Method for manufacturing silicone rubber tubes for internal pressure molding

Abstract

To efficiently manufacture silicone rubber tubes for internal pressure molding that conform to the shape of internal pressure molded products having sections with different diameters. [Solution] The method comprises a winding step of winding silicone 30 around a mandrel 20 to form a pre-formed body 40, a molding step of heating the pre-formed body 40 in a mold 50 to form a molded pre-formed body 60 in which a silicone rubber tube 10 is wound around the mandrel 20, and a decore step of decore the mandrel 20 from the molded pre-formed body 60. In the winding step, a mandrel 20 having a small diameter section 21 and a large diameter section 22 is used to wind silicone 30 with an A hardness of 15° to 39°.

Description

Technical Field

[0001] The present invention relates to a method for producing a silicone rubber tube for internal pressure molding.

Background Art

[0002] It is known to mold a fiber-reinforced resin hollow molded article by an internal pressure molding method using a silicone rubber tube. For example, when a cylindrical hollow molded article is molded by the internal pressure molding method, the following procedure is taken as an example. First, a silicone rubber tube having a fiber-reinforced resin prepreg wound around its outer surface is placed in a mold having a cylindrical cavity. Subsequently, a heated pressurized fluid is supplied into the silicone rubber tube to expand the silicone rubber tube. As a result, the prepreg is pressed against the inner surface of the mold, and the resin in the fiber-reinforced resin is thermally cured to obtain a hollow molded article in the shape of the cavity.

[0003] Incidentally, there are cases where a cylindrical hollow molded article whose diameter is not constant over the length direction and partially varies in diameter is subjected to internal pressure molding. In this case, if a silicone rubber tube whose diameter partially changes so as to conform to the shape of the internal pressure molded article is used, it is easy to mold the article into a desired shape.

[0004] Patent Document 1 describes a method for internal pressure molding of a golf club shaft with a varying cross-sectional perimeter, a racket frame for tennis or the like. As the tube for internal pressure molding, a tube whose cross-sectional perimeter is changed in correspondence with the cross-sectional perimeter of the cavity of the mold is used. A tube having a constant cross-sectional perimeter over the entire length is prepared, a predetermined region in the length direction is heated, and then both ends thereof are gripped and pulled to reduce the diameter of the predetermined region. It is possible to adjust the cross-sectional perimeter to a set value by the amount of pulling.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the method of stretching a heated and softened tube involves complicated adjustments of heating temperature, heating time, tensile force, and tensile amount to achieve the desired shape. There is room for improvement in efficiently manufacturing tubes for internal pressure molding that conform to the shape of the internal pressure molded product. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a method for manufacturing a silicone rubber tube for internal pressure molding, comprising: a winding step of winding silicone around a mandrel to form a pre-form; a molding step of heating the pre-form in a mold to form a molding pre-form with a silicone rubber tube wound around the mandrel; and a decore step of decore the mandrel from the molding pre-form, wherein in the winding step, a mandrel having a small diameter portion and a large diameter portion is used to wind silicone with an A hardness of 15° to 39°.

[0008] According to the above configuration, a preliminary body is formed by winding silicone around a mandrel with sections of different diameters, and then the preliminary body is heated. If a mandrel conforming to the shape of the internally molded product is used, a silicone rubber tube with sections of different diameters can be manufactured in a single molding process. This eliminates the need for large equipment, resulting in lower manufacturing costs and shorter cycle times.

[0009] Furthermore, by using silicone with an A hardness of 15° to 39°, it is possible to mold a silicone rubber tube that is easily stretchable and can conform to differences in diameter. Tearing and other damage to the silicone rubber tube are less likely to occur during mandrel decoreization. It also exhibits excellent strength and durability against pressure during internal pressure molding of hollow molded products. Silicone rubber tubes conforming to the shape of internally molded products can be manufactured efficiently.

[0010] Silicone is defined as "a polymer having a main chain in which silicon and oxygen atoms, each with an organic substituent, are alternately bonded." In the above configuration, it is preferable that in the winding step, a dome portion is provided between the small-diameter portion and the large-diameter portion, wherein the mandrel used is a curved surface in which the axial cross-section of the dome portion is convex outward with a radius of curvature R of 26 mm or more and 40 mm or less.

[0011] With the above configuration, the silicone rubber tube is less likely to tear or break during the removal of the mandrel core. In the above configuration, it is preferable to use a mandrel in which the ratio of the diameter of the thicker portion to the diameter of the thinner portion is less than 4.5 during the winding process.

[0012] With the above configuration, when removing the core from the mandrel, the silicone rubber tube stretches to follow the expansion of the larger diameter portion of the mandrel, allowing for efficient core removal. In the above configuration, it is preferable to use a mold in which a cavity in the shape of the molded pre-form is formed in the molding process, and which comprises an upper mold and a lower mold, and in which grooves extending along the cavity are formed on the periphery of the cavity on the lower surface of the upper mold and the upper surface of the lower mold.

[0013] According to the above configuration, ribs can be formed in the molded silicone rubber tube at positions corresponding to the parting lines of the upper and lower molds. Therefore, the strength of the silicone rubber tube at the parting line is improved when the mandrel is removed. The silicone rubber tube is less prone to tearing. [Effects of the Invention]

[0014] According to the present invention, a silicone rubber tube for internal pressure molding can be efficiently manufactured to conform to the shape of an internal pressure molded product having portions of different diameters. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram for describing a silicone rubber tube for internal pressure molding. (a) is a side view, and (b) is a cross-sectional view taken along line 1-1 of (a). [Figure 2] (a) to (c) are diagrams for describing a method for manufacturing a silicone rubber tube. [Figure 3] It is a partially enlarged view of a mandrel. [Figure 4] It is a cross-sectional view of a mold, which is a cross-sectional view taken along line 4-4 of Fig. 2(b). [Figure 5] It is a top view of the lower mold. [Mode for Carrying Out the Invention]

[0016] The silicone rubber tube of the internal pressure molding method of the present embodiment and its manufacturing method will be described based on Fig. 1 to Fig. 5. <Regarding Silicone Rubber Tube 10> As shown in Fig. 1(a), the silicone rubber tube 10 of the present embodiment has a small diameter portion 11, a large diameter portion 12, and a dome portion 13 whose diameter continuously changes between the small diameter portion 11 and the large diameter portion 12. In the present embodiment, for the purpose of simplifying and describing the shape of the silicone rubber tube 10, a silicone rubber tube 10 is exemplified which has a shape in which small diameter portions 11 of the same diameter are formed at both ends of the large diameter portion 12, and which is line-symmetric with respect to the axial center of the large diameter portion 12. In the silicone rubber tube 10, the diameter of the small diameter portion 11 is, for example, about 15 mm, and the diameter of the large diameter portion 12 is, for example, about 60 mm.

[0017] As shown in Fig. 1(b), the silicone rubber tube 10 is formed in a cylindrical shape with a circular radial cross section. Each of the small diameter portion 11, the dome portion 13, and the large diameter portion 12 has a circular radial cross section. A rib 14 extending in the axial direction is formed on the inner peripheral surface of the silicone rubber tube 10.

[0018] <Regarding the Manufacturing Method of Silicone Rubber Tube 10> As shown in Figs. 2(a) to (c), the method for manufacturing the silicone rubber tube 10 includes a winding step, a molding step, and a core removal step. The winding step is a step of winding the silicone 30 around the mandrel 20 to form a preliminary body 40. The molding step is a step of heating the preliminary body 40 in a mold 50 to mold a molded preliminary body 60 in a state where the silicone rubber tube 10 is wound around the mandrel 20. The core removal step is a step of removing the mandrel 20 from the molded preliminary body 60 and turning the silicone rubber tube 10 inside out at the same time.

[0019] As shown in Fig. 2(a) and Fig. 3, the mandrel 20 has a small-diameter portion 21, a large-diameter portion 22, and a dome portion 23 whose diameter continuously changes between the small-diameter portion 21 and the large-diameter portion 22. Each of the small-diameter portion 21, the large-diameter portion 22, and the dome portion 23 has a circular radial cross section. The ratio (D2 / D1) of the diameter D2 of the large-diameter portion 22 to the diameter D1 of the small-diameter portion 21 is preferably less than 4.5, and more preferably less than 4.3. The diameter in this case refers to the diameter of the circle. When the ratio (D2 / D1) is within this range, the small-diameter portion 11 of the silicone rubber tube 10 obtained by the molding step can be stretched to approximately the diameter D2 of the large-diameter portion 12. The mandrel 20 can be easily removed in the core removal step, and tearing or the like of the silicone rubber tube 10 during the core removal step can be suppressed.

[0020] The dome portion 23 is formed such that the axial cross section of the mandrel 20 is an outwardly convex curved surface. The curvature radius R of the curved surface is preferably 26 mm or more and 40 mm or less, and more preferably 30 mm or more and 40 mm or less. When the curvature radius R is within this range, the small-diameter portion 11 of the silicone rubber tube 10 easily follows the shape of the dome portion 23 during the core removal step. The mandrel 20 can be easily removed in the core removal step.

[0021] The silicone 30 used in the winding process preferably has a durometer A hardness of 15° to 39°, more preferably 20° to 30°, and even more preferably 20° to 25°. When the silicone 30 has an A hardness within this range, it can be wound well onto the mandrel 20, and a silicone rubber tube 10 can be obtained that is stretchable and resistant to tearing. During the decorening process, the small diameter portion 11 of the silicone rubber tube 10 stretches, making it easier to conform to the shape of the dome portion 23 and the large diameter portion 22. In addition, because the silicone rubber tube 10 has good stretchability, it easily conforms to the cavity shape during molding of the internal pressure molded product, allowing for accurate molding of the internal pressure molded product.

[0022] In the winding process, several types of silicone 30 are prepared, which are stretched to a predetermined thickness and then cut into predetermined shapes. The thickness of the silicone 30 is preferably 1 mm to 2 mm. When the thickness of the silicone 30 is within this range, tearing of the silicone rubber tube 10 during the molding process is suppressed, and the elongation of the silicone rubber tube 10 during the decoreping process is good. A suitable balance between elongation and strength can be maintained.

[0023] The silicone 30, stretched to a predetermined thickness, is shaped according to the portion to be wrapped around the mandrel 20. For example, the silicone 30 to be wrapped around the small diameter portion 21 is prepared by cutting it into a rectangular shape with one side having the axial length of the small diameter portion 21 and one side having the circumferential length of the small diameter portion 21. The same applies to the large diameter portion 22. The silicone 30 to be wrapped around the dome portion 23 is prepared by cutting it into strips.

[0024] In the winding process, a rectangular piece of silicone 30 is wound around the narrow-diameter section 21 and the wide-diameter section 22, respectively, for one full turn. In addition, a strip of silicone 30 is wound spirally around the dome section 23. Through this winding process, a preliminary body 40 is obtained in which silicone 30 is wound over almost the entire length of the mandrel 20, excluding both ends of the narrow-diameter section 21.

[0025] As shown in Figure 2(b), in the molding process, the pre-formed body 40 is heated in the mold 50 to form a molding pre-formed body 60 in which the silicone rubber tube 10 is wrapped around the mandrel 20.

[0026] As shown in Figures 4 and 5, the mold 50 comprises an upper mold 51 and a lower mold 52. When the upper mold 51 and the lower mold 52 are clamped together, a cavity 53 in the shape of a silicone rubber tube 10 is formed inside. A groove 54 extending along the cavity 53 is formed on the periphery of the cavity 53 on the lower surface of the upper mold 51. A groove 55 extending along the cavity 53 is formed on the periphery of the cavity 53 on the upper surface of the lower mold 52. The groove 54 is formed to have the same width and depth along its entire length. The groove 55 is formed to have the same shape and size as the groove 54.

[0027] The heating temperature and heating time in the molding process can be set as appropriate. For example, the heating temperature can be adjusted within the range of 80 to 200°C, and the heating time can be adjusted within the range of 5 to 60 minutes. The molding process yields a molded pre-form 60 in which the silicone rubber tube 10 is wrapped around the mandrel 20.

[0028] As shown in Figure 2(c), the molded pre-form 60 is removed from the mold 50. The silicone rubber tube 10 of the molded pre-form 60 has axially extending ribs 14 formed on its outer circumference. After removing the mandrel 20 from the molded pre-form 60, the silicone rubber tube 10 is inverted so that the ribs 14 are located on the inner circumference.

[0029] <Regarding the function of silicone rubber tube 10> The silicone rubber tube 10 is formed by winding silicone 30 with an A hardness of 15° to 39° around a mandrel 20. When winding the silicone 30, it is stretched to a wall thickness of 1 mm to 2 mm. The mandrel 20 has a ratio of the diameter D2 of the wide-diameter section 22 to the diameter D1 of the narrow-diameter section 21 that is less than 4.5, and the axial cross-section of the dome section 23 is a curved surface that is convex outward with a radius of curvature R of 26 mm to 40 mm. Grooves 54 and 55 are formed at the parting line positions of the mold 50. Therefore, the silicone rubber tube 10 is formed to have a wall thickness of 1 mm to 2 mm and to have the same shape as the outer shape of the mandrel 20. Ribs 14 are formed in the silicone rubber tube 10 at positions corresponding to the parting line of the mold 50.

[0030] When the hardness A of the silicone 30 is 20°, the silicone rubber tube 10 can stretch, for example, more than 800%. During the decoreization process, tearing of the silicone rubber tube 10 when the small diameter section 11 passes through the large diameter section 12 is suppressed. Furthermore, by setting the ratio of the diameters D1 and D2 of the small diameter section 21 and the large diameter section 22 of the mandrel 20 (D2 / D1), and the radius of curvature R of the dome section 23, the silicone rubber tube 10 can easily follow changes in the diameter of the mandrel 20. Tearing during decoreization is further suppressed. In addition, the ribs 14 suppress molding defects during molding of the silicone rubber tube 10, and also suppress tearing during demolding and decoreization.

[0031] When internal pressure molding a hollow molded product made of fiber-reinforced resin using a silicone rubber tube 10, for example, a fiber-reinforced resin prepreg is wound around the outer surface of the silicone rubber tube 10. This is then placed in a mold having a cavity in the shape of the internal pressure molded product, and pressurized fluid is supplied into the silicone rubber tube 10 to expand it. The internal pressure of the silicone rubber tube 10 presses the prepreg against the inner surface of the mold, and the heat curing of the resin in the fiber-reinforced resin yields a hollow molded product in the shape of the cavity.

[0032] If the silicone rubber tube is too narrow relative to the diameter of the internally molded product, excessive pressure load may be applied during expansion during internal molding, potentially causing the silicone rubber tube to rupture. Conversely, if the silicone rubber tube is too wide relative to the diameter of the internally molded product, the silicone rubber tube may not be able to expand sufficiently, potentially causing wrinkles in the internally molded product.

[0033] In this respect, the silicone rubber tube 10 of this embodiment is molded to conform to the shape of an internally molded product having portions of different diameters. When pressurized fluid is supplied to the silicone rubber tube 10 during internal pressure molding, it expands with a similar pressure load to the portions of different diameters. It easily conforms to the shape of the internally molded product. This can contribute to the efficient internal pressure molding of high-precision internally molded products.

[0034] According to this embodiment, the following effects can be obtained. (1) The silicone rubber tube 10 is formed by winding silicone 30 around a mandrel 20 having a small diameter section 21 and a large diameter section 22. Therefore, a silicone rubber tube 10 for forming internal pressure molded products having sections of different diameters can be manufactured with high precision in a single molding process. Furthermore, since large equipment is not required, it can be manufactured at low cost and the cycle time can be shortened.

[0035] (2) In the winding process, silicone 30 with a durometer A hardness of 15° to 39° is wound. Therefore, it is possible to follow the mandrel 20 which has a portion where the diameter changes. When the mandrel 20 is decored, the occurrence of tearing in the silicone rubber tube 10 is suppressed. Silicone rubber tubes 10 that conform to the shape of the internally molded product can be manufactured efficiently. In addition, silicone rubber tubes 10 with excellent strength and durability against pressure during internal pressure molding of hollow molded products can be manufactured efficiently.

[0036] (3) The axial cross-section of the dome portion 23 of the mandrel 20 is a curved surface that is convex outward with a radius of curvature R of 26 mm or more and 40 mm or less. Therefore, during the decoreization process, the small diameter portion 11 can easily follow the dome portion 23 of the mandrel 20, and tears or other damage to the silicone rubber tube 10 are less likely to occur.

[0037] (4) The ratio of the diameter D2 of the wide-diameter section 22 to the diameter D1 of the narrow-diameter section 21 of the mandrel 20 (D2 / D1) is less than 4.5. Therefore, during the decoreization process, the narrow-diameter section 11 of the silicone rubber tube 10 can easily stretch to about the diameter D2 of the wide-diameter section 12. Not only is decoreization of the mandrel 20 easy, but rupture of the silicone rubber tube 10 can also be suppressed.

[0038] (5) At the position of the parting line of the mold 50, grooves 54 and 55 are formed on the periphery of the cavity 53 of the mold 50, extending along the cavity 53. The grooves 54 and 55 form ribs 14 at positions corresponding to the parting line in the silicone rubber tube 10. As a result, the strength of the silicone rubber tube 10 at the parting line is improved during the decoreization process. The silicone rubber tube 10 is less likely to tear.

[0039] The above embodiment can be modified as follows. Note that the above embodiment and the following modifications can be combined and applied to the extent that they do not contradict each other technically. The shape of the silicone rubber tube 10 is not limited to that of the above embodiment. For example, in addition to the small diameter portion 11 and the large diameter portion 12, there may be portions of different diameters.

[0040] The silicone rubber tube 10 does not have to have a circular radial cross-section; it may have a square cross-section. The silicone rubber tube 10 does not necessarily need to have ribs 14 formed on it.

[0041] • In the winding process, the thin-diameter portion 21 and the thick-diameter portion 22 of the mandrel 20 may also be wound spirally with strips of silicone 30. • In the molding process, a mold 50 without grooves 54 and 55 may be used.

[0042] During the wrapping process, the silicone 30 may be wrapped so that it becomes thicker at the position that will become the parting line of the mold 50. The technical concept understood from the above embodiments is described below.

[0043] (i) A method for manufacturing a silicone rubber tube for internal pressure molding, comprising: a winding step of winding silicone stretched to a uniform thickness onto a mandrel to form a pre-form; a molding step of heating the pre-form in a mold to form a molding pre-form with a silicone rubber tube wound onto the mandrel; and a decore step of decore the mandrel from the molding pre-form, wherein in the winding step, a mandrel having a small diameter portion and a large diameter portion is used to wind silicone with an A hardness of 15° to 39°.

[0044] (b) The method for manufacturing a silicone rubber tube for internal pressure molding according to (a) above, wherein in the winding step, silicone stretched to a wall thickness of 1 mm or more and 2 mm or less is wound around to form the pre-form.

[0045] (h) A silicone rubber tube for internal pressure molding, having a narrow diameter section and a wide diameter section, and made of silicone with an A hardness of 15° to 39°. (ii) A silicone rubber tube for internal pressure molding as described in (iii), wherein a dome portion is formed between the small diameter portion and the large diameter portion, and when the direction in which the small diameter portion and the large diameter portion are aligned is the axial direction, the axial cross-section of the dome portion is a curved surface that is convex outward with a radius of curvature R of 26 mm or more and 40 mm or less.

[0046] (e) The silicone rubber tube described in (c) above, wherein the ratio of the diameter of the thicker portion to the diameter of the thinner portion is less than 4.5. [Examples]

[0047] The silicone rubber tube 10 of this embodiment will be described in more detail based on the following examples. However, the present invention is not limited to the configurations described in the Examples section. <Investigation of silicone hardness> (Example 1) Silicone was wrapped around a mandrel with narrow diameter sections formed at both ends of a large diameter section. The mandrel used had a large diameter section of 59.0 mm and a narrow diameter section of 14.3 mm. The ratio of the diameter of the large diameter section to the diameter of the narrow diameter section was 4.12. The axial cross-section of the dome section between the large and narrow diameter sections was a curved surface with a radius of curvature R35 mm and convex outward. The silicone used had a durometer A hardness of 20° (445AR, manufactured by Takehara Rubber Processing Co., Ltd.).

[0048] The silicone was stretched out to a thickness of 1 mm to 2 mm by pressing it, and then a preliminary model was created by wrapping the entire mandrel with the silicone. Sheets of silicone were wrapped around the large and small diameter sections of the mandrel, while thin sheets of silicone were spirally wrapped around the dome section.

[0049] A pre-molded mold was placed in a mold pre-set to 185°C and heated for 17 minutes to cure the silicone and obtain a molded pre-molded mold. The mold used had grooves extending along the cavity formed around the periphery of the cavity on the lower surface of the upper mold and the upper surface of the lower mold. After the mold cooled, the molded pre-molded mold was removed. The mandrel was decored from the molded pre-molded mold to obtain the silicone rubber tube of Example 1. Ten silicone rubber tubes of Example 1 were produced.

[0050] (Example 2) The silicone rubber tube in Example 2 is the same as in Example 1, except that the silicone used has a durometer A hardness of 30°.

[0051] (Comparative Example 1) The silicone rubber tube in Comparative Example 1 is the same as in Example 1, except that the silicone used has a durometer A hardness of 40°.

[0052] <Evaluation of silicone rubber tubing> (Evaluation during the molding process) As part of the evaluation during the molding process, we checked whether any molding defects had occurred in the molded prototype after the molding process. The evaluation during the molding process was as follows:

[0053] ○; No tears were found in the silicone rubber tubes of the molding prototypes in any of the 10 samples, and the external shape was good. △; In 1 to 5 out of 10 samples, no tears were found in the silicone rubber tubes of the molded prototypes, and the external shape was good.

[0054] (Evaluation during the decore removal process) As part of the evaluation of the decoreization process, we confirmed whether it was possible to decore the mandrel. The evaluation of the decoreization process is as follows:

[0055] ◎; All 10 cores could be removed. ○; It was possible to remove the lead from 6 or more out of 10 pencils. △; It was possible to remove the lead from 1 to 5 out of 10 pencils.

[0056] ×; I was unable to remove the lead from any of the 10 tubes. The results of the silicone hardness study are shown in Table 1.

[0057] [Table 1] Table 1 shows that all silicones with durometer A hardness of 20°, 30°, and 40° were successfully wrapped around the mandrel and molded, and no rupture occurred in the resulting silicone rubber tubes. On the other hand, with a durometer A hardness of 40°, the elasticity of the silicone rubber tube was insufficient, and the silicone rubber tube got caught in the dome section, preventing decore removal.

[0058] <Consideration of ribs in the parting line> (Comparative Example 2) The mold used was the same as in Example 1, except that grooves extending along the cavity were not formed on the lower surface of the upper mold and the upper surface of the lower mold. The evaluation results for Example 1 and Comparative Example 2 are shown in Table 2.

[0059] [Table 2] The results in Table 2 show that when a groove extending along the cavity is formed at the parting line of the mold, the silicone rubber tube is less likely to tear after molding, and the external shape is good. Also, when ribs are formed on the silicone rubber tube of the molded prototype, decore removal is performed well. On the other hand, when no groove is formed in the mold, tears are observed in the silicone rubber tube at the parting line during molding. Furthermore, when no ribs are formed on the silicone rubber tube, even if no tears occur during molding, the parting line becomes weaker, and tears may occur during decore removal.

[0060] <Examination of the radius of curvature of the axial cross-section of the dome section> (Comparative Example 3) The procedure was the same as in Example 1, except that the mandrel used had a curved surface with a radius of curvature R of 25 mm in the axial cross-section of the dome section. The evaluation results for Example 1 and Comparative Example 3 are shown in Table 3.

[0061] [Table 3] Table 3 shows that when the radius of curvature R of the axial cross-section of the dome section was 35 mm, winding onto the mandrel and molding were good, and no tears occurred in the resulting silicone rubber tube. Decorening was also performed well. On the other hand, when the radius of curvature R was 25 mm, molding was good, but the narrow diameter section of the silicone rubber tube did not easily conform to the shape of the dome section of the mandrel, and tears sometimes occurred.

[0062] <Examination of the outer diameter ratio between the large diameter section and the small diameter section> (Comparative Example 4) The procedure was the same as in Example 1, except that a mandrel with a diameter of 67.3 mm in the large diameter section and a diameter of 14.8 mm in the small diameter section, and a diameter ratio (large diameter section / small diameter section) of 4.55 was used. The evaluation results for Example 1 and Comparative Example 4 are shown in Table 4.

[0063] [Table 4] The results in Table 4 show that when the ratio of the diameter of the large-diameter section to the small-diameter section was 4.12, winding onto the mandrel and molding were good, and no tears occurred in the resulting silicone rubber tubes. Decorening was also performed well. On the other hand, when the diameter ratio was 4.55, molding was good, but in some cases, decorening was not possible because the elongation of the silicone rubber tube could not keep up with the diameter of the large-diameter section.

[0064] <Consideration of silicone wall thickness> (Comparative Example 5) The procedure for creating the preliminary model is the same as in Example 1, except that the silicone was stretched to a thickness of less than 1 mm.

[0065] (Comparative Example 6) The procedure for creating the preliminary model is the same as in Example 1, except that the silicone was stretched to a thickness of more than 2 mm.

[0066] The properties of the silicone rubber tubes in Example 1 and Comparative Examples 5 and 6 were examined. As a result, the silicone rubber tube of Example 1, which was formed by winding silicone stretched to a wall thickness of 1 mm to 2 mm, showed satisfactory elongation and strength. On the other hand, the silicone rubber tube of Comparative Example 5 had sufficient elongation but weak strength, and sometimes ruptured during internal pressure molding. Furthermore, the silicone rubber tube of Comparative Example 6 was difficult to decore due to its poor elongation. [Explanation of Symbols]

[0067] D1, D2... diameter R…curvature radius 10…Silicone rubber tube 20… Mandrel 21...Narrow part 22…Large diameter part 23…Dome section 30…Silicone 40... Reserve 50…Mold 51...Upper mold 52…Lower mold 53... Cavity 54, 55...Groove 60…Preparation body for molding

Claims

1. A winding process in which silicone is wrapped around a mandrel to form a preliminary body, A molding process in which the pre-form is heated in a mold to form a molding pre-form with a silicone rubber tube wrapped around the mandrel, A decorening step in which the mandrel is decored from the molded pre-form Equipped with, A method for manufacturing a silicone rubber tube for internal pressure molding, wherein in the winding step, a mandrel having a small diameter section and a large diameter section is used to wind silicone having an A hardness of 15° to 39°.

2. The method for manufacturing a silicone rubber tube for internal pressure molding according to claim 1, wherein in the winding step, a dome portion is provided between the small diameter portion and the large diameter portion, the diameter of which changes continuously, and the axial cross-section of the dome portion is a curved surface that is convex outward with a radius of curvature R of 26 mm or more and 40 mm or less.

3. The method for manufacturing a silicone rubber tube for internal pressure molding according to claim 1, wherein in the winding step, the mandrel is used in which the ratio of the diameter of the thicker portion to the diameter of the thinner portion is less than 4.

5.

4. A method for manufacturing a silicone rubber tube for internal pressure molding according to any one of claims 1 to 3, wherein in the molding step, a cavity in the shape of the molding pre-form is formed, and a mold comprising an upper mold and a lower mold is used, wherein grooves extending along the cavity are formed on the periphery of the cavity on the lower surface of the upper mold and the upper surface of the lower mold.

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