JP2009006697A - Method of manufacturing duct - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thin and high strength inner duct the cross sectional area of which are of approximately the same at the body and the end or greater with the body. <P>SOLUTION: The inner duct is produced from a thermoplastic resin such as PET or PEN by stretch blow molding. More specifically, the manufacturing method comprises molding the resin into a cylindrical preform 20 in which the larger diameter parts 20a at the ends are narrowed down to the middle part 20b in the cross sectional area, heating the preform 20 and blowing high pressure gas into the inside of the preform 20. In the stretch blow process, the cross sectional area of the middle part 20b narrowed in the molded preform 20 is stretch blow-molded in the radial direction until it becomes approximately the same as that of the larger diameter parts 20a. The manufacturing method can be suitably used for producing an inner duct with a thin wall and yet a high strength. Since the resultant molding does not have a bottom, no additional step to cut off the bottom is required and no waste is produced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a duct for flowing a fluid such as air.

In recent years, there has been an increasing demand for noise reduction in automobiles, and the intake noise generated by the intake pulsation of the engine is also the subject. As a technique for reducing this intake noise, the present applicant has proposed a silencer duct that is attached to an intake duct of an engine (see Patent Document 1).
This silencer duct has a body part to be silenced and a fastening part (both ends) to which a hose is attached, the body part is made of a thin film, and the fastening part is made of a thick wall.
Conventional ducts are generally manufactured by direct blow molding. Direct blow molding is a method in which a cylindrical parison made of a thermoplastic material is sandwiched between molds and blown into the interior by pressurized air.

However, the silencer duct is difficult to manufacture by direct blow molding because the thickness of the body portion is as thin as 0.5 mm or less. That is, in direct blow molding, it is possible to change the thickness of the molded product by well-known parison control, but if the thickness of the parison is adjusted so that the thickness of the molded product is 0.5 mm or less, the parison However, it is difficult to actually form a thin film of 0.5 mm or less.
In direct blow molding, since a bottomed portion is formed when the parison is clamped, it is necessary to cut a bottomed portion unnecessary as a duct in a subsequent process. As a result, waste materials are generated, and equipment costs required for subsequent processes are factors that increase product costs.
Therefore, as shown in Patent Document 2, a cylindrical parison (preform) penetrating in the axial direction is stretched, and air is supplied to the inside to bulge out the hollow peripheral wall portion to form a cylindrical body such as a pipe. A method for producing is known.
Japanese Patent Application No. 2007-119651 JP-A-5-154896

However, in the known technique disclosed in the above-mentioned Patent Document 2, the diameter of the central part is smaller than the diameter of the opening of both ends of the parison having a pipe shape before stretch blow molding. In the case of using a material such as PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) that can be stretched, it is hardly stretched in the radial direction even if blow-molded. Can not.
In other words, like a duct, a cylindrical body having a cross-sectional area of the opening at both ends and a cross-sectional area of the central portion (body portion) is substantially equal, or the cross-sectional area of the body portion is larger than the openings at both ends. In the case of manufacturing by stretch blow molding, the known technique disclosed in Patent Document 2 cannot increase the strength even if a material such as PET or PEN is used.
The present invention has been made based on the above circumstances, and its purpose is to have a cross-sectional area in which the opening at both ends and the body part are substantially equal, or the body part has a larger cross-sectional area than the openings at both ends. In the duct which has this, it is providing the manufacturing method of a duct with a thin wall thickness and high intensity | strength.

(Invention of Claim 1)
The present invention includes a preform molding process for molding a preform having a cylindrical shape in which both end portions are open and a cross-sectional area is smaller at the center portion than both end portions, and the molded preform is heated. A method of manufacturing a duct that is manufactured through a heating process and a stretch blow process in which a heated preform is stretch blow molded in an axial direction and a radial direction, and a material used when molding the preform is A thermoplastic material whose strength is increased by stretching, and the central portion of the preform is bundled by an amount that can ensure a predetermined strength by stretching, and in the stretch blow process, the preform is molded. Stretch blow molding is performed in the radial direction until the cross-sectional area of the central portion is equal to or greater than the cross-sectional area of both end portions.

According to the present invention, since the thickness can be reduced by stretch blow molding the preform, it is not necessary to reduce the thickness of the preform more than necessary at the stage of molding the preform. As a result, it is possible to manufacture a duct having a thin film (for example, a thickness of 0.5 mm or less), which is difficult with direct blow molding. In addition, a duct with high strength can be obtained by performing stretch blow molding in the axial direction and the radial direction until the cross-sectional area of the central part is equal to or larger than the cross-sectional area of the both end parts from the preform with the central part constricted with respect to both end parts. Can be manufactured.
The meaning of “strength is increased by stretching” means that a duct manufactured by a method that does not include a stretch blow step when manufacturing a duct having the same thickness from the same material, and the duct of the present invention. That is, it means that the duct of the present invention can obtain higher strength when compared with a duct produced by a method including a stretch blow process.

In addition, “the amount that can secure a predetermined strength by stretching is bundled” means that the center portion of the preform is bundled by an amount that can be stretched to the required magnification for the material that increases the strength by stretching. Say that.
In addition, in the “stretch blow process, stretch blow molding is performed in the radial direction until the cross-sectional area of the central portion that is bundled at the stage of forming the preform is equal to or greater than the cross-sectional area of both end portions”. Needless to say, it includes those that are stretch blow molded in the radial direction until the cross-sectional area becomes substantially equal to or larger than the cross-sectional area.

(Invention of Claim 2)
In the duct manufacturing method according to claim 1, in the stretch blow step, both ends of the preform formed into a cylindrical shape are gripped and stretched in the longitudinal direction, and then high-pressure gas is introduced into the stretched preform. It is characterized by being blown and inflated in the radial direction.
According to the present invention, since a cylindrical preform having both ends opened is stretch blow molded, a bottomed portion does not occur in the molded product. Thereby, post-processing for cutting the bottomed portion is unnecessary, and no waste material is generated.

(Invention of Claim 3)
In the duct manufacturing method according to claim 1, in the stretch blow step, high-pressure gas is blown into the preform while holding both ends of the preform formed into a cylindrical shape and stretched in the longitudinal direction. It is characterized by inflating.
According to the present invention, since a cylindrical preform having both ends opened is stretch blow molded, a bottomed portion does not occur in the molded product. Thereby, post-processing for cutting the bottomed portion is unnecessary, and no waste material is generated.

(Invention of Claim 4)
The duct manufacturing method according to claim 2 or 3, wherein the duct has a central portion which is bundled at a stage where the preform is formed, is stretched in a longitudinal direction by a stretch blow process, and is expanded in a radial direction. The thickness of the body portion is thinner than the thickness of both end portions in the longitudinal direction.
Since the thickness of both ends of the duct can be made thicker than the thickness of the body portion, when connecting a hose or the like to the duct, the strength of both ends of the duct serving as a fastening portion can be secured. Further, by reducing the thickness of the body part, the weight of the duct can be reduced.

(Invention of Claim 5)
The method for manufacturing a duct according to any one of claims 1 to 4, wherein the thermoplastic material whose strength is increased by stretching is PET (polyethylene terephthalate) or PEN (polyethylene naphthalate).
PET or PEN can be used as an example of a thermoplastic material whose strength increases by stretching.

  The best mode for carrying out the present invention will be described in detail with reference to the following examples.

FIG. 1A is a longitudinal sectional view of the inner duct 2 used in the silencer 1, and FIG. 1B is a radial sectional view (AA sectional view) of the inner duct 2.
The silencer 1 of the present embodiment has a function of reducing intake noise of the internal combustion engine, for example, and as shown in FIG. 2A, an inner duct 2 that forms a part of the intake passage of the internal combustion engine, The outer duct 3 is arranged outside the inner duct 2 via an air layer.
As shown in FIG. 1B, the inner duct 2 includes a body portion 2A in which a cross-sectional shape perpendicular to the air flow direction is formed in a circle, and a longitudinal direction of the body portion 2A as shown in FIG. It has a duct end 2B that forms openings at both ends in the direction, and the cross-sectional area of the body 2A and the cross-sectional area of the duct end 2B are formed substantially the same.

The body portion 2A has a thickness of 0.5 mm or less, preferably 0.2 mm.
The duct end 2B is provided as, for example, a fastening portion for connecting a hose or the like to the inner duct 2, and the thickness thereof is set to be thicker (for example, 2 mm) than the thickness of the body portion 2A. One duct end 2B is connected to an outlet of an air cleaner (not shown), for example, and the other duct end 2B is connected to an inlet of a throttle body (not shown), for example.
The inner duct 2 is manufactured by stretch blow molding described later.
As shown in FIG. 2 (b), the outer duct 3 is configured by combining a pair of half-cracked ducts having a semicircular arc-shaped cross-sectional shape, and both the duct ends 2B of the inner duct 2 are sandwiched therebetween. The flange portions 3a provided in the half crack duct are fixed together.

Next, a method for manufacturing the inner duct 2 according to the present invention will be described with reference to FIGS.
(A) Preform molding step: For example, the preform 20 is molded by injecting a molten thermoplastic material into a mold by a known injection molding method. As shown in FIG. 3A, the preform 20 includes both a large diameter portion 20a that forms the duct end portion 2B after molding, and a central portion 20b that has a smaller sectional area than the large diameter portion 20a. The large-diameter portion 20a and the central portion 20b are provided with a tapered portion 20c.
As shown in FIGS. 2B and 2C, the central portion 20b and the large-diameter portion 20a each have a circular cross-sectional shape, and the central portion 20b has a cross-sectional area that is larger than that of the large-diameter portion 20a. It is formed small. That is, the preform 20 is formed into a drum-shaped cylindrical shape in which the central portion 20b is constricted via the tapered portion 20c with respect to the large diameter portion 20a.
As the thermoplastic material, a material whose strength is increased by stretching, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or the like is used.
(B) Heating step: As shown in FIG. 4, the molded preform 20 is heated to an appropriate temperature.

(C) Stretching step: As shown in FIG. 5, the upper mold 4 and the lower mold 5 hold both large diameter portions 20a of the preform 20 and stretch them in the longitudinal direction (the vertical direction in the figure). At this time, for example, in a state where the lower large-diameter portion 20a of the preform 20 is fixed by the lower mold 5, the upper mold 4 is pulled upward in the figure (in the direction of the arrow), and the upper large-diameter portion 20a of the preform 20 is raised. By pulling, the central portion 20b and the tapered portion 20c are stretched in the longitudinal direction to form a thin wall. In addition, the upper mold | type 4 and the lower mold | type 5 have closed the opening surface of the large diameter part 20a in the state which hold | gripped the large diameter part 20a of the preform 20, respectively.
(D) Blow molding step: As shown in FIG. 6 (a), the mating die 6 for blow molding is sandwiched between the upper die 4 and the lower die 5 and arranged on the outer periphery of the tapered portion 20c and the central portion 20b. After that, for example, high pressure gas is blown into the preform 20 from the blow hole 5 a provided in the lower mold 5. As a result, as shown in FIG. 6B, the body portion 2A of the inner duct 2 is formed by extending in the radial direction until the tapered portion 20c and the central portion 20b are in close contact with the inner peripheral surface of the mating die 6. .

(Effect of Example)
In the duct manufacturing method described in the present embodiment, the inner duct 2 having high strength can be manufactured by using a thermoplastic material (PET, PEN) whose strength increases by stretching. That is, the drum-shaped preform 20 in which the central portion 20b is constricted with respect to the large-diameter portion 20a extends in the axial direction and the radial direction until the cross-sectional area of the central portion 20b is substantially the same as the cross-sectional area of the large-diameter portion 20a. By performing blow molding, a large stretching ratio in the radial direction can be obtained, so that the body portion 2A having high strength can be formed.

  Moreover, since the inner duct 2 of the present embodiment is manufactured by stretch blow molding, the thickness of the body portion 2A can be reduced to 0.5 mm or less. That is, by stretching the preform 20 in the longitudinal direction by the stretching process shown in FIG. 5, the thickness of the central portion 20b (the part where the body portion 2A is finally formed) can be reduced, so the preform 20 is molded. It is not necessary to make the thickness of the preform 20 thinner than necessary at the stage. As a result, it is possible to manufacture the inner duct 2 having the body portion 2A having a thickness of 0.5 mm or less, which is difficult with the conventional direct blow molding.

Further, since the outer peripheral surface of the large-diameter portion 20a of the preform 20 is held by the upper mold 4 and the lower mold 5 when blow molding is performed, the large-diameter portion 20a is radially aligned when high pressure gas is blown. Does not bulge outside. That is, the thickness of the large-diameter portion 20a is not reduced by blow molding, and can be thicker than the body portion 2A formed by extending in the radial direction and the axial direction. 2B strength can be secured.
Further, in the above manufacturing method, since the drum-shaped preform 20 having both ends opened is stretch blow molded, a bottomed portion does not occur in the molded product. As a result, post-processing for cutting the bottomed portion is unnecessary, and no waste material is generated.

7A is a longitudinal sectional view of the inner duct 2, FIG. 7B is a sectional view of the body portion 2A (EE sectional view), and FIG. 7C is a sectional view of the duct end portion 2B (F). -F sectional view).
In the first embodiment, an example of the inner duct 2 having a circular cross section is described. However, the inner duct 2 having a polygonal cross section (for example, a hexagon) as shown in FIG. Can also be manufactured.
When this inner duct 2 is used in the silencer 1 described in the first embodiment, each plane portion constituting the polygon forms a vibration surface that vibrates due to the generation of the intake sound, and the thickness of the vibration surface. Is set to 0.5 mm or less, preferably 0.2 mm. In addition, the manufacturing process of the inner duct 2 is the same as that of the first embodiment, and has a preform molding process → heating process → stretching process → blow molding process, and in the stretching process, the central portion 20b of the preform 20 is in the axial direction. And the inner duct 2 having high strength can be manufactured by stretching in the radial direction.
Further, in the manufactured inner duct 2, the cross-sectional area S1 of the body portion 2A and the cross-sectional area S2 of the duct end portion 2B are formed substantially the same.

(Modification)
In the method for manufacturing the inner duct 2 described in the first and second embodiments, the inner duct 2 is manufactured by stretch blow molding from a cylindrical preform 20 having both ends open, but at least one end side is closed. The inner duct 2 can be manufactured by cutting the bottomed portion after carrying out stretch blow molding from the shaped preform 20.
Moreover, in Example 1 and Example 2, although the blow molding process is implemented after the extending process, it is also possible to perform the extending process and the blow molding process simultaneously. That is, it is possible to blow the high-pressure gas into the preform 20 and expand it in the radial direction while holding the large-diameter portion 20a of the preform 20 and extending it in the longitudinal direction.

Moreover, in Example 1 and Example 2, it shape | molds so that the cross-sectional area after shaping | molding of the center part 20b which the preform 20 is constricted may become substantially the same as the cross-sectional area of both ends (large diameter part 20a). However, you may shape | mold so that the cross-sectional area of the said center part 20b may become larger than the cross-sectional area of both ends (large diameter part 20a).
The duct manufacturing method of the present invention is not limited to the manufacturing of the inner duct 2 used in the silencer 1, and the duct manufacturing method used for various applications such as an air duct and an exhaust duct for air conditioning. It can also be applied to.

(A) Longitudinal sectional view of the inner duct, (b) Radial sectional view (AA sectional view) of the inner duct (Example 1). (A) Longitudinal sectional view of the silencer, (b) Radial sectional view (BB sectional view) of the silencer (Example 1). (A) Longitudinal cross-sectional view of preform, (b) Cross-sectional view of central portion of preform (CC cross-sectional view), (c) Cross-sectional view of large-diameter portion of preform (DD cross-sectional view) is there. It is explanatory drawing of a heating process. It is explanatory drawing of an extending process. It is explanatory drawing of a blow molding process. (A) Longitudinal sectional view of the inner duct, (b) Cross sectional view of the body part (EE sectional view), (c) Cross sectional view of the duct end part (FF sectional view) (Example 2) .

Explanation of symbols

2 Inside duct (duct)
2A Body of inner duct 2B Duct end 20 Preform

Claims (5)

A preform molding step for molding a preform having a cylindrical shape that is narrowed so that the cross-sectional area is smaller at the center than at both ends while opening both ends,
A heating step of heating the molded preform;
A duct manufacturing method that is manufactured through a stretch blow process in which a heated preform is stretch blow molded in an axial direction and a radial direction,
The material used when molding the preform is a thermoplastic material whose strength increases by stretching,
The center portion of the preform is bundled by an amount that can ensure the predetermined strength by stretching,
In the stretch blow step, the duct is characterized in that stretch blow molding is performed in the radial direction until the cross-sectional area of the central portion bundled at the stage of forming the preform is equal to or greater than the cross-sectional area of both end portions. Production method. In the manufacturing method of the duct according to claim 1,
In the stretch blow step, the both ends of the preform formed into a cylindrical shape are gripped and stretched in the longitudinal direction, and then a high pressure gas is blown into the stretched preform to expand in the radial direction. A method for manufacturing a duct. In the manufacturing method of the duct according to claim 1,
In the stretching blow step, a duct characterized by inflating in the radial direction by blowing high-pressure gas into the preform while grasping both ends of the preform formed into a cylindrical shape and stretching the preform in the longitudinal direction. Production method. In the manufacturing method of the duct according to claim 2 or 3,
In the duct, the central portion that is bundled at the stage of forming the preform is stretched in the longitudinal direction by the stretch-blow process and is expanded in the radial direction to form a body portion, and the thickness of the body portion is increased. Is formed thinner than the thickness of both end portions in the longitudinal direction. In the manufacturing method of the duct in any one of Claims 1-4,
The said thermoplastic material which intensity | strength increases by extending | stretching is PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), The manufacturing method of the duct characterized by the above-mentioned.

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