JPH03221423A - Production of plastic tubular body and structure of mold - Google Patents

Abstract

PURPOSE:To sufficiently secure the supporting strength of a core by injecting molten plastic in a state wherein the midway part of the combined core is supported by a supporting member and thereafter retreating the supporting member and also filling molten plastic into the cavity formed by this retreating action. CONSTITUTION:The free ends of a first core 12 and a second core 13 are allowed to abut with each other and both cores 12, 13 are set in a main mold 11 as a combined core 14. In this state, the supporting pins 15... are advanced from the forming face 11a of the main mold and projected into the forming space part 10a until the tip parts 15a of the respective pins 15 are engaged with the inside of the pin receiving part 14a of the core 14. Then in this state, molten plastic material is injected and filled into the space part 10a. After injection and filling are completed, the pins 15... are retreated in the meantime wherein the temp. of molten plastic is lowered close to the temp. of a forming mold 10. At this time, the injected and filled plastic material is allowed to dwell at the secondary pressure lower than the initial pressure. The plastic material pressurized by this secondary pressure is filled into the cavity part formed by the retreating action of the pins 15....

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a plastic tube and a mold structure of a mold used for manufacturing the same.

[Prior Art] Conventionally, as a manufacturing method for plastic tubes, a core that forms the hollow portion of the tube is set in a main mold having a molding surface that forms the outer shape of the tube, and this core is Molten plastic is injected into the molding space formed by the molding surface of the main mold and the molding surface of the main mold. After this molten plastic hardens, the main mold is opened and the core is removed from the molded product to form a predetermined shape. Methods for obtaining tubes are generally well known. According to this method, a straight pipe (straight pipe) whose length to diameter ratio is below a certain level and which can ensure sufficient support strength for the core can be produced with relatively high precision. Moreover, it can be integrally molded efficiently.

However, when manufacturing a tube body (bent tube) bent into a predetermined shape from plastic, it is difficult to remove the core from the molded product after injection molding, so the above method is generally not applied. I can't. For this reason, a method is known in which a molded product is made into a divided structure so that the core can be removed, the divided parts are individually molded, and then these parts are bonded together and integrated. However, this method has problems in that injection molding requires multiple steps, an additional bonding step is required after molding, which increases the number of man-hours, and it is also disadvantageous in maintaining the precision of the molded product.

To solve this problem, for example, as shown in FIG.
2. Match the free ends of 53 and assemble the core 5
4, and the surface of this combination core 54 and the main mold 51
Molten plastic is injected into the molding space 50a formed by the molding surface, and after the molten plastic hardens,
The cores 52 and 53 are rotated and removed from the molded product 55, the mold 50 is opened, and the plastic bent tube 5 is removed.
5 is known.

[Problem to be solved by the invention] However, in this method, the combination core 54
However, if the length to diameter ratio is above a certain level, it is difficult to ensure sufficient support strength for the core 54, and the injection pressure of molten plastic may cause deformation or misalignment of the core 54, causing the tube to become damaged. There is a problem in that problems such as deformation of the inner surface of the body 55 or uneven thickness occur.

The present invention has been made in view of the above-mentioned problems, and provides a manufacturing method that can ensure sufficient support strength for the core when integrally injection molding a plastic tube, and a molding method used for the manufacturing. Its purpose is to provide a type structure for types.

[Means for Solving the Problem] Therefore, the first invention of the present application is to combine a pair of cantilevered cores with their free ends abutting each other, so that the surface of the combined core and the main In a manufacturing method in which a tube is manufactured by injecting molten plastic into a molding space formed by a molding surface of a mold, a support for protruding an intermediate portion of the combined core from the molding surface of the main mold toward the core side. The molten plastic is injected into the molding space while supported by the member, and then, while the molten plastic is cooling down, the supporting member is retreated to the molding surface of the main mold, and the molten plastic is applied with a predetermined pressure. The hollow portion formed by the retreat of the support member under pressure is also filled with molten plastic, and after the temperature of the plastic falls to a predetermined value, the core is removed.

Further, the second invention of the present application is to combine a pair of cores each supported by a cantilever by abutting their free ends,
In this mold for manufacturing a plastic tube in which a molding space is formed between the surface of the combination core and the molding surface of the main mold, the support member that supports the middle part of the combination core is connected to the main mold. It is provided so that it can move forward and backward from the molding surface of the mold toward the core side.

[Effects of the Invention] According to the first invention of the present application, molten plastic is injected with the middle part of the combination core supported by the support member, and then the support member is retreated and the support member is Since the hollow part formed by the retracting motion is also filled with molten plastic, by using a combination core, a bent pipe can be easily integrally molded, and the length relative to the diameter of the core can be easily formed. Even when the ratio is large, sufficient support strength for the core can be ensured. Therefore, it is possible to prevent the core from being deformed or displaced due to the injection pressure of the molten plastic.

Further, according to the second invention of the present application, the support member that supports the intermediate part of the combination core is provided so as to be movable back and forth from the molding surface of the main mold toward the core side, so that the molten plastic is When injecting into the molding space, the support member is advanced toward the core to support the core, and after the injection is completed, the support member can be retreated, and the manufacturing method according to the first invention It becomes possible to apply the method.

[Example] Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

As shown in FIGS. 8 and 9, the plastic tube l according to this embodiment has a connecting flange portion 2 at each end.
f, 3 f are integrally molded, and the center line L 2 has a predetermined radius of curvature Rt, Rs, respectively.
It has an upper half 2 and a lower half 3 bent along the curved line Ls, and the upper half 2 and the lower half 3 are integrally injection molded.

As shown in FIG. 1, a mold for forming the tube l! 0 includes a main mold 11 having a molding surface 11a that forms the outer shape of the tube 1, and a core 14 that forms the hollow portion of the tube 1.
The core 14 is composed of a first core 12 that forms the hollow part of the upper half 2 of the tube l, and a second core 13 that forms the hollow part of the lower half 3. ing.

These first and second cores 12 and 13 are connected to the arm portion 12
a and 13a, respectively, and the arm portions 12a and 1
The terminal portions of 3a are rotatably supported relative to the main mold 11 via hinge shafts 12b and 13b, respectively. By rotating these rain cores 12 and 13 together toward the inside of the main mold 11 and combining them by abutting their free ends, a combined core 14 can be formed, and this combination Surface of core 14 and main mold 1
A molding space 10a is formed by the molding surface 11a of the first molding surface 11a.

Then, a molten plastic material is injected and filled into this molding space 10a, and after the temperature of the plastic material falls to a predetermined value, the main mold 11 is opened and the first
By rotating the second cores 12 and 13 toward the outside of the main mold 11, respectively, the tube body 1 having the predetermined shape and dimensions shown in FIGS. 8 and 9 can be obtained. It has become.

The above main mold 1.1 has a mold parting surface 1'J2 (see Fig. 9).
It has a two-part structure divided along the line, and can be opened and closed in the direction of the plane of the paper in FIG.

Further, although not shown in the drawings, the mold lO is provided with upper and lower press molds for molding the end face portions of the connecting flange portions 2f, 3f of the tubular body l. When the combination core 14 is set in the main mold 11 and the presser mold is tightened, the combination core 14 has a mounting structure in which both upper and lower ends are fixed.
4 have the same shape and dimensions, when injecting molten plastic, both ends of the core 14 will be more stable than with a mounting structure in which one end is fixed and the other end is free, or one end is fixed and the other end is simply supported. The maximum moment load acting on the fixed part of the can be significantly reduced.

In this embodiment, the core 14 is stably supported against the injection pressure of the plastic material at an intermediate portion of the combined core 14, for example, at a matching portion between the first core 12 and the second core 13. Support bins 15, . . . , 15 are provided for the purpose. As shown in FIGS. 2 and 3, a plurality of support bins 15 (for example, three) are provided at equal intervals around the circumference, and each support bin 15 is connected to the main mold 11 as shown in detail in FIG. A rack 15c is carved into the main body portion 15b, which meshes with a pinion 16 which is driven by an electric motor 17 to rotate in forward and reverse directions. When the pinion 16 is rotated by the electric motor 17, the support bin 15 is moved back and forth between the main mold molding surface 11a and the core 14 via the pinion 16 and the rack 15c. A bottle receiving portion 14a is formed in the abutting portion of the core 14, into which the tip portion 15a of the support bottle I5 is fitted.

In addition, the rack 15c, the pinion 16, and the electric motor 1
Instead of the drive mechanism configured with 7, for example, a drive mechanism using a hydraulic cylinder operated by a hydraulic pump, a solenoid valve, etc. may be used.

Although not specifically illustrated, the electric motor 17 is electrically connected to a control section of the tube injection molding apparatus, and operates to open and close the mold IO and rotate the cores 12 and 13. The support bin 15. ..., 15 are controlled to move forward or backward.

Below, the above support pin 15. . . , 15 operations will be explained.

First, in a state in which the first core I2 and the second core 13 are set in the main mold 11 as a combination core 14 by abutting their free ends, the support pins 15. ..., 15 is advanced from the main mold molding surface 11a side toward the core 14 side, and molding is performed until the tip portion 15a of each support pin 15 is fitted into the pin receiver portion 14a of the core 14. It is made to protrude into the space part 10a.

Next, in this state, the molten plastic material is poured into the molding space 1.
Inject and fill into 0a (see Figure 2).

That is, taking as an example a case of nylon resin containing about 30% by weight of glass fiber as a reinforcing material,
For example, as shown in FIGS. 6 and 7, injection is performed at a predetermined initial pressure (for example, about 1000 kg/am") and a predetermined injection temperature (for example, about 300° C.). At this time, the core 14 The movement in the radial direction is particularly restricted by the support pins 15, .

After the injection and filling are completed, while the temperature of the molten plastic is decreasing to around the mold temperature T+o of the mold 0 (for example, at the time when it has decreased to a predetermined temperature Tp), the support pin 15. ..., 15 is the main mold molding surface 11a
Back up until the road surface is -.

At this time, the plastic material injected and filled into the molding space 10a is held at a secondary pressure lower than the initial pressure (for example, about 400 kg/am"), and is pressurized by this secondary pressure. The cavity formed by the retracting movement of the support pins 15.., 15 is also filled with plastic material (see FIG. 3).

Above support pin 15. ..., the operation timing of I5 is set so that the retracting operation of I5 is performed in a temperature range where the fluidity of the molten plastic material is sufficiently maintained and the cavity can be filled with the molten plastic by the secondary pressure. has been done. More preferably, the gate portion for injecting the molten plastic into the molding space 10a is located as close as possible to the placement locations of the support pins 15, . . . , 15 so that the cavity can be filled smoothly. It is set in.

Next, after the plastic is cured until the temperature of the injected and filled plastic material drops to around the mold temperature Tm of the mold lO, the first core 12 and the second core I3 are respectively inserted into the main mold 11. These cores 1 are rotated outward.
2.13 is removed from the molded product l, and then removed from the mold lO.
By opening the tube, a tube 1 as shown in FIGS. 8 and 9 can be obtained.

In this case, in the portion corresponding to the core abutting portion of the tube body 1, as shown in FIG. 4, the pin receiver 1? IJ14a
Correspondingly, three convex portions 1a are formed on the inner peripheral portion, while, for example, 311 recessed portions 1b are formed on the outer peripheral portion depending on the retracted position of the support pin 15. The allowable ranges of the size, depth, etc. of the convex 1151a and the concave ff1b are determined depending on the functions and uses required of the tube l. In addition, support pin 15. . . , 15 are formed into curved shapes that follow the surface shape of the core 14, and the tips of the support pins 15, .
By supporting the core 14 by contacting or pressing against the surface of the core 14, the pin receivers of the core 14 are connected to the portions 14a, . . . , 1.
4a (that is, the convex portions 1a, ..., la on the inner surface of the tube l)
) can be eliminated. In this case, the support pins 15°..., 15 are not necessarily connected to the first core 12 and the second core.
It is no longer necessary to provide it at the matching portion with the core 13, but it can be provided at any intermediate portion of the combined core 14.

As explained above, according to the present embodiment, the plurality of support pins 1 supporting the middle part of the combination core 14 are provided.
5 is provided so that it can move forward and backward from the molding surface 11a of the main mold 11 toward the core 4 side, so when injecting molten plastic into the molding space 10a, the support pin 1
5. ..., advance the core 15 toward the core I4 side and remove the core 14.
while supporting the support pin 15 after injection is completed.
．． ..., 15 can be retracted to the main mold molding surface 11a. And this support pin 15. ..., 1
Since the cavity formed by the retreating motion in step 5 is also filled with molten plastic, by using the above-mentioned combination core 14, a bent pipe can be easily integrally molded, and the core 14 can be supported. Sufficient strength can be ensured, and the injection pressure of the molten plastic makes the core 1
This makes it possible to prevent the deformation or positional shift of item 4 from occurring.

Incidentally, the above embodiment has a curved line forming a part of a circular arc.

Although the present invention is directed to the case of manufacturing the bent pipe 1 bent along L3, the present invention is not limited to the above-mentioned case. For example, as shown in FIG. The present invention can also be effectively applied to the case of manufacturing a tube body 21 equipped with 23. That is, the plurality of support pins 27 that support the combined core 26 obtained by abutting the first core 24 and the second core 25 can be moved back and forth, for example, at the abutting portion of the core 27. It is good to set it to . Further, as shown in FIG. 11, for example, the present invention can be effectively applied to the production of a long straight tube 3I in which the ratio of the length to the diameter of the core 32 is large. In this case, support pin 33. ..., 33 is formed into a curved shape that follows the surface shape of the core 32, and the support pins 33.・・・
, 33 may be set at any position that is most advantageous for supporting the integral core 32.

[Brief explanation of drawings]

Fig. 1 is an explanatory longitudinal cross-sectional view of a mold and a tube body according to an embodiment of the present invention, Fig. 2 is an explanatory cross-sectional view taken in the direction A-A of Fig. 1 when the support pin is moving forward, and Fig. 3 is an explanatory view of the support pin in the direction A-A. Fig. 4 is an explanatory cross-sectional view of the tube body in the A- direction of Fig. 1 when retracting, Fig. 5 is an enlarged view showing the driving part of the support pin. A cross-sectional view, FIG. 6 is a graph showing the temporal change in the injection pressure of plastic, FIG. 7 is a graph showing the temporal change in the temperature of the plastic injected into the mold, and FIG. 8 is related to the above example. A front view of the tube, FIG. 9 is a plan view taken along the line B-B in FIG. 8, and FIG.
11 are longitudinal cross-sectional explanatory views of a mold and a tube body according to another embodiment of the present invention, and FIG. 12 is a longitudinal cross-sectional explanatory view of a mold and a tube body according to a conventional example. 1.21.31... Tube body, 10... Molding mold, 10a
... Molding space, 11... Main mold, lla... Main mold molding surface, 12.24... First core, 13.25...
Second core, 14.26...Combination core, 15,2
7.33...Support pin.

Claims (2)

[Claims] (1) A pair of cantilevered cores are assembled with their free ends abutting each other, and molten plastic is injected into the molding space formed by the surface of the assembled core and the molding surface of the main mold. In the manufacturing method for manufacturing a tube body, the molten plastic is injected into the molding space while the intermediate part of the combined core is supported by a support member protruding from the molding surface of the main mold toward the core. Next, while the temperature of the molten plastic is decreasing, the support member is retreated to the molding surface of the main mold, and the molten plastic is pressurized with a predetermined pressure to cause the melt to also melt in the cavity formed by the retreat of the support member. 1. A method of manufacturing a plastic tube, comprising filling the tube with plastic and then removing the core after the temperature of the plastic has dropped to a predetermined value. (2) A plastic product made by combining a pair of cantilevered cores with their free ends abutting each other, and forming a molding space between the surface of the combined core and the molding surface of the main mold. A plastic tube for manufacturing a tube, characterized in that a support member for supporting an intermediate portion of the combination core is provided so as to be movable forward and backward from the molding surface of the main mold toward the core side. Mold structure of a mold for body manufacturing.