JP5896050B1 - Rubber roll manufacturing apparatus and rubber roll manufacturing method - Google Patents

Abstract

[PROBLEMS] To produce a crown-shaped rubber roll by changing the conveying speed of a core metal, compared with a case where the conveying speed of the core metal is larger than 120% with respect to the extrusion speed of a rubber material. An apparatus for manufacturing a rubber roll and a method for manufacturing a rubber roll that can suppress variation are obtained. The conveying speed of the core metal is set to 100% to 120% with respect to the extrusion speed of the rubber material. For this reason, the degree of change in the pressure loss of the rubber material is reduced. As a result, when a crown-shaped rubber roll is manufactured by changing the conveying speed of the core metal, the outer diameter of the rubber roll is larger than that when the conveying speed of the core metal 22 is larger than 120% with respect to the extrusion speed of the rubber material. It is suppressed that the diameter varies. [Selection] Figure 1

Description

  The present invention relates to a rubber roll manufacturing apparatus and a rubber roll manufacturing method.

  In Patent Document 1, a metal core is sequentially fed into a central portion of a rubber material extruded into a cylindrical shape at intervals, a rubber roll portion in which the outer peripheral surface of the metal core 22 is covered with a rubber material, and a metal core with a rubber material. A rubber roll manufacturing apparatus including an extruder that alternately discharges hollow portions that are hollow is described.

JP 2013-103473 A

  As described in Patent Document 1, when a space is provided between the front core bar and the rear core metal, the outer periphery of the core metal is formed by a rubber material in a merging region where the core metal and the cylindrical rubber material merge. The rubber roll part with which the surface was coated and the hollow part formed between the metal core and the metal core pass alternately. For this reason, the pressure loss of the rubber material pushed out to the merge area changes.

  Due to this change in pressure loss, the outer diameter of the rubber material coated on the core metal may vary. It is also known that when the outer diameter on the axial center side of the rubber roll is made larger than the outer diameter on the end side (in the case of a crown shape), the conveying speed of the core metal is changed. Thus, by changing the conveying speed of the metal core, the variation in the outer diameter of the rubber material due to the change in the pressure loss described above may become remarkable.

  The object of the present invention is to produce a crown-shaped rubber roll by changing the conveying speed of the core metal, compared with the case where the conveying speed of the core metal is larger than 120% with respect to the extrusion speed of the rubber material. It is to suppress the variation in the outer diameter.

  In the rubber roll manufacturing apparatus according to claim 1, the core metal is sequentially fed to the central portion of the unvulcanized rubber material extruded in a cylindrical shape, and the outer peripheral surface of the core metal is covered with the rubber material. An extruder for alternately extruding a rubber roll part and an intermediate part having no metal core in the central part of the rubber material between a front metal core and a rear metal core, and controlling the extruder to control the core By changing the gold conveyance speed between 100% and 120% with respect to the extrusion speed of the rubber material, the outer diameter on the central side in the axial direction of the rubber roll portion is changed to the outer diameter on both end sides in the axial direction. And a control unit that is larger than the control unit.

  In the method of manufacturing a rubber roll according to claim 2, the core metal is sequentially fed to the center portion of the unvulcanized rubber material extruded in a cylindrical shape at intervals, and the outer peripheral surface of the core metal is covered with the rubber material. In the step of alternately discharging the rubber roll portion and the intermediate portion where the core metal does not exist in the central portion of the rubber material between the front core metal and the rear core metal, the conveyance speed of the core metal is set to the rubber material The first step of increasing the outer diameter on the central side in the axial direction of the rubber roll portion relative to the outer diameter on both ends in the axial direction by changing between 100% and 120% with respect to the extrusion speed of And a second step of performing a vulcanization process on the rubber material, and a third step of cutting off the rubber material at a portion covering both ends of the core metal.

  According to the rubber roll manufacturing apparatus of claim 1, compared with the case where the change range of the core metal transport speed is not defined, compared to the case where the core metal transport speed is greater than 120% with respect to the rubber material extrusion speed. And it can suppress that the outer diameter of a rubber roll varies.

  According to the rubber roll manufacturing method of claim 2, when manufacturing the crown-shaped rubber roll by changing the core metal transport speed, the core metal transport speed is greater than 120% with respect to the rubber material extrusion speed. As compared with the above, variation in the outer diameter of the rubber roll can be suppressed.

It is the expanded sectional view which showed the merge area in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention. It is the expanded sectional view which showed the merge area in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention. It is drawing which showed the evaluation result at the time of manufacturing a rubber roll using the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, and the rubber roll manufacturing apparatus which concerns on a comparison form with a table | surface. It is the block diagram which showed the separation mechanism in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, a drawer, etc. It is the block diagram which showed the separation mechanism in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, a drawer, etc. It is the block diagram which showed the separation mechanism in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, a drawer, etc. It is the block diagram which showed the separation mechanism in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, a drawer, etc. It is the block diagram which showed the separation mechanism in the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention, a drawer, etc. It is sectional drawing which showed the rubber roll manufactured by the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention. It is sectional drawing which showed the rubber roll manufactured by the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention. It is the block diagram which showed the manufacturing apparatus of the rubber roll which concerns on embodiment of this invention.

  An example of a rubber roll manufacturing apparatus and a rubber roll manufacturing method according to an embodiment of the present invention will be described with reference to FIGS. Note that an arrow H shown in the figure indicates the vertical direction of the apparatus (vertical direction), and an arrow W indicates the width direction of the apparatus (horizontal direction).

(overall structure)
A rubber roll 70 (see FIG. 10) manufactured by a rubber roll manufacturing apparatus and a rubber roll manufacturing method according to the present embodiment is in contact with a photosensitive drum of an electrophotographic image forming apparatus, for example, while being driven and rotated. Used as a charging roll for charging a body drum. In order to suppress variation in charging of the photosensitive drum, the outer diameter of the rubber roll 70 needs to be within a predetermined allowable range.

  As shown in FIG. 11, the rubber roll manufacturing apparatus 10 according to the present embodiment includes an extruder 12 composed of a so-called crosshead die, a pressing machine 14 disposed below the extruder 12, and a pressing machine. 14 and a drawer 16 disposed on the lower side. Moreover, the rubber roll manufacturing apparatus 10 includes a control unit 78 that controls each unit.

(Extruder)
The extruder 12 includes a rubber material supply unit 18 that supplies an unvulcanized rubber material, an extrusion unit 20 that extrudes the rubber material supplied from the rubber material supply unit 18 in a cylindrical shape, and is extruded from the extrusion unit 20 into a cylindrical shape. And a metal core supply unit 24 for supplying the metal core 22 to the center of the rubber material.

[Rubber supply section]
The rubber material supply unit 18 is disposed on the right side of the main body 26 in the figure, a screw 28 disposed inside the cylindrical main body 26, a heater (not shown) for heating the rubber material in the main body 26. And a drive motor 30 that rotationally drives the screw 28. Further, a charging port 32 for charging a rubber material is arranged on the drive motor 30 side of the main body 26.

  In this configuration, the rubber material input from the input port 32 is sent out toward the extrusion portion 20 while being kneaded by the screw 28 inside the main body portion 26.

[Extruded part]
The extrusion unit 20 includes a cylindrical case 34 connected to the rubber material supply unit 18, a columnar mandrel 36 disposed inside the case 34, and a discharge head 38 disposed below the mandrel 36. I have. The mandrel 36 is held in the case 34 by a holding member 40, and the discharge head 38 is held in the case 34 by a holding member 42. A rubber material flows annularly between the outer peripheral surface of the mandrel 36 (in part, the outer peripheral surface of the holding member 40) and the inner peripheral surface of the holding member 42 (in part, the inner peripheral surface of the discharge head 38). An annular channel 44 is formed.

  A passage hole 46 through which the core bar 22 is inserted is formed at the center of the mandrel 36. On the other hand, the lower part of the mandrel 36 has a tapered shape toward the tip (lower end). A region below the tip of the mandrel 36 is a joining region 48 where the core metal 22 supplied from the passage hole 46 and the rubber material supplied from the annular channel 44 join. That is, the rubber material is pushed out in a cylindrical shape toward the merging region 48, and the cored bar 22 is fed into the central portion of the rubber material pushed out in the cylindrical shape.

[Core metal supply section]
The cored bar supply unit 24 includes a roller pair 50 disposed on the upper side of the mandrel 36. A plurality of pairs (for example, three pairs) of roller pairs 50 are provided, and a roller on one side (left side in the figure) of each roller pair 50 is connected to a driving roller 54 via a belt 52. When the driving roller 54 is driven, the cored bar 22 sandwiched by each roller pair 50 is sent toward the passage hole 46 of the mandrel 36. The core metal 22 has a predetermined length, and the rear core metal 22 fed by the roller pair 50 presses the front core metal 22 existing in the passage hole 46 of the mandrel 36, whereby a plurality of core bars 22 are formed. 22 sequentially pass through the passage hole 46.

  In this configuration, the driving of the driving roller 54 is temporarily stopped when the tip of the front cored bar 22 reaches the tip of the mandrel 36 (see FIG. 4). Then, the rubber material is extruded into a cylindrical shape in the merging region 48, and the core metal 22 is sequentially fed into the central portion of the rubber material with an interval. Accordingly, a rubber roll portion 56 in which the outer peripheral surface of the metal core 22 is covered with a rubber material, and a hollow portion 58 as an example of an intermediate portion in which the inside of the rubber material is hollow between the metal core 22 and the metal core 22, Are alternately discharged from the discharge head 38 (details will be described in the later-described operation). In addition, a primer is applied in advance to the outer peripheral surface of the cored bar 22 in order to improve the adhesiveness with the rubber material. Moreover, the conveyance speed of the metal core when feeding the metal core 22 into the passage hole 46 will be described later.

[Pressing machine]
The pressing machine 14 includes a pair of semi-cylindrical pressing members 60. The pair of pressing members 60 are disposed to face each other so as to sandwich the rubber roll portion 56 discharged from the extruder 12. Each pressing member 60 is formed with a pressing portion 62 that protrudes toward the center. Each pressing member 60 is movable in the left-right direction in the figure by a drive mechanism (not shown).

[Drawer]
The drawer 16 has a pair of semi-cylindrical gripping members 64. The pair of gripping members 64 are disposed to face each other so as to sandwich the rubber roll portion 56 discharged from the extruder 12. Each gripping member 64 is formed with a gripping portion 66 having a shape corresponding to the outer peripheral surface shape of the rubber roll portion 56. Each gripping member 64 is movable in the left-right direction and the up-down direction by a drive mechanism (not shown).

(Operation of the overall configuration)
Next, a manufacturing method for manufacturing the rubber roll 70 using the rubber roll manufacturing apparatus 10 will be described.

  As shown in FIG. 11, the rubber material introduced into the insertion port 32 of the rubber material supply unit 18 is heated by a heater (not shown) inside the main body part 26 and is kneaded by the rotating screw 28 while being extruded. It is sent out toward.

  The rubber material fed from the rubber material supply unit 18 to the extrusion unit 20 and supplied to the extrusion unit 20 can be annularly formed in an annular flow path 44 formed inside the extrusion unit 20. The rubber material flowing through the annular flow path 44 flows toward the joining area 48 and is pushed out as a cylindrical rubber member 72 in the joining area 48.

  On the other hand, the cored bar 22 is supplied to the passage hole 46 of the mandrel 36 by the cored bar supply unit 24. The rear core metal 22 supplied by the roller pair 50 of the core metal supply section 24 presses the front core metal 22 existing in the passage hole 46 of the mandrel 36, so that the front core metal 22 becomes the merging area 48. Is fed into the center of the rubber member 72 extruded in a cylindrical shape. As a result, the rubber roll portion 56 whose outer peripheral surface of the cored bar 22 is covered with the rubber member 72 is discharged from the discharge head 38.

  Here, as shown in FIG. 4, when the rear end of the mandrel 36 reaches the front end of the mandrel 36 and the rear core 22 stops, the gripping members 64 are moved in a direction approaching each other. The rubber roll portion 56 is gripped by the 64 gripping portions 66.

  Then, as shown in FIG. 5, each gripping member 64 moves downward while gripping the rubber roll portion 56. That is, the rubber roll portion 56 is pulled out from the extruder 12 by each gripping member 64. Further, as described above, the rubber material is extruded as the cylindrical rubber member 72 in the merge area 48. As a result, a hollow portion 58 in which the inside of the rubber material is hollow is formed.

  Further, the feeding of the cored bar 22 is resumed, and the hollow portion 58 moves to the position where the pair of pressing members 60 are opposed, as shown in FIG. And when the hollow part 58 moves to the opposing position of a pair of press member 60, as FIG. 7 shows, each press member 60 is moved to the direction which mutually approaches, and rubber | gum of the hollow part 58 (refer FIG. 6) The material is pressed inward by the pressing portion 62 of each pressing member 60. Thereby, the end surface 68 of the front metal core 22 and the end surface 68 of the rear metal core 22 are covered with the rubber material.

  Further, as shown in FIG. 8, the pressing members 60 move in directions away from each other, the front rubber roll portion 56 and the rear rubber roll portion 56 are separated, and the core metal 22 is formed into a bag-like shape. 74 is formed (first step).

  Each gripping member 64 moves downward by an appropriate distance while gripping the separated rubber roll body 74, and then is a virtual line (two-dot chain line) in FIG. 4 as a standby position for gripping the next rubber roll portion 56. Move to the position indicated by.

  The bag-bound rubber roll 74 is put in a vulcanization furnace in the next step. Thereby, a vulcanization process is performed on the rubber material covering the cored bar 22 (second step).

  The vulcanized rubber roll body 74 is processed in the next step. Specifically, the rubber material at both ends is cut out so that the cored bar 22 is exposed for a certain length at the both ends of the rubber roll body 74 (see FIGS. 9 and 10). Thereby, the rubber material of the part which covers the end surface 68 of the metal core 22 is cut out, and the rubber roll 70 is manufactured (third process).

  The reason why the cored bar 22 has a bag-like shape is that the cored bar 22 is produced when the rubber material is vulcanized as compared with the case where the rubber material at both ends of the cored bar 22 is open. This is to suppress the deformation of the rubber material at both end portions of 22.

(Main part configuration)
Next, as a configuration of the main part, the core bar conveying speed for feeding the core bar 22 into the passage hole 46 in the first step described above will be described.

  The controller 78 controls the cored bar supply unit 24 to change the conveying speed of the cored bar between 100% and 120% with respect to the extrusion speed of the rubber material, thereby the rubber roll unit 56. The outer diameter on the center side in the axial direction is made larger than the outer diameter on both end sides in the axial direction. In other words, the crown-shaped rubber roll 70 is manufactured by changing the conveying speed of the core metal within the above-described range. Specifically, the conveyance speed of the core metal 22 when the central side of the core metal 22 is covered with the rubber material is compared with the conveyance speed of the core metal 22 when both ends of the core metal 22 are covered with the rubber material. By slowing down, the crown-shaped rubber roll 70 is manufactured.

  The rubber material extrusion speed refers to the movement speed of the metal core when the unloaded metal core 22 is inserted into the central portion of the rubber member 72 extruded in a cylindrical shape by using the rubber roll manufacturing apparatus 10. It is. That is, when the unloaded cored bar 22 is inserted into the passage hole 46, the cored bar conveyance speed becomes 100% of the rubber material extrusion speed.

(Effects of main components)
Next, the operation of the main configuration will be described together with the evaluation results of the rubber roll manufacturing apparatus of the present embodiment and the rubber roll manufacturing apparatus of the comparative embodiment.

  First, the evaluation of the rubber roll manufacturing apparatus of the present embodiment and the rubber roll manufacturing apparatus of the comparative embodiment will be described.

[Evaluation specifications]
1. The rubber material is 100 parts by mass of epichlorohydrin rubber (trade name: EPION301, company name: Daiso), 1 part by weight of processing aid (trade name: stearic acid Tsubaki, company name: Japanese fats and oils), carbon black (trade name: # 3030B, company name: Mitsubishi Chemical) 12 parts by mass, calcium carbonate (trade name: Viscoexcel-30, company name: Shiraishi Kogyo) 40 parts by mass, plasticizer (trade name: DB02, company name: Daiso) 3 parts by mass, Sealed rubber material containing 6 parts by mass of sulfur (trade name: Noxeller DM, company name: Ouchi Shinsei Chemical) and 5 parts by mass of a vulcanization accelerator (trade name: 2 types of zinc oxide, company name: Shodo Chemical) An unvulcanized product was obtained by kneading using a mold kneader and a roll machine. The Mooney viscosity of JISK6300-1 (2001) in the rubber material was 50.

  2. The metal core 22 is made of stainless steel (SUS) having L (full length) = 354.5 [mm] and an outer diameter of 8.0 [mm].

  3. As an extruder, a 60 [mm] extruder manufactured by Mitsuha Seisakusho was used, the screw rotation speed was 10 [rpm], the die diameter (C dimension in FIG. 4) was 12.5 [mm], and the extrusion pressure of the rubber material Was 23 [MPa].

  The target value of the outer diameter of the rubber roll 74 (see FIG. 9) is 12.1 [mm] on the center side (Dm dimension in FIG. 9), and 12 on both ends (Df dimension in FIG. 9). 0.0 [mm], and the rubber roll 74 (rubber roll 70) has a crown shape with a crown amount of 0.1 [mm]. In FIG. 9, the crown amount is exaggerated.

  4). The unvulcanized rubber material described above was extruded using an extruder, and at the same time, the cored bar 22 was sequentially passed through the passage hole to form a rubber roll 74. Thereafter, the mixture was put into a hot air furnace at 165 [° C.] for 75 minutes for vulcanization, and a vulcanized rubber layer of rubber material was formed on the cored bar 22. And the rubber roll 70 was obtained by cut | disconnecting the rubber material of the both ends of the vulcanized rubber roll body 74, and exposing the metal core 22 (FIG. 10). The exposed length of the cored bar 22 was 15 [mm].

  5-1. In Example 1, the rubber roll 70 was formed into a crown shape by changing the conveying speed of the core metal between 105% and 115% with respect to the extrusion speed of the rubber material.

  5-2. In Example 2, the rubber roll 70 was formed into a crown shape by changing the conveying speed of the core metal between 100% and 120% with respect to the extrusion speed of the rubber material.

  5-3. In Comparative Example 1, the rubber roll was formed into a crown shape by changing the conveying speed of the core metal between 115% and 125% with respect to the extrusion speed of the rubber material.

  5-4. For Comparative Example 2, the rubber roll was crown-shaped by changing the conveying speed of the core metal between 120% and 130% with respect to the extrusion speed of the rubber material.

[Evaluation Item / Evaluation Method]
The outer diameter of the rubber roll was evaluated (measured).

  In order to measure the outer diameter of the rubber roll, a light-shielding laser outer diameter measuring device (manufactured by Asaka Riken: ROLL2000) was used. Specifically, the outer diameter of one round was measured by supporting the both ends of the rubber roll to be measured and rotating the rubber roll once, and the difference (error) from the reference value (reference profile) was obtained. Regarding the measurement location, in the axial direction of the rubber roll, the pitch was 10 mm from the end of the rubber roll in the roll axial direction, and the largest numerical value among the errors was the maximum error.

〔Evaluation criteria〕
When the maximum error is less than 10 [μm], when this rubber roll is used as a charging roll of an electrophotographic image forming apparatus, the charging variation of the photosensitive drum falls within an allowable range, so “◯” is given. .

  On the other hand, when the maximum error is 10 [μm] or more, when this rubber roll is used as a charging roll of an electrophotographic image forming apparatus, the charging variation of the photosensitive drum does not fall within an allowable range. "

〔Evaluation results〕
FIG. 3 shows the evaluation results in a table. As shown in this table, Example 1 and Example 2 are “◯” because the maximum error is less than 10 μm, and Comparative Examples 1 and 2 have a maximum error of 10 μm. Since it is above, it became "x".

[Discussion]
The reason why the outer diameter of the rubber roll varies with respect to the reference value will be considered.

  Consider the pressure loss of a rubber material that is extruded in a cylindrical shape toward the merge region 48.

  As shown in FIG. 1, when the hollow portion 58 is located in the merging region 48, the outer peripheral surface of the rubber material pushed into the merging region 48 is the inner periphery of the discharge head 38 constituting the merging region 48. Adhere to the surface. This is because the inner peripheral surface of the rubber material pushed out to the merging region 48 is not in contact with the cored bar 22, so that the lower side loaded on the rubber material pushed into the merging region 48 by the conveyed cored bar 22. This is because the pulling force to is small.

  For this reason, when the hollow part 58 is located in the confluence | merging area 48, the pressure loss of a rubber material becomes large.

  On the other hand, as shown in FIG. 2, when the rubber roll portion 56 in which the outer peripheral surface of the cored bar 22 is covered with the rubber member 72 is located in the joining area 48, the rubber material pushed out to the joining area 48 is A part of the outer peripheral surface is peeled off from the inner peripheral surface of the discharge head 38 constituting the merge area 48. This is because the inner peripheral surface of the rubber material pushed out to the merging region 48 is in contact with the cored bar 22, so that the lower side loaded on the rubber material pushed into the merging region 48 by the conveyed cored bar 22. This is because the tensile force to is large.

  For this reason, when the rubber roll part 56 is located in the confluence | merging area 48, the pressure loss of a rubber material becomes small.

  And since the hollow part 58 and the rubber roll part 56 are located in the merge area 48 alternately (pass), the change of the pressure loss of a rubber material is repeated at the same space | interval. As described above, the pressure loss of the rubber material extruded in a cylindrical shape toward the merge region 48 changes, and thus the outer diameter of the rubber roll varies with respect to the reference value.

  Also, the greater the degree of change in the pressure loss of the rubber material, the greater the degree of variation in the outer diameter of the rubber roll with respect to the reference value, and the smaller the degree of change in the pressure loss of the rubber material, the more variable the outer diameter of the rubber roll. The degree is reduced. In particular, the degree to which the outer diameters at both ends of the rubber roll vary with respect to the reference value increases.

  Here, when the conveying speed of the core metal is made larger than 120 [%] of the extrusion speed of the rubber material, the rubber material is compared with the case where the conveying speed of the core metal is set to 120 [%] or less of the extrusion speed of the rubber material. The degree of change in pressure loss increases. Thereby, about the comparative examples 1 and 2, the degree to which the outer diameter of a rubber roll varies compared with Examples 1 and 2 becomes large.

  In addition, if the conveyance speed of the metal core is made smaller than 100 [%] of the rubber material extrusion speed, it is difficult to adjust the amount of the rubber material covered on the metal core 22, and the rubber roll cannot be formed.

(Summary)
In this embodiment, the conveying speed of the metal core is set to 100% to 120% with respect to the extrusion speed of the rubber material. For this reason, when a crown-shaped rubber roll is manufactured by changing the conveying speed of the core metal, the outer diameter of the rubber roll is larger than that when the conveying speed of the core metal 22 is larger than 120% with respect to the extrusion speed of the rubber material. It is suppressed that the diameter varies.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments can be taken within the scope of the present invention. This will be apparent to those skilled in the art. For example, in the above embodiment, the space between the front metal core 22 and the rear metal core 22 is a hollow portion 58 in which the inside of the rubber material is hollow. The inside of the rubber material between the gold 22 may not be hollow.

DESCRIPTION OF SYMBOLS 10 Rubber roll manufacturing apparatus 12 Extruder 22 Core metal 56 Rubber roll part 58 Hollow part (an example of an intermediate part)
78 Control unit

Claims (2)

The core metal is sequentially fed at intervals to the center of the unvulcanized rubber material extruded into a cylindrical shape, and the rubber roll portion in which the outer peripheral surface of the core metal is covered with the rubber material, the front core metal and the rear core metal An extruder for alternately extruding an intermediate portion in which a core metal does not exist at the center of the rubber material between the core
By controlling the extruder and changing the conveying speed of the core metal between 100% and 120% with respect to the extrusion speed of the rubber material, the outer diameter of the rubber roll portion on the center side in the axial direction A control unit for increasing
A rubber roll manufacturing apparatus comprising: A cored bar is sequentially fed into the center of an unvulcanized rubber material extruded into a cylindrical shape at intervals, a rubber roll part in which an outer peripheral surface of the cored bar is covered with the rubber material, a front cored bar and a rear cored bar In the step of alternately discharging between the cored bar and the intermediate part where the cored bar does not exist at the center part of the rubber material, the conveying speed of the cored bar is 100% or more and 120% with respect to the extrusion speed of the rubber material. By changing between the following, the first step of increasing the outer diameter of the center side in the axial direction of the rubber roll portion as compared with the outer diameter of both end sides in the axial direction;
A second step of vulcanizing the rubber material;
A third step of cutting off the rubber material of the portion covering both ends of the core;
A method for producing a rubber roll comprising: