JPH0692099B2 - Mold for molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molding die mainly used for injection molding, and more particularly to a die having improved gas release in a cavity.

[Prior Art] In the case of injection molding, if gas such as air remains in the cavity, a gas pool is generated and the appearance of the product is impaired. Also, in the reaction injection molding (RIM) of urethane, air in the cavity or volatile gas from the material is trapped, which is a cause of poor appearance such as silver streak and lack of wall.

Therefore, as a method for venting the gas in the cavity, conventionally, a die is provided with a gas vent passage formed of fine slits or through holes having a diameter of 3 to 50 μm, which communicates the cavity with the outside. Specifically, a method of providing a slit on the mold splitting surface, a method of forming a through hole for communicating a sintered alloy with the outside by forming a part of the mold surface with a porous sintered alloy,
A method of providing a gap between the knock pin and the pin hole, a method of forming a nested structure having fine through holes, and the like are known.

[Problems to be Solved by the Invention] In the above-described conventional molding die, the degassing passages are fine slits or through holes through which the molding material does not pass but the gas passes. However, in such a mold, the gas vent passage is clogged, and the mold must be regularly cleaned or replaced. Alternatively, since the diameter of the gas vent passage is very small, there is a problem that the ventilation resistance is large and the gas escape rate is slow.

The present invention has been made in view of such circumstances,
While increasing the diameter of the gas vent passage. The purpose is to prevent the molding material from entering the degassing hole.

[Means for Solving the Problems] In the case of injection molding, the air in the cavity is pressed by the injected molding material. Therefore, there is no air in the portion of the molding material filled in the cavity, and the air exists in a compressed state on the front side of the advancing molding material. Moreover, the injected molding material has a large internal pressure.

Therefore, the inventors of the present invention have completed the present invention as a result of diligent research, remembering that the gas is released in front of the advancing molding material and the gas vent passage is closed by utilizing the internal pressure of the molding material.

That is, the molding die of the present invention includes a gas vent passage formed in one of the split dies and opening to the die surface of the split die to communicate with the outside, and an elastic body held in one of the split dies and covering the opening of the gas vent passage. A seat surface is formed in the opening of the gas vent passage to close the gas vent passage by contacting the valve member, and the valve member has a gap between the seat surface and the seat surface when no stress is applied. It is characterized in that it is formed to open the gas vent passage, and is elastically deformed by the stress applied from the molding material at the time of molding to come into contact with the seat surface to close the gas vent passage.

The greatest feature of the present invention is that a valve member that is elastically deformable is arranged in the gas vent passage. This valve member
It is made of an elastic material such as rubber or spring steel and is deformed by the internal pressure of the molding resin. For example, the valve member
It is possible to form a lip shape in which one end is held in a mold and the other end is swingable. This case can be utilized when the molding material advances from one direction. Further, it may be a disk shape having a through hole in the center. This case is useful when the molding material advances from both sides toward the through hole.

When the molding material is not injected, the internal pressure does not act on the valve member, so that the valve member restores to a predetermined shape by its own elastic force and opens the gas vent passage. The width and depth of the gas vent passage can be arbitrarily selected, and can be set to, for example, 0.5 mm or more, which is larger than that of the conventional gas vent hole. The seating surface and the valve member may be directly provided on one of the split dies, but the core having the seating surface and the valve member is fixed to one of the split dies by providing a gas vent passage communicating with the gas vent hole. It is preferable that This simplifies the structure of the mold and reduces the cost required to manufacture the mold. It is also easy to replace the core. The position where the valve member is provided is preferably the weld portion of the molding cavity, but is not particularly limited.

[Operation] In the molding die of the present invention, before injection of the molding material, the valve member is restored to a predetermined shape by its elastic force and a gap is formed between the valve member and the seat surface. In that state, the molding material is injected into the cavity, and when the molding material advances in the cavity, the gas in the cavity is pressed by the molding material and becomes compressed. The compressed gas is discharged to the outside from the gap between the valve member and the seat surface through the gas vent passage.

When the molding material reaches the position of the valve member, the internal pressure of the molding material is transmitted to the valve member, the force overcomes the elastic force of the valve member, and the valve member elastically deforms in the direction of approaching the seat surface. At this time, for example, if the valve member is formed in a disk shape having an opening in the center,
The opening is located farthest from the peripheral edge of the valve member, and whichever direction the molding material reaches the valve member, the valve member similarly elastically deforms before reaching the opening. When the molding material reaches the position of the opening, the valve member is in close contact with the seat surface and the communication between the opening and the gas vent passage is cut off, so that the molding material does not enter the gas vent passage. Be blocked.

That is, gas is smoothly discharged from the opening through the gas vent passage until the molding material moves on the surface of the valve member and reaches the position of the opening. When the molding material reaches the position of the opening, the valve member elastically deforms and seals the seat surface in close contact, so that the molding material is prevented from entering the degassing passage.

[Effect of the Invention] Therefore, according to the molding die of the present invention, since the molding material is prevented from entering the degassing passage, the frequency of cleaning or replacement as in the conventional case is greatly reduced. The number of steps can be reduced. Further, since the diameter of the gas vent passage can be increased, the ventilation resistance is reduced, and various obstacles to the molded product such as a gas pool can be prevented.

[Examples] Specific examples will be described below.

(Embodiment 1) FIGS. 1 to 3 show a molding die according to an embodiment of the present invention. This mold comprises a fixed mold 1 and a movable mold 2, and a molding cavity 12 filled with the injected urethane resin 100 is formed between the fixed mold 1 and the movable mold 2. Movable type 2
A gas vent passage 20 is formed in a portion of the urethane resin 100 where welding occurs, and the core 3 is fixed to the opening of the gas vent passage 20.

Here, the core 3 includes a mounting seat 31 having a seat surface 30 projecting conically toward the cavity 12, and a rubber valve member 32 having a substantially cylindrical shape.
And a ring-shaped holding member 33 that holds the valve member 32. The holding member 33 holds the valve member 32 and is fixed to the mounting seat 31 by a flat bolt 34. Also holding member
The 33 and the mounting seat 31 are fixed to the movable mold 2 by flat bolts 35.

The valve member 32 has an opening 32a in the center and a substantially conical center hole portion whose thickness gradually increases from the opening 32a toward the other end,
The inner peripheral surface of the central hole portion faces the seat surface 30 of the mounting seat 31 and the like at a distance, and forms a flow path 36 communicating with the gas vent passage 20. Ring-shaped grooves 32b are formed on the outer surface and the inner surface of the valve member 32, respectively, and the valve member 32 is elastically deformable in the axial direction around the groove 32b.

In the molding die of the present embodiment configured as described above, when the urethane resin 100 is injected and moves forward in the cavity 12, the compressed gas causes a gap between the valve member 32 and the seat surface 30 from the opening 32a. And is smoothly discharged from the degassing passage 20 to the outside through the flow path 36. Then, when the urethane resin 100 reaches the peripheral portion of the valve member 32 and proceeds from both sides toward the center of the valve member 32, the valve member 32 is pressed by the internal pressure of the urethane resin 100 and elastically deforms in the direction approaching the seat surface 30. To do. When the urethane resin 100 further advances and reaches the position of the opening 32a, the inner peripheral surface of the valve member 32 is brought into pressure contact with the seat surface 30 of the mounting seat 31, and as shown in FIG. It is in a closed state. Therefore, in this state, the urethane resin 100 cannot enter the inside of the valve member 32 through the opening 32a, and the resin is prevented from entering the gas vent passage 20.

When the movable mold 2 and the fixed mold 1 are opened after the resin has solidified, the valve member 32 is restored to its original shape by its own elastic force and a gap is formed between the valve member 32 and the seat surface 30 to form the gas vent passage. Open 20 openings.

Therefore, according to the molding die of this embodiment, the gas can be surely vented, and the resin is prevented from entering the gas vent passage. Therefore, a molded product of good quality can be formed, the frequency of cleaning and replacement of the core is extremely low, and the number of steps can be significantly reduced compared to the conventional case.

(Embodiment 2) FIG. 4 shows a molding die according to a second embodiment of the present invention. This molding die has a cylindrical member 4 provided in the gas vent passage 20 of the movable mold 2 and having a female screw portion, a central hole 50 that is screwed with the tubular member 4 and communicates with the gas vent passage 20, and has a tip end. It is composed of a shaft member 5 having a seat surface 51 and a tubular valve member 6 whose one end is held by the shaft member 5.

The center hole 50 of the shaft member 5 is open to the seat surface 51 and an end portion on the side opposite to the seat surface 51. Further, the valve member 6 has a bending portion 60 on one end surface similar to the valve member 32 of the first embodiment, and the other end portion is engaged with the shaft member 5 so that the valve member 6 is held by the shaft member 5 and is movable. It is fixed to the mold 2.

In the molding die of this embodiment, gas can be released smoothly as in Embodiment 1, and the resin is prevented from entering the gas vent passage. Further, since it is configured to be held in the gas vent passage 20 provided in the movable die, it is more compact than in the first embodiment.

(Embodiment 3) FIGS. 5 and 6 show a molding die according to an embodiment of FIG. 3 of the present invention. In this embodiment, a cylindrical core 7 is held by the movable die 2 at the end of the cavity 12. This core 7
The movable seat 2 includes a mounting seat 71 having a central hole 70 communicating with the gas vent passage 20, a plate-shaped valve member 72, and a tubular holding member 73 holding the valve member 72. The valve member 72 has a triangular cross section in which the wall thickness gradually increases from one end to the other end, and the thick portion is held by the holding member 73. Further, the mounting member 73 is formed with a tapered seat surface 74 facing the inner surface of the valve member 72, and an opening 75 is formed between the tip of the valve member 72 and the seat surface 74 in a state before molding. ing.

In the molding die of this embodiment, the slit-shaped opening 75 between the valve member 72 and the seat surface 74 communicates with the central hole 70, and the central hole 70 communicates with the gas vent passage 20. Thus the cavity
The gas pressed to the terminal end of 12 can be smoothly discharged to the outside through the slit-shaped opening 75. Further, when the molding material reaches the valve member 72, the valve member 72 is elastically deformed in the direction approaching the seat surface 74, and is pressed against the seat surface 74 to prevent the molding material from entering the degassing passage 20. .

[Brief description of drawings]

1 to 3 relate to a molding die according to an embodiment of the present invention, in which FIG. 1 is a sectional view taken along the line AA of FIG. 2 showing a state in the middle of molding, and FIG. FIG. 3 is a plan view of the core, and FIG. 3 is a cross-sectional view of essential parts showing a state after molding. FIG. 4 is a cross-sectional view of an essential part of the molding die of the second embodiment of the present invention, showing the state before molding. FIGS. 5 and 6 relate to a molding die of a third embodiment of the present invention, FIG. 5 is a sectional view of an essential part shown in a state before molding, and FIG. 6 is a plan view of a core. 1 ... Fixed type, 2 ... Movable type, 3 ... Core 4 ... Cylindrical member, 5 ... Shaft member, 6 ... Valve member 7 ... Core, 72 ... Valve member 12 ... Cavity, 20 ... Gas vent passage 30, 51, 74 ... Seat surface, 32a, 75 ... opening

Claims (1)

[Claims] 1. A gas vent passage formed in one of the split dies and opening to a die surface of the split die to communicate with the outside, and an elastic body held by the one split die and covering the opening of the gas vent passage. A seat surface is formed at the opening of the gas vent passage for closing the gas vent passage by contacting the valve member, and the valve member is provided between the seat surface and the seat surface in a non-stressed state. A molding die characterized in that a gap is formed in the opening to open the gas vent passage, and elastically deformed by a stress applied from a molding material at the time of molding to contact the seat surface to close the gas vent passage. .