JPS60149428A - Mold for blow molding - Google Patents

Abstract

PURPOSE:To uniformize moldings having non-uniform thickness and obtain a high dimensional stability by providing a parision sucker which can freely come in and out of the cavity. CONSTITUTION:When a parision 3 is injected, a parision sucker 4 is projected into the cavity, the parision 3 is attracted by a vacuum cap 4a, and the parision sucker 4 is retracted into a recession 2a as molds 1 and 1' are started closing. While the parision 3 is uniformly stretched, it is attracted into the recession 2a, and at a time when the sucker 4 is completely housed in the mold 1, air is blown into the parision.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a mold for a blow molding machine.

[Background technology]

In the blow molding method, generally, a tube-shaped molding material (parison) extruded from an extruder on a molding machine is held between molds that are opened and closed using a hydraulic cylinder, etc., and air is blown into the inside from an air inlet to create a hollow shape. molding products.

However, as shown in Figure 1, for example, in a molded product that is asymmetrical with respect to the injection direction of the parison and has a large convex portion on one side, the wall thickness of the convex portion becomes extremely thin and the overall wall thickness becomes uneven. It may become.

This will be explained in detail below based on FIGS. 2 to 4.

Figure 2 shows the parison 3 injected into the mold cavity 2 with the mold 1.1' open, and Figure 3 shows the mold 1.1' closed. The positional relationship between mold cavity 2 and parison 3 cannot be corrected. Figure 4 shows
This figure shows the wall thickness distribution of the parison 3 after air is blown. As shown in the figure, when air is blown, the elongation of the parison at the convex part of the molded product becomes significantly large.
The wall thickness of this part is extremely thin compared to other parts, so conventionally, when molding a molded product with such a convex shape, in order to control the wall thickness of the parison around the convex part, ,
A method has been adopted in which the thickness of the parison is increased to increase the thickness of the A section.

However, according to this method, the thickness of parts that do not need to be increased, such as the part on the opposite side of the convex part, increases, and the weight of the entire molded product increases, causing an increase in cost. In addition, if the weight of the molded product increases, the molding cycle becomes longer, which is disadvantageous in terms of productivity, and there are various problems such as large variations in wall thickness distribution and uneven shrinkage after molding. Difficult to secure desired molding dimensions.

[Purpose of the invention]

This invention was made in view of the above circumstances, and provides a blow molding mold that can increase the thickness of molded products with unevenness and efficiently mold molded products with high dimensional stability. The purpose is to provide.

[Disclosure of the invention]

In order to achieve the above object, the blow molding mold of the present invention is a mold for blow molding molded products having an asymmetrical convex portion, and a parison suction device that can freely move in and out is attached to the cavity. This suction tool ensures the thickness of the convex portion of the molded product and at the same time increases the thickness of the entire molded product. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing examples.

5 to 8 show a process of molding a parison using the blow molding die according to the present invention. This mold has a recess 2a, and a parison suction tool is provided in this recess. The parison suction tool 4 consists of a vacuum cup 4a, a shaft 4b to which the cup 4a is fixed at the tip, and an operation source 5 for moving the shaft 4b in and out. The operation source 5 is
The vacuum cup 4a, which is attached to a through hole 1a provided in a recess (thin wall part) of the mold cavity 2 and is fixed to the tip of the shaft 4b, is moved in and out of the cavity by moving the shaft 4b in and out. A vacuum hose 6 is attached to the vacuum cup 4a, and this hose 6 moves in and out of the cavity 2 in accordance with the movement of the shaft 4b.

As the operation source 5, a pneumatic cylinder, a hydraulic cylinder, or the like is generally used.

FIG. 9 shows details of the vacuum cup 4a. In addition to the circular shape shown in the figure, the vacuum cup 4a can have various shapes depending on the shape of the molded product.

Next, a molding process using the molding die according to the present invention will be explained.

As shown in FIGS. 5 to 8, when the parison 3 is injected, the parison suction tool 4 is propelled into the cavity 2 by the operating source 5, and the vacuum cup 4a suctions the parison 3. When the cup 4a adsorbs the parison 3, the mold 1.1
′ is closed. Simultaneously with the start of closing of the molds 1, 1', the parison suction tool 4 begins to retreat into the recess 2a of the mold 1, and the suctioned parison 3 does not come into contact with the molds 1, 1'. As the vacuum cup 4a retreats, it is uniformly stretched and drawn into the recess 2a in the cavity 2. If air is blown once the suction tool 4 is completely contained within the mold 1, a molded product with uniform wall thickness can be obtained, as shown in FIG.

By the way, depending on the thickness of the parison, the shape of the product, and the size and shape of the vacuum cup, the parison may show local elongation when pulled by the suction tool. in this case,
As shown in FIG. 10, in the mold 1' on the opposite side, that is, in the mold 1' to which the parison suction device is not attached, at a position opposite to the suction device 4, a hole is inserted into and out of the cavity 2'. It is preferable to provide a flexible parison presser 7. This presser foot 7
The holding part 7a is operated by the same mechanism as the suction tool 4, and the holding part 7a fixed to the tip of the shaft 7b moves in and out of the mold cavity 2' using a pneumatic or hydraulic cylinder as the operating source 8. do.

Similarly to the vacuum cup 4a, this holding portion 7a can also have a shape that matches the shape of the molded product as appropriate.

Next, a process of molding a parison using the blow molding mold to which both the suction tool 4 and the presser tool 7 described above are attached will be described.

As shown in FIGS. 10 to 13, when the parison 3 is injected, the suction tool 4 moves forward and the vacuum cup 4a suctions the parison 3. Thereafter, at the same time as the mold 1.1' begins to close, the suction tool 4 retreats into the recess 2a, while the presser tool 7 moves forward from within the mold 1', so that the parison is closed, as shown in FIG. 3 is pulled by the suction tool 4 and pressed by the presser 7, thereby preventing local elongation. When the suction tool 4 is completely housed in the mold 1, the presser tool 7 is moved back and is housed in the mold 1'. By subsequently blowing air, a molded product with uniform wall thickness as shown in FIG. 13 can be obtained. The presser 7 may be moved back by the blowing pressure when air is blown.

Generally, the diameter of the parison is set depending on the size and shape of the molded product, but when the diameter of the parison is large relative to the mold, the mold will sandwich the parison around its entire circumference.

The molding die according to the present invention can also be effectively used in the above-mentioned applications.

In the following, as shown in FIG. 14, which explains the process of molding a parison with a large diameter using a mold according to the present invention, after the parison 3 is injected, the suction device 4 and the presser 7 are operated, and the vacuum cup is 4a and the holding part 7a, and at the same time, the suction tool 4 is retreated into the recessed part 2a,
The presser portion 7a is advanced from within the mold 1' to draw the entire parison 3 toward the four portions 2a of the cavity 2. parison 3
When the mold contacts the bottom surface of the recess, the molds 1 and 1' are closed, as shown in FIG. Then, the large-diameter parison 3 is placed in the mold 1.1 with its center shifted toward the recess 2a.
' will be sandwiched between. When air is blown in this state, the parison 3 is restrained by the contact points of the molds 1 and 1', so it stretches evenly within each of the molds 1 and 1', resulting in more even meat. A thick molded product can be obtained. In other words, in this case, by closing the molds 1 and 1', the parison 3 is fixed in a shifted state toward the recess, so that by simply adjusting the timing of closing the molds 1 and 1', the inside of each cavity is fixed. This is because a predetermined blow ratio can be easily set at 2.2'.

When a molded article having a convex portion requires a thicker wall, it is effective to match the shape of the vacuum cup of the suction tool to the shape of the cavity recess. For a vacuum cup shaped like the one shown in the figure, parison 3
After coming into contact with the periphery of the cup 4a, it is vacuum-formed within the cup. Therefore, the thickness t of parison 3 and the aperture ratio D/H
Therefore, the necessary wall thickness can be adjusted. FIG. 18 shows an example using the above vacuum cup.

〔Effect of the invention〕

As described above, in the blow molding mold of the present invention, a parison suction tool is installed inside the mold, and this goes in and out of the cavity and suctions the parison to ensure the wall thickness of the recess. It is possible to prevent the convex portion of the molded product from becoming thinner and to easily make the molded product thinner. Therefore, it is possible to obtain a molded product that shrinks uniformly after molding, has high dimensional stability, and is free from warping and distortion. In addition, since there is no need to locally increase the thickness of the parison at the convex part of the molded product, the weight of the molded product can be reduced, and as a result, the molding cycle including cooling time can be shortened. , productivity improves.

[Reference 1] Conventionally, in blow molding, as shown in Fig. 19, a parison (resin) 3 extruded from the top of a molding machine is sandwiched between a molding die 1.1' operated by a hydraulic cylinder 9 or the like. , air was blown from the air injection port 10 for molding.

Below, the changes in the wall thickness of parison 3 during molding are explained as follows:
Let me explain in more detail.

FIG. 20 shows the change in the parison 3 after the mold 1.1' is tightened when molding a molded product having a convex portion. As shown in the figure, the parison 3 is restrained at positions 1, a, and b. When air is blown into the parison 3 in state C in the figure, the parison 3 freely expands with a uniform thickness until it contacts the mold surfaces e, f, and g (state d in the figure). After this, by further blowing,
Expansion of the parison occurs in the mold recess 2a.

21 and 22 show the state of change of the parison in the mold recess 2a, and in FIG. 22, the region 3a with scattered dots is located at the positions f and g in FIG. 20. shows the parison part in contact with the mold 1. The parison that has come into contact with the mold 1 at points f and g is restrained by the mold surface at this point and therefore does not expand any further. For this reason, the mold recess 2
In a, as shown in Fig. 21, the parison 3 in the contact surface
Kinuta (a) continues to expand toward the bottom surface (p) of the recess while following the vertical direction of the mold recess. Then, by further blowing, the parison expands toward the concave corners k and l in the figure.

The parison wall thickness when the parison contacts f and g in the figure is t.
Let t2 be the thickness of the parison when it contacts the bottom p of the recess, the value of t2 is tI+ α, β, as shown in Fig. 21.
Determined by the value of γ.

Therefore, the larger T/β and α/β, the more 1,
The smaller t2 becomes, the thinner it becomes.

Conventionally, in order to ensure the thickness of t2, the thickness of tl was increased by vertical parison control, but this method had the disadvantage of significantly increasing the weight of the entire molded product. was there.

Therefore, in blow molding, in order to prevent thinning of t2 and equalize the thickness of the entire molded product without increasing the weight of the entire molded product, it is preferable to use the following molding die. That is, this is a blow molding mold in which a plate that can freely move in and out of a mold cavity is provided in a mold having a recess.

This mold will be explained in detail below.

As shown in FIG. 23, in the mold 1 having the recess 2a,
A plate 11 that can be freely moved in and out is installed in the cavity 1, and this plate 11 is reciprocated by an operating source 12 such as a hydraulic cylinder or a pneumatic cylinder that is also installed in the mold 1. To explain based on the process, when the parison 3 is injected into the cavity, the plate 11 moves forward with respect to the parison 3 which transitions from state C to state d in FIG. 20, and its surface comes into contact with the injected parison 3. do. For this reason, the plate 11 is set so as to maintain a distance m from the inner surface of the mold. The distance m is
The distance must be sufficient to prevent the parison 3 from contacting the mold surface before contacting the plate 11.

As shown in FIG. 20, when the plate 11 contacts the parison 3 as described above at the stage of transition from the C state to the d state due to the free expansion of the parison 3, the surface of the parison in contact with the plate 11 is The shaded area in Figure 23 is cooled and becomes difficult to stretch. In this state, the plate 11 is moved back into the recess 2a by the operation source 12, and is completely housed in the mold 1. After this, the parison is freely expanded by blowing and becomes a molded body, but the part of the parison 3 that has cooled down after contacting the plate 11 (the shaded part in the figure) is difficult to stretch compared to other parts, so its wall thickness is If it is not maintained, it will come into contact with the bottom surface of the recess 2a.

As a result, the wall thickness t2' (Fig. 24) of the convex part of the molded product molded by this molding die is thicker than the wall thickness t2 (Fig. 21) of the molded product molded by the conventional method. This prevents the wall from becoming thinner, and there is no need to adjust the wall thickness by parison control, so the overall weight of the molded product can be reduced.

[Reference 2] In blow molding, in order to eliminate local thickness unevenness of molded products with convex parts and increase the amount of parison supplied to the concave parts of the mold, the following molding mold is used. It is convenient. That is, this is a blow molding mold in which a pin that can freely move in and out of a mold cavity in accordance with the timing of blowing is provided in a mold having a recessed portion. Hereinafter, this will be explained in detail based on reference embodiments and drawings.

As shown in FIG. 25, in this molding die, a plurality of pins 13 are provided around the part where the convex part of the molded product is formed, that is, the concave part 2a, and protrude by a distance S from the mold. There is. This pin 13 is connected to the mold 1 as shown in FIG.
A source of motion 1, such as a hydraulic or pneumatic cylinder fixed in the
2, it can be moved into and out of the mold cavity.

Below, the changing state of the parison will be explained based on the molding process using the mold to which the pin is attached.

As shown in FIG. 20, the parison injected into the cavity comes into contact with a plurality of pins 13 propelled into the cavity by the operating source 12 at the stage of transition from the C state to the D state by blowing. At this time, as shown in FIG. 26, the pin contact portion q of the parison is restrained by the pin 13 and therefore becomes difficult to stretch. When further blowing is applied, the parison 3a around the pins 13 or between the pins 13 expands and expands toward the bottom p of the recess of the mold 1. When compared with FIG. 22, this parison 3a expands in a state close to free expansion until it comes into contact with the side surfaces n, o of the mold recess or the bottom surface p of the recess. This will be explained in more detail by comparing FIGS. 22 and 26. In these figures, regions 3a with scattered dots all indicate parisons located at the upper edge of the recess 2a. These are the recesses 2a when blowing.
It flows within. From this, the amount of parison supplied to the mold recess 2a is smaller in the case of the pin 13 in FIG.
It can be seen that the average wall thickness of the parison in the mold recess is larger than that in FIG. 22 by the amount of elongation caused by the elongation.

Further, in FIG. 25, after the parison contacts the pin 13, the expansion form of the parison until it hits points n and o on the side surface of the mold recess is close to free expansion when compared with FIG. 21. In free expansion, the parison wall thickness changes uniformly in proportion to the surface area, so the parison wall thickness change ratio ←L + t2")/l
+ will be close to the parison surface area ratio. Therefore, the ratio of change in wall thickness 5 is smaller than that in the case of expansion while constantly contacting the mold surface.

By adjusting the distance S and the set position of the pin according to the shape of the recess, the positions of n and o can be brought closer to the bottom surface p of the recess. By doing so, the degree of free expansion of the parison increases, so the wall thickness change ratio (t+ t2)/l+
It is possible to make it smaller.

In addition to the operation source as described above (FIG. 27), this pin can also be installed in the mold with the following structure.

In other words, as shown in FIGS. 28 and 29, the pin shaft 15
A spring 14 is mounted on the outside, one end of the spring 14 is received in the groove in the mold 1, and the other end is received in the contact part 1 of the tip of the pin.
It is a structure that pushes up 3. In the figure, 16 is pin 13
Do not remove it.

As shown in FIG. 29, as the blow pressure increases, the pin 13 is housed in the mold 1 by the action of the spring 14.

As seen above, the parison in contact with the pin is supplied to the mold recess in a form close to free expansion6, so there is no concern that only the convex part will be thinner than the wall thickness of the molded product body. This makes it possible to equalize the wall thickness of the entire molded product.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of a molded product having a left-right asymmetrical convex portion, Figs. 2 to 4 are explanatory views of the molding process using a conventional blow molding die, and Figs. 5 to 8 are , FIG. 9 is an explanatory view of the molding process showing one embodiment of the present invention, and FIGS. 14 to 16 are explanatory drawings of the molding process showing other embodiments of the present invention, FIG. 17 is a sectional view showing another embodiment of the vacuum cup according to the present invention, and FIG. The figure is an explanatory diagram of the molding process using a mold in which the inner surface of the vacuum cup has the shape of a convex part of the molded product. Figures 19 to 22 are cross-sectional views of conventional examples. Figures 23 and 24 are for reference. 25 and 26 are cross-sectional views showing other reference examples, and FIGS. 27 to 29 are cross-sectional views showing the embodiment.
The figures are cross-sectional views of two examples of pin operation sources. 1.1'... Mold 2.2'... Cavity 2a
...Mold recess 3...Parison 4...Parison adsorption tool 4a...Adsorption part 4b...Shaft 5, 8, 9.
12...Operating source 6...Vacuum hose 7...Presser 7a...Presser 7b...Shaft agent Patent attorney Takehiko Matsumoto 9 -17) - Ku-Public Relations N Ward Ward OF − Ajibo District District Peng Peng

Claims (3)

[Claims] (1) A mold for blow molding a molded product having asymmetrical convex portions, characterized in that a parison suction device that can be moved in and out is attached to a cavity. (2) The blow molding mold according to claim 1, wherein the suction tool is cup-shaped. (3) A mold for blow molding according to claim 2, wherein the inner surface of the suction tool has the shape of a convex part of the molded product. (4) A parison holder that can freely move in and out of the cavity at a location facing the suction tool. A blow molding mold according to any one of claims 1 to 3, to which a tool is attached.