JP2839121B2 - Flat dies for blow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, when performing blow molding by a blow molding machine, a molten resin supplied from an extruder is stored in an amount corresponding to the amount of a molded product, and then moved by moving a plunger of an injection device (not shown). The resin is discharged into a tube from the die discharge port into a parison, and air is blown to obtain a desired product. On the outer peripheral surface of the core metal of such a die for a blow molding machine, the resin distributed in two directions, that is, the direction opposite to the resin supply port of the die housing to which the discharge port of the extruder is connected and the side opposite to the resin supply port by 180 °, merges at the downstream part. In general, a molten resin is injected as a cylindrical parison, but a flat parison may be desirable depending on the shape of the mold cavity.
In recent years, applications to flat structures such as doors and panels of vehicles, bumpers and spoilers, etc. have been attempted. In such cases, the shape of the resin discharge port is made to be a flat shape such as an ellipse, and a flat parison is injected. Has started to form.

[0003]

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

Further, in the parison injection die of the conventional blow molding machine, since the shape of the resin discharge port is constant according to a preset product, the required parison shape changes every time the product shape changes. Accordingly, it is necessary to take measures such as changing the shape of the resin discharge port so that a parison can be ejected according to an individual product, for example, a deep object or a thin object. In such a case, conventionally, in order to obtain a parison suitable for the molded product, it is common practice to replace the entire die each time the molded product is different, or to form a molded product using a dedicated blow molding machine. is there.

[0005] If the shape and size of the molded product are different, if the entire die is to be replaced every time the molded product is different, replacement of a heavy die is not easy and involves a risk. Further, there is a drawback that the operation rate of the blow molding machine is reduced when the molding is performed by a dedicated blow molding machine for each molded product.

In order to solve these problems, there is a method in which only the lower die housing and the core are replaced to change the parison size. Normally, a flat die having a basic shape is configured so that the pressure loss of the resin passing through the resin flow path at the lower major axis and the minor axis at the lower part of the die is the same in the circumferential direction. Is possible. However, the lower die, that is, the lower die housing and the lower mandrel,
Or, when the dies are replaced with smaller dies, the lengths of the resin flow paths on the long diameter side and the short diameter side of the flat die are inevitably changed. As a result, the pressure loss of the resin passing through the resin flow path varies in the circumferential direction, and the parison extruded from the die has a poor diameter on the long diameter side, and the resin flows only on the short diameter side, resulting in an uneven parison. There was a problem that the desired parison molding was difficult.

SUMMARY OF THE INVENTION The present invention is directed to a flat die for blow molding, which allows quick discharge of old resin at the time of resin change while paying attention to the conventional problems. It is to be.

[0008]

In order to achieve the above object, a flat die for blow molding according to the present invention comprises a core housing inserted in a die housing to form a resin passage, and an extruder is provided in the resin passage. A resin inlet from the side is opened at a symmetrical position, and a manifold is formed from each of the resin inlets to the core metal surface in a circumferentially left and right direction, the passage cross-sectional area is reduced, and the manifold is curved in the extrusion direction. and it causes the manifold end of the other resin inlet merging respectively, cross-section and configured to be oval or elliptical circular as it descends downwardly the resin passageway having an annular passage from above, further, the core Protrusions provided at the bottom of gold
Narrow the resin passage on the short diameter side of the flat die, or
Is the resin passage on the long diameter side of the flat die where the molten resin does not easily flow
And the flow of molten resin
The passage area of the resin passage on the short diameter side of
Thus, the cross-sectional area of the opening is set so as to obtain a uniform pressure loss in the circumferential direction.

[0009]

According to the above construction, the resin flows into the resin passage in the die from the resin inlet for each shot, but flows down along the manifold and simultaneously overflows the land. The junction of the manifold is formed at the dam lip portion, from which the resin flows down, and at the same time, the resin flows down from the land to the dam lip portion. The height of the land is lower than that of the dam lip, and the overflow from the manifold is approximately equal along the path from the resin inlet, and the resin is uniformly wrapped around the entire die in the entire circumferential direction and is injected by the parison. Is uniform in thickness. In addition, the die is formed by a lower housing material and a mandrel that can be replaced only with the lower die, and a projection is provided in the middle of the resin flow path so as to obtain a uniform parison corresponding to the size of the molded product. By making the gap between the major-diameter resin flow paths larger than that of the minor-diameter resin flow path, the pressure loss in the resin flow path between the molten resin on the major and minor diameter sides of the flat die is reduced. Be uniform in the circumferential direction of the road.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the flat die for blow molding according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a structure of a die according to one embodiment. As shown in the figure, the die 10 has a die housing 12, and 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. Such a through-hole 14 is opened at the lower end surface of the housing 12 in a state where the equivalent diameter is gradually reduced from the middle to the lower end surface of the housing 12. A metal core 16 having a smaller diameter than the through-hole 14 and having a circular cross-section at the top and having an oval or elliptical cross-section in the middle is inserted into the housing 12. A resin passage 18 is formed between the outer peripheral surface of the metal core 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. The resin passage 18 is formed below the cored bar 16, and the elliptical or elliptical portion from the circular cross-section above the cored bar 16 to the lower portion. Resin passage 1
8 is also configured to change shape from an annular passage to an oval or elliptical annular passage.

As described above, the upper end portion of the cored bar 16 has a circular cross-sectional structure in close contact with the through-hole 14, so that the cross-sectional shape of the outer peripheral surface of the upper die housing 12a is also circular. I have. Further, the thickness of the upper die housing 12a is configured to be considerably thinner than that of the lower die housing 12b. This is because the upper portion of the die 10 has a circular shape, and the extruding pressure from the extruder (not shown) at the time of parison injection acts uniformly in the circumferential direction of the resin passage 18 so that the die 10 is biased to one side. No pressing force acts on the upper die housing 12a, so that concentrated stress is less likely to be generated.

Further, the cross-sectional shape of the outer peripheral surface of the lower die housing 12b has a rectangular shape in accordance with the flat resin passage 18. Therefore, the lower die housing 1
2b is configured to be considerably thicker than the thickness of the upper die housing 12a. Since the lower part of the die 10 has a flat shape, the pressing force applied to the surface of the resin passage 18 where the extruding pressure from the extruder (not shown) at the time of parison molding is parallel to the major axis is smaller. The pressure receiving area, which is larger than the pressing force acting on the resin passage 18 facing the minor diameter side, is increased by an amount corresponding to the larger pressure receiving area.
This is for preventing the lower die housing 12b from being cracked and damaged due to the occurrence of a flexure on the eight surfaces such that the interval between the resin passages 18 expands and the occurrence of concentrated stress due to the expansion pressing force.

A resin supply path 20 is provided inside the metal core 16.
Which is branched in the direction of the equivalent diameter of the core 16,
The resin passage 18 has a pair of openings. The opening is set in the resin passage 18 on the wide side as shown in FIG.

In such a basic configuration, the outer surface of the cored bar 16 is branched left and right in the circumferential direction with the respective resin inflow ports 22 as a starting point, and the passage cross-sectional area is gradually reduced at a predetermined ratio and at 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 each other at a position substantially 90 degrees from the resin inlet 22 and the manifold 24 on the opposite surface which is symmetrical. And this confluence part 26
A dam lip portion 28 that forms a shallow passage along the circumferential direction of the metal core 16 corresponding to the portion is formed. The dam lip portion 28 is provided corresponding to the throttle passage portion of the resin passage 18 and is set so as to narrow the gap with the through hole 14 of the die housing 12 so that the passage resistance is uniform over the entire circumference. I have. In this case, the junction 26
Are joined and joined so that the symmetrical manifolds 24 are in contact with a line along the axis of the metal core 16. As a result, the flow lines of the resin flowing down each manifold 24 are parallel at the junction.

The entire resin passage 18 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 flow passage depth of the dam lip portion 28 portion. The part 30 is formed. This is formed by adjusting the shaving depth of the outer surface of the cored bar 16 as described above.

Below the die body 10, a lower die housing 12b surrounds the outer periphery of the core 15 around the core 15.
A resin passage between the core 15 and the lower die housing 12b
The path 18 has an oval or elliptical ring shape and the lower die housing
Mans arranged at the lower end of the ring 12b and the lower end of the core 15.
A flat annular outlet slit 17 (die lip gap) is formed with the drain lip 29 . The lower end of the resin passage 18 is connected to the outlet slit 17, and when the plunger of the resin injection device (not shown) is pushed forward, the resin passage 1
The molten resin in 8 is extruded out of the main body through the exit slit 17 so that a parison 32 is formed.

Here, the projection 40 according to the embodiment of the present invention is described.
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 height of the projections 40 is such that 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. It is decided.

In the present embodiment, the core 15 protrudes from the core 15 in the X direction on the short diameter side in the middle of the resin passage 18 below the die 10.
A protrusion 40 is provided to make the pressure loss in the circumferential direction the same when the molten resin passes through the resin passage 18 in the lower die housing 12b. However, the present invention is not limited to this, and as shown in FIG. In addition to increasing the passage area of the resin passage 18 on the long diameter side Y where the molten resin is less likely to flow, the passage area of the resin passage 18 on the short diameter side X where the molten resin easily flows is reduced, so that the pressure loss in the circumferential direction becomes the same. You may do so.

The operation of the dice configured as described above will be described. The molten resin that has flowed into the resin inlet 22 from the extruder 23 via the resin supply path 20 branches right and left in the manifold 24 to reach the junction 26, and flows down from the lower edge of the manifold 24 to the land 30 together with the branch flow. The resin overflows sequentially, and the resin flows uniformly all around the resin passage 18. 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 flows down in a state where the pressure is readjusted by the dam lip portion 28 to have a uniform thickness. It is injected as a parison 32.

Under these circumstances, if blow molding is performed using, for example, engineering plastic resin having a higher viscosity than general-purpose resin as the molten resin, the molten resin passes through the narrow exit slit 17 together with high-speed injection. In this case, a large pressure loss occurs, and the opening cross-sectional area ratio and the flow path length differ between the short diameter side X and the long diameter side Y.
Due to this difference, the pressure loss in the circumferential direction of the resin passage 18 becomes uneven, and as a result, the thickness of the parison 32 ejected from the outlet slit 17 becomes uneven.

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 circumference of the resin in 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 parison 32 becomes uniform in the circumferential direction.

In the case of molding a large molded product different from the conventionally molded product, if the length of the resin passage 18 in the lower die housing 12b increases as the diameter of the parison 32 increases, A parison 32 having a non-uniform wall thickness in which the difference in pressure loss between the major diameter side Y and the minor diameter side X becomes significant.
Is easily formed. Conversely, when the diameter of the parison 32 decreases, the length of the resin passage 18 generally decreases, and the parison 32 having a relatively uniform wall thickness with a small pressure loss difference between the long diameter side Y and the short diameter side X is formed. Easy to be. Based on these results, the lower die housing 12b, the core 15 having the protruding portion 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. It is exchanged with.

As described above, the lower die housing 12b, the core 15, the mandrel lip 29 and the like constituting the outlet slit 17 for forming the parison of the die 10 are detachably attached to the upper die housing 12a by, for example, bolts or lock nuts. Or other upper die housing 12 attached to a parison control rod (not shown).
a, because it can be easily replaced with the cored bar 16,
The parison 32 according to the shape and size of the molded product can be easily formed without replacing the entire die 10. Therefore, when molding molded products of different molded product sizes, it can be handled without installing a dedicated blow molding machine, and the operation efficiency of the blow molding machine is improved and the cost of products is reduced. Can be.

In the flattening die 10 for blow molding according to the embodiment of the present invention, the uniformity around the resin can be achieved by providing the manifold 24 and the dam lip portion 28, so that there is no resin stagnant portion, and especially the resin confluence. The changeability of the resin in the portion 26 is significantly improved, and the deterioration of the changeability of the resin can be prevented. Furthermore, since a plurality of stages of dam lips as in the related art are not required, the length of the die 10 itself can be shortened, and there is an advantage that the weight of the die 10 can be reduced.

[0026]

As described above, in the blow molding flat die according to the present invention, a resin passage is formed by inserting a metal core into a die housing, and a resin inlet from the extruder side is formed in the resin passage. Are opened at symmetrical positions and branch from the respective resin inlets to the core metal surface in the circumferential direction to the left and right to form a manifold having a reduced passage cross-sectional area and curved in the extrusion direction. together to merge each manifold end of the cross-section is configured to be oval or elliptical circular as it descends downwardly the resin passageway having an annular passage from above, further, the projection portion to the core metal lower The short diameter of the flat die provided
Narrow the resin passage on the side or reduce the flow of molten resin.
Increase the passage area of the resin passage on the long diameter side of the flat die
And the short diameter of the flat die, where the molten resin easily flows.
The passage area of the resin passage on the side is reduced and the cross-sectional area of the opening is set so as to achieve a uniform pressure loss in the circumferential direction, so that the resin flow stays in the die while performing uniform parison injection. Preventing it from being created at a fixed position,
Thus, an excellent effect that the old material can be quickly discharged at the time of color change or the like can be obtained. In addition, since the deflection and stress of the upper die housing are evenly distributed in the circumferential direction and their values are reduced, the members of the upper die housing can be made thinner, and the overall weight of the die can be significantly reduced. Further, the flat parison can be injected uniformly by setting the opening cross-sectional area so as to have a uniform pressure loss in the circumferential direction of the resin passage. In addition, by replacing the lower housing material and core, etc., which form a molding material discharge port suitable for obtaining a parison corresponding to the product size, molded products of different product sizes can be easily manufactured without replacing the entire die. Obtainable. Furthermore, it is possible to respond without installing a dedicated die or molding machine, thereby improving the operating efficiency of the molding machine and reducing the product cost.

[Brief description of the drawings]

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

2 is a cut planar view as seen from A-A in FIG. 1 (2).

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Dice 12 Dice housing 12a Upper die housing 12b Lower die housing 14 Through-hole 15 Core 16 Core bar 17 Outlet slit 18 Resin passage 20 Resin supply passage 22 Resin inlet 24 Manifold 26 Merge part 28 Dam lip 29 Mandrel lip 30 Land part 32 parison 40 protrusion

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B29C 49/78 B29C 49/78 // B29L 22:00 (56) References JP-A-6-182857 (JP, A) (58 ) Surveyed field (Int.Cl. ⁶ , DB name) B29B 11 / 10,11 / 14 B29C 47 / 20,49 / 04,49 / 42,49 / 78

Claims (1)

(57) [Claims] 1. A resin passage is formed by inserting a metal core into a die housing, a resin inlet from an extruder side is opened at a symmetric position in the resin passage, and a resin inlet is formed from each resin inlet to a surface of the metal core. Branches left and right in the circumferential direction, the cross-sectional area of the passage decreases,
A manifold curved in the extrusion direction is formed, and the manifold end and the manifold end from the other resin inlet are respectively merged. The shape of the manifold is changed from circular to long as the resin passage having an annular passage is lowered from above to below. configured as a circle or an ellipse, further wherein
A protruding part is provided at the lower part of the metal core to allow the resin
Reduce the width of the road, or use a flat
Increase the passage area of the resin passage on the long diameter side of the chair
In addition, resin flow on the short diameter side of the flat die where molten resin flows easily
A flat die for blow molding, wherein an opening cross-sectional area is set so as to reduce a passage area of a path and to obtain a uniform pressure loss in a circumferential direction.