JP6853073B2 - Blow molding method - Google Patents

Description

The present invention relates to a blow molding method.

In blow molding, the molding material is melted by an extruder to form a tubular parison through the head. Then, this parison is sandwiched between molds, gas is blown into the inside thereof, and the parison is pressed against the inner surface of the mold by the pressure to form a blow molded product (hollow molded body).

Regarding this blow molding, Patent Document 1 discloses the following technique. That is, two blow pins are inserted from the side of the parison at the same time, and a cooling medium is blown to expand the parison. Next, a blow molding method is disclosed in which a cooling medium is blown into the parison from one blow pin and the cooling medium in the parison is discharged from the other blow pin to cool the parison.

Japanese Unexamined Patent Publication No. 7-88944

However, there is a problem that when the cooling medium is blown into the parison in the blow molding die with a blow pin and discharged, the cooling medium stagnate and heat is trapped.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to suppress stagnation of a cooling medium in a parison and to perform effective cooling.

The blow molding method of the present invention
A blow molding method for molding blow molded products.
This is a blow molding method characterized by allowing the cooling medium to flow along the inner surface of the parison when the cooling medium is blown into the parison in the blow molding die with a blow pin and discharged.

According to this configuration, since the cooling medium flows along the inner surface of the parison, the stagnation of the cooling medium is suppressed, the heat retention is reduced, and the parison can be effectively cooled.

It is a schematic diagram which shows the extrusion process of Example 1. FIG. It is a schematic diagram which shows the parison adsorption process and the parison cutting process of Example 1. FIG. It is a schematic diagram which shows the parison transfer process of Example 1. FIG. It is a schematic diagram which shows the pre-blow process of Example 1. FIG. It is a schematic diagram which shows the mold closing process of Example 1. FIG. It is a schematic diagram which shows the main blow process of Example 1. FIG. It is a schematic diagram which shows the mold opening process of Example 1. FIG. It is a schematic diagram which shows the taking-out of the product of Example 1 and the burr cutting. It is a schematic diagram which shows the secondary cooling process of Example 1. FIG. It is a schematic diagram which shows the flow of the cooling medium in the parison of Example 1. FIG. It is a front view which shows an example of the blow pin used in Example 1. FIG. It is a schematic diagram which shows the flow of the cooling medium in the parison of the conventional example. It is a front view which shows an example of the blow pin used in the conventional example.

(1) In the blow molding method of the present invention, it is preferable that the cooling medium swirls in the parison.
According to this configuration, since the cooling medium swirls and flows well, the stagnation of the cooling medium is further suppressed, and the parison can be effectively cooled.

(2) The blow molding method of the present invention preferably has a configuration in which the blow pin ejects the cooling medium in one direction.
In this configuration, since the blow pin is configured to eject the cooling medium in one direction, the flow of the cooling medium can be reliably created with a simple configuration.

Next, Example 1 which embodies the blow molding method of the present invention will be described with reference to the drawings.

<Example 1>
In the blow molding method for molding the blow molded product of the first embodiment, when the cooling medium is blown into the parison in the blow molding mold with a blow pin and discharged, the cooling medium flows along the inner surface of the parison. It is characterized by doing.

First, the flow of the blow molding method of this embodiment will be described.
A blow molding apparatus is used as the blow molding method. The blow molding apparatus is an extrusion machine 1 that extrudes a tubular molten resin called a parison 3, a pair of dies 7 that sandwich the parison 3 from both sides, and a pair of dies 7 that are brought close to each other and separated from each other to close and separate the dies. It is equipped with a mold drive mechanism (not shown) that opens.

The blow molding method of this embodiment includes an extrusion step, a parison adsorption step, a parison cutting step, a parison transfer step, a pre-blow step, a mold closing step, a main blow step, a mold opening step, and a secondary cooling step.
FIG. 1 shows the extrusion process. In this step, as shown in FIG. 1, a tubular molten resin is extruded by an extruder 1 to form a parison 3. The left figure of FIG. 1 shows a state in the middle of extrusion, and the right figure of FIG. 1 shows a state in which extrusion is completed. The specific form of the parison 3 is not particularly limited, but for example, as shown in FIG. 1, the diameter gradually increases toward the lower end, and the lower end side is inclined with respect to the vertical direction. are doing.

Next, the parison adsorption step shown in the left figure of FIG. 2 is performed. In this step, the parison 3 is gripped in a state of being sucked by the robot hand 5. At this time, a vacuum suction method is adopted in which the upper and lower ends of the parison 3 are left open and the vicinity of the upper end portion of the parison 3 is gripped by suction.
After that, the parison cutting step shown in the right figure of FIG. 2 is performed. In this step, the parison 3 is cut to a predetermined length. The length of one parison 3 is appropriately adjusted according to the size of the product 15.

Next, the parison transfer step shown in FIG. 3 is performed. The parison 3 is conveyed by the robot hand 5 until it is located between the pair of molds 7. At this time, the mold 7 is in the mold open state.
Subsequently, the pre-blow step shown in FIG. 4 is performed. First, as shown in the left figure of FIG. 4, the pre-blow pin 9 is inserted from the lower side of the parison 3. Then, as shown in the middle figure of FIG. 4, the pinch plates located above and below the parison 3 are closed. In this state, as shown in the right figure of FIG. 4, a cooling medium is blown into the parison 3 from the pre-blow pin 9 to slightly inflate (pre-blow) the parison 3.

Subsequently, the mold closing step shown in FIG. 5 is performed. From the state shown on the left in FIG. 5, the pair of molds 7 are brought close to each other by the mold driving mechanism to close the mold, and the state shown on the right in FIG. 5 is obtained.

Next, the main blow step shown in FIG. 6 is performed. In this step, as shown in the left figure of FIG. 6, the blow pin 13 is driven into the parison 3 in the mold closed state. The mold 7 is formed with a hole (not shown) into which the blow pin 13 can be inserted (insertable). Subsequently, as shown in the right figure of FIG. 6, in this state, a cooling medium is blown into the parison 3 from the blow pin 13 to inflate the parison 3 (this blow).

After that, the mold opening step shown in FIG. 7 is performed. In this step, the mold is opened and the product 15 is taken out. Then, as shown in FIG. 8, burrs are cut out from the product 15. Subsequently, the secondary cooling step shown in FIG. 9 is performed. In this step, as shown in the left figure of FIG. 9, the product 15 is placed in the cooling mold 17. Then, as shown in the middle figure of FIG. 9, after the secondary cooling is completed, the product 15 is taken out from the cooling mold 17 and cured at room temperature as shown in the right figure of FIG.

Here, the features of the first embodiment will be described. In the first embodiment, the cooling medium is made to flow along the inner side surfaces 3A and 3B of the parison 3 at the time of the main blow of FIG. This feature will be described with reference to FIG. FIG. 10 schematically shows the inside of the parison 3 in the mold 7. Three blow pins 13A, 13B, and 13C are inserted into the parison 3 from one of the molds 7 of the pair of molds 7. Of the three blow pins 13A, 13B, 13C, the blow pins 13A and 13B are used exclusively for blowing, and the blow pins 13C are used for both blowing and exhausting.

Of the blow pins 13A, 13B and 13C, at least the blow pins 13A and 13B are configured so that the cooling medium can be ejected in one direction. That is, instead of ejecting the cooling medium by diffusing it radially, the cooling medium flowing in one direction is ejected. For example, specifically, as shown in FIG. 11, the blow pins 13A and 13B have a rod-like shape with a sharp tip, and the inside is hollow so that a cooling medium can flow through, and a single blowout is made near the tip. Holes 19A and 19B are formed. The tip portions of the blow pins 13A and 13B are sharply pointed so that they can be easily inserted into the parison 3, and the angle is appropriately selected according to the type of resin and the like.

When the cooling medium is ejected from the single outlet holes 19A and 19B, the cooling medium can be ejected in one direction. The blowout holes 19A and 19B have a substantially circular shape. By making the blowout holes 19A and 19B substantially circular, the turbulence of the flow of the blown-out cooling medium is suppressed. If the blowout holes 19A and 19B are made rectangular, the flow of the cooling medium is likely to be disturbed near the corners. Therefore, in order to create a flow of the cooling medium along the inner side surface 3A of the parison 3, it is preferable that the blowout holes 19A and 19B are substantially circular.

The blowout hole 19A of the blow pin 13A inserted into the parison 3 faces in the direction along the inner surface 3A of the parison 3 in the vicinity where the blow pin 13A is inserted. That is, the blow pin 13A is open in the circulation direction along the inner side surface 3A.
Similarly, the blowout hole 19B of the blow pin 13B inserted into the parison 3 faces in the direction along the inner surface 3B of the parison 3 in the vicinity where the blow pin 13B is inserted. That is, the blow pin 13B is open in the circulation direction along the inner side surface 3B.
Further, in the first embodiment, the direction in which the blow-out hole 19A of the blow pin 13A faces and the direction in which the blow-out hole 19B of the blow pin 13B faces are set to face in opposite directions. In this way, the swirling cooling medium flow shown by the broken line in FIG. 10 is created.
The blow pin 13C is inserted near the corner of the parison 3. The blow pin 13C is also used for exhaust, but by inserting the blow pin 13C into the corner of the parison 3, it is possible to efficiently exhaust the portion of the cooling medium where stagnation is likely to occur.

As shown in FIG. 10, the blow pins 13A and 13B are inserted in the vicinity of the inner side surfaces 3A and 3B of the parison 3. Generally, inside the parison 3, the stagnation of the cooling medium tends to occur in the vicinity of the inner surfaces 3A and 3B of the parison 3. In the first embodiment, by inserting the blow pins 13A and 13B in the vicinity of the inner side surfaces 3A and 3B of the parison 3, the cooling medium can flow as if it crawls on the inner side surfaces 3A and 3B, so that the cooling medium stagnate. Can be effectively suppressed. Further, it is preferable that the blow pins 13A and 13B are inserted in the vicinity of the inner side surfaces 3A and 3B of the opposing parisons 3, respectively. By inserting the blow pins 13A and 13B in such a positional relationship, a cooling medium that largely rotates inside the parison 3 can flow, and the cooling efficiency is improved.

Here, the action and effect of Example 1 will be described in comparison with the conventional example. FIG. 12 shows a conventional example. In the conventional example, the same components as those in the first embodiment are designated by the same reference numerals.
Conventionally, the blow pin 21 shown in FIG. 13 has been used for this blow. The blow pin 21 has a rod-like shape with a sharp tip, and the inside is hollow so that a cooling medium can flow through. A plurality of small blowout holes 21A are formed in the vicinity of the tip over the entire circumference in the radial direction. .. In this way, the blow pin 21 diffuses the cooling medium in a radial manner and ejects the cooling medium.

In the case of the conventional example of FIG. 12, at the time of the main blow, three blow pins 21, 21, 25 are inserted into the parison 3 from the mold 7. In the initial state of the main blow, the cooling medium is blown from the three blow pins 21, 21, 25, and the blow pins 25 are switched for exhaust in the middle. When the cooling medium was blown into the parison 3 from the blow pins 21 and 21, the cooling medium flowed only in the vicinity of the blow pins 21 and 21. Therefore, in the vicinity of the corner of the parison 3 indicated by reference numeral 23 in FIG. 12, the cooling medium was stagnant, the cooling medium was hardly circulated, and heat was trapped. Therefore, the cooling efficiency of the parison 3 was low. Since the cooling efficiency is low in this way, the cycle time is long and the productivity is lowered. Further, in the cooling process of the product 15, a place where the temperature was locally high was formed inside, and the dimensional change was likely to occur, and the dimensional was not stable.

On the other hand, in Example 1, the following effects are exhibited. That is, as shown in FIG. 10, at the time of the main blow, three blow pins 13A, 13B and 13C are inserted into the parison 3 from the mold 7. In the initial state of the main blow, the cooling medium is blown from the three blow pins 13A, 13B, 13C, and the blow pins 13C are switched for exhaust in the middle. In this state, the cooling medium flows along the inner surfaces 3A and 3B of the parison 3 as shown in FIG. Specifically, the cooling medium swirls in the parison 3, and stagnation of the cooling medium hardly occurs. Therefore, the parison 3 can be effectively cooled. Since the cooling efficiency is high in this way, the cycle time can be shortened and the productivity is improved. Further, in the cooling process of the product 15, the dimensional change caused by the locally high temperature is suppressed, and the dimensional accuracy is improved.

Further, in the first embodiment, the parison 3 can be effectively cooled by a simple means of improving the configurations of the blow pins 13A and 13B. Therefore, the first embodiment is very advantageous in terms of cost.
In the first embodiment, single blowout holes 19A and 19B are formed in the blow pins 13A and 13B, respectively. Since the single blowout holes 19A and 19B are easy to form, the manufacturing cost of the blow pins 13A and 13B is reduced.
Further, since the single blowout holes 19A and 19B have a substantially circular shape, they are easier to form than a rectangle. Moreover, the substantially circular single blowout holes 19A and 19B have large openings, and the blown-out cooling medium is less disturbed than when a plurality of small holes are used, and the flow of the cooling medium is easily formed.
Further, in the first embodiment, the blow pins 13A and 13B are inserted in the vicinity of the inner side surfaces 3A and 3B of the opposing parison 3, respectively, and as shown in FIG. 10, the flow of the cooling medium that largely goes around the inside of the parison 3. And the cooling efficiency is extremely high. If a plurality of small swirling cooling medium flows are formed inside the parison 3, the cooling media are likely to stagnate in a portion where the swirling cooling medium flows are close to each other. In the first embodiment, since there is only one flow of the cooling medium that swirls, stagnation of the cooling medium is unlikely to occur.

<Other Examples>
The present invention is not limited to the examples described by the above description and drawings, and for example, the following examples are also included in the technical scope of the present invention.

(1) In the first embodiment, the number of blow pins 13 is three, but the number of blow pins 13 is not particularly limited.
(2) In Example 1, the blow-out hole of the blow pin 13 has a specific shape, but it can be appropriately changed according to the size, form, and the like of the manufactured product 15.
(3) In the first embodiment, the vacuum suction method is adopted when the parison 3 is gripped by the robot hand, but the pinch method in which the parison is sandwiched and gripped may be adopted.
(4) In the first embodiment, the blow pins 13A and 13B are opened in the circulation direction, but the opening is not limited to the circulation direction, and the blown cooling medium collides with the inner side surface and then opens to the inner side surface. It may be in a direction that flows in the circulation direction along the line.
(5) In the present invention, the cooling medium is not limited to air, and may be mist or the like.
(6) The blow pins 13A and 13B may be configured to be rotatable around an axis.

1 ... Extruder 3 ... Parison 3A, 3B ... Inner surface 5 ... Robot hand 7 ... Mold 9 ... Pre-blow pin 13 ... Blow pin 15 ... Product 17 ... Cooling mold 19 ... Blow-out hole 19A ... Blow-pin A blow-out hole 19B ... Blow pin B blow-out hole 21 ... Blow pin 21A ... Blow-out hole 23 ... Cooling medium stagnation 25 ... Other blow pins

Claims (2)

A blow molding method for molding blow molded products.
When the cooling medium is blown into the parison in the blow molding die with a blow pin and discharged, the cooling medium is allowed to flow along the inner surface of the parison .
A blow molding method characterized in that the cooling medium swirls in the parison. The blow molding method according to claim 1, wherein the blow pin is configured to eject the cooling medium in one direction.

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