JPH049650B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a vent-type injection control system that removes volatile matter and moisture contained in molten resin as well as air existing in a mold cavity before injection. Regarding the method.

During the injection process, if the resin itself contains liquid or moisture, or if air is present in the mold, these gaseous substances will be trapped between the resin surface and the cavity surface while the cavity is being filled with molten resin. This caused molding defects such as silver streaks and gas discoloration. Therefore, one method is to perform preliminary drying outside the injection molding machine, but this is expensive, and therefore a vent-type injection molding machine has been proposed to remove the gaseous substances inside the injection molding machine.

[Prior art]

An example of a conventional vent type injection molding machine will be described with reference to FIG. A screw 12 that can move forward and backward and rotate is inserted into the heating cylinder 11, and a vent port 13 is provided in the middle of the screw 12, from which volatile matter and moisture are released into the atmosphere or sucked in by a vacuum pump (not shown). Was. In this case vent port 13
If the resin pressure is not lowered sufficiently, the resin will overflow here and close the vent port 13, making it impossible to function. Therefore, as shown in Figure 3, the dimension of the screw 12 is separated between the first stage part 12A and the second stage part. It was divided into 2 parts, 12B and 12B.

Then, the transfer capacity of the second stage section 12B is set to the first stage.
It was necessary to design the transfer capacity sufficiently to exceed the transfer capacity of the stage section 12A.

For this reason, the overall length of the screw 12 has to be increased, which increases the cost and places great restrictions on the screw design. Because of the screw dimension that maintains the vent port 13 at a low pressure as described above, resin tends to stay in the vent port 13, which causes retention burns and failure to replace the resin when replacing the resin.

Furthermore, since it is impossible to remove the air present in the cavity with such a conventional venting method, a vacuum molding device may be used. In this equipment, a vacuum suction part with a sufficient cross-sectional area is installed in the mold to draw a vacuum, but when injecting resin, it is necessary to prevent resin from leaking from the vacuum suction part, from the viewpoint of not deteriorating the appearance of the product. Mold design is also subject to restrictions.

FIG. 4 shows an example of the vacuum mold forming apparatus described above. A movable mold 23 is provided, which is in contact with a fixed mold 22 through a nozzle 21 when the heating cylinder 11 moves forward, and moves back and forth in opposition to the fixed mold 22. A space 24 (this space 24
A cover 25 is provided to surround the movable mold 23 (which becomes a cavity when both molds 22 and 23 are closed), and a hole 26 is provided in the movable mold 23 as a vacuum suction section. The hole 26 needs to have a sufficient cross-sectional area in order to perform vacuum suction at high speed, but it has nothing to do with the cavity formed when both molds 22 and 23 are closed so as not to receive resin pressure during injection. No outside parting surface. As shown in the figure, from the time when the space 24 is surrounded by the cover 25, the hole 26
A vacuum is drawn through the space 24 to bring the space 24 into a vacuum state. However, it requires vacuum suction of a volume much larger than the actual cavity volume, which results in a large vacuum device, and also has the disadvantage of lengthening the forming cycle as it requires a certain period of time for vacuum suction before closing the final mold. It was hot.

[Purpose of the invention]

The present invention eliminates these drawbacks, and its purpose is to provide a vent port in the nozzle of a conventional non-vent type injection molding machine, thereby reducing volatile matter, moisture, and An object of the present invention is to provide a vent type injection control method that makes it possible to suck residual air in a cavity.

[Key points of the invention]

In the vent-type injection control method of the present invention, a nozzle having a vent port that can be opened and closed is arranged at the tip of a heating cylinder that is controlled to an arbitrary temperature, and a screw that can rotate and move forward and backward is inserted into the inside of the heating cylinder. In an in-line screw type injection molding machine, the screw is moved back far beyond the metering stroke in a non-rotating state prior to the resin metering process, and then the screw is rotated at an arbitrarily determined number of rotations for an arbitrarily determined period of time. The feature is that it can be measured.

[Embodiments of the invention]

FIG. 1, which shows one embodiment of the present invention, will be described below. A screw 32 that rotates and moves back and forth is inserted into the heating cylinder 31, which is controlled to an arbitrary temperature by a heater (not shown), and a hopper 14 (not shown) is located on the right side of the heating cylinder 31 (see Fig. 3). ) is attached, but the intermediate vent port 13 is not provided. An A nozzle 33 is fixed to the tip (left end) of the heating tube 31 by screwing, and a housing 34 is screwed to the outer periphery of the A nozzle 33 so as to be fixed directly to the heating tube 31. Good too. Inside the housing 34, a B nozzle 36, which is constantly pressed forward by a spring 35, is slidably inserted coaxially with the A nozzle 33. The vent port 37 provided in the housing 34 is arranged so that most of it does not touch the B nozzle 36 when it is in the left position as shown, that is, in the gap between the open mating surfaces of the A nozzle 33 and the B nozzle 36. Therefore, it is arranged so as to communicate with the inside of the cavity 40 and the heating cylinder 31. Note that 38 is a fixed mold, 39 is a movable mold, and 40 is a cavity.

Next, the operation of the embodiment described above will be explained. When the injection process is finished, the screw 32 is non-rotating and B
The nozzle 36 is in contact with the fixed mold 38, and both nozzles 33 and 36 are in close contact with each other. In this state, the screw 32 is moved back by a distance greater than the metering stroke required for molding, and then the screw 32 is rotated at an arbitrarily determined number of revolutions and measured for an arbitrarily determined time. When the measurement is completed, the molten resin A inside the heating cylinder 31 is stored on the screw 32 side with a space left on the tip (left) side, as shown in Fig. 1, and the volatile resin contained in the molten resin is The fraction is vaporized and separated. The vent port 37 is now in a state where it can be evacuated. Note that both molds 38 and 39 and the molded product (not shown) are cooled from the time the injection process is completed.

When the metering is completed, the screw 32 stops rotating and the heating cylinder 31 is moved back (moves to the right), so that the B nozzle 36 is separated from the fixed mold 38 and both nozzles 33 and 36 are also separated. At this time, since the above-mentioned cooling has been completed, the movable mold 39 is moved backward (leftward) to take out the molded product, and then the movable mold 39 is moved forward to clamp the mold. Subsequently, the heating cylinder 31 is moved forward to touch the B nozzle 36 to the fixed mold 38, with both nozzles 33 and 36 being in an open state. FIG. 1 shows this state. Here, by leaving the vent port 37 open to the atmosphere, or by connecting it to a vacuum source (not shown) when the B nozzle 36 touches the fixed mold 38, the resin is separated from the molten resin inside the heating cylinder 31. The volatile matter and moisture that have been turned into gases and the air present in the cavity 40 are removed. After removing the volatile matter, the heating cylinder 31 is moved forward again to bring both nozzles 33 and 36 into close contact and the vent port 37 is closed. Also, if evacuation is being performed, stop it and move the screw 32 forward. Then start the injection process. This operation is then repeated to obtain a desired number of molded products.

FIG. 2 shows the main part of another embodiment of the present invention, and this embodiment differs from the first embodiment in FIG. 1 only in the approach and separation of the B nozzle. A housing 51 is screwed onto the A nozzle 33 fixed to the tip of the heating cylinder 31, but it may be fixed directly to the heating cylinder 31. A B nozzle 52 is slidably inserted into the small diameter portion of the housing 51.
2 is the same as the first embodiment in that when the heating cylinder 31 moves forward, it touches a fixed mold (not shown). Arm 52A extending vertically in the diagram of B nozzle 52
is fixed to the piston rod 54 of a pair of cylinders 53 fixed to the tips of the heating cylinder 31, so that the B nozzle 52 can be moved to the forward position shown in the figure and the switching valve 56 that controls the pressure fluid of the pressure source 55 to the cylinder 53. It has two positions: a retracted position when switching to the right ventricle. Further, a vent port 37 is provided in the large diameter portion of the housing 51, and its function and effect are the same as in the first embodiment.

The operation of this embodiment differs from the first embodiment only in that the switching valve 56 is in the right ventricle when the nozzles 33, 52 are in close contact with each other in the backward movement, whereas it is in the left ventricle in the forward movement when the nozzles 33, 52 are separated. Therefore, detailed explanation will be omitted.

〔Effect of the invention〕

As explained above, in the vent type injection control method of the present invention, by providing a vent port in the nozzle part, it is possible to mold highly hygroscopic resin with a standard non-vent injection molding machine without pre-drying.

Furthermore, since the air in the cavity is simultaneously sucked when removing volatile matter and moisture contained in the resin, the present invention has many advantages, such as enabling vacuum molding with a normal mold. In addition, the screw can be short, making it possible to carry out vent-type injection molding at a low cost, and since the cavity is in a vacuum, it has the advantage that it will not burn due to adiabatic compression during filling with molten resin.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of the present invention, FIG. 2 is a sectional view of a main part of another embodiment, and FIGS. 3 and 4 are sectional views of a conventional example having a different shape. 31... Heating cylinder, 32... Screw, 33... A nozzle, 34, 51... Housing, 36, 52... B nozzle, 37... Vent port, 38, 39... Mold.

Claims (1)

[Scope of Claims] 1. An in-line screen in which a nozzle having an opening and a closable vent port is arranged at the tip of a heating cylinder that is controlled to an arbitrary temperature, and a screw that can rotate and move back and forth is inserted into the heating cylinder. In a Y-type injection molding machine, prior to the process of measuring resin, the screw is moved back in a non-rotating state by a distance greater than the metering stroke, and then the screw is rotated at an arbitrarily determined number of rotations for an arbitrarily determined period of time for metering. Vent type injection control method. 2. The vent-type injection control method according to claim 1, wherein the vent port is closed at least during the injection process. 3. Claim 1, characterized in that opening and closing of the vent port is operated by pressure fluid.
The vent-type injection control method according to item 1 or 2. 4. According to claim 1 or 2, the vent port is normally open due to elastic force and is closed by pressing the nozzle against the mold with a desired force. vent type injection control method. 5. The vent-type injection control method according to claims 1 to 4, wherein the vent port is open to the atmosphere in an open state. 6. Claim 1, characterized in that the vent port is connected to a vacuum source in the open state.
The vent type injection control method according to items 1 to 4.