 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention relates to a continuous kneading apparatus capable of
kneading a variety of material and having a small construction.
Conventionally, there have been known continuous kneading apparatus having
the following construct ion. A feed section and a kneading section are
formed such that material fed through a supply port into a cylinder
provided with a rotatable screw shaft therein is continuously kneaded
while being fed according to rotation of the screw shaft, and then
extruded. Further, there has been disclosed a continuous kneading
apparatus having a small construction, and yet capable of carrying out
sufficient kneading. Such a continuous kneading apparatus is disclosed in,
for example, Examined Japanese Patent Publication No. 2-92. In this
apparatus, fixed doughnut members mounted on a cylinder and rotatable
discs mounted on a rotatable shaft are alternately opposed to each other,
and projected portions and recessed portions extending in radial
directions are formed on opposing side faces of the rotatable discs and
fixed doughnut members. With this arrangement, the shear force is applied
to the material while the material is passing between the rotatable discs
and fixed doughnut members.
In the latter apparatus, the material is subjected to the shear force while
being fed radially outwards from center portions of the rotatable disc or
being fed radially inwards from the outer portions thereof. Accordingly,
the magnitude of the shear force acting on the material differs in a
region close to the center portion and a region away therefrom based on a
difference in the relative speed of the rotatable discs and fixed doughnut
members in a circumferential direction. Thus, the material is caused to
remain locally, and therefore this apparatus suffers the problem that a
proper shear force cannot be applied to the entire material. More
specifically, the shearing stress .tau. (kgf/cm) acting on the material
can be expressed in the following equation.
.tau.=.eta..nu./t
where
.eta. denotes viscosity (poise);
.nu. denotes shear rate (cm/s); and
t denotes thickness of a shear layer.
In the above equation, the shear rate .nu. is proportion to the relative
speed of the rotatable discs and fixed doughnut members. Since the
thickness of the shear layer is normally fixed, the shearing stress .tau.
varies in proportion to the above relative speed. Accordingly, the proper
shear force cannot be applied to the entire material.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome the foregoing problems in the
prior art and to provide a continuous kneading apparatus which has a small
construction and yet is capable of kneading (compressing and shearing)
material efficiently, and of applying a proper shear force to the entire
material by preventing the material from locally remaining in the kneading
apparatus.
Accordingly, a kneading apparatus of the invention comprises a cylinder, a
rotatable shaft disposed in the cylinder, the rotatable shaft having a
helical thread defined on an outer circumferential surface thereof so as
to feed fluid material in an extending direction thereof, a plurality of
rotatable discs each mounted on the rotatable shaft, and a plurality of
fixed members in the form of doughnut mounted on an inner wall of the
cylinder coaxially with the rotatable discs. The plurality of rotatable
discs and fixed members are arranged alternately in the extending
direction of the rotatable shaft so that the side faces of the rotatable
discs oppose the corresponding side faces of the fixed members. Projected
portions and recessed portions are formed on opposite side faces of the
rotatable discs and fixed members, the projected portions and recessed
portions extending radially and arranged alternately in a circumferential
direction on each side face. The projected portions and recessed portions
of the rotatable discs and fixed members are formed such that the distance
between the opposing rotatable discs and fixed members along the extending
direction of the rotatable shaft is increased in proportion to the
distance from a center of a rotatable shaft.
With the kneading apparatus thus constructed, a shear force produced by
relative rotation of the rotatable discs and fixed members is applied
uniformly to the entire material between the rotatable disc and fixed
members, thereby preventing the material from remaining in the apparatus.
As means to increase the distance between the opposing rotatable discs and
fixed members, the recessed portions formed on either the rotatable discs
or fixed doughnut members, or recessed portions formed on both the
rotatable discs and fixed doughnut members may be formed such that the
depth thereof is increased in proportion to the distance from a center of
the rotatable shaft.
Further, boundary lines between two adjacent projected portions and
recessed portions formed on one and the other side faces of the rotatable
discs may be formed to extend in such directions that the material fed
between one side faces of the rotatable discs and fixed members is fed
radially outwards, and then fed radially inwards between the other side
faces of the rotatable discs and next fixed members through space between
outer circumferential surfaces of the rotatable discs and the inner wall
of the cylinder.
These and other objects, features and advantages of the present invention
will become more apparent upon a reading of the following detailed
description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical sectional view showing a center portion of a kneading
apparatus embodying the invention:
FIG. 2 is a sectional view taken along the line II--II in FIG. 1;
FIGS. 3a-3b are front and rear views showing a rotatable disc;
FIG. 4 is a front view showing a fixed doughnut member;
FIG. 5 is an enlarged sectional view showing a kneading unit shown in FIG.
1:
FIG. 6 is a partial sectional view showing a kneading process;
FIG. 7 is a partial sectional view enlargedly showing the kneading process
shown in FIG. 6; and
FIG. 8 is a an enlarged partial sectional view showing recessed portions of
a modified shape.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 is a vertical sectional view showing a center portion of a kneading
apparatus embodying the invention. In this figure, indicated at 1 is a
cylinder. To the cylinder 1 is connected a hopper 4 by way of a supply
port 1c and a quantity measuring feeder 1a. A rotatable shaft 31 which is
rotated by a driving device 2 is inserted in cylinder 1. Threads are
formed on the rotatable shaft 31 almost entirely from a base end up to a
forward end thereof. A thread 3 formed on the base end portion of the
shaft 31 and another thread 59 formed on the forward end portion thereof
constitute a feeding section F and an extruding section X respectively.
Notatable discs 6, 9, and 11 are disposed at specified intervals between
the feeding section F and extruding section X. Further, another rotatable
disc 13 having a width larger than that of the discs 6, 9, and 11 is
disposed between the disc 11 and the extruding section X. The rotatable
discs 6, 9, and 11 constitutes a kneading section K1 and the rotatable
disc 13 constitutes a venting section V. Threads 10 are formed on the
shaft 31 between these rotatable discs 6, 9, 11, and 13.
Between the hollow cylinder 1 at a base portion and a hollow cylinder 30 at
a forward end are provided annular members 14, 17, and 20 corresponding to
the rotatable discs 6, 9, and 11, fixed doughnut members 16, 18, and 21
disposed between the discs 6, 9, and 11, annular member 22 having a vent
hole 12, and fixed doughnut member 28 disposed down stream of the member
22 with respect to a direction of feed of material. These members are
integrally joined between the hollow cylinders 1 and 30 in the above
described order by a tie rod 24, and constitute a joined hollow cylinder.
On outer circumferential surfaces of the hollow cylinders are disposed
heaters 5. In an upper portion of the inside of the hollow cylinder is
defined a groove 8 extending continuously in a shaft direction. An
upstream end of groove 8 is in communication with a vent hole 7 opening
outwards as shown in FIG. 2.
As shown in FIGS. 3a, 3b, and 5, a plurality of projected portions 32 are
formed on opposite side faces of the rotatable discs 6, 9, and 11. On each
of the side faces of the discs 6, 9, and 11, the projected portions 32
extend radially from its centers and equally and circumferentially spaced
apart. Between two adjacent projected portions 32 is formed a recessed
portion 43. The projected portion 32 and the recessed portion 43 are
defined by a boundary line 33. The recessed portion 43 is formed such that
the depth thereof is shallower at the center than at a radially outer
portion of the rotatable disc. Outer radial ends of the projected portions
32 project radially outwardly of the outer circumferential ends of the
rotatable discs 6, 9, and 11, and extend spirally in the shaft direction,
thereby forming threads on the outer circumferential surfaces of the discs
6, 9, and 11. On inner circumferential surfaces of the annular members 14,
17, and 20 opposing the outer circumferential surfaces of the rotatable
discs 6, 9, and 11 are formed grooves 23 extending in the shaft direction.
As shown in FIGS. 4 and 5, three recessed portions 39 are formed on each of
side faces of the fixed doughnut members 16, 18, and 21 opposing the
respective rotatable discs 6, 9, and 11 with the recessed portions equally
and circumferentially spaced apart. Between two adjacent recessed portions
39 is formed a projected portion 29. The recessed portion 39 is formed
such that the depth thereof is shallower at the center than at an radially
outer portion of the fixed doughnut member. The projected portions 32
formed on the respective rotatable discs extend radially outwards with
slight tilting. Specifically, the projected portions 32 formed on the side
face of the rotatable discs facing an inlet side of the kneading apparatus
extend in such a direction as to tilt relative to the radial directions
thereof more in a direction of rotation at the radially outer portions. On
the other hand, the projected portions 32 formed on the side face of the
rotatable discs facing an outlet side of the kneading apparatus extend in
such a direction as to tilt relative to the radial directions thereof more
in a direction reverse of the direction of rotation at the radially outer
portions. With these rotatable discs thus formed, material fed into the
kneading apparatus is fed through space between the thread 3 and hollow
cylinder 1 and along the inlet facing side face of the rotatable disc 6 in
a radially outward direction. After passing over the outer circumferential
surface of the rotatable disc 6, the material is further fed through space
between the outlet facing side face of the rotatable disc 6 and the fixed
doughnut member 14 in a radially inward direction. The material is further
fed between the rotatable discs 9, 11 and the fixed doughnut members 14,
17 in the similar manner. Opposite side faces of the rotatable disc 13 and
fixed doughnut member 28 are formed similarly to those of other rotatable
discs and fixed doughnut members.
The rotatable discs and fixed doughnut members may be arranged in such a
manner that an area defined therebetween, i.e. a flow passage area of
material, becomes smaller at a downstream portion of the kneading
apparatus. To this end, the rotatable disc and fixed doughnut members may
be formed with an increased number of the projected portions or shallower
recessed portions at the downstream portion of the kneading apparatus.
Further, it may be appropriate to set an optimum number of the rotational
disc and fixed doughnut members to be arranged or to determine the optimum
number and shape of projected portions and recessed portions formed
thereon according to material to be kneaded and kneading conditions.
Further, a plurality of grooves 23 extending in the shaft direction are
formed on inner circumferential surfaces of the annular members 14, 17,
and 20. The annular members and rotatable discs are arranged such that the
inner circumferential surfaces of the annular members oppose the outer
circumferential surfaces of the rotatable discs. Accordingly, the
projected portions and recessed portions formed on the circumferential
surfaces of the annular members and rotatable discs are alternately
opposed to each other similarly to the arrangement of the projected
portions and recessed portions formed on the side faces of the rotatable
discs and fixed doughnut members. The outer circumferential surface of the
rotatable disc 13 and the inner circumferential surface of the annular
member 22 are formed similarly to those of other rotatable discs and
annular members. The cross-sections of the recessed portions 39 and 43 are
variously changeable in shape although FIG. 7 illustrates those formed
with a fixed radius of curvature R. For instance, as shown in FIG. 8, it
may be appropriate to form recessed portions 391 and 431 whose
cross-sections are formed with a combination of a larger radius of
curvature R and a smaller radius of curvature r. Such recessed portions
may be formed in such a manner that rear walls thereof, with respect to a
material feeding direction, have the smaller radius of curvature r. The
recessed portions thus formed will serve to strongly compress the material
being fed.
Next, operations of this kneading apparatus will be described. Firstly, the
rotatable shaft 31 is rotated by the driving device 2 and the quantity
measuring feeder 1a is actuated to feed material form the hopper 4 into
the hollow cylinder 1 by a specified amount. Since the inside of the
hollow cylinder i is heated by the heater 5, the material fed into it
dries as they are fed towards the rotatable disc 6. Gases produced during
this time are discharged through the groove 8 and vent hole 7. The
material reaching the rotatable disc 6 is fed through the space between
the outer circumferential surface of the disc 6 and inner circumferential
surface of the annular member 14, and then fed radially inwards by
relative movement of the opposing side faces of the disc and fixed
doughnut member 16. The material is then fed to a more downstream side by
the thread 10 through the space between the inner circumferential surface
of the fixed doughnut member 16 and an outer circumferential surface of
the thread 10, and further fed radially outwards through the space between
opposing side faces of the rotatable disc 9 and fixed doughnut member 16.
Thereafter, the material is subjected to the compressive action and
shearing action while being fed between the rotatable discs and fixed
doughnut members in the same manner.
As shown in FIGS. 6 and 7, the passage for the material is formed such that
the width thereof, i.e. the distance between the rotatable disc and fixed
doughnut member, is wide in regions where the recessed portions 43 are
opposing to the recessed portions 39, is slightly narrow in regions where
the recessed portions 43 are opposing to the projected portions 29, and is
very narrow in regions where the projected portions 29 are opposing to the
projected portions 32. Accordingly, when the rotatable disc is rotated in
an arrow direction B, rear walls 390 and 430 of the respective recessed
portions 39 and 43 come closer to each other, reducing the distance
defined between them. As a result, the material held between the rear
walls 390 and 430 is subjected to the strong compressive action. The
material subjected to the compressive action is pushed out to the space
between the recessed portion 43 and projected portion 29, and pushed into
the space between the projected portions 32 and 29, thereby becoming
subjected to strong shearing action. These actions are carried out in a
similar manner along a circumferential direction of the rotatable discs
and fixed doughnut member. In other words, a compression process P and a
shearing process S are alternately repeated in the circumferential
direction. The magnitude of the compressive and shearing actions is in
proportion to a relative speed of the rotatable discs and fixed doughnut
members in the circumferential direction, and this relative speed is in
proportion to the distance from a center rotation. In view of this,
provided that the depth of the recessed portions is fixed, i.e. the volume
of the recessed portions is fixed, the following can be said. The closer
to the center of rotation, the smaller the magnitude of the compressive
and shearing actions. Thus, the material is more likely to remain in
regions closer to the center of rotation. However, in the above
construction, the depth of the projected portions formed on the rotatable
discs and fixed doughnut members is increased in proportion to the
distance from the center of rotation. Accordingly, the magnitude of the
compressive and shearing actions is maintained substantially fixed over a
range between the center regions and outer circumferential regions of the
rotatable discs. Thus, the kneading apparatus of the invention is free
from the problem that the material remains in the regions close to the
center of rotation where the relative speed of the rotatable discs and
fixed doughnut members is slow.
Concerning the radial directions of the rotatable discs and fixed doughnut
members, the projected portions 32 of the rotatable discs extend
slantingly with respect to the radial directions thereof as described
above. The projected portions 32 on one side faces of the rotatable discs
are formed so as to gradually oppose the projected portions 29 as they
extend radially outwards from the centers of the rotatable discs.
Accordingly, when the force working in the circumferential direction is
applied to the material, the force working in the radial direction acts on
the material at the same time, and thereby the material is fed radially
outwards. The projected portions 32 on the other side faces of the
rotatable discs are slanting with respect to the radial directions thereof
in a direction reverse of the slating direction of the former projected
portions 32, and thereby the material is fed radially inwards.
As described above, the projected portions and recessed portions formed on
the rotatable discs and fixed doughnut members are formed in such a manner
that the distance of the space defined between the rotatable discs and
fixed doughnut members opposing to each other along the extending
direction of the screw shaft is increased in proportion to the radial
distance from the center of the screw shaft. Accordingly, the shear force
acting on the material is not to vary in the regions close to the screw
shaft and away therefrom depending upon the difference in the relative
speed in the circumferential direction between the rotatable discs and
fixed doughnut members. Therefore, the compressive and shearing actions
are carried out uniformly entirely between the rotatable discs and fixed
doughnut members, thereby preventing the material from remaining locally
in the kneading apparatus.
Although water or the like contained in the material is gasified during the
kneading process, the produced gas is discharged through the vent hole 12
while passing through the outer circumferential portions of the rotatable
disc 13. The material having the gas present therein completely extracted
while passing through the disc 13 is fed through the extruding section X,
and consequently extruded from a leading end portion of the extruding
section X. In the foregoing embodiment, both recessed portions on the
rotatable discs and fixed doughnut members are formed so that the depth
thereof is increased in proportion to the distance from the center of
rotation. However, it may be appropriate to regulate the depth of the
recessed portions on only either the rotatable discs or fixed doughnut
members in such a manner that the space defined between the recessed
portions of the opposing rotatable disc and fixed doughnut member is
increased in proportion to the distance from the center of rotation.
As described above, in accordance with the invention, projected portions
and recessed portions are formed on opposing side faces of rotatable discs
and fixed doughnut members, thereby enabling efficient kneading of
material in a small construction. Further, in the above construction, the
recessed portions are formed in such a manner that the depth thereof is
increased in proportion to a distance from a center of rotation.
Accordingly, compressive and shearing actions can be given to the material
uniformly entirely, and therefore it can be reliably prevented that the
material locally remain in the kneading apparatus.
Although the present invention has been fully described by way of example
with reference to the accompanying drawings, it is to be understood that
various changes and modifications will be apparent to those skilled in the
art. Therefore, unless otherwise such changes and modifications depart
from the scope of the present invention, they should be construed as being
included therein.
* * * * *
|
|
 |
|
 |
Description |
|
