Method for forming cylindrical rubber member

Abstract

A method for forming a cylindrical rubber member includes bringing a die 11 close to a forming drum 2, forming a winding start portion S1 by extruding a rubber S and simultaneously starting to rotate the forming drum 2 to gradually increase an extruding amount to an amount Q1 and gradually increase a distance between the die 11 and the forming drum 2 to a distance D2 corresponding to a desired thickness of the cylindrical rubber member, winding the rubber S by maintaining the extruding amount at the amount Q1, and maintaining the distance between the die 11 and the forming drum 2 at the distance D2, and forming a winding end portion S2 on the winding start portion S1 by maintaining the distance between the die 11 and the forming drum 2 at the distance D2 and gradually reducing the extruding amount from the amount Q1.

Claims

1. A method for forming a cylindrical rubber member in which rubber extruded by an extruder through a die is wound around a rotation-supporting body, and a winding start portion and a winding end portion are bonded to each other to form a cylindrical shape, the method comprising: a preparation step of bringing the die close to the rotation-supporting body; a winding start step of forming a winding start portion having a wedge-shaped cross section by starting to extrude the rubber from the die which is brought close to the rotation-supporting body and simultaneously starting to rotate the rotation-supporting body to gradually increase an extruding amount of the rubber to a predetermined amount and gradually increase a distance between the die and the rotation-supporting body to a predetermined distance which is equal to a thickness of the cylindrical rubber member; a winding step of winding the rubber by maintaining the extruding amount of the rubber at the predetermined amount, and maintaining the distance between the die and the rotation-supporting body at the predetermined distance; and a winding end step of forming a winding end portion having a wedge-shaped cross section on the winding start portion by maintaining the distance between the die and the rotation-supporting body at the predetermined distance and gradually reducing the extruding amount of the rubber from the predetermined amount.

2. The method for forming a cylindrical rubber member according to claim 1, wherein an extruding amount of the rubber per unit time is set to be equal to a volume obtained by multiplying an area of a clearance between the die and a surface of the rotation-supporting body as viewed from a rotation direction by a moving distance, per unit time, of the surface of the rotation-supporting body, the moving distance being obtained by rotation.

3. The method for forming a cylindrical rubber member according to claim 1, wherein a gear pump having a pair of gears is provided between the extruder and the die, the number of rotations of a screw incorporated in the extruder is PID-controlled such that pressure on an inlet side of the gear pump becomes constant with respect to the number of rotations of the gears which are programmed and operated, and a parameter of the PID control differs between the preparation step, the winding start step, the winding step, and the winding end step.

4. The method for forming a cylindrical rubber member according to claim 1, wherein the cylindrical rubber member has a thin and wide cross-sectional shape having a thickness of 3.0 mm or less and a width of 150 mm or more.

5. The method for forming a cylindrical rubber member according to claim 1, wherein in the preparation step, the die is brought close to the rotation-supporting body as close as 0.1 mm or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing one example of a configuration of forming equipment for forming a cylindrical rubber member.

(2) FIG. 2 is a block diagram showing a function of a control system of the forming equipment.

(3) FIG. 3 is a flowchart showing one example of a procedure in forming the cylindrical rubber member.

(4) FIGS. 4(a) to 4(g) are schematic diagrams showing a manner of forming the cylindrical rubber member.

(5) FIG. 5(a) is a graph showing a relation between a rotation angle of a forming drum and an extruding amount of rubber, and FIG. 5(b) is a graph showing a relation between the rotation angle of the forming drum and a distance from a die to the forming drum.

(6) FIG. 6 is a schematic diagram showing a configuration of forming equipment according to another embodiment.

MODES FOR CARRYING OUT THE INVENTION

(7) Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing one example of a configuration of forming equipment for forming a cylindrical rubber member. The forming equipment shown in FIG. 1 includes an extruder 1, a gear pump 10, a die 11, a forming drum (corresponding to rotation-supporting body) 2, and a control device 3.

(8) The extruder 1 includes a cylindrical barrel 1a, a hopper 1b connected to a supply port of the barrel 1a, a screw 1c which kneads rubber and feeds the rubber toward a tip end of the extruder 1, and a screw motor 1d which rotates and drives the screw 1c. The number of rotations of the screw motor 1d is controlled by a control device 3 as will be described later.

(9) The gear pump 10 is connected to a tip end side of the extruder 1 in an extruding direction thereof, and a tip end side of the gear pump 10 is connected to the die 11. Rubber material kneaded by the extruder 1 is supplied to the gear pump 10, and the gear pump 10 supplies a given amount of rubber to the die 11. Rubber S is extruded in a predetermined extruding amount from the die 11.

(10) The gear pump 10 has a pair of gears 10a, and has a function of feeding rubber to an outlet side toward the die 11. The pair of gears 10a is respectively rotated and driven by gear motors (not shown), and the number of rotations of the gears 10a is controlled by the control device 3. By controlling the number of rotations of the gear motors and the number of rotations of the screw motor 1d in association with each other by the control device 3, it is possible to control the extruding amount of the rubber S extruded from the die 11. Although the pair of gears 10a is arranged in a vertical direction in FIG. 1 for the sake of illustration, the gears 10a may actually be arranged in a plane direction (direction in which rotation shaft of gear 10a is oriented in vertical direction in FIG. 1).

(11) A first pressure sensor 12 is provided on an inlet side of the gear pump 10, i.e., a side close to the extruder 1, and the first pressure sensor 12 detects pressure of rubber which is supplied from the extruder 1. A second pressure sensor 13 is provided on an outlet side of the gear pump 10, and the second pressure sensor 13 detects pressure of rubber S extruded from the die 11.

(12) Pressure on the inlet side of the gear pump 10 is determined by a feeding amount of rubber fed by the gears 10a of the gear pump 10 and the screw 1c of the extruder 1. By keeping pressure on the inlet side constant, the gear pump 10 can supply a given amount of rubber to the die 11, and the extruding amount from the die 11 is also stabilized. However, if pressure on the inlet side is unstable, the extruding amount from the die 11 varies, and it becomes difficult to form a cylindrical rubber member having a desired dimension.

(13) As a method of controlling pressure on the inlet side of the gear pump 10, there is known a method in which PID control is performed on the number of rotations of the gears 10a of the gear pump 10 and the number of rotations of the screw 1c of the extruder 1. The PID control is generally used when rubber is extruded continuously in a given amount. The forming method of the present invention includes a plurality of steps such as a preparation step, a winding start step, a winding step, and a winding end step which will be described later, and the extruding amount of rubber differs between these steps. In such a case, if a parameter of the PID control in the winding step in which the number of rotations of the gears 10a is fixed and a predetermined amount of rubber is continuously extruded is used in the winding start step and the winding end step in which the number of rotations of the gears 10a is greatly varied and the extruding amount is greatly varied, it is not possible to keep the pressure on the inlet side constant. Hence, in this embodiment, the parameter of the PID control is made different between the preparation step, the winding start step, the winding step, and the winding end step. More specifically, although the gears 10a do not rotate and are stopped in the preparation step, it is necessary to keep the pressure on the inlet side constant. Therefore, the screw 1c is slightly moved and a variation amount in the number of rotations is small. Therefore, the parameter is determined so that the PID control reacts insensitively. In the winding step, since it is necessary to rotate the gears 10a at high speed and keep the pressure on the inlet side constant, the screw 1c also rotates at high speed. At that time, rubber gradually generates heat due to kneading action, and viscosity of the rubber is also lowered. Under such influence, pressure on the inlet side also tends to lower, and to compensate the lowered pressure, the PID control is conducted to follow influence of disturbance in a high speed region. On the other hand, in the winding start step, a variation amount of the number of rotations of the gears 10a is large, and a programmed operation is conducted from a resting state to the high speed region instantaneously. Nevertheless, to keep the pressure on the inlet side constant, it is necessary to determine the parameter which sensitively reacts so that the number of rotations of the screw 1c also instantaneously follows. In the winding end step, contrary to the winding start step, a programmed operation is conducted so that variation in the gears 10a is instantaneously lowered from the high speed region to the resting state. Also at this time, to keep the pressure on the inlet side constant, it is necessary to determine the parameter which sensitively reacts so that the number of rotations of the screw 1c also instantaneously follows. According to these configurations, the pressure on the inlet side of the gear pump 10 can stably be kept substantially constant in all of the steps.

(14) This embodiment shows an example of a so-called external gear pump in which the gear pump 10 is connected to the tip end side of the extruder 1 in the extruding direction. Alternatively, it is also possible to use a gear pump built-in type extruder in which the gear pump is incorporated in the extruder. As shown in FIG. 6, the gear pump-built-in type extruder has a structure in which a gear groove 1e is formed in a tip end of the screw 1c, and the gear groove 1e and the gears 10a of the gear pump 10 mesh with each other so that the gears 10a of the gear pump 10 rotate with rotation of the screw 1c. It is possible to control rotation of the gear pump 10 only by controlling rotation of the screw 1c, and rubber can be extruded in a given amount. In the present invention, as compared with an extruder to which an external gear pump is connected, the gear pump-built-in type extruder is more preferable in that the extruding amount can be easily controlled and that a tip end of the extruder can be made compact since a gear motor is not required.

(15) The forming drum 2 can be rotated by a servomotor 20 (see FIG. 2) in a direction R. The number of rotations of the servomotor 20 is controlled by the control device 3. Rubber extruded through the die 11 is supplied to the forming drum 2, and the rubber can be wound along the circumferential direction by rotating and driving the forming drum 2 in the direction R with the rubber being adhered to the forming drum 2. A pressure roller (not shown) which pressure-bonds rubber supplied to the forming drum 2 may be provided.

(16) Next, a function of the control system of the forming equipment according to this embodiment will be described with reference to a block diagram in FIG. 2. The control device 3 has a function of controlling operations of various portions of the forming equipment.

(17) Screw motor control means 31 controls the number of rotations of the screw motor 1d of the extruder 1 based on the pressure on the inlet side of the gear pump 10 detected by the first pressure sensor 12. Gear motor control means 32 controls the number of rotations of a gear motor 10b based on a predetermined control program (by coefficient of time). Servomotor control means 33 controls the number of rotations of the servomotor 20.

(18) The extruder 1, the gear pump 10, and the die 11 can integrally be moved forward and backward in the extruding direction by a forward/backward driving device 14, and can move toward and away from the forming drum 2. Such forward and backward movements are also controlled by forward/backward driving device control means 34 of the control device 3.

(19) <Method for Forming Cylindrical Rubber Member>

(20) Next, a method for forming a cylindrical rubber member using the above forming equipment will be described. The method for forming a cylindrical rubber member according to the present invention includes: a preparation step of bringing the die 11 close to the forming drum 2; a winding start step of forming a winding start portion having a wedge-shaped cross section by starting to extrude rubber S from the die 11 which is brought close to the forming drum 2 and simultaneously starting to rotate the forming drum 2 to gradually increase an extruding amount of the rubber S to a predetermined amount and gradually increase a distance between the die 11 and the forming drum 2 to a predetermined distance corresponding to a desired thickness of the cylindrical rubber member; a winding step of winding the rubber S by maintaining the extruding amount of the rubber S at the predetermined amount, and maintaining the distance between the die 11 and the forming drum 2 at the predetermined distance; and a winding end step of forming a winding end portion having a wedge-shaped cross section on the winding start portion by maintaining the distance between the die 11 and the forming drum 2 at the predetermined distance and gradually reducing the extruding amount of the rubber S from the predetermined amount.

(21) FIG. 3 is a flowchart showing one example of a procedure in forming the cylindrical rubber member. FIGS. 4(a) to 4(g) are schematic diagrams showing states of forming the cylindrical rubber member. FIG. 5(a) shows a relation between a rotation angle of the forming drum 2 and the extruding amount of the rubber S. FIG. 5(b) shows a relation between the rotation angle of the forming drum 2 and the distance from the die 11 to the forming drum 2.

(22) First, the extruder 1, the gear pump 10 and the die 11 are integrally moved forward (#1), and the die 11 is brought close to the forming drum 2 as shown in FIG. 4(a). At this time, the die 11 is brought close to a surface of the forming drum 2 as close as a predetermined distance D1. It is preferable that D1 is 0.1 mm or less. Timing at which the die 11 is brought close to the forming drum 2 is not particularly limited as long as the predetermined distance is provided until the rubber S is extruded from the die 11.

(23) Next, rubber material of the rubber S adjusted in the previous-step is charged in the hopper 1b of the extruder 1. Here, rubber material is not particularly limited. For example, material to be mixed is kneaded by an ordinary method into general rubber raw material such as natural rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR), and the obtained material is adjusted such that the rubber can be crosslinked. A shape of the rubber material to be charged is not particularly limited. Examples of such a shape include a ribbon shape, a sheet shape, and a pellet shape.

(24) The rubber material which is charged into the hopper 1b is kneaded by the screw 1c of the extruder 1, is fed toward the tip end in the extruding direction, and is supplied to the gear pump 10 (#2, 3). The rubber material supplied to the gear pump 10 is fed to the outlet side toward the die 11 by the pair of rotating gears 10a (#4).

(25) The rubber material which is supplied to the die 11 is extruded from an opening of the die 11 as rubber S (#5). If the tip end of the extruded rubber S is adhered to and fixed to an outer surface of the forming drum 2 as shown in FIG. 4(b), the forming drum 2 starts rotating and driving as shown in FIG. 4(c) (#6). Actually, the extruding motion of the rubber S from the die 11 and rotation of the forming drum 2 are started simultaneously (or substantially simultaneously).

(26) By controlling the number of rotations of the gears 10a and the number of rotations of the screw 1c substantially simultaneously with start of rotating and driving of the forming drum 2, the extruding amount of the rubber S extruded from the die 11 is gradually increased to the predetermined amount (#7). Further, the extruding amount of the rubber S is increased and the die 11 is gradually moved backward as shown in FIG. 4(c), and the distance between the die 11 and the forming drum 2 is gradually increased (#7). Accordingly, a cross section of the winding start portion S1 of the rubber S is formed into the wedge shape.

(27) More specifically, as shown in FIG. 5(a), the extruding amount of the rubber S is gradually increased to a predetermined amount Q1 until the rotation angle of the forming drum 2 becomes equal to . Further, as shown in FIG. 5(b), the die 11 gradually moves backward until the rotation angle of the forming drum 2 becomes equal to , and the distance between the die 11 and the forming drum 2 is gradually increased from D1 to a predetermined distance D2.

(28) Thereafter, the extruding amount of the rubber S is maintained at the predetermined amount Q1, the distance between the die 11 and the forming drum 2 is maintained at the predetermined distance D2. While keeping this state, the forming drum 2 continues to rotate and drive. Here, the predetermined distance D2 corresponds to a desired thickness of a cylindrical rubber member to be formed, and the extruded rubber S passes through the clearance between the die 11 and the surface of the forming drum 2 and a thickness of the rubber S becomes equal to D2. Accordingly, a cross section of the winding start portion S1 of the rubber S is formed into the wedge shape, and thereafter, the thickness of the rubber S becomes equal to the constant thickness D2 as shown in FIG. 4(d).

(29) As shown in FIG. 4(e), if the winding start portion S1 of the rubber S comes close to the die 11, the extruding amount of the rubber S extruded from the die 11 is gradually reduced from the predetermined amount Q1 by controlling the number of rotations of the gears 10a and the number of rotations of the screw 1c (#8).

(30) More specifically, as shown in FIG. 5(a), the extruding amount of the rubber S is maintained at the predetermined amount Q1 until the rotation angle of the forming drum. 2 becomes equal to 360, and the extruding amount of the rubber S is gradually reduced from the predetermined amount Q1 before the rotation angle becomes equal to (360+). At this time, the distance between the die 11 and the forming drum 2 is maintained at the predetermined distance D2 as shown in FIG. 5(b). Accordingly, as shown in FIG. 4(f), across section of the winding end portion S2 of the rubber S is formed into the wedge shape, and the rubber S is formed by superposing the winding end portion S2 on the winding start portion S1. Accordingly, a cylindrical rubber member is formed in which a thickness of the joint between the winding start portion S1 and the winding end portion S2 is substantially equal to thicknesses of other portions.

(31) Lastly, as shown in FIG. 4(g), the die 11 moves backward, and the forming operation of the cylindrical rubber member is completed (#9).

Other Embodiment

(32) In the present invention, if the extruded rubber S is not directly wound around the forming drum 2 (rotation-supporting body) and another rubber is already wound around the forming drum 2 (rotation-supporting body), it is also possible to wind the rubber S around an outer surface of the other rubber.

(33) Although the extruder 1 is moved forward and backward to move the extruder 1 toward and away from the forming drum 2 in the above embodiment, it is also possible to move the forming drum 2 forward and backward to move the forming drum 2 toward and away from the extruder 1.

DESCRIPTION OF REFERENCE SIGNS

(34) 1 extruder 1c screw 2 forming drum 3 control device 10 gear pump 10a gear 11 die 12 first pressure sensor 13 second pressure sensor 14 forward/backward driving device 20 servomotor D2 predetermined distance Q1 predetermined amount S rubber S1 winding start portion S2 winding end portion