~
annular processing passage described in those ~F~ee *5==~
comprise a rotatable element carrying at least one annular
processing channel and a stationary element providing a coaxial
surface cooperative with the channel to form an enclosed
processing passage. The stationary element has an inlet to
feed material to the passage for processing and an outlet spaced
apart from the inlet a major portion of the circumferential
distance about the processing passage to discharge processed
material from the passage. A member providing a liquid material
collecting end wall surface is arranged with the stationary
element and located in the passage near the outlet to obstruct
or restrain movement of material fed to the passage and to coact
with the rotating channel walls to provide relative movement
between the material and the internal surfaces of the channel
walls rotated toward the outlet~ This distinctive coaction
permits only liquid material in contact with the internal ~urfaces
of the rotating channel to be dragged forward to the liquid
material collecting end wall surface for controlled processing
and/or discharge.
.
:, .
7~5
--3--
In the preferred embodiment of the invention described
in U.S. Patent Nos.4,142,805 and 4,194,841, the essential
elements of the processing apparatus are arranged so that the
rotatable channel carrying element is adapted for rotation in
a stationary housing or chamber (the stationary element). The
described processing channel and preferably a plurality of
processing channels are formed in the cylindrical surface of
a rotor with each channel having opposing side walls extending
inwardly from the rotor surface. The stationary housing or
~0 chamber described has an internal, cylindrical surface providing
the cooperative coaxial surface which together with the annular
processing channel(s) form an enclosed processing assage(s).
~te~n~S
The method and apparatus of the Tadmor App~irD~I=r~ are
described as useful for conveying of solids, melting or plasticat-
ing plastic or polymeric material; conveying, pumping or
pressurizing viscous liquid material; mixing, blending,
dispersing and homogenizing material; and devolatilizing and/or
bringing about molecular or microscopic or macroscopic structural
changes by chemical reactions such as polymerization.
Because of the versatility and adaptability of the
basic individual processing passage, a plurality of them are
generally employed to provide processors usually with one or
more passages performing a different operation or function.
For example, one or more of the individual passages could be
assigned the function of receiving
--4--
and transporting material from one passage to another or, one
or more individual passages could be assigned the function of
melting or mixing or devolatilizing or discharging polymeric or
plastomeric material (s) . The particular function assigned an
individual passage usually determines the pressure characteristics
S of that passage. For example, some assigned functions such as
melting or discharging can imply the generation of very high
pressures. Other functions such as devolatilizing can involve
the generation of low pressures while mixing operations may involve
moderate pressures. Also, the distribution of pressure along
10 the circumference of each passage can vary depending upon the
function or operation assigned the passage. For some functions,
pressure may increase linearly along the complete circumference
or along only a portion of the circumference or, some functions
provide pressure characteristics involving one or more pressure
15 rises followed by one or more sharp drops along the circumference.
Moreover, oftentimes basic, individual processing passages having
particular pressure characteristics - such as high pressure -
are positioned or arranged beside or between units having completely
different pressure characteristics - such as low pressure.
In most instances it is desirable to provide effective sealing
for some or all of the individual basic passages of a multi-passage
processor to prevent unwanted leakage of material from at least
some of the passages. The unwanted leakage for example can
be external leakage from one or both of the end passages of a
multi-passage processor. Also, unwanted leakage can occur
1~1795
internally between adjacent 1ndividual processing passages.
In all instances however, the leakage of particular concern
occurs at a clearance required between the peripheral or top
surface of the rotatable cylindrical channel wall(s) and the
stationary interior coaxial annular surface particularly of
those portions of the passage where high pressures are generated.
External and internal leakage problems are particularly
complicated in multi-unit rotary processors because of the
differential radial pressures usually established along the
circumference of the passage(s). For example, generally the
pressure of the inlet of a passage is low while the pressure
at the member providing the material collecting end wall surface
can be extremely high. In fact, the differential in radial
pressures can be great encugh to cause deflectionjof the rotor
or shaft thereby imposing an undesirable constraint on the
tolerances available for the requisite clearance between the top
surface of the rotatable cylindrical channel wall(s) and the
stationary interior coaxial annular surface. This deflection
problem is described in detail together with a manner for
adjusting or compensating for it in U.S. Paten~ ~o. 4,227,816 by
Zehev Tadmor and Peter Hold, two of the inventors of this
Application. The rotor or shaft deflection problem and its
effect on clearances between the top surfaces of the rotatable
channel wall(s) and the stationary interior coaxial annular
surface is also described in detail in U.S. Patent No. 4,289,319
Pat~,~t
~P also by Zehev Tadmor and Peter Hold. In that Applic_~i4~, sealing
...
--6--
means comprising nested truncated conical members of thin
stiffly resilient material are provided for rotary processors.
The present invention is also addressed to the
leakage problem in rotary processors and presents to the art
improved, novel rotary processors having sealing means which
can effectively minimize or prevent leakage at high or low
pressures between substantially coaxial surfaces which move
relative to each other.
BRIEF SUMMAR~ OF THE INVENTION
The present invention presents to the art a novel low friction
seal which controls leakage of material between relatively moving
coaxial annular surfaces. The novel sealing means of this invention
are particularly adapted to control leakage of liquid between the
5 relatively narrow peripheral portion adjacent a rotatable channel
in a rotor and the stationary coaxial annular surface closing the
channel and in which the clearance between the surfaces permits
entry of only a thin film of liquid material. A seal is provided
which can effectively minimize or prevent leakage of that thin
10 film of liquid material between two surfaces at or near the clearance
and which move relative to each other. Essentially, that seal
is provided by a plurality of preferably parallel, helical or oblique
sealing channels arranged on one of the relatively moving surfaces
so that liquid moved into the clearance during relative movement
15 can penetrate the sealing channels. The effective width of the
surface carrying the helical channels and the number and the
angle of the helical channels on the surface and the dimensions
or geometry of the helical channels are selected so that relative
motion between the surface carrying the helical channels and
20 the other surface provides an effective pumping action which opposes
and resists ilow of liquid material through the clearance to thereby
control the length of penetration of liquid into the channel.
The invention and particularly the preferred embodiments
of it also provide novel seals which minimize or reduce power
25 loss at the seal between the relatively moving surfaces and can
795
effectively minimize or prevent external leakage of material
from end passages of rotary processors or internal leakage of
material from one passage of the processor to another.
According to a further broad aspect of the present
invention there is provided an apparatus for processing materials
which comprises a rotatable element having a surface carrying at
least one processing channel including opposed channel side walls;
a stationary element providing a coaxial surface spaced apart
from said surface of the rotatable element by a close clearance
and cooperatively arranged with the processing channel to form
an enclosed annular processing passage; the stationary element also
having associated with it an inlet for feeding material to the
passage, an outlet spaced apart from the inlet for discharging
material from the passage and a member located n the channel
providing a surface for restraining movement of the main body of
material in the passage so that on rotation of the rotatable
element in a direction from the inlet toward the material
restraining surface, the rotatable element and the restraining
surface providing member coact so that material in contact with
the channel side walls is dragged toward the restraining surface
and pressure increases along the length of travel of the channel
side walls from the inlet towards the restraining surface and,
dynamic sealing means for preventing leakage of the pressurized
material past the clearance including a plurality of helical
sealing channels carried by one of the surfaces, arranged so
that the liquid material can penetrate the sealing channels, the
width of the one surface, the number, angle and geometry of the
sealing channels being selected so that the outward penetration
of the clearance and the sealing channels by the pressurized
liquid is opposed by the inward force applied to the liquid in
the sealing channels as the surfaces are relatively rotated to
resist the extent of outward penetration of pressurized liquid
in any of the sealing channels.
~A~
795
g
DESCRIPTIO~ OF THE DRAWq~GS
Figure 1 is a side elevation with parts broken away
to show a rotor, channel and annular coaxial surface providing
individual basic processing units of a multi-unit rotary
processor of the type described in U.S. Patent ~o. 4,142,805.
Figure 2 is a portion of Figure 1 on an enlarged
scale showing the relationship between two surfaces providing
a dynamic seal of this invention.
Figure 3 is a diagrammatic view showing further
relationships between the surfaces providing a dynamic seal
of this invention.
~. .
Figure 4 is a diagrammatic view of the cylindrical,
peripheral portion of one of the surfaces shown in Figures 2 and
3 developed into a plane and having a plurality of helical
sealing channels.
Figure 5 is a graphic representation of the pressure
profile developed along the circumference of a typical basic
processing passage of a multi-unit rotary processor of Figure 1.
Figure 6 is a graphic representation of the computed
length of penetration of liquid into helical sealing channels
obtained for the pressure profile of Figure 5.
~.~
--10--
Figure 7,which is on the same sheet of drawings as
Figure 1, is a side elevation partly in section of an end channel
wall of a multi-passage rotary processor showing the relationship
between a stationary scraper and a rotating surface carrying a
plurality of helical sealing channels.
Figure 7a, which is on the same sheet of drawings as
Figure 1, is a top view of the end channel wall and scraper of
Figure 7.
Figure 7b, which is on the same sheet of drawings as
Figure 1, is a section of the end channel wall and scraper taken
along line 7b-7b of Figure 7a.
.~
Figure 8, which is on the same sheet of drawings as
Figure 1, is a side elevation partly in section of interior walls
for adjacent channels of a multi-unit rotary processor showing
the relationship of a stationary scraper and a rotating surface
carrying a plurality of helical sealing channels.
Figure 8a, which is on the same sheet of drawings as
Figure 1, is a top view of the channel wall and scraper of
Figure 8.
Figure 8b, which is on the same sheet of drawings as
Figure 1, is a section of the channel wall and scraper of Figure
8 taken along line 8b-8b of Figure 8a.
Figure 9 (like Figure 5) is a graphic representation
of the pressure profile developed along the circumference of a
typical basic processing passage of a multi-unit rotary
processor of Figure 1.
Figure 10 i9 a graphic representation of the computed length
of penetration of liquid into helical sealing channels obtained for
the pressure profile of Figure 9 and showing the effect on the
length of penetration of liquid by periodically scraping liquid
from surfaces providing the dynamic seal of this invention.
s
Figure 11 is a section of a channel showing an alternative
embodiment of the invention.
Figure lla is an end view of one of the surfaces providing
10 the dynamic seal of the alternative embodiment shown in Figure
11 .
Figure llb is a top view partly in section of the dynamic seal
of Figure 11 showing the relationship of a stationary scraper and
15 a rotating surface carrying a plurality of helical sealing channels.
Figure 12 is a view similar to Figure 11 showing still another
alternative embodiment of the invention.
Figure 12a is an end view of one of the surfaces providing
the dynamic seal of the alternative embodiment shown in Figure
12 .
Figure 12b is a top view of the parts shown in Figure 12 showing
25 the relationship of a scraper with a stationary surface carrying
--12--
a plurality of helical sealing channels.
Figure 13 is a fractional sectional view on an enlarged scale
showing an alternative embodiment of this invention.
Figures 14 and 14a are similar to Figures 3 and 4 respectively
showing an alternative embodiment of the invention.
Figures 15 and 15a are also similar to Figures 3 and 4 respectively
showing an alternative embodiment of the invention.
Figures 16 and 17 are each fractional sectional views on an
enlarged scale each showing an alternative embodiment of the
invention .
lS Figures 18, 19 and 20 are graphical representations of the
penetration length oE liquid into a plurality of helical sealing channels
in response to different conditions such as the number and angle
of helical sealing channels and the speed of rotation of the sealing
channel carrying surface.
il~l795
-13-
DESCRIPTIO~ OF T~E PREFERRED EMBODIMENT
The invention will be described in relation to its use
in a multi-passage rotary processor apparatus such as shown in
referenced U.S. Patent ~o. 4,142,805 and U.S. Patent ~o. 4,194,841.
It should be understood however that the dynamic seals described
are useful in other applications where a seal is needed between
surfaces rotating relative to each other.
As described in greater detail in U.S. Patent ~o.
4,142,805 and U.S. Patent ~o. 4,194,841 rotary processor apparatus
(see Figure 1) includes a rotatable element comprising a rotor
10 which is mounted for rotation in housing 12 having a
cylindrical interior surface 14, the rotor being supported on
._ ;. ..
drive shaft 16 journalled in end walls 18 of housing 12. Rotor
10 has a plurality of channels 20, each including opposed side
walls 24 in fixed relation to each other, and top surface portions
26, coaxial with, and in close, spaced relation to, stationary
interior surface 14 of housing 12 on each side of channel 20.
Rotatable channel 20 and stationary interior surface 14 of the
housing 12 form a basic processing passage into which material
is introduced for processing through an inlet opening 28.
Movement of the channel drags material in contact with the
channel walls 24 to a member providing a material collecting
end wall surface (not shown). Collected processed material is
discharged through outlet opening 29 in housing 12. Pressure
is generated by dragging of material on channel walls 24 toward
the material collecting end wall surface so that the channel
becomes a region of high pressure increasing in the direction
of rotation.
1795
As shown in Figure 1, there is a close clearance 50
between top surface(s) 26 and stationary interior surface 14
of housing 12. Ideally, clearance 50 should be about 10 mils
or less and preferably between about 3-5 mils. Generally,
clearance 50 should be substantially constant about the
circumference of the passage. However, as described in
referenced U.S. Patent No. 4,227,816 and U.SO Patent ~o.
4,289,319 mentioned before, maintenance of such a close,
constant clearance can be complicated by the differential
radial pressures generated along the circumference of the
channel. This imbalance of radial pressures may be sufficient
.. ; .
to cause shaft or rotor deflection from a high pressure region
toward a low pressure region~ Obviously, any deflection can
affect the maintenance of the desired close, constant clearance
because additional clearance must be provided to compensate
for the extent of any deflection. In U.~. Patent ~o. 4,227,816
deflection is controlled by disposing flow director units in
radially opposing relation so that the radial pressures generated
in one part of a procesqing passage or group of processing
passages are balanced by radial pressures generated in another
part. While shaft deflection control can reduce leakage, it is
oftentimes desirable to provide auxiliary or additional sealing
means to minimize leakage to the greatest extent possible. This
invention provides novel sealing means for controlling leakage
between surfaces moving relative to each other at or near
clearance 50.
11~17~5
-14a-
One form of dynamic seal of this invention is
shown in Figures 2, 3 and 4 where a plurality of oblique,
preferably parallel 7 narrow,
--15-
sealing channels 27 are formed in and/or carried by surface 26
between channel side walls 24 to provide a dynamic seal between
surface 26 and the stationary coaxial surface 14 of housing 12.
As shown, the oblique sealing channels 27 are preferably cut
into surface 26 and move relative to the smooth surface 14 of housing
5 12. The most important relationships between the various design
parameters of the dynamic seal of this invention are given in Figures
3 and 4 and reference should be made to those Figures in connection
with the following description and explanation of the dynamic
seals of this invention.
As mentioned, essentially the above described dynamic seal
is achieved by providing one of two relatively moving surfaces
near or at clearance 50 with a plurality of oblique, preferably
parallel sealing channels. In effect, each oblique sealing channel
functions as a segment of an extruder screw flight with stationary
lS coaxial surface 14 acting as a barrel for the plurality of sealing
channels (or plurality of extruder screw flight segments) . Accordingly,
the net flow q of liquid across the width ~) of surface 26 may
be determined using the same analysis which applies to a screw
extruder. Thus, the net flow is the difference between the drag
20 flow in one direction and the pressure flow in the opposite direction
or
q qD qP (Equation A)
~17~5
--16--
where: qD is the theoretical drag flow,
q i8 the theoretical pressure flow.
For illustrative purposes, the dynamic seal of Figures 2-4
is shown graphically in Figure 4 acting against a constant pressure
S and the total net flow q equals zero under equilibrium conditions
or, q =q . The drag flow q is only a function of sealing channel
geometry and the speed of operation. However, the pressure
flow, qp for a given pressure is inversely proportional to the
length of penetration of liquid in the channel, i . e. to the length
10 of channel which is filled with liquid. Under conditions, as shown
in Figures 3 and 4, equil;brium therefore will be reached as soon
as the liquid has penetrated the sealing channels to a length which
reduces the pressure flow (which tries to move the liquid into
the channel) to a value which is equal to the drag ~low. If that
5 length of penetration measured in the axial direction is less than
the length of the sealing channel 27, no liquid will leak across
the width (~) of helical sealing channel carrying surface 26 .
The dynamic seal of this invention however does not operate
under conditions of constant pressure as discussed in connection
20 with Figure 4. Instead, Figure 5 illustrates a typical pressure
profile developed along the circumference of a rotary processor
passage. After a period of relatively low pressure, the pressure
in the ases gradually, reaches a maximum value at the end of
the passage and then drops suddenly beyond an obstruction such
25 as a channel block bac~ to the original low level. The dynamic
7~5
seal of this invention therefore usually works against variable
pressure which repeats periodically during each revolution of
channel walls 24. The length of penetration of liquid into helical
sealing channels 27 for the pressure profile shown in Figure 5
has been computed by an appropriate dynamic model and is shown
5 in Figure 6 opposite the pre.~sure profile. One can see that as
soon as the pressure drops suddenly, the length of penetration
of liquid in a sealing channel i9 gradually reduced to a point
roughly opposite to the onset of pressure increase. From there
on, the length of penetration of liquid in a sealing channel increases
10 again. In general it can be said that the net flow q (equation A)
never reaches equilibrium during any one revolution. Due to
the time required to empty the liquid from a sealing channel when
the pressure is lowest or to refill it with the liquid when the pressure
is the greatest, the length of penetration of liquid in a sealing
15 channel lags or lead~ the pressure profile. For example, after
the sudden drop of pressure indicated in Figure 5, there is only
a gradual reduction in the length of penetration of liquid in a
sealing channel. However, by making the length of each sealing
channel long enough so that the length of penetration of liquid
20 never exceeds the length of the helical sealing channel (s), unwanted
leakage cannot occur across the width ( j~) of a surface carrying
a plurality of helical sealing channels.
The preferred dynamic seals of this invention are those which
are multi-flighted and have many, preferably parallel, helical
25 sealing channels - with a relatively small helix angle t~) . The
L7~5
--18--
small helix angle ~ is desirable in order to provide sealing channels
having minimum penetration lengths for a sealing channel bearing
surface having a relatively narrow width (~) . Helix angles (~
below about 20 are especially suitable for the dynamic seals of
this invention
The number of sealing channels employed to provide the dynamic
sealing means of this invention is an important consideration.
Because channel wall 24 has a relatively large outside diameter
O.D. a multi-flighted sealing channel carrying surface 26 is particularly
10 desirable because the lead L of the helical sealing channel 27
is larger than the width (~) of the sealing surface 26. Accordingly,
a plurality of preferably parallel helical sealing channels are
formed to provicle an effective dynamic seal. There is also another
reason for using a plurality of helical sealing channels. For a
5 net flow q equal to ~ero, pressure flow and drag flow have to
be equal. However, as the ratio of sealing channel depth H (Figure
3) to sealing channel width W (Figure 4) increases, i.e. with
decreasing channel width W, the pressure flow value in Equation
A decreases faster than the drag flow value. Referring to Equation
20 A above, it is apparent that under these circumstances, namely
for decreasing channel width W, the seal becomes more efficient
which means that ~ero net flow can be achieved at lower penetration
lengths of liquid in the sealing channel. Also, it is apparent
from the equation for channel width W (Figure 4 ) that an increasing
25 number of channels results in a reduction of channel widths.
Narrow sealing channel widths W are particularly desirable in
the practice of the invention because of the differential radial
pressures encountered about the circumference of the passage.
By using a plurality of parallel, helical sealing channels having
narrow widths W, the pressure variations acting on each individual
S sealing channel at any time is held to a small value and each channel
acts independently.
Referring again to Figure 6, the boundary of penetration of
liquid shown represents the area over which the sealing channels
27 are filled during a complete revolution of the helical sealing
10 channel carrying surface 26. That area also corresponds to the
area of stationary coaxial interior annular surface 14 which is
contacted with liquid. This contact of liquid with the helical
sealing channel carrying sur~ace 2B and coaxial interior annular
surface 14 creates a shearing action providing the desirable drag
15 flow which limits the extent of penetration of liquid in the sealing
channels. However, this shearing action also provides an undesirable
power loss at the seal because of dissipation of energy into heat.
In accordance with a particularly preferred embodiment of
this invention, power loss at the novel dynamic seals can be substantially
20 reduced by breaking liquid contact between the surfaces forming
the dynamic seal during a portion of each revolution of one of
the surfaces providing the dynamic seal. This embodiment is
illustrated in Figures 7, 7a, 7b, in Figures 8, 8a 8b and in Figures
9 and 10. As shown in Figures 7, 7a and 7b, a scraper 30 is positioned
25 on the inlet side of a channel block 19 (Fig. 7a) to scrape liquid
o'1'3~
--20-
off the helical sealing channel bearing surface 26 which provides
a dynamic seal designed to prevent unwanted external leakage
from the end passage of a rotary processor. The scraping clearance
between the scraper 30 and peripheral portions 26 of helical sealing
channels 27 must be close. Preferably, the scraping clearance
should be close enough to scrape off most of the liquid contacting
the helical sealing channel surface 26 and stationary interior coaxial,
annular surface 14. Accordingly, after scraping, liquid contact
between the surface 26 carrying helical sealing channels 27 and
surface 14 is broken and the sealing channels 27 remain filled
with liquid to the extent they were filled before the scraping.
Power loss by dissipation of energy at the dynamic seal is therefore
reduced after scraping and does not increase again until sufficient
liquid is pumped into the helical sealing channel (s) to reestablish
liquid contact between the coaxial annular surfaces of the dynamic
seal. Liquid material scraped off the helical sealing channel
carrying surface is discharged into the inlet at low pressures.
Figures 8, 8a and 8b illustrate a scraper 31 cooperating with
an alternate form of dynamic seal of this invention established
between the surfaces defining clearance 50. As shown, two sets
of intersecting helical sealing channels 27 and 27a are arranged
on the peripheral surface 26 between the channel walls 24 of adjacent
processing passages with the helices of the sealing channels of
each set opposed to each other. The scraper 31 is positioned on
the inlet side of the channel blocks 19 (Fig. 8a) and is maintained
in close scraping relationship with the helical sealing channel
17~5
--21-
bearing surface 26 to break liquid contact between the dynamic
seal providing surfaces and to discharge the scraped material
into the inlet.
The advantages of breaking liquid contact between surfaces
of dynamic seals of this inven~ion are further illustrated in Figures
9 and 10. Figure 9 (like Figure 5) illustrates a typical pressure
profile developed along the circumference of a rotary processor
passage. The computed length of penetration of liquid into helical
sealing channels for the pressure profile of Figure 9 but having
a scraper cooperating with the helical sealing channel carrying
sur:Eace as illustrated and described before, is shown in Figure
10. As shown there, scraping is done at the inlet or at or near
the low pressure area of the passage. The scraping breaks liquid
contact between the surfaces of the dynamic seal but leaves the
helical sealing channels filled to some level with liquid. Because
the layer providing liquid contact between the surfaces of the
dynamic seal is removed, there is reduced power loss and very
little penetration of liquid in the area extending *om the back
of the scraper 30 or 31 up to about 13 on the scale of Figure 10.
However, once the pressure starts increasing, length of liquid
penetration immediately and very closely follows the pressure
profile with maximum penetration occuring rather close to maximum
pressure. A comparison of Figure 10 with Figure 5 shows that
the area of maximum liquid penetration of Figure 10 is considerably
smaller than the maximum liquid penetration area of Figure 5.
Consequently, a scraper provides reduced power losses without
- 2 2 -
the efficiency of the dynamic seal.
In the embodiments of the invention described so far, the
dynamic seals are established between the surfaces defining clearance
50 (Figures 2 and 3) However, dynamic seals within the scope
of this invention can be established between other surfaces located
near -rather than at- clearance 50. Figures 11, lla, llb, 12, 12a
and 12b illustrate such alternative embodiments of the invention.
Figure 11 illustrates a dynamic seal in which a portion of the external
surface 32 of rotor 10 is provided with a plurality of oblique sealing
channels 35 extending along the external surface 32. The portion
10 of the external surface 32 carrying the plurality of sealing channels
35 is shown as width (~) (Fig. 11 and lla) . Surface 32 carrying
the sealing channels moves in rotation relative to stationary surface
33 spaced apart from the sealing channel carrying surface by
a fixed, close clearance 51 which can be the same, or greater
15 than, or less than clearance 50 but usually is about 10 mils or
less~ Stationary surface 33 is provided by a stationary annular
element 34 securely fixed to stationary interior surface 14 of the
housing 12. Figure lla is a view of the exterior surface 32 of
rotor 10 showing a plurality of spiral sealing channels 35 provided
20 in width (~?) which extends about the outer circumferential regions
of the exterior surface 32. While the grooves are shown in Figure
lla in curved spiral form, the grooves also may be straight and
obliquely arranged without departing from the scope of the invention.
Figure llb is a top view showing the relationship between the
25 surfaces 32 and 33 forming the dynamic seal of Figure 11 and a
--23-
scraper 36. As shown, scraper 36 is fixedly in stationary annular
member 34 and extends outwardly from surface 33 to break liquid
contact between surface 33 and surface 32. Scraper 36 extends
at least across width ~) and is positioned at or near the inlet
(not shown) of the passage.
Figure 12, 12a and 12b illustrate another alternate form of
dynamic seal established between surfaces near - rather than
at - clearance 50. In the embodiment shown, a plurality of helical
or oblique sealing channels 37 are provided on a stationary surface
38 of an annular element 39 fixed to stationary interior surface
10 14 of the housing 12. Width (~) of stationary channel carrying
surface 38 is positioned spaced apart from a portion of an external
surface 40 of rotor 10 by clearance 51. Figure 12a is a schematic
side view of annular element 39 showing the plurality of sealing
channels 37 provided in width (Z) of surface 38. Figure 12b is
15 a top view showing the relationship between the surfaces forming
the dynamic seal of Figure 12 and a scraper 41. Scraper 41 is
fixedly positioned in and firmly held by stationary annular member
39 and extends outwardly from surface 38 to break liquid contact
between surfaces 38 and 40. As shown in Figure 12a, scraper
20 41 extends at least across width ( .? ) and, as in the case of all
scrapers described before, is positioned at or near the inlet (not
shown) or in a low pressure area of the passage.
The dynamic seal illustrated in Figures 12, 12a and 12b differs
somewhat from the dynamic seals described before in that the
25 plurality of sealing channels were carried by a rotating surface.
7~5
-24--
In the dynamic seal of Figures 12, 12a and 12b, the plurality of
sealing channels are formed in a stationary surface. As already
discussed, the length of penetration of liquid into each sealing
channel carried by a rotating cylindrical surface will vary progressively
during each revolution because of the differential pressures encountered
along the circumference of the passage, as graphically illustrated
in Figures 5, 6, 9 and 10. This variation in length of penetration
of the liquid into each helical sealing chamber is not encountered
during each revolution with dynamic seals having a stationary,
helical sealing channel carrying surface. Instead, because each
sealing channel is always at a fixed position about the circumference
of the passage, each helical sealing channel always "sees" the
same head pressure during every revolution of channel walls
24 of rotor 10. Accordingly, the length of penetration of liquid
into each stationary sealing channel will differ but the maximum
5 length of penetration into any given channel will always be sub9tantially
constant so long as a constant pressure is applied to that sealing
channel during each revolution of rotor lO. Again however, so
long as the length of penetration of liquid into any of the helical
channels on the stationary surface does not exceed the length
20 of any sealing channel, unwanted leakage between the surfaces
will not occur.
Figure 13 illustrates another alternate dynamic seal of this
invention also formed between the cylindrical surfaces defining
gap 50 but which functions in the same manner as described for
25 the dynamic seal of Figures 12, 12a and 12b. As shown in Figure
C,~5
-25-
13, the helical sealing channels 42 are formed in the stationary
interior surface 14 of housing 12 which is coaxial with and spaced
apart from top surface portions 26 of rotor 10 by clearance 50.
Accordingly, the length of penetration of liquid into each helical
sealing channel 42 carried by the stationary interior surface 14
will vary. But as in the dynamic seal of Figures 12, 12a and 12b,
the maximum length of penetration of liquid into any given helical
channel 42 at a fixed pressure position along the rotating channel
wall will always be substantially constant so long as constant
pressure is applied at that fixed position. Accordingly, so long
as the length of penetration of liquid into any stationary helical
.~ealing channel 42 does not exceed the length of the channel,
leakage of liquid across the dynamic seal established between
the surfaces at clearance 50 will not occur.
In the description of the invention so far, leakage of liquid
at the clearance defined by the two coaxial surfaces is controlled
by a plurality of helical or oblique sealing channels carried by
one of the surfaces, Such features of the sealing channels as the
number, geometry, dimensions and angle are selected so that
the length of liquid penetration into each sealing channel does
not exceed the length of the sealing channel penetrated. It should
be understood however, that the prime function of the dynamic
seals of this invention is to resist the extent of penetration of
fluid in the channel to thereby control the amount of liquid leakage
at the clearance. A degree of that control can still be achieved
even though the length of penetration of leakage fluid into a channel
--26--
exceeds the length of the channel penetrated. Under such circumstances,
some leakage of the liquid will occur at the clearance but the helical
sealing channels would provide control over the amount of leakage
and the amount would be less than that which would occur without
the sealing channels.
S Figures 14, 14a, 15 and l5a illustrate embodiments of this invention
in which effective control of liquid leakage at the clearance can
be achieved even though the penetration of liquid leakage exceeds
the length of the sealing channel. The embodiment shown in Figures
14 and 14a involves a plurality of helical sealing channels 27 carried
on the peripheral surface 26 of channel wall 24. As shown there,
the width (~) of the sealing channel carrying surface does not
extend across the total width of surface 26 and the penetration
of liquid into channels 27 can exceed the length of channels 27.
However, a liquid penetration collecting channel 57 is provided
to collect the liquid penetrating channels 27 and retain the collected
liquid until it can be discharged through channels 27 at the low
pressure regions of the passage. Liquid penetration collecting
channel 57 preferably has about the same depth H (Figure 4) as
channel (s) 27.
Figures 15 and 15a illustrate a modification of the embodiment
shown in Figures 14 and 14a. Again, the width (~) of the sealing
channel carrying surface only occupies a portion of the total width
of surface 26. Instead, recessed portion 59, the width of the sealing
channel carrying surface (~) and liquid penetration collecting
25 channel 57 are arranged across the total width of surface 26 of
11~17~5
-27-
channel wall 24. The depth of liquid penetration collecting
channel should preferably be the same as depth H (Figure 4) of
channel(s) 27. The depth of recessed portion 59 can be the
same or different depth of channel(s) 27 or recessed portion 59
may be tapered downward (not shown) from surface 26.
The various alternate forms of dynamic seals are
described with reference to multi-passage rotary processors
comprising at least one but preferably a plurality of the dynamic
seals of this invention to prevent unwanted external leakage of
liquid from one or more end units of the processor or to prevent
unwanted internal leakage of liquid from one or more channels
to another. Accordinglyt the dynamic seals of this invention
are preferably integrated with multi-passage rotary processors
of the type generally described in U.S. Patent ~o. 4,142,805 to
Zehev Tadmor. Essentially, the multi-unit processors of that
Application are those in which the rotor carrying the processing
channels has cylindrical portions between the processing channels
which are in close relation to the housing of the rotor.
In a preferred form of such processors as described in
U.S. Patent ~o. 4,227,816 transfer passages between channels are
provided by removable flow director units which are held by the
processor housing and include surface portions forming part of
the surface of the annular housing and with the transfer channels
formed in these surface portions of the flow director units.
The flow director units may also carry the channel end blocks
~- which extend into the processing channels of the rotor. In a
17~5
-28-
further form, transfer passages and end blocks are circumferen-
tially and/or axially disposed to reduce bearing load to develop
opposed radial forces in the processing channels. For example,
the annular passages, blocking members and transfer passages
may be arranged to develop radial forces in at least one of the
annular passages to oppose radial forces developed in at least
one other annular passage to provide substantial axial balance
of radial forces. Axial balance of radial forces is desirable
because shaft or rotor deflection is minimized thereby providing
closer and better control over clearances between the surfaces
providing the dynamic seals of this invention.
The dynamic seals of this invention are generally
adapted to provide sealing between surfaces spaced apart from
each other by clearances up to about 10 mils. However, the
dynamic seals of this invention are particularly effective if
the surfaces providing the seals are spaced apart from each
other by clearances of about 5 mils or less. Accordingly, the
degree of shaft or rotor deflection is a factor that should be
considered in selecting the particular dynamic seal of this
invention for use in a rotary processor.
Still other advantages can be obtained by integrating
the dynamic seals of this invention with the structure of the
seal described in U.S. Patent No. 4~289,319 by Peter Hold and
ra ~e nt
Zehev Tadmor. According to that ~pp~i~ts~n the seal includes
nested truncated conical members of stiffly-resilient material
-29-
positioned between relatively rotatable coaxial surfaces with
inner edge portions of the members providing a surface adjacent
and in flow resistent relation to one coaxial surface, and outer
edge portions providing a surface adjacent and in flow resistant
relation to the other coaxial surface. Marginal portions at
either the inner or outer portions..of the members are held to
enable pressure against the members to force the outer or innqr
edges respectively into improved sealing relation to their
adjacent surfaces.
Figures 16 and 17 illustrate the integration of the
dynamic sealing means of the present invention with the seal
structure described in U.S. Patent No. 4,289,319. As shown in
Figures 16 and 17, truncated coni-cal members 44 are carried by
rotor 10 in an orientation such that surfaces 43 of member 44
slope toward channel 20, i.e. the high pressure region. The
inner edges 45 of member 44 farthest from channel 20 are held
against axial movement and in sealing relation to the rotor by
shoulder 46 and a retaining member, such as a ring 47. Retaining
member 47 acts on the member 44 farthest from the channel to
keep member 44 in nested relation against shoulder 46. The outer
free edges 48 of the members closest to channel 2Q provides a
surface 49 which is in sealing relation to interior cylindrical
surface 14 so that members 44 seal the space between surface 49
and interior surface 14 of housing 12. According to the embodiment
of the invention shown in Figure 16, surface 49 can be provided
with a plurality of helical sealing channels 52 to improve sealing
between surface 49 and surface 140 The embodiment of the invention
-30--
shown in Figure 16 is particularly preferred if deflections of the
shaft require that clearances greater than about 0 . 005 inch be
maintained between surface 49 and surface 14. Figure 17 shows
an alternative arrangement of the elements of the dynamic seal
of Figure 16. As shown in Figure 17, a plurality of helicai sealing
channels are provided on interior surface 14 to provide a dynamic
seal between helical sealing channel carrying surface 14 and surface
4g .
Additional details relating to the invention will be appreciated
by reference to Figures 18, 19 and 20. These Figures illustrate
10 computation of the maximum liquid penetration length into each
sealing channel versus RPM for several values of 7~ . The width
(V of the sealing channel bearing surface and the number and
geometry of the sealing channels as well as other operating conditions
are described in each Figure. These Figures indicate that about
5 10 or more channels of the defined geometry and having an axial
length of about . 5" can control leakage of liquid across width
(~), particularly if the value of ~ is low, e.g. below 15Q It should
be mentioned that the maximum pressure of 1000 psi is well above
that normally expected to be generated in a passage of a rotary
20 processor. The maximum pressure however was selected to determine
maximum axial penetration lengths of liquid into the sealing channels
of the indicated geometry or dimensions under extreme operational
conditions .
From the above description it should be apparent that the
25 present invention presents to the art novel sealing means for controlling
J
-31--
leakage of liquid between two relatively rotatable, coaxial closely
spaced apart surfaces. The sealing means of this inv~ntion is
particularly adaptable to rotary processors for processing liquid
and/or solid polymeric materials in a more efficient fashion providing
a low friction positive seal for controlling external or internal
5 leakage of liquid with minimal power loss at the seal. Accordingly,
this invention presents to the art new and useful apparatus providing
particularly desirable and unexpectedly improved overall performance
characteristics over apparatus known to the art at the time this
invention was made.
