JP3121659B2 - Core support method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of supporting a core when a tubular body is formed by injection molding.

[0002]

2. Description of the Related Art For example, an oil filler pipe of an automobile is often formed into a curved curved tube.
A core that can be extracted through the openings at both ends of the molded body after molding cannot form a curved inner shape. On the other hand, for example, JP-A-2-263610 discloses a method of forming a curved tubular body by forming a core with a soluble material such as a low-melting point metal. That is, as shown in FIG. 10, for example, a curved core 53 made of a fusible material is formed, and skirting boards 53a and 53b at the upper and lower ends of the core 53 are sandwiched by the molding dies 51 and 52. Then, the space 54 between the core 53 and the mold surfaces 51a and 52a of the molding dies 51 and 52 is filled with a product resin and cured. Thereafter, the molds 51 and 52 are opened, the molded product is taken out together with the core 53, and the core 53 made of a fusible material is dissolved and removed, whereby a curved tubular body can be formed.

[0003]

However, when the method disclosed in the above publication is adopted to form a tubular body by injection molding, a core made of a soluble material such as a low melting point material is used. Since the rigidity of the core 53 is usually not so large, the core 53 is easily deformed in the molding die by an injection pressure when the product resin is injected into the molding die. Variations occur, causing a problem that sufficient shape accuracy cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to form a tubular body having good shape accuracy even when a core having low rigidity is used. At the same time, without impairing the appearance
Another object of the present invention is to provide a core supporting method that can improve workability.

[0005]

According to a first aspect of the present invention, there is provided a method of supporting a core, wherein a tubular body is formed by injection molding using a core made of a fusible material. In the method of supporting the core, when having a melting point equal to or slightly lower than the temperature of the product resin injected into the molding die, and a gap member made of a material of the same system as the product resin, the outer peripheral surface of the core It is formed in accordance with the gap dimension between the mold and the mold surface, and the gap member is externally fitted at a position between the baseboard portions at both ends in the axial direction of the core.

According to a second aspect of the present invention, there is provided the core supporting method according to the first aspect, wherein the gap member has a plurality of openings penetrating in a flow direction of the product resin in the molding die. It is characterized in that the aperture ratio is changed in the circumferential direction.

According to a third aspect of the present invention, there is provided the core supporting method according to the first or second aspect, wherein the gap member is formed in a spiral shape.

[0008]

According to the core supporting method of the first aspect of the present invention, the core has a gap member externally fitted at a position between the skirting portions at both ends of the core. Since it functions to maintain the gap between the cores, deformation of the core due to the injection pressure of the product resin is suppressed, whereby a tubular body with reduced wall thickness fluctuation and good shape accuracy can be formed. In addition, the above-mentioned gap member is embedded in the injected product resin, which has a melting point equal to or slightly lower than the product resin temperature at the time of injection, and is made of a material of the same family as the product resin. As a result, the surface in contact with the product resin is partially melted and hardened together with the product resin, thereby forming an integrated state without a boundary line with the product resin, thereby suppressing a reduction in appearance. You.

According to the core supporting method of the present invention, when the product resin is filled into the mold through the opening of the gap member, the flow speed is changed in the opening ratio in the circumferential direction. Will be adjusted accordingly. In other words, in general, the flow rate of the product resin is higher on the side closer to the injection port of the product resin than the distant side with the core interposed therebetween. Acts as a force to push the core, which causes the core to bend and deform. Therefore,
By changing the opening ratio of the opening so as to adjust the flow resistance when passing through the gap member so that the above-mentioned flow speed becomes uniform across the core, uniform flow occurs in the circumferential direction. As a result, the deformation of the core is further reduced, and the shape accuracy of the formed tubular body is improved.

According to the core supporting method of the third aspect, since the gap member is formed in a helical shape, elastic deformation is also caused in the axial direction between both ends in the circumferential direction, so that
That the spread exceeding the outer diameter of the core occurs,
It can be performed relatively easily without the need for excessive force. As a result, it is possible to easily attach the gap member to the predetermined attachment position of the core from the side, thereby improving workability.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the apparatus for molding a synthetic resin tubular body according to this embodiment is provided with a fixed mold 2 and a movable mold 1 that can be brought into contact with and separated from the fixed mold 2. Mold 1 ・
For example, a space (hereinafter, referred to as a tubular body forming cavity) 9 corresponding to the external shape of the curved tubular body along the S-shape is formed on the mating surface of the two. An S-shaped core 3 is provided in the tubular body forming cavity 9 along the inner shape of the tubular body.

The core 3 is formed, for example, by molding a water-soluble resin such as Belland polymer (trade name, manufactured by Belland USA) into the above shape. this is,
Even after molding as the core 3 as described above, the core 3 is dissolved by immersion in water.

The core 3 has upper and lower ends,
Baseboard portions 3a and 3 projecting from tubular body molding cavity 9
The core 3 is inserted into the tubular body forming cavity 9 by fitting these baseboard portions 3a and 3b into fitting recesses 5 and 6 formed in the molds 1.2. Is fixed in a state of penetrating through.

Further, support rings 7.7 serving as gap members are externally fitted to the core 3 at two portions located inside the tubular body forming cavity 9. These support rings 7 are made of a resin of the same system as a later-described product resin that is injection-molded into the tubular body molding cavity 9 and have compatibility with the product resin, and have the same or slightly higher injection temperature as the product resin. It has a low melting point. As an example of a specific material, when the product resin is a nylon resin containing glass fibers, the support ring 7 is made of the same type of nylon resin containing no glass fibers.

As shown in FIGS. 2 to 4, the support ring 7 is a cylindrical body having a short axial length, and a part thereof is cut away in the axial direction. The support ring 7 is provided with a plurality of through-holes (openings) 7b penetrating between both end surfaces in the axial direction, and is arranged circumferentially over substantially the entire circumference except for the notch 7a. .

The support ring 7 is formed such that its inner diameter matches the outer diameter of the core 3. The support ring 7 is fitted to the outer periphery of the core 3 from the side by expanding the notch 7 a. . The outer diameter of the support ring is formed according to the outer diameter of the tubular body to be molded. Therefore, as shown in FIG. 1, the outer peripheral surface of the support ring 7 abuts on the mold surfaces 1 a and 2 a of the molds 1 and 2 in the clamped state, and as a result, the core 3 and the molds 1 and 2 Gap 4 between surfaces 1a and 2a
The core 3 is also supported in the tubular body molding cavity 9 so that it is maintained by the support rings 7.

With the core 3 disposed as described above, a product resin such as nylon mixed with glass fiber is injected into the tubular molding cavity 9 from a lower injection port (not shown). The product resin is located at each of the support rings 7
The fluid flows upward through the notch 7a and the through-holes 7b and is filled in the space inside the tubular body forming cavity 9.
When the product resin filled in this way cures,
The mold is opened, and the formed tubular article is taken out together with the core 3. Then, this is immersed in running water to dissolve and remove the core 3 made of a water-soluble resin, thereby producing a tubular body having a predetermined inner and outer shape.

In the above molding process, when the product resin is filled into the tubular body molding cavity 9, the core 3
Is supported by the support rings 7, 7,
Even when the bending rigidity of the core 3 made of a water-soluble resin is low, the core 3 is prevented from being deformed in the tubular body molding cavity 9 by the injection pressure. That is, the core 3 and the mold surface 1
The gap 4 with a.2a is maintained, whereby a tubular body having a uniform thickness throughout is formed.

The support rings 7.7 are embedded in the filled product resin. As described above, the support rings 7.7 are compatible with the product resin and are not injected. Since the support ring 7 is made of a resin having a melting point equal to or slightly lower than the temperature, the surface of the support ring 7 in contact with the product resin is partially melted, and then hardened together with the product resin. This results in an embedded state in which the product resin is in an integrated state without a boundary line. As a result, in particular, a tubular body in which the deterioration of appearance is suppressed as much as possible is formed.

Note that the injection pressure of the product resin is large, so that the mounting position of the support ring 7 is shifted by the product resin flowing in the tubular body molding cavity 9 so that the support state of the core 3 becomes unstable. In such a case, as shown in FIG.
A step 3a having a width corresponding to the height of the support ring 7 and having a width of, for example, about 0.5 mm is provided on the outer periphery of the core 3, and the support ring 7 is fitted at the position of the step 3a. Can also. Thus, the displacement of the mounting position of the support ring 7 as described above is prevented, and the immovable state of the core 3 can be made more reliable.

Also, through holes 7b provided in the support ring 7 are provided.
By providing various shapes in the circumferential direction,
It is possible to adjust the flow state of the product resin in the tubular body molding cavity 9. For example, in FIG. 1, when a product resin is injected from the side of the fixed mold 2 to the lower end side in the tubular body molding cavity 9, this resin is injected on the mold surface 2 a side of the fixed mold 2 close to the injection side. It rises faster than the mold surface 1a side of the movable mold 1 far from the injection side. Therefore, a force acting on the core 3 in a direction toward the movable mold 1 is exerted by the product resin flowing into the space on the fixed mold 2 side.

Therefore, the shape and arrangement of the through-holes 7b are set so that a larger flow resistance is generated on the fixed mold 2 side than on the movable mold 1 side when flowing through the support ring 7. As a result, the rising level of the resin becomes uniform in the circumferential direction, and the generation of the above-described force is suppressed. As a result, deformation of the core 3 is further suppressed, so that a product with better shape accuracy can be obtained.

On the other hand, in place of the above-mentioned support ring 7, FIG.
It is also possible to use a second form of support ring 8 having the shape shown in FIG. This is formed by providing a ring portion 8b thinner than the gap 4 on the inner peripheral side, and providing protrusions 8a at appropriate intervals on the outer peripheral surface thereof. The outer surfaces of the projections 8a are shaped along a cylindrical surface that comes into contact with the mold surfaces 1a and 2a of the molds 1.2. In this support ring 8, a flow path for product resin corresponding to the through hole 7b of the support ring 7 is formed between the projections 8a. In this case, it is necessary to provide a difference in the flow resistance of the product resin in the circumferential direction as described above, as shown in FIG.
By changing the distance between a and 8a, the shape and arrangement of the through-holes 7b in the support ring 7 can be changed to a simpler shape, so that it can be manufactured at lower cost. .

In order to fit the cylindrical support rings 7 and 8 to the core 3 from the side as described above, a part of the core 3 is cut out, and the cutout is formed in the outer diameter of the core 3. Must be spread out until it exceeds, but if it is formed of a hard material with poor elasticity, an excessive force is required to spread it out, and the mounting work becomes complicated, or the notch It is necessary to make the shape with a larger width. In this case, the flow resistance cannot be adjusted at the notch.

Therefore, instead of the cylindrical support rings 7 and 8 described above, a third form of support ring 21 formed in a spiral shape as shown in FIGS. 7 and 8 can be used. According to this structure, even if the distance between both ends in the circumferential direction is reduced, the distance between the both ends is expanded in the circumferential direction and expanded in the axial direction, so that the insertion gap corresponding to the outer diameter of the core 3 is excessively large. It can be obtained relatively easily without applying great force. Therefore, the problems with the cylindrical support rings 7 and 8 described above are eliminated, and in particular, the work of attaching the core 3 to the predetermined attachment position from the side can be easily performed.

The support ring 21 of the third embodiment is
As shown in FIG. 9, a configuration is also provided in which hemispherical projections 22 are provided at appropriate intervals on the outer surface of the spiral band portion 21a on the inner surface side. In this case, the apexes of the projections 22 are in point contact with the mold surfaces 1a, 2a of the molds 1, 2 to support the core 3. As an example of the specific shape and dimensions, the width of the strip 21a is 5 mm, the thickness is 1 mm, the diameter of the projection 22 is 3 mm, and the tip is formed in a hemispherical shape with a radius of 1.5 mm. .

Only the apexes of the projections 22 are exposed on the outer peripheral surface of the tubular body formed by using the above-mentioned support ring 21. As a result, almost no trace remains on the surface. Appearance is further improved. Further, in the spiral-shaped support ring 21, as described above, the distance between both ends in the circumferential direction can be reduced. Therefore, as shown in FIG. It can be provided over almost the entire circumference. As a result, the flow state can be adjusted over substantially the entire circumference of the core 3, so that the force for deforming the core 3 in the bending direction is further reduced, whereby the tubular body having a more uniform thickness is obtained. Can be molded.

In the above embodiment, the case where nylon resin is used for the product resin and the support ring has been described as an example. For example, polypropylene is used as the product resin, and the support ring at this time is made of polyethylene. Other combinations, such as forming, can be employed.

[0030]

As described above, the core supporting method according to the first aspect of the present invention has a melting point equal to or slightly lower than the temperature of the product resin injected into the molding die, and has the same melting point as the product resin. A gap member made of a material of the system is formed in accordance with the gap dimension between the outer peripheral surface of the core and the mold surface of the molding die. It fits in the position between.

Thus, the core is supported by the gap members at positions between the baseboard portions at both ends thereof, so that deformation of the core due to the injection pressure of the product resin is suppressed, and as a result, wall thickness fluctuations are suppressed. It is possible to mold a tubular body having reduced shape accuracy. In addition, since the gap member that is embedded in the product resin is in an integrated state without a boundary line with the product resin, it is possible to suppress an external appearance from being deteriorated.

According to a second aspect of the present invention, in the core supporting method, the gap member is provided with a plurality of openings penetrating in the flow direction of the product resin in the molding die while changing the opening ratio in the circumferential direction. .

As a result, the flow state of the product resin can be made uniform in the circumferential direction around the core, so that the deformation of the core can be further reduced, and the shape accuracy of the formed tubular body can be further improved. It works.

In the core supporting method according to the third aspect,
The gap member is formed in a spiral shape.

Thus, an excessive force is required to cause the expansion beyond the outer diameter of the core by elastically deforming in the axial direction between both ends in the circumferential direction of the gap member. As a result, it is possible to easily externally fit the core at a predetermined mounting position from the side, so that it is possible to improve the workability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a molding apparatus showing an arrangement state of a core with a support ring externally fitted thereto according to an embodiment of the present invention.

FIG. 2 is a perspective view of the support ring.

FIG. 3 is a plan view of the support ring.

FIG. 4 is a front view of the support ring.

FIG. 5 is an enlarged cross-sectional view of a mounting portion to a core adopting the support ring displacement prevention structure.

FIG. 6 is a perspective view of a second embodiment of a support ring used in the molding apparatus.

FIG. 7 is a perspective view of a third embodiment of a support ring used in the molding apparatus.

FIG. 8 is a plan view of a support ring according to the third embodiment.

FIG. 9 is an enlarged sectional view of a support ring according to the third embodiment.

FIG. 10 is a cross-sectional view of a main part of a molding apparatus showing a state in which a core is provided when a conventional tubular body is molded.

[Explanation of symbols]

 1.2 Mold (molding mold) 1a ・ 2a Mold surface 3 Core 3a ・ 3b Skirting part 7.8 ・ 21 Support ring (gap member) 7b Through hole (opening)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-38733 (JP, A) JP-A-64-51914 (JP, A) JP-A-3-39220 (JP, A) 72506 (JP, A) JP-A-60-223640 (JP, A) JP-A-56-34363 (JP, A) JP-A-5-169470 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/26-45/44 B29C 33/00-33/76

Claims (3)

(57) [Claims] In a core supporting method for molding a tubular body by injection molding using a core made of a soluble material, the core has a melting point equivalent to or slightly lower than the temperature of a product resin injected into a molding die. And, a gap member made of a material of the same system as the product resin is formed in accordance with the gap dimension between the outer peripheral surface of the core and the mold surface of the mold, and the gap member is formed in the axial direction of the core. A method for supporting a core, wherein the core is fitted to a position between the baseboard portions at both ends. 2. The core according to claim 1, wherein the gap member is provided with a plurality of openings penetrating in a flow direction of the product resin in the molding die with an opening ratio being changed in a circumferential direction. Support method. 3. The core supporting method according to claim 1, wherein said gap member is formed in a spiral shape.