U.S. patent application number 13/437218 was filed with the patent office on 2012-12-13 for apparatus and method for manufacturing raw rubber strip.
Invention is credited to Yoshinobu NAKAMURA.
Application Number | 20120313287 13/437218 |
Document ID | / |
Family ID | 46261929 |
Filed Date | 2012-12-13 |
United States Patent
Application |
20120313287 |
Kind Code |
A1 |
NAKAMURA; Yoshinobu |
December 13, 2012 |
APPARATUS AND METHOD FOR MANUFACTURING RAW RUBBER STRIP
Abstract
An apparatus for intermittently manufacturing a raw rubber strip
comprises a screw extruder, an extruder head having a preforming
nozzle, a gear pump therebetween, a pair of calender rolls, a
roll-gap changer for switching between a close state and an open
state of calender rolls, and a controller for controlling the gear
pump, the calender rolls and the roll-gap changer to let the
calender rolls in the open state prior to the stopping of the
rotation of the calender rolls.
Inventors: |
NAKAMURA; Yoshinobu;
(Kobe-shi, JP) |
Family ID: |
46261929 |
Appl. No.: |
13/437218 |
Filed: |
April 2, 2012 |
Current U.S.
Class: |
264/175 ;
425/155; 425/325 |
Current CPC
Class: |
B29C 48/92 20190201;
B29C 48/08 20190201; B29C 43/245 20130101; B29C 2948/92961
20190201; B29C 48/07 20190201; B29L 2030/00 20130101; B29K 2021/00
20130101; B29C 48/37 20190201; B29C 48/2552 20190201; B29C 48/2694
20190201; B29C 48/397 20190201; B29D 30/30 20130101; B29C 48/355
20190201; B29C 2948/92923 20190201; B29C 2948/92876 20190201; B29C
48/387 20190201; B29C 48/2528 20190201; B29C 2948/92647 20190201;
B29C 43/24 20130101; B29C 48/0011 20190201; B29C 43/222 20130101;
B29C 2948/9259 20190201 |
Class at
Publication: |
264/175 ;
425/325; 425/155 |
International
Class: |
B29C 69/00 20060101
B29C069/00; B29C 47/08 20060101 B29C047/08; B29C 47/92 20060101
B29C047/92 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2011 |
JP |
2011-127573 |
Claims
1. An apparatus for intermittently manufacturing a raw rubber
strip, comprising a rubber extruder unit, a calender unit disposed
in front of the rubber extruder unit, and a controller, the rubber
extruder unit comprising: a screw extruder; an extruder head
disposed at a front end of the rubber extruder unit; and a gear
pump therebetween, the screw extruder comprising: an extruder screw
for kneading rubber materials supplied and pushing the kneaded
rubber materials towards its outlet at the front end thereof, the
extruder head comprising: a nozzle block having a preforming nozzle
for preforming the rubber extruded therefrom, the gear pump having
gears and positioned between the preforming nozzle and said outlet
of the screw extruder so that, corresponding to on/off of the
rotation of the gears, the rubber received from the outlet of the
screw extruder is intermittently extruded from the preforming
nozzle, the calender unit comprising: a calender disposed in front
of the extruder head; and a roll-gap changer, the calender
comprising: a pair of calender rolls at least one of which is
driven to rotate and between which the preformed rubber extruded
from the preforming nozzle is roll shaped into the row rubber strip
having a finished thickness, the roll-gap changer switches between
a close state in which the calender rolls come close to each other
in order to make the roll shaping and an open state in which the
calender rolls get away from each other not to make the roll
shaping, the controller controls the rotation of the gears of the
gear pump, the rotation of the calender rolls of the calender, and
the switching of the roll-gap changer to let the calender rolls in
the open state prior to the stopping of the rotation of the
calender rolls.
2. The apparatus according to claim 1, wherein the controller lets
the calender rolls in the close state after the starting of the
rotation of the calender roll.
3. The apparatus according to claim 1 or 2, wherein the calender
rolls has: a constant rotating speed state; an accelerating state
from the starting of the rotation of the calender rolls to a
constant rotating speed state; and a slowing-down state from the
constant rotating speed state to the stopping of the rotation, the
gear pump has: a constant rotating speed state; an accelerating
state from the starting of the rotation of the gears to the a
constant rotating speed state; and a slowing-down state from the
constant rotating speed state to the stopping of the rotation, and
the controller lets the time period t2c of the slowing-down state
of the calender rolls shorter than the time period t2g of the
slowing-down state of the gear pump.
4. The apparatus according to claim 3, wherein by the controller,
the starting of the rotation of the calender rolls is delayed from
the starting of the rotation of the gear pump, and the starting of
the slowing-down state of the calender rolls is delayed from the
starting of the slowing-down state of the gear pump.
5. A method for intermittently manufacturing a raw rubber strip by
the use of the apparatus according to claim 1, in which the
roll-gap changer is operated to let the calender rolls in the open
state prior to the stopping of the rotation of the calender
rolls.
6. The method according to claim 5, wherein the roll-gap changer is
operated to let the calender rolls in the close state with a time
delay from the starting of rotation of the calender rolls.
7. The method according to claim 5 or 6, wherein the calender rolls
have: a constant rotating speed state; an accelerating state from
the starting of the rotation of the calender rolls to the constant
rotating speed state; and a slowing-down state from the constant
rotating speed state to the stopping of the rotation, the gear pump
has: a constant rotating speed state; an accelerating state from
the starting of the rotation of the gears to the constant rotating
speed state; and a slowing-down state from the constant rotating
speed state to the stopping of the rotation, and the time period
t2c of the slowing-down state of the calender rolls is controlled
to be shorter than the time period t2g of the slowing-down state of
the gear pump.
8. The method according to claim 7, wherein the starting of the
rotation of the calender rolls is delayed from the starting of the
rotation of the gear pump, and the starting of the slowing-down
state of the calender rolls is delayed from the starting of the
slowing-down state of the gear pump.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus and a method
for intermittently manufacturing a raw rubber strip with a steady
accurate cross sectional shape.
[0002] In recent years, it is highly appreciated by the tire
manufacturers to make a rubber tire component for example tread
rubber, sidewall rubber, bead clinch rubber and the like by
spirally winding a raw rubber strip or tape around a building drum
a number of times.
[0003] In such a manufacturing method, usually the raw rubber tape
is formed by a rubber extruder. The extruded raw rubber tape is
supplied to the building drum through a festoon type tape
accumulator or the extruded raw rubber tape is once wound around a
tape reel and supplied to the building drum from the reel. The
reason for this is that the consumption of the tape is intermittent
in order to remove the wound rubber component from the building
drum whereas the production (extruding) of the tape is continuous
to make the cross sectional shape and thickness of the tape
constant and stable and to prevent breakage of the tape. In either
case, therefore, the installation space of the apparatus for
manufacturing a rubber tire component is inevitably increased due
to the accumulator or reel.
SUMMARY OF THE INVENTION
[0004] It is therefore, an object of the present invention to
provide an apparatus and a method for manufacturing a raw rubber
strip which can intermittently manufacture a raw rubber strip with
a steady accurate cross sectional shape and accordingly can remove
the need of the accumulator or reel.
[0005] According to the present invention, an apparatus for
intermittently manufacturing a raw rubber strip, comprises a rubber
extruder unit, a calender unit disposed in front of the rubber
extruder unit and a controller, wherein
[0006] the rubber extruder unit comprises a screw extruder, an
extruder head disposed at a front end of the rubber extruder unit,
and a gear pump therebetween,
[0007] the screw extruder comprises an extruder screw for kneading
rubber materials supplied and pushing the kneaded rubber materials
towards its outlet at the front end thereof,
[0008] the extruder head comprises a nozzle block having a
preforming nozzle for preforming the rubber extruded therefrom,
[0009] the gear pump has gears and is positioned between the
preforming nozzle and said outlet of the screw extruder so that,
corresponding to on/off of the rotation of the gears, the rubber
received from the outlet of the screw extruder is intermittently
extruded from the preforming nozzle,
[0010] the calender unit comprises a calender disposed in front of
the extruder head, and a roll-gap changer,
[0011] the calender comprises a pair of calender rolls at least one
of which is driven to rotate and between which the preformed rubber
extruded from the preforming nozzle is roll shaped into the row
rubber strip having a finished thickness,
[0012] the roll-gap changer switches between a close state in which
the calender rolls come close to each other in order to make the
roll shaping and an open state in which the calender rolls get away
from each other not to make the roll shaping,
[0013] the controller controls the rotation of the gears of the
gear pump, the rotation of the calender rolls of the calender, and
the switching of the roll-gap changer to let the calender rolls in
the open state prior to the stopping of the rotation of the
calender rolls.
[0014] The apparatus according the present invention may be further
provided with the following optional features:
[0015] the controller lets the upper and lower calender rolls in
the close state after the starting of the rotation of the calender
roll;
[0016] the controller lets the time period t2c of a slowing-down
state of the calender rolls shorter than the time period t2g of a
slowing-down state of the gear pump; and
[0017] by the controller, the starting of the rotation of the
calender rolls is delayed from the starting of the rotation of the
gear pump, and the starting of the slowing-down state of the
calender rolls is delayed from the starting of the slowing-down
state of the gear pump.
[0018] According to the present invention, a method for
intermittently manufacturing a raw rubber strip includes the use of
the above-mentioned apparatus.
[0019] Therefore, in the apparatus and method according to the
present invention, in the state when the calender rolls' rotation
is off, the preformed rubber existing between the calender rolls is
released from the compression by the calender rolls to prevent
creep and a resultant decrease in the rubber thickness. Thus, the
breakage of the rubber strip at the time of halting can be avoided,
and the rubber strip can be manufactured intermittently with a
steady accurate cross sectional shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic cross-sectional view of an apparatus
for manufacturing a raw rubber strip according to the present
invention.
[0021] FIG. 2 is a diagram for explaining an apparatus for
manufacturing a raw rubber tire component according to the present
invention.
[0022] FIG. 3 is a schematic cross-sectional view of a pneumatic
tire in which the raw rubber strip is wound as its rubber tire
component.
[0023] FIG. 4(a) is a cross sectional view of a raw rubber strip
taken along line A-A in FIG. 1.
[0024] FIG. 4(b) is a cross sectional view of the raw rubber strip
taken in the direction of arrows B-B in FIG. 1
[0025] FIG. 5(a) is a graph showing rotational speed of the gears
of the gear pump.
[0026] FIG. 5(b) is a graph showing rotational speed of the
calender rolls.
[0027] FIG. 5(c) is a graph showing the open/close state of the
calender rolls.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Embodiments of the present invention will now be described
in detail in conjunction with accompanying drawings.
[0029] In the drawings, an apparatus 1 for manufacturing a raw
rubber strip according to the present invention is to
intermittently manufacture a raw rubber strip GS.
[0030] In this embodiment, the apparatus 1 for manufacturing a raw
rubber strip constitutes a part of an apparatus for manufacturing
rubber tire components (t) for a pneumatic tire (T) which as shown
in FIG. 2 comprises: a rotatable building drum (h) around which the
raw rubber strip GS is wound, and an applicator (f) for applying
the raw rubber strip GS to the rotating building drum (h), the
applicator (f) comprising a conveyer (e) for conveying the raw
rubber strip GS from the apparatus 1 to the building drum (h).
Thus, the raw rubber strip GS is wound spirally around the building
drum (h) to form a rubber tire component (t).
[0031] The pneumatic tire (T) is, as shown in FIG. 3, made up of
rubber tire components (t), e.g. inner liner rubber Ga, sidewall
rubber Gb, chafer rubber Gc, breaker cushion Gd, tread rubber Ge
and the like in addition to rubberized cord layers, e.g. a carcass
A1, a breaker A2 and the like.
[0032] The apparatus 1 is used to manufacture a plural kinds of
rubber strips (generically the "rubber strip GS") having different
compositions to form the inner liner rubber Ga, sidewall rubber Gb,
chafer rubber Gc and the like. Such rubber strips GS are
sequentially wound around the building drum (h) in its cylindrical
state and form a cylindrical raw tire to be subjected to shaping
into a toroidal shape.
[0033] During removing the raw tire (namely, the wound rubber tire
components) from the building drum, the apparatus 1 needs to stop
because the accumulator, reel and the like are not provided. Thus,
the apparatus 1 needs to manufacture the rubber strip
intermittently.
[0034] As shown in FIG. 1, the apparatus 1 for manufacturing a
rubber strip comprises:
[0035] a rubber extruder unit 2 for preforming and intermittently
extruding rubber G2;
[0036] a calender unit 3 disposed on the extruding side of the
rubber extruder unit 2 and rolling the preformed extruded rubber G2
into the rubber strip GS having the finished thickness; and
[0037] a controller 4 for controlling the rubber extruder unit 2
and the calender unit 3 such that the apparatus 1 outputs the
rubber strip GS intermittently synchronously with the cycle of need
in the formation process of the rubber tire component (t).
[0038] The rubber extruder unit 2 comprises:
[0039] an extruder 5 which kneads the supplied rubber materials G
and pushes or conveys the rubber materials G towards its outlet H
at the front end thereof;
[0040] a gear pump 6 which is disposed on the front side of the
extruder 5, and receives the kneaded rubber from the outlet H, and
extrudes the rubber from its outlet; and
[0041] an extruder head 7 which preforms the rubber G1 extruded
from the gear pump 6.
[0042] The extruder 5 has a conventional structure in which an
extruder screw 5b is disposed in a bore of a main body 5a having an
inlet 5c for the rubber materials G. By turning on an electric
motor (not shown) for rotating the extruder screw 5b, the supplied
rubber materials G are kneaded and pushed or conveyed forward by
the rotating extruder screw 5b, and extruded from the outlet H
formed at the front end of the extruder main body 5a.
[0043] The gear pump 6 in this embodiment is an external gear pump
having a conventional structure in which two external spur gears 6b
are disposed in a casing 6a. By turning on an electric motor M1 for
rotating the gears 6b, the kneaded rubber G1 received from the
outlet H is extruded toward the extruder head 7 from its outlet
formed at the front end of the casing 6a.
[0044] The extruder head 7 comprises:
[0045] a block-like head main portion 7a having a through hole and
interchangeably attached to the gear pump 6 on the front side
thereof; and
[0046] a nozzle block 7b interchangeably attached to the head main
portion 7a and having a through hole and a preforming nozzle Y
opened at the front end thereof.
The through hole of the head main portion 7a and the through hole
of the nozzle block 7b constitute one through hole of which cross
sectional shape gradually changes from a circle to a rectangle and
finally opened at the front end of the nozzle block as the
preforming nozzle Y. The opening shape of the preforming nozzle Y
is a relatively-small horizontally-long rectangle as shown in FIG.
1 and FIG. 4(a). Thus, the preformed rubber G2 has a rectangular
cross sectional shape which is substantially same as the opening
shape of the preforming nozzle Y. Of course, it is also possible to
preform the kneaded rubber G1 to have a cross-sectional shape
different from a rectangle. By the extruder head 7, the kneaded
rubber G1 is preformed and extruded as the preformed rubber G2.
[0047] It is not essential but preferable that the preformed rubber
G2 has a thickness t1 of not less than 0.4 mm and not more than 6
mm and a width w1 of not less than 4 mm and not more than 40 mm. If
the sizes are too small, it becomes difficult to maintain the
shaping accuracy. If the sizes are too large, it becomes difficult
to realize the desirable cross-sectional shape of the rubber
component by winding the rubber strip.
[0048] By employing the gear pump 6, the output power of the
extruder 5 can be reduced and that of the rubber extruder unit 2 as
whole is also reduced. Thus, the downsizing of the rubber extruder
unit 2 is possible.
[0049] The calender unit 3 comprises a calender 10 and a roll-gap
changer 9 as shown in FIG. 1.
[0050] The calender 10 comprises:
[0051] a pair of upper and lower calender rolls 8a and 8b
(generically the "calender roll 8A");
[0052] a main frame 8c disposed at the front end of the extruder
head 7 and supporting the calender rolls 8A therein rotatably and
movably up and down while keeping the rotation axes of the calender
rolls 8A in substantially parallel with each other; and
[0053] an electric motor M2 for rotating the calender rolls 8A. The
calender 10 shapes the preformed rubber G2 into the rubber strip GS
during passing through between the upper and lower calender rolls
8a and 8b.
[0054] The roll-gap changer 9 is to switch between a close state
and open state of the upper and lower calender rolls 8a and 8b. The
close state is such that the upper and lower calender rolls 8a and
8b come close to each other in order to make a roll shaping. The
open state is such that the upper and lower calender rolls 8 and 8b
get away from each other not to make or stop the roll shaping.
[0055] The roll-gap changer 9 in this embodiment comprises:
[0056] a liner actuator such as hydraulic cylinder and air cylinder
having a rod 9a and fixed to the main frame 8c; and
[0057] a bearing unit 8d attached to the end of the rod 9a of the
liner actuator and rotatably supporting the upper calender roll
8a.
The actuator is operated with fluid pressure controlled by the use
of at least one regulator, e.g. solenoid valve, voltage-to-pressure
(E/P) transducer and the like. By the liner motion of the rod 9a,
the upper calender roll 8a is moved up and down and switches
between the close state and the open state.
[0058] It is not essential but desirable that the rubber strip GS
has a thickness t2 of not less than 0.3 mm and not more than 5 mm
and a width w2 of not less than 5 mm and not more than 50 mm. If
the sizes are too small, there is a possibility that the rubber
strip GS is broken during winding around the building drum. If the
sizes are too large, it becomes difficult to realize the desirable
cross-sectional shape of the rubber component by winding the rubber
strip.
[0059] If the calender rolls 8A are stopped in the close state of
the calender rolls between which the rubber strip is compressed,
creep is caused and the rubber thickness is gradually decreased. As
a result, the rubber is very liable to break when the apparatus
restarts. Further, it is necessary to control the extruder and
calender so that the rubber strip is not subjected to a large
tensile stress in order to prevent the breakage of the rubber
strip.
Therefore, to solve such problems, the controller 4 controls the
on/off of the operation of the gear pump 6, the on/off of the
operation of the calender rolls 8A and the close/open state of the
roll-gap changer 9. For example, a programmable sequencer, a
microcomputer, a personal computer or the like can be used as the
controller 4.
[0060] The functions of the controller 4 are described hereinafter
in conjunction with a method for manufacturing a rubber strip which
uses the apparatus 1.
[0061] In the stopped state or halting state of the apparatus 1,
the rubber extruder unit 2 and calender unit 3 are also stopped,
and the upper and lower calender rolls 8a and 8b are in the open
state.
[0062] In the open state, it is preferable that the rubber strip GS
existing between the calender rolls 8A is supported between the
calender rolls 8A with a very small roll pressure which can not
reduce the thickness of the rubber strip GS but can transfer the
rotational force of the calender rolls to the rubber strip GS
because by rotating the calender rolls 8A, it is possible to move
the rubber strip GS forward immediately. In this application, the
"open state" means such a very small roll pressure state.
For that purpose, the roll pressure between the calender rolls 8A
in the open state is preferably set in a range of 0.04 to 0.06 MPa.
In order to achieve such a roll pressure value, the distance to
between the upper and lower calender rolls 8a and 8b in the open
state is controlled to be less than the thickness t1 of the
preformed rubber G2 and preferably not less than 150% of the
distance tB between the upper and lower calender rolls 8a and 8b in
the close state. Accordingly, in the stopped state, a part of the
rubber strip GS sandwiched between the calender rolls 8A is
prevented from decreasing in the thickness. Thus, even if the
calender is stopped for a long time, the necessary thickness can be
maintained, and the breakage of the rubber strip at the time of the
restart can be avoided. On the other hand, the roll pressure
between the calender rolls 8A in the close state is preferably set
in a range of 0.7 to 0.9 MPa.
[0063] To start the apparatus 1 from such stopped state, the
controller 4 enables the gear pump 6, the calender 10, the roll-gap
changer 9 and the extruder 5 and controls these devices as
explained later to produce the rubber strip GS.
[0064] FIGS. 5(a), 5(b) and 5(c) shows operating states of the
respective devices (gear pump 6, calender rolls 8A) as a function
of the time elapsed from the start of the rotation of the gear pump
6. Here, the axis of ordinate denotes the change in the operating
state, but the coordinate does not necessarily mean the amount of
change.
[0065] As shown in FIG. 5(a), the gear pump 6 has:
a constant rotating speed state P2 (namely, a steady state) where
the rotating speed is constant; an accelerating state p1 from the
starting of the rotation of the gears 6b to the steady state p2;
and a slowing-down state p3 from the steady state p2 to the
stopping of the rotation.
[0066] As show in FIG. 5(b), the calender rolls 8A have: a constant
rotating speed state r2 (namely, a steady state) where the rotating
speed is constant;
an accelerating state r1 from the starting of the rotation of the
calender rolls 8A to the steady state r2; and a slowing-down state
r3 from the steady state r2 to the stopping of the rotation.
[0067] In contrast, the calender rolls 8A has only two states as
show in FIG. 5(c), which are the above-mentioned close state and
open state.
[0068] As show in FIGS. 5(a) and 5(b), the gear pump accelerating
state pl is started before the starting of the calender
accelerating state r1 by the controller.
In other words, the calender accelerating state r1 starts after the
starting of the gear pump accelerating state p1 As a result, the
rubber G2, which exists between the nozzle block 7b and calender
rolls 8A and is not yet successively extruded, is not subjected to
a tensile force due to the rotation of the calender rolls 8A.
Therefore, the decrease in the thickness is prevented, and the
breakage of the rubber G2 can be prevented. Preferably, the time
difference K1 between the starting of the gear pump accelerating
state p1 and the starting of the calender accelerating state r1 is
set in a range of from 0.01 to 0.1 sec. If the time difference K1
is large, there is a possibility that the rubber G2 can not be sent
forward in good order.
[0069] In the case of the rubber strip GS made of a
natural-rubber-based compound for example used to form a sidewall
rubber Gb of a pneumatic tire, there is a tendency that shrink
becomes relatively large. Therefore, it is preferable that the time
period tic of the accelerating state of the calender rolls 8A is
set to be more than the time period t1g of the accelerating state
of the gear pump 6 by controlling the rotating speed of the
electric motor(s) by the controller.
Preferably, the time period t1c of the accelerating state is set in
a range of from 1.2 to 2.5 times the time period t1g of the
accelerating state. This decreases the tensile stress applied to
the rubber G2 existing between the nozzle block 7b and the calender
rolls 8A at the time of startup, and thereby the prevention of the
breakage of the rubber G2 is further assured. Incidentally, the
time period t1c of the accelerating state is determined
experimentally not to cause substantial tension and looseness on
the rubber G2 between the nozzle block 7b and the calender rolls
8A, and such data is stored in the controller.
[0070] In the case of the rubber strip GS made of a
synthetic-rubber-based compound for example used to form a tread
rubber G of a pneumatic tire, in order to suppress the increase in
the volume of the rubber when freed from the pressure of the
extruder, it is desirable that the time period t1c of the
accelerating state of the calender rolls 8A is set to be less than
1.0 times the time period t1g of the accelerating state of the gear
pump 6 by controlling the rotating speed of the electric motor(s)
by the controller.
Preferably, the time period t1c of the accelerating state is more
than 0.8 times the time period t1g.
[0071] As show in FIGS. 5(b) and 5(c), it is preferred that the
controller 4 lets the calender rolls 8A in the close state when the
calender rolls are within the accelerating state r1. In other
words, the calender rolls 8A are switched to the close state after
the starting of the accelerating state r1 of the calender rolls
8A.
As a result, when the calender rolls 8A become in the close state,
the part of the rubber strip GS sandwiched between the calender
rolls 8A in the stopped state or halting state of the calender 10
has been moved forward. Accordingly, the sandwiched part can not be
further compressed by the closing calender rolls 8A, and thereby
the breakage of the rubber strip GS is prevented. If the time
difference K2 between the starting of the rotation of the calender
rolls 8A and the switching to the close state is too long, however,
the thickness of the rubber strip GS tends to increase over the
desired thickness. For this reason, the time difference K2 between
the starting of the rotation of the calender rolls 8A and the
switching to the close state is preferably set in a range of from
0.01 to 0.1 sec.
[0072] To stop the apparatus, the starting of the slowing-down
state r3 of the calender rolls 8A is delayed from the starting of
the slowing-down state p3 of the gear pump 6 as show in FIGS. 5(a)
and 5(b).
[0073] This is because, for a certain period of time immediately
after the starting of the slowing-down state p3 of the gear pump 6,
the rubber is still extruded from the nozzle block 7b at the same
rate as in the constant rotating speed state due to the elasticity
of the rubber G2. Therefor, if the starting of the slowing-down
state r3 of the calender rolls 8A occurs at the same time as the
starting of the slowing-down state p3 of the gear pump 6, then it
is difficult to smoothly convey the rubber G2 onwards from the
calender rolls 8A and there is a possibility that the thickness of
the rubber strip GS increases over the targeted thickness.
[0074] Preferably, the time delay of the starting of the
slowing-down state r3 of the calender rolls 8A from the starting of
the slowing-down state p3 of the gear pump 6 is set to be
substantially equal to the sum of
the time when the extruding rate of the rubber begins to decrease
measured from the starting of the slowing-down state p3 of the gear
pump 6 and the time required for the extruded rubber to reach to
the calender rolls 8A. Thereby, the feeding of the rubber strip GS
becomes smooth and the thickness variation can be reduced. However,
if the starting of the slowing-down state r3 of the calender rolls
8A is delayed too much from the starting of the slowing-down state
p3 of the gear pump 6, the rubber G2 is subjected to a large
tensile force and liable to be broken. For this reason, the time
difference K3 between the starting of the slowing-down state r3 of
the calender rolls 8A and the starting of the slowing-down state p3
of the gear pump 6 is determined experimentally based on the
materials of the rubber, the shape or configuration of the rubber
G2 and the like, but usually it is set to be about 0.2 to 0.4
sec.
[0075] As shown in FIGS. 5(b) and 5(c), it is necessary to let the
calender rolls 8A in the open state prior to the stopping of the
rotation of the calender rolls 8A, namely, within the time period
t2c of the slowing-down state r3 of the calender rolls 8A. As a
result, the creep can be prevented and the thickness of the rubber
strip GS becomes stable. And at the time of stopping the apparatus
1, the rubber G2 existing between the nozzle block 7b and the
calender rolls 8A is applied by a moderate tensile stress capable
of preventing the shrinkage.
[0076] In addition, it is preferable that the switching to the open
state from the close state by the roll-gap changer 9 is made when
the surface speed of the calender rolls 8A is decreased down to
within a range of from 50 to 150 mm/sec.
[0077] Further, as show in FIGS. 5(a) and 5(b), it is preferable
that the time period t2c of the slowing-down state r3 of the
calender rolls 8A is set to be less than the time period t2g of the
slowing-down state of the gear pump 6. Preferably, the time period
t2c is set to be not less than 0.6 times but less than 1.0 times
the time period t2g. This helps to decreases the tensile stress of
the rubber G2 existing between the nozzle block 7b and the calender
rolls 8A and prevent the breakage of the rubber.
[0078] It is preferable that the stopping of the rotation of the
calender rolls 8A occurs prior to the stopping of the rotation of
the gear pump 6. This further helps to prevent the breakage of the
rubber.
[0079] As to the electric motors M1 and M2 for rotating the gears
and calender rolls 8A, preferably used is an electric motor driven
by a variable-voltage variable-frequency generator (inverter) in
order to easily change the time periods t1c and t2c of the
accelerating state and slowing-down state of the calender rolls 8A
and the time periods t1g and t2g of the accelerating state and
slowing-down state of the gear pump 6.
[0080] As explained above, the controller 4 program-controls the
timing of the various states of the gear pump 6, calender 10,
roll-gap changer 9 and extruder 5 not to cause an excessive tensile
stress on the rubber strip GS, therefore, even if the apparatus 1
intermittently manufactures the rubber strip, the breakage of the
rubber is completely prevented, and further the shape or
configuration of the rubber strip becomes stable. Therefore, the
accuracy of the rubber component formed therefrom can be
improved.
* * * * *