JP2024067182A - Method and apparatus for producing rubber extrusion product - Google Patents

Abstract

To provide a method and apparatus for producing a rubber extrusion product, which can suppress variation in weight of the rubber extrusion product after extrusion of a rubber material is resumed, without complicating the apparatus, and can maintain stable quality.SOLUTION: When a process of continuously extruding a rubber material R as a rubber extrudate Rx in a constant weight state from an extrusion port 7a by rotating a screw 4 of an extruder 2 at a rotation speed of a specification value Vc is resumed after a pause, based on a temperature difference tx between a pre-grasped temperature tp at the time of extrusion of the rubber material R continuously extruded at the constant weight and a temperature tr of the rubber material R at a head 6 just before resuming extrusion, or a time length L of the pause, a rotation increase rate α determined by an operation part 10 is multiplied by the specification value Vc to calculate a resumed rotation speed V1, and the rubber material R is continuously extruded from the extrusion port 7a by controlling a control part 9 to reduce the rotation speed from the resumed rotation speed V1 to the specification value Vc during a predetermined period T after resuming extrusion.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and apparatus for producing rubber extrusions, and more specifically, to a method and apparatus for producing rubber extrusions that can suppress weight variations in the rubber extrusions and maintain stable quality from the time when extrusion of the rubber material is resumed without complicating the equipment.

When manufacturing rubber products such as tires, there is an extrusion process in which unvulcanized rubber material is molded into a predetermined shape using an extruder and extruded as a rubber extrusion. In the extrusion process, the extrusion of the rubber material may be temporarily stopped due to equipment changes or the convenience of previous or subsequent processes. When the extrusion of the rubber material is temporarily stopped, the temperature of the rubber material remaining inside the extruder drops. If the rubber material with a lowered temperature is extruded as is, the amount of rubber material extruded is reduced compared to when the rubber material before the temperature drop is extruded. As a result, the difference in the amount of rubber material extruded becomes larger between the initial time when extrusion is resumed and thereafter. In other words, the weight of the rubber extrusion varies greatly until the rubber material inside the extruder rises to the temperature before the temperature drop, and this also causes variation in quality.

A method has been proposed for stabilizing the quality of rubber extrusions from the time when extrusion of rubber material is resumed (see Patent Document 1). This proposal requires the extruder to be provided with a flow regulator that changes the cross-sectional area of the extrusion flow path, temperature sensors that detect the temperature of the rubber material upstream and downstream of the flow regulator, a pressure sensor that detects the internal pressure of the extrusion flow path, and an opening/closing unit that opens and closes the extrusion flow path near the extrusion port, which complicates the manufacturing equipment. Therefore, there is room for improvement to suppress weight variations in rubber extrusions and maintain stable quality from the time when extrusion of rubber material is resumed without complicating the equipment.

JP 2020-44773 A

The object of the present invention is to provide a method and apparatus for manufacturing rubber extrusions that can suppress variation in the weight of the rubber extrusions and maintain stable quality from the time extrusion of the rubber material is resumed without complicating the equipment.

In order to achieve the above object, the method for manufacturing rubber extrusions of the present invention rotates the screw of an extruder at a set rotational speed of a specified value, and continuously extrudes unvulcanized rubber material as a rubber extrusion product from an extrusion port of a die attached to the head of the extruder at a constant weight. When the extrusion of the rubber material is resumed after a temporary stop, a rotational speed increase rate with respect to the specified value is determined based on the temperature difference between the previously known temperature at the time of extrusion of the rubber material continuously extruded at a constant weight from the extrusion port and the temperature of the rubber material at the head immediately before the extrusion is resumed, or based on the length of the temporary stop, and the restart rotational speed is calculated by multiplying this rotational speed increase rate by the specified value, and the rotational speed is controlled to be reduced from the calculated restart rotational speed toward the specified value during a predetermined period from the restart of the extrusion, thereby continuously extruding the rubber material.

The rubber extrusion manufacturing device of the present invention has an extruder having a screw, a cylinder in which the screw is installed, and a die attached to the head at the tip of the cylinder, and a control unit that controls the rotation speed of the screw, and the screw rotates while the rotation speed is controlled to a specification value by the control unit, and an unvulcanized rubber material is continuously extruded as a rubber extrusion product at a constant weight from an extrusion port formed in the die. When the extrusion of the rubber material is resumed after a temporary stop, a calculation unit determines a rotation increase rate relative to the specification value based on the temperature difference between the temperature of the rubber material continuously extruded at a constant weight from the extrusion port that is known in advance and the temperature of the rubber material at the head immediately before the extrusion is resumed, or the length of the temporary stop, and the rotation increase rate is multiplied by the specification value to calculate the restart rotation speed, and the control unit controls the rotation speed to be reduced from the restart rotation speed to the specification value for a predetermined period from the restart of the extrusion, thereby continuously extruding the rubber material.

According to the present invention, by rotating the screw at a rotation speed increased from the specification value when the extrusion of the rubber material is resumed, the decrease in the extrusion amount of the rubber material, the temperature of which is reduced by the temporary suspension of the extrusion, can be compensated for. Then, by reducing the rotation speed of the screw from the restart rotation speed toward the specification value during the specified period, the rubber material can be smoothly extruded from the extrusion port continuously as the rubber extrusion product at a constant weight. In this way, since it is sufficient to control the rotation speed of the screw in a feedforward manner, it is advantageous for suppressing the variation in the weight of the rubber extrusion product and maintaining stable quality from the time when the extrusion of the rubber material is resumed without complicating the device.

FIG. 1 is an explanatory diagram illustrating a plan view of an apparatus for producing a rubber extrusion product according to the present invention. FIG. 2 is an explanatory diagram illustrating the rubber extrusion manufacturing apparatus of FIG. 1 in a side view. FIG. 13 is a graph illustrating control of the screw rotation speed after resuming extrusion. FIG. 1 is a graph illustrating data for determining a rotation increase rate. FIG. 4 is a graph illustrating the change over time in the extrusion weight of a rubber extrudate after resumption of extrusion.

The method and apparatus for producing rubber extrusions of the present invention will be described below based on the embodiment shown in the figures.

The rubber extrusion manufacturing apparatus 1 (hereinafter referred to as the manufacturing apparatus 1) illustrated in Figures 1 and 2 includes an extruder 2, a control unit 9 that controls the extruder 2, and a calculation unit 10 that is communicatively connected to the control unit 9. The calculation unit 10 performs various calculation processes using input data, etc. Known computers are used as the control unit 9 and the calculation unit 10. In this embodiment, the control unit 9 and the calculation unit 10 are provided separately, but, for example, a single computer can be used as the control unit 9 and the calculation unit 10.

The extruder 2 has a cylindrical cylinder 3, a screw 4 installed inside the cylinder 3, a head 6 installed at the tip of the cylinder 3, and a die 7 installed on the head 6. A drive motor 5 for rotating the screw 4 is arranged at the rear end of the cylinder 3. An inlet 3a is formed on the upper surface of the rear end side of the cylinder 3, and a hopper 3b is attached so as to surround the inlet 3a. The screw 4 has helical screw blades arranged at intervals in the axial direction of the screw shaft (the longitudinal direction of the cylinder 3). An extrusion flow path 6a is formed in the head 6, and the die 7 has an extrusion port 7a that communicates with the extrusion flow path 6a. The die 7, which has an extrusion port 7a of a desired shape, is freely attachable to and detachable from the head 6.

In this embodiment, the manufacturing device 1 further includes a take-up conveyor 11 disposed in front of the extruder 2, a temperature sensor 8a disposed in the head 6, and a non-contact type temperature sensor 8b disposed at the upstream end of the take-up conveyor 11. The temperature sensors 8a and 8b each sequentially detect the temperature of the rubber material R at the position where they are disposed. Any known temperature sensor can be used as long as it can detect the temperature of the rubber material R. The temperature data detected by the temperature sensors 8a and 8b is sequentially input to the calculation unit 10.

Next, an example of the procedure for the method for producing the rubber extrusion product of the present invention will be described.

In this manufacturing device 1, unvulcanized rubber material R is fed into the cylinder 3 through the feed port 3a, and is sent to the head 6 while being heated and kneaded by the rotating screw 4. The rubber material R sent to the head 6 is continuously extruded from the extrusion port 7a through the extrusion flow path 6a as rubber extrusion product Rx. As the rubber material R passes through the extrusion port 7a, it becomes a long rubber extrusion product Rx molded into a desired cross-sectional shape. In tire manufacturing, examples of the rubber extrusion product Rx include various tire components such as tread rubber, side rubber, and bead filler. This rubber extrusion product Rx is transported to another process by a take-up conveyor 11 located in front of the extruder 2.

In more detail, a fixed specification value Vc is set for the number of revolutions of the screw 4 for each type of rubber material R, and this specification value Vc is input and stored in the calculation unit 10. The control unit 9 rotates the screw 4 at the specification value Vc stored in the calculation unit 10 for each type of rubber material R, thereby continuously extruding the rubber material R inside the cylinder 3 from the extrusion port 7a at a constant weight as rubber extrusion product Rx. In other words, by rotating the screw 4 at the specification value Vc, the extrusion weight (extrusion amount) of the rubber extrusion product Rx per unit time from the extrusion port 7a is set to be within a certain range. The period during which the rubber extrusion product Rx is continuously extruded at a constant weight in this manner is hereinafter referred to as the steady extrusion period Nt.

When rubber material R is extruded from extrusion port 7a to produce rubber extrusion product Rx, the extrusion of rubber material R may be temporarily stopped due to equipment changes or the convenience of previous or subsequent processes. During the temporary stop of extrusion, rotation of screw 4 is also stopped, and the temperature of rubber material R remaining inside cylinder 3 gradually drops.

Then, the screw 4 is rotated to resume extrusion of the rubber material R, and the steady-state extrusion period Nt is entered to produce the rubber extrusion product Rx. However, the temperature of the rubber material R remaining inside the cylinder 3 is lower than the temperature of the rubber material R inside the cylinder 3 during the steady-state extrusion period Nt. Therefore, when the extrusion of the rubber material R is resumed, even if the screw 4 is rotated at the specification value Vc, the extrusion weight of the rubber extrusion product Rx is insufficient compared to the steady-state extrusion period Nt. The reason for this is that even if the same energy is applied to the rubber material R by rotating the screw 4 at the specification value Vc, if the temperature of the rubber material R is lower, more energy is consumed to heat the rubber material R, and the weight of the rubber extrusion product Rx extruded from the extrusion port 7a is thought to decrease in proportion to the increased energy consumption.

Therefore, from when extrusion of the rubber material R is resumed until the temperature of the rubber material R inside the cylinder 3 rises to the temperature of the rubber material R inside the cylinder 3 during the steady extrusion period Nt, the extrusion weight of the rubber extrusion product Rx is smaller than that during the steady extrusion period Nt. As a result, there is variation in the weight of the rubber extrusion product Rx between the specified period T from when extrusion of the rubber material R is resumed until the steady extrusion period Nt and the steady extrusion period Nt thereafter, and this also causes variation in quality.

Therefore, in order to suppress the variation in the weight of the rubber extrusion product Rx, the present invention employs a special technique. That is, when the extrusion of the rubber material R is resumed after a temporary stop, in order to compensate for the shortage in the extrusion weight of the rubber extrusion product Rx caused by the temperature drop of the rubber material R remaining inside the cylinder 3, feedforward control is performed to increase the rotation speed of the screw 4 relative to the specification value Vc until the steady extrusion period Nt is reached, as illustrated in FIG. 3. That is, during the predetermined period T from the resumption of extrusion of the rubber material R to the steady extrusion period Nt, the rotation speed of the screw 4 is not maintained at a constant specification value Vc, but is feedforward controlled to be faster than the specification value Vc.

To explain this feedforward control in detail, first, the temperature tp of the rubber material R during the steady extrusion period Nt is determined in advance. To this end, the temperature of the rubber extrusion product Rx is detected by the temperature sensor 8b during the steady extrusion period Nt, and the detected temperature tp is stored in the calculation unit 10. Note that the temperature of the rubber material R at the head 6 detected by the temperature sensor 8a during the steady extrusion period Nt can also be used as this temperature tp.

When the extrusion of the rubber material R is resumed after being temporarily stopped, the temperature tr of the rubber material R at the head 6 immediately before the extrusion is resumed is detected. For this purpose, the temperature tr of the rubber material R remaining in the head 6 is detected by the temperature sensor 8a, and the detected temperature tr is input to the calculation unit 10. Due to the temporary stop of the extrusion of the rubber material R, the temperature tr is lower than the temperature tp (tr<tp).

Next, the calculation unit 10 calculates the temperature difference tx (= tp - tr) between the previously determined temperature tp and the detected temperature tr, and determines the rotation increase rate α for the specification value Vc based on this temperature difference tx. The rotation increase rate α is a value greater than 1 (α > 1).

As shown in FIG. 4, correlation data between the rotation increase rate α and the temperature difference tx (or correlation data between the rotation increase rate α and the length of time L during which extrusion is temporarily stopped) is obtained in advance, and this correlation data is input and stored in the calculation unit 10. When correlation data between the rotation increase rate α and the temperature difference tx is stored in the calculation unit 10, the calculation unit 10 uses this correlation data and the temperature difference tx to determine the rotation increase rate α that corresponds to the temperature difference tx, as indicated by the dashed arrow.

The correlation data between the rotation increase rate α and the temperature difference tx shown in FIG. 4 is obtained by conducting a preliminary test using this extruder 2 or a similar extruder. Specifically, the extent to which the extrusion weight of the rubber extrusion product Rx changes depending on the magnitude of the temperature difference tx is determined (data 1 is obtained). Then, the extent to which the extrusion weight of the rubber extrusion product Rx changes depending on the change in the screw rotation speed is determined (data 2 is obtained). Based on the relationship between the obtained data 1 and data 2, the correlation data between the rotation increase rate α and the temperature difference tx shown in FIG. 4 can be obtained.

The temperature tp during the extrusion of the rubber material R during the steady extrusion period Nt may be data detected using one representative type of rubber material R, but this temperature tp differs slightly for each type of rubber material R. Therefore, it is preferable to know in advance this temperature tp for each type of rubber material R. When the extrusion of the rubber material R is resumed after a temporary stop, if the rotation increase rate α is determined based on the temperature difference tx between the previously known temperature tp and the above-mentioned temperature tr, it is advantageous to reduce the weight variation of the rubber extrusion product Rx for each type of rubber material R from the time when extrusion is resumed. Therefore, it is preferable to obtain the correlation data between the rotation increase rate α and the temperature difference tx shown in FIG. 4 for each type of rubber material R.

The rotation increase rate α can also be determined based on the length of time L during which extrusion is temporarily stopped. That is, when correlation data between the rotation increase rate α and the length of time L during which extrusion is temporarily stopped, as shown in FIG. 4, is stored in the calculation unit 10, the calculation unit 10 uses this correlation data and the length of time L during which extrusion is temporarily stopped to determine the rotation increase rate α corresponding to the length of time L during which extrusion is temporarily stopped, as shown by the dashed arrow.

The correlation data between the rotation increase rate α and the length of time L during which extrusion is temporarily stopped, as shown in FIG. 4, is obtained by conducting a preliminary test using this extruder 2 or a similar extruder. Specifically, the extent to which the temperature of the rubber material R at the head 6 changes depending on the length of time L during which extrusion is temporarily stopped is determined (data 3 is obtained). This data 3 may be data that determines the extent of the temperature difference tx depending on the length of time L during which extrusion is temporarily stopped.

Then, data 1 and data 2 are acquired as described above. Based on the relationship between the acquired data 1, data 2, and data 3, correlation data between the rotation increase rate α and the length of time L during which extrusion is temporarily stopped can be acquired, as shown in FIG. 4.

The change in temperature of the rubber material R at the head 6 according to the length L of the temporary suspension of the extrusion of the rubber material R may be data detected using one representative type of rubber material R, but this temperature change varies slightly for each type of rubber material R. Therefore, it is preferable to grasp in advance the temperature change of the rubber material R at the head 6 according to the length L of the temporary suspension of the extrusion of the rubber material R for each type of rubber material R. Then, when the extrusion of the rubber material R is resumed after being temporarily suspended, if the rotation increase rate α for the specification value Vc is determined based on the temperature change of the rubber material R at the head 6 based on the length L of the temporary suspension, it is advantageous to reduce the weight variation of the rubber extrusion product Rx for each type of rubber material R from the time when extrusion is resumed. Therefore, it is preferable to obtain the correlation data between the rotation increase rate α and the length L of the temporary suspension of the extrusion, as shown in FIG. 4, for each type of rubber material R.

After the rotation increase rate α is determined as described above, the calculation unit 10 calculates the restart rotation speed V1 (=α×Vc) by multiplying the determined rotation increase rate α by the specification value Vc. The determined restart rotation speed V1 is input to the control unit 9. As illustrated in FIG. 3, the control unit 9 performs feedforward control to reduce the rotation speed of the screw 4 from the calculated restart rotation speed V1 toward the specification value Vc during a predetermined period T from the restart of extrusion. In FIG. 3, the rotation speed of the screw 4 is uniformly (linearly) reduced from the restart rotation speed V1 to the specification value Vc from the time when extrusion is restarted toward the start of the steady extrusion period Nt. As illustrated in FIG. 3, the rotation speed of the screw 4 can be reduced not only linearly between the time when extrusion is restarted and the start of the steady extrusion period Nt, but also in a slightly curved line.

The predetermined period T is about 1 to 2 minutes, and is appropriately determined within this range. The predetermined time T should be determined based on the amount of rubber material R remaining inside the cylinder 3 when the extrusion of the rubber material R is temporarily stopped. Specifically, the predetermined time T is set to be approximately equal to the time required for all of the rubber material R remaining inside the cylinder 3 when the extrusion is temporarily stopped to be extruded as the rubber extrusion product Rx after the extrusion is resumed. The volume of the cylinder 3 (the amount of rubber material R that can be filled into the cylinder 3) is known. In addition, the rotation speed of the screw 4 and the extrusion amount of the rubber extrusion product Rx are also known. Therefore, the extrusion amount of the rubber extrusion product Rx at the predetermined time T is calculated based on the rotation speed of the screw 4 at the predetermined time T illustrated in FIG. 3, and the predetermined time T is set so that the calculated extrusion amount of the rubber extrusion product Rx is the same as the amount of rubber material R remaining inside the cylinder 3 when the extrusion is temporarily stopped.

During the predetermined time T from when the extrusion of the rubber material R is resumed until the steady-state extrusion period Nt begins, the control unit 9 controls the rotation speed of the screw 4 as shown in FIG. 3 to continuously extrude the rubber material R from the extrusion port 7a as rubber extrusion product Rx. After the predetermined time T has elapsed, the steady-state extrusion period Nt begins.

In Figure 5, the thick solid line shows the extrusion weight of the rubber extrusion product Rx when the rotation speed of the screw 4 is feedforward controlled as described above. The thick dashed line shows the extrusion weight of the rubber extrusion product Rx when extrusion is resumed at the specification value Vc without feedforward control of the rotation speed of the screw 4. Figure 5 also shows the target value G of the extrusion weight of the rubber extrusion product Rx and its allowable range Aw.

According to this embodiment, by rotating the screw 4 at a rotation speed increased compared to the specification value Vc when the extrusion of the rubber material R is resumed, it is possible to compensate for the decrease in the extrusion amount when extruding the rubber material R remaining inside the cylinder 3, the temperature of which has decreased due to the temporary suspension of the extrusion. Then, by reducing the rotation speed of the screw 4 from the restart rotation speed V1 toward the specification value Vc during the specified period T, it is possible to smoothly transition from the specified period T to the steady extrusion period Nt.

As described above, this manufacturing apparatus 1 only requires feedforward control of the rotation speed of the screw 4, so there is no need to equip various devices to suppress variations in the weight of the rubber extrusion product Rx when extrusion is resumed, which is advantageous in avoiding the device becoming too complicated. As a result, the present invention can be easily applied to existing extruders 2.

As illustrated by the thick solid line in Figure 5, this is advantageous for suppressing variations in the weight of the rubber extrusion product Rx and maintaining stable quality from the time when extrusion of the rubber material R is resumed. In other words, according to the present invention, it is advantageous for maintaining the extrusion weight of the rubber extrusion product Rx within the allowable range Aw of the target value G from the time when extrusion of the rubber material R is resumed.

The manufacturing apparatus 1 and the manufacturing method of the rubber extrusion product Rx described above can be used to manufacture the rubber extrusion product Rx that is a component of various rubber products such as tires. In addition, the manufacturing apparatus 1 can be applied to both cases where a rubber material R that does not contain a vulcanization-based compounding agent is extruded as a rubber extrusion product Rx, and cases where a rubber material R that contains a vulcanization-based compounding agent is extruded as a rubber extrusion product Rx.

Reference Signs List 1 Rubber extrusion product manufacturing apparatus 2 Extruder 3 Cylinder 3a Feeding port 3b Hopper 4 Screw 5 Drive motor 6 Head 6a Extrusion flow path 7 Die 7a Extrusion ports 8a, 8b Temperature sensor 9 Control unit 10 Calculation unit 11 Take-up conveyor R Unvulcanized rubber material Rx Rubber extrusion product

Claims (5)

A method for producing a rubber extrusion product, comprising the steps of: rotating an extruder screw at a preset rotation speed; extruding an unvulcanized rubber material continuously at a constant weight from an extrusion port of a die attached to a head of the extruder;
When the extrusion of the rubber material is resumed after a temporary suspension, a rotation increase rate with respect to the specification value is determined based on the temperature difference between a previously determined temperature during extrusion of the rubber material continuously extruded at a constant weight from the extrusion port and the temperature of the rubber material at the head immediately before the extrusion is resumed, or based on the length of the temporary suspension, and the restart rotation speed is calculated by multiplying this rotation increase rate by the specification value, and control is performed to reduce the rotation speed from the calculated restart rotation speed toward the specification value over a predetermined period of time from the resumption of the extrusion, thereby continuously extruding the rubber material. The method for producing a rubber extrusion product according to claim 1, wherein the predetermined period is determined based on the amount of the rubber material remaining in the extruder when extrusion of the rubber material is temporarily stopped. The method for producing rubber extrusions according to claim 1 or 2, wherein the temperature during extrusion of the rubber material, which is continuously extruded at a constant weight from the extrusion port, is grasped in advance for each type of rubber material, and when the extrusion of the rubber material is resumed after a temporary stop, the rotation increase rate is determined based on the temperature difference between the previously grasped temperature and the temperature of the rubber material at the head immediately before the extrusion is resumed. The method for producing rubber extrusions according to claim 1 or 2, in which the temperature change of the rubber material at the head according to the length of the pause is grasped in advance for each type of rubber material, and when the extrusion of the rubber material is resumed after the pause, the rotation increase rate for the specification value is determined based on the temperature change of the rubber material at the head based on the length of the pause. An apparatus for producing a rubber extrusion product, comprising: an extruder having a screw, a cylinder in which the screw is disposed, and a die attached to a head at the tip of the cylinder; and a control unit for controlling the number of revolutions of the screw, wherein the screw rotates while the number of revolutions is controlled to a specified value by the control unit, and an unvulcanized rubber material is continuously extruded as a rubber extrusion product at a constant weight from an extrusion port formed in the die,
When the extrusion of the rubber material is resumed after a temporary suspension, a calculation unit determines a rotation increase rate with respect to the specification value based on the temperature difference between a previously determined temperature during extrusion of the rubber material continuously extruded at a constant weight from the extrusion port and the temperature of the rubber material at the head immediately before the extrusion is resumed, or based on the length of the temporary suspension, and the restart rotation speed is calculated by multiplying the rotation increase rate by the specification value, and the control unit controls the rotation speed to be reduced from the restart rotation speed toward the specification value for a predetermined period of time after the extrusion is resumed, thereby continuously extruding the rubber material.

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