JP2002178335A - Air vent structure of mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the novel air vent structure of a mold hard to generate air vent failure. SOLUTION: The air vent structure is formed so as to communicate with the cavity of a mold for a polymeric material molded article and equipped with a first vent passage 62 formed between a columnar vent core 60 and the vent core fitting surface with a vent core fitting recessed part 66 of the mold main body 30 and the second vent passage 64 formed to the mold main body 30 so as to communicate with the first vent passage 62. A helix groove (vent groove) 62a equipped with the part crossing the bus of the vent core 60 is formed to the peripheral surface of the vent core 60 to form the first vent passage 62.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air vent structure formed in communication with a cavity in a molding die for a polymer material molded article. In particular, rubber having a seal / sound insulation lip provided inside a vehicle such as dust covers (including grommets), boots (constant velocity joint boots, pin boots, rack / pinion steering boots), etc., and is required to have seal / sound insulation. This is a mold air vent structure suitable for air venting (gas release) when molding a molded product.

Here, a case in which a dust cover type grommet is injection-molded using a rubber material will be mainly described as an example, but the invention is not limited to this.

[0003] As products, not only other dust covers, but also applicable to air cleaner hoses, bellows hoses, grommets, bushes (cushion rubber), piston cups, and the like. Instead, the present invention can be applied to a solid molded product (including a cylindrical molded product with a bottom).

The molding material is applicable not only to rubber materials but also to thermoplastic elastomers and thermoplastic / thermosetting plastic materials. Furthermore, the molding method is not limited to injection molding, and is not particularly limited as long as it includes a step of injecting a fluid material into a cavity, such as transfer and blow molding.

[0005]

2. Description of the Related Art When a grommet 16 of a dust boot type is formed using a rubber material, an air flaw (particularly, the tip cylindrical portion 2) due to a defective air vent is formed on the tip cylindrical portion of the grommet.
0 inner seal lip 20a) (see FIG. 1).
reference).

[0006] In particular, when molding is performed by taking a large number of pieces, a variation in the filling amount of the rubber material in each product cavity is likely to occur, and this air vent defect is likely to occur.

[0007] In view of the above, an object of the present invention is to provide a novel mold air vent structure in which an air vent failure is unlikely to occur.

[0008]

DISCLOSURE OF THE INVENTION The mold air vent structure of the present invention solves the above problems by the following constitution.

An air vent structure formed in communication with a cavity in a molding die for a polymer material molded product, wherein a vent core is fitted between a columnar vent core and a vent core fitting recess of a mold body. A first vent passage formed between the mating surfaces,
And a second vent passage formed in the mold body in communication with the first vent passage, and a portion intersecting the generatrix of the vent core on one or both surfaces between the vent core fitting surfaces. Wherein the first vent passage is formed by a vent groove provided with:

By providing the vent groove with a portion intersecting with the core bus, the vent groove is formed so that the main flow direction of the material (usually, the axial direction of the cylindrical molded product, ie, the core bus direction). , The flow of the material that has flowed into the vent groove is hindered, and the vent groove distance is also long, so that the material reaches the second vent passage via the tip of the vent core. Possibility is reduced. Therefore, the second vent passage formed at the tip of the vent core does not become clogged, and the operation of removing the rubber in the second vent passage becomes unnecessary.

In the above configuration, the number of the vent grooves constituting the vent passage is usually a plurality, preferably four or more. If the number of the vent grooves is one, the material may flow into the vent passage and be closed before the product cavity is completely filled (the last fusion site of the material in the product cavity (the last filling site). ) Varies from injection molding to injection molding.)

In the above configuration, it is desirable that the vent passage is formed in a helical shape. This is because it is easy to form the vent passage and to easily secure the distance of the vent groove.

If the vent groove is formed on the peripheral surface of the vent core, it is easy to process the vent groove.

[0014] It is desirable that the fitting between the vent core and the bent core fitting recess be taper fitting. By adopting the taper fitting, the fitting and sliding are facilitated, so that the rubber material does not flow into the portion other than the first vent passage (vent groove). Therefore, burrs do not occur at the first vent passage forming portion (between the vent core and the fitting surface of the vent core), and the number of finishing steps after deburring the molded product can be reduced.

[0015] When a polymer material molded article is molded using the core having the vent structure of each of the above-described structures, air scars are less likely to occur. Therefore, the mold having the vent structure of the present invention is suitable for forming a cylindrical product having a seal lip that requires sealing properties on the inner periphery, such as a grommet of a dust boot type.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a wire harness (wire-h
A description will be given of an embodiment in which a rubber dust boot-type grommet (arrangement: wiring bundle) is formed. The grommet will be described below.

[0017] A wire harness (wire-h
arness (hereinafter simply referred to as “harness”) 12 is a sheet metal of a vehicle body (for example, a partition wall between an engine room and a vehicle compartment: dash panel)
In order to insert the wiring hole 14a, the rubber dust cover (grommet) 1 is usually inserted into the wiring hole 14a.
6 and attach the harness (cord) 1 to the dust cover 16
Wire through 2. The harness 12 is prevented from being damaged at the edge of the wiring hole 14a.
This is to prevent dust and noise from entering the inside of the vehicle through 4a.

In recent years, a higher degree of sealing performance for preventing dust and noise from entering a vehicle has been required more than ever before. For this reason, dust boot type grommets have been frequently used.

An annular mounting base 18, an outer cylindrical portion 20 and an inner cylindrical portion 22 are provided.
The outer tubular portion 20 and the inner tubular portion 22 are connected to each other via a curved portion (an inverted bowl-shaped portion) 24 and a bellows portion (a stepped portion) 26.

The annular mounting base 18 has a flange 18a and an annular mounting groove 18b formed on the vehicle outside of the flange 18a. An outer peripheral sealing lip 18c is provided at the bottom of the annular mounting groove 18b. ing. The outer cylindrical portion 20 is provided with a plurality of (three in the illustrated example) inner peripheral seal lips 20a on the inner peripheral side. Each of these seal lips 20a is for ensuring the sealing property, and the reason why the grommet 16 is a dust boot type is for ensuring the flexibility of the harness 12. Grommet 16
Is fixed to the harness by using a wiring tape (adhesive tape) 28 between the tip of the outer and inner cylindrical portions and the harness.
And winding.

The grommet 16 as described above is
The rubber mold having the air vent structure of the present embodiment as shown in FIGS.

The mold has the same configuration as the conventional one, except for the air vent structure, as described below.

The mold body 30 basically includes an upper mold 32,
It comprises a middle mold (slide core) 34, a lower mold 36 and a core 38.

The upper die 32 is mounted on an upper die mounting plate 35 via a heat insulating plate 40. The upper mold 32 is not necessarily divided, but is usually divided into an upper mold upper part 32a holding the sprue bush 42 and an upper mold lower part 32b from the viewpoint of mold production. The reason why the upper mold 32 is attached via the heat insulating plate 40 is to prevent the rubber material from generating scorch (burn, early vulcanization). A sprue 43 communicating with the injection nozzle of the injection molding machine is formed in the upper mold 32,
A runner 44 and a gate (ring gate in the illustrated example) 46 are formed on the mating surface with the middle mold 34. The gate 46 has a molded product cavity (product cavity) 48.
Is in communication with

The product cavity 48 includes a core outer surface 39 for forming a grommet inside (molded product inside) for forming a grommet and an upper mold / middle mold / shape for closing a mold for forming a grommet outside (molded product outside). It is formed by the concave surface 50 of the lower mold assembly.

The middle mold 34 is divided in the left-right direction, and a pair of slide molds 34a, 34 which can be separated and approached with an axis therebetween.
a.

The lower die 36 is mounted on a lower die mounting plate 54 via a spacer 52.

An extrusion pin (ejection pin) 56 for extruding (protruding) a molded product is disposed at a central position of the lower mold mounting plate 54 via an extrusion plate (ejection plate) 58.

An air vent (air escape passage) structure is required at the final material filling portion of the cavity 48 in order to release the air pushed out of the product cavity 48 due to the material filling and the gas generated during vulcanization.

The reason why the air vent structure is formed in this portion is that air is easily generated in the inner peripheral seal lip-formed portion of the cylindrical portion-formed cavity 48 a formed in the outer cylindrical portion 20 of the grommet 16. It is. This air pool is
It becomes an air flaw of the inner peripheral seal lip 22 in the cylindrical portion 20 of the grommet 16.

The air vent structure of the present embodiment passes through the peripheral surface of the columnar vent core 60 integrated with the upper end of the product core 38, ie, the fitting of the vent core 60 and the vent core of the mold body. It is assumed that air is released (air vent) from between the fitting surfaces with the concave portions 62.

That is, the vent core 60 and the upper mold lower part 32
b (upper die 32) formed vent core fitting recess 32c
A vent groove 62a for forming the first vent passage 62 is formed on one or both surfaces between the fitting surfaces (opposing surfaces) with the first and second vent passages 62. A second vent passage 64 is formed to form an air vent structure.

The heat insulating plate 40 is formed by compression molding of inorganic fibers, and the interface between the heat insulating plate 40 and the upper mold 32 is a contact that can form an air passage (gap) that can sufficiently release air. ing.

In the present embodiment, the columnar vent core 60 and the vent core fitting recess 32c of the mold body 30 (upper die 32) are formed on one or both of the fitting surfaces (between the facing surfaces). A first vent passage 62 is formed by a vent groove 62 a having a portion that intersects the generated core of the vent core 60. This will be described more specifically below.

In the illustrated embodiment, the column shape of the vent core 60 is tapered (frusto-conical shape) so that the vent core 60 and the vent core fitting recess 32c of the mold can be easily rubbed.
It is. At this time, the inclination of the taper is 1/5 to 1/5.
0, preferably 1/10 to 1/30. The column shape is not limited to the truncated cone shape, and may be a truncated pyramid shape, a columnar shape, a prismatic shape, and further, when the vent core 60 is not extended from the product core 38 side, that is, from the upper mold 32 side. When it is formed, it may have an inverted tapered shape (particularly in the case of a solid molded product).

Although the vent groove 62a is formed on the vent core 60 side, it may be formed on the fitting recess 32c side, or may be formed on both surfaces at the same position or shifted. Groove processing is easier if it is formed on the vent core 60 side.

The vent groove 62a having a portion that intersects the generatrix of the vent core 60 is a helix groove in the illustrated example. The helix groove 62a is right-handed in the illustrated example, but may be left-handed.

The effect of the present invention can be obtained if the vent groove 62a is not a helix groove but has a shape having a portion that intersects the generatrix of the vent core 60. As a groove form other than the helix, a zigzag shape (rectangular wave, waveform) or the like may be formed along the generatrix. Naturally, processing is difficult, but the helix itself may be a wavy line (zigzag line).

By making the vent groove 62a a helical groove, it is easy to secure a distance from the material through the first vent passage 62 to the second vent passage 64. Therefore, the lead angle (inclination angle) of the helical winding is determined according to the flow characteristics of the material, and is usually 5 to 80 °, preferably 10 to 45 °.
Is appropriately selected from the range.

If the lead angle is too small, it is difficult to arrange multiple leads, and it is difficult for air to escape. If the lead angle is too large, it is difficult to secure the distance of the first vent passage, and it is difficult to achieve the effects of the present invention.

The number of vent grooves (helical grooves) 62a is eight in the illustrated example. Normally, the material fusion site cannot be determined and varies slightly with each injection molding (material injection).
At least two, preferably four or more, more preferably six or more. Although the number of the vent grooves 62a may be ten or more, the number of groove processing steps increases. The number of vent grooves (helical grooves) may be one if the material fusion site is known in advance and can be determined.

The cross section of the helix groove 62a is
The shape is arbitrary such as a semicircle (U-shape), a triangle, and a rectangle, but is usually a V-shape. The groove diameter at that time varies depending on the molding material. In the case of a rubber material, the groove diameter is usually 5 to 500 μm, preferably 20 to 50 μm, and more preferably about 30 μm.

If the groove diameter is too small, it is difficult to secure a sufficient air escape (venting effect). If the groove diameter is too large, the material flow increases.

As in the present embodiment, the vent groove 62 a forming the first vent passage 62 is provided with a portion that intersects with the generatrix of the vent core 60, so that the vent groove 62 a
Since a is in a direction crossing the main flow direction of the material (usually, the axial direction of the cylindrical molded product, that is, the generatrix direction of the vent core 60), the flow of the material flowing into the vent groove 62a is hindered. In addition to the fact that the distance between the vent grooves 62a also increases, the possibility that the material reaches the second vent passage (air release hole) 64 via the tip of the vent core 60 decreases. Therefore, the vent core 60
The clogging of the second vent passage (air release hole) formed at the front end of the nozzle is almost eliminated. Therefore, grommet 1
In the case where 6 is formed, air scars are less likely to occur on the inner peripheral seal lip 20a and the like of the outer cylindrical portion 20, and the work of removing the rubber material flowing into the second vent passage 64 becomes unnecessary.

Next, an outline of a method for molding a rubber molded product using the mold having the vent structure of the above embodiment is as follows.

First, the lower mold 36 is raised (elevated) until it comes into pressure contact with the upper mold 32 to close the mold. Thereafter, the injection nozzle 68 of the rubber injection molding machine is advanced to inject the rubber material. Then, the rubber material is sprue 43, runner 44
And into the product cavity 48 via the ring gate 46. The rubber material is filled from below by the action of gravity, so that the cylindrical-shaped cavity 48a is finally filled. At this time, the cylindrical portion shaped cavity 48a communicates with the first vent passage 62 formed by the helical groove 62a, and the air quickly escapes to the first vent passage 62, and further, the second vent passage 64 and the upper It is discharged out of the mold via the mold 32 / insulation board 40 interface. Therefore, air flaws do not occur on the inner peripheral seal lip 20a of the grommet 16 formed by the cylindrical portion forming cavity 48a. Even if the material flows into the vent groove (helical groove) 62a, since the distance of the helical groove 62a is long, the upper upper mold 3
The rubber material does not flow into and clog the second vent passage 64 formed in 2a.

When vulcanization of the rubber filling in the product cavity is completed, the middle mold (slide core) 34 is opened right and left, and the lower mold 36 is lowered. At this time, since the extrusion pin 56 and the extrusion plate 58 do not descend, the molded product is pushed upward, and the mold can be released.

The above embodiment (FIG. 3 in which the vent groove 62a is a helix groove (diameter: about 30 μm, lead angle: 20 °))
When the grommet was molded using an ethylene propylene rubber (EPDM) material using a vent core 62 shown in (1), the defective rate (occurrence of air defects) in the inner peripheral seal lip became 0%. The rate of occurrence of rubber clogging in the second vent passage was also 0%.

The conventional vent structure (vent groove 62b)
Is a straight U-shaped groove (width: 0.5 mm) using a vent core 62A shown in FIG.
% And the rate of occurrence of rubber clogging was 5%. In the case of the conventional vent structure, a communication groove 62c for communicating with the second vent passage 64 is also formed on the upper surface of the vent core 62A.

In the case of the present invention, since there is a gap (usually about 3/100 mm) on the flat surface of the top, the communication groove is not required.

FIG. 5 is a partial sectional view of a mold showing a vent structure according to another embodiment of the present invention.

This mold is a mold 72 for molding an air cleaner hose, and a nest (core) formed to form a detector insertion port 74a in a part of a hose (rubber molded product) 74.
76 and a vent core. Specifically, it is as follows.

The mold body 72 basically includes an upper mold 80, a lower mold 82, and a core 84. And the upper mold 80
Has an upper upper die 80a and a lower upper die 80b, and the insert 76 is screwed and held in the upper die 80a.

The vent core 76 is cylindrical and has a plurality of vent grooves (helical grooves) 78a having a starting point at the end face position of the detector insertion port 74a (four in the illustrated example).
The first vent passage 78 is formed.

The upper end corner of the vent core 76 is corner-cut (C-cut) so that an air pocket 86 can be formed between the upper upper die 80a and the lower upper die 80b. The air pool 86 temporarily stores air from the vent groove 78a and gradually releases the air from the PL surfaces of the upper upper die 80a and the lower upper die 80b.

The venting action of this embodiment is the same as that of the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a dust cover type grommet to which a mold air vent structure of the present invention is applied.

FIG. 2 is a schematic sectional view of a main part of an injection molding die for molding the grommet of FIG.

FIG. 3 is a partial front view of a vent core used in an embodiment of the present invention and an end view taken along line AA thereof.

FIG. 4 is a partial front view showing an example of a conventional vent core and a top end view thereof.

FIG. 5 is a schematic cross-sectional view of a main part of an injection mold having a vent structure according to an embodiment of the present invention when molding an air cleaner hose.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 16 Dust cover type grommet 20 Car outer side cylindrical part 22 Inner circumference seal lip 30 Mold main body 32 Upper mold 32a Upper mold upper part 32b Upper mold lower part 34 Medium mold (slide core) 36 Product core 60 Vent core 62 First vent passage 62a vent groove 64 second vent passage (air escape hole) 66 vent core fitting concave

Claims (9)

[Claims] 1. An air vent structure formed in communication with a cavity in a molding die for a polymer material molded product, wherein a vent between a columnar vent core and a vent core fitting recess of a mold body is provided. A first vent passage formed between the child fitting surfaces, and a second vent passage formed in the mold main body in communication with the first vent passage; Alternatively, the first vent passage is formed by a vent groove having a portion intersecting with the generatrix of the vent core on both surfaces. 2. The mold air vent structure according to claim 1, wherein the number of the vent grooves is plural. 3. The mold air vent structure according to claim 1, wherein said vent groove is formed on a peripheral surface of said vent core. 4. The mold air vent structure according to claim 1, wherein the vent groove has a helix shape. 5. The mold air vent structure according to claim 1, wherein the fitting between the vent core and the bent core fitting recess is a taper fitting. 6. A method for molding a polymer material molded article, comprising molding the polymer material molded article using the mold having the vent structure according to claim 1, 2, 3, 4, or 5. 7. The method for molding a polymer material molded article according to claim 6, wherein the polymer material molded article has a cylindrical portion at a tip end. 8. The method according to claim 7, wherein the molded polymer material is a rubber molded product. 9. The method for molding a polymer material molded article according to claim 8, wherein said rubber molded article is a dust cover type grommet and has an inner peripheral seal lip at a tip cylindrical portion. .