JPH0242432Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to a synthetic resin injection molding machine, particularly to an injection mechanism of a plunger type injection molding machine.

(Prior Art) As is well known, synthetic resin injection molding is a process in which synthetic resin pellets are heated and melted into a fluid state and then injected into a mold at high speed through a nozzle under high pressure.

The injection mechanism section that executes the above-mentioned process is the most important part of the functions of an injection molding machine that influences various properties such as the properties, appearance, and dimensional accuracy of the molded product.

Injection mechanisms are roughly divided into plunger type and screw type.In recent years, synthetic resin pellets are plasticized and melted by heating with a heating cylinder and frictional heat generated by the rotation of the screw, and the synthetic resin is molded by the forward movement of the screw. The screw type, which injects from a nozzle, is widely used because plasticizing and melting of the synthetic resin pellets is uniformly carried out and good molded products can be obtained.

However, the screw type requires the power to rotate the screw to be provided separately from the power to move the screw forward, making the mechanism complicated, making the molding machine expensive, and making it difficult to clean the cylinder. The disadvantage is that it is difficult to adapt to high-mix, low-volume production where raw materials are frequently changed.

On the other hand, the plunger type, in which the plasticized and molten synthetic resin supplied to the heating cylinder is injected from the nozzle by simply pressing the plunger, has a simple mechanism, the molding machine is inexpensive, and the plunger is easy to clean. It is easy to change and is well suited for trial production or high-mix, low-volume production.

However, unlike the screw type, the plunger type does not stir inside the heating cylinder, so it is difficult to uniformly heat the synthetic resin pellets fed into the cylinder, resulting in separation of the synthetic resin or uniform plasticization. Since it is injected without being melted,
This method has a disadvantage in that the appearance, physical properties, etc. of the obtained molded product tend to be non-uniform.

In order to solve the problem of non-uniform plasticization and melting of the synthetic resin pellets in the plunger-type cylinder as described above, conventional injection mechanisms have been used in which a torpedo is provided in the vicinity of the nozzle in the cylinder as shown in Fig. 4. was used a lot.

In Fig. 4, 1 is a cylinder, 2 is a cylinder head with a nozzle 3, 4 is a band heater, 5 is a plunger, and 6 is a torpedo, which guides the flow of synthetic resin placed in the cylinder. By the action of the torpedo, the synthetic resin is made to flow in a thin layer near the inner surface of the cylinder wall, and the synthetic resin is heated uniformly by the band heater wound around the outer periphery of the cylinder wall.

(Problems to be solved by the invention) The conventional plunger-type injection mechanism in which the above-mentioned torpedo is installed in a cylinder has a remarkable effect on uniformly heating the synthetic resin, but the torpedo does not control the flow of synthetic resin. It is necessary to form a complicated shape in consideration of the above, and manufacturing it is not easy.Furthermore, since the torpedo needs to be fixed to the inner surface of the cylinder via a mounting arm, etc., it is not easy to manufacture the cylinder. was.

The present invention was devised in view of the current situation as described above, as a result of intensive studies to develop an injection mechanism that has a simple structure and is capable of uniformly heating synthetic resin.

(Means for Solving the Problems) That is, the present invention allows synthetic resin, which is supplied into a cylinder having a nozzle at its tip and plasticized by heating, to be pushed into the mold by the pressing force of a plunger fitted into the cylinder. In a plunger type injection molding machine for injecting at the same time, the plunger has a rear end rotatably attached to a pressing rod and rotates forward in the cylinder toward the nozzle via a grooved cam mechanism. This is the injection mechanism of an injection molding machine.

(Function) The present invention is constructed as described above, and the plunger that presses the synthetic resin supplied into the cylinder toward the nozzle is rotated by the action of the grooved cam mechanism, so the synthetic resin is stirred and heated within the cylinder. Plasticization and melting is performed uniformly.

In addition, the processing applied to the plunger etc. for the grooved cam mechanism is relatively simple and easy, so the processing cost is low, and cleaning when changing the raw resin is easy, so the raw resin can be changed frequently. It is well suited for high-mix, low-volume production carried out in the industry, and there is no need to provide any special power to provide rotational motion to the plunger.

(Embodiment) Fig. 1 shows an injection mechanism of a rigid plunger type injection molding machine showing an embodiment of the present invention.
is a fitting 1 fixed to a hydraulic rod 12 for pressing.
The rear end portion is rotatably mounted on the shaft 3 via a thrust ball bearing 14.

A toothed portion 8 is formed at the center of the plunger 7, and a stirring blade 9 is formed at the tip.

10 is a receiving part 1 connected to the rear end of the cylinder 1
This is a plunger receiver in which a grooved cam part 11 is bored in the plunger 5 to mesh with the tooth part 8 of the plunger 7 which is fixed by a support arm 16.

The synthetic resin pellets 17, which have been dried and stored in the hopper, fall into the receiving part 15 in predetermined amounts, slide down the slope of the receiving part 15, and enter the cylinder 1.

The synthetic resin 17 in the heating cylinder 1 is layered in the following order: from the molten resin layer near the nozzle 3, indicated by the △ mark, to the mixed layer of pellet-like resin and molten resin, indicated by the ○ mark, and then to the pellet-like resin layer. .

When the synthetic resin 17 is injected from the nozzle 3, a hydraulic mechanism (not shown) is activated to lower the hydraulic rod 12 and the plunger 7 moves downward.

At this time, the plunger 7 is formed with a toothed portion 8, which meshes with the grooved cam portion 11 of the plunger receiver 10, and is rotatably attached to the fixture 13, so that the plunger 7 rotates forward. do exercise,
The synthetic resin 17 is moved toward the nozzle 3 while being stirred by the stirring blade 9 at the tip, and is finally injected from the nozzle 3 in a uniformly melted state.

After the injection of the synthetic resin 17 is completed as described above, the hydraulic rod 12 is moved upward by the hydraulic mechanism, and at this time, the plunger 7 retreats to the top dead center while rotating in the opposite direction to that at the time of injection. Ready for the next injection operation.

In order to perform the above-mentioned injection operation smoothly, it is preferable to partially control the heating by the band heater 4 wound around the cylinder 1. For example, the temperature of the part near the receiving part 15 and the part near the nozzle 3 is It is preferable to perform control such as lowering the temperature and increasing the temperature in the center.

The plunger 7 can be freely removed from the fixture 13, so when changing the resin raw material to be molded, it can be removed and cleaned easily. In this case, of course, the plunger receiver 10 is also replaced.

FIGS. 2 and 3 show another embodiment in which the grooved cam mechanism for rotating and forward-swinging the plunger is slightly different from the previous embodiment.

FIG. 2 shows an embodiment in which a grooved cam 19 is bored on the inner circumferential surface of the cylinder 18, and a guide protrusion 21 is provided in the cylinder 20. FIG. This is an embodiment in which the cylinder 22 is provided with a guide protrusion 23, and the cylinder 24 is provided with a grooved cam 25.Of course, the embodiment shown in FIG. 3 is more practical due to ease of manufacture and ease of cleaning. The quality is high.

(Effects) The present invention has the above-described configuration and operation, and thereby provides a plunger type injection molding machine that has an extremely simple structure and can be manufactured at low cost.
It is possible to easily and inexpensively produce synthetic resin prototypes or produce a wide variety of products in small quantities.

[Brief explanation of the drawing]

Figure 1 shows the first embodiment of the present invention, Figure 2 shows the second embodiment.
FIG. 3 shows a third embodiment, and FIG. 4 shows a conventional example. 1, 18, 22...Cylinder, 7, 20, 24
... Plunger, 8 ... Teeth, 10 ... Plunger receiver, 11, 19, 25 ... Groove cam portion, 21,
22...Guiding protrusion.

Claims (1)

[Scope of utility model registration request] In a plunger type injection molding machine, a synthetic resin supplied into a cylinder having a nozzle portion at the tip and plasticized by heating is injected into the mold from the nozzle by the pressing force of a plunger fitted to the cylinder.
An injection mechanism for an injection molding machine, wherein the plunger has a rear end rotatably attached to a pressing rod and rotates forward in the cylinder toward the nozzle via a grooved cam mechanism.