JPS6076321A - Injection molding process - Google Patents

Abstract

PURPOSE:To obtain the product excellent in property, injecting always the constant amount of molten resin into the cavity of a mold by a method in which even if the close timing of the check ring for preventing the back flow of the molten resin is fluctuated, it is automatically corrected. CONSTITUTION:After plasticizing measurement has been finished, the pressure in the pressure chamber 16 of a cylinder which is lower than the injection pressure of molten resin into a cavity is kept for a constant time or during the time until said pressure rises to a constant pressure, and preliminary injection is carried out, thereby retracting a check ring 23 and placing it at a back flow preventing position. The screw position at the time of the preliminary injection- finish is memorized, and the screw 12 is controlled to advance from this position by a specified distance. Consequently, because the back flow has been prevented by the check ring at the time of the screw advance, the volume by the screw advance is same as the injection amount of molten resin into the cavity. Therefore, every shot injects the same amount of the resin.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an injection molding method.

In order to ensure stable molded product accuracy, it is important to minimize the weight variation of the molded product, and for this purpose, it is necessary to accurately inject a fixed amount of plasticized molten resin into the mold cavity. need to be injected.

[Prior art]

In order to achieve this purpose, conventionally, a fixed amount of molten resin is injected into the cavity at a position where the screw has moved forward a certain distance from the position where plasticization and metering has finished, and this is the position at which the filling of the molten resin into the cavity is completed. This was the way it was done.

However, this method has problems with the timing of closing the check ring that is attached to the tip of the screw to prevent backflow during injection of molten resin, variations in the time from the start to the end of closing the check ring, and the amount of plasticizing needles. Variations in the degree of injection influenced the magnitude of the injection amount, making it impossible to obtain a stable and accurate injection amount, resulting in poor quality molded products.

[Purpose of the invention]

The present invention has been made from this point of view, and its purpose is to automatically correct any misalignment of the block tie of the check ring, so that a certain amount of the #4 bath melt is always kept in the mold. An object of the present invention is to provide an injection molding method in which a high-quality molded product can be obtained by injecting into the cavity of a mold.

[Key points of the invention]

In the injection molding method of the present invention, in an injection molding machine in which backflow of molten resin is prevented by a check ring, a trowel in which the bath molten resin is plasticized, and a pressure chamber of an injection cylinder are injected with the injection pressure of the molten resin into a cavity. By performing preliminary injection by maintaining a low pressure for a certain period of time or while the above pressure rises to a constant pressure, a check ring is removed to prevent backflow, and the screw position at the time of completion of preliminary injection is memorized. It is characterized in that a fixed amount of fused resin is injected into the glossy cavity by advancing the screw a fixed distance from the memorized position.

[Embodiments of the invention]

The following Figures 1 and 2 show one embodiment of the present invention.
This will be explained using figures. FIG. 1 is a sectional view of a main part of a commonly used in-line injection molding machine, showing the state when plasticization and metering are completed. heating cylinder 11
A screw 12 is inserted to control the internal pressure so that it can rotate and move forward and backward, a nozzle 13 is attached to the tip of the heating cylinder 11 (the left end in the figure), and a screw 12 is attached to the rear end of the heating cylinder 11.
2 is attached to an injection cylinder 15 into which a piston 14 is inserted which cannot move in the axial direction but is rotatably attached. Pressure oil is sent to the hydraulic chamber 16 of the injection cylinder 15 from a hydraulic pump (not shown) and is controlled by a pressure regulating valve 17 .

Further, a pressure sensor 18 is connected to the hydraulic chamber I6.

The axial movement of the IJ unit 12 is detected by a position detector such as a potentiometer or an encoder 19, and detection signals from the encoder etc. 19 and the pressure sensor I8 are sent to the storage/calculation unit 20.

(3) Figure 2 is an enlarged view of the tip of the screw 12, and the screw head η is screwed onto the tip of the screw 12 with a spacer 2] placed thereon, and the screw head η has a substantially conical shape toward the tip. The rear side of the same conical shape (right side in the figure) is stepped and has a small diameter, and a check ring that can freely slide in the axial direction is inserted into this small diameter part, and A large number of Tl 424 are formed in the area to smoothly communicate with the small diameter part.

Next, the operation of the present invention will be explained. When the plasticization meter 1 is started, the screw 12 is located to the left of the position shown in Fig. 1 (the tip or left end of the screw 12 is at the A position, which is the forward limit).
When the screw 12 is rotated while a light back pressure is applied to the hydraulic chamber 16 by the pressure regulating valve 17, resin is supplied from the hot arm (not shown) to the right end side of the screw, and this resin is supplied to the right end of the screw. While being sent to the left by the molten resin, it becomes molten resin and is stored in the chamber 6 on the left side of the screw 12. As the molten resin is stored in the chamber δ, the screw 12
When it moves backward and reaches position B (retreat limit) shown in Figure 1,
For example, when the U1 switch (not shown) detects this, the rotation of the screw 12 is stopped and the plasticization measurement is completed.

When the plasticization metering is completed, a pressure lower than that at the time of injecting the molten resin into the cavity, that is, at the time of injection, is applied to the hydraulic chamber 16, for example, a pressure equal to or slightly higher than the above-mentioned back pressure is applied. In this case, if the nozzle 13 is an open type, the resin filled in the previous shot is cooled and pressed against the clogged cavity, so a low pressure is applied to the hydraulic chamber 1.
Even if 6Vc is applied, it will not adversely affect the molded product or cavity. On the other hand, if the nozzle 13 is of the no-yat-off type, it is closed except during injection, so there is no problem at all. Preliminary injection is a state in which a low pressure is applied to the hydraulic chamber 16, and this preliminary injection is carried out for a certain period of time, usually about 0.5 seconds to 1 second, or because it is preliminary injection, the resin pressure in the chamber 5 increases. Since the pressure in the hydraulic chamber 16 also increases, the pressure is maintained until the pressure sensor 18 detects that the pressure has increased above a certain pressure. During this preliminary injection, the resin pressure in the chamber δ increases, so the check ring moves back from the solid line position in FIG. Prevent backflow. 9 detects the position of the screw 12 at the time when the pre-injection has elapsed for a certain period of time or when the pressure sensor 8 detects the position, and stores the detected position signal in the storage/calculation section and adjusts the pressure in the hydraulic chamber 16 to the pressure. The regulating valve 17 injects the molten resin into the chamber to a high pressure. At this time, the screw 12 is advanced by a certain amount S from the above-mentioned storage position by the storage/calculation section 20. At this time, since the check ring has already retreated and its right end is in contact with the spacer 21, preventing backflow, all of the molten R/E resin that has traveled a certain distance is injected into the cavity. be done. The tip of the screw 12 that advances a certain distance S in this way reaches position C, and at this position the injection process is switched to the pressure holding process, and then A
Proceed to position.

At the same time as the preliminary injection, the screw 12 is turned at low speed to insert the plasticizing needle f.
If the check ring n is rotated in the opposite direction, the resin pressure on the spacer 21 side in FIG. 2 decreases, creating a pressure difference between the check ring n and the chamber δ, which makes the rightward movement of the check ring n more reliable, which is preferable.

〔Effect of the invention〕

As explained above, in the injection molding method of the present invention, after plasticization and metering is completed, the pressure chamber of the injection cylinder is maintained at a pressure lower than the pressure at which the molten resin is injected into the cavity for a certain period of time or up to the above-mentioned constant pressure. To perform preliminary injection while maintaining the rising period, the check ring is moved back and placed at a position to prevent backflow.Then, the screw position at the end of preliminary injection is memorized and the screw advances a certain amount from this memorized position. For this reason, when the screw advances, the check ring has already prevented backflow, so the amount of screw advancement and the amount of molten resin injected into the cavity are the same, so the same amount of molten resin is always injected in each shot. , is injected into the cavity.Therefore, the weight of the molded product is the same and has the advantage that a stable and high-quality molded product can be obtained.

[Brief explanation of drawings]

Each figure shows an embodiment of the present invention, and FIG. 1 is a sectional view of a main part of an injection molding machine, and FIG. 2 is an enlarged sectional view of the tip of a screw. 12...Screw, 15...Injection cylinder, 16.
...Pressure chamber. Applicant: Toshiba Machine Co., Ltd. (9)-109-

Claims (1)

[Scope of Claims] 1) A trowel in which the molten resin is plasticized and measured under an injection molding machine pressure in which backflow of the molten resin is prevented by a check ring;
The check ring is retracted by performing preliminary injection by maintaining a pressure lower than the injection pressure of the molten resin into the cavity in the pressure chamber of the injection cylinder for a certain period of time or while the pressure increases to a certain level. An injection molding method that prevents backflow, memorizes the screw position at the time of completion of the preliminary injection, and injects a certain amount of the molten resin into the cavity by moving the screw forward a certain distance from this memorized position. . 2) The injection molding method according to claim 1, characterized in that during preliminary injection, the screw is rotated at 5tC in a direction opposite to that during pre-injection.