JPH0664007A - Injection mold - Google Patents

Abstract

PURPOSE:To widen the flow passage area of molten resin at a gate and, at the same time, realize the just enough charging of resin. CONSTITUTION:At the gate 8 of a mold, a movable gate cut pin 11 is provided. A core 10, which forms some part of the gate 8, is provided movably. Thus, by retreating the core 10, the internal volume of the gate 8 is made larger. At the gate cutting, by advancing the gate cut pin 11, pushed-out resin is flown toward the gate 8, the internal volume of which is enlarged, and simultaneously the gate cut pin 11 is advanced, resulting in charging just enough resin in a product part regardless of the passage area of the gate and, at the same time, allowing to cut the gate part 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding die which is improved so that the flow path area of a gate of the injection molding die can be increased and the resin can be filled with the resin in an appropriate amount.

[0002]

2. Description of the Related Art In injection molding, a high pressure must be applied to a molten resin and the molten resin must be uniformly filled in every corner of a product while the fluidity of the molten resin is sufficient. . In order to make the conditions of pressure, fluidity (temperature) of molten resin, and time uniform over the entire area of the product part, the number and arrangement of gates that supply the molten resin to the product part are important factors. Since the flow resistance of the gate acts as a pressure loss when the molten resin is pressure-fed to the product portion, reducing the flow resistance of the gate is also an important factor.

On the other hand, from the viewpoint of the quality of the injection-molded product, when the molten resins flowing from the respective gates come into contact with each other and merge, a so-called weld line is generated at the contact portion. If a weld line is generated in the area, the strength of that part may be reduced and the appearance may be impaired. Therefore, it is contrary to the above conditions of pressure, temperature and time, but the number of gates should be reduced as much as possible. Must be done.

As shown in FIG. 4, a gate portion of a conventional injection molding die is provided with a gate portion 3 between a runner portion 1 and a product portion 2, and a gate cut pin 4 is provided so as to cross the gate portion 3. It is provided. Then, as shown in (a), when the molten resin is being injected, the gate cut pin 4 is retracted by a cylinder (not shown) so that the tip thereof forms a part of the gate 3 and the injection is completed. After a certain period of time (when the injected resin has hardened to some extent), the gate cut pin 4 is advanced by the cylinder (not shown) to cross the gate 3 to cut the gate 3 as shown in (b). I am trying to do it. Substantially the same structure as the gate portion is disclosed in Japanese Patent Application Laid-Open No. 61-94733.

In Japanese Utility Model Laid-Open No. 3-62812, a mixer block having a gate portion is movably provided, and the mixer block is moved so that the gate portion formed in the mixer block and the product portion are communicated with each other. Is filled in the product part, and then the mixer block is moved to interrupt the communication state between the gate part formed in the mixer block and the product part.

[0006]

Since the resin after injection filling shrinks as the cooling progresses from the molten state, a holding pressure for supplementing the resin by this shrinkage is required. Therefore, since the gate cannot be closed during this time, the gate is cut after the resin has cooled to some extent and the resin is in the semi-solidified state or the solidified state.

Therefore, in the above-mentioned conventional example in which the gate is cut by using the gate cut pin, the pressures of the runner portion 1 and the product portion 2 are the same, so the gate cut pin 4 is advanced to move the gate 3 When the resin is cut, the semi-solidified or solidified resin is pushed by the tip of the gate cut pin 4 and pushed into the product portion 2, and between the resin filled in the product portion 2 and the pushed resin. There is a problem that a fault (crack) is generated at the contact part of and the strength of that part decreases, and because the pressed part is locally overfilled, a striped pattern occurs in that part and the product In addition to impairing the external appearance, there is a problem that plating cannot be performed on a product that is plated.

In order to reduce such a problem, it is conceivable to reduce the cross-sectional area of the gate (the flow area of the molten resin) to reduce the amount of resin pushed by the gate cut pin. Since the flow resistance of the gate becomes large when this is set, many gates are required to make the pressure, temperature, and time that are the conditions for injection molding uniform over the entire area of the product part. There is a problem in that it becomes difficult to set and the number of weld lines is increased and the quality of the product deteriorates.

Further, when an acrylic resin is injection-molded using a gate having such a small cross-sectional area, the acrylic resin has poor fluidity and is hard and brittle, so that the flow resistance of the gate portion is increased. It becomes so large that it cannot be applied to injection molding of acrylic resin. Therefore, in the injection molding of acrylic resin, the fact is that a gate with a large cross-sectional area must be used. Also, if a gate with a large cross-sectional area is used to cut the gate with a gate cut pin, the above problem becomes noticeable. As a result, in the case of injection molding of an acrylic resin, it is common to perform a cutting (mechanical or manual cutting) of a gate portion which is attached to a product and molded as a post process. Therefore, the injection molding of acrylic resin has a problem that productivity is low, and the number of man-hours required for mechanical work for gate cutting or manual work is large, which is problematic in terms of economy.

Next, in the prior art disclosed in Japanese Utility Model Laid-Open No. 3-62812, the gate is cut by rubbing the product portion on the surface of the mixer block, so the gate is cut when the resin is solidified. In this case, the product is likely to be scratched, and when the resin is melted or semi-solidified and the gate is cut, the pressure-holding filling of this part is insufficient and a recess occurs, resulting in a defective product. There is a problem of high possibility.

The present invention provides an injection molding die which solves all the above problems by increasing the flow area of the molten resin in the gate and filling the resin in an appropriate amount.

[0012]

Means for Solving the Problems According to the present invention for solving the above problems, an injection molding is provided in which a gate cut pin that connects a runner portion of a mold and a product portion is provided with a retractable gate cut pin. In the mold for use, a core forming a part of the gate portion is provided so as to be capable of advancing and retracting.

[0013]

Since the present invention is constructed in this way, it has the following actions. That is, a gate cut pin that connects the mold runner part and the product part is provided with a retractable gate cut pin, and a core that forms a part of the gate part is provided so that it can be retracted. It is possible to increase the internal volume of the gate. As a result, the gate cut pin can be advanced while flowing the resin pushed out by advancing the gate cut pin at the time of gate cutting toward the gate part having a large internal volume, so regardless of the flow passage area of the gate, In addition, it is possible to cut the gate while filling the product portion with the resin just enough.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. First, the entire mold will be described with reference to FIG. The runner portion 7 is composed of the fixed die 5 and the movable die 6,
A gate portion 8 and a product portion 9 are formed, and a core 10 and a gate cut pin 11 are movably provided on the gate portion 8. Reference numeral 13 is a core driving cylinder for moving the core 10 via the connector 12, and 14 is a gate cut cylinder for driving the gate cut pin 11. Reference numeral 15 is an extrusion plate to which the extrusion pin 16 is attached. 17 is a molding machine nozzle.

The gate portion 8 is partially formed by the tip of the core 10 and the tip of the gate cut pin 11, and will be described in more detail with reference to FIG. Has a locking member 18 fixed, and the locking member 18 is engaged with an inclined slit 19 provided at an end portion of the connector 12 to move the connector 12 up and down by a core driving cylinder 13 to move the core 10. I am trying to do it. Further, the movable die 6 is provided with a space portion 20 for allowing the core 10 to move.

The operation of the present embodiment thus constructed will be described below. In FIG. 3 showing the injection molding process,
Since the core 10 and the gate cut pin 11 are both movably provided in the step (a) of filling the product portion 9 with the molten resin from the molding machine nozzle 17, the size of the flow passage cross-sectional area of the gate portion 8 is set. Regardless of this, the core 10 and the gate cut pin 11 are moved forward by the core cylinder 13 and the gate cut cylinder 14 to move the core 10 and the gate cut pin 11 forward.
It becomes possible to form a part of the gate portion 8 by the tip of the.

Next, at the stage where the filling of the molten resin is completed and the filled resin is semi-solidified, the core 10 can move independently of the gate cut pin 11,
As shown in (b), only the core 10 is retracted to form the space portion 21 and the inner volume of the gate portion 8 can be increased.

In this way, only the core 10 is retracted so that the space
21 is formed to increase the inner volume of the gate portion 8,
When only the gate cut pin 11 is moved forward, the resin in the gate portion 8 is pushed toward the product portion 9 side and pressure-filled to flow into the gate portion 8 having a large inner volume. As a result, there is no local filling in the product portion 9 and the pressure is maintained, so that the product portion 9 can be filled exactly as shown in (c), and the gate portion 8 can be cut. It will be possible.

Thus, the core 10 and the gate cut pin
The step of forming a part of the gate portion 8 by the tip of 11, the step of retreating only the core 10 to increase the inner volume of the gate portion 8 and the gate cut pin 11 while flowing the resin to the gate portion 8 side. The step of moving forward to cut the gate portion 8 can be performed regardless of the size of the flow passage cross-sectional area of the gate portion 8, and the product portion 9 is not locally filled and is kept in a pressure-held state. Since the filling is performed without excess or deficiency, it becomes possible to increase the flow passage cross-sectional area of the gate portion 8. In addition, since the resin in the gate portion 8 is filled while flowing in this way without excess or deficiency, it becomes possible to reduce the occurrence of faults in the product portion 9.

Since the flow passage cross-sectional area of the gate portion 8 can be increased in this manner, the flow resistance in the gate portion 8 can be reduced, and the number of gate portions 8 can be reduced. .

In the above description, the core 10 is retracted first to increase the inner volume of the gate portion 8, and then the gate cut pin 11 is advanced to cut the gate portion 8. However, the core 10 is retracted. It is also possible to move the gate cut pin 11 in synchronization with the forward movement of the gate cut pin 11. In this way, the core 10 moves backward and the gate cut pin 11 moves forward in synchronization with each other, and the gate cut pin 11 is pushed in to move the core 10 back by an amount corresponding to the decrease in the internal volume of the gate part 8. When the product is not substantially changed, the gate portion 8 can be cut even if the solidified state of the resin in the gate portion 8 is softer than semi-solidified, and the fault occurring in the product portion 9 is further reduced. It will be possible. The selection of the cutting conditions for the gate portion 8 can be arbitrarily selected depending on the properties of the resin and the injection molding conditions.

[0022]

As described above in detail, according to the present invention, a gate cut pin that connects a runner portion of a mold and a product portion is provided with a retractable gate cut pin, and a core forming a part of the gate portion. Since the core is retracted, the inner volume of the gate is increased by retracting the core, and when the gate is cut, the resin is pushed out by advancing the gate cut pin and flowing toward the gate part with the larger volume. Move the pin forward, regardless of the gate flow area
In addition, the gate can be cut while the resin is being filled in the product portion without excess or deficiency. As a result, it becomes possible to use a gate having a large flow passage area, the number of gates can be reduced and the occurrence of weld lines can be reduced, and filling can be performed without excess or deficiency.
It is possible to improve the quality of products by preventing the occurrence of faults (cracks) and the occurrence of striped patterns. Moreover, even if a gate with a large cross-sectional area is used, the gate can be cut without the occurrence of faults and stripe patterns, so it becomes possible to adapt to acrylic resin injection molding dies and cut the gate. Therefore, it is possible to improve productivity and economic efficiency by omitting the subsequent process.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is a partial vertical cross-sectional view showing the entirety of a mold to which the embodiment of FIG. 1 is applied.

FIG. 3 is an injection molding process diagram showing a longitudinal cross section of a state in which injection molding is performed according to the embodiment shown in FIG.

FIG. 4 is an injection molding process diagram showing a longitudinal cross-section of a state in which injection molding is performed using a conventional mold.

[Explanation of sign]

 5 Movable type 6 Fixed type 7 Runner section 8 Gate section 9 Product section 10 Core 11 Gate cut pin

Claims (1)

[Claims] 1. An injection molding die comprising a gate cut pin that connects a runner portion and a product portion of the die with a gate cut pin that can move back and forth, and a core that forms a part of the gate portion can move forward and backward. A mold for injection molding, which is provided on the.