JPS6321120A - Injection molder - Google Patents

Abstract

PURPOSE:To improve the yield of raw injection molding material to a far greater extent by a method wherein a cylinder for driving a small-sized plunger is formed in a main plunger, which reciprocates in an injection nozzle, so as to push the small-sized plunger from the tip of the main plunger to a runner. CONSTITUTION:Molten resin is filled through a feed pipe 30 into an empty injection nozzle 15. After that, a valve 26 is closed and a plug 22 is opened and at the same time a main plunger 12 is advanced. Thus, the molten resin in the nozzle 15 is sent under pressure through a runner 7 and a gate 6 so as to be filled into a cavity 7, when the plunger 12 is advanced to the tip of the nozzle 15. In succession, a small-sized plunger 13 is advanced so as to further send the molten resin, which is filled into a small-sized plunger insertion hole 21 and a sprue 24, under pressure. At this time, the pressure in the runner 5 becomes maximum, resulting in allowing to fill the molten resin in all parts of the cavity.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in injection molding machines.

[Conventional technology]

In recent years, injection molding has come to be used for parts that are produced in small quantities.

Therefore, it has become increasingly necessary to make the mold itself into a shape that is easy to manufacture.

In addition, as for mold manufacturing technology, it goes without saying that there will be no stringing, sink marks, cracks, etc., but in addition to this, the yield of molding raw materials must also be good. .

The conventional example shown in FIG. 3 is a mold used when the production quantity is relatively small, and a cold sprue 4 is provided between the nozzle touch part 3 and the runner 5.

The cold sprue 4 has a conical shape that widens toward the runner 5 in order to prevent stringing.

By doing this, the boundary between the low-temperature solidification part on the fixed mold 1 side and the high-temperature contact part on the nozzle 39A (nozzle touch 3 side) is made clear, and the stringing phenomenon is eliminated. Further, the effect of preventing the stringing phenomenon is greater if the hole diameter of the inlet 9 of the cold sprue 4 is made as small as possible.

Also, the other reason why Cold Sprue 4 was changed to Suehiro Shi is,
This is to provide a draft angle when removing dust.

In the Hiko diagram, 2 is the movable mold, 6 is the gate, and 7 is the product part (
8 is a cooling medium passage, 10 is a joint between the cold sprue and the runner, and 11d is an extrusion pin.

[Problems to be Solved by the Invention] The conventional mold described above has the following problems because it has a cold sprue that widens at the end.

That is, when the molten resin passes through the inlet 9 of the cold sprue 4, its flow resistance increases, and therefore a high injection pressure is required.

As a result, there are problems in that a large capacity pressure source is required and special design considerations such as pressure resistance of the injection nozzle are required.

Furthermore, when molten resin is injected from a cold sprue with such high pressure spreading out, there is a problem in that jetting flow marks, sink marks, and burns are likely to occur.

! i! Since the joint 10 between the cold sprue 4 and the runner 5 is thick, it takes time to cool this part, lengthening the molding cycle time and reducing productivity. Because it has a conical shape,
The process does not require wire-cut electric discharge machining or special reaming, and the mold is easy to process, and even if cold sprue is used, the stringing phenomenon cannot be completely eliminated, and in summer In this case, there was a problem in that the cold sprue was deformed, which caused interference with the unloading machine, making it difficult to automatically unload the product.

The present invention aims to provide an injection molding machine that solves all of these problems.

[Specific measures to solve the problem]

In order to solve the above problems, the present invention forms a cylinder within the main plunger that reciprocates within the injection cylinder, and provides a small plunger that reciprocates with the cylinder so as to completely penetrate the tip of the main plunger. The small plunger is inserted into the runner portion through a small plunger insertion hole at the tip of the injection cylinder and a sprue provided in the mold.

[Effect]

With the above configuration, the molten resin (injection raw material) filled into the injection cylinder is filled into the cavity through the runner and the gate by the main plunger. Next, the small plunger is pushed out to further fill the cavity with molten resin, filling every corner of the cavity with the swatch. After that, the pressure is held for a certain period of time.

〔Example〕

An embodiment of the present invention will be described in detail below. In FIG. 1, 12 is a main plunger. This main plunger 12 reciprocates within the injection cylinder 15.

14 is a cylinder for reciprocating the main plunger 12, and 17 and 18 are hydraulic ports. A small plunger cylinder 16 is formed in the main plunger 12 . A small plunger 13 is provided within the small plunger cylinder 16 and reciprocates so as to protrude from the tip of the main plunger 12. It is a hydraulic boat with r9, 20Vi and 16 cylinders for small plungers. 2 is a small plunger insertion hole formed at the tip of the injection cylinder 15, and the positioning pin 2
3, when the injection cylinder 15 is positioned at the nozzle touch part, the axes of the small plunger insertion hole 21 and the sprue 24 provided in the mold coincide, and the small plunger 13 is inserted into the small plunger insertion hole 21. It extends through the hole 21 and sprue 24 so that it can be inserted up to the runner 25. 22F'i, a plug for opening and closing the small plunger insertion hole 21; The positioning pin 23 is attached to the injection nozzle 15, and the positioning pin 23 is attached to the mold side.
A hole is drilled to insert 3. This hole is elongated in the PA expansion direction of the mold in consideration of the thermal expansion difference between the mold and the injection nozzle 15.

27 is a hopper for injection molding raw materials, 28 is a plasticizing screw, and 29 is a heater. 26d.

This pulp is provided in the middle where the molten resin supplied by the plasticizing screw 28 is supplied to the injection cylinder 15 through the supply pipe 30. 31 is a motor that drives the plasticizing screw 28.

The operation of this embodiment configured as described above will be explained next. In FIG. 2 (1), the pulp 26 is open, the plug 22 is closed, the main plunger 12 and the small plunger 1
3 is retracted, and the injection nozzle 15 is in an empty state with the small plunger insertion hole 21 closed by the plug 22, and the injection waste 315 in the above state is filled with molten resin through the supply pipe 30. By this filling, the volume of the injection nozzle 15 predetermined corresponding to the product (cavity) is filled with the molten resin, and the minimum necessary amount of the molten resin (injection molding raw material) is measured. After filling the injection nozzle 15, as shown in FIG. 2 (2) K, the pulp 2
6 is closed and the plug 22 is opened, hydraulic pressure is applied from the hydraulic boat 18 and the main plunger 12 is advanced. As a result, the molten resin filled in the injection nozzle yjs is pumped through the small plunger insertion hole 21 and the sprue 24.

Then, as shown in Fig. 2 (3), the main plunger 1
When the injection nozzle 2 advances to the end of the injection nozzle 15, the molten resin passes through the runner 5 and the gate 6 and fills the cavity 7. Next, as shown in Figure 2 (4), the hydraulic boat 1
The small plunger 13 is advanced by applying hydraulic pressure from 9, and the molten resin filled in the small plunger insertion hole 21 and the sprue 24 is further pumped. At this time, the pressure inside the runner 5 reaches its maximum, and every corner of the cavity 7 is filled with the molten resin. By holding the pressure for a certain period of time, the molten resin in the cavity 7 is replenished by the final stroke of the small plunger 13.

In the injection process, the molten resin flows through a channel having a constant cross-sectional area in which the small plunger insertion hole 21 and the sprue 24 communicate with each other, so that the flow resistance caused by the shape of the channel is extremely small. (In terms of fluid dynamics, if there is a constriction part or a widening part in the middle of the flow path, a flow resistance commensurate with the shape will occur).

Furthermore, even if the small plunger 13 is inserted up to the runner 5, the molten resin remains in the sprue 24.

As a result, the cooling and solidification of the molten resin is accelerated, and stringing does not occur due to complete isolation between the solidified part and the molten part, and the tip of the small plunger 13 is inserted as far as the runner 5. Because of this, the draft angle during demolding is guaranteed.

After the injection is completed, apply hydraulic pressure to the hydraulic boat 20 to
The plunger 13 is moved back, and then hydraulic pressure is applied to the hydraulic boat 17 to move the main plunger 12 back. Thereafter, the small plunger insertion hole 21 is closed with the plug 22, and the next injection operation is started.

〔effect〕

As detailed above, according to the injection molding machine of the present invention, the main plunger that reciprocates within the injection nozzle is provided with a cylinder for driving the small plunger, and the small plunger is moved from the tip of the main plunger to the runner by this cylinder. Since the injected molten resin is extruded until it reaches a certain point, all of the injected molten resin is effectively injected without remaining in a part of the gel, and the portion of the injection molding raw material that is wasted is extremely small. This made it possible to significantly improve the yield of injection molding raw materials. In addition, since there is almost no flow resistance when the molten resin is injected, injection can be performed with a small pressure, and there is no need for special technical consideration of the pressure resistance of molds, etc., and the sprue is Since the hole has a shape that is easy to process, it can be used for making molds even for parts that are produced in small quantities, and has excellent industrial effects. In addition to the low pressure mentioned above, since the sprue has a straight hole, the injection speed is slow, reducing molding defects such as sinking, jetting, flow marks, and sink marks, and improving product yield. This improved performance and greatly increased productivity. In addition, since no molten resin remains in the sprue, the cooling rate is faster, and the melting and cooling solidification parts are completely isolated, eliminating stringiness and making it easier to remove the product. It has excellent effects, such as easier production, fewer product defects due to stringing, and further improved productivity.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of embodiments of the present invention; (1) shows the main plunger and the state where the plug is opened after filling with small melted resin and starts injection; (3) F'i, the main (4) shows the state injected with a plunger, and (4) shows the state injected with a small plunger. FIG. 3 is a longitudinal sectional view showing a conventional mold. 12... Main plunger, 15... Small plunger, 14... Main plunger cylinder, 15... Injection cylinder, 16... Small plunger cylinder, 21... Small plunger insertion hole, 22. ...Plug, 24...Sprue, 25...Runner. Utility model registration applicant Toyota Motor Corporation Figure 2 Figure 2

Claims (1)

[Claims] A cylinder is formed in a main plunger that reciprocates within the injection cylinder, a small plunger that reciprocates with the cylinder is provided so as to pass through the tip of the main plunger, and a small plunger insertion hole is provided at the tip of the injection cylinder, An injection molding machine characterized in that the forward end of the small plunger is inserted through the small plunger insertion hole and a sprue provided in the mold to a runner section.