JPH06198721A - Flat die for blow molding - Google Patents

Abstract

PURPOSE:To improve the operation rate of a molding machine by injecting uniformly a flat parison to achieve the cost reduction of products by designing the cross section of an opening to make the pressure loss uniform along the circumference of a ring-shaped resin passage which changes from a circlular to an elliptic form as resin descends. CONSTITUTION:A core 16 is inserted into a die housing 12 to form a resin passage 18, to which an inlet 22 for resin flow from an extruder is opened at a corresponding position. The resin passage 18 branches right and left in the circumferential direction on the surface from the inlet 22 to the core 16 to reduce its cross section, and a manifold 24 is formed which is warped in the extrusion direction. One end of the manifold 24 is combined with the other end of the manifold 24 from the inlet 22. The cross section of the ring-shaped resin passage 18 is formed to change from circle to ellipse as resin descends from its upper part. The cross section of the opening is designed to make the pressure loss uniform along the circumference of the resin passage 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a blow molding flat die for molding a flat product.

[0002]

2. Description of the Related Art Conventionally, when performing blow molding by a blow molding machine, after the molten resin supplied from the extruder is stored in an amount corresponding to the quantity of the molded product, the plunger of an injection device (not shown) is moved. A parison is formed by ejecting resin in a tube shape from the die discharge port, and air is blown to obtain the desired product. On the outer peripheral surface of the core metal of the blow molding die, the resin distributed in two directions, 180 ° opposite to the resin supply port direction side of the die housing to which the discharge port of the extruder is connected, joins at the downstream part thereof. It is common to inject molten resin as a cylindrical parison, but a parison with a flat cross section may be desirable depending on the shape of the mold cavity.
In recent years, it has been applied to flat-plate structures such as vehicle doors and panels, or bumpers and spoilers. In such a case, the resin discharge port should be a flat shape such as an oval to eject a flat parison. It started to form.

[0003]

However, the resin distribution passage has a complicated flow passage shape, resulting in a portion where the flow of the molten resin is extremely slow or a residence portion. This stagnation is particularly noticeable on the wall surface where the cross-sectional area of the flow path is large and the flow velocity is slow, and at the corners or confluences where the shape of the flow path changes. There is a problem that a large amount of resin and working time are wasted due to the replacement of the old resin with the new resin that remains, resulting in a decrease in productivity.

Further, in the conventional parison injection die of the blow molding machine, since the shape of the resin discharge port is constant according to the preset product, the required parison shape changes every time the product shape changes. Along with this, it is necessary to take measures such as changing the shape of the resin discharge port so as to inject a parison according to individual products, for example, deep and thin products. In such a case, conventionally, in order to obtain a parison suitable for the molded product, it is common to replace the entire die for each molded product or mold the molded product with a dedicated blow molding machine. is there.

If the shape and size of the molded product are different, it is not easy to replace the heavy die, and it is dangerous if the entire die is replaced for each different molded product. In addition, there is a drawback in that the operation rate of the blow molding machine is reduced if molding is performed using a dedicated blow molding machine for each molded product.

In order to solve these problems, there is one in which only the lower die housing and the core are replaced to change the parison size. Normally, in a flat die with a basic shape, the pressure loss of the resin passing through the resin flow path on the major diameter side and the minor diameter side of the lower part of the die is the same in the circumferential direction, so a uniform parison is formed. Is possible. However, if the lower part of the die, that is, the lower die housing and the lower mandrel, is larger than usual,
Or, if the die is replaced with a smaller die, the length of the resin flow path on the major diameter side and the minor diameter side of the flat die will inevitably change. For this reason, the pressure loss of the resin passing through the resin flow path differs in the circumferential direction, and the parison extruded from the die has poorer performance on the major diameter side, and the resin flows only on the minor diameter side, resulting in a non-uniform parison. There is a problem that it is difficult to mold the desired parison.

Focusing on the above-mentioned conventional problems, the present invention provides a flat die for blow molding capable of performing a uniform parison injection and rapidly discharging the old resin when changing the resin. It is to be.

[0008]

In order to achieve the above object, in a flat die for blow molding according to the present invention, a core metal is inserted into a die housing to form a resin passage, and an extruder is provided in the resin passage. The resin inlets from the side are opened at symmetrical positions, and the manifolds are branched from the respective resin inlets to the surface of the core metal to the left and right in the circumferential direction to reduce the cross-sectional area of the passage and curved in the extrusion direction. And the manifold ends from the other resin inflow port are joined together, and the cross section of the resin passage having an annular passage is configured so as to become a circle from an ellipse or an ellipse as it descends from above. The opening cross-sectional area is set so that the pressure loss is uniform in the circumferential direction of the passage.

[0009]

According to the above construction, the resin flows into the resin passage in the die from the resin inflow port for each shot, but this flows down along the manifold and simultaneously overflows to the land portion. The merging portion of the manifold is formed in the dam lip portion, and the resin flows down from there, and at the same time, the resin also flows down from the land portion to the dam lip portion. The height of the land is lower than that of the dam lip, and the flow rate of overflow from the manifold is almost equal along the path direction from the resin inlet, and the resin uniformly wraps around the entire die and is injected into the parison. Is uniform in thickness. In addition, the die is formed by a lower housing material in which only the lower die can be replaced and a mandrel, and a protrusion is provided in the middle of the resin flow path so that a uniform parison corresponding to the size of the molded product can be obtained, or By making the gap of the resin path on the major diameter side at that location larger than the gap on the resin path of the minor diameter side, pressure loss in the resin flow path between the molten resin on the major diameter side and the minor diameter side of the flat die can be reduced. Be even in the circumferential direction of the road.

[0010]

EXAMPLES Specific examples of the blow molding flat die according to the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows the structure of a die according to one embodiment. As shown in the figure, the die 10 has a die housing 12, which is composed of an upper die housing 12a and a lower die housing 12b, which are detachably connected by fastening bolts or the like. Dice housing 12
A through-hole 14 having a substantially circular cross section is formed along the vertical center line of the. Such a through hole 14 is opened in the lower end surface of the housing 12 in a state in which the corresponding diameter is gradually reduced from the middle thereof to the lower end surface of the housing 12. Then, a core metal 16 having a diameter smaller than that of the through-hole 14 and having a circular cross-section at the upper portion and having a shape changed from an intermediate portion to an oval or elliptical cross-section is inserted into the housing 12. A resin passage 18 is formed between the outer peripheral surface of the core metal 16 and the inner peripheral surface of the through hole 14. The upper end portion of the cored bar 16 has a cross-sectional structure that is in close contact with the through-hole 14, and the resin passage 18 is formed in the lower part of the cored bar 16. As the shape changes to the cross section, the resin passage 1
8 is also configured to change its shape from an annular passage to an oval or elliptical annular passage.

Since the upper end portion of the cored bar 16 has a circular cross-sectional structure which comes into close contact with the through hole 14, as described above, the outer peripheral surface of the upper die housing 12a also has a circular cross-sectional shape. There is. Further, the thickness of the upper die housing 12a is configured to be considerably thinner than that of the lower die housing 12b. Since the upper part of the die 10 has a circular shape, the extrusion pressure from the extruder (not shown) at the time of injection of the parison acts evenly in the circumferential direction of the surface of the resin passage 18 so that it is offset to either side. The pressing force does not act on the upper die housing 12a, so that concentrated stress is less likely to occur, so that the upper die housing 12a has a thin wall structure.

Furthermore, the cross-sectional shape of the outer peripheral surface of the lower die housing 12b is rectangular in conformity with the flat resin passage 18. Therefore, the lower die housing 1
2b is configured to be considerably thicker than the wall thickness of the upper die housing 12a. This is because the lower part of the die 10 has a flat shape, and therefore the pushing force from the extruder (not shown) at the time of parison molding acts on the surface of the resin passage 18 parallel to the major axis. Since the pressure receiving area is larger than the pressing force acting on the surface of the resin passage 18 facing the minor diameter side, the resin passage 1 is parallel to the major diameter.
This is to prevent the lower surface of the lower die housing 12b from being cracked and broken due to a concentrated stress acting on the eight surfaces due to the expansion of the distance between the resin passages 18 and the expansion pressing force.

A resin supply passage 20 is provided inside the core 16.
Is pierced, which branches in the direction of the diameter of the core metal 16,
A pair of openings is provided in the resin passage 18. The opening is set in the resin passage 18 on the wide side as shown in the drawing, and this serves as a resin inlet 22.

In such a basic structure, the outer surface of the cored bar 16 is branched from the respective resin inlets 22 to the left and right in the circumferential direction, and the passage cross-sectional area is gradually reduced at a predetermined rate while maintaining a predetermined curvature. A manifold 24 having a semicircular cross section that curves in the extrusion direction is formed. And this manifold 24
The ends are formed so as to merge with the manifold 24 on the opposite side, which is symmetrical, and at a position of approximately 90 degrees from the resin inlet 22. And this confluence part 26
A dam lip portion 28 that forms a shallow passage is formed along the circumferential direction of the core metal 16 corresponding to the portion. The dam lip portion 28 is provided so as to correspond to the throttle passage portion of the resin passage 18, and the gap between the dam lip portion 28 and the through-hole 14 of the die housing 12 is narrowed so that the passage resistance is uniform over the entire circumference. There is. In this case, the merging portion 26
Are joined and joined so that the manifolds 24 having merging symmetry are in contact with the line along the axis of the core 16. As a result, the resin flow lines flowing down the respective manifolds 24 are parallel at the merging portion.

The entire resin passage 18 extending from the lower edge of the manifold 24 to the dam lip portion 28 is shallower than the passage cross-sectional depth of the manifold 24 portion and forms a passage deeper than the passage depth of the dam lip portion 28 portion. The part 30 is formed. This is formed by adjusting the scraping depth of the outer surface of the cored bar 16 as described above.

At the bottom of the die body 10, a lower die housing 12b surrounds the outer periphery of the core 15,
A flat annular exit slit 17 (die lip gap) is formed between the core 15 and the lower die housing 12b. The lower end of the resin passage 18 is connected to the outlet slit 17, and when a plunger of a resin injection device (not shown) is pushed forward, the molten resin in the resin passage 18 is pushed out of the main body through the outlet slit 17 and the parison 32 is removed. To be formed.

Here, the protrusion 40 according to the embodiment of the present invention.
As shown in FIG. 2, the resin passage 18 on the minor diameter side X is narrowed by being provided in the core 15. This is because the pressure loss on the short diameter side X where the molten resin easily flows and the pressure loss on the long diameter side Y where the molten resin does not easily flow are constantly the same in the circumferential direction of the resin passage 18 so that the height of the protrusion 40 is high. Is decided.

In this embodiment, a protrusion 40 is provided in the middle of the resin passage 18 of the lower die housing 12b,
Molten resin passes through the resin passage 1 inside the lower die housing 12b.
Although the pressure loss in the circumferential direction when passing through 8 is the same, the present invention is not limited to this, and as shown in FIG. 3, the passage area of the resin passage 18 on the major diameter side Y where the molten resin does not easily flow is increased. In addition, the passage area of the resin passage 18 on the short diameter side X where the molten resin easily flows may be reduced so that the pressure loss becomes the same in the circumferential direction. Reference numeral 29 indicates a mandrel lip.

The operation of the die part configured as described above will be described. The molten resin that has flowed into the resin inlet 22 from the extruder 23 through the resin supply path 20 branches left and right in the manifold 24 and reaches the confluence section 26. At the same time as the branched flow down, from the lower edge of the manifold 24 to the land section 30. The resin overflows successively, and the resin flows uniformly around the entire circumference of the resin passage 18. Further, since the groove cross-sectional area of the manifold 24 is set to be gradually reduced, the pressure distribution in the circumferential direction becomes uniform and the dam lip portion 28 flows down in a state of being readjusted to have a uniform wall thickness. It is ejected as a parison 32.

Under such circumstances, if an attempt is made to perform blow molding using an engineering plastic resin having a viscosity higher than that of a general-purpose resin as a molten resin, the molten resin will pass through a narrow outlet slit 17 together with high-speed injection. In this case, a large pressure loss is generated, and the opening cross-sectional area ratio and the flow path length are different between the short diameter side X and the long diameter side Y.
Due to this difference, the pressure loss becomes non-uniform in the circumferential direction of the resin passage 18, so that the thickness of the parison 32 ejected from the outlet slit 17 becomes non-uniform.

Thus, as in the embodiment of the present invention shown in FIGS. 1 to 3, the protrusion 4 is formed in the resin passage 18 on the short diameter side X.
By providing 0, the resin around the die 10 in the circumferential direction becomes uniform, the thickness of the parison 32 to be injected becomes uniform in the circumferential direction, and at the same time, the length of the injection parison 32 becomes uniform in the circumferential direction.

When molding a large molded product different from the molded product that has been molded so far, the length of the resin passage 18 in the lower die housing 12b increases as the diameter of the parison 32 increases. The parison 32 has a non-uniform wall thickness due to a remarkable pressure loss difference between the long diameter side Y and the short diameter side X.
Is easy to mold. On the contrary, when the diameter of the parison 32 is reduced, the length of the resin passage 18 is generally shortened, the difference in pressure loss between the major diameter side Y and the minor diameter side X is small, and the parison 32 having a relatively uniform thickness is formed. Easy to be affected. Based on these results, the lower die housing 12b, the core 15 having the protrusion 40, and the mandrel lip 29, so that the pressure loss of the molten resin in the resin passage 18 becomes the same on the major diameter side Y and the minor diameter side X, respectively. Exchange for.

In this way, the lower die housing 12b, which constitutes the outlet slit 17 for forming the parison of the die 10, the core 15, the mandrel lip 29, etc., can be detachably attached by, for example, bolts or lock nuts. And the parison control rod (not shown), other upper die housing 12
a, because it can be easily replaced with the core metal 16,
It is possible to easily form the parison 32 according to the shape, size, etc. of the molded product without replacing the entire die 10. Therefore, when molding molded products of different molded product sizes, etc., it is possible to deal with it without installing a dedicated blow molding machine, improving the operation efficiency of the blow molding machine and reducing the product cost. You can

Further, in the flat die 10 for blow molding according to the embodiment of the present invention, by providing the manifold 24, the dam lip portion 28, and the like, the resin around can be made uniform, so that the resin stagnation portion is eliminated, and especially the resin merging portion is eliminated. The resin replaceability in the portion 26 is remarkably improved, and deterioration of the resin replaceability can be prevented. Further, since the conventional multi-stage dam lips are not required, the length of the die 10 itself can be shortened and the weight of the die 10 can be reduced.

[0026]

As described above, in the flat die for blow molding according to the present invention, the core metal is inserted into the die housing to form the resin passage, and the resin inlet from the extruder side is formed in the resin passage. Open at symmetrical positions and form a manifold that is branched from each resin inlet to the surface of the metal core in the circumferential direction to the left and right in the circumferential direction and has a curved passage cross-sectional area and is curved in the extrusion direction. The ends of the manifolds are joined together, and the cross section of the resin passage having an annular passage is configured so as to become a circle from an ellipse or an ellipse as it descends from the top to the bottom. By setting the opening cross-sectional area so that the pressure loss will be uniform, the resin stagnation part is generated at the fixed position in the die while performing the uniform parison injection. Preventing the door, an excellent effect that it is possible to perform rapid discharge of the old material during such color change obtained with. Further, since the deflection and stress of the upper die housing are evenly distributed in the circumferential direction and their values are small, the member of the upper die housing can be made thin, and the weight of the entire die can be remarkably reduced. Further, by setting the opening cross-sectional area so that the pressure loss is uniform in the circumferential direction of the resin passage, the flat parison can be uniformly ejected. Also, by replacing the lower housing material and the core that form the molding material discharge port suitable for obtaining the parison corresponding to the product size, it is possible to easily manufacture molded products of different product sizes without replacing the entire die. Obtainable. Furthermore, it is possible to handle without installing a dedicated die or molding machine, improving the operating efficiency of the molding machine and reducing the product cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a flat die according to an embodiment.

FIG. 2 is a sectional view taken along line AA of FIG. 1 (2).

FIG. 3 is a cut plan view of a die showing another embodiment of the present invention.

[Explanation of symbols]

 10 dice 12 die housing 12a upper die housing 12b lower die housing 14 through-hole 15 core 16 core metal 17 exit slit 18 resin passage 20 resin supply passage 22 resin inlet 24 manifold 26 joining portion 28 dam lip portion 30 land portion 32 parison 40 Protrusion

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B29C 49/78 7619-4F // B29L 22:00 4F

Claims (1)

[Claims] 1. A resin passage is formed by inserting a core metal into a die housing, and a resin inflow port from the extruder side is opened at a symmetrical position in the resin passage, and each resin inflow port is provided on the surface of the metal core. It branches to the left and right in the circumferential direction and the passage cross-sectional area decreases,
In addition, a manifold curved in the extrusion direction is formed, and the manifold end and the manifold end from the other resin inlet are joined together, and the cross section of the resin passage has a circular shape, and the resin passage has a circular shape and a long shape. A flat die for blow molding, characterized in that it is formed into a circle or an ellipse, and the opening cross-sectional area is set so as to have a uniform pressure loss in the circumferential direction of the resin passage.