Device and method for forming sheet-like rubber

The sheet-like rubber forming device has a die body which has an opening having a predetermined cross sectional shape, and a variable die lip which is arranged in a front side of the die body and can change the height of the opening. The variable die lip is constructed by a first movable body and a second movable body. The die lip control unit controls the variable die lip so as to drive the first movable body in an opening direction from a state in which the first movable body and the second movable body are closed when the forming is started, hold the positions of the first movable body and the second movable body after reaching a predetermined height, and drive the second movable body in a closing direction when the forming is finished.

TECHNICAL FIELD

The present invention relates to a sheet-like rubber forming device and method for forming a tire constituting member having a predetermined width and height by extruding a sheet-like rubber from a die head of an extruder.

BACKGROUND ART

As an example of the sheet-like tire constituting member, there is a tread rubber. The sheet-like tire constituting member is tabular in an expanded state as shown inFIG. 6(a), however, when being formed in a tire shape, it is necessary to join an end portion and an end portion on a forming drum. However, if an overlap is generated or a gap is generated when the end portions are joined with each other, uniformity is lowered, and there is a risk that a tire performance is adversely affected (refer toFIGS. 6(b) and 6(c)).

Accordingly, it is necessary to form front and rear end portions of the sheet-like tire constituting member so that a thickness thereof is changed little by little, as shown inFIG. 7(a). As a result, the end portions can be overlapped with each other so that a thickness is entirely uniform, as shown inFIG. 7(b). In order to achieve the formation of the rubber having the shape as mentioned above, there has been a known rubber layer forming method by a variable die head which is disclosed in the following patent document 1.

Specifically, it is disclosed inFIG. 6of the patent document 1. The variable die head is controlled so as to change a dimension in a width direction of an opening of the die head little by little. Further, in order to form a tread portion which has a comparatively large thickness, the tread portion is formed by overlapping several layers of rubbers each having a small thickness.

PRIOR ART DOCUMENTS

Patent Document

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, the variable die head disclosed in the above patent document 1 has a problem that it takes a long time for forming since several layers of thin rubbers are overlapped as well as a metal mold structure is complicated.

The present invention has been made in view of the above actual condition, and an object thereof is to provide a sheet-like rubber forming device and method in which a metal mold structure is not complicated, and a forming time can be shortened.

Means for Solving the Problems

In order to solve the problem mentioned above, in accordance with the present invention, there is provided a sheet-like rubber forming device for forming a tire constituting member having a predetermined width and height, by extruding a sheet-like rubber from a die head of an extruder, the sheet-like rubber forming device comprising a die body which constructs the die head and has an opening having a predetermined cross sectional shape, a variable die lip which is arranged in a front side of the die body and can change the height of the opening, and a die lip control unit which controls motion of the variable die lip, wherein the variable die lip is constructed by a first movable body which is positioned in one side in a height direction, and a second movable body which is positioned in the other side in the height direction, and wherein the die lip control unit controls the variable die lip so as to drive the first movable body in an opening direction little by little from a state in which the first movable body and the second movable body are closed when the forming is started, hold the positions of the first movable body and the second movable body after reaching a predetermined height, and drive the second movable body in a closing direction little by little when the forming is finished.

A description will be given of an operation and an effect of the sheet-like rubber forming device having the above structure. First of all, the die head is constructed by the die body in an upstream side and the variable die lip in a downstream side. The die body is fixed and has the opening having the predetermined cross sectional shape. In order to vary a height of the opening, the variable die lip is provided with the first movable body and the second movable body. When the forming is started, the first movable body and the second movable body are positioned so as to close the opening. Next, the height of the extruded and formed rubber member is increased little by little from 0 by driving the first movable body in the opening direction little by little. When the first movable body reaches the predetermined height, then the first movable body and the second movable body keep the position for a while. Accordingly, the rubber member having a fixed cross sectional shape is extruded and formed. Further, when the forming is finished, the second movable body is driven and moved toward the closing direction little by little. As a result, the height of the extruded and formed rubber member heads for 0 little by little. The tire constituting member having the shape as shown inFIG. 7(b)is formed by controlling the variable die lip in the manner as mentioned above. The structure of the variable die lip only has two movable bodies, and is inhibited from being complicated. Further, since the thin rubber members are not overlapped in layers, it is possible to shorten the forming time. As mentioned above, it is possible to provide the sheet-like rubber forming device in which the metal mold structure is not complicated, and the forming time can be shortened.

In the sheet-like rubber forming device in accordance with the present invention, it is preferable that the sheet-like rubber forming device comprises a gear pump which is arranged in an upstream side of the die head, and a gear pump control unit which controls drive of the gear pump, wherein the gear pump control unit controls the gear pump so as to control a rubber discharge amount from the die body when the control of the variable die lip is carried out by the die lip control unit.

Since the gear pump is provided, it is possible to supply a fixed amount of rubber toward the die head. Further, since the cross sectional shape of the extruded and formed rubber is changed between the forming start time and the forming end time, it is necessary to supply the rubber in conformity to the change of the cross sectional shape. Accordingly, the rubber can be supplied to the die head in conformity to the cross sectional shape of the extruded and formed rubber, by controlling a speed of rotation or the like of the gear pump.

In order to solve the problem mentioned above, in accordance with the present invention, there is provided a sheet-like rubber forming method of forming a tire constituting member having a predetermined width and height by extruding a sheet-like rubber from a die head of an extruder, while using the sheet-like rubber forming device mentioned above, comprising a step of driving the first movable body in an opening direction little by little from a state in which the first movable body and the second movable body are closed, when the forming of the tire constituting member is started, a step of holding the positions of the first movable body and the second movable body after the first movable body reaches a predetermined height, and a step of driving the second movable body in a closing direction little by little when the forming is finished.

The operation and the effect of the sheet-like rubber forming method according to the above structure are already mentioned. In other words, the metal mold structure is not complicated, and the forming time can be shortened.

In the sheet-like rubber forming method in accordance with the present invention, it is preferable that the sheet-like rubber forming method comprises a step of controlling drive of a gear pump which is arranged in an upstream side of the die head, and a step of controlling a discharge amount of the rubber from the die body by controlling the gear pump, at the start time of the forming and the end time of the forming that the control of the variable die lip is carried out.

According to the above structure, as already mentioned, the rubber can be supplied to the die head in conformity to the cross sectional shape of the extruded and formed rubber.

It is preferable to have a step of directly attaching the tire constituting member according to the present invention to the forming drum. As a result, it is possible to shorten the forming step and it is possible to efficiently form the tire constituting member.

MODE FOR CARRYING OUT THE INVENTION

A description will be given of a preferable embodiment of a sheet-like rubber forming device and method according to the present invention with reference to the accompanying drawings.FIG. 1is a schematic view showing a structure of the sheet-like rubber forming device.

InFIG. 1, a sheet-like rubber forming device A is provided with an extruder1, a gear pump2which is arranged in a downstream side of the extruder1, a die head3which is arranged in a downstream side of the gear pump2, and a movable body drive portion4which drives a variable die lip31(which will be described later) constructing the die head3. Further, a forming drum5for winding a tire constituting member which constructs the tire is provided.

The extruder1is provided with a screw10for mixing a rubber which is thrown from a hopper (not shown), and a screw drive portion11for rotationally driving the screw10. The rubber mixed by the screw10is fed to the gear pump2. The gear pump2is constructed by a pair of gears20, and is driven by a gear pump drive portion21. The gear pump2has a function of supplying a fixed amount of rubber to the die head3in the downstream side, and can accordingly carry out a stable rubber supply. A supply amount can be defined by controlling a speed of rotation of the gear pump2.

The die head3is constructed by a die body30and a variable die lip31. The die body30is provided in its internal portion with a passage for the rubber, and an opening having a predetermined cross sectional shape is formed in the die body. Viewing the die body30from a front surface side (a side from which the rubber discharges), a trapezoidal opening32is formed. A shape of the opening32corresponds to a shape of the tire constituting member to be formed, and a description will be given of an example in which a sheet-like tread portion is formed, in the present embodiment.

The variable die lip31is provided in a front side (a downstream side) of the die body30, and is provided with a first movable body310and a second movable body311. The first and second movable bodies310and311are driven by the movable body drive portion4. Details of the variable die lip31and the movable body drive portion4will be mentioned later.

The rubber extruded from the die head3so as to be formed is attached to an outer surface of the forming drum5. The forming drum5is a rotation body having a cylindrical shape, and is driven by a drum drive portion50.

A controller6has a function of controlling motion of each of the portions of the sheet-like rubber forming device A. A die lip control unit60controls drive of the variable die lip31. A gear pump control unit61controls a speed of rotation of the gear pump2. A screw control unit62carries out drive control of the screw10of the extruder1. A drum control unit63controls a speed of rotation and drive timing or the like of the forming drum5. An extruder drive portion12is a drive portion for moving a whole of the extruder1, the die head3and the movable body drive portion4close to and away from the forming drum5. An extruder control unit64controls the extruder1or the like so that a distance between the extruder1and the forming drum5becomes appropriate. The controller6is provided with a computer structure, such as a CPU, and a memory, and control of the controller6is carried out based on a control program65.

<Structure of Die Head>

Next, a description will be given of a detailed structure of the die head3with reference toFIG. 2.FIG. 2(a)is a side cross sectional view andFIG. 2(b)is a front elevational view. As shown inFIG. 2, a flow path33in which the rubber flows is provided in an inner portion of the die body30, and is set such that a cross sectional area becomes smaller little by little from an upstream side in which the gear pump2is arranged, toward a downstream side in which the opening32is formed.

The variable die lip31is provided with the first movable body310and the second movable body311, and is formed as a thick plate shape. The first movable body310is driven in a vertical direction inFIG. 2by a first drive motor40, a horizontal drive shaft41and a vertical drive shaft42. The horizontal drive shaft41and the vertical drive shaft42are transmitted their drive by a bevel gear. A drive screw42is formed in a lower portion of the vertical drive shaft42, and is threadably engaged with the first movable body310. Accordingly, the first movable body310can be driven in a vertical direction by driving the first drive motor40and turning the vertical drive shaft42.

The second movable body311is driven in a vertical direction inFIG. 2by a second drive motor43, a horizontal drive shaft44and a vertical drive shaft45in the same manner as the first movable body310. A drive screw45ais formed in an upper portion of the vertical drive shaft45, and is threadably engaged with the second movable body311. Accordingly, the second movable body311can be driven in a vertical direction by driving the second drive motor43and turning the vertical drive shaft45.

The first drive motor40is mounted on a support table46, and the support table46is attached to an upper surface of the die body30. The second drive motor43is mounted on a support table47, and the support table47is attached to a lower surface of the die body30. The support tables46and47are provided with bearing functions for the vertical drive shafts42and45.

As shown inFIG. 2(b), the opening32is formed as the trapezoidal shape as seen from a front surface, and a lower side is longer than an upper side. A lower end portion310aof the first movable body310and an upper end portion311aof the second movable body311come into contact with each other before starting the forming. Therefore, the opening32is in a completely closed state. The opening32is exposed by driving the first and second movable bodies310and311in the vertical direction, and the rubber corresponding to an exposed area is extruded and formed. The first and second movable bodies310and311are driven only in the vertical direction, and are not driven in a width direction (a lateral direction inFIG. 2).

<Forming Step of Tire Constituting Member>

Next, a description will be given of a forming step of a tread rubber which is the tire constituting member. The description will be given with reference to a flowchart inFIG. 3, andFIGS. 4A to 4F.

First of all, the variable die lip31is set to an initial state shown inFIG. 2. In other words, the first movable body310and the second movable body311come into contact with each other, and the opening32of the die head3is closed (S1). Next, the first drive motor40is controlled by the die lip control unit60of the controller6, and driving the first movable body310upward is started (S2,FIG. 4A). The second movable body311is in a fixed state. As a result, the opening32is exposed little by little, and the rubber is extruded and formed. A cross sectional shape of the rubber becomes larger little by little (FIG. 4B).

A state in which the first movable body310is driven at a predetermined height is shown inFIG. 4C(S3). At this time, the opening32is in an approximately exposed state. A stage that the first movable body310moves to the predetermined height is defined as a forming start time, and is shown by a reference sign P1inFIG. 7.

After the first movable body310is driven to the predetermined height, the first movable body310is held at the position (S4). Further, the second movable body311still remains at the initial position. Accordingly, the rubber having a fixed cross sectional shape is extruded and formed thereafter. Specifically, the rubber having the shape of the opening32is extruded and formed. This state is defined as a stationary time, and is shown by a reference sign P2inFIG. 7.

Next, the second drive motor43is controlled by the die lip control unit60toward the end of the forming, so as to start driving the second movable body311upward (S5,FIG. 4D). The first movable body310remains stopping in the upward side. As a result, the opening32is closed little by little (FIG. 4E).

Discharge of the rubber is finished at a time point that the second movable body311moves upward, and the lower end portion310aof the first movable body310comes into contact with the upper end portion311aof the second movable body311(S6). A section until the second movable body311moves upward so as to stop is defined as a forming end time, and is shown by a reference sign P3inFIG. 7. At this time, the opening32comes to a state in which the opening32is completely closed, as shown inFIG. 4F.

Since both the first movable body310and the second movable body311are in an upward moving state in the state inFIG. 4F, they are returned to the initial positions shown inFIG. 2until the next forming of the tire constituting member is started (S7). In other words, the first and second movable bodies310and311are driven downward by driving both the first drive motor40and the second drive motor43.

FIG. 5shows a tire constituting member G in a state in which the tire constituting member is attached to an outer surface of the forming drum5. A joint portion between end portions of the tire constituting member G is shown by a reference sign G1. According to the forming method of the present invention, since the thickness of the rubber in the end portions becomes thinner little by little, the tire constituting member G having a uniform thickness can be obtained as a whole, by overlapping the end portions.

Next, in the forming step described inFIG. 4, a relative positional relationship between the die head3and the forming drum5will be described. When the forming is started and the forming is finished, the control is carried out so that the die head3comes as close as possible to the forming drum5. Further, from the start of the forming to the stationary time, the control is carried out so that the distance between the forming drum5and the die head3becomes longer little by little. Further, at the stationary time, the distance between the forming drum5and the die head3is kept constant. Further, to the end of the forming, the control is carried out so that the die head3again comes close to the forming drum5.FIG. 5shows a state in which the die head3comes close to the forming drum5.

Next, a description will be given of a control of the gear pump2at the start time of the forming and the end time of the forming. At the start time of the forming and the end time of the forming, the cross sectional shape of the extruded and formed rubber changes little by little. Therefore, it is preferable to change an amount of the rubber which is supplied to the die head3from the gear pump2while working with the change of the cross sectional shape. Accordingly, at the start time of the forming, the control is carried out so that the speed of rotation of the gear pump2is increased little by little. At the stationary time, the rotation of the gear pump2is kept at a fixed speed. Further, at the end time of the forming, the control is carried out so that the speed of the rotation of the gear pump2is reduced little by little. It is possible to supply an appropriate amount of rubber to the die head3by working with the control of the gear pump2as mentioned above, and the shape of the extruded and formed rubber can be precisely formed.

It is possible to join so that the joint portion does not generate any step and has a uniform thickness, by using the tire constituting member which is formed by the present invention, and uniformity is improved. Further, in comparison with the forming method according to the strip build which is described in the conventional art, the forming time can be shortened and productivity is exponentially improved.

Other Embodiments

In the present embodiment, the structure using the gear pump is described, however, the present invention can be applied to a case that the gear pump is not provided.

In the present embodiment, the tread portion is exemplified as the tire constituting member, however, the present invention can be applied to a case that the other tire constituting members than the tread portion are formed. Further, with regard to the cross sectional shape of the tire constituting member, various modified examples can be considered, and the cross sectional shape is not limited to the particular shape.

With regard to the drive mechanism of the variable die lip31, various modified examples can be employed. In the present embodiment, the description was given of the structure in which the opening32is closed by the first movable body310as shown inFIG. 2, however, a structure in which the opening32is closed by the second movable body311may be employed. In this case, the second movable body311is driven downward so as to open the opening32at the start of the forming, and the first movable body310is driven downward so as to close the opening32at the end of the forming. Accordingly, the moving directions of the first and second movable bodies310and311when the opening32is opened and closed are not limited to the particular directions. A speed when the opening32is opened and closed can be appropriately set. In addition, the specific structure of the movable body drive portion4can employ various modified examples.

DESCRIPTION OF REFERENCE SIGNS